Atomic spectrometry update. Review of advances in the analysis of metals, chemicals and functional materials
Bridget
Gibson
a,
Simon
Carter
b,
Andy S.
Fisher
c,
S.
Lancaster
*d,
John
Marshall
e and
Ian
Whiteside
f
aIntertek Sunbury Technology Centre, Shears Way, Sunbury, Middlesex, TW16 7EE, UK
bHull Research & Technology Centre, BP, Saltend, East Yorkshire, HU12 8DS, UK
cSchool of Geography, Earth and Environmental Sciences, Plymouth University, Drake Circus, Plymouth, PL4 8AA, UK
dDomino Printing Sciences Ltd, Bar Hill, Cambridge, CB23 8TU, UK. E-mail: Steven.Lancaster@domino-uk.com
eGlasgow Caledonian University, Glasgow Scotland, G40BA, UK
fTata Steel, Steelmaking and Casting Department, Grangetown, Middlesborough, Cleveland, TS6 6US, UK
First published on 26th September 2014
Abstract
This review covers developments in the analysis of chemicals, metals and functional materials. We have strengthened the criticality of this review and have included only those papers dealing with advances in the analysis of these materials. Other papers which the reader may find useful because they cover interesting applications are included in the tables. It follows last year's review1 and should be read in conjunction with other reviews in the series.2–5 Significant developments during this review period include the continued expansion of the use of LIBS in remote analysis, especially of explosives, metals and nuclear materials. The stand-off capability of the technique makes it very desirable in these areas. The use of chemometrics for removing substrate interferences is proving to be effective in making the technique more robustly quantitative and a number of papers developing the understanding of plasma physics to improve the technique of LIBS are reviewed. Multiple spectroscopic techniques are being developed to maximize the knowledge which can be derived from the analysis, especially of high value samples, for example the combination of LIBS and Raman measurements to gain molecular and atomic spectral information. Advances in the analysis of nanomaterials and single particles are reviewed and papers dealing with single particle analysis, field flow fractionation and related techniques coupled with ICP-MS are advancing the analytical chemistry in the field. These techniques are also increasingly being used in vivo and in biological areas. Depth profiling of semiconductor materials is an important area during this review period, especially for the determination of dopant elements. There are significant changes to the writing team this year. Mike Hinds has left the team and we are pleased to welcome Bridget Gibson and Ian Whiteside.
1 Metals
Many of the papers reviewed continue to demonstrate a range of valuable applications to a variety of metals. The trend in applications based on multiple spectroscopic techniques continues with a growing need for detailed micro-structural and compositional information. Many papers were based on a mature platform of commercially available instrumentation and focussed more on application than innovation. These have not been included in this review and emphasis has been given to papers presenting fundamental development of instrumentation and associated methodologies.Details of some of the key papers are highlighted to illustrate the most advanced level of development and progressive trends to profile state-of-the-art metals analysis.
1.1. Ferrous metals
Many of the reviewed papers covering the analysis and characterization of ferrous metal exploit the synergy of multiple spectroscopic methods to provide the required level of information. It is notable that this approach has been adopted by many research groups from a diverse range of disciplines with a focus more on application than development. A strong interest in applications to modern surface modification has been noted within this reporting period. In the work of Escalada et al.6 Grazing Angle X-ray Diffraction (GA-XRD), SIMS, SIMS with Focussed Ion Beam (SIMS-FIB) and EDX were used to determine the composition, microstructure and depth of a stainless steel surface modified by TiN deposition. Nitride surface engineering enhances the tribological properties of metals to extend their use into wear resistance applications. The formation of surface TiN by cathodic deposition in combination with plasma ion implantation was studied. The spectroscopic methods used showed a collective sensitivity capable of differentiating between the effects of the two separate coating processes. The authors presented results showing a superior coating thickness, corrosion and wear resistance from the combined surface treatment not matched by the separate surface modifications. Similar work was carried out by Dalibon et al.7 who provided a detailed structural analysis of the nitride coating using the same instrumentation with the addition of dark field TEM adding valuable information on lattice expansion and internal stresses. Both papers illustrate the analytical support for the development of modern advanced steel coatings. In these examples analytical capability has been demonstrated and the basis for a routine method outlined.Analysis of corrosion has been approached in a similar way to coatings, using multiple spectroscopic methods to provide structural and compositional information. Ardigo et al.8 utilized SEM-EDX and SIMS to identify the corrosive processes in a high temperature water vapour electrolysis unit, designed for hydrogen production. This work focussed on oxide scale growth processes on ferritic stainless steel, K41X (AISI 441) in the cathode atmospheres (10% H2, 90% H2O). Ageing tests covering a period up to 1000 hours revealed the formation of a duplex oxide scale: an inner layer consisting of protective chromia and an outer layer comprised of a magnetite-type iron oxide. These results allowed the authors to propose a diffusion mechanism controlling corrosion and the roles played by hydrogen and water.
Analytical spectroscopy has become a vital part of archaeology, providing scientific detail to supplement the historical record. It has become common to utilize more than one spectroscopic method to provide the required level of information. Necemer et al.9 utilized the synergy of ED-XRF and PIXE to analyse ancient Asian daggers to ascertain the materials involved, methods of manufacture and provenance. Elemental analysis was provided by ED-XRF with PIXE focussed to provide compositional data for the non-metallic inclusions indicating the possible use of meteoric iron in the manufacturing process. More papers detailing advances in the analysis of archaeological artefacts are reviewed in Sections 2.2.1 and 3.1.1.
Analysis using LIBS continues to be a popular research and development topic; applications to ferrous metals have largely focussed on improvements to quantitative sensitivity. The complex nature of the laser-sample interaction imparts an inherent level of variability into LIBS analysis. This originates from the necessity to use pulsed lasers (Q-switched) to provide sufficient energy for atomization and excitation of the solid sample surface. As a result, the quantitative sensitivity is generally accepted as the Achilles' heel of LIBS. This is underlined by the number of papers which focussed on improving fundamental sensitivity; the majority topic for papers on LIBS within this review period. It has become standard practice to develop and optimize applications based on a fundamental model of plasma physics coupled with spectroscopic measurements. Underpinning this central model is the justified assumption that laser induced plasma is in local thermodynamic equilibrium (LTE). From this, plasma temperature can be determined via the Boltzmann Plot method using two or more atomic lines to form an integrated line intensities ratio. In addition, Stark Broadening of spectral lines can be used to measure the electron number density. With an array of laser and spectrometer variables available to the analyst for optimization, this approach has become central to many research groups.10
Improvements to the detection sensitivity through the use of internal standards to compensate for LIBS variability is accepted practice. Thermodynamic principles are often applied to matching analyte to reference element based on comparable excitation potentials. This principle is valid during conditions of LTE which are only satisfied during part of the of the plasma cycle. Labutin et al.11 considered the difficulties establishing when LTE could be assumed within the transient plasma events. Considering the errors in the resulting analysis if thermodynamic principles are applied inappropriately, the authors proposed an additional selection criterion. For the selection of Fe internal reference lines for steel analysis it was proposed that the most robust approach was to establish the best correlation between the intensities of the various analyte and Fe emission lines. For the determination of Mn in high alloy steels, a homologous pair of Mn I 404.136 nm and Fe I 411.854 nm was recommended for LIBS analysis. A long linear range was reported with high linearity (R2 = 0.996) and good signal-to-noise ratio. An alternative approach by Shah et al.12 exploited advances in modern fast electronic time-gating to study the temporal evolution of emissions from the plasma events. The intensity ratio of two Fe I lines was measured and matched to its theoretical value; the delay times where the plasma is optically thin and is also in LTE were found to be 800, 900 and 1000 nanoseconds.
Guo et al.13 demonstrated that the size of the crater formed during ablative plasma formation can influence detection sensitivity. Referenced pairs of emission lines for V (V I 440.85 nm and Fe I 438.35 nm), Cr (Cr I 425.43 nm and Fe I 425.08 nm) and Mn (Mn 476.64 nm and Fe 492.05 nm) were used to monitor elements present in trace amounts in a steel matrix. It was demonstrated that single shot excitation at 1064 nm at a power density of 49.2 J cm−2 produced the highest level of sensitivity and accuracy from the bottom of a 5 mm diameter cut into the steel surface. The authors reported enhancement to the emission intensity of V, Cr, and Mn lines by factors of 4.2, 3.1, and 2.87, respectively. Improvements were attributed to the confinement of the plasma by the cavity and enhancing the spatial uniformity. This work highlights another variable available to the analyst for optimising LIBS applications.
Sample surface preparation by removal of surface material through ablation as part of the analytical cycle is an important advantage of LIBS. Scharun et al.14 exploited this in the development of a hand held probe which delivers 1.33 mJ single laser shots to the metal sample surface via a fibre-optic at a repetition rate of 30 kHz. Advances in the production of high purity fibre-optics have permitted the delivery of this level of laser intensity sufficient for LIBS. Emission radiation can also be transmitted to the spectrometer via fibre-optic allowing the sensing head to be miniaturized with the laser and spectrometer located remotely. This development illustrates some of the unique strengths of LIBS making it inherently suitability for at-site/in situ analysis. For several years these attributes have been exploited as a pragmatic approach to scrap sorting. The work of Kashiwakura and Wagatsuma15 used a Nd:YAG laser combined with a spectrometer and an Imaging Charged Coupled Detector (ICCD) detection to identify steel scrap, based on Cu content. Standard reference materials were used to establish optimum detection parameters reported as requiring relatively short delay times and longer gate times. For Cu detection the Cu I line at 327.396 nm was identified as having least spectral interferences allowing detection down to 0.004% based on 200 pulsed laser shots.
Another aspect of at-site analysis is direct analysis of molten metal, an application uniquely achievable by LIBS. In this situation LIBS makes good use of the high pulse repetition rate to follow a process in real-time with high precision. Pan et al.16 investigated the quantitative analysis of steel at high-temperature and in the molten state under different reduced pressure environments. This work is linked to steel degassing in which the molten steel is subjected to partial vacuum. This is a critical stage for many steel grades and this paper constitutes a feasibility study for this application from the spectroscopic perspective. Using a Q-switched laser, quantitative data were recorded for a range of steel temperatures around 1600 °C at pressures down to 1 × 10−4 Pa. Spectroscopic data indicated that the whole system functioned well and it was considered suitable for application to molten metal analysis under a reduced pressure environment. Linking this work with industrial steel processing places an analytical need for nitrogen analysis as this processing stage is carried out to remove nitrogen from molten steel. Exploiting LIBS to provide continuous compositional analysis within the vacuum chamber during refining would be a valuable process control facility but would present considerable engineering challenges.
For bulk analysis, enhanced sensitivity may be obtained through the use of dual-pulse LIBS in which the plasma, formed on the sample surface from the first ablation laser pulse, is further excited by a second re-heat pulse following 0.1 to 1 μs later. Jiang et al.17 observed spectral lines emitted by ions in the shorter wavelength vacuum ultraviolet (VUV) spectral region to study the plasmas generated on steel targets. Time-integrated, spatially-resolved LIBS was used to investigate spectral emissions from laser-induced plasmas generated on steel targets. Single-pulse and dual-pulse LIBS experiments were performed on standardized steel samples. In the case of the double-pulsed LIBS, two synchronized lasers were used, an ablation laser (200 mJ/15 ns), and a reheating laser (665 mJ/6 ns) in a collinear beam geometry. Spatially resolved and temporally integrated laser induced plasma emission in the VUV were studied under dual-pulse operation with specific attention given to the dependence on inter-pulse delay. The VUV spectral line intensities were enhanced in the dual-pulse configuration and were significantly affected by inter-pulse delay time. Additionally, the influence of ambient conditions was investigated by employing low pressure nitrogen, argon or helium as buffer gases in the ablation chamber. For C emission at 97.7 nm, argon was reported to be the ideal gas environment to maximize sensitivity.
In steel production the need for in situ analysis is paramount. Although LIBS and LA-ICP-OES have been applied over the years they have not been fully deployed due to engineering and maintenance issues. A novel approach by Aula et al.18 investigated the possibility of utilising atomic emissions from the arc discharges of a production electric arc furnace. The aim of achieving a dynamic monitor of slag composition during processing was considered in a series of laboratory tests. The CrOx/FeOx and MnO/SiO2 ratios for different slag compositions were studied for arc discharge conditions similar to those from an industrial electric arc furnace including authentic voltage variations. A good correlation between the arc discharge and the corresponding samples, analysed by XRF, was reported. If dynamic slag analysis could be realized on an industrial scale, partitioning of elements between the slag and metal could be monitored during processing. The analytes Cr and Mn are of particular interest as partitioning is controllable and if monitored in real-time would facilitate tighter process control. Currently no effective methods of real-time slag analysis are available so this initiative could provide data that would not be available otherwise.
A study of the factors affecting optical emission sensitivity from a microwave-induced plasma using an Okamoto-cavity has been reported by Zhang and Wagatsuma.19 The structure of micro-wave plasma within an Okamoto-cavity was visualized using 2-dimensional images of atomic and ionic Cr emissions. With molecular band heads of nitrogen also studied in 2-dimensions, the influence of oxygen concentration on the emission intensity of Cr was studied. The authors reported that atomic Cr line emission is greatly increased with increasing levels of oxygen in the nitrogen plasma gas up to a concentration of 10%. Conversely, the intensities of ionic chromium lines and the nitrogen bands were both reduced when oxygen gas was added to the nitrogen plasma. This result implies that the ionization of chromium, which dominates through collisions with nitrogen excited species, can be suppressed because the nitrogen excited species would be consumed through collisions with oxygen molecules causing dissociation. Understanding the critical instrumental factors affecting detection sensitivity is a progressive step towards the development of this technique. The potential for improved signal-to-noise from higher power inputs and lower background emission intensities in comparison to ICP, offers potential for improved steel analysis.
Although the majority of papers are based on solid sample analysis, several focus on developing methods requiring sample pre-treatment. This is often required to remove the metal matrix for trace analysis. Hasegawa20 used solid phase extraction to selectively remove the iron matrix from acid digests of iron and steel samples to improve sensitivity of ICP-OES analysis. This approach avoided the need for EDTA masking agent and pH buffering. Detection limits (3σ) in steel samples were reported for a range of trace elements at the ppb level (Mo 1.06) and below (Nb 0.025) with aspects of the method designed to maximize precision through automation.
Many modern steel grades require a detailed characterization of non-metallic inclusions within the iron matrix. The properties of steel products which are drawn to wire or rolled to thin sheet are critically dependant on the size, morphology and composition of non-metallic inclusions. In addition to product release testing, analysis of inclusions is a diagnostic tool for many processing problems. Analysis by selective chemical dissolution is a popular method of quantifying and characterising non-metallic inclusions. Bellot and Lamesle21 used selective chemical dissolution of the iron matrix, to expose the non-metallic inclusions in a super alloy treated steel grade. It was reported that the size and morphology of the precipitates could be accurately measured using high-resolution SEM for a large range of dimensions down to 10 nm. Dissolution of the particles and elemental analysis by ICP-OES established the relative amounts of Ti, Al and Nb exclusively from the inclusions; quantitatively linking precipitation to the alloyed concentrations of the elements of interest in the steel prior to heat treatment. Non-metallic inclusions can be analysed directly from solid metal samples via spark-OES and LIBS; however, it is difficult to define size and morphology. Microscopy also requires interpretation as inclusions are sectioned randomly. Matrix extraction provides a route to a definitive analysis of size, morphology and composition.
1.2. Non-ferrous metals
As in the previous section, the use of multiple spectroscopic methods has been shown to be a powerful approach to a wide range of applications. Depth profiling of corrosion layers or coated metals often relies on SIMS to provide the required depth and compositional sensitivity. Pillatsch et al.22 exploited the He+ and Ne+ ion beam of a helium ion microscope to perform SIMS analysis in a prototype system. The authors reported that the high lateral resolution of microscopy combined with high sensitivity chemical mapping had improved the quality of SIMS information. Applied across a range of metallic (Al, Ni and W) and semiconductor samples (Si, Ge, GaAs, and InP), a lateral resolution of less than 50 nm was achieved. Detection at the ppm level was reported using a Ne+ ion beam albeit at a reduced lateral resolution of 100 nm.LIBS features strongly in the papers reviewed as opportunities for application across a range of metals continue to emerge. With the many factors now known to influence LIBS analysis each new application generates publishable material. This may account for the high representation of LIBS papers within this review period.
Advances in opto-electronics for LIBS have reduced pulse duration beyond the nanosecond range with modern lasers capable of providing femtosecond pulses with great precision. Theoretically, femtosecond lasers interact with the sample by a mechanism which avoids the excessive plasma heating associated with nanosecond pulses. Freeman et al.23 investigated the plasma characteristics resulting from nanosecond and femtosecond laser pulse irradiation of brass samples. Using identical energy densities, it was reported that the emission spectrum from nanosecond pulse irradiation showed high continuum with elemental emissions predominantly from lower charged ions. In contrast, negligible continuum and dominance of emissions from neutral species was observed from femtosecond pulse irradiation. The temporal characteristics of the plasma were similar in terms of temperature and electron density for both pulse durations although the expansion rate for femtosecond lasers was reported to be twice that of the nanosecond pulse. In addition, it was noted that the ambient gas surrounding the plasma has a significant effect on the plasma temperature. The ambient gas is described as affecting the containment of the plasma which can enhance and sustain the temperature and density. It was proposed that ambient gases which sustain hot plasma will delay emissions. By this mechanism the ambient gas is shown to be a significant factor in the temporal emission profile. Indeed, Nakimana et al.24 showed that an Ar atmosphere provided the best environment for analysing Al samples using femtosecond LIBS at relatively low pressures (1 KPa). It was shown that He provides the higher analytical sensitivity at relatively high pressures.
Diwakar et al.25 investigated the excitation parameters of dual-pulse LIBS principally the influence of inter-pulse delay and laser excitation wavelength. Both collinear and orthogonal configurations were included in this work. The Nd:YAG laser harmonics 1064 nm, 532 nm and 266 nm were used for the initial ablative, pre-analysis pulse and the infra-red harmonic at 1064 nm was used as the analytical reheat pulse in all cases. Several emission lines were used including Al (281.65 nm and 466.30 nm) and Si (288.15 nm) to derive plasma temperatures and electron density. These parameters were used to measure the spectroscopic effects of laser wavelength and inter-pulse delay. The dual pulse configuration of 1064 nm ablation and excitation at the same wavelength showed the most sensitivity to variations in the inter-pulse delay but all dual pulsed configurations were reported to produce higher detection sensitivities. Ablation at the UV wavelength of 266 nm and excitation using the infra-red wavelength of 1064 nm produced the highest absolute emission intensity. This configuration required an inter-pulse delay of 250 nanoseconds. Farid et al.10 confirmed that the highest plasma temperatures of 16![[thin space (1/6-em)]](https://www.rsc.org/images/entities/char_2009.gif)
304 K was achieved using the 1064 nm Nd:YAG infra-red harmonic for a W target. However, the maximum electron density of 1.12 × 1018 cm−3 was observed for the 355 nm harmonic.
Notable work by Chen et al.26 utilized ICP-MS to identify stable Pb isotopes in a variety of ancient coins made of copper, brass and bronze. Analysis by bulk dissolution was compared with sample introduction via solid sample ablation using a femtosecond laser integrated to form a LA-ICP-MS system. The authors reported good agreement for both methods of sample introduction and provided an isotopic fingerprint which added to the archaeological knowledge base. The importance of stable isotopic identification in archaeology highlights the value of LA-ICP-MS to this and other disciplines; however, the micro-analytical aspect is often overlooked. Inclusions in archaeological artefacts are large in comparison to modern metals and detection sensitivity may be less problematic. Isotopic information exclusively from non-metallic inclusion would be expected to improve archaeological interpretation in the areas of processing, manufacture and provenance.
As in the previous section, multiple spectroscopic methods are of increasing importance and many of the reviewed papers cover a wide range of applications. The importance of non-destructive techniques in archaeometallurgy is illustrated by Modlinger et al.27 using SEM-EDX, PIXE, Time of Flight Neutron Diffraction (TOF-ND) and Prompt Gamma NAA (PGAA) to reconstruct the manufacturing process of a Bronze Age metal helmet. This range of techniques was required to establish differences in the alloy composition of the component parts and the methods used to join them. Many of the reviewed papers deal with a wide range of applications to characterize and understand metal surface modifications and interfacial chemistry, these generally require destructive techniques involving sputtering to analyse through a surface layer.
Several methods have been developed to overcome analytical difficulties arising from the majority element in the sample matrix. Wei et al.28 used bromine separation to remove the Sn matrix to allow impurities to be analyse directly using ICP-MS. The authors proposed this method for analysing impurities in high purity Sn up to the 99.999% level.
2 Chemicals
2.1. Fuels and lubricants
This area has yielded a fair number of papers however many were not novel with considerable “re-inventing of the wheel” for applications for which there are long standing industry standard methods. This is particularly the case for combustion AA methods for Hg determination. Overly complex applications making use of a particular instrument regardless of whether it is suitable or cost effective are also well represented. There are significant numbers of papers using AAS or GFAAS although the fuel industry has largely moved to ICP-OES/MS applications due to ease of use and safety concerns with running fuel samples on AAS systems. There is a large representation from South American and Chinese institutions probably reflecting the developing fuel industries in these parts of the world.A method for the determination of Mn, Ni and V in petroleum products and biofuels using ICP-MS equipped with a high temperature single pass spray chamber was developed.32 Sample introduction was by a heated Torch Integrated Sample Introduction System (hTISIS). Three elements Mn, Ni and V were determined because of their importance in the petroleum industry. Sample injection was accomplished by introducing a low sample volume (2.5 μg L−1) into a carrier stream of air. Two sets of samples were chosen the first being xylene, kerosene, nonane, undecane and hexadecane and the second was biodiesel, diesel, kerosene, superethanol and gasoline. The chamber temperature was varied and it was found that sensitivity peaked at 110 °C, however, non-spectral interferences caused by differences in the matrix composition became less severe when the temperature was increased and were virtually eliminated at 150 °C for alkanes and 200 °C for real samples. When compared with a default spray chamber (i.e. a conical chamber with an impact bead) 3 to 6 times lower LODs were obtained. At 150 °C, LODs of approximately 80 ng L−1 for V and Ni to 140 ng L−1 for Mn were obtained. By using a temperature of 200 °C it was possible to carry out accurate ICP-MS determinations by applying external calibration. Additional advantages of this approach are that no oxygen was required to avoid soot deposition and a Ni sampler cone was able to be used instead of the standard platinum one.
Quantification of S at low concentrations in biodiesel and diesel fuels using isotope dilution and sector field inductively coupled plasma mass spectrometry (ID-SF-ICP-MS) has been reported.33 Closed vessel microwave-assisted digestion was employed using a diluted nitric acid and hydrogen peroxide decomposition medium to reduce sample dilution volumes. Medium resolution mode was employed to eliminate isobaric interferences at 32S and 34S related to polyatomic phosphorus and oxygen species, and sulfur hydride species. The method outlined yielded respective LOD and LOQ of 0.7 mg kg−1 S and 2.5 mg kg−1 S in the sample. The LOD was constrained by instrument background counts at 32S but was sufficient to facilitate value assignment of total S mass fraction in NIST (2723b sulfur in diesel fuel oil) at 9.06 ± 0.13 mg kg−1. No statistically significant difference at a 95% confidence level was observed between the measured and certified values for certified reference material NIST SRM 2773 B100 (biodiesel, animal-based). This method is instrumentally very interesting, however, in light of the fact that WD-XRF can obtain a LOD of approx. 5 mg kg−1 and micro coulometry 0.2 mg kg−1 it seems a little over complicated compared with industry standard methods.
Two review articles were in this year's crop of papers. One by Soares et al.34 containing 73 references describes “contributions of flow analysis for quality control of automotive fuels”. This review focuses on analytical approaches for on-line sample pretreatment and flow-based determination of organic and inorganic contaminants in automotive fuels. Before consumption, fuel composition can be modified by inadequate transport, storage and handling, as well as illegal adulteration. Automotive fuels require strict quality control to maximize energy yield as well as to avoid additional environmental pollution and evasion of taxes. This focuses on analytical approaches for on-line sample pre-treatment and flow-based determination of organic and inorganic contaminants in automotive fuels, including a discussion of advantages and limitations of these strategies. Sanchez et al.35 produced a review containing 270 references titled “Determination of trace elements in petroleum products by inductively coupled plasma techniques: A critical review”. This discussed the fundamentals, applications and latter developments of petroleum product analysis using ICP-OES and ICP-MS. Sample preparation procedures for the direct analysis of fuels by using liquid sample introduction systems are critically reviewed and compared. The most employed methods are sample dilution, emulsion or micro-emulsion preparation and sample decomposition. The first is the most widely employed due to its simplicity. Once the sample has been prepared, an organic matrix is usually present and the performance of the sample introduction system (i.e. nebulizer and spray chamber) depends strongly upon the nature and properties of the solution finally obtained. Many different devices have been assayed and the obtained results are shown. Other sample introduction systems are discussed; samples can be introduced into the plasma by using an electrothermal vaporization (ETV) device or a laser ablation system (LA). The recent results published in the literature showing the feasibility, advantages and drawbacks of these alternatives are also described.
A method for quantitative elemental detection of size segregated particles using LIBS has been reported.38 Particles were classified by an Anderson cascade impactor and their composition measured using the output of a 1064 nm Nd:YAG laser, a spectrograph and an ICCD camera. The plasma conditions are dependent on the size of particles and these effects were corrected to obtain quantitative information. The plasma temperature was corrected by the emission intensity ratio from the same atom. Using this correction method the contents of particles were measured quantitatively in fixed experimental parameters. This method was applied to coal and fly ash from a coal-fired burner to measure unburned carbon and other contents. The acquired results demonstrate that the LIBS technique is able to measure size-segregated particle contents in real time.
Zheng et al.39 investigated laser energy in multi-element detection in a pulverized coal flow with LIBS. Pulverized coal particles of less than 200 μm in diameter were passed through a screw feeder and the rate of flow was controlled. Emissions were collected following excitation with a pulsed laser at 1064 nm. The intensity and fluctuation of emission spectra at various laser energy levels were studied. A suitable range of laser power density was found from 14.4 to 34.4 GW cm−2, and the optimum laser power density was 19.5 GW cm−2 for multi-element analysis of pulverized coal flow with LIBS.
A new distance correction method for S determination in coal using on-line XRF measurement has been reported.40 When XRF technology is used to measure S concentrations in coal online, the measurement accuracy is affected by the coal's uneven surface and the particle size. In order to improve the accuracy of this method an online measurement system, consisting of a portable X-ray fluorescence instrument and an auxiliary distance correction module was developed. By measuring standard coal samples of known S concentrations a calibration curve was obtained that could be used to determine S concentration. The relationship between the X-ray fluorescence intensity (I) and the distance (D) from surface to instrument was studied. The results showed that there was a good linear relationship between I and D. Based on this knowledge, a distance correction formula of X-ray fluorescence intensity was proposed. By applying the distance correction formula to experimental S concentration measurements it was demonstrated that the measurement accuracy can be significantly improved.
An in situ measurement for simultaneous detection of K, KCI and KOH vapours released during combustion of solid biomass fuel in a single particle reactor has been developed using collinear photofragmentation atomic absorption spectroscopy (CPFAAS).41 The technique utilizes a UV laser pulse to dissociate alkali chloride molecules to alkali metals and chlorine atoms, and a narrow bandwidth laser diode to monitor the concentration of the alkali metal atom. The collinear alignment of the two beams through the sample volume enables the detection of temporally increased alkali atom concentration within the volume determined by the UV beam. The large absorption cross-sections and the narrow absorption profiles of the alkali atoms favour their detection when interfering fragments such as O2, exist. The experimental setup was applied to determine K, KCI, and KOH release from 10 mg spruce bark samples combusted at temperatures of 850, 950 and 1050 °C with 10% O2. The combustion experiments provided data on the formation of K vapours and their release during different combustion phases and at different temperatures. The measured release histories agreed with earlier studies of K release.
Combinations of techniques are increasingly being used to maximize the information which can be obtained during analysis and Raeva et al.42 described a method using a combination of GFAAS and TGA-DSC to simulate the trace element (TE) evolution from the excluded mineral fraction during coal combustion. A combination of GFAAS and TGA-DSC was used to simulate the gas-melt partitioning of semi-volatile trace elements such as As, Sb and Se from excluded minerals during the initial dynamic step of coal combustion. To properly simulate exclusion, the effect of carbon in the graphite furnace tubes on TE vaporization was minimized by coating the tube with an inert metal oxide (either ZrO2 or WO3). The Arrhenius activation energies of TE volatilization/atomization obtained upon fast heating in such a carbon-free GFAAS microenvironment, with and without mineral matrices were measured. They were compared with those obtained in uncoated tubes to verify that the influence of carbon had been eliminated and to obtain insights on the mechanism of TE evolution. Cationic inorganic matrices such as Ca and Fe influenced the carbon-free evolution of Se and Sb in different ways than in the presence of carbon indicating that TE partitioning from mineral exclusions during coal combustion may be significantly different from TE partitioning from organically associated material and mineral inclusions. Calcium increases the Se (and, to some extent, As) retention in the solid phase due to common acid–base chemistry, whereas iron as well as anionic matrices, such as aluminate and silicate, do not influence TE atomization in mineral exclusions. By contrast, in inclusions these minerals decrease the extent of TE atomization by shielding it from the reducing action of carbon. A significant chemical reduction of As to its elemental form was observed which does not appear to be influenced by the presence of carbon. By contrast, the extent of Sb and Se atomization depends on this factor which is different in exclusions compared with inclusions. Therefore the presented method provides information that can be used to predict the predominant TE speciation in the gas phase.
A method for the determination of S in coal and ash slurry has been described.43 The slurry was prepared by mixing 50 mg of the sample with 5% v/v nitric acid and 0.04% m/v Triton X-100 and was homogenized manually. The determination was performed via continuum source electrothermal molecular absorption spectrometry at 257.592 nm, and the optimized vaporization temperature was 2500 °C. The accuracy of the method was evaluated by analysis of certified reference materials NIST SRM 1632b (trace elements in coal) and NIST SRM 1633b (coal fly ash). External calibration was used with aqueous standards prepared in the same medium as the slurry. Good agreement with the certified reference materials was achieved within the 95% confidence interval. The LOD was 0.01% w/w.
