Advances in atomic spectrometry and related techniques
E. Hywel
Evans
*a,
Jason A.
Day
b,
Christopher D.
Palmer
c and
Clare M. M.
Smith
d
aSchool of Geography, Earth and Environmental Sciences, University of Plymouth, Drake Circus, Plymouth, UK PL4 8AA
bDepartment of Earth Sciences, University of Cambridge, Cambridge, UK CB2 3EQ
cWadsworth Center, New York State Department of Health, P.O. Box 509, Empire State Plaza, Albany, NY 12201-0509, USA
dSt. Ambrose High School, Blair Road, Coatbridge, Lanarkshire, UK ML5 2EW
First published on 9th May 2011
Abstract
This is the third iteration of this review covering developments in ‘ Atomic Spectrometry ’. It covers atomic emission, absorption, fluorescence and mass spectrometry , but excludes material on speciation and coupled techniques which is included in a separate review. 1 It should be read in conjunction with the other related reviews in the series.2–5 A critical approach to the selection of material has been adopted, with only novel developments in instrumentation, techniques and methodology being included. There have been few novel advances during the review period with the notable exception of the development of UV photochemical and electrochemical vapour generation methods; and miniaturisation of LIBS instrumentation for use in space exploration.
1. Sample introduction
1.1 Liquid
Although not an on-line sample pre-treatment step itself, ultrasound-assisted extraction continues to be used with on-line methods, three noteworthy publications describing ultrasound extraction should be mentioned. Lavilla et al.8 discussed an ultrasound-assisted emulsification of cosmetic samples prior to ET-AAS, ICP-OES, FAAS, and CV-AAS analysis, Shah et al.9 optimised an ultrasonic-assisted acid extraction of Hg in muscle tissues of fish using a multivariate strategy, and Lopez et al.10 discussed a rapid extraction and speciation of Hg using a microtip ultrasonic probe followed by LC-ICP-MS.
1.1.1.1 Solid phase extraction . The following section will discuss recent developments concerning solid phase extraction procedures. To aid the reader, this section is organised in the alphabetical order of the chemical symbol of the target analyte element. Procedures involving the determination of more than one analyte will be grouped at the end of the section.
Ben-Issa et al.11 separated inorganic arsenic species from drinking water on both a strong base anion exchange (SBAE) resin and a hybrid (HY) resin. At pH 7.50, the SBAE resin bound more than 370 μg g−1 of AsV while the HY resin bound more than 4150 μg g−1 of AsIII, and more than 3500 μg g−1 of AsV. SBAE was used to selectively preconcentrate AsV, while the HY resin was used to preconcentrate total As. Zheng and Hu12 used a dual column capillary microextraction (CME) system consisting of N-(2-aminoethyl)-3-aminopropyltrimethoxysilane (AAPTS)-silica coated capillary (C1) and 3-mercaptopropyl trimethoxysilane (MPTS)-silica coated capillary (C2) for the sequential separation/preconcentration of AsIII, AsV, MMA, and DMA in the extracts of hair. It was found that at pH 9, AsV and MMA could be retained by C1, and only AsIII could be retained by C2. Mirsha and Ramaprabhu13 developed a magnetite decorated multiwalled carbon nanotube based supercapacitor for As removal and desalination of seawater. Performance of the filter, made up of nanocomposite-based electrodes was examined by ICP-OES. Chandrasekaran et al.14 used a homemade PTFE micro-column loaded with 50 mg of polyaniline, for the on-line separation of AsIII and AsV, by FI-HG-ICP-MS. Uluozlu et al.15 speciated AsIII and AsV in water and food samples by solid-phase extraction on Streptococcus pyogenes immobilised on Sepabeads SP 70. The capacity of biosorbent for AsIII was 7.3 mg g−1, with a preconcentration factor of 36 obtained. Zhang et al.16 also used a ‘biosorbent’ for AsV retection; eggshell membrane (ESM), which contains several surface functional groups such as amines, amides and carboxylic groups. Under the optimal conditions AsV could be easily extracted by an ESM packed cartridge, and the breakthrough adsorption capacity was found to be 3.9 μg g−1.
Afzali et al.17 used modified multi-walled carbon nanotubes to preconcentrate AuIII ions. The nanotubes were oxidised with concentrated HNO3, and then modified with 5-(4′-dimethylamino-benzyliden)-rhodanine, the sorption of AuIII ions was quantitative in the pH range 2.0–5.0. The sorbent capacity of the solid phase for AuIII was 7.3 mg g−1 sorbent.