An ETV procedure for the direct determination of Cl in petroleum coke by ICP-MS has been developed by Antes et al.44 The ETV system consists of a high power lamp enclosed in glass chamber equipped with solenoid valves. The temperature and heating time were optimized. Pyrolysis and vaporization temperatures were set at 350 °C and 900 °C, respectively while the Ar flow rate was 1.2 L min−1 and the plasma power 1300 W. Up to 5 mg of petroleum coke sample can be analysed by this method. Calibration was carried out by standard addition. The relative standard deviation was lower than 9% (n = 4) and the LOQ (10σ) of Cl was 3.5 μg g−1. Results obtained for Cl in petroleum coke samples were in agreement with those obtained using other validated methods for Cl determination. The time of analysis (approximately 2 min per sample), risk of contamination, analyte losses and waste generation are drastically reduced in comparison with techniques that require sample digestion for Cl determination.
Speciation is becoming more prevalent in all fields and Sun et al.45 described a method for speciation analysis of inorganic As in coal samples that employed microwave-assisted extraction and high performance liquid chromatography coupled to hydride generation atomic fluorescence spectrometry (HG-AFS). Extraction of AsIII and AsV in coal samples was achieved by using 1.0 mol L−1 H3PO4 and 0.1 mol L−1 ascorbic acid. Under optimized conditions, the LOD was 0.01 μg L−1 and 0.02 μg L−1, and the RSDs were 2.4% and 3.3% (10.0 μg L−1, n = 7). Recoveries were 102.5% and 96.5% for As(III) and As(V).
A different approach on the same theme was taken by Caldas et al.48 who proposed a novel approach for the sample preparation of used lubricating oils to determine Cu, Fe and Mn by FAAS. This method is based on extraction induced by emulsion breaking in which the elements of interest are transferred to an aqueous phase before measurement by FAAS. In the method, each sample of used lubricating oil was diluted with toluene (20% v/v) and the resulting solution was emulsified with a Triton X-114 solution containing HNO3. The water-in-oil emulsion was then broken by centrifugation for 30 min at 3500 rpm, producing a system with two well-separated phases; the upper phase containing the used lubricating oil diluted in toluene and the lower aqueous phase containing the analytes that were extracted from oil. The lower phase was collected, diluted with water and the analytes were determined by FAAS. The limits of quantification for Cu, Fe and Mn were 2.9, 77 and 8.2 ng g−1 respectively. The accuracy of the method was evaluated by comparison with the reference method based on the total digestion of the samples in a closed-vessel microwave oven. There was agreement between the results obtained with the proposed method and the reference one except for Fe in the cases where the Fe concentration was higher than 80 μg g−1.
Luz et al.49 proposed niobium carbide as a modifier for Si determination in petrochemical products by emulsion-based sampling GFAAS. Emulsion-based sample preparation was carried out using 200 mg of samples (crude oil, diesel or gasoline), 125 μL of hexane (only for crude oil) and 7.5 mL of Triton X-100 (20% v/v). The mixture was stirred manually for few seconds then placed in an ultrasound bath for 30 min and diluted to 25 mL. NbC was used as a modifier to avoid the formation of thermally stable SiC and combined with 20 μg of Pd to avoid losses of volatile Si. After heating program optimization the pyrolysis and atomization temperatures were 1300 °C and 2600 °C, respectively. The LOD and LOQ, were 2.6 μg L−1 and 8.6 μg L−1. The accuracy was checked by the analysis of oil-based Si standards and the found values were in accordance with the reference values at 95% confidence level. Addition of 30 μg L−1 of Si in crude oil, gasoline and diesel samples resulted in recoveries ranging from 95% to 111%.
The technique of LIBS was applied to wear metal analysis in oils by using a thin oil layer on metallic target by Xiu et al.50 The authors evaluated the performance of LIBS for quantitative analysis of wear metals in oils with a specific ablation configuration of a thin layer of oil covering the polished surface of a pure aluminium target. A set of reference samples containing 12 metallic elements (Ag, Al, Cr, Cu, Fe, Mg, Na, Ni, Pb, Si, Sn and Ti) was prepared by dilution with a 75 cSt hydrocarbon base oil for the concentration range from 20 to 500 μg g−1. Calibration curves were established for these elements with an echelle spectrometer and then with a Czerny–Turner spectrometer. The obtained results show high linearity for the calibration curves established with the two types of spectrometer. The correlation coefficient R2 of all the calibration curves was better than 0.99. The LODs with an echelle spectrometer varied in the range from 0.29 to about 10 μg g−1 with an average value of 6.02 μg g−1 for the 9 elements (Al, Na and Pb excluded). The use of a Czerny–Turner spectrometer reduced the LODs to between 0.24 and 10 μg g−1 with an average value over the 10 elements (Al and Na excluded) of 4.04 μg g−1. Comparison with the previously published data shows the efficiency of the introduced ablation configuration as one of the most suitable methods for highly sensitive and precise wear metal determination in oils.
Pereira et al.51 described a method using high-efficiency microwave-assisted digestion combined with in situ ultraviolet radiation for the determination of rare earth elements (REEs) by ultrasonic nebulization ICP-MS in crude oils. Pressurized systems using conventional acid digestion are not best for efficient crude oil digestion particularly for heavy and extra heavy crude oils that generally contain high amounts of asphaltenes and resins. In the proposed method, UV radiation is generated in situ by immersed electrodeless Cd discharge lamps positioned inside the quartz vessels. The use of 1–14.4 mol L−1 HNO3 and 1–4 mol L−1 H2O2 was evaluated for heavy and extra-heavy crude oil digestion. In the proposed method the residual carbon content was lower than 13 mg per 100 mg of sample, and it was possible to digest sample masses up to 500 mg using 4 mol L−1 HNO3 and 4 mol L−1 H2O2. Interferences caused by excessive acid concentration and carbon content in the digests were minimized, producing limits of quantification for REEs as low as 0.3 ng g−1. The combination of microwave heating with UV was considered a suitable and effective way to digest crude oil allowing determination of low concentrations of REE by ICP-MS.
Barbier et al.52 described a SEC-ICP-MS procedure to investigate the size distribution of nickel and vanadium complexes to monitor the behaviour and fate of Ni and V during vacuum residue hydrotreatment and fraction separation. Sample preparation included asphaltene–maltene separation and asphaltene fractionation by cross-flow ultrafiltration. Results showed that metals in the asphaltene fraction are associated with molecules that present a complex continuum of polydispersed compounds with a majority of metal complexes found at 15 kDa polystyrene equivalent. The Ni is generally present in higher molecular weight compounds compared with V. The size of the metal compounds impacts significantly on their reactivity during hydrotreatment, metals present in high molecular weight compounds being more refractory to conversion and only the light metal complexes being easily converted.
Zhao et al.53 investigated the separation and characterization of vanadyl porphyrins in Venezuela Orinoco heavy crude oil. Crude oil was sequentially separated into several sub-fractions to determine the contents and types of vanadyl porphyrins contained in the products. The V content in each subfraction was detected using an AAS instrument combined with the characterization of vanadyl porphyrins by UV-Vis spectroscopy and positive-ion ESI Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR MS). Six types of petroleum vanadyl porphyrins, which have been identified previously, were well-characterized along with three new series of vanadyl porphyrins corresponding to molecules of CnHmN4VO2, CnHmN4VO3, and CnHmN4VO4, respectively.
A review article with 43 references was produced by Doyle et al.54 on spectrometric methods for the determination of chlorine in crude oil and petroleum derivatives. In petroleum products the determination of Cl is performed to evaluate the concentrations of organochloride compounds which are used as additives. These determinations are currently performed following official guidelines from the ASTM and from the United States Environmental Protection Agency as well as protocols indicated by Universal Oil Products Inc. X-ray fluorescence spectroscopy plays an important role in many of these official methods. In contrast, other spectrometric methods based on optical and mass detection have limitations related to both the fundamental characteristics of non-metals and to the complex sample matrices. In this review, the current status of the spectrometric methods, especially the role played by X-ray fluorescence spectrometry is evaluated in terms of the determination of Cl in crude oil and petroleum derivatives. Comparison of the performance of the methods, limitations and potential new approaches to ensure proper spectrometric determinations of Cl are discussed.
Emulsions were also used by Pereira et al.56 although this method also used emulsion breaking to extract the metals. Their paper “Novel extraction induced by emulsion breaking as a tool for the determination of trace concentrations of Cu, Mn and Ni in biodiesel by electrothermal atomic absorption spectrometry” describes an emulsion extraction approach to sample preparation. The extraction was performed using an emulsifier solution containing 2.1 mol L−1 of HNO3 and 7% m/v of Triton X-100. The extraction time had a large influence on the efficiency of the process with an agitation time of 60 min being necessary to achieve maximum extraction. The LOQ were below 1 μg L−1 for the three analytes in the study. The accuracy of the method was evaluated by a recovery test where recovery percentages between 89% and 109% were achieved.
Another approach was taken by de Magalhaes et al.57 using dissolution in ethanol as a sample preparation procedure for the determination of Ca, K, Mg and Na in biodiesel by FAAS. This medium enabled the use of aqueous standards. The analytical curves showed linear correlation coefficients (r) higher than 0.99, and the slopes obtained using different matrices indicated that the matrix had no influence on quantification of the analytes. The instrumental LOD and LOQ for all metals were in the ranges 0.05–0.31 mg kg−1 and 0.17–1.02 mg kg−1, respectively. These results suggest that ethanol dissolution can be used as an alternative method of sample preparation for determination of Ca, K, Mg and Na in biodiesel samples by FAAS.
A procedure examining the possibility of using ratios of element mass fractions as markers for origin determination of soya and canola based biodiesels has been reported.58 This was a feasibility study on three samples of soya beans, three samples of canola/rape seeds and the six corresponding biodiesel products. Sample digestion was performed with acids in a high pressure asher or a microwave oven depending on samples, followed by evaporation to dryness for the digests and re-dissolution of the solid residues in 2% HNO3. For raw plant materials, a final dilution step with 2% HNO3 (1:100 and 1:1000) was performed. Mass fractions of B, Cu, Fe Mg, P, S, Sn, V and Zn were measured in all samples by ICP-MS. Procedure validation consisted of identifying the factors influencing the results, estimating combined uncertainties and assessing trueness from recovery tests on the CRM BCR-191 and simulated biodiesel samples. Ratios of mass fractions were computed for all possible combinations of results obtained for these elements in all samples. These ratios appeared to be good markers of the biological origin of the raw products in this study.
The direct determination of Cr, K, Na and V in biodiesel fuel by tungsten coil atomic emission spectrometry has been demonstrated.59 High levels of K and Na can be present in biodiesel fuel and contribute to corrosion, reduced performance and shorter engine lifetime. Trace amounts of Cr and V can also increase the emission of pollutants during biodiesel combustion. In this work, tungsten filaments extracted from microscope light bulbs were used to successively decompose the organic matrix of the biodiesel, atomize and excite the analytes to allow determination of Cr, K, Na and V by tungsten coil atomic emission spectrometry (WCAES). No sample preparation other than simple dilution in methanol or ethanol was required. Direct analysis of 10 μL sample aliquots using heating cycles with less than 150 s resulted in LODs as low as 70, 70, 20, and 90 μg kg−1 for Cr, K Na, and V, respectively. The accuracy of the procedure was checked by determining K and Na in a biodiesel reference sample and carrying out spike experiments for Cr and V. No statistically significant differences were observed between reference and determined values for all analytes at a 95% confidence level. The procedure was applied to three different biodiesel samples at concentrations between 6.08 and 95.6 mg kg−1 for Na and K, and between 0.22 and 0.43 mg kg−1 for V. The procedure is simple, fast and environmentally friendly.
An interesting method for determination of iron in biodiesel based on fluorescence quenching of CdTe quantum dots was described by Rodrigues et al.60 In this work an effective and simple quantification method using water soluble mercaptopropionic acid capped CdTe quantum dots (QDs) was implemented for the fluorescence quantification of iron in biodiesel obtained from different vegetable oils and fat. The methodology was based on the capacity of Fe to establish surface interactions with the nanocrystals that result in a quenching of the fluorescence intensity proportional to the iron concentration. Size and concentration of QDs, and pH and concentration of the buffer solution showed a strong effect on the quenching efficiency influencing linear working range and sensitivity of the methodology. An ultrasonic bath was used for the extraction of iron from oil samples with a mixture of 1:1 (v/v) concentrated HCl and H2O2. The extraction efficiency was approximately 100% after 50 min. Under the optimized conditions, a linear working range was obtained for iron concentrations from 4.16 to 100.0 μg L−1 (R = 0.9996, n = 6). The LOD was about 1.25 μg L−1. Six biodiesel samples were analysed by the proposed methodology, and the results revealed good agreement with those obtained through a high-resolution continuum source graphite furnace atomic absorption spectrometry (HR-CS GFAAS).
Andersen et al.61 evaluated a typical commercial multi-element method using a WDXRF spectrometer for analysis of biomass. With the increasing utilization and trade of biomass there is a growing need for quick and reliable quantitative chemical analysis of the inorganic elemental composition. X-ray fluorescence spectroscopy is an attractive method because of the limited sample preparation necessary, however universal multi-element analysis can be very hard to implement mainly due to problems with matrix corrections. Users of XRF therefore often rely on commercial pre-calibrated or standard less methods supplied with their XRF spectrometer. These methods are often sold without any guarantee of performance. A typical example of such methods recently purchased with a 4 kW WDXRF spectrometer was investigated. The accuracy was determined by analysing certified inorganic elements in 13 CRMs of diverse vegetal/plant origin. The certified elements detected by the XRF are Al, As, Ba, Ca, Cl, Cr, Cu, Fe, K, Mg, Mn, Mo, Na. Ni, P, Pb, Rb, S, Sr, V and Zn. The relative systematic error (bias, trueness) was found to be better than ±20% for elements in the range 25 to 100 ppm, better than ±15% for the range 100 to 1000 ppm, and better than ±10% for concentrations above 1000 ppm. The relative precision (measured as the relative standard error) was better than ±5% (typically ±1–2%) for concentrations >25 ppm. Occasionally, larger relative biases of up to ±40% can occur for certain elements in certain samples so care has to be taken to carefully test the applied method for the particular samples and elements of interest. The XRF method can further be used to estimate the ash yield from biomass combustion with a relative bias (trueness) typically better than ±15%. This involves the determination of Si and Ti by XRF. The choice of matrix composition in the matrix correction model and the influences of sample moisture and sample grain-size were also addressed.
Two-dimensional LIBS mapping of liquefied petroleum gas and electrolytic oxy-hydrogen flames has been reported.62 There have been several successful applications of LIBS to combustion analyses which include the identification of industrial exhausts and the determination of fuel equivalence ratio and the composition measurements of hydrocarbons. Thus far the application of LIBS to combustion diagnostics has focussed on the measurement of chemical species in small local volumes or along a one-dimensional line. In this work they considered flames of liquefied petroleum gas (LPG) and electrolytic oxy-hydrogen (EOH) for chemical analysis via LIBS. Two-dimensional mapping allowed for spatial dimensionality in a conventional LIBS point measurement. Information about the dissociated chemical species (gas phase) and soot (solid particle phase) unattainable via any other means was provided by the system. Both atomic and molecular chemical contours of LPG, LPG–EOH mixture, and LPG–air mixture flames were presented. A brown gas generator generated EOH gas, which was mixed with LPG gas using mass flow controllers to control the flow rates. The mixed fuel was fed into a burner through a co-axial nozzle with its inner hole (0.68 mm diameter) and outer hole (3.1 mm diameter) separated by a 2 mm circular wall. The burner traverses along the x and y axes for resolved point measurements at varied grid positions to construct 2-D images. The plasma is generated by a laser beam with a wavelength of 532 nm through a convex lens that has a 120 mm focal length. Since the flame density differs according to the fuel, the laser energy that generates plasma was changed for different fuel mixtures. The C/N LIBS signal represents concentration of the LPG fuel. The H/O LIBS signal provides the fuel/air equivalence ratio in the flame. Thus, additional flame information, unavailable via other means such as density, atomic and molecular concentrations, and fuel/air equivalence ratio, is provided by the two-dimensional LIBS mapping technique presented in this paper.
Zhang et al.63 described a method for continuous monitoring of Hg in fuel gas using chemical looping combustion pre-treatment prior to CVAAS detection. Previous methods using gold traps eliminate interferences from aromatic hydrocarbons but are only a semi-continuous measurement. This study proposed a novel Hg continuous emissions monitor (CEM) to measure the Hg concentration in fuel gases. The pre-treatment unit consisted of an electric-heated quartz tube reactor filled with an oxygen carrier (NiO), dispersed into quartz sand. The gas at a controlled flow rate was fed into the reactor at an elevated temperature. All the flammable gases were converted into CO2 and H2O, and all Hg species were transformed into elemental vapour. The product gases were then introduced into the condenser to remove water and finally the concentration of elemental Hg in CO2 was detected by CVAAS without any interference issues. The oxygen carrier is reduced to metal by the fuel in the fuel reactor, and then oxidized in air in the air reactor, forming an oxide to complete the looping. Two types of gases containing Hg (toluene and coal pyrolysis gas) were continuously measured by the proposed Hg CEM. The results showed that satisfactory Hg recoveries were attained with CLC pre-treatment, whereas the data without CLC pre-treatment were totally distorted.
2.2. Organic chemicals and solvents
A large number of papers dealing with applications, rather than with advances in the analysis of organic chemicals have been published during this review period. However, as with the other sections, we have reviewed only those dealing with advances in the analytical chemistry of these materials. A small number of papers which the reader may find useful which deal with interesting applications are included in Table 1.| Element | Matrix | Technique; atomization; presentation | Comments | Reference |
|---|---|---|---|---|
| Several | Parchment | XRF; FTIR; Raman, —, S | Elemental and molecular spectroscopic techniques employed to characterize the dead sea scrolls. characterization of the writing media will contribute to an understanding of their history. Additionally, characterization of the parchment is assisting with the debate on their provenance | 251 |
| Several | Paintings | XRF, —, S | XRF imaging of paintings | 252 |
| Several | Paintings | Various, — S | Spectroscopic characterization of paintings | 253 |
| Various | Inked linen | LIBS, —, S | Characterization of linen | 254 |
| B | Graphite powder | MS, ICP, L; | The graphite powder was made into a sodium carbonate paste and fused in a furnace. The fusion was then mixed with glycerol, the solid separated and the B measure in the glycerol. Recovery was 92–96% and LOD was 90 ng g−1 | 255 |
| Pb(II), Mn(II) | Various | AAS, flame, L | This paper describes a novel pre-concentration technique involving magnetic multi-wall carbon nanotubes. Enabling ppb level determination in a range of matrices | 256 |
| As, Cd, Hg, Pb | Active pharmaceutical ingredients | MS, ICP, L | The authors present a critical study of digestion methods for the determination of toxic elements in active pharmaceutical ingredients, | 257 |
| Hg | Cosmetic samples | MS, ICP, L | Direct determination of Hg by isotope dilution | 88 |
| Various | Ink on documents | MS, laser desorption, S | Differentiation of red ink on seals on documents | 258 |
| Various | Ink on documents | MS, LA, S | Discrimination of blue ballpoint pen ink on documents | 259 |
| Cr | Hair dyes | LIBS, —, S | Detection of carcinogenic Cr in hair dyes | 260 |
| Various | Fingerprints | TOF-MS, ICP, LA | Forensic analysis of trace evidence | 261 |
Advances in instrumentation include the development of portable instrumentation and the first commercially available mobile instrument for in situ scanning macro-XRF (MA-XRF) investigations of historical paintings has been reported by Alfeld et al.64 The technique of MA-XRF is a variant of XRF imaging which allows for the visualization of elemental distribution on flat macroscopic surfaces. This kind of analysis has enabled the elemental distribution within images to visualize hidden paint layers, providing unique insights into the creative process employed by the artist and the conservation history of the painting. The instrument is capable of imaging the distribution of the main constituents of the surface and sub-surface layers of paint over an area of 80 cm by 60 cm, with dwell times below 10 ms and a lateral resolution of better than 100 μm. The elemental capability of this instrument ranges from Ta to Mo with K-line sensitivity for these elements being presented. For many elements present at 1% m/m, signals of more than 1000 cps were achieved, giving 1 s LOD of around 100 ppm for these elements. Heavier elements such as Au, Hg and Pb were also easily imaged, as their L-lines fall within this range. It should be noted that for many heavier elements including Cd the absorption of the L-lines by covering layers of paint precluded the imaging of these elements in hidden paint layers. The authors acknowledged that the instrument suffered a lack of sensitivity for lines more energetic than for those of Rh (20.2 KeV). Visualizing heavier elements including Cd, Sn, and Sb by their K-lines was problematic as they are crucial elements in the study of many paintings.
In a similar application, Zielinska et al.65 developed an XRF system with the capability to image simultaneously large surface areas of paintings, as opposed to pixel-by-pixel scanning. This instrument utilized a wide field uniform excitation X-ray beam and a position sensitive energy dispersive detector. The fluorescence from a 10 cm by 10 cm was acquired and projected onto a gas electron multiplier detector of the same area. Compared with conventional imaging techniques, this new instrument reduced analysis time by 2 or 3 orders of magnitude and represents a significant advance in imaging capability.
Hybridization of LIBS with LA-TOF-MS makes use of the obvious synergies of the laser technology. A significant development in the combination of the two techniques was made on the basis of a hybrid experimental set up for the characterization of paint materials and pigments commonly found in culturally significant objects.66 The optical emission spectra from the LIBS process led to rapid elemental identification and the mass spectra yielded information on the isotopic content and molecular nature of the samples. The experimental set up facilitated either simultaneous or sequential acquisition of LIBS spectra and mass spectra. Sequential acquisition was found preferable for materials having lower fluence thresholds for desorption and ionization, relative to plasma formation.
The use of multiple spectroscopic techniques has been popular. LIBS lends itself to a combination with Raman spectroscopy as both elemental and molecular information is generated within one analysis, using a single device. The reader may find a review of combined LIBS and Raman spectroscopy of interest. This review contains 90 references and describes historical instrumental developments, basic instrumental principles and technological aspects of this instrumentation, together with a range of diverse applications.67 This kind of multiple analytical technology is likely to yield much more information than single technique analyses on many sample types. For example, the examination of oil paintings on copper plate substrates by XRF, XRD, Raman and diffuse reflectance FTIR,68 the study of historical paintings by imaging spectroscopy and XRF,69 the study of Roman murals by XRD, LIBS, Raman and FTIR70 and the characterization of an ancient Japanese lacquer by non-invasive XRF and neutron radiography71 are examples of applications of multiple analytical techniques being used to yield much more information than would otherwise be possible with single techniques.
The reader may find a review on mobile depth profiling and sub-surface imaging techniques for historical paintings of interest.72 This review, containing 171 references covers mobile non-destructive techniques which allow for the in situ investigation of paintings and includes X-ray radiography and infra-red reflectography. The element and species imaging capability of these techniques has been extended by the introduction of energy and wavelength resolved measurements. Scanning macro-XRF has enabled the determination of elemental distribution images in situ and optical coherence tomography has enabled the study of paint layers in cross-sections. These techniques and their variants are presented alongside THz imaging, NMR depth profiling and laser-based interference methods. The authors presented several case studies and critically evaluated the capabilities and limitations of the techniques. A review of synchrotron-based multiple techniques, including macro – to micro – X-ray beams for XRF, XAS and XRD for the characterization of paintings may also be of interest.73
In an example of the fundamental study of the chemistry of colours and the mechanism of colour fade, Gervais et al.74 presented a study of Prussian blue (PB), a dye widely employed in various artworks and one which exhibits some interesting magnetic and optical properties. The fading of PB is due to the reduction of FeIII to FeII and is strongly dependent on the substrate. The authors examined the role played by the substrate in affecting the structure of PB and how this modifies the redox process. They employed Fe-K-edge XAS on faded and unfaded samples to show that the structural changes in PB occur by contact with the substrate prior to fading. They proposed a roadmap to investigate further the highly complex processes involved in the fading of PB. This reviewer believes that this application may be of interest to those involved in surface coatings and inks.
Moros et al.75 have employed a multi-stage architecture algorithm built from a suitable combination of 3 learning classifiers, to classify fingerprints into a particular class. Neural network classifiers trained by the Levenberg–Marquardt rule were decided within 3D scatterplots projected onto the subspace of the most useful features extracted from the LIBS spectra. When fingerprints present on a manuscript containing one of six explosives (chloratite, ammonal, DNT, TNT, RDX and PETN) and a range of non-hazardous interferents, including butter, fuel oil and hand cream were analysed by LIBS, the algorithm was able to sort the fingerprints according to their hazardous character, even though their spectra were virtually identical in appearance. False positive and negative results were reported to be no higher than 10%. This demonstrates the power of a chemometric approach in obtaining maximum information from LIBS spectra.
Remote detection of fingerprints thought to contain explosives residues has also been demonstrated by Lucena et al.76 In this case, the detector was placed at a distance of 31 M from the target. Spatial distribution of chemicals in 2-dimensions, based on CN and Na emissions were used to detect chloratite, dinitrotoluene (DNT), trinitrotoluene (TNT), cyclotrimethylenetrinitramine (RDX) and pentaerythritol tetranitrate (PETN) residues on aluminium and glass substrates and 100% success rate was claimed.
As was the case in the analysis of metals (see Section 1), this review period produced several papers presenting fundamental studies of the processes occurring within LIBS plasmas. Delgado et al.77 presented a fundamental study on coincidence ion-photon detection of plasmas of high energy organic compounds, specifically TNT and DNT in a condensed phase irradiated with UV laser pulses. The authors described an advanced instrument for simultaneously monitoring the LIBS emission spectra and the ions formed in the plasma plume using laser ionization mass spectrometry (LIMS). The simultaneous measurement of the LIBS spectra and the LIMS spectra, described as optical-mass coincidental information was obtained from solid DNT and TNT samples. The formation and decay of atomic and molecular species, and rearrangement reactions were followed within the time scale of the plasma. Emission trends were correlated with the formation of atomic species (H, C, N, O), molecular ion species (24C2+, 26CN+/C2H2+) and molecular bands (C2 and CN). This indicated a correlation between time scales of the formation of these species and the energetics of the species, particularly of the ring-opening nitrotoluenes. The same group78 has also undertaken a fundamental investigation into the vibrational emission of CN molecules (B2Σ–X2Σ band) occurring during LIBS of organic molecules. This band is one of the strongest emissions appearing in organic compounds when analysed by LIBS in an air atmosphere. The authors found that this emission was dependent on the molecular structure of the materials, on the time scale of the measurement and on the nature of the sample surface. They also found that alterations in the distribution of the emissions in terms of relative intensities were dependent on the molecular structure of every material investigated. In a further paper from this group, Serrano et al.79 employed LIBS together with classification algorithms (supervised learning classifiers) to facilitate the discrimination of explosives from the organic substrates and various interfering substances which are often present. The use of chemometric techniques in conjunction with a fundamental knowledge of the processes occurring within a plasma is likely to widen the applicability of LIBS in the future.
De Lucia and Gottfried reported several important advances in last year's review1 and continued their important work on improving the understanding of the LIBS processes. They have reported the influence of molecular structure on the plasma emission of the explosive cyclotrimethylenetrinitramine (RDX) and organic polymers.80 In this work, the emissions were studied in an argon atmosphere and the relationship between molecular structure and emission was established. The percentage of atomic species (C, H, N, O) and bond types (C–C, C![[double bond, length as m-dash]](https://www.rsc.org/images/entities/char_e001.gif)
C, C–N) were correlated with atomic and molecular emission intensities and decay rates. Time resolved spectra were acquired and decay rates were attributed to molecular structure of the analyte molecules. The authors reflected on the possibility that this could be used to improve the discrimination of explosives on organic substrates.
Yang et al.81 have employed molecular emissions arising from the LIBS of organic molecules to compliment the elemental information gained during the analysis. In this case, molecular emissions in the mid IR to far IR spectra (4–12 μm) were obtained. Perhaps unsurprisingly, Yang et al. found that the LIBS molecular emissions in this region were closely correlated with their liquid phase FTIR spectra. Interestingly, this did show that intact molecules do survive the LIBS event. The combination of atomic and IR spectra may be another important technique in the advancement of LIBS for the classification of compounds.
Although preconcentration methods add a level of complexity and remove much of the ability for remote analysis, Fujiyama-Novak et al.82 employed a preconcentration/separation system coupled to a micro-hollow glow discharge (MHGD) plasma detector for the analysis of explosives. Separation eliminated air interferences and preconcentration yielded detection limits of less than 5 ppb for triacetate peroxide and dinitrotoluene. The authors claimed that the miniaturized system was field portable.
The boundaries between the different scientific disciplines are becoming increasingly fuzzy and nowhere is this more apparent than in the use of chemical analytical techniques for the determination of traditional biological parameters, including bacteria, for example through cell wall analysis. In an interesting application of LIBS, Putnam et al.83 described the classification of live bacteria from thirteen taxonomic bacterial classes. They used sums, ratios and complex ratios of the atomic emission lines and employed a discriminant function analysis to determine the individual variables required for optimal classification. A model constructed of 80 independent variables from simple and complex emission line ratios provided greatest sensitivity and specificity.
One area where there is much development still to be done is in the determination of light elements by LIBS. A review of the current state of LIBS determination of light elements was presented containing 98.84 The review contains some interesting papers on LIBS performed in the far and vacuum UV as well as in the UV, visible and NIR regions of the spectrum. Applications cover many non-conducting materials including gases, aerosols, soil, cement and a range of organic compounds and includes a range of elements from Li to Cl. Developments in instrument technology are also included and touch upon anticipated improvements in sensitivity for light elements by employing femto second laser pulses and diode lasers.
A low temperature dielectric barrier discharge (DBD) device has been developed by Han et al.86 This is an atmospheric pressure device with low power consumption which excites C emission. The emission is detected in a microplasma carbon atomic emission detector which was constructed in-house and employed as a GC detector for volatile organic compounds. The paper described the construction of the DBD device and its evaluation via the analysis of a series of organic compounds including formaldehyde, ethyl acetate, methanol, ethanol and a series of n-alcohols. Absolute detection limits were between 0.12 and 0.28 ng which is slightly higher than can be achieved with a flame ionization detector (FID). However, the advantage was that compounds which are not detectable by FIDs, including formaldehyde, CO and CO2, could be detected. Molecular emission may also be carried out in tandem with other detectors to spectrally resolve overlapping peaks.
The determination of Hg presents multiple analytical challenges due to its volatility and propensity to stick to surfaces. A number of papers dealing with mercury determination appeared during this review period, mainly in cosmetics and pharmaceuticals. Several of these are applications describing the large concentrations of Hg in a variety of samples which are of interest from the point of view of potential health effects but do not advance the analytical chemistry of Hg determination. These have therefore not been included in this review. Papers outlying advances in the determination of Hg including Hg speciation and isotope dilution procedures are included.
Holtkamp et al. presented an interesting paper outlining complexation and oxidation strategies for improved determination of Hg in vaccines, using TXRF.87 Whilst Hg determination by TXRF is often perceived to be relatively straightforward, certain challenges need to be addressed. These include poor reproducibility, caused by time dependence of the Hg signal due to the volatility of the analyte when on the measurement disc. Dimercaptosuccinic acid (DMSA) and EDTA were investigated as complexation reagents. Ammonium pyrrolidine-dithiocarbamate and ammonium persulfate were investigated as oxidizing agents. For each reagent, the time-dependent decrease in the Hg signal was measured. For untreated samples, up to 50% loss of signal over 15 minutes and around 75% loss after 40 minutes was observed, even when Hg was present as HgCl2. The addition of ammonium persulfate limited the loss to around 25% and EDTA resulted in no measurable loss of signal after 60 minutes. With EDTA, RSD figures over this time were 1.63% and 0.60% for 0.5 mg L−1 and 5 mg L−1 respectively. The addition of the oxidant, DMSA yielded similar results to the EDTA. The reagents, DMSA and EDTA were then tested with methyl mercury chloride, ethyl mercury chloride and thiomersal and were also found to stabilize the Hg signal in these compounds over at least 60 minutes.
Direct determination of Hg in cosmetic samples has been achieved by isotope dilution photochemical vapour generation (PVG) ICP-MS.88 Cosmetic samples were dissolved directly in formic acid solution prior to PVG for the reduction of Hg into its elemental form. Highly enriched 201Hg was the isotope spike which was added to the samples. Quantitation was based on the measurement of the ratio of 201Hg/202Hg. Matrix effects were virtually eliminated using isotope dilution calibration and detection limits of 0.6 pg mL−1 were reported.
The determination of platinum group metals (PGM) catalyst residue in active pharmaceutical ingredients is an important analytical requirement and simple procedures are required which demonstrate sufficient sensitivity. Bench top TXRF methodology has been developed for the determination of Ir, Pd, Pt and Rh in various active pharmaceutical ingredients API samples.89 A range of sample pretreatments was presented (dissolution and digestion of the solid samples) and validated according to the requirements of the United States Pharmacopeia (USP), with LOQ of 2–4 mg kg−1 being reported. It is likely that TXRF will become more widely used in the future, due to its wide applicability, sensitivity and relative freedom from matrix effects.
A microwave-based thermal nebulizer (MWTN) has for the first time been used as an on-line preconcentration device in ICP-AES.90 The MWTN was operated either as a pure nebulizer or as both a preconcentration device and nebulizer, depending on the microwave power employed. At a power of greater than 100 W with highly alcoholic solutions, the energy per solvent mass was high enough to evaporate all the solvent within the nebulizer, thus depositing the analyte on the inner walls of the MWTN capillary. On reducing the power, the retained analyte was swept into the plasma by the aerosol. Detection limits for a range of elements (Al, Ca, Cd, Cr, Cu, Fe, K, Mg, Mn, Na, Pb, Zn) were claimed to be an order of magnitude lower than when the MWTN was operating purely as a nebulizer. Analyte recoveries ranged from 93% to 107% when commercial spirit samples were measured.
Legislation is driving the need for the analysis of toxicologically relevant elements in pharmaceutical samples and many procedures continue to follow traditional digestion procedures. However, the determination of Os is prone to errors due to the formation of various volatile species on oxidation of the matrix. This has been addressed by the development of a novel approach to stabilize Os, described in a Technical Note.91 Traditionally Os species have been stabilized by nitric acid, however, this leads to the formation of volatile Os species as demonstrated by the deterioration of the analytical signal of Os over time when stored in nitric acid. The authors investigated alternative strategies for use during oxidative pressure vessel digestion and determined the recoveries of Os from CRMs using the different strategies. Analysis was by both quadrupole ICP-MS with collision cell and sector field ICP-MS. In all cases, matrix matching was required, as simple matrix adjustment with HCl and HNO3 resulted in significantly elevated (up to 222%) recovery. Matrix adjustment with an optimized stabilization solution containing acetic acid (0.5% v/v), thiourea (0.01 M) and ascorbic acid (0.1 g L−1) resulted in recoveries of between 92% and 110% and 7% RSD (n = 6) for a range of CRMs with concentrations between 1 μg L−1 and 10 μg L−1. Recovery of 82% in spiked excipient material was reported. This was well within the required acceptance criteria. The authors are to be commended for rigorously determining limits of quantitation (LOQ) based on a set of methodological blanks (n = 10), and LOQ of around 0.02 μg g−1 were quoted.
2.3. Inorganic chemicals, catalysts and acids
This year has seen a greater focus to produce a concise review of papers that demonstrate the advancement of methodology and application of analytical atomic spectrometry. Consequently, the catalyst section has been moved to a subsection within this part of the review together with forensic applications, the analysis of building materials and minerals and laser-based techniques.The determination of the muzzle to target distance is an important aspect of the investigation of firearm related crime as it can help determine the relative positions of the persons involved and allude to the shooters intent. Turillazzi et al.94 reported the quantification of GSR from skin around a gunshot wound using ICP-OES as a means of estimating this distance. A total of 50 test shots were fired into pig skin targets from distances between 0.2 and 150 cm and a 10 cm radius of skin was excised from two opposite sides of the entry hole. Samples were freeze dried before digestion using 2 mL concentrated HNO3 in a sealed PTFE vessel at 120 °C for 8 h. The analytes of interest included Al, Ba, Cu, Pb, Sb, Sr and Zn and calibrations were performed using common aqueous stock solutions. Perhaps somewhat predictably, the concentration of analytes decreased with increasing muzzle to target distance. However, the technique enabled quantification of GSR at distances up to 150 cm compared with the traditional chemographic staining test limits of approximately 50 cm. The same correlation of Ba, Cu, Pb, Sb and Zn concentration as a function of shooting distance was determined by directly measuring GSR deposited on cloth using EDXRF.95 A polarized excitation source, with Mo secondary target, was collimated to a 1.5 cm analysis area and quantification was performed using fundamental parameters. The obvious benefits of this method are that it is non-destructive and without chemical treatment and therefore samples can be analysed repeatedly or used for further tests.
The forensic analysis of laser printed ink by XRF and plume laser excited atomic fluorescence (plume-LEAF) for the determination of ink origin and illicit overprinting was presented by Chu et al.96 Four branded black toner samples were selected that are widely used and similar in composition. Text of various font sizes was printed onto standard copier paper for analysis. Elemental composition were determined by XRF using a handheld analyser, collecting spectra at three voltage ranges (<19 KeV, 19–23 KeV and >23 KeV) for a total of 90 seconds. The results indicated that for large printed areas the technique could discriminate between the inks. However, at small font sizes (<20), the concentration of many of the characteristic elements, such as Fe and Zn, fell below the LOD. Multi-element pulse-LEAF analysis was performed on the same samples using a custom two-laser-pulse probe pioneered by the authors. Briefly, a Nd:YAG 355 nm laser pulse was focussed on to a 100 μm spot at the surface of the print, forming a plume. Seven microseconds later, the ablated plume was intercepted transversely by an ArF 193 nm laser pulse, vaporising the toner particles to produce analyte atoms. The trailing portion of the same laser pulse induced the analytes to fluoresce. Characteristic emissions were detected by an intensified charge-coupled device. The sensitivity of the technique was exceptional, the theoretical LOD for Sr 460.7 nm was claimed to be in the region of 180 attogram (180 × 10−18 g) in the 620 pg of sample ablated, meaning fewer pulses were required, hence less sample destruction. Discrimination of the four toner samples was possible after only two pulses and identification using principle component analysis was 100% successful over 1870 replicates.
The speciation power of ToF-SIMS was utilized to better understand the catalytic functionality of TiO2–ZrO2 supported Pd for the total oxidation of trichloroethylene.99 Positive and negative polarity measurements were performed using pulsed Bi3+ primary ions (25 KeV, 0.25 pA) over a 150 μm2 area for 200 s, maintaining static conditions. Investigation of the Pd fragment ions was hindered due to isotopic interference from 90ZrO+, 92ZrO+ and 94ZrO+, although fragments containing 104Pd+ and 105Pd+ gave evidence of dispersion as PdO and PdO2 in the first top layers or fresh prepared catalysts. The analysis of used catalyst indicated surface retention of Cl, characterized by intense Cl−, ClO− and Cl2− peaks. Interestingly, neither TiCl− nor ZrCl− ions were observed, whilst TiO2Cl− and ZrO2Cl− ions were clearly detected indicating that Cl did not directly affect the support metal atoms. By contrast, PdCl2− ions were always detected, signifying a change in Pd species. Further work was suggested to rule out the formation PdCl2 from acidic digestion due to a combined presence of HCl and H2O during the reactor shut down procedure. ToF-SIMS was used in conjunction with XPS and XRD to understand the interactions of Pd and co-metals in Pd-M supported catalysts (where M = In, Bi, Te) used in hydrogen transfer reactions.100 For each of the three catalysts systems studied, ToF-SIMS spectra revealed the presence of binary metallic species which could be correlated to catalytic performance. For example, Pd–Bi supported catalysts with BiPd bimetallic surface species were found to be active for the hydrodechlorination of 2,4-dichlorophenol. However, an increase of Bi concentration led to a reduction in activity which was related to the formation of a Bi2Pd surface species identified by ToF-SIMS. Further examples covering Pd–In supported and Pd–Te supported catalyst systems were also included.
Further papers of interest published during this review period include a review of thermo-analytical and spectroscopic techniques for the study of metal oxide electrocatalytic thin film evolution, 32 ref. 101. In the opinion of the reviewer this appears to be a somewhat narrow topic to review. It does however, contain an interesting discussion on depth profiling of thin films using SIMS. An online preconcentration procedure for the determination of Ag+and Pd2+in water, cream and anode slimes by FAAS was descried by Cetin et al.102 The paper describes in detail the optimization of a flow injection system with a new chelating resin, poly(DPMAAm-co-DVP-co-AMPS), for the preconcentration of analyte prior to determination. Under optimum conditions detection limits were calculated to be 2.4 μg L−1 Ag and 1.7 μg L−1 Pd for a 4 minute analysis time.
Generally, LIBS is considered a portable technique allowing analysis of specimens in the field. However, the high excitation potential and low degree of atomization of Cl in plasma limits the sensitivity of conventional LIBS systems and demands an inert gas flush to lower detection limits. A double pulsed LIBS set up that allowed the determination of Cl in concrete without the need for an inert gas flush, opening up the possibility of a mobile device for on-site analysis.104 Radiation from Nd:YAG 532 nm and Nd:YALO (Nd doped Yttrium orthoaluminate crystal) 540 nm lasers were pulsed onto the sample surface with a 4 μs interpulse delay. The Cl 837.60 nm line in the near-IR range was selected as the analytical line together with Mg 279.08 nm as an internal standard. A linear calibration was produced using standards prepared from Portland cement spiked with SrCl2 and the LOD was calculated to be 50 mg Kg−1 under optimum conditions, compared with 2500 mg Kg−1 in conventional LIBS, which will allow early detection of cement degradation. It was proposed that the increased sensitivity was due to the formation of monochlorides, CaCl etc. in the initial plasma, which were dissociated through the action of the second laser pulse.
Panda and colleagues at the Archaeological Survey of India discussed the importance of the chemical analysis of ancient mortar when selecting modern alternatives for restoration.105 They used a combination of XRD and SEM to understand the structural properties in combination with elemental information from PIXE experiments performed on the 9SDH-2 pelletron tandem accelerator using a 3 MeV proton beam. In addition to the elements commonly found in mortar (Ca, Fe and K) a number of trace metals were observed including P from the addition of cow dung as a filler, Ti added to increase strength and durability as well as Mn, Ni and Zn added for similar purposes.
The determination of Al:Si ratios and their chemical environment in zeolite and other silica-alumina structures is key to understanding their properties. Yamamoto et al. discussed the analysis of Al coordination state by extended X-ray emission fine structure spectroscopy (EXEFS) performed using a commercially available WDXRF spectrometer.106 The team measured the energy shift of the K-LL radiative Auger peak for Al in different coordination environments using a Rh excitation tube and TAP (100) analyser crystal. They found that a shift to increasing energy correlated with increased coordination number of the compound studied and tied well with XANES and high resolution WDXRF measurements. The potential to gain coordination information of materials without specialist equipment would be very appealing to research communities. However, the technique will be limited to materials with a high Al concentration due to sensitivity of the satellite analytical lines. A calibration-free LIBS approach for the determination of Al:Si ratios was presented by Horňáčková et al.107 The fundamental theory of calibration-free LIBS was discussed at length, together with detailed description of the spectra processing required. The application of the technique for the determination of Al and Si in three zeolite samples prepared as pressed pellets was presented. Results were in good agreement with wet chemical analysis without the need of matrix matched reference materials, which can be a limiting factor for LIBS analysis. Results can only be considered semi-quantitative, although with further refinement full quantification may become possible. Developments like this could result in LIBS becoming more widely accepted in quantitative analytical applications. X-ray scattering spectroscopy was also proposed as a non-destructive technique for the determination of Al in silicates.108 Scattering measurements were performed using a bench top EDXRF instrument with a Rh anode X-ray tube and calibration with a combination of mechanically and chemically mixed Al in silica sources. A good agreement between predicted and measured concentrations of Al was observed. This is an example of the versatility of commercial XRF instruments; however, introduction of another element would require the construction of a new calibration model. Therefore, there is no advantage over conventional XRF measurements.
Cassiterite (SnO2) is specified as a ‘conflict mineral' by a U.S. Government Act and companies are required to verify materials they use are not from conflict zones. The application of LA-ICP-MS fingerprinting of trace metal concentration in cassiterite as a means of verifying its origin was published by Gäbler et al.109 Analysis was performed using a 10 Hz, 193 nm laser ablation system with a 50 μm spot size. Ablated material was transported to a sector field ICP-MS instrument using a helium carrier gas. In the absence of certified cassiterite reference materials non-matrix matched calibration standards were used which, predictably, produced a bias in the results. However, fingerprinting of materials did not necessarily require accurate values because element ratios were used as the key discriminator between samples. Therefore, as long as the technique remained constant the results would remain valid. The team used this approach to successfully build a database of 185 cassiterite materials from 155 locations.
Two papers were published discussing the potential application of LIBS for the ‘at site’ analysis of scale deposits. Siozos et al. proposed a straightforward analysis based on linear correlation of LIBS spectra to discriminate scale samples into three main groups; Fe-rich, Ca-rich and Ba-rich.110 A Q switched Nd:YAG, 1064 nm, excitation laser was used and emission spectra collected across a wavelength range 200–660 nm. S emission lines in the NIR at 860–960 nm were recorded allowing further discrimination between sulfates and carbonates. Although results were not quantitative they allowed quick identification of the main mineral type assisting in deciding an appropriate dissolution strategy. Petroleum pipeline scales were analysed by LIBS using a double-pulse calibration free approach.111 Two collinear Nd:YAG, 1064 nm, laser pulses with a 1 μs inter-pulse delay were used as the excitation source and spectra collected from 200 nm to 975 nm. Elements that are characteristic of petroleum (C, H, N, O, Fe, Mg, Na and V) were detected in addition to Ca, Al and Si which form the matrix of the scale. A calibration-free LIBS model was presented by Pedarnig et al. and its accuracy evaluated for the on-site analysis of industrial slag materials.112 Data obtained using LIBS for major oxides of Al, Ca, Fe, Mg, Mn and Si correlated with concentrations determined using a standardised XRF method in the laboratory.
Quantitative analysis of doped rare earth elements, La and Nd, in phosphors using LIBS was reported.113 Calibration materials were prepared in-house by mixing various ratios of La2O3 and Nd2O3 with sulfur, sodium carbonate and potassium phosphate followed by fusion at 1150 °C and washing with hydrochloric acid. Formation of a single phase oxysulfide was confirmed by XRD. The LIBS spectra were collected from the plasma generated using a 355 nm Nd:YAG laser. Calibration curves were constructed for both La and Nd using oxygen as an internal standard. Linear calibrations were produced with regression coefficients of 0.991 and 0.960 for La/O and Nd/O respectively.
The determination of F in commercially available toothpaste using LIBS was presented by Gondal et al.114 Analysis was not straightforward because samples were in a semi-solid form, resulting in a change in the distance from the focusing lens to the sample surface due to excessive pitting during the ablation process. To overcome this, samples were pressed into a die and annealed at 60 °C prior to analysis, making the sample target harder and less prone to excessive pitting. Experimental parameters such as gate/time delay and laser energy were optimized in order improve the signal to noise ratio, LOD and linearity of 731.1 nm F spectral line. The LOD for the detection of F in toothpaste was estimated to be 150 ppm using this methodology.
Finally, an interesting paper by Orsel et al. described the use of laser induced fluorescence spectroscopy (LIF) to map ground state populations of Al and AlO in plasma plumes generated by laser ablation of LaAlO3 during pulsed laser deposition.115 The paper details a custom build system where a KrF laser beam causes ablation of the target material, LaAlO3, and a tuneable dye laser to excite Al and AlO species in the plasma plume. The team were able to map the density of species throughout the plasma plume and gained understanding of the deposition process. The application of this technique to analytical laser ablation could aid the understanding of the ablation processes that can affect transport of species to the plasma.
EDTA functionalized cellulose fibres were synthesized and employed as a solid-phase extraction material for the preconcentration of Pb from salt and water samples prior to determination by FAAS.117 Analytical parameters such as pH, sample/eluent volume, flow rate etc. were optimized to achieve a 1.5 μg L−1 limit of detection. The quantitative recovery of Pb from various samples with a RSD of 0.6–2.2% reflected the validity and the accuracy of the method. Furthermore, the sorbent material could be reused at least 50 times without any loss of efficiency.
Holzlechner et al. proposed a modified “collimated burst alignment” ToF-SIMS operation mode to enable more accurate determination of oxygen isotopic fraction with sub 100 nm lateral resolution.118 This was achieved by modification of the beam guidance in the primary ion gun. This modification reduced the detector dead-time effects and ion interactions to a minimum and secondary ion intensities could be obtained more accurately. The benefits of this optimization were demonstrated by measuring the natural isotope abundances of several oxides including SrTiO3 and LaCoO3.
A paper evaluating the potential of commercial WDXRF spectrometers to perform practical speciation analysis of Cr in solid materials was published by Malherbe and Claverie.119 Measurements across the Kβ spectral envelope were made using a standard WDXRF system fitted with a Rh X-ray Tube, GeIII analysing crystal and flow proportional counter. Several pure compounds of Cr0, CrII, CrIII and CrIV were analysed and the K′β, Kβ1,3, K′′β and Kβ2,5 lines observed. The main Kβ1,3 line originates from the 3p-1 s transition of the central metallic atom and its energy was directly linked to the oxidation state of Cr. The higher the oxidation state of Cr, the lower the observed energy of the Kβ1,3 peak maxima. The additional lines have origins in valence-core transitions, and hence shifts in these peaks could be attributed to the chemical environment of the Cr species. This could be an alternative technique to XPS, which is surface limited, and offer a screening method prior to XANES experiments which are less readily accessible due to limited synchrotron light sources.
2.4. Nuclear materials
The analysis of nuclear materials has again proven to be an extremely popular topic. The papers discussed in this review have largely concentrated on the measurement of analytes in nuclear fuels and components of reactors. Those papers discussing the determination of radioactive contaminants in environmental samples have, in the main, been ignored. The exceptions to this are those that have analysed single particles or swipe samples or which have undertaken some type of nuclear safeguards/dating analysis. Similarly, those papers that have discussed instrumental developments have also been largely ignored. Instead, they will be reviewed in a sister publication.2 Given the potentially very hazardous nature of the sample types analysed, it is unsurprising that many of the techniques used have been capable of standoff or remote analysis.Reviews are always a helpful addition to the literature because they summarize subject areas. One such publication was prepared by Kutschera120 who discussed, with the aid of 267 references, the applications of accelerator mass spectrometry (AMS) to environmental analysis. The review started with a map showing the locations of approximately 100 laboratories with this facility and went on to list the isotopes capable of measurement using the technique. Applications of AMS in several different compartments of the environment, e.g. lithosphere, cosmosphere, hydrosphere and cryosphere were summarized. The main area of interest to this review is where the author has discussed the use of AMS in the technosphere. Included in this section of the review was the analysis of man-made nuclides, half-life measurements, reaction studies for nuclear astrophysics, neutron dosimetry of the Hiroshima bomb and applications that involve nuclear safeguards. Potential future developments were also listed and these included the development of ways to decrease the sample size required, the decrease in size of the instrumentation and new methods for isobar suppression of negative ions. A review by Zheng et al.121 discussed (with 289 refs) the key role of atomic spectrometry in radiation protection. The capabilities and characteristics of different techniques such as thermal ionization mass spectrometry (TIMS), AMS and ICP-MS were summarized and compared with non-atomic spectrometric techniques such as alpha spectrometry, gamma spectrometry and beta counting. Also discussed briefly, were the techniques of PIXE and synchrotron radiation XRF. A useful table summarising the detection limits for different isotopes using different techniques was also presented, along with the reference the work came from. The review went on to discuss papers that have reported work on different nuclear accidents, e.g. Chernobyl, the JCO criticality incident, Fukushima etc. and also discussed the fallout from nuclear bomb tests, as well as the Hiroshima and Nagasaki bombs. The review finished by predicting some future applications, with an emphasis on those involving the Fukushima nuclear incident.
Other studies that have reported the use of LIBS for deposit characterization include ones by Malaquias et al.,126 Fantoni et al.127 and Xiao et al.128 All of these papers are related, with many of the same authors appearing on each of them. The work was undertaken on tiles at the International Thermonuclear Experimental Reactor (ITER). Another related study, by van der Meiden et al.129 used LIBS in a qualitative manner to measure the surface composition and the depth profile of tiles from ITER after plasma exposure. Laser induced desorption-quadrupole mass spectrometry and thermal desorption spectrometry were also utilized during the study. Also used was an advanced Thomson scattering system for electron density measurements and electron temperature profiles. The LIBS system used in this study appears quite basic in that the spectrometer has a spectral range of only 60 nm, but the light collection system was efficient, enabling more light to be collected compared with echelle spectrometers. Improvements to the system are anticipated. A further paper, by Paris et al.130 also used LIBS to monitor the erosion of coatings and changes to the surface structure on materials that had been exposed to nuclear plasma.
Other LIBS applications have focussed on the analysis of fuels, coolants or waste products rather than components. A paper by Wang et al.131 described a micro-LIBS system comprising a Nd:YAG laser operating at 266 nm, a microscope and an XY translation stage. The instrumental setup was described in detail and a schematic diagram provided. The laser beam was focussed on the sample through a microscope with a ×40 UV objective lens. The laser then formed the plasma on the sample and the light produced was transmitted through a fibre-optic, back through the microscope, to a spectrometer furnished with an intensified CCD detector. A further CCD was used with the microscope so that the focus of the laser spot could be monitored. The system was applied to the analysis of a nuclear waste molybdenum-rich glass-ceramic. Analysis of a 1.6 × 1.2 mm2 area giving 160 × 120 laser firings took approximately one hour. Craters formed in the sample were examined using AFM and were less than 7 μm in diameter. The protocol was validated using LA-ICP-MS with NIST certified glass samples being used as calibrants. Analytical data obtained from the LIBS system were subjected to PCA to investigate the correlation of elements in the two phases of the glass-ceramic. A correlation between Ca, Mo, Sr and the REEs indicated their preferential incorporation into the calcium molybdate phase, whereas the anti-correlation between Al, Fe, Mo and Zr demonstrated their affinity for the glass phase.
The purity of liquid sodium coolant used in fast nuclear reactors was assessed by Maury et al.132 Approximately 300 g of the liquid sodium was contained in a hermetic oven at 150 °C. The Nd:YAG laser operating at 266 nm, with a duration of 5 ns and a frequency of 20 Hz, was focussed though an optical window into the oven and light emitted from the resulting plasma was transmitted via the optical collection system and a fibre-optic to a Czerny–Turner spectrometer and an intensified CCD detector. The analytes chosen were In and Pb and calibration was achieved using the method of standard additions. Some problems associated with signal fluctuations and intensity drift were observed and these were associated with different pressures within the oven. However, these problems were largely overcome by using background subtraction and/or normalization. The authors described this process. The LOD obtained were 6 and 5 ppm for Pb and In respectively. The last paper in this sub-section to be discussed is by Barefield et al.133 who used LIBS to identify and assign complex atomic emission spectra from mixed actinide oxides such as uranium dioxide–plutonium dioxide and uranium dioxide–plutonium dioxide–americium dioxide–neptunium dioxide simulated fuel pellets. For the latter sample, over 800 atomic emission lines were identified. The Am, Pu and U wavelengths were consistent with those found in the literature. However, only a few of the Np lines could be identified with confidence. It was concluded that if the LIBS system had a resolving power of 20000, it was capable of determining analytes in a complex mixture of actinides.
Certified reference materials and reference methods for nuclear safeguards and security is clearly an important subject and has been discussed by Jakopic et al.134 who reported that IRMM is currently replacing some of its exhausted stocks of CRMs with new ones and that some of the existing materials are being re-examined in an attempt to improve the uncertainties associated with their measurement. The authors described how most safeguards methods measure the ratios of major isotopes such as 235U/238U or 240Pu/239Pu but that work was in progress to also include some of the minor isotope ratios. Using 238Pu/234U, 239Pu/235U and 240Pu/236U the age of NBS 946 was calculated to be 40.35, 40.43 and 40.48 years respectively. This meant that it had been separated in May 1970. In other work, TIMS was used to measure Pu isotopes in the materials IAEA 135 and IAEA 368. Mention was also made of the inter-laboratory comparisons REIMEP-17 and NUSIMEP-8 for measurements of U and Pu amount content and isotopic abundances in fissile material and environmental samples. Two papers from the Argonne facility have discussed the re-certification or analysis of a certified reference material.135,136 Kraiem et al.135 re-certified the material CRM 125-A, an enriched uranium oxide pellet using three different types of TIMS measurements; namely TIMS with internal standardization, TIMS with total extraction and TIMS with modified total extraction. The total evaporation method gives excellent precision for major-based ratios, but minor isotope intensity measurements are biased because of peak tailing from the major isotopes. The modified total extraction method overcomes this problem by allowing measurement of backgrounds, internal yield calibration of the secondary electron multiplier detector, peak centring and ion beam focusing. It also enables internal mass bias correction by using the externally corrected 235U/238U values to determine an appropriate correction value. Six pellets were analysed for the isotope ratios 234U/238U, 235U/238U and 236U/238U, yielding results of 0.00039130(38), 0.042301(25) and 0.0000040754(47), respectively. No 233U was observed and the results for all six pellets were concordant. The analytical uncertainties were significantly smaller than on the original certificate. The second paper, by Mathew et al.,136 used the same approach for the depleted uranium assay standard CRM 115. Another paper by Mathew et al.137 confirmed the finding that the total evaporation method yielded excellent ratios for major isotopes, but that peak tailing caused bias for minor ones.
Two papers have discussed the measurement of different isotope ratios for safeguards purposes. Pointurier et al.138 dated small amounts of uranium (sub-μg quantities) by determining 230Th/234U. Their preferred method was to eliminate the matrix using the resin AG1 X8 in a hydrochloric acid medium because it diminished the possibility of contamination from reagents or the environment. The Th extraction efficiency was greater than 90%, the amount of 230Th introduced was negligible and using ICP-MS as a detection technique, the LOD for Th was at the femtogram level. A similar approach was taken by Eppich et al.139 who dated uranium materials using the 235U/231Pa chronometer. The 231Pa was determined using a 233Pa spike that had been prepared from a 237Np source. The Pa prepared in this way was separated from the neptunium matrix using AG1 X8, with the neptunium matrix being eluted with HCl. The Pa was eluted from the resin using 2% nitric acid containing 25 μL of saturated boric acid. The Pa eluted was then retained on quartz wool, where it went through several cycles of elution/retention prior to finally being eluted using 2% nitric acid containing 0.005 M HF. The 231Pa had to be separated from the uranium sample matrix using a similar protocol. Analysis was achieved using ID with a MC-ICP-MS instrument. The combined uncertainty for age dating using this methodology ranged from 1.5–3%, which was an improvement on that obtained using alpha spectrometry. The methodology was applied to the dating of five uranium standard materials with the ages calculated using 235U/231Pa and 234U/230Th being concordant for each.
Surface oxidation can disrupt the dating process since the chronology depends on the 230Th being produced from the parent 234U and any oxidation may disrupt the natural ratio. Therefore, achieving an adequate etching to reach the natural metal is required to obtain the most accurate radiological dating. The effects of different etching procedures to remove surface oxidation of a uranium sample were determined by Meyers et al.140 A robust etching technique produced the most reliable data whereas more mild conditions led to estimates in the radiological age that were between 15 and hundreds of years older than the known age.