Sahan et al.18 described an online procedure for the preconcentration of Bi, prior to FAAS detection. Lewatit TP-207 chelating resin, including an immodiacetate group, was packed into a minicolumn. The method was applied to the determination of Bi in pharmaceutical creams, SRM's and various natural water samples. Wu et al.19 determined Bi by FI-HG-AFS following online sorption of Bi on a multi-walled carbon nanotube-packed microcolumn. With a 120 s sorption time, the HG-AFS detection limit for Bi was 0.8 ng L−1.
Pourreza and Ghanemi20 retained CdII ions on a column packed with sulphur powder modified with 2-mercaptobenzothiazole (2-MBT) in 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim]+PF6−). The retained ions were eluted with HCl, and measured by HG-AAS. The procedure was validated against NRCC DORM-3, dogfish muscle. Zhao et al.21 retained CdII on a microcolumn packed with HCl-treated bamboo charcoal. With a preconcentation time of 80 s, an enhancement factor of 63 was obtained compared to conventional FAAS. Alam et al.22 synthesised a polymer supported organic-inorganic composite and strongly acidic cation-exchanger polyaniline CeIVmolybdate, and found it to be highly selective for CdII. The selectivity of the material varied depending upon its composition and the composition of the eluting solvent. Its selectivity was examined, and some important binary separations such as CdII–PbII, CdII–HgII, CdII–ZnII and CdII–NiII were also achieved.
Chen et al.23 reported a new protocol for directly pre-concentrating Hg using AG 1 x 4 ion-exchange resin, which allows the measurement of Hg isotope composition in freshwater samples. The measurement mass bias was corrected using modified empirical external normalisation (MEEN) with Tl as internal dopant. Bai and Fan24 extracted methylmercury, phenylmercury and HgII from biological samples using a 3-mercaptopropyltrimethoxysilane coated capillary. Meanwhile, Krishna et al.25 preconcentrated HgII and methylmercury in fish tissues using a microcolumn filled with polyaniline (PANI) coupled to FI-CV-ICP-MS. At a pH < 3, i-Hg could be selectively sorbed onto the column, whereas at pH 7, both i-Hg and MeHg could be retained on the column.
Faraji et al.26 preconcentrated HgII based on the adsorption of the analytes, as mercury-Michler's thioketone [Hg-2(TMK)4]2+ complex on the negatively charged surface of sodium dodecyl sulphate-coated magnetite nanoparticles (SDS-coasted Fe3O4 NPs). Measurement was made by FI-ICP-OES. Using a sample volume of 1000 mL, an enrichment factor of 1230 was obtained. Zhai et al.27 used 1,5-diphenylcarbazide doped magnetic Fe3O4 nanoparticles as extractant. These Hg loaded nanoparticles could be separated from aqueous solution by applying an external magnetic field. The HgII ions could be eluted from the composite magnetic particles using 0.5 M HNO3.
Zierhut et al.28 described a reagent-free, fully automated FI-AFS system for the determination of Hg in waters following preconcentration on activated gold. The authors investigated the limitations of the system arising with matrix constituents, such as dissolved organic carbon (DOC). A broad variety of water matrices (seawater, river water, moorland water, effluent from a wastewater treatment plant) were investigated in order to check the feasibility of the method.
Anthemidis et al.29 packed poly(etheretherketone) (PEEK) into an on-line column in the form of turnings, for trace Pb preconcentration from environmental samples. The sample and ammonium diethyl-dithiophosphate (DDPA) reagent were mixed online, and the PbII-DDPA complex was retained on the PEEK. Isobutyl methyl ketone (IBMK) was adopted for efficient analyte complex elution. Zhao and Chinese co-workers30 used PAN-doped SiO2 packing material for the online preconcentration of PbII in biological and environmental samples prior to FAAS determination. Under the optimal conditions, an enhancement factor of 101 was achieved, the sample throughput was 45 h−1. Baysal et al.31 preconcentrated Pb on nano-silver coated silica gel impregnated with ammonium pyrrolidine-dithiocarbamate (APDC). PbII was retained quantitatively at pH ≥ 7 and eluted with 3.0 M of HNO3.
Sabermahani and Taher32 preconcentrated Pd on a polyethyleneimine (PEI) water-soluble polymer coated onto alumina. Thiourea and HCl solution could efficiently elute adsorbed PdII. The method was applied to the determination of Pd in an alloy standard and anodic slime.