Several papers were published that describe the analysis of individual uranium or plutonium particles. The group from Iberaki, Japan has produced three papers in this area during this review period, two analysing uranium particles141,142 and one analysing plutonium particles.143 In one paper, SIMS was used to analyse particles obtained through wiping from a nuclear facility.142 The certified materials U050, U350 and U500 with a 235U content of 5.010, 35.190 and 49.696%, respectively, were used for alpha track detection and U350 was also used for mass bias correction for the SIMS analysis. For the alpha track detection, the particles were transferred from the wiping material onto silica wafers, covered with polycarbonate and then placed in contact with a CR-39 detector for a period of up to 28 days. The detectors were then removed, etched in 7 M NaOH at 70 °C for three hours and then the tracks counted using microscopy. For the SIMS analysis, a similar protocol was adopted, but once the particles had been encased with polycarbonate, they were placed on a glassy carbon planchet and ashed at a power of 300 W for 30 min. An oxygen primary beam with an energy of 15 keV was used to produce secondary ions of 234U+, 235U+, 236U+, 238U+ and 238U1H+ which were detected in peak jump mode. The combined alpha track – SIMS analysis was applied to three real samples. Using this combined approach, it was possible to measure significantly higher 235U/238U (in the range 0.0072–0.25) than that with SIMS alone, indicating that samples with significantly higher 235U than normal could be measured accurately. Both SIMS and solution nebulization ICP-MS were used for the analysis of uranium particles in the other paper.141 This paper also used a micro-sampling technique and automated particle measurement. The results for 235U/238U for automated particle measurement and ICP-MS were similar, but both were higher than those obtained using SIMS. For the plutonium paper,143 particles as small as 1 μm were age-dated. The particles had been prepared from the reference material SRM-947 and then stored for 3.9 years since the last purification. After dissolution of the particles, the Am and Pu were separated using anion exchange chromatography and their isotopic ratio measured using high resolution ICP-MS. Precision and accuracy of the dating were both improved using a spike of 243Am. The experimental results agreed well with the known age, with deviation being in the range 7 days–105 days and precision 0.16–0.5 years.
Another group that is working in this area is based in Arpajon, France. Pointurier et al.144 described the use of LA-ICP-MS for the analysis of single, micron-sized uranium particles. Results for 235U/238U from this technique were compared with those obtained using SIMS and from fission track-TIMS. The results obtained were in good agreement between all of the methods, with the age determined by LA-ICP-MS deviating by no more than 3% from those calculated using the other techniques. Precision was less impressive for LA-ICP-MS (7%) compared with 4.5% for fission track TIMS and 3% for SIMS. A second paper by the same group145 reported the use of SIMS for the analysis of single micron-sized uranium particles for U isotopic ratios as well as for F. Both O2+ and Cs+ were tested as primary ions, but the Cs+ source produced no discernible U signals. Therefore, the O2+ ions were used for all subsequent work. Normally, the IAEA recommendation is that samples are baked at 400 °C after deposition. The authors therefore undertook a study of the effects of heating and found that the 238UF signal dropped to 12% of that in a non-heated sample and that for UF4 it decreased by a factor of 30 if the sample was heated to 400 °C for 30 min. No baking was therefore used during this study. The results of the study enabled the authors to discriminate between uranium ore concentrate particles and particles coming from a conversion plant; something that U isotope ratios alone could not do. It was also established that no significant loss of F occurred even though the samples were simply stored in a plastic bag in the dark.
| Element | Matrix | Technique; atomization; presentation | Comments | Reference |
|---|---|---|---|---|
| 10B | Enriched steel samples | MS; ICP; LA | Steel samples enriched in 10B to an isotopic fraction of between 90 and 97% analysed using two different LA protocols. One used ns and the other fs laser shot duration. The instrumental setups were described. Although B distribution was inhomogeneous, the ratios remained constant throughout. Technique of EPMA also used | 262 |
| Cs and Sr | Radioactive samples | MS; ICP; L | A chromatographic separation of 134Cs, 135Cs, 137Cs and 87Sr from 134Ba, 135Ba, 137Ba and 87Rb isobars. All isotopes could be determined in one run using isocratic conditions (0.1 M oxalic acid neutralized with ammonia to pH 4.5–5.5). Retention time of all elements did not exceed 15 min when Zorbax SCX 300 or IonPac CS5A columns used. Activity of 134Cs and 137Cs calculated from ICP-MS data are comparable to those obtained using gamma spectroscopy | 263 |
| 237Np | Spent nuclear fuel samples | MS; ICP; L | 239Np used as a spike for the determination of 237Np using ID-ICP-MS. Recovery from synthetic samples was 95.9 ± 9.7%. Content of 237Np in three spent nuclear fuel samples was 0.15, 0.25 and 1.06 μg mg−1 U and these values were compared with those obtained using the ORIGEN-2 code. Results were in “fairly good agreement” | 264 |
| Pu | Planchets from alpha spectrometry | MS; ICP; L | Known concentrations of 239Pu and 242Pu placed on planchet. Two extraction methods compared. Both used nitric acid (50 mL of 0.36 M) for between 30 min and 180 min and at a temperature of 60 °C. One used a hotplate and the other an ultrasonic system. Both then dried the solution and re-suspended it in 10 mL of dilute nitric. A desolvation device was used to introduce sample to SF-ICP-MS instrument to avoid interference from 238U1H. Both processes achieved 70% extraction for 239Pu and 80% for 242Pu after 120 min; whereas the ultrasonic system was marginally better after 180 min, with extraction efficiencies being 96 and 98.2% for 239Pu and 242Pu, respectively. The hotplate achieved only 93.4 and 93.7% | 265 |
| Ru | Spent nuclear fuel | TIMS; —; s | Conditions for thermal ionization isotope dilution mass spectrometry (Ti-IDMS) optimized. Silica gel, boric acid and barium nitrate as an ionization enhancer and sucrose and hydroiodic acid solution as a reducing agent needed to be loaded onto the rhenium filament with the sample. Use of single filaments led to large peaks, increased stability and reduced isobaric effects when compared with double filament. Filament needed to be raised to 5 A at a rate of 0.1 A min−1 to obtain good results | 266 |
| 99Tc | Radioactive waste | MS; ICP; L | Analyte separated from matrix using TEVA resin and then determined using ICP-MS. Concentrations two orders of magnitude lower than those estimated using liquid scintillation counting, because the latter suffered interferences from other nuclides | 267 |
| Xe | Uranium dioxide | SIMS; —; s | Samples implanted with 136Xe at 800 keV and then either annealed at 1400–1600 °C or irradiated with 182 MeV iodine at room temperature, 600 °C or 1000 °C. Depth profiles of Xe determined using SIMS. Results indicated that Xe is mobile during irradiation at 1000 °C, but thermal treatment alone causes no migration. | 131 |
| Various (19) | Uranium–zirconium fuel ingots | TOF-MS; ICP; L | Dual solvent extraction system employed to remove zirconium (with 2-thionyltrifluoroacetone in the presence of tributyl phosphine oxide in 1,2 dichloroethane) and uranium (with tributyl phosphate and carbon tetrachloride). Recoveries >90% for 17 analytes and >83% for Cd and V. Detection limits in the range 1–99 μg kg−1 Method validated using gamma spectrometry | 268 |
| Various | Trinitite | MS; ICP; LA | Analysis of trinitite (the glassy residue left on the desert floor after the Trinity bomb) using LA-ICP-MS with high spatial resolution. 235U/238U and 240Pu/239Pu determined. Also detected was some fission material, e.g.137Cs. Positive correlation between Pu, Fe, Ca, U and 137Cs. Negative correlation between Pu ion signals and SiO2 and K2O. Results indicate that Pu is not incorporated into the unmelted crystalline grains of the precursor minerals | 269 |
| Various | Uranium oxide | TXRF; —; s | Conditions for determining low atomic number analytes (chiefly Al and Mg) were optimized. Uranium matrix had to be removed. Two CRMs dissolved in nitric acid and the uranium removed using 30% tri-n-butyl phosphate in dodecane. Aqueous liquid phase then analysed after the addition of scandium as an internal standard. Data for Mg were in good agreement with certified values. Data for Al were in very poor agreement (2.5 times higher). This was attributed to either a neighbouring silicon K peak or a residual uranium Mα peak | 270 |
There have been several interesting ICP-MS – based applications. Tanimizu et al.148 used a tandem quadrupole ICP-MS-MS in conjunction with oxygen addition to the collision cell to determine ultra-low 236U/238U isotope ratios in synthetic solutions and seawater. The U in the seawater was retained on a chelating disk and then eluted with nitric acid, enabling simultaneous matrix removal and preconcentration. The sample was finally spiked with NIST SRM 997, a material of known 205Tl/203Tl, to correct for mass bias. Sample introduction was through a desolvating nebulizer to ensure that only a dry sample reached the plasma. The introduction of oxygen to the collision cell enabled the authors to determine 236U16O/238U16O in the range 10−9 to 10−7 without the need to correct for spectral interferences. Another paper described a novel method for determining 249Bk/248Cm and 249Cf/248Cm in a sample of curium enriched with 248Cm to a concentration of 97%.149 The sample was first irradiated in a thermal neutron flux, dissolved in nitric acid and then the Bk and Cf separated using a strong cation exchange column. Including the chromatographic separation, a five-stage analysis was required that involved the use of both ICP-MS and TIMS. The authors explained their analytical strategy and gave a convenient schematic. Relative uncertainties of the Cf isotopic ratios ranged from 0.3–0.5%, whereas the uncertainty values for 249Bk/248Cm and 249Cf/248Cm were 6.1% and 3.2%, respectively. The level of uncertainty was in agreement for the requirement for transmutation studies. A method for determining 34S/32S in uranium ore concentrates for origin assessment was described by Han et al.150 Sulfate was leached from the sample and then 34S/32S determined using a multicollector ICP-MS instrument. A study of the effect of sample composition on the accuracy was undertaken and, even after optimization, it was necessary to match the sample to the bracketing standard to obtain best accuracy. Method validation was achieved by analysis of the SRMs IAEA-S-2, IAEA-S-3 and IAEA-S-4. The delta 34S values could be determined with uncertainties of between 0.45 and 1.9 parts per thousand. The method was applied to uranium ore concentrates from around the World.
Wang et al.151 extracted UF2− ions from a uranium tetrafluoride sample in an attempt to use AMS to improve measurement accuracy and sensitivity of 236U. Normally, the UO−/UO2 or UO−/U3O8 ratio is used, but the UF2−/UF4 approach enabled a higher beam current of extracted U-containing ions to be extracted whilst also decreasing interferences from other ions, e.g.235U. Analysis of a reference material with a 236U/238U of 10−10 gave results in good agreement with the reference value, with uncertainty being 4%. In comparison, the UO−/U3O8 measurement gave a value of only 10−9. The authors speculated that had a high resolution TOF detection system been used, their methodology could approach a sensitivity of 10−13 or even lower.
The potential of high resolution ICP-OES for elemental and isotopic analysis of americium was discussed by Krachler et al.152 A commercial instrument was calibrated using a stock solution of 241Am that had been prepared in-house through a chemical separation of a 115 g L−1 plutonium solution. A sector field ICP-MS instrument was used as well as both alpha and gamma spectrometry to characterize the americium and plutonium solutions in terms of their purity, isotopic abundance and their actual concentration prior to use with ICP-OES. The 241Am and 243Am had identical signal patterns and the isotopic shift between the two was generally small with the maximum shift being 3.7 pm at a wavelength of 450.945 nm. A very high efficiency sample introduction device enabled exceptionally low LOD to be obtained. The best LOD (0.07 μg kg−1) was achieved at a wavelength of 283.226 nm, but the Th wavelength at 283.231 nm would, potentially, cause interferences if a thorium-rich matrix was analysed. The authors provided a list of wavelengths available for Am determination and highlighted the interferences observed at each of them.
3 Functional materials
3.1. Ceramics and refractories
The analysis of ceramics during this review period may be summarized by stating that there has been an increase in the number of papers published. More specifically, this increase has been in the area of archaeological/historical heritage-type samples. Reports of the analysis of other ceramics has diminished somewhat. Of the papers that have reported the analysis of ceramics, the use of solid sampling techniques has proven popular because ceramics are materials designed to function at high temperature and tend to have high measures of hardness. In addition, they also have substantial chemical resistance. These properties make them quite difficult to analyse because they do not readily dissolve without recourse to extreme acids, e.g. hydrofluoric or sulfuric at very elevated temperatures, and are also not readily fused into soluble forms.It has been known for years that slurry introduction offers several advantages, e.g. the possibility of calibrating against aqueous standards, no necessity for the use of harsh chemicals or conditions for sample preparation etc. However, if certain precautions are not taken, slurry nebulization is a method that has the potential to obtain the wrong answers very rapidly. One of the most important factors is that of particle size. Nebulizer/spray chamber assemblies of ICP instrumentation will discriminate against particles that are too large and hence, these may never reach the plasma. A further complication is that the maximum particle size that can be transported to the plasma varies depending on the density of the material being analysed. The analysis of ceramics complicates things further because they are so resistant to heat. Even if a particle is transported as far as the plasma, there is a possibility that it may not be atomized completely, leading to an underestimate of concentration. Dispersants are normally required to minimize agglomeration of the particles. Wang et al.153 investigated the analysis of aluminium oxide presented as a slurry to an ICP-OES instrument. The effects of nebulizer gas flows, particle size and spray chamber geometry as well as the vaporization efficiency were all studied. Although there was some element of re-inventing the wheel, the paper did have some merits. Particles of size 7–10 μm could reach the plasma, but only those of 7 μm and below could be vaporized completely. Particles of 8 μm diameter had a vaporization efficiency of only 68% when the nebulizer gas flow was 0.8 L min−1. A dispersant of 0.5% polyacrylate amine was used. Results obtained for the slurry nebulization of the material were in good agreement with those obtained after it had undergone a high temperature (230 °C), microwave dissolution using sulfuric acid. Analysis of NIST SRM 699 using both methods also yielded data in good agreement with certified values. The only strange thing about this paper was that the authors used an alumina mortar for the grinding of the samples prior to slurry preparation.
Zhou et al.154 used LA-ICP-MS to analyse silicon carbide powders. The sample was first mixed with carbon powder at a ratio of 3:1 and then mechanically mixed. An aliquot was then pressed into a disc for 30 s at 10 MPa and this was heated to 1000 °C for two hours using a five-step temperature program. The LA-ICP-MS operating conditions were optimized to give good sensitivity and stability. Glass reference materials (NIST SRMs 610, 612, 614 and 616) were used as calibrants and, by using 29Si as an internal standard, correlation coefficients of the calibration curves ranged from 0.9981 to 0.9999. Precision was better than 5% RSD and LOD for B, Co, Cr, Cu, Fe, Mn, Ni, Sr and Ti were 0.02, 0.004, 0.04, 0.07, 0.01, 0.005, 0.02, 0.006 and 0.08 mg kg−1 respectively. A comparison of data obtained using LA-ICP-MS with those from sample nebulization into ICP-OES following an acid dissolution involving sulfuric, hydrofluoric and nitric acids in an oven at 230 °C, were in good agreement. Analysis of the reference material BAM-S003 yielded results that were in reasonable agreement with certified values, although the Cu was only approximately 65% of the certified value. The accuracy of the digestion method was superior, but precision was similar between the different introduction systems. The LA-ICP-MS protocol was applied to the analysis of silicon carbide powders of different particle size.
Another method for solid sample introduction was demonstrated by Hashimoto et al.155 who used ETV-ICP-OES employing a tungsten boat furnace vaporizer to determine Cl in fine ceramics. Sample (approx. 12 mg) was weighed into a cuvette and 10 μL of 1.8% potassium hydroxide solution added as a modifier. The cuvette was then put on a hotplate at 110 °C for three minutes or until the solvent had evaporated. The cuvette was then placed in a tungsten boat furnace, heated at 75 °C to remove remaining solvent and then to 1800 °C over seven seconds and maintained at that temperature for three seconds for the volatilization to occur. Sample vapour was transported to the ICP instrument by a carrier gas comprising 35 mL min−1 hydrogen and 465 mL min−1 argon. The transient Cl signal obtained was monitored at 134.724 nm. Calibration was achieved by pipetting known Cl concentrations into the cuvette containing ceramic powder known not to contain Cl as a contaminant since it had been previously baked at 1800 °C. The LOD was 0.71 ng (0.59 ng g−1) and precision for 10 replicate measurements was 3.2% RSD. The method was applied successfully to the analysis of the certified materials JCRM R004 and JCRM R006 silicon nitride powders and JCRM R022 and JCRM R023 silicon carbide powders.
An important industrial application of ceramic analysis was reported by Campos et al.156 Ceramic bricks or tiles are used as liners of furnaces and the ceramic is prone to attack and subsequent degradation by corrosive gases. These authors studied the effect of manganese vapour produced during the process of steel sintering on the ceramic bricks. The iron/manganese powder (50 g) was placed in an alumina tray and then covered with different alumina (corundum) tiles. The mixture was heated to 1120 °C at a ramp rate of 5 °C min−1 and then maintained at that temperature for three hours in an atmosphere of 90% nitrogen and 10% hydrogen. The atmosphere was then changed to pure nitrogen and the sample cooled at a rate of 5 °C min−1. This constituted one cycle. Samples were exposed to between one and six cycles each. The iron/manganese powder mix was replaced every cycle to ensure constant amounts of Mn. The alumina tiles were then examined using XRF, SEM-EDS, XRD and optical microscopy. A green film was produced on the tile and this was identified using XRD to be galaxite (MnO·Al2O3). The extent that the Mn penetrated the alumina was assessed using XRF and the authors concluded that after six consecutive cycles, huge amounts of Mn entered the alumina through the pores and penetrated throughout its entire width. There was no evidence of grain boundary migration.
Since virtually all of the papers reporting the analysis of cultural heritage samples appear in archaeological journals, they are often a little sparse with analytical details. As such, they are best summarized in Table 3. An exception to this is a paper prepared by Glaus et al.157 who used a portable LA unit to sample objects in the field, collect the particles produced on filters and then either acid digest and analyse these filters off-line using multicollector ICP-MS, or undertake fast-scanning LA of the filters and analyse using ICP-MS on-line. Isotope ratio analysis of materials such as ceramics, a lead ore (galena) and the metallic lead standard NIST SRM 981 was undertaken. The LA – sample collection – digestion protocol with external standards enabled Pb isotope ratios of better than 0.1% parts per thousand for the Pb isotope standard to be obtained. This was sufficiently high to indicate that a small amount of isotopic fractioning occurred during the sampling procedure. The LA of the filter resulted in poorer precision compared with the dissolution/nebulization approach but, as the authors stated, it did allow a simple on-line procedure to be developed in which the LA plume from the filter was transported to both MC-ICP-MS and a standard quadrupole-based instrument simultaneously enabling isotopic analysis and elemental analysis, respectively. An overview paper that discussed the use of XRF for the differentiation between real and forged cultural heritage materials was prepared by Galli and Bonizzoni.158 Materials such as paintings (pigments) ceramics and metal objects were all discussed and case studies given. The authors emphasized the necessity to maintain the sample, i.e. to cause the absolute minimum amount of damage.
| Element | Matrix | Technique; atomization; presentation | Comments | Reference |
|---|---|---|---|---|
| Pb | Cypriot pottery | MS; ICP; — | Pb isotopes used to determine provenance of pottery from four major geological zones of Cyprus. Distinction between three Pb isotope fields could be made. Differentiation between local-ware and imports was also possible | 271 |
| Several | Lead glazed potteries from Izmir, Turkey | WDXRF; —; s | 18 sherds analysed using WDXRF (as well as XRD, μ-Raman and SEM-EDS). Principle component analysis (PCA) of WDXRF data enabled provenance determination, with all but two of the sherds coming from the same group of potteries. Firing temperatures were measured approximately by the use of XRD | 272 |
| Several (17) | Tang Sancai pottery | EDXRF; —; s | 174 sherds from four different production centres analysed. The chemometric technique PCA used on the analytical data to differentiate between the samples from different kilns. Results indicated that samples from the four different potteries had very different composition enabling provenance determination of the sherds | 273 |
| Several | Hellenistic and Roman fine pottery | XRF; —; s | 51 samples of fine pottery from Syracuse analysed using optical microscopy and XRF. Multivariate statistical analysis enabled differentiation of Syracuse pottery from others (Messina and Gela) | 274 |
| Several | Neolithic pottery from polyplatanos, Greece | μ-XRF; —; s | Several types of pottery (crusted, classical Dimini, black on red, cream on red and graphite) analysed using μ-XRF. Multivariate techniques (e.g. PCA) used on the data. Novel technological information obtained, especially for the crusted type of pottery. Provenance associations also obtained | 275 |
| Several | Italian Renaissance lustred majolica | OES; ICP; —, AAS; ETA; — | Numerous techniques including non-atomic spectrometric ones (XRD, UV-Vis, SEM-EDS) used to characterize the samples enabling information on nanostructure and chemical composition to be obtained. Over 50 sherds analysed. Chemometric analysis enabled the samples to be identified as originating from specific kilns | 276 |
| Several | Overglaze tiles from Persia | P-XRF; —; s | Portable XRF as well as UV-Vis, μ-Raman and SEM-EDS. Data from XRF and UV-Vis used to choose the samples to be analysed using SEM-EDS. Data obtained from SEM-EDS analysed using PCA | 277 |
| Several | Megalithic sarcophagi potsherds from India | EDXRF; —; s | Numerous analytical techniques used including FTIR, thermogravimetry-differential thermal analysis (TG-DTA), SEM-EDS, powder XRD. Hierarchical analysis and PCA used on EDXRF data enabled grouping and structuring of the data. Other techniques yielded information on firing temperature and manufacturing techniques | 278 |
| Several | Bricks from medieval monastery in Italy | XRF; —; s, P-XRF; —; s, TXRF; —; s | XRF used to obtain fully quantitative data (11 analytes) and then PCA used to compare variables. For semi-quantitative TXRF analysis, 60 mg of crushed and powdered sample was mixed with 6 mL of pure water. The mixture was then placed in an ultrasonic bath for 30 min, an aliquot (20 μL) removed and placed in a sample cell, dried and then analysed (12 analytes). Portable XRF also used in situ. Operating conditions and calibration strategies for each spectrometer were given | 279 |
| Several | Bronze age pottery from Aeolian Islands | MS; ICP; LA | A Nd:YAG laser operating at 213 nm used for LA. Any instrumental drift was corrected for by the analysis of NIST SRM 612 and applying a linear correction for signal intensities. Electron microprobe also used for the determination of analytes at high concentration. Data obtained analysed using PCA and discriminant analysis | 280 |
| Several | Phoenician pottery from Tyre | XRF; —; s | Samples were pulverized and then fused at 1125 °C with lithium tetraborate prior to analysis. Other techniques used included XRD and SEM. Analytical data used to form dendrograms to identify production groups | 281 |
| Several | North Apulian coarse cooking wares and fine painted wares from Herdonia and Canusium | XRF; —; s, OES; ICP; L, MS; ICP; L | Fusions and different types of acid digestion methods used for ICP sample analysis. Cluster analysis, PCA and classification tree methodology used to interrogate analytical data. The latter statistical method was newly developed. Neutron activation analysis and XRD also used. Sample destructive techniques | 282 |
| Several | Lustre compositions from Egypt | OES; LIBS; s | Both LIBS and ion beam analysis (IBA) used for characterizing lustre. Spatially resolved data collection and spot analysis undertaken to obtain information about nanoparticles present in glaze and lustre | 283 |
| Several | Moroccan enamelled terracotta tiles | μ-XRF; —; s | Two μ-XRF spectrometers used to obtain elemental distribution and composition data from five different articles dating from between the 13th and 20th century. Capabilities and operating conditions of both instruments were given. Glaze and ceramic body analysed independently | 284 |
| Several | Oriental porcelain glazes and blue underglaze pigments | μ-EDXRF; —; s | μ-Raman and variable pressure SEM also utilized for analysis of artefacts from Ming dynasty. Cobalt aluminate identified as the pigment. Comparison of blue and dark blue pigments was performed by comparing ratios of Co, Fe and Mn oxides. The dark blue pigment contained manganese oxide compounds. Migration of Mn also identified | 285 |
| Several | Ancient pottery from Kaveripakkam, India | EDXRF; —; s | Sherds ground with boric acid and then made into a pellet using a hydraulic press. Analysis then by EDXRF. Thermal analysis (TG-DTA), powder XRD, FTIR and SEM also used to characterize materials. Firing temperatures and conditions elucidated | 286 |
| Several (>20) | Black-coated pottery from Pompeii | EDXRF; —; s | Sherds ground with boric acid and then made into a pellet using a hydraulic press. Analysis then by EDXRF. Optical microscopy, XRD, Raman and SEM-EDS also used. Firing conditions (duration of reducing step and cooling rate) elucidated | 287 |
| Several | Potsherds from Mleiha, Sharjah | XRF; —; s | Samples were milled into a fine powder and then analysed using XRF microscopy. Standard-less fundamental parameter algorithm used to deconvolute spectra. Validation using reference materials SARM 69 and NIST SRM 679 | 288 |
| Several | Chinese porcelain from 18th century | XRF; —; s | XRF and Raman used. Samples were cut, embedded and polished so that a transverse section could be analysed. This enabled the different layers to be analysed separately. Different colours were identified as cobalt-aluminium oxide (blue), haematite (red) copper oxide and malachite (Cu2CO3(OH)2) (Green), PbSn(1−x)SixO3 (yellow) and lead arsenate (white) | 289 |
| Several | Egyptian pottery shards from three different time periods | OES; LIBS; s | Nd:YAG laser operating at 1064 nm used for LIBS analysis. Complementary techniques of SEM-EDS and XRF also used. The LIBS analysis enabled a spatial analysis with micron range resolution without leaving a trace of damage | 290 |
| Several | Roman ceramics | XANES; —; s | Three different types of full field hard X-ray transmission microscopes used with different detector types and operating conditions. Data analysed using PCA. Complementary techniques of Raman and XRD spectroscopies also used. Instruments were capable of investigating areas of hundreds of square micrometres with resolution of 30–300 nm. When coupled with tomography, sample porosity and links with chemical composition may be made. Two vessels dated to within 50–80 years of each other had undergone very different firing technology | 291 |
| Several (24) | Floor tiles from Sicily | OES; ICP, L | Cotton bud soaked in hydrofluoric acid used to swab tiles ranging in date from 16th–20th century. Cotton bud then immersed in 2% HNO3 to release analytes. Minimal damage caused. Precision (n = 3) ranged from 1–8% RSD. Validation was by spike/recovery experiments of leachate solutions | 292 |
| Several (10) | Proto-Celadon from Han dynasty, China | MS; ICP; LA | Ablation achieved using Nd:YAG laser operating at 213 nm. Detection was by using a double focussing high resolution ICP-MS instrument. Validation achieved through analysis of five standard samples including NIST SRM 610 and NIST SRM 612 glass materials. Samples from three kilns analysed. Different firing temperatures and different materials/elemental composition between North and South China samples, with Ca and Fe being higher for the North, but Mg being lower | 293 |
| Several | Earthenware from pre-Hispanic Philippines | MS; ICP; LA | Clay body, temper, slip or glaze could be analysed using 230 nm Nd:YAG laser and an ICP-MS instrument. Instrumental drift was monitored and corrected for by the analysis of NIST SRM 610 glass and NIST SRM 679 brick clay every 10–15 samples. Of 52 analytes determined, data from 36 were analysed using PCA. Data from the other analytes were not used because of poor precision. Five distinct groups of samples identified | 294 |
| Several | Pottery from Florida | MS; ICP; LA | Samples ablated using a Nd:YAG laser operating at 213 nm in a helium atmosphere. Ablation plume was then mixed with argon and transported to ICP-MS instrument. Data compared with those obtained using INAA. Agreement between two methods was patchy as was demonstrated by the use of bivariate plots. Presence of monazites and zircons also caused spikes in levels of Ce, Hf, La, Nd, Th and Zr when determined using LA-ICP-MS | 295 |
3.2. Semiconductor materials and devices
The structure of this section of the review has been reorganized this year to provide a clearer focus on applications rather than technique. The literature received continues to reflect developments in the analysis of semiconductor wafers and including depth profiling of dopant elements, the creation and characterization of thin films and complex multi-layered materials intended primarily but not exclusively for use in electronic applications and an understandable continuing interest in solar cell devices. Applications to the characterization of electronic equipment and devices are also considered.| Element | Matrix | Technique | Sample treatment/comments | Reference |
|---|---|---|---|---|
| Ag | Ge2Sb2Te5 thin films | EPMA and SIMS | Study of Ag bulk content and photo diffusion into films at a level of 5.20 at.% using EPMS for quantification and SIMS for depth profiling | 296 |
| As | Silicon/silicon dioxide | SIMS | Characterization of ultra-shallow As implants using a calibration correction model for quantitative ultra-low energy SIMS analysis | 161 |
| As | Deep UV photoresist | TOF-SIMS | Depth profiling of As using Ar cluster beam as sputter species | 297 |
| B | Silica thin films | SIMS | Measurement of the B dopant concentration profile in the films | 298 |
| C | CO2 and SiO2 films on silicon | SIMS | Depth profiling of C content of CO2 layer diffusion into SiO2 and Si layers. | 299 |
| Ge | Si1−xGex materials | SIMS | Quantitative determination of Ge using low energy Cs+ and O2+ ion beams using the ratio of secondary emission intensities and composition ratios to correct for interference effects | 160 |
| In | Multilayer capacitor structures | TOF-SIMS | Study of In diffusion between device layers | 300 |
| In | InSb surfaces | AAS | Study of wet etching of material surface using Br2 and H2O2 as oxidants. | 301 |
| In | Silicon | SIMS | Method for the direct observation of precipitates derived from ion implantation doping of In | 302 |
| Li | Li2O–SiO2 glasses | LA-ICP-MS and SIMS | Measurement of Li diffusion profiles | 303 |
| Li | Lithium ion battery anode | ICP-OES | Monitoring of accumulation of Li at graphite battery anode after cycle or storage | 304 |
| Mg | GaN | XANES | Detection of Mg dopant at very low levels using a high intensity synchrotron radiation source and by optimizing spectral region of interest | 305 |
| Ni | Silicon wafers | ICP-MS | Study of removal of transition metals form wafers using treatment with HCl | 306 |
| O | CO2 and SiO2 films on silicon | SIMS | Quantitative depth profiling of O content of film layers using narrow resonance profiling technique | 299 |
| P | Li ion battery electrolytes | ICP-OES | Comparison with ESI-MS for determining P-containing species associated with battery ageing | 307 |
| Si | InGaN/GaN Al2O3multilayer devices | TOF-SIMS | Depth profiling of n-type dopant and diffusion across device junctions | 308 |
| Te | Silicon | SIMS | Investigation of Te contamination of silicon materials | 309 |
| Te | InGaP layers | SIMS | Depth profiling of Te in several nm thick layered material | 310 |
| U | NIST SRM 610,612, 614 and 616 glasses | LA-ICP-MS | A Fs laser was used to sample glasses and a multi-collector instrument was used to measure U isotope ratios; results for 235U showed deviation from certificate values | 311 |
| Zn | Si substrates | SIMS | Depth profiling of Zn in material damaged after multi-stage thermal treatment. | 312 |
| Various (15) | Automotive glass | EDXRF | Direct determination of 15 low and medium Z elements; investigation of effects of Fe and Zr content on glass properties reported | 313 |
| Various (6) | Computer monitor glass screens and printed wiring circuit boards | FAAS | A Standard digestion procedure was used prior to determination of hazardous elements (Cd, Cr, Cu, Ni, Pb and Zn); all elements detected were below total threshold limit concentrations | 314 |
| Various (3) | Glass beads used in highway surfaces | ICP-OES | Microwave assisted acid digestion of samples based on EPA method 3052; evaluation of H3BO3 and ZrOCl2 to remove excess F; LOQ reported were: 30 mg kg−1 for As,10 mg kg−1 for Sb and 5 mg kg−1 for Pb | 315 |
| Various (3) | Glass beads used in highway marking | XRF | Eighteen batches of glass beads were analysed using a field-portable instrument; for US produced samples the levels found were 8 mg kg−1 for As, 23 mg kg−1 for Pb, and 55 mg kg−1 for Sb | 316 |
| Various (5) | Electronic wastes | FAAS, ICP-OES and ICP-MS | Study of bioleaching from electronic wastes by citric and oxalic acids and Aspergillus niger prior to determination of Al, Fe, Sn, Co and Au | 317 |
| Various (5) | Printed circuit board ash | XRF | Determination of Ag, Au, Co, Ni, Pd, in ground ash using powdered calibration standards under 6 μm polypropylene film | 318 |
| Various (15) | ZnO light emitting diodes | SIMS | Relative sensitivity factor values for SIMS using O2+ primary beam were reported for various ion implants and impurity elements (Ag, Al, As, Cd, F, Ga, H, K, Li, mg, N, Na, Se, Sr and Te) | 319 |
| Various (3) | Sodium β alumina, battery Ni–Al–NiCl2 cathodes | XRF and XANES | Measurement of element spatial distribution by XRF mapping and chemical state by XANES for Cl, Fe, derived from a battery additive and Ni and Cl from cathodic material | 320 |
| Various (4) | Micro-SD memory card | XRF | Surface analysis and depth profiling of Au, Cu, Ni and Ti using 2D μ-XRF and confocal μ-XRF instruments | 321 |
| Various (6) | Hg Cd Se layers on ZnTe buffer layered/Si substrate | SIMS | Detection of Br, C, Cl, F, O and Si at layer interfaces | 322 |
| Various (4) | Multicomponent chalcogenide glassy semiconductors | XRF | Determination of As, Ge, Se using a correction function to account for element signal dependencies; the model was unsuccessful in application to measurement of Te | 323 |
| Various (44) | High purity silicon | ICP-OES | Comparison of method with Russian state standard (GOST) procedures for the determination of impurities in the range 10−8 to n × 10−6 wt% | 324 |
| Various (22) | Solar grade silicon | ICP-MS | Samples were dissolved in a mixture of HF and HNO3 and elements determined using a multicollector MS instrument and three point standard addition method; LOD of the order of 120 ng kg−1 were reported | 325 |
| Various (7) | Solar grade silicon | ICP-OES | Measurement of main elemental impurity levels (Al, B, Ca, Fe, K, Mg and Na); average material purity levels reported in the range 99.76–99.96% | 326 |
| Various (3) | Solar grade silicon | GD-OES | Study of trace element impurities (Cu and Fe) and dopant (B) distribution in multi-crystalline silicon grain boundaries and dislocations | 327 |
As ever, SIMS continues to dominate the literature describing the characterization of semiconductor materials. Improving quantification remains a major theme of research work, partly because the calibration of responses from ultrathin films on the surface of substrates of entirely different composition is challenging. The use of ion sources operated at low energy has been studied for these important applications, and alternatives have also been evaluated. For example, an O2+ probe has been used to obtain high resolution depth profiles from a Si–Ge type quantum well structure.159 It was shown that when primary ion beam energies above 500 eV were used, depth profiles became unrepresentative. However below this threshold, quantification could be achieved, and it was reported that good agreement was obtained with data derived from TEM and X-ray techniques. An investigation of the use of low energy Cs+ and O2+ ion beams in the quantification of Ge in Si–Ge type materials has also been reported.160 It was found that at beam energy of 250 eV, there was a significant change in Ge ion yield in comparison to the Si–Ge matrix, but that this was not observed when an O2+ ion beam was used. However, it was noted that secondary ion intensities could still be used to achieve quantification with a Cs+ ion beam, as these correlated monotonically with Si–Ge composition. In a similar vein, a quantification model has been developed to perform calibration correction in the ultra-low energy SIMS determination of As implants in a silicon substrate.161 The model took into account different sputtering regimes in SiO2 and Si materials and corrected analyte response at the interface between the two. The SIMS results obtained were similar to those obtained from medium energy ion scattering (MEIS) which was considered to be an accurate method of depth profiling.
There is a continuing demand to improve lateral resolution in the characterization of semiconductors. These advantages have been claimed for a SIMS instrument that uses a high brightness He+/Ne+ ion source.22 Usable ion yields in the range of 10−4 to 3 × 10−2 were obtained using O2 or Cs flooding yields and LODs in the atomic % range were reported for semiconductor materials (Si, Ge, GaAs and InP) and metals (Al, Ni, W). Lateral resolutions as low as 10 nm were achieved for SIMS imaging when Ne+ bombardment was used. Improvements in lateral resolution have also been achieved using a TOF-SIMS instrument. In this approach, Bi primary ion clusters were used to remove sample material to uncover buried object layers while maintaining lateral resolution in the sub 50 nm range to a depth of 20 mm. The system was applied to CRM and real world samples. In another novel, but not necessarily intuitive instrument development, an EDXRF device was incorporated within a Cameca SIMS ion system.162 The capability of the combined instrument to perform efficient quantitative analysis was demonstrated in application to thick AlxGa1−xN epitaxial layers and thin SixGe1−x films.
X-ray techniques offer particular advantages in the characterization of semiconductor materials because they are responsive to surface composition. However, there can be limitations in relation to sensitivity and/or quantification that can arise as a result of these properties. The ISO Technical Committee 201 Working Group 2 has investigated the use of vapour phase treatment to improve LODs in the trace metal analysis of silicon wafers by TXRF spectrometry.163 It was found via round robin testing that this treatment improved TXRF intensity by 1.2 to 4.7 for samples intentionally contaminated with Fe and Ni at a level of 5 × 109 and 5 × 1010 atoms cm−1 respectively. It is well established that TRXRF can be used in combination with a synchrotron radiation source to improve surface sensitivity for trace analysis of semiconductors materials. This technique has been applied in a micro-beam configuration to investigate the lateral distribution of 23 elements deposited on a silicon wafer surface for the purposes of calibration.164 It was reported that the temperature of the drying process used to deposit the calibration solution had an influence on the uniformity of elemental distributions and residual element morphology. The X-ray and SEM images obtained were used to improve the quality of statistical analysis with the aim of improving the quantification by TXRF and grazing incidence XRF which are surface sensitive.
Laser induced breakdown spectrometry continues to be used as a viable alternative approach for depth profiling of silicon wafers. In one study165 an Al thin film approximately 800 nm thick was deposited on a silicon substrate using a magnetron sputtering process. Depth profiling was carried out on samples with and without post-annealing at 300 °C and 610 °C in air in order to investigate Al diffusion. Sampling was carried out under atmospheric conditions using laser pulse energy of 16 J cm−2. This resulted in an ablation rate of 200 nm per pulse. The LIBS method was able to perform satisfactory depth profiling in wafers in comparison with an energy dispersive spectroscopy approach which had limited efficacy due to a lack of sensitivity. The LIBS technique was also used for the detection of a metal layer buried deep within a silicon material.166 An 800 nm fs laser was used for the dual purposes of micromachining precise holes within the semiconductor structure while at the same time measuring elemental content and profiles. Using a laser fluence of 1.4 J cm−2, drilling rates of 30 nm per pulse could be achieved using low intensity flat top beam profiles.
Advances in fabrication technologies have allowed the creation of complex functional nano-structures featuring multiple layers. This has necessitated the development of new analytical approaches that describe not just the chemical composition but also the physical distribution of elements of interest within the sample. Complex structures are challenging to analyse because there is, by definition, a lack of available reference materials. It is worth drawing attention therefore to a round robin exercise for the depth profiling of Mo/B4C–Si and Mo–Si multilayer nanostructures deposited on Si.167 Thus SIMS with TOF, and magnetic sector analysers, GD-OES and a TOF-low energy ions scattering quadrupole SIMS instrument were used in a technique comparison. The advantages and disadvantages of these approaches in terms of depth resolution and speed of analysis were critically assessed.
Secondary ion mass spectrometry remains the technique of choice for characterization of multilayer materials, but it is evident from the literature that depth resolution depends on the instrumental conditions employed. An appreciation of these effects is an essential prerequisite for accurate analysis. For example, an investigation has been made of the use of TOF-SIMS with a low energy (250 eV) sputter ion (O2+) and a high energy primary ion (30 keV Bi+) in depth profiling of delta doped B multilayers in silicon.168 The intensity ratio of the first peak and the subsequent valley in B+ depth profile for specific instrument conditions was used to evaluate depth resolution. It was found that sample damage correlated to the ratio of current density of sputter ion to primary ion, thereby affecting depth resolution. An isotopic comparative method has been described for the characterization of thick Si–Ge alloy films.169 These materials ranged in composition from almost pure Si to pure Ge but only two isotopic reference samples were required for quantification. Using an Ar+ ion beam negative secondary ion yields for both Si and Ge were found to be virtually consistent whereas the positive ion yield for Si decreased significantly. This observation allowed a matrix effect free method to be developed for the analysis of these alloys.
There has been renewed interest in chemical processes for controlled erosion in semiconductor manufacturing due to selectivity achieved by this means. For example, the process of reactive ion etching of silicon has been monitored using optical emission spectrometry online.170 The emission spectra of F at 703.8 nm and CS compounds at 257.6 nm were measured and found to change in intensity during etching. It was possible to correlate this fall in emission intensity with breakthrough of the passivation layer and to establish net silicon etch time. It was concluded that OES could be used in process optimization in mask generation. In an alternative approach to the study of materials etching, ICP-MS has been used to examine acid erosion of As, Ga and In substrates.171 An instrument fitted with an octopole reaction cell in He was used to attenuate interferences arising from HCl and H2SO4 etchants. The low part per billion sensitivity achieved allowed the determination of As, Ga and In at an amount equivalent to a sub nm material layer.
Another approach to the critical issue of calibration of LIBS response by comparing CIGS bulk and thin film measurements has been reported.177 It was found that calibration results based on Ga(Ga + In) ratio obtained from this set of data were in agreement, demonstrating that pre-analysed bulk samples can provide a useful LIBS reference for the analysis of CIGS films. Classification methods based on linear correlation and artificial neural networks have been applied in the monitoring of solar cells by LIBS.178 The approach was used in the assessment of selective scribing of Cu–In–Se2 cells in which the laser was used to remove material to reach the underlying film without damaging the bottom layer. Thus plasma emission was monitored using the classification methods in two spectral bandwidths. This procedure was demonstrated to permit control of the three processing steps in solar cell manufacture and it was considered that it offered the potential to be implemented as an on-line monitoring tool in a production environment.
The capability of X-ray techniques to provide non-destructive quantitative analysis has been exploited in the characterization of solar cell materials. Grazing incidence XRF offers the possibility of depth profiling by varying the angle of incidence of the primary radiation beam. This feature of the technique was exploited in the reference-free depth analysis of Ga and In in Cu(In,Ga)Se2 absorber films.179 This was achieved by use of a monochromatic synchrotron radiation excitation source and modelling of calculated X-ray intensities fitted to fluorescence measurements. Results obtained demonstrated the viability of the approach to detect Ga double gradients in the materials. In a similar manner, quantification can also be achieved by determining relative sensitivity factors for particular applications. This approach has been adopted for the examination of CuInSe2 and In2Se3 solar cell high purity standard materials.180 The depth of penetration of X-rays and electrons in EDS, Auger and XPS techniques was determined by calculation and via Monte Carlo simulations to achieve the correct relative sensitivity factors for films of >0.5 μm. The data obtained, which will be useful to anyone considering such an approach for non-destructive analysis of such materials, were compared with published handbook information.
Mass spectrometry has also been applied extensively to the characterization of thin film solar cell materials. The elemental composition and depth profiling of CIGS thin films has been investigated by TOF-SIMS using a cluster ion technique.181 Changes in the depth dependent stoichiometry of Ga and In greatly affect solar cell efficiency. The detection of MCs+ clusters was used for semi-quantitative analysis and to investigate the effect of stoichiometry on analyte species intensities. No matrix effects were observed for In and Ga using this approach. The results of bulk analysis by HR-ICP-MS were found to correlate with integrated GaCs+ and InCs+ SIMS intensities confirming the validity of the approach. The composition of ZnO buffer layers in CIGS with thicknesses below 100 nm was determined by SNMS and SIMS.182 In the former case, an evaluation algorithm was developed to overcome mass interferences from doubly charged ions and dimers for the quantification of depth profiles of Zn(O, S) layers.
Favourable reports have been published describing the application of GD-TOF-MS to the analysis of solar cell layers. For example, a radiofrequency GD-TOF-MS instrument has been applied to depth profiling of a CdTe solar cell.183 The reported advantages of the technique included large area sampling (4 mm diameter) at moderate vacuum conditions and 3D analysis with lateral resolution at the sub μm level. The performance of the GD-TOF-MS system was compared with that of TOF-SIMS and in the main good agreement was obtained. A different GD-TOF-MS instrument was used in a separate study of depth profiling of As in Cd1−xZnxS/CdTe solar cells.184 Good agreement was reported with those obtained by SIMS in this case also, suggesting that the technique has significant potential in applications of this type.
For example, the capability of LIBS to perform direct analysis of products has been used to assess waste electronic and electrical equipment.185 The results were interrogated using a chemometrics approach and this was used to assign the source of manufacture, identify counterfeit products and classify materials for recycling purposes. The combination of μ-XRF with SEM using energy dispersive detection has been systematically evaluated for the determination of RoHS elements.186 Unsurprisingly, it was found that the μ-XRF technique provided LODs up to two orders of magnitude better than those for electron microprobe analysis. The non-destructive capabilities of XRF have been exploited in the examination of printed wiring boards up to 30 years old.187 Noble, precious and rare metals were determined by EDXRF while Br containing flame retardant and Pb content was identified using a microbeam XRF technique. The relationship of the source of origin and year of construction of the items was also investigated. It is gratifying to note that the concentrations of the elements of concern were higher the older the items were, suggesting that the environmental impact of electronic waste will become less of a problem going forward.
There has been a noticeable growth in reports concerning the characterization of the contents of lithium ion batteries as these products are now used globally in portable electronic devices. Thus, Lithium ion battery electrodes have been examined by GD-OES.188 In the first example Li was quantified in both positive and negative electrodes of the devices and the emission intensities derived by GD-OES correlated linearly with ICP-MS data. Further analytical improvement was achieved by use of intensity ratios to correct for sputtering variations. In another application, GD-OES was applied to depth profiling of a lithium ion battery graphite electrode.189 Reactive sputtering with oxygen and hydrogen added to the Ar plasma was used to improve sensitivity and speed of analysis. Overall there was also less redeposition of sputtered material and Ar+ implantation observed under these conditions. Confocal μ-XRF and XANES have been used in combination to study lithium ion battery cathodic (LiNi0.5 Mn1.5O4) material.190 The surface oxidation states and deeper layers of the electrode were investigated, including Mn oxidation reactions at the cathode electrolyte interface. It was suggested that the non-destructive nature of the combined measurement approach made it suitable for process monitoring during battery cycling.
3.3. Glasses
The year under review saw continued interest in the analysis of glasses, but much of the published work demonstrated little that was new to such applications. In some cases, glass materials were used to demonstrate the analytical utility of a new technique, but in applications in which other perfectly satisfactory alternative methods already exist. Incremental development of existing sample preparation methods was also evident, and where these have some relevance for practical analysis they are summarized in Table 4. This section is devoted to advances in the characterization of modern glasses. Application for the analysis of ancient glasses can be found in the cultural heritage section of the review.Phosphate glasses offer potential as bioactive materials and have unique optical properties. The characterization of polyphosphate glasses is challenging because of the complexity of the material structure. A TOF-SIMS study of the surface chemistry of these materials has been reported which may assist with the development of these materials in these and other applications.191 Thus, Fe and Zn phosphate glasses have been studied and the patterns of phosphate ion fragments in negative ion SIMS examined. It was found that at higher masses fragments containing up to four P atoms were observed. It was reported that using SIMS ion intensities and related fragmentation patterns it was possible to discriminate between polyphosphates of different chain length. The depth profiling of Na in silica glass has been studied by TOF-SIMS.192 The measurements were carried out using a Bi primary ion and a buckminsterfullerene (C60) sputter ion beam. It was reported that the 23Na+ profile could be acquired successfully without optimizing operating conditions and that Na did not migrate during the sputtering process. The LOD obtained using this method was similar to that for the existing method of dynamic SIMS using a Cs primary ion beam.
The forensic analysis of glass remains a current topic of research activity and reports of inter-laboratory trials may be of particular interest to those active in this field. An 18 laboratory comparative trial has been carried out using four tests designed to evaluate the performance of match criteria for the elemental composition of glasses.193 The techniques used were μ-XRF, ICP-MS, LA-ICP-OES and LA-ICP-MS. It was reported that the application of these tests allowed the differentiation of glass samples manufactured in different locations or in separate production batches. In another inter-laboratory comparison involving 16 forensic science laboratories, the elemental composition of reference materials NIST SRM 612, NIST SRM 1831, float glass reference materials FGS 1, and FGS 2 Bundeskriminalamt Weisbaden were determined using μ-XRF, ICP-MS and LA-ICP-MS.194 Unsurprisingly, the ICP-MS methods out performed μ-XRF and achieved relative precision of 5%, inter-laboratory reproducibility of 10%, and LODs in the range 0.03 to 9 μg g−1. The reasons behind the observed inferior performance of μ-XRF might be explained in part by consideration of a tutorial article on the concepts of SNR, LOD and LOQ in forensic glass analysis using the technique.195 The use of Pb isotope ratios has been exploited in order to discriminate between common glass samples for forensic purposes.196 A multi-collector ICP-MS system using laser ablation sample was shown to be able to distinguish the origin of glass fragments as small as 0.1 mg which is of considerable importance in criminal investigations where samples particle sizes are often below 1 mm. The use of lead isotope ratios for comparing glass objects for forensic purposes has also been evaluated using IRMS.197 Thus 35 glass samples were analysed and five Pb isotope ratio pairs were measured. Principal components analysis of the IRMS data demonstrated that the 208Pb/204Pb ratio gave the best results, generating the least number of false positives.
The advantages of using femtosecond laser ablation sample introduction with ICP-MS for the direct analysis of glass have been explored in fundamental198 and applied studies.199 In the latter case, a 266 nm fs excimer laser was coupled to a multi-collector ICP-MS instrument and used for the determination of lead isotope ratios in 13 glass reference materials. The results obtained were in good agreement with published values. The determination of Nd isotope ratios in glasses without external standardization has also been described.200 A multiple collector ICP-MS system was used under operating conditions that minimize molecular oxide formation at the interface which permitted the accurate determination of Nd isotope ratios using excimer laser sample introduction. Since it was not necessary to correct for mass bias, it was possible to carry out standardless determination of Nd in NIST SRM 610 glass.
One unusual application involved the application of 3D LA-ICP-MS to the investigation of the weathering of glass.201 A multi-element mapping procedure was used to define laser drilling on a virtual grid on the sample surface. Laser pulses (50) at a repetition rate of 1 Hz on each grid point were used to generate elemental depth maps. Each laser pulse penetrated 150 nm into the glass sample. High speed ICP-MS data acquisition (58 ms for 19 elements) was employed to monitor laser pulses. The system generated 50 2D depth maps which could subsequently be viewed as time lapse videos or as images of the sampled volume. The technique was successfully used to investigate causes of weathering of glasses.
Finally, new reports of the application of LIBS to the analysis of glass are worth mentioning. The study of line selection in the detection of U in glass matrices has been investigated.202 Uranium exhibits a complex line rich spectrum making the determination by emission spectrometry problematic. The selection of appropriate analytical lines was examined in the context of spectral interferences from other elements, making use of the possibilities for temporally resolved spectral measurements. It was confirmed that detection limits in the part per million range could be achieved using LIBS with a medium resolution spectrometer. However, this performance should be considered in the context of the capabilities of existing techniques such as XRF. The determination of F is problematic using most atomic spectrometric techniques and any report of a new approach is of interest. Thus LIBS has been applied to the detection of F in glass ionomer cements.203 Two double pulse LIBS devices were evaluated. It was found that the best sensitivity for F was achieved in a helium atmosphere. Using optimized gate widths, the LODs were reported in the range 1.18–0.47 wt%.
3.4. Nano-structures
The use and diversity of use of engineered nanoparticles continues to increase. They have been used as drug delivery vehicles, magnetic resonance imaging contrast agents, catalysts, as nano-electronic components and in many other applications. Similarly, the methods of manufacture have also diversified, with laser ablation, electromagnetic cavitation, chemical reduction, chemical vapour deposition, sol gel and hydrothermal routes all finding use. In addition, there have also been reports of plants being used to produce particles. However, the purpose of this review is to report recent applications and advances in atomic spectroscopy and not to provide an overview of the whole subject of nanoparticles. Consequently, only those applications that report novel aspects of atomic spectroscopy will be discussed and those applications that report routine analysis of products will largely be ignored, irrespective of the novelty of manufacture or use.To summarize the analysis of nanoparticles during this review period, there has been an increase in the number of papers reporting the use of ICP-MS single particle analysis, field flow fractionation (FFF) or asymmetric flow FFF (A4F) coupled with ICP-MS to characterize materials. In addition, as well as the more theoretical and proof of concept studies reported previously, this review period has also seen reports of these techniques being used for real in vivo or biological applications. For some years now, there has been concern among the toxicology community that any adverse effects in organisms that had been ascribed to nanoparticles may, in fact, arise through ions formed through the partial dissolution of the said nanoparticles. There have been studies reported during this review period that have attempted to address these concerns. The applications that have reported these techniques, along with other novel ones will be discussed in more detail below.
There have been three reviews or overviews of the analysis of nanoparticles during this review period. The first, by Bustos et al.204 concentrated on the use of different types of mass spectrometry as a means of characterizing nanoparticles. It contained 40 references and discussed both molecular and elemental mass spectrometry along with coupling with an assortment of separation techniques. Applications of particle sizing and size distribution analysis were also given. A review by Adams and Barbante205 containing 39 references overviewed the recent developments and trends whilst also providing some potential future directions. Also discussed in this review were the emerging concerns about health and environmental issues. A review entitled “advanced analytical and related techniques for the growing challenges in nanotoxicology” by Chen et al.206 contained 205 references. In accordance with the other reviews, this one also discussed both nuclear and optical methods of analysis but also discussed in vitro analysis, quantification of bio-distribution, bio-accumulation and transformation of nanomaterials in vivo. Again, potential future directions were also discussed.
A paper by Bednar et al.207 compared the coupling of FFF (both symmetric and asymmetric) with numerous detection systems including UV, dynamic light scattering and ICP-AES and ICP-MS. The different systems were used to characterize gold and silver nanoparticles as well as carboxylated quantum dots containing Cd, Se and Zn. A helpful table of operating conditions for the FFF separations was given as well as the instrumental operating conditions for the detectors. A table of LOD was provided which showed that ICP-MS tended to be at least an order of magnitude superior to the other techniques for the Ag, Au and Cd, but was only 2–5 times superior for the other analytes. Detection of S during the analysis of the silver nanoparticles enabled an estimation of the environmental aging of the particles since it was a direct measure of the state of the sulfide coating. A paper by Geiss et al.208 used A4F coupled on-line with both UV and ICP-MS to characterize citrate-stabilized Ag nanoparticles in aqueous matrices. The A4F separation of commercially available silver nanoparticles of known size was optimized in terms of the liquid carrier composition (ultrapure water adjusted to pH 9.2 using 0.1 M NaOH) and the cross flow rate. A regenerated cellulose membrane was used for the analysis and these were stable for approximately 50 injections before separation efficiency was compromised. On exiting the UV detector, the nanoparticle solutions were acidified with 5% HNO3 and then mixed with a Rh internal standard solution prior to detection using ICP-MS. The LOD for UV and ICP-MS were similar for all nanoparticle sizes except for those of 100 nm, where the ICP-MS had a LOD of 6.7 μg L−1 compared with the UV one of 33 μg L−1.
Meermann et al.209 also used A4F coupled on-line with ICP-MS to characterize silver nanoparticles. A good baseline separation was achieved using nanoparticles of 30 ± 2.1 nm, 60 ± 5.2 nm and 75 ± 3.9 nm as size calibrants. Gold nanoparticles of a certified size were also used to validate the size separation. A linear relationship between size and elution time (r2 = 0.987) was obtained. These authors developed “post-channel species-unspecific on-line isotope dilution” methodology. Effluent from the A4F system was mixed on-line with a constant flow of enriched 107Ag and a change in isotopic abundance could be detected when the natural isotopic abundance Ag nanoparticles mixed with it. The fractograms produced were essentially a plot of time (and hence mass) against 109Ag/107Ag. Validation of this on-line ID approach was achieved by off-line fraction collection followed by Ag determination. A bias of between 2.9 and 16.4% was observed for both approaches, indicating that the on-line methodology was working adequately. The LOD was 1.6 μg L−1. A third paper to use A4F-UV-ICP-MS to characterize silver nanoparticles was prepared by Bolea et al.210 These authors discriminated between Ag ions and nanoparticles in culture media and human hepatoma cells used in cytotoxicity tests. The UV provided information on the nature of the eluted species (organic or nanoparticle) whereas the Ag was monitored by the ICP-MS instrument. The cells were first treated using tetramethylammonium hydroxide (TMAH) and Triton X-100 which released the Ag species ready for analysis. Fractions collected from the A4F instrument also underwent analysis using TEM which confirmed the results. After 24 hours, a shift in particle size was observed for the nanoparticles in the culture medium. The authors attributed this to a protein corona effect. Silver ions in the culture medium were also detected and this was described as a consequence of nanoparticle oxidation. Unsurprisingly, 16 times the mass of Ag as nanoparticles was required to show the same toxicity as Ag ions.
The technique of A4F-ICP-MS has also been applied to other nanoparticle types. Regelink et al.211 used the combined technology to characterize iron (hydr)oxide nanoparticles in soil extracts. These authors used a high resolution ICP-MS instrument to detect the iron nanoparticles with particle size range between 1 and 150 nm coming from three different horizons of a podzol. Since these nanoparticles are natural rather than engineered, this paper will not be discussed further. However, it does demonstrate how the technique can be used for real-life applications rather than just laboratory-made situations.
A paper by Cornelis and Hassellov213 discussed a signal deconvolution approach to discriminate smaller nanoparticles from ions using SP-ICP-MS. Gold nanoparticles with nominal diameters of 10, 15 and 30 nm were used during the study as well as Au ions. The deconvolution protocol was summarized in a useful figure which takes the reader through the numerous steps required. The paper does, however, go into the detail in the text, where all of the relevant equations required for the calculations are given. In summary, Au ions were parameterized as a function of concentration using a mixed polygaussian probability mass function. The curves were then fitted to the lower intensity signals of samples containing nanoparticles so that the “dissolved” signal could be subtracted from the total signal. The accuracy of the deconvolution process was confirmed by independent analysis of samples using TEM. The final paper to be discussed in this section was prepared by Ho et al.214 These authors used gold nanoparticles of 80, 100, 150 and 200 nm and used SP-ICP-MS to obtain a calibration curve of signal against concentration for each of the particle sizes. Linear calibration was observed for all particle diameters, but the slope decreased with increasing diameter. This was attributed to incomplete vaporization of the particles and to a different diffusion of the ions formed. Such phenomena would, of course, have ramifications for all nanoparticle research. The authors developed a computer simulation that takes these parameters into account. Calibration curves generated by the simulator also curved at high mass. However, the sampling depth from the plasma was found to be fundamental to the complete vaporization of the particles. The authors produced an equation that enabled them to determine the optimal sampling position. It was proposed that the equation could be used for particulates produced by LA as well as for engineered nanoparticles.
Other papers have had a more applications-based approach to SP-ICP-MS. One by Walczak et al.215 used SP-ICP-MS along with dynamic light scattering (DLS) and SEM-EDX to determine the behaviour of 60 nm silver nanoparticles and ions in an in vitro human gastrointestinal digestion model. The techniques were employed after the nanoparticles had been exposed to saliva, gastric and intestinal digestion. The number of particles observed decreased markedly after the gastric digestion, but increased again after the intestine. This phenomenon was investigated using SEM-EDX and was found to originate through clustering of the particles and subsequent re-dispersion. The process was attributed to the presence of protein, although the larger agglomerates also contained significant amounts of Cl. More importantly still, Ag ions (introduced as silver nitrate) also formed nanoparticles in the presence of proteins. These nanoparticles, of diameter 20–30 nm, were composed of Ag, Cl and S. A paper by Gray et al.216 used TMAH to extract Ag and Au nanoparticles from tissues originating from beef, Daphnia Magna (a species of freshwater water flea) and Lumbriculus variegatus (a species of worm). The extracts were then analysed using SP-ICP-MS. The Daphnia were exposed to 98 μg L−1 of 100 nm Au particles and 4.8 μg L−1 of 100 nm Ag particles. Although the body burdens varied significantly (Au was 613 ± 230 μg kg−1 and Ag was 59 ± 52 μg kg−1) the particle size distribution of the extracted particles was the same as that found in the exposure media, indicating minimal transformation within the organism. The mass and number-based recovery of spiked nanoparticles for all tissue types ranged between 83 and 121%. The on-line coupling of the complementary sizing techniques hydrodynamic chromatography and SP-ICP-MS for the characterization of gold nanoparticles was reported by Rakcheev et al.217 The nanoparticles were agglomerated under controlled conditions and then the coupling of the two analytical techniques enabled the mass of the particles (the peak height of the ICP-MS signal) and the diameter of the agglomerates (the retention time) to be estimated. The authors used the data to follow the morphological evolution of the agglomerates over time during the agglomeration process.
Audinot et al.222exposed HepG2 cells to copper oxide nanoparticles (25 μg mL−1 for 24 hours) and Daphnia major to 20 nm Ag nanoparticles (0.1 mg L−1), 21 nm TiO2 nanoparticles (50 mg L−1) and 25 nm SiO2 nanoparticles (250 mg L−1) for 48 hours. For the daphnia, ten creatures were then embedded in epoxy resin and 300 nm sections taken and placed on silicon wafers (for creatures exposed to the Ag and Ti-based nanoparticles) and on germanium wafers for those exposed to the Si-based nanoparticles. The wafers were then analysed using nano-SIMS employing a Cs+ primary ion beam at an energy of 16 keV and a current of 1 pA. The raster size was dependent on the tissue being investigated, with sections of daphnia over 40 × 40 μm2 and the HepG2 cells over 20 × 20 μm2. Multiple isotopes were monitored including 107Ag, 109Ag, 63Cu, 65Cu, 28Si, 30Si and the Ti-based molecules 48Ti16O and 50Ti16O. A resolution above 4000 was required to remove polyatomic interference effects exerted by 31P16O2+ on the 63Cu+ signal. The technique of TEM was used as an alternative to the nano-SIMS method and results were in good agreement. The SiO2 and TiO2 nanoparticles were both found in the lumen of the daphnid's gut, implying that they did not cross the epithelial barrier. Most of the Ag nanoparticles were also observed in the lumen, but traces were also found in the tissues of the organism, implying partial uptake.
The interaction of magnetic nanoparticles (Fe2O3and CoFe2O4) with U87MG cells was studied by Gianoncelli et al.223 using synchrotron radiation X-ray microscopy and XRF microspectroscopy. Cells were exposed for 24 hours to nanoparticle suspensions with concentrations ranging from 5 to 250 μg mL−1, washed using a buffer, fixed with 4% formaldehyde solution in buffer and then analysed. An energy of 1.1 keV and a spot size of 650 nm was used for the measurement. In addition, eight silicon drift detectors arranged in a circle enabled elemental monitoring of the K and L fluorescence from elements in the 150 to 2000 eV range. This included analytes such as B, P and metals including Cu, Fe, Mg, Mn and Zn. Two dimensional rasters were made enabling a map to be obtained. The different types of nanoparticle had different intra-cellular distribution patterns, enabling the authors to deduce different mechanisms of toxicity.
Two papers have used XRF to image gold nanoparticles used as contrast agents to identify tumour location.224,225 In the first of these two papers, two systems were described. One was a step and scan system in which the authors described the focussing polycapillary optics, the SiLi detector and the procedure for obtaining Au imaging in two dimensions. This system was capable of measuring Au down to 1 μg g−1 and could resolve Au concentrations differing by a factor of five enabling it to differentiate between tumour and non-tumour tissue. The other system was a “one-shot” system. Again, the instrumentation and theory was described in detail, with a controlled drift detector and collimating polycapillary optics being employed. Although tissue penetration was not huge, the system was capable of detecting the Au in near-surface small animal studies and for imaging in vitro cellular constructs. The other paper225 discussed the use of a benchtop instrument to detect L-shell XRF emitted from Au nanoparticles. This was a proof of principle study in which a calibration series of different concentrations of gold nanoparticles were placed in 12 mm wide water-filled cylindrical tubes and then the same tube was filled with a tissue equivalent gel and structures mimicking gold nanoparticle loaded blood vessels and a tumour of volume 1 cm3. The fluorescence was detected at right angles using a Si–PIN detector placed behind a 2.5 mm lead collimator. The XRF signal processing involved the use of an algorithm which the authors discussed briefly. The LOD was estimated to be 0.35 μg per 1.73 × 10−2 cm3.
There has been uncertainty for some years now that the toxicological effects observed using some nanoparticulates may arise through their dissolution and hence actually be caused by the individual ions. Some workers have attempted centrifugation to separate the ionic and nanoparticulate components, but this is not an ideal approach since it accelerates agglomeration and has other drawbacks, e.g. extremely small nanoparticulates remain in the liquid phase. Several studies published during this review period have attempted to differentiate between ions and nanoparticles. Khan et al.226 used isotopically labelled 68ZnO nanoparticles, of diameter 7.8 ± 1.2 nm, 68Zn ions and 68ZnO bulk particulates (2 μm) in a study that determined their waterborne uptake by the estuarine snail Peringia ulvae. The snails were dosed for seven days with 20 μg L−1 Zn in its different forms and then depurated for 28 days. The 68Zn was then determined in digests of the snail using high precision multiple collector ICP-MS. The nanoparticles initially underwent aggregation but then up to 60% dissolved within 12 days. The bulk and the ionic Zn were far more bioavailable than the nanoparticulate. However, once dissolution had been corrected for, the uptake rate constants for ionic and nanoparticle Zn were very similar (0.074 L−1 g−1 day−1 and 0.070 L−1 g−1 day−1, respectively). The rate constants for loss of the 68Zn for ionic and nanoparticles forms were identical. The results suggested that the bioaccumulation of Zn from ZnO nanoparticles is primarily dependent on their solubility.
A recirculating tangential flow filtration system that uses a diffusion-driven filtration method that retains large particles within the continuous flow path whilst allowing the ions to pass through molecular filters by lateral diffusion was described by Maurer et al.227 The methodology enabled Ag nanoparticles to be separated from the ions and permitted quantification using ICP-MS or enabled a comparison of bioassay exposures. The study compared the behaviour of 10 nm and 50 nm silver nanoparticles over time and demonstrated that the dissolution of the nanoparticles was dependent on parameters such as the exposure time and the temperature and chemical composition of the exposure solution. A different approach to separating Ag ions and nanoparticles was described by Mwilu et al.228 who used magnetic particles coated with either dopamine or glutathione to separate and preconcentrate the nanoparticles. These magnetic nanoparticles showed no retention ability for the ions. The paper discussed the preparation of the magnetic nanoparticles and their characterization using SEM. The magnetic nanoparticles could preconcentrate the Ag nanoparticles by a factor of up to 250 with a recovery of >99% under ideal, laboratory conditions. After separation of the magnetic nanoparticles from the sample solution (the flow cell was described) and digestion of the magnetic nanoparticles (again, this was described), analysis was achieved using ICP-MS. Spiking of real waters (tap, fresh and saline) yielded recoveries of better than 97%. The system worked for 75 nm diameter Ag nanoparticles coated with PVP or with citrate with both types showing full retention within 30 minutes.
The final paper to be discussed in this section was prepared by Fabricius et al.229 These authors used a number of different nanoparticle types (Ag, TiO2, CeO2, ZnO and Au) with two different sizes. The particle size distributions were all characterized using DLS and nanoparticle tracking analysis and, where agglomeration was observed, ultrasonic homogenization was employed. The total elemental analysis of the nanoparticle suspensions was undertaken using ICP-MS (comparing microwave assisted acid digestion, acidification and direct aspiration of suspensions) and gravimetry. In general, the microwave digestion and acidification yielded similar data, with the direct aspiration yielding lower concentrations and usually with a much poorer precision. Since the Au results for the ICP-MS and gravimetry differed, GFAAS was also employed and these results were in agreement with those obtained using ICP-MS. Six methods to determine the dissolved fraction were then compared. These methods included ultrafiltration, dialysis, ion selective electrode, cloud point extraction, centrifugation and tangential flow filtration. Results indicated that dialysis and cloud point extraction were inappropriate for these measurements whereas the others could be used, although they all had limitations. Overall, in terms of precision, time taken and applicability, the authors recommended microwave digestion and ultrafiltration to determine “total” and “dissolved” concentrations.
Another paper to compare several methods of discriminating dissolved Ag from different types of coated or uncoated Ag nanoparticles was prepared by Hadioui et al.230 The methods compared were ion exchange using Dowex 50W-X8, SP-ICP-MS and centrifugal ultrafiltration using a filter with a three kDa cut off. The methodology of each was described and optimized. All three techniques had positive aspects, with the ultrafiltration being the most simple (but also providing data with the worst precision), the SP-ICP-MS providing significant data in the shortest time, but being valid only over a very short range of concentration and the ion exchange providing the best LOD and having a long linear working range but at the cost of largest volume of sample use and being time-consuming. As would be expected, the concentration of Ag ions increased with increasing Ag nanoparticle concentration. However, somewhat unexpectedly, a proportionally greater number of Ag ions were produced at lower nanoparticle concentration. The authors hypothesized why this may be.
Most of the rest of the papers to be discussed in this section of the review describe the use of individual techniques. This section will review some of those that have used any of the numerous versions of XRF. Two papers have discussed the use of grazing incidence XRF (GIXRF). One by Motellier et al.231 described the direct quantification of TiO2 nanoparticles in aqueous suspensions and concluded that it was perfectly viable as long as certain precautions were taken. One of these precautions included the binding of the deposited material on the substrate to maintain its homogeneity. A test using Ti ions and two types of Ti-based nanoparticles demonstrated that the linear regressions obtained using the ions were similar at the beginning and at the end of four months, but that those obtained using the nanoparticles were very different. It was hypothesized that this may be because of capillary action, gravity (they were stored vertically), or possibly even physical loss of the larger particles that may not have been sufficiently embedded in the adhesive. The operating conditions for the benchtop TXRF instrument used were optimized over a range of angles covering 0–2°. The Ti signal increased up to 0.2°, but then halved rapidly and then remained constant. The Cr signal from the internal standard decreased until 0.3° and then began to rise again. The optimal angle was therefore 0.2° since both the analyte and the internal standard signals did not change radically. Limits of detection of 18 μg L−1 and 54 μg L−1 were obtained using incidence angles of 0.2° and 0.75°, respectively. The other GIXRF paper was prepared by Nowak et al.232 These authors developed a geometrical optics algorithm that yielded data for simulations that were in good agreement with those obtained using absolute measurements of two different types of nanoparticle (NaCl and Cr) distributed on a flat surface. The paper takes the reader through the theory, giving numerous equations.
The final selection of papers to be reviewed described novel methods of analysis. Sovago et al.233 used both Raman spectroscopy and LIBS to identify and quantify as well as determine the size of TiO2 and Ho2O3 nanoparticles in aqueous solution with the overall intent to facilitate the on-line or in-line monitoring and optimization of production. Two different LIBS configurations were tested. One configuration was very simple and enabled LIBS data to be collected even for small volumes of sample. However, there were problems with the shock wave causing the sample to splash over the collection optics. The other configuration was more complex but was more suitable for bulk samples such as those found during preparation of the nanoparticles. The use of an aluminium target in the sample increased the LIBS signal significantly and negated the requirement for double pulse LIBS. It was noted that the LIBS signal did not manifest itself as the traditional emission peaks. Instead, the nanoparticle dispersions absorb some of the continuum emission via the inverse Bremstrahlung effect leading to dips in the LIBS spectrum.
The metals Co, Fe, Ni and Pb are often present as impurities in carbon nanotubes. Resano et al.234 developed a method using solid sampling high resolution ETAAS to determine these analytes. Sample was weighed directly onto a platform and Pd matrix modifier added before the platform was placed in the atomizer and a standard ETAAS temperature programme run. An external calibration using similar methodology was used. The signal over the wavelength range 283.168 and 283.481 nm was monitored enabling all four analytes to be determined simultaneously and with sufficient sensitivity. This was, according to the authors, the first time this had been achieved using this commercially available instrument type. Absolute LOD were 23 pg for Pb, 6 ng for Fe, 65 ng for Ni and 86 ng for Co. As with all solid sampling techniques, precision was not great; typically ranging from 7 to 15% for five replicate measurements.
A monodisperse micro-droplet generator capable of introducing >95% of a sample to the plasma of an ICP-MS instrument was described by Gschwind et al.235 Two different configurations were evaluated; one vertical and the other horizontal. The horizontal one resulted in a shorter measurement time and this was attributed to a five-fold reduction in the temporal jitter. The technique developed was compared with established methodology (TEM and AF4) and advantages and limitations of the procedure were discussed.
3.5. Polymers and composites
In this review period, the actual identification of the polymer has proven to be a popular topic. Another popular topic was the determination of analytes leached from plastics into simulated foodstuffs. Numerous other applications were reported and the more interesting of these will be discussed in this section of the review.Other techniques have also been used to identify plastics. Pulsed glow discharge (GD)-TOF-MS was used by de Vega et al.239 to identify polymer coatings. A comparison of two Grimm-type designs was made, one of which was made in-house (a brief description was given) and the other was based on a commercial design. Operating conditions for both units were optimized and were similar, with the power being 15 W for both. The argon gas pressure was 150 Pa for the in-house design and 200 Pa for the commercial one. These soft settings were ideal for minimizing the thermal decomposition of the samples. The commercial design gave a greater sensitivity and was richer in polyatomic information. This polyatomic information came from molecules from the sample rather than recombination-based interferences. The improvement in sensitivity compared with the in-house design was attributed to a higher distance between the sample and the MS interface. The design of the interface was also responsible for the formation of the polyatomic ions. The use of an argon pre-chamber to prevent the ingress of air (which may otherwise cause interferences) was also a feature. Four polymers (polyaniline, polyphenylene sulfide, polypyrrole and polythiophene) were examined. All four materials contain only C, H and either N or S. Despite this, it was possible to identify polyatomic ions that originated from the monomer of the materials and hence it was possible to distinguish between them. The authors claimed that it was a “notorious step forward” in the identification of polymers using GD technology. Other advantages of the technique are that no sample preparation is required and an analysis time of less than five minutes was required per sample.
Another paper to report the leaching of Sb from PET trays into food and food simulants was prepared by Haldimann et al.241 Total Sb in the material was determined using a microwave digestion protocol prior to ICP-MS detection. Since no PET CRM was available, the authors resorted to validation using a polyethylene CRM (ERM CE680k) with a certified Sb content of 10.1 ± 1.6 mg kg−1. An alternative XRF method was also used. Here, the PET was ground cryogenically in the presence of liquid nitrogen. Particles of the material of less than 0.50 mm diameter were then used as a base onto which differing amounts of Sb2O3 was added to form a calibration series. The mixtures were then pelletized prior to XRF analysis. Acetic acid (3%) was used as the food simulant medium over a temperature range of 20–150 °C and at a nitrogen pressure of between 50 and 90 bar to prevent boiling. The Sb leached into the acetic acid was determined using ICP-MS and the results used to construct a linear Arrhenius plot so that diffusion coefficients could be calculated. An isotope dilution analysis of food samples was also undertaken in which isotopically enriched 123Sb (98.6%) was spiked into the foodstuffs prior to SF-ICP-MS analysis.
Two other papers have reported the determination of numerous metals from food packaging materials.242,243 In the former, Kiyataka et al. also used 3% acetic acid as a food simulant as well as yoghurt to determine the leaching rates of As, Cd, Hg and Pb from high density polyethylene. The plastic and the yoghurt were digested using a high pressure ashing device prior to ICP-OES analysis. Although the plastic contained a significant amount of Pb (462.3 mg kg−1), the level in the yoghurt after a 45 day exposure at 4 °C was still below LOQ. Leaching into the acetic acid was also minimal, with concentrations of As, Cd and Hg being 10, 5 and 5 μg kg−1, respectively. Accuracy, precision, linearity, LOD and LOQ were all assessed. The second of the two papers, by Whitt et al.243 used ICP-OES to survey Cd, Cr, Ni, Pb and Sb contamination in PET that had been made using recycled plastic flake that had potentially been in contact with electronic waste. Of 200 samples analysed, 29 were contaminated, although the average concentrations in these 29 samples were well below the threshold levels set by California's “Toxics in Packaging Prevention Act” of 2006.
Two papers reported the determination of Ag (both ionic and nanoparticulate) from food packaging materials. von Goetz et al.244 used water, 10% ethanol, 3% acetic acid and olive oil as food simulants and ICP-MS as a means of detection. The highest migration of Ag occurred for the acid with 30 ng cm−2 being released at 20 °C over 10 days. However, when re-used, the migration rate dropped by a factor of 10, meaning that even after three cycles of use/re-use, a maximum Ag content of 34 ng cm−2 was obtained. Of the Ag released, 88% was ionic and 12% particulate. A similar study by Echegoyen and Nerin245 used ICP-MS and SEM-EDX to detect Ag in different food simulants and after different exposure times. Their Ag migration values ranged from 1.66 to 31.46 ng cm−2, which were lower than permissible levels.
Another application that used solid sampling GFAAS was presented by Rodrigues et al.248 who determined Fe, Mg, Mn and Na in polymeric diphenylmethane dianiline, a raw material for polyurethane production. Sample of mass between 0.5 and 35 mg was used and calibration was against aqueous standards. Precision (where n was between 14 and 23) was better than 15% which, although high, is common with solid sampling GFAAS protocols. Method validation was achieved using alternative techniques. A microwave assisted digestion and a microwave induced combustion method were used, both followed by ICP-OES analysis. No statistical differences between any of the methods were observed. However, the LOD obtained using the solid sampling GFAAS method were significantly better, ranging from 0.06–0.27 ng g−1 compared with those from microwave digestion (12–4890 ng g−1) and microwave induced combustion (35–5443 ng g−1).
A paper by Mihaltan et al.249 described the determination of As and Sb in non- and bio-degradable materials, such as acrylonitrile butadiene styrene copolymer from electronic waste, polyethylene shopping bags and PET water bottles. After sample decomposition using nitric and sulfuric acids in a microwave system, the digests were introduced by HG to a capacitively coupled plasma mini-torch operating with a power of 25 W, at a frequency of 13.56 MHz and with a flow rate of 0.41 L min−1 argon. The protocol was validated by analysis of the granulated polyethylene certified materials ERM-EC 680K and ERM-EC 681K, with results being in excellent agreement with certified values. The microwave program was described as well as the HG process. The latter was optimized carefully and involved the use of L-cysteine at 90 °C for 10 min to pre-reduce AsV and SbV to AsIII and SbIII. The operating conditions for the plasma were also optimized. Under ideal conditions, the protocol yielded LOD of 1.5 and 0.3 mg kg−1 for As and Sb in the solid plastics. Precision was acceptable (<7%). The only drawback to the system was that the analytes had to be determined separately because of the very different optimal viewing heights.
A paper by Mine and Houssiau250 described the simultaneous use of OES and TOF-SIMS for low-energy depth-profiling of polystyrene. The authors modified their commercial TOF-SIMS instrument by attaching an OES spectrometer to the 45° backwards-facing flange so that light emission from the discharge could be monitored. This spectrometer had three different gratings, one with 600, another with 1800 and the last with 2400 lines/mm, and enabled measurements over the wavelength range 200–950 nm. The OES detection was achieved using a CCD camera. Several surprising observations were made. Intense atomic Cs emission was detected throughout the depth profile of the polystyrene sample. However, when oxygen or xenon were used as the primary ions, no emission from either O or Xe was observed.
4 Glossary of terms
| 3D | Three dimensional |
| AAS | Atomic absorption spectrometry |
| AFFF | Asymmetric field flow fractionation |
| A4F | Asymmetric flow field flow fractionation |
| AFS | Atomic fluorescence spectrometry |
| AFM | Atomic force microscopy |
| AMS | Accelerator mass spectrometry |
| APT | Atom probe tomography |
| BCR | Community bureau of reference |
| CCD | Charge coupled device |
| CRM | Certified reference material |
| CPFAAS | Collinear photofragmentation atomic absorption spectrometry |
| CS | Continuum source |
| CV | Cold vapour |
| DLS | Dynamic light scattering |
| DSC | Differential scanning calorimetry |
| EBA | Ion beam analysis |
| EBS | Elastic back scattering spectroscopy |
| EDAX | Energy dispersive X-ray analysis |
| EDTA | Ethylenediamine tetra-acetic acid |
| EDXRD | Energy dispersive X-ray diffraction |
| EDXRF | Energy dispersive X-ray fluorescence |
| ERDA | Elastic recoil detection analysis |
| ESI-MS | Electrospray ionization mass spectrometry |
| ETAAS | Electrothermal atomic absorption spectrometry |
| ETV | Electrothermal vaporization |
| EXAFS | Extended X-ray absorption fine structure |
| FAAS | Flame atomic absorption spectrometry |
| FFF | Field flow fractionation |
| FI | Flow injection |
| FTIR | Fourier transform infrared |
| FWHM | Full width at half maximum |
| GA-XRD | Grazing angle X-ray diffraction |
| GC | Gas chromatography |
| GD-MS | Glow discharge mass spectrometry |
| GD-OES | Glow discharge optical emission spectrometry |
| GI-SAXS | Grazing incidence small angle X-ray scattering |
| GI-XRD | Grazing incidence X-ray diffraction |
| GI-XRF | Grazing incidence X-ray fluorescence |
| HG | Hydride generation |
| HPLC | High performance liquid chromatography |
| hTISIS | heated torch integrated sample introduction system |
| IAEA | International Atomic Energy Agency |
| IBA | Ion beam analysis |
| ICCD | Integrated charged couple device |
| ICP | Inductively coupled plasma |
| ICP-MS | Inductively coupled plasma mass spectrometry |
| ICP-QMS | Inductively coupled plasma quadrupole mass spectrometry |
| ICP-TOF-MS | Inductively coupled plasma-time-of-flight mass spectrometry |
| ID | Isotope dilution |
| IL-DLLME | Ionic liquid-dispersive liquid–liquid microextraction |
| IRMS | Isotope ratio mass spectrometry |
| ISO | International organization for standardization |
| LA | Laser ablation |
| LASIL | Laser ablation of sample in liquid |
| LEIS | Lowe energy ion scattering |
| LIBS | Laser induced breakdown spectrometry |
| LIF | Laser induced fluorescence |
| LIPS | Laser induced plasma spectrosocopy |
| LOD | Limit of detection |
| LOQ | Limit of quantification |
| LTE | Local thermodynamic equilibrium |
| MALDI-TOF | Matrix assisted laser desorption ionization time-of-flight |
| MC | Multicollector |
| MEIS | Medium energy ion scattering |
| MHGD | Micro-hollow glow discharge |
| MS | Mass spectrometry |
| MWCNT | Multi-walled carbon nanotube |
| MWTN | Microwave thermal nebuliser |
| Nd:YAG | Neodymium doped-yttrium aluminium garnet |
| NMR | Nuclear magnetic resonance |
| NRA | Nuclear reaction analysis |
| OES | Optical emission spectrometry |
| ND | Neutron diffraction |
| ND-YAG | Neodymium doped yttrium aluminium garnet |
| NIST | National Institute of Standards and Technology |
| PCA | Principal component analysis |
| PGAA | Prompt gamma neutron activation analysis |
| PGM | Platinum group metals |
| PIGE | Particle-induced gamma ray emission |
| PIXE | Particle-induced X-ray emission |
| PL-PSDA | Polymer Labs particle size distribution analysis |
| PLS | Partial least squares |
| PLS-DA | Partial least squares discriminant analysis |
| ppb | Part per billion |
| ppm | Part per million |
| PGM | Platinum group metal |
| PVG | Photochemical vapour generation |
| RBS | Rutherford backscattering spectrometry |
| RDA | Regularized discriminant analysis |
| REE | Rare earth element |
| rf | Radiofrequency |
| RIMS | Resonance ionization mass spectrometry |
| RSD | Relative standard deviation |
| SEM | Scanning electron microscopy |
| SF | Sector field |
| SIMCA | Soft independent modelling of class analogy |
| SIMS | Secondary ion mass spectrometry |
| SP | Single particle |
| SR | Synchrotron radiation |
| SRM | Standard reference material |
| SRS | Synchrotron radiation source |
| SXRF | Synchrotron X-ray fluorescence SWCNT single-walled carbon nanotube |
| TE | Trace element |
| TEM | Transmission electron microscopy |
| TGA | Thermogravimetric analysis |
| TIMS | Thermal ionization mass spectrometry |
| TPR | Temperature programmed reduction |
| TXRF | Total reflection X-ray fluorescence |
| UV-VIS | Ultraviolet-visible |
| VOC | Volatile organic carbon |
| VUV | Vacuum ultra-violet |
| WDXRF | Wavelength dispersive X-ray fluorescence |
| XAFS | X-ray absorption fine structure spectrometry |
| XANES | X-ray absorption near-edge structure |
| XAS | X-ray absorption spectroscopy |
| XPS | X-ray photoelectron spectroscopy |
| XRD | X-ray diffraction |
| XRF | X-ray fluorescence |
| XRR | X-ray reflectometry |
References
- S. Carter, A. S. Fisher, M. W. Hinds, S. Lancaster and J. Marshall, J. Anal. At. Spectrom., 2013, 28(12), 1814–1869 RSC.
- E. H. Evans, M. Horstwood, J. Pisonero and C. M. M. Smith, J. Anal. At. Spectrom., 2013, 28(6), 779–800 RSC.
- R. Clough, C. F. Harrington, S. J. Hill, Y. Madrid and J. F. Tyson, J. Anal. At. Spectrom., 2013, 28(8), 1153–1195 RSC.
- M. West, A. T. Ellis, P. J. Potts, C. Streli, C. Vanhoof, D. Wegrzynek and P. Wobrauschek, J. Anal. At. Spectrom., 2013, 28(10), 1544–1590 RSC.
- O. T. Butler, W. R. L. Cairns, J. M. Cook and C. M. Davidson, J. Anal. At. Spectrom., 2014, 29(1), 17–50 RSC.
- L. Escalada, J. Lutz, S. P. Bruhl, M. Fazio, A. Marquez, S. Mandl, D. Manova and S. N. Simison, Surf. Coat. Technol., 2013, 223, 41–46 CrossRef CAS PubMed.
- E. L. Dalibon, P. B. Bozzano and S. P. Bruhl, Acta Microsc., 2013, 22(1), 4–11 CAS.
- M. R. Ardigo, I. Popa, S. Chevalier, S. Weber, O. Heintz and M. Vilasi, Oxid. Met., 2013, 79(5–6), 495–505 CrossRef CAS.
- M. Necemer, T. Lazar, Z. Smit, P. Kump and B. Zuzek, Acta Chim. Slov., 2013, 60(2), 351–357 CAS.
- N. Farid, C. Li, H. B. Wang and H. B. Ding, J. Nucl. Mater., 2013, 433(1–3), 80–85 CrossRef CAS PubMed.
- T. A. Labutin, S. M. Zaytsev, A. M. Popov, I. V. Seliverstova, S. E. Bozhenko and N. B. Zorov, Spectrochim. Acta, Part B, 2013, 87, 57–64 CrossRef CAS PubMed.
- M. L. Shah, A. K. Pulhani, B. M. Suri and G. P. Gupta, Plasma Sci. Technol., 2013, 15(6), 546–551 CrossRef.
- L. B. Guo, Z. Q. Hao, M. Shen, W. Xiong, X. N. He, Z. Q. Xie, M. Gao, X. Y. Li, X. Y. Zeng and Y. F. Lu, Opt. Express, 2013, 21(15), 18188–18195 CrossRef CAS PubMed.
- M. Scharun, C. Fricke-Begemann and R. Noll, Spectrochim. Acta, Part B, 2013, 87, 198–207 CrossRef CAS PubMed.
- S. Kashiwakura and K. Wagatsuma, Anal. Sci., 2013, 29(12), 1159–1164 CrossRef CAS.
- C. Y. Pan, X. W. Du, N. An, Z. Y. Han, S. B. Wang, W. Wei and Q. P. Wang, Spectrosc. Spectr. Anal., 2013, 33(12), 3388–3391 CAS.
- X. Jiang, P. Hayden, R. Laasch, J. T. Costello and E. T. Kennedy, Spectrochim. Acta, Part B, 2013, 86, 66–74 CrossRef CAS PubMed.
- M. Aula, A. Makinen and T. Fabritius, Appl. Spectrosc., 2014, 68(1), 26–32 CrossRef CAS PubMed.
- L. Zhang and K. Wagatsuma, ISIJ Int., 2013, 53(12), 2201–2205 CrossRef CAS.
- S. Hasegawa, ISIJ Int., 2014, 54(1), 131–135 CrossRef CAS.
- C. Bellot and P. Lamesle, J. Alloys Compd., 2013, 570, 100–103 CrossRef CAS PubMed.
- L. Pillatsch, N. Vanhove, D. Dowsett, S. Sijbrandij, J. Notte and T. Wirtz, Appl. Surf. Sci., 2013, 282, 908–913 CrossRef CAS PubMed.
- J. R. Freeman, S. S. Harilal, P. M. Diwakar, B. Verhoff and A. Hassanein, Spectrochim. Acta, Part B, 2013, 87, 43–50 CrossRef CAS PubMed.
- A. Nakimana, H. Y. Tao, X. Gao, Z. Q. Hao and J. Q. Lin, J. Phys. D: Appl. Phys., 2013, 46(28), 6 CrossRef.
- P. K. Diwakar, S. S. Harilal, J. R. Freeman and A. Hassanein, Spectrochim. Acta, Part B, 2013, 87, 65–73 CrossRef CAS PubMed.
- K. Y. Chen, C. Fan, H. L. Yuan, Z. A. Bao, C. L. Zong, M. N. Dai, X. Ling and Y. Yang, Spectrosc. Spectr. Anal., 2013, 33(5), 1342–1349 CAS.
- M. Modlinger, P. Piccardo, Z. Kasztovszky, I. Kovacs, Z. Szokefalvi-Nagy, G. Kali and V. Szilagyi, Mater. Charact., 2013, 79, 22–36 CrossRef CAS PubMed.
- J. J. Wei, C. Y. Lang, L. F. Lin, L. Zheng and J. X. Li, Chin. J. Anal. Chem., 2013, 41(6), 927–930 CAS.
- G. L. Donati, R. S. Amais, D. Schiavo and J. A. Nobrega, J. Anal. At. Spectrom., 2013, 28(5), 755–759 RSC.
- M. S. Luz, A. N. Nascimento and P. V. Oliveira, Talanta, 2013, 115, 409–413 CrossRef CAS PubMed.
- C. Viana, D. Bohrer, L. M. de Carvalho, P. C. do Nascimento and M. B. da Rosa, TrAC, Trends Anal. Chem., 2014, 53, 49–59 CrossRef CAS PubMed.
- R. Sanchez, C. Sanchez, J. L. Todoli, C. P. Lienemann and J. M. Mermet, J. Anal. At. Spectrom., 2014, 29(2), 242–248 RSC.
- R. S. Amais, S. E. Long, J. A. Nobrega and S. J. Christopher, Anal. Chim. Acta, 2014, 806, 91–96 CrossRef CAS PubMed.
- V. R. B. Soares, F. R. P. Rocha and L. S. G. Teixeira, Anal. Lett., 2013, 46(11), 1621–1639 CrossRef CAS.
- R. Sanchez, J. L. Todoli, C. P. Lienemann and J. M. Mermet, Spectrochim. Acta, Part B, 2013, 88, 104–126 CrossRef CAS PubMed.
- T. B. Yuan, Z. Wang, Z. Li, W. D. Ni and J. M. Liu, Anal. Chim. Acta, 2014, 807, 29–35 CrossRef CAS PubMed.
- A. Haider, M. A. Rony and K. M. Abedin, Energy Fuels, 2013, 27(7), 3725–3729 CrossRef CAS.
- Z. Z. Wang, Y. Deguchi, M. Kuwahara, T. Taira, X. B. Zhang, J. J. Yan, J. P. Liu, H. Watanabe and R. Kurose, Spectrochim. Acta, Part B, 2013, 87, 130–138 CrossRef CAS PubMed.
- J. P. Zheng, J. D. Lu, B. Zhang, S. H. Chen, S. C. Yao, F. P. Pan, X. Dong and X. Zhang, Spectrosc. Spectr. Anal., 2014, 34(1), 221–225 CAS.
- W. B. Jia, Y. Zhang, C. G. Gu, D. Q. Hei, Y. S. Ling and Q. Shan, Sci. China: Technol. Sci., 2014, 57(1), 39–43 CrossRef CAS.
- T. Sorvajarvi, N. DeMartini, J. Rossi and J. Toivonen, Appl. Spectrosc., 68(2), 179–184 CrossRef CAS PubMed.
- A. A. Raeva, N. Dongari, A. A. Artemyeva, E. I. Kozliak, D. T. Pierce and W. S. Seames, Fuel, 2014, 124, 28–40 CrossRef CAS PubMed.
- F. V. Nakadi, L. R. Rosa and M. da Veiga, Spectrochim. Acta, Part B, 2013, 88, 80–84 CrossRef CAS PubMed.
- F. G. Antes, E. Dullius, A. Ben da Costa, R. F. Molz, J. N. G. Paniz, E. M. M. Flores and V. L. Dressler, Microchem. J., 2013, 109, 117–121 CrossRef CAS PubMed.
- M. Sun, G. J. Liu, Q. H. Wu and W. Q. Liu, Talanta, 2013, 106, 8–13 CrossRef CAS PubMed.
- J. M. Andrade, S. Carballo-Paradelo, J. Teran-Baamonde, A. Carlosena, R. M. Soto-Ferreiro and D. Prada-Rodriguez, Anal. Methods, 2013, 5(16), 4039–4046 RSC.
- S. Carballo, J. Teran, R. M. Soto, A. Carlosena, J. M. Andrade and D. Prada, Microchem. J., 2013, 108, 74–80 CrossRef CAS PubMed.
- L. F. S. Caldas, D. M. Brum, C. E. R. de Paula and R. J. Cassella, Talanta, 2013, 110, 21–27 CrossRef CAS PubMed.
- M. S. Luz and P. V. Oliveira, Fuel, 2014, 116, 255–260 CrossRef CAS PubMed.
- J. S. Xiu, V. Motto-Ros, G. Panczer, R. Zheng and J. Yu, Spectrochim. Acta, Part B, 2014, 91, 24–30 CrossRef CAS PubMed.
- J. S. F. Pereira, R. S. Picoloto, L. S. F. Pereira, R. C. L. Guimaraes, R. A. Guarnieri and E. M. M. Flores, Anal. Chem., 2013, 85(22), 11034–11040 CrossRef CAS PubMed.
- J. Barbier, J. Marques, G. Caumette, I. Merdrignac, B. Bouyssiere, R. Lobinski and C. P. Lienemann, Fuel Process. Technol., 2014, 119, 185–189 CrossRef CAS PubMed.
- X. Zhao, Y. Liu, C. M. Xu, Y. Y. Yan, Y. H. Zhang, Q. Y. Zhang, S. Q. Zhao, K. Chung, M. R. Gray and Q. Shi, Energy Fuels, 2013, 27(6), 2874–2882 CrossRef CAS.
- A. Doyle, A. Saavedra, M. L. B. Tristao, L. A. N. Mendes and R. Q. Aucelio, Spectrochim. Acta, Part B, 2013, 86, 102–107 CrossRef CAS PubMed.
- M. T. Lisboa, C. D. Clasen, D. C. D. Vellar, E. Q. Oreste, T. D. St Pierre, A. S. Ribeiro and M. A. Vieira, J. Braz. Chem. Soc., 2014, 25(1), 143–151 CAS.
- F. M. Pereira, R. C. Zimpeck, D. M. Brum and R. J. Cassella, Talanta, 2013, 117, 32–38 CrossRef CAS PubMed.
- M. R. L. de Magalhaes, A. I. Barros, A. P. de Oliveira, A. D. da Silva and R. Dalla Villa, Curr. Anal. Chem., 2014, 10(1), 166–171 CrossRef.
- E. Paredes, S. Z. Can and C. R. Quetel, Fuel, 2014, 123, 248–255 CrossRef CAS PubMed.
- S. E. Dancsak, S. G. Silva, J. A. Nobrega, B. T. Jones and G. L. Donati, Anal. Chim. Acta, 2014, 806, 85–90 CrossRef CAS PubMed.
- S. S. M. Rodrigues, A. S. Lima, L. S. G. Teixeira, M. D. A. Korn and J. L. M. Santos, Fuel, 2014, 117, 520–527 CrossRef CAS PubMed.
- L. K. Andersen, T. J. Morgan, A. K. Boulamanti, P. Alvarez, S. V. Vassilev and D. Baxter, Energy Fuels, 2013, 27(12), 7439–7454 CrossRef CAS.
- S. H. Lee, H. T. Hahn and J. J. Yoh, Spectrochim. Acta, Part B, 2013, 88, 63–68 CrossRef CAS PubMed.
- B. Zhang, P. Xu, J. J. Ma, H. Wu, G. Q. Luo, M. H. Xu and H. Yao, Energy Fuels, 2014, 28(1), 192–198 CrossRef CAS.
- M. Alfeld, J. V. Pedroso, M. V. Hommes, G. Van der Snickt, G. Tauber, J. Blaas, M. Haschke, K. Erler, J. Dik and K. Janssens, J. Anal. At. Spectrom., 2013, 28(5), 760–767 RSC.
- A. Zielinska, W. Dabrowski, T. Fiutowski, B. Mindur, P. Wiacek and P. Wrobel, J. Instrum., 2013, 8, 15 Search PubMed.
- O. Kokkinaki, C. Mihesan, M. Velegrakis and D. Anglos, J. Mol. Struct., 2013, 1044, 160–166 CrossRef CAS PubMed.
- Q. Y. Lin, G. H. Niu, Q. H. Wang, Q. L. Yu and Y. X. Duan, Appl. Spectrosc. Rev., 2013, 48(6), 487–508 CrossRef CAS.
- A. Pitarch, A. Ramon, A. Alvarez-Perez, K. Castro, J. M. Madariaga and I. Queralt, Spectrosc. Lett., 2014, 47(1), 38–51 CrossRef CAS.
- E. Rebollo, L. Nodari, U. Russo, R. Bertoncello, C. Scardellato, F. Romano, F. Ratti and L. Poletto, J. Cult. Herit., 2013, 14(3), E153–E160 CrossRef PubMed.
- F. Toschi, A. Paladini, F. Colosi, P. Cafarelli, V. Valentini, M. Falconieri, S. Gagliardi and P. Santoro, Appl. Surf. Sci., 2013, 284, 291–296 CrossRef CAS PubMed.
- F. Salvemini, F. Grazzi, A. Agostino, R. Iannaccone, F. Civita, S. Hartmann, E. Lehmann and M. Zoppi, Archaeol. Anthropol. Sci., 2013, 5(3), 197–204 CrossRef PubMed.
- M. Alfeld and J. A. C. Broekaert, Spectrochim. Acta, Part B, 2013, 88, 211–230 CrossRef CAS PubMed.
- K. Janssens, M. Alfeld, G. Van der Snickt, W. De Nolf, F. Vanmeert, M. Radepont, L. Monico, J. Dik, M. Cotte, G. Falkenberg, C. Miliani and B. G. Brunetti, in Annual Review of Analytical Chemistry, ed. R. G. Cooks and J. E. Pemberton, Annual Reviews, Palo Alto, 2013, vol. 6, pp. 399–425 Search PubMed.
- C. Gervais, M. A. Languille, S. Reguer, M. Gillet, S. Pelletier, C. Garnier, E. P. Vicenzi and L. Bertrand, J. Anal. At. Spectrom., 2013, 28(10), 1600–1609 RSC.
- J. Moros, J. Serrano, F. J. Gallego, J. Macias and J. J. Laserna, Talanta, 2013, 110, 108–117 CrossRef CAS PubMed.
- P. Lucena, I. Gaona, J. Moros and J. J. Laserna, Spectrochim. Acta, Part B, 2013, 85, 71–77 CrossRef CAS PubMed.
- T. Delgado, J. M. Vadillo and J. J. Laserna, J. Anal. At. Spectrom., 2013, 28(9), 1377–1384 RSC.
- A. Fernandez-Bravo, T. Delgado, P. Lucena and J. J. Laserna, Spectrochim. Acta, Part B, 2013, 89, 77–83 CrossRef CAS PubMed.
- J. Serrano, J. Moros, C. Sanchez, J. Macias and J. J. Laserna, Anal. Chim. Acta, 2014, 806, 107–116 CrossRef CAS PubMed.
- F. C. De Lucia and J. L. Gottfried, J. Phys. Chem. A, 2013, 117(39), 9555–9563 CrossRef CAS PubMed.
- C. S. C. Yang, E. E. Brown, E. Kumi-Barimah, U. H. Hommerich, F. Jin, S. B. Trivedi, A. C. Samuels and A. P. Snyder, Appl. Spectrosc., 2014, 68(2), 226–231 CrossRef CAS PubMed.
- J. H. Fujiyama-Novak, C. K. Gaddam, D. Das, R. L. Vander Wal and B. Ward, Sens. Actuators, B, 2013, 176, 985–993 CrossRef CAS PubMed.
- R. A. Putnam, Q. I. Mohaidat, A. Daabous and S. J. Rehse, Spectrochim. Acta, Part B, 2013, 87, 161–167 CrossRef CAS PubMed.
- M. A. Khater, Opt. Spectrosc., 2013, 115(4), 574–590 CrossRef CAS.
- A. A. Hummer and A. Rompel, Metallomics, 2013, 5(6), 597–614 RSC.
- B. J. Han, X. M. Jiang, X. D. Hou and C. B. Zheng, Anal. Chem., 2014, 86(1), 936–942 CrossRef CAS PubMed.
- M. Holtkamp, T. Elseberg, C. A. Wehe, M. Sperling and U. Karst, J. Anal. At. Spectrom., 2013, 28(5), 719–723 RSC.
- Y. Gao, Z. M. Shi, Q. X. Zong, P. Wu, J. Su and R. Liu, Anal. Chim. Acta, 2014, 812, 6–11 CrossRef CAS PubMed.
- E. Margui, I. Queralt and M. Hidalgo, Spectrochim. Acta, Part B, 2013, 86, 50–54 CrossRef CAS PubMed.
- G. Grindlay, L. Gras, V. Hernandis and J. Mora, Talanta, 2013, 107, 11–17 CrossRef CAS PubMed.
- C. Venzago, M. Popp, J. Kovac and A. Kunkel, J. Anal. At. Spectrom., 2013, 28(7), 1125–1129 RSC.
- M. E. Christopher, J. W. Warmenhoeven, F. S. Romolo, M. Donghi, R. P. Webb, C. Jeynes, N. I. Ward, K. J. Kirkby and M. J. Bailey, Analyst, 2013, 138(16), 4649–4655 RSC.
- F. S. Romolo, M. E. Christopher, M. Donghi, L. Ripani, C. Jeynes, R. P. Webb, N. I. Ward, K. J. Kirkby and M. J. Bailey, Forensic Sci. Int., 2013, 231(1–3), 219–228 CrossRef CAS PubMed.
- E. Turillazzi, G. P. Di Peri, A. Nieddu, S. Bello, F. Monaci, M. Neri, C. Pomara, R. Rabozzi, I. Riezzo and V. Fineschi, Forensic Sci. Int., 2013, 231(1–3), 142–149 CrossRef CAS PubMed.
- J. F. Fonseca, M. M. Cruz and M. L. Carvalho, X-Ray Spectrom., 2014, 43(1), 49–55 CrossRef CAS.
- P. C. Chu, B. Y. Cai, Y. K. Tsoi, R. Yuen, K. S. Y. Leung and N. H. Cheung, Anal. Chem., 2013, 85(9), 4311–4315 CrossRef CAS PubMed.
- A. V. D'Yachkova, A. D. Kirillov, T. Y. Alekseeva and Y. A. Karpov, Inorg. Mater., 2013, 49(14), 1272–1276 CrossRef.
- Y. V. Antonova, A. V. Zablotskii, O. I. Lyamina, Y. A. Karpov, A. Y. Kuzin, T. A. Kupriyanova and M. N. Filippov, Meas. Tech., 2013, 56(9), 1088–1091 CrossRef CAS.
- N. Nuns, J. F. Lamonier, J. M. Giraudon, S. Siffert and B. L. Su, Surf. Interface Anal., 2013, 45(1), 566–569 CrossRef CAS.
- I. A. Witonska, M. J. Walock, P. Dziugan, S. Karski and A. V. Stanishevsky, Appl. Surf. Sci., 2013, 273, 330–342 CrossRef CAS PubMed.
- J. Kristof, E. Horvath and S. Daolio, Electrocatalysis, 2013, 4(4), 196–202 CrossRef CAS.
- T. Cetin, S. Tokalioglu, A. Ulgen, S. Sahan, I. Ozenturk and C. Soykan, Talanta, 2013, 105, 340–346 CrossRef CAS PubMed.
- N. Silva, L. P. Tang and S. Rauch, Mater. Struct., 2013, 46(8), 1369–1381 CrossRef CAS.
- T. A. Labutin, A. M. Popov, S. N. Raikov, S. M. Zaytsev, N. A. Labutina and N. B. Zorov, J. Appl. Spectrosc., 2013, 80(3), 315–318 CrossRef CAS.
- S. S. Panda, P. K. Mohapatra, R. K. Chaturvedi and S. K. Kar, Curr. Sci., 2013, 105(6), 837–842 CAS.
- T. Yamamoto, T. Kudo and J. Kawai, Microporous Mesoporous Mater., 2013, 182, 239–243 CrossRef CAS PubMed.
- M. Horňáčková, M. Hornacek, J. Rakovsky, P. Hudec and P. Veis, Spectrochim. Acta, Part B, 2013, 88, 69–74 CrossRef PubMed.
- K. Goraieb, M. C. Chiaradia, K. E. Collins, C. H. Collins and M. Bueno, X-Ray Spectrom., 2013, 42(3), 165–170 CrossRef CAS.
- H. E. Gäbler, S. Rehder, A. Bahr, F. Melcher and S. Goldmann, J. Anal. At. Spectrom., 2013, 28(8), 1247–1255 RSC.
- P. Siozos, A. Philippidis, M. Hadjistefanou, C. Gounarakis and D. Anglos, Spectrochim. Acta, Part B, 2013, 87, 86–91 CrossRef CAS PubMed.
- G. H. Cavalcanti, A. A. Rocha, R. N. Damasceno, S. Legnaioli, G. Lorenzetti, L. Pardini and V. Palleschi, Spectrochim. Acta, Part B, 2013, 87, 188–191 CrossRef CAS PubMed.
- J. D. Pedarnig, P. Kolmhofer, N. Huber, B. Praher, J. Heitz and R. Rossler, Appl. Phys. A: Mater. Sci. Process., 2013, 112(1), 105–111 CrossRef CAS.
- V. K. Unnikrishnan, R. Nayak, P. Devangad, M. M. Tamboli, C. Santhosh, G. A. Kumar and D. K. Sardar, Mater. Lett., 2013, 107, 322–324 CrossRef CAS PubMed.
- M. A. Gondal, Y. W. Maganda, M. A. Dastageer, F. F. Al Adel, A. A. Naqvi and T. F. Qahtan, Opt. Laser Technol., 2014, 57, 32–38 CrossRef CAS PubMed.
- K. Orsel, R. Groenen, H. M. J. Bastiaens, G. Koster, G. Rijnders and K. J. Boller, J. Instrum., 2013, 8, 7 Search PubMed.
- R. M. de Jesus, L. O. B. Silva, J. T. Castro, A. D. D. Neto and S. L. C. Ferreira, Talanta, 2013, 106, 293–297 CrossRef CAS PubMed.
- Y. Akama and T. Ueda, Cellul. Chem. Technol., 2013, 47(5–6), 479–486 CAS.
- G. Holzlechner, M. Kubicek, H. Hutter and J. Fleig, J. Anal. At. Spectrom., 2013, 28(7), 1080–1089 RSC.
- J. Malherbe and F. Claverie, Anal. Chim. Acta, 2013, 773, 37–44 CrossRef CAS PubMed.
- W. Kutschera, Int. J. Mass Spectrom., 2013, 349, 203–218 CrossRef PubMed.
- J. Zheng, K. Tagami, S. Homma-Takeda and W. T. Bu, J. Anal. At. Spectrom., 2013, 28(11), 1676–1699 RSC.
- G. S. Maurya, A. Jyotsana, A. K. Pathak, A. Kumar and A. K. Rai, Optic. Laser. Eng., 2014, 56, 13–18 CrossRef PubMed.
- G. S. Maurya, A. Jyotsana, R. Kumar, A. Kumar and A. K. Rai, J. Nucl. Mater., 2014, 444(1–3), 23–29 CrossRef CAS PubMed.
- D. Y. Zhao, N. Farid, R. Hai, D. Wu and H. B. Ding, Plasma Sci. Technol., 2014, 16(2), 149–154 CrossRef CAS.
- R. Hai, N. Farid, D. Y. Zhao, L. Zhang, J. H. Liu, H. B. Ding, J. Wu and G. N. Luo, Spectrochim. Acta, Part B, 2013, 87, 147–152 CrossRef CAS PubMed.
- A. Malaquias, V. Philipps, A. Huber, A. Hakola, J. Likonen, J. Kolehmainen, S. Tervakangas, M. Aints, P. Paris, M. Laan, A. Lissovski, S. Almaviva, L. Caneve, F. Colao, G. Maddaluno, M. Kubkowska, P. Gasior, H. J. van der Meiden, A. R. Lof, P. A. Z. van Emmichoven, P. Petersson, M. Rubel, E. Fortuna and Q. Xiao, J. Nucl. Mater., 2013, 438, S936–S939 CrossRef CAS PubMed.
- R. Fantoni, S. Almaviva, L. Caneve, F. Colao, A. M. Popov and G. Maddaluno, Spectrochim. Acta, Part B, 2013, 87, 153–160 CrossRef CAS PubMed.
- Q. Xiao, A. Huber, G. Sergienko, B. Schweer, P. Mertens, A. Kubina, V. Philipps and H. Ding, Fusion Eng. Des., 2013, 88(9–10), 1813–1817 CrossRef CAS PubMed.
- H. J. van der Meiden, M. A. van den Berg, S. Brons, H. Ding, H. J. N. Van Eck, M. H. J. t. Hoen, J. Karhunen, T. M. de Kruif, M. Laan, C. Li, A. Lissovski, T. W. Morgan, P. Paris, K. Piip, M. J. van de Pol, R. Scannell, J. Scholten, P. H. M. Smeets, C. Spork, P. A. Z. van Emmichoven, R. Zoomers and G. De Temmerman, J. Instrum., 2013, 8, 16 Search PubMed.
- P. Paris, A. Hakola, K. Bystrov, G. De Temmerman, M. Aints, I. Jogi, M. Kiisk, J. Kozlova, M. Laan, J. Likonen and A. Lissovski, J. Nucl. Mater., 2013, 438, S754–S757 CrossRef CAS PubMed.
- X. Wang, V. Motto-Ros, G. Panczer, D. De Ligny, J. Yu, J. M. Benoit, J. L. Dussossoy and S. Peuget, Spectrochim. Acta, Part B, 2013, 87, 139–146 CrossRef CAS PubMed.
- C. Maury, J. B. Sirven, M. Tabarant, D. L'Hermite, J. L. Courouau, C. Gallou, N. Caron, G. Moutiers and V. Cabuil, Spectrochim. Acta, Part B, 2013, 82, 28–35 CrossRef CAS PubMed.
- J. E. Barefield, E. J. Judge, J. M. Berg, S. P. Willson, L. A. Le and L. N. Lopez, Appl. Spectrosc., 2013, 67(4), 433–440 CrossRef CAS PubMed.
- R. Jakopic, M. Sturm, M. Kraiem, S. Richter and Y. Aregbe, J. Environ. Radioact., 2013, 125, 17–22 CrossRef CAS PubMed.
- M. Kraiem, R. M. Essex, K. J. Mathew, G. J. Orlowicz and M. D. Soriano, Int. J. Mass Spectrom., 2013, 352, 37–43 CrossRef CAS PubMed.
- K. J. Mathew, G. L. Singleton, R. M. Essex, A. Hasozbek, G. Orlowicz and M. Soriano, J. Radioanal. Nucl. Chem., 2013, 296(1), 435–440 CrossRef CAS.
- K. J. Mathew, G. O'Connor, A. Hasozbek and M. Kraiem, J. Anal. At. Spectrom., 2013, 28(6), 866–876 RSC.
- F. Pointurier, A. Hubert and G. Roger, J. Radioanal. Nucl. Chem., 2013, 296(2), 593–598 CrossRef CAS PubMed.
- G. R. Eppich, R. W. Williams, A. M. Gaffney and K. C. Schorzman, J. Anal. At. Spectrom., 2013, 28(5), 666–674 RSC.
- L. A. Meyers, S. E. Glover, S. P. LaMont, A. M. Stalcup and H. B. Spitz, J. Radioanal. Nucl. Chem., 2014, 299(3), 1833–1837 CrossRef CAS.
- F. Esaka, M. Magara and T. Kimura, J. Anal. At. Spectrom., 2013, 28(5), 682–688 RSC.
- F. Esaka and M. Magara, Talanta, 2014, 120, 349–354 CrossRef CAS PubMed.
- Y. Miyamoto, F. Esaka, D. Suzuki and M. Magara, Radiochim. Acta, 2013, 101(11), 745–748 CrossRef CAS.
- F. Pointurier, A. Hubert and A. C. Pottin, J. Radioanal. Nucl. Chem., 2013, 296(2), 609–616 CrossRef CAS.
- A. L. Faure, C. Rodriguez, O. Marie, J. Aupiais and F. Pointurier, J. Anal. At. Spectrom., 2014, 29(1), 145–151 RSC.
- C. Degueldre, C. Borca and C. Cozzo, Talanta, 2013, 115, 986–991 CrossRef CAS PubMed.
- C. Degueldre, C. Cozzo, M. Martin, D. Grolimund and C. Mieszczynski, J. Solid State Chem., 2013, 202, 315–319 CrossRef CAS PubMed.
- M. Tanimizu, N. Sugiyama, E. Ponzevera and G. Bayon, J. Anal. At. Spectrom., 2013, 28(9), 1372–1376 RSC.
- A. Gourgiotis, H. Isnard, A. Nonell, M. Aubert, G. Stadelmann, E. Dupont, I. AlMahamid, G. Tiang, L. Rao, W. Lukens, P. Cassette, S. Panebianco, A. Letourneau and F. Chartier, Talanta, 2013, 106, 39–44 CrossRef CAS PubMed.
- S. H. Han, Z. Varga, J. Krajko, M. Wallenius, K. Song and K. Mayer, J. Anal. At. Spectrom., 2013, 28(12), 1919–1925 RSC.
- X. G. Wang, K. J. Dong, M. He, S. Y. Wu and S. Jiang, Nucl. Technol., 2013, 182(2), 235–241 CAS.
- M. Krachler, R. Alvarez-Sarandes, P. Carbol, R. Malmbeck and S. Van Winckel, Microchem. J., 2013, 110, 425–434 CrossRef CAS PubMed.
- Z. Wang, J. Y. Zhang, H. J. Zou, M. Dong, D. R. Qiu and P. Y. Yang, Talanta, 2013, 107, 338–343 CrossRef CAS PubMed.
- H. Zhou, Z. Wang, Y. Zhu, Q. Li, H. J. Zou, H. Y. Qu, Y. R. Chen and Y. P. Du, Spectrochim. Acta, Part B, 2013, 90, 55–60 CrossRef CAS PubMed.
- B. Hashimoto, H. Daidoji, H. Uchihara, K. Iwasaki, Y. Okamoto and T. Fujiwara, Anal. Lett., 2013, 46(8), 1299–1305 CrossRef CAS.
- M. Campos, J. A. Sicre-Artalejo, J. M. Torralba, H. Zbiral, H. Danninger and P. Pena, Ceram. Int., 2014, 40(2), 3063–3070 CrossRef CAS PubMed.
- R. Glaus, L. Dorta, Z. G. Zhang, Q. L. Ma, H. Berke and D. Gunther, J. Anal. At. Spectrom., 2013, 28(6), 801–809 RSC.
- A. Galli and L. Bonizzoni, X-Ray Spectrom., 2014, 43(1), 22–28 CrossRef CAS.
- R. J. H. Morris, M. G. Dowsett, R. Beanland, A. Dobbie, M. Myronov and D. R. Leadley, Surf. Interface Anal., 2013, 45(1), 348–351 CrossRef CAS.
- R. Pureti and W. Vandervorst, Surf. Interface Anal., 2013, 45(1), 402–405 CrossRef CAS.
- E. Demenev, D. Giubertoni, M. A. Reading, P. Bailey, T. C. Q. Noakes, M. Bersani and J. A. van den Berg, Surf. Interface Anal., 2013, 45(1), 413–416 CrossRef CAS.
- Y. Kudriavtsev and R. Asomoza, Surf. Interface Anal., 2013, 45(1), 506–509 CrossRef CAS.
- H. Takahara, Y. Mori, H. Shibata, A. Shimazaki, M. B. Shabani, M. Yamagami, N. Yabumoto, K. Nishihagi and Y. Gohshi, Spectrochim. Acta, Part B, 2013, 90, 72–82 CrossRef CAS PubMed.
- A. Kubala-Kukus, D. Banas, M. Pajek, J. Szlachetko, P. Jagodzinski, J. Susini and M. Salome, Radiat. Phys. Chem., 2013, 93, 117–122 CrossRef CAS PubMed.
- J. Zhang, X. S. Hu, J. H. Xi, Z. Kong and Z. G. Ji, J. Anal. At. Spectrom., 2013, 28(9), 1430–1435 RSC.
- S. P. Banerjee, Z. J. Chen, I. Utkin and R. Fedosejevs, Appl. Phys. A: Mater. Sci. Process., 2013, 111(3), 791–798 CrossRef CAS.
- B. Ber, P. Babor, P. N. Brunkov, P. Chapon, M. N. Drozdov, R. Duda, D. Kazantsev, V. N. Polkovnikov, P. Yunin and A. Tolstogouzov, Thin Solid Films, 2013, 540, 96–105 CrossRef CAS PubMed.
- A. Murase, T. Mitsuoka, M. Tomita, H. Takenaka and H. Morita, Surf. Interface Anal., 2013, 45(8), 1261–1265 CrossRef CAS.
- G. Prudon, C. Dubois, B. Gautier, J. C. Dupuy, J. P. Graf, Y. Le Gall and D. Muller, Surf. Interface Anal., 2013, 45(1), 376–380 CrossRef CAS.
- S. Leopold, L. Mueller, C. Kremin and M. Hoffmann, J. Micromech. Microeng., 2013, 23(7), 6 CrossRef.
- J. Rip, D. Cuypers, S. Arnauts, F. Holsteyns, D. H. van Dorp and S. De Gendt, ECS J. Solid State Sci. Technol., 2014, 3(1), N3064–N3068 CrossRef CAS PubMed.
- J. H. In, C. K. Kim, S. H. Lee, H. S. Shim and S. Jeong, J. Anal. At. Spectrom., 2013, 28(6), 890–900 RSC.
- C. K. Kim, J. H. In, S. H. Lee and S. Jeong, Spectrochim. Acta, Part B, 2013, 88, 20–25 CrossRef CAS PubMed.
- C. K. Kim, S. H. Lee, J. H. In, H. J. Lee and S. Jeong, Opt. Express, 2013, 21(22), A1018–A1027 CrossRef PubMed.
- C. K. Kim, J. H. In, S. H. Lee and S. Jeong, Opt. Lett., 2013, 38(16), 3032–3035 CrossRef CAS PubMed.
- J. H. In, C. K. Kim, S. H. Lee, H. J. Lee and S. Jeong, J. Anal. At. Spectrom., 2013, 28(8), 1327–1337 RSC.
- C. K. Kim, S. H. Lee, J. H. In, H. S. Shim, D. S. Kim and S. Jeong, Thin Solid Films, 2013, 546, 393–397 CrossRef CAS PubMed.
- D. Diego-Vallejo, D. Ashkenasi, A. Lemke and H. J. Eichler, Spectrochim. Acta, Part B, 2013, 87, 92–99 CrossRef CAS PubMed.
- C. Streeck, S. Brunken, M. Gerlach, C. Herzog, P. Honicke, C. A. Kaufmann, J. Lubeck, B. Pollakowski, R. Unterumsberger, A. Weber, B. Beckhoff, B. Kanngiesser, H. W. Schock and R. Mainz, Appl. Phys. Lett., 2013, 103(11), 5 CrossRef PubMed.
- M. P. Herrera-Gorocica, P. Bartolo-Perez, C. Calderon and J. L. Pena, Acta Microsc., 2012, 21(1), 15–23 CAS.
- K. Kaufmann, S. Wahl, S. Meyer and C. Hagendorf, Surf. Interface Anal., 2013, 45(1), 434–436 CrossRef CAS.
- A. Eicke, T. Ciba, D. Hariskos, R. Menner, C. Tschamber and W. Witte, Surf. Interface Anal., 2013, 45(13), 1811–1820 CrossRef CAS.
- C. Gonzalez-Gago, J. Pisonero, N. Bordel, A. Sanz-Medel, N. J. Tibbetts and V. S. Smentkowski, J. Vac. Sci. Technol., A, 2013, 31(6), 7 Search PubMed.
- G. Kartopu, A. Tempez, A. J. Clayton, V. Barrioz, S. J. C. Irvine, C. Olivero, P. Chapon, S. Legendre and J. Cooper, Mater. Res. Innovations, 2014, 18(2), 82–85 CrossRef CAS PubMed.
- M. A. Aguirre, M. Hidalgo, A. Canals, J. A. Nobrega and E. R. Pereira, Talanta, 2013, 117, 419–424 CrossRef CAS PubMed.
- V. Rackwitz, M. Ostermann, U. Panne and V. D. Hodoroaba, J. Anal. At. Spectrom., 2013, 28(9), 1466–1474 RSC.
- T. Roth, M. Wolf, M. Pohlein and R. van Eldik, Anal. Bioanal. Chem., 2013, 405(23), 7215–7229 CrossRef CAS PubMed.
- H. Takahara, M. Shikano and H. Kobayashi, J. Power Sources, 2013, 244, 252–258 CrossRef CAS PubMed.
- H. Takahara, A. Kojyo, K. Kodama, T. Nakamura, K. Shono, Y. Kobayashi, M. Shikano and H. Kobayashi, J. Anal. At. Spectrom., 2014, 29(1), 95–104 RSC.
- M. Menzel, A. Schlifke, M. Falk, J. Janek, M. Froba and U. E. A. Fittschen, Spectrochim. Acta, Part B, 2013, 85, 62–70 CrossRef CAS PubMed.
- M. Crobu, A. Rossi and N. D. Spencer, Surf. Interface Anal., 2013, 45(1), 579–582 CrossRef CAS.
- D. Kobayashi, Y. Yamamoto and T. Isemura, Surf. Interface Anal., 2013, 45(1), 113–116 CrossRef CAS.
- T. Trejos, R. Koons, P. Weis, S. Becker, T. Berman, C. Dalpe, M. Duecking, J. Buscaglia, T. Eckert-Lumsdon, T. Ernst, C. Hanlon, A. Heydon, K. Mooney, R. Nelson, K. Olsson, E. Schenk, C. Palenik, E. C. Pollock, D. Rudell, S. Ryland, A. Tarifa, M. Valadez, A. van Es, V. Zdanowicz and J. Almirall, J. Anal. At. Spectrom., 2013, 28(8), 1270–1282 RSC.
- T. Trejos, R. Koons, S. Becker, T. Berman, J. Buscaglia, M. Duecking, T. Eckert-Lumsdon, T. Ernst, C. Hanlon, A. Heydon, K. Mooney, R. Nelson, K. Olsson, C. Palenik, E. C. Pollock, D. Rudell, S. Ryland, A. Tarifa, M. Valadez, P. Weis and J. Almirall, Anal. Bioanal. Chem., 2013, 405(16), 5393–5409 CrossRef CAS PubMed.
- T. Ernst, T. Berman, J. Buscaglia, T. Eckert-Lumsdon, C. Hanlon, K. Olsson, C. Palenik, S. Ryland, T. Trejos, M. Valadez and J. R. Almirall, X-Ray Spectrom., 2014, 43(1), 13–21 CrossRef CAS.
- K. E. Sjastad, T. Andersen and S. L. Simonsen, Spectrochim. Acta, Part B, 2013, 89, 84–92 CrossRef PubMed.
- A. Martyna, K. E. Sjastad, G. Zadora and D. Ramos, Talanta, 2013, 105, 158–166 CrossRef CAS PubMed.
- P. K. Diwakar, J. J. Gonzalez, S. S. Harilal, R. E. Russo and A. Hassanein, J. Anal. At. Spectrom., 2014, 29(2), 339–346 RSC.
- K. Y. Chen, H. L. Yuan, Z. A. Bao, C. L. Zong and M. N. Dai, Geostand. Geoanal. Res., 38(1), 5–21 CAS.
- J. I. Kimura, Q. Chang and H. Kawabata, J. Anal. At. Spectrom., 2013, 28(9), 1522–1529 RSC.
- J. T. van Elteren, A. Izmer, M. Sala, E. F. Orsega, V. S. Selih, S. Panighello and F. Vanhaecke, J. Anal. At. Spectrom., 2013, 28(7), 994–1004 RSC.
- I. Choi, G. C. Y. Chan, X. L. Mao, D. L. Perry and R. E. Russo, Appl. Spectrosc., 2013, 67(11), 1275–1284 CrossRef CAS PubMed.
- T. Kratochvil, M. Pouzar, K. Novotny, V. Havranek, T. Cernohorsky and M. Zvolska, Spectrochim. Acta, Part B, 2013, 88, 26–31 CrossRef CAS PubMed.
- A. R. M. Bustos, J. R. Encinar and A. Sanz-Medel, Anal. Bioanal. Chem., 2013, 405(17), 5637–5643 CrossRef CAS PubMed.
- F. C. Adams and C. Barbante, Spectrochim. Acta, Part B, 2013, 86, 3–13 CrossRef CAS PubMed.
- C. Y. Chen, Y. F. Li, Y. Qu, Z. F. Chai and Y. L. Zhao, Chem. Soc. Rev., 2013, 42(21), 8266–8303 RSC.
- A. J. Bednar, A. R. Poda, D. M. Mitrano, A. J. Kennedy, E. P. Gray, J. F. Ranville, C. A. Hayes, F. H. Crocker and J. A. Steevens, Talanta, 2013, 104, 140–148 CrossRef CAS PubMed.
- O. Geiss, C. Cascio, D. Gilliland, F. Franchini and J. Barrero-Moreno, J. Chromatogr. A, 2013, 1321, 100–108 CrossRef CAS PubMed.
- B. Meermann, A. L. Fabricius, L. Duester, F. Vanhaecke and T. Ternes, J. Anal. At. Spectrom., 2014, 29(2), 287–296 RSC.
- E. Bolea, J. Jimenez-Lamana, F. Laborda, I. Abad-Alvaro, C. Blade, L. Arola and J. R. Castillo, Analyst, 2014, 139(5), 914–922 RSC.
- I. C. Regelink, L. Weng, G. F. Koopmans and W. H. Van Riemsdijk, Geoderma, 2013, 202, 134–141 CrossRef PubMed.
- F. Laborda, J. Jimenez-Lamana, E. Bolea and J. R. Castillo, J. Anal. At. Spectrom., 2013, 28(8), 1220–1232 RSC.
- G. Cornelis and M. Hassellov, J. Anal. At. Spectrom., 2014, 29(1), 134–144 RSC.
- K. S. Ho, K. O. Lui, K. H. Lee and W. T. Chan, Spectrochim. Acta, Part B, 2013, 89, 30–39 CrossRef CAS PubMed.
- A. P. Walczak, R. Fokkink, R. Peters, P. Tromp, Z. E. H. Rivera, I. Rietjens, P. J. M. Hendriksen and H. Bouwmeester, Nanotoxicology, 2013, 7(7), 1198–1210 CrossRef CAS PubMed.
- E. P. Gray, J. G. Coleman, A. J. Bednar, A. J. Kennedy, J. F. Ranville and C. P. Higgins, Environ. Sci. Technol., 2013, 47(24), 14315–14323 CrossRef CAS PubMed.
- D. Rakcheev, A. Philippe and G. E. Schaumann, Anal. Chem., 2013, 85(22), 10643–10647 CrossRef CAS PubMed.
- S. T. Kim, H. K. Kim, S. H. Han, E. C. Jung and S. Lee, Microchem. J., 2013, 110, 636–642 CrossRef CAS PubMed.
- J. G. Coleman, A. J. Kennedy, A. J. Bednar, J. F. Ranville, J. G. Laird, A. R. Harmon, C. A. Hayes, E. P. Gray, C. P. Higgins, G. Lotufo and J. A. Steevens, Environ. Toxicol. Chem., 2013, 32(9), 2069–2077 CrossRef CAS PubMed.
- K. Loeschner, J. Navratilova, C. Kobler, K. Molhave, S. Wagner, F. von der Kammer and E. H. Larsen, Anal. Bioanal. Chem., 2013, 405(25), 8185–8195 CrossRef CAS PubMed.
- V. Motto-Ros, L. Sancey, X. C. Wang, Q. L. Ma, F. Lux, X. S. Bai, G. Panczer, O. Tillement and J. Yu, Spectrochim. Acta, Part B, 2013, 87, 168–174 CrossRef CAS PubMed.
- J. N. Audinot, A. Georgantzopoulou, J. P. Piret, A. C. Gutleb, D. Dowsett, H. N. Migeon and L. Hoffmann, Surf. Interface Anal., 2013, 45(1), 230–233 CrossRef CAS.
- A. Gianoncelli, P. Marmorato, J. Ponti, L. Pascolo, B. Kaulich, C. Uboldi, F. Rossi, D. Makovec, M. Kiskinova and G. Ceccone, X-Ray Spectrom., 2013, 42(4), 316–320 CrossRef CAS.
- K. Ricketts, C. Guazzoni, A. Castoldi, A. P. Gibson and G. J. Royle, Phys. Med. Biol., 2013, 58(21), 7841–7855 CrossRef CAS PubMed.
- N. Manohar, F. J. Reynoso and S. H. Cho, Med. Phys., 2013, 40(8), 6 CrossRef PubMed.
- F. R. Khan, A. Laycock, A. Dybowska, F. Larner, B. D. Smith, P. S. Rainbow, S. N. Luoma, M. Rehkamper and E. Valsami-Jones, Environ. Sci. Technol., 2013, 47(15), 8532–8539 CAS.
- E. I. Maurer, M. Sharma, J. J. Schlager and S. M. Hussain, Nanotoxicology, 2014, 8(7), 718–727 CAS.
- S. K. Mwilu, E. Siska, R. B. N. Baig, R. S. Varma, E. Heithmar and K. R. Rogers, Sci. Total Environ., 2014, 472, 316–323 CrossRef CAS PubMed.
- A. L. Fabricius, L. Duester, B. Meermann and T. A. Ternes, Anal. Bioanal. Chem., 2014, 406(2), 467–479 CrossRef CAS PubMed.
- M. Hadioui, S. Leclerc and K. J. Wilkinson, Talanta, 2013, 105, 15–19 CrossRef CAS PubMed.
- S. Motellier, S. Derrough, D. Locatelli, M. Amdaoud and K. Lhaute, Spectrochim. Acta, Part B, 2013, 88, 1–9 CrossRef CAS PubMed.
- S. H. Nowak, F. Reinhardt, B. Beckhoff, J. C. Dousse and J. Szlachetko, J. Anal. At. Spectrom., 2013, 28(5), 689–696 RSC.
- M. Sovago, E. J. Buis and M. Sandtke, Spectrochim. Acta, Part B, 2013, 87, 182–187 CrossRef CAS PubMed.
- M. Resano, E. Bolea-Fernandez, E. Mozas, M. R. Florez, P. Grinberg and R. E. Sturgeon, J. Anal. At. Spectrom., 2013, 28(5), 657–665 RSC.
- S. Gschwind, H. Hagendorfer, D. A. Frick and D. Gunther, Anal. Chem., 2013, 85(12), 5875–5883 CrossRef CAS PubMed.
- Y. Yu, Z. Q. Hao, C. M. Li, L. B. Guo, K. H. Li, Q. D. Zeng, X. Y. Li, Z. Ren and X. Y. Zeng, Acta Phys. Sin., 2013, 62(21), 7 Search PubMed.
- V. K. Unnikrishnan, K. S. Choudhari, S. D. Kulkarni, R. Nayak, V. B. Kartha and C. Santhosh, RSC Adv., 2013, 3(48), 25872–25880 RSC.
- S. Barbier, S. Perrier, P. Freyermuth, D. Perrin, B. Gallard and N. r. Gilon, Spectrochim. Acta, Part B, 2013, 88, 167–173 CrossRef CAS PubMed.
- C. G. de Vega, B. Fernandez, N. Bordel, R. Pereiro and A. Sanz-Medel, J. Anal. At. Spectrom., 2013, 28(7), 1054–1060 RSC.
- M. Sanchez-Martinez, T. Perez-Corona, C. Camara and Y. Madrid, Food Chem., 2013, 141(2), 816–822 CrossRef CAS PubMed.
- M. Haldimann, A. Alt, A. Blanc, K. Brunner, F. Sager and V. Dudler, Food Addit. Contam., Part A, 2013, 30(3), 587–598 CrossRef CAS PubMed.
- P. H. M. Kiyataka, S. T. Dantas and J. A. L. Pallone, Food Addit. Contam., Part A, 2014, 31(1), 156–163 CrossRef CAS PubMed.
- M. Whitt, K. Vorst, W. Brown, S. Baker and L. Gorman, J. Plast. Film Sheeting, 2013, 29(2), 163–173 CrossRef PubMed.
- N. von Goetz, L. Fabricius, R. Glaus, V. Weitbrecht, D. Gunther and K. Hungerbuhler, Food Addit. Contam., Part A, 2013, 30(3), 612–620 CrossRef CAS PubMed.
- Y. Echegoyen and C. Nerin, Food Chem. Toxicol., 2013, 62, 16–22 CrossRef CAS PubMed.
- M. R. Florez and M. Resano, Spectrochim. Acta, Part B, 2013, 88, 32–39 CrossRef CAS PubMed.
- A. T. Duarte, M. B. Dessuy, M. G. R. Vale and B. Welz, Anal. Methods, 2013, 5(24), 6941–6946 RSC.
- L. F. Rodrigues, J. C. P. Mattos, R. C. Bolzan, E. M. M. Flores and F. A. Duarte, J. Anal. At. Spectrom., 2014, 29(2), 324–331 RSC.
- A. I. Mihaltan, T. Frentiu, M. Ponta, D. Petreus, M. Frentiu, E. Darvasi and C. Marutoiu, Talanta, 2013, 109, 84–90 CrossRef CAS PubMed.
- N. Mine and L. Houssiau, Surf. Interface Anal., 2013, 45(1), 61–64 CrossRef CAS.
- M. Bronzato, P. Calvini, C. Federici, S. Bogialli, G. Favaro, M. Meneghetti, M. Mba, M. Brustolon and A. Zoleo, Chem.–Eur. J., 2013, 19(29), 9569–9577 CrossRef CAS PubMed.
- P. Campos, E. A. M. Kajiya, M. A. Rizzutto, A. C. Neiva, H. P. F. Pinto and P. A. D. Almeida, Radiat. Phys. Chem., 2014, 95, 362–367 CrossRef CAS PubMed.
- A. M. Cardeira, S. Longelin, A. Le Gac, I. Nogueira, M. L. Carvalho and M. Manso, Appl. Spectrosc., 2013, 67(12), 1376–1381 CrossRef CAS PubMed.
- H. E. Ahmed and O. A. Nassef, Anal. Methods, 2013, 5(12), 3114–3121 RSC.
- S. Thangavel, K. Dash, S. M. Dhavile and A. C. Sahayam, Anal. Methods, 2013, 5(20), 5799–5803 RSC.
- G. D. Tarigh and F. Shemirani, Talanta, 2013, 115, 744–750 CrossRef PubMed.
- J. S. Barin, B. Tischer, R. S. Picoloto, F. G. Antes, F. E. B. da Silva, F. R. Paula and E. M. M. Flores, J. Anal. At. Spectrom., 2014, 29(2), 352–358 RSC.
- X. F. Wang, Y. Zhang, Y. Wu, J. Yu and M. X. Xie, Forensic Sci. Int., 2014, 236, 99–108 CrossRef CAS PubMed.
- F. Alamilla, M. Calcerrada, C. Garcia-Ruiz and M. Torre, Forensic Sci. Int., 2013, 228(1–3), 1–7 CrossRef CAS PubMed.
- M. A. Gondal, Y. W. Maganda, M. A. Dastageer, F. F. Al Adel, A. A. Naqvi and T. F. Qahtan, Appl. Opt., 2014, 53(8), 1636–1643 CrossRef CAS PubMed.
- M. I. Szynkowska, K. Osinglowska, A. Pawlaczyk, K. Palinska, M. Marcinek, J. Rogowski, A. Czubak and A. Parczewski, Przem. Chem., 2013, 92(6), 1125–1133 CAS.
- C. Kurta, L. Dorta, F. Mittermayr, K. Prattes, B. Hattendorf, D. Gunther and W. Goessler, J. Anal. At. Spectrom., 2014, 29(1), 185–192 RSC.
- D. Plausinaitis, E. Naujalis, A. Prokopchik and A. Budreika, Curr. Anal. Chem., 2014, 10(1), 140–148 CrossRef CAS.
- K. Joe, S. H. Han, B. C. Song, C. H. Lee, Y. K. Ha and K. Song, Nucl. Eng. Technol., 2013, 45(3), 415–420 CrossRef CAS.
- H. Hernandez-Mendoza and A. Yllera, J. Radioanal. Nucl. Chem., 2013, 298(2), 1417–1420 CrossRef CAS PubMed.
- Y. S. Jeon, Y. S. Park, J. S. Kim, S. H. Han and Y. J. Park, Asian J. Chem., 2013, 25(12), 7044–7046 CAS.
- L. S. Chen, T. H. Wang, Y. K. Hsieh, L. W. Jian, W. H. Chen, T. L. Tsai and C. F. Wang, J. Radioanal. Nucl. Chem., 2014, 299(3), 1883–1889 CrossRef CAS.
- A. Saha, S. B. Deb, B. K. Nagar and M. K. Saxena, At. Spectrosc., 2013, 34(4), 125–132 CAS.
- C. Wallace, J. J. Bellucci, A. Simonetti, T. Hainley, E. C. Koeman and P. C. Burns, J. Radioanal. Nucl. Chem., 2013, 298(2), 993–1003 CrossRef CAS PubMed.
- S. Dhara, N. L. Misra, S. K. Aggarwal, D. Ingerle, P. Wobrauschek and C. Streli, X-Ray Spectrom., 2014, 43(2), 108–111 CrossRef CAS.
- V. Renson, A. Jacobs, J. Coenaerts, N. Mattielli, K. Nys and P. Claeys, Geoarchaeology, 2013, 28(6), 517–530 Search PubMed.
- M. Ozcatal, M. Yaygingol, A. Issi, A. Kara, S. Turan, F. Okyar, S. P. Tas, I. Nastova, O. Grupce and B. Minceva-Sukarova, Ceram. Int., 2014, 40(1), 2153–2160 CrossRef CAS PubMed.
- B. Ma, L. Liu, S. L. Feng, Q. Xu and X. Q. Feng, Nucl. Instrum. Methods Phys. Res., Sect. B, 2014, 319, 95–99 CrossRef CAS PubMed.
- G. Barone, P. Mazzoleni, A. Aquilia and G. Barbera, Archaeometry, 2014, 56(1), 70–87 CrossRef CAS PubMed.
- A. J. Sakalis, N. A. Kazakis, N. Merousis and N. C. Tsirliganis, J. Cult. Herit., 2013, 14(6), 485–498 CrossRef PubMed.
- G. Padeletti and P. Fermo, Appl. Phys. A: Mater. Sci. Process., 2013, 113(4), 825–833 CrossRef CAS.
- P. Holakooei, F. Tisato, C. Vaccaro and F. C. Petrucci, J. Archaeol. Sci., 2014, 41, 447–460 CrossRef CAS PubMed.
- R. Ravisankar, G. R. Annamalai, A. Naseerutheen, A. Chandrasekaran, M. V. R. Prasad, K. K. Satpathy and C. Maheswaran, Spectrochim. Acta, Part A, 2013, 115, 845–853 CrossRef CAS PubMed.
- L. Bonizzoni, A. Galli, M. Gondola and M. Martini, X-Ray Spectrom., 2013, 42(4), 262–267 CrossRef CAS.
- D. Brunelli, S. T. Levi, P. Fragnoli, A. Renzulli, P. Santi, E. Paganelli and M. C. Martinelli, Appl. Phys. A: Mater. Sci. Process., 2013, 113(4), 855–863 CrossRef CAS.
- E. M. Gascon and J. B. I. Garrigos, Appl. Clay Sci., 2013, 82, 79–85 CrossRef PubMed.
- E. Gliozzo, M. Turchiano, M. Lombardi, I. T. Memmi, G. Volpe and M. J. Baxter, Archaeometry, 2013, 55, 423–448 CrossRef CAS PubMed.
- H. Sadek, A. Khedr, M. Simileanu and R. Radvan, Dig. J. Nanomater. Biostruct., 2013, 8(4), 1357–1363 Search PubMed.
- R. Bendaoud, A. Guilherme, A. Zegzouti, M. Elaatmani, J. Coroado, M. L. Carvalho and I. Queralt, Appl. Radiat. Isot., 2013, 82, 60–66 CrossRef CAS PubMed.
- M. L. Coutinho, V. S. F. Muralha, J. Mirao and J. P. Veiga, Appl. Phys. A: Mater. Sci. Process., 2014, 114(3), 695–703 CrossRef CAS.
- R. Ravisankar, A. Naseerutheen, G. R. Annamalai, A. Chandrasekaran, A. Rajalakshmi, K. V. Kanagasabapathy, M. V. R. Prasad and K. K. Satpathy, Spectrochim. Acta, Part A, 2014, 121, 457–463 CrossRef CAS PubMed.
- R. Scarpelli, R. J. H. Clark and A. M. De Francesco, Spectrochim. Acta, Part A, 2014, 120, 60–66 CrossRef CAS PubMed.
- A. G. Attaelmanan and M. Mouton, J. Archaeol. Sci., 2014, 42, 519–524 CrossRef CAS PubMed.
- J. Van Pevenage, D. Lauwers, D. Herremans, E. Verhaeven, B. Vekemans, W. De Clercq, L. Vincze, L. Moens and P. Vandenabeele, Anal. Methods, 2014, 6(2), 387–394 RSC.
- A. Khedr and M. A. Harith, Appl. Phys. A: Mater. Sci. Process., 2013, 113(4), 835–842 CrossRef CAS.
- F. Meirer, Y. J. Liu, E. Pouyet, B. Fayard, M. Cotte, C. Sanchez, J. C. Andrews, A. Mehta and P. Sciau, J. Anal. At. Spectrom., 2013, 28(12), 1870–1883 RSC.
- S. Orecchio, Microchem. J., 2013, 108, 137–150 CrossRef CAS PubMed.
- W. T. Hao, T. X. Zheng, Y. D. Li, J. M. Zheng, J. Zhu, M. D. Glascock and C. S. Wang, Ceram. Int., 2013, 39(6), 6325–6332 CrossRef CAS PubMed.
- L. C. Niziolek, J. Archaeol. Sci., 2013, 40(6), 2824–2839 CrossRef CAS PubMed.
- N. J. Wallis and G. D. Kamenov, Archaeometry, 2013, 55(5), 893–909 CrossRef CAS PubMed.
- S. Kumar, D. Singh and R. Thangaraj, Appl. Surf. Sci., 2013, 273, 437–443 CrossRef CAS PubMed.
- T. Conard, A. Franquet, D. Tsvetanova, T. Mouhib and W. Vandervorst, Surf. Interface Anal., 2013, 45(1), 406–408 CrossRef CAS.
- R. Tiwari, S. Chandra and B. R. Chakraborty, Mater. Sci. Semicond. Process., 2013, 16(6), 2013–2020 CrossRef CAS PubMed.
- G. Deokar, M. D'Angelo, E. Briand and C. D. Cavellin, Nucl. Instrum. Methods Phys. Res., Sect. B, 2013, 304(1), 67–71 CrossRef CAS PubMed.
- I. Krylov, A. Gavrilov, M. Eizenberg and D. Ritter, Appl. Phys. Lett., 2013, 103(5), 3 CrossRef PubMed.
- D. Aureau, R. Chaghi, I. Gerard, H. Sik, J. Fleury and A. Etcheberry, Appl. Surf. Sci., 2013, 276, 182–189 CrossRef CAS PubMed.
- K. J. Dudeck, E. Huante-Ceron, A. P. Knights, R. M. Gwilliam and G. A. Botton, Semicond. Sci. Technol., 2013, 28(12), 12 CrossRef.
- U. Bauer, A. M. Welsch, H. Behrens, J. Rahn, H. Schmidt and I. Horn, J. Phys. Chem. B, 2013, 117(48), 15184–15195 CAS.
- Y. Kobayashi, T. Kobayashi, K. Shono, Y. Ohno, Y. Mita and H. Miyashiro, J. Electrochem. Soc., 2013, 160(8), A1181–A1186 CrossRef CAS PubMed.
- T. Yonemura, J. Iihara, Y. Saito and M. Ueno, Jpn. J. Appl. Phys., 2013, 52(12), 4 Search PubMed.
- J. Hampel, P. Ehrenreich, N. Wiehl, J. V. Kratz and S. Reber, Phys. Status Solidi A, 2013, 210(4), 767–770 CrossRef CAS.
- L. Terborg, S. Weber, F. Blaske, S. Passerini, M. Winter, U. Karst and S. Nowak, J. Power Sources, 2013, 242, 832–837 CrossRef CAS PubMed.
- N. Karar, R. Opila, T. Beebe, O. Toader and F. Naab, ECS J. Solid State Sci. Technol., 2012, 1(4), P164–P168 CrossRef CAS PubMed.
- M. L. Polignano, D. Codegoni, G. Delcastello, A. Del Vitto, S. Grasso and R. Piagge, ECS J. Solid State Sci. Technol., 2013, 2(1), N28–N34 CrossRef CAS PubMed.
- R. Kudela, J. Soltys, A. Vincze and J. Novak, Phys. Status Solidi RRL, 2013, 7(6), 443–446 CrossRef CAS.
- A. M. Duffin, G. L. Hart, R. C. Hanlen and G. C. Eiden, J. Radioanal. Nucl. Chem., 2013, 296(2), 1031–1036 CrossRef CAS PubMed.
- K. Shcherbachev, V. Privezentsev, V. Kulikauskas, V. Zatekin and V. Saraykin, J. Appl. Crystallogr., 2013, 46, 882–886 CrossRef CAS PubMed.
- N. Civici and E. Vataj, Rom. Rep. Phys., 2013, 65(4), 1265–1274 CAS.
- P. O. Iniaghe, G. U. Adie and O. Osibanjo, Toxicol. Environ. Chem., 2013, 95(7), 1108–1115 CrossRef CAS.
- E. J. dos Santos, A. B. Herrmann, S. K. Prado, E. B. Fantin, V. W. dos Santos, A. V. M. de Oliveira and A. J. Curtius, Microchemical Journal, 2013, 108, 233–238 CrossRef CAS PubMed.
- N. K. Sandhu, L. Axe, P. K. Ndiba and K. Jahan, Environ. Eng. Sci., 2013, 30(7), 387–392 CrossRef CAS.
- M. Kolencik, M. Urik, M. Bujdos, K. Gardosova, P. Littera, L. Puskelova, M. Gregor and P. Matus, Chem. Listy, 2013, 107(2), 182–185 CAS.
- Y. Hirokawa, Y. Shibata, T. Konya, Y. Koike and T. Nakamura, X-Ray Spectrom., 2013, 42(3), 134–140 CrossRef CAS.
- F. A. Stevie, P. Maheshwari, J. M. Pierce, B. T. Adekore and D. P. Griffis, Surf. Interface Anal., 2013, 45(1), 352–355 CrossRef CAS.
- M. E. Bowden, K. J. Alvine, J. L. Fulton, J. R. Lemmon, X. Lu, B. J. Webb-Robertson, S. M. Heald, M. Balasubramanian, D. R. Mortensen, G. T. Seidler and N. J. Hess, J. Power Sources, 2014, 247, 517–526 CrossRef CAS PubMed.
- T. Nakazawa and K. Tsuji, X-Ray Spectrom., 2013, 42(3), 123–127 CrossRef CAS.
- K. Doyle, C. H. Swartz, J. H. Dinan, T. H. Myers, G. Brill, Y. P. Chen, B. L. VanMil and P. Wijewarnasuriya, J. Vac. Sci. Technol., B: Nanotechnol. Microelectron.: Mater., Process., Meas., Phenom., 2013, 31(3), 5 Search PubMed.
- G. A. Bordovskii, A. V. Marchenko, M. Y. Kozhokar, F. S. Nasredinov and P. P. Seregin, Glass Phys. Chem., 2013, 39(4), 377–381 CrossRef CAS.
- A. V. Shaverina, A. R. Tsygankova, I. R. Shelpakova and A. I. Saprykin, Inorg. Mater., 2013, 49(14), 1283–1287 CrossRef CAS.
- M. Balski, H. Kipphardt, A. Berger, S. Meyer and U. Panne, Anal. Methods, 2014, 6(1), 77–85 RSC.
- M. Khalifa, M. Hajji and H. Ezzaouia, Bull. Mater. Sci., 2013, 36(6), 1097–1101 CrossRef CAS.
- C. Modanese, L. Arnberg and M. Di Sabatino, Mater. Sci. Eng., B, 2014, 180, 27–32 CrossRef CAS PubMed.
| This journal is © The Royal Society of Chemistry 2014 |