Ghaseminezhad et al.33 preconcentrated Rh ions on 1-(2-pyridylazo)-2-naphthol (PAN) in the pH range 3.2–4.7, then the Rh-PAN formed was absorbed onto oxidised modified multiwalled carbon nanotubes. The complex was eluted with N,N-dimethylformamide (DMF), prior to FAAS determination. The sorption capacity of the oxidised MWCNTs for RhIII was 6.6 mg g−1. The same solid phase, PAN-modified SiO2 was used by Kaur and Gupta34 to preconcentrate SbIII from water samples. The absorption equilibrium of SbIII was achieved in 10 min. SbIII was easily eluted with 4 mL 2 M HCl.
Lukaszczyk and Zyrnicki35 developed a method for the preconcentration and speciation of SbIII and SbV in meglumine antimontate, the first choice drug for leishmaniasis treatment. Dowex I x 4 resin was used as the solid phase, ICP-OES was used for the determination of Sb. The interfering effects of As, Bi, Cd, Cu, Mn, Pb and Zn were examined, and only Bi was found to be a significant interferent.
Silva and Brazilian co-workers36 selectively determined tributyltin in the presence of SnIV in environmental samples using HG-ICP-OES and saccharomyces cerevisiae (Baker's yeast) as sorbing material. The procedure was based on the retention of TBT by the yeast at pH 6. A detection limit of 1.9 μg L−1 was obtained.
Mukhtar and Limbeck37 used a FI-FAAS procedure for the online determination of water-soluble Zn in airborne particulate matter. The method was based on a preliminary extraction of samples with water under dynamic conditions, and the subsequent on-line FAAS measurement of the dissolved fraction of Zn. With the use of two 9 mm filter punches for analysis, an IDL of 2 ng Zn was obtained, which translated to an MDL of approximately 0.4 ng m−3 when considering the volumes of air collected per investigated aerosol sample. Escudero et al.38 precipitated Zn, and retained it on a minicolumn filled with ethyl vinyl acetate (EVA) at pH 9.0, without using a complexing agent. Zn was eluted with 10% (v/v) HCl. The ICP-OES based method was validated against a certified VKI reference material, QC Metal LL1 DHI (Water and Environment) Denmark.
There were several reports of researchers preconcentrating 2 target analytes on solid phase materials. Cheng et al.39 preconcentrated Au and Pd from geological and water samples using single-walled carbon nanotubes (SWNTs) as a SPE adsorbent. Meanwhile, Rozmaric et al.40 isolated U and Th from natural samples by UTEVA and TRU resins and anion exchanger Amberlite CG-400. Due to the difference in binding strength in HCl and HNO3 respectively, U and Th can be easily separated from each other on columns filled with TRU resin. Furthermore, Th binds to anion exchanger in nitrate form from alcohol solutions of HNO3 solution, whereas U does not. Anthemidis et al.41 preconcentrated Ni and Zn on a low-cost microcolumn packed with polytetrafluoroethylene-turnings. The metals formed on-line complexes with ammonium pyrrolidine dithiocarbamate from acidified solutions (pH 2.0) in the FI-FAAS manifold, and were retained in the column. The preconcentrated analytes were eluted quantitatively with isobutylmethylketone, and injected directly into the nebuliser for atomisation and measurement.
Gao et al.42 prepared a new sorbent 1-acylthiosemicarbazide-modified activated carbon (AC-ATSC) for removing 3 analytes, CuII, HgII, and PbII from water samples, prior to ICP-OES. The metals were eluted by 3.0 mL of 2% CS(NH2)2 and 2.0 M HCl solution. Common existing ions did not interfere with the separation. Mohammadi et al.43 investigated the potential of modified multiwalled carbon nanotubes for the preconcentration of PbII, CdII, and NiII from biological and water samples. Liu and Wang44 used a microcolumn packed with immobilised 1-phenyl-3-methyl-4-bonzoil-5-pyrazone (PMBP) on nanometer Al2O3 powder, for preconcentrating the rare earth elements ScIII, YIII, and LaIII prior to ICP-AES. The analytes could be retained on the column at pH 4.5, and eluted with 0.5 M HCl. The method was applied to the determination of trace Sc, Y, and La in Tricholma giganteum with satisfactory results.
Hassanien45 modified silica glass with flavonoid derivatives for the preconcentration of 4 elements, AsV, CdII, HgII, and PbII in water samples, prior to determination by ICP-MS. The Quercetin (3,3′,4′,5,7-pentahydroxyflavone) was chemically bonded through the pyran rearrangement on modified controlled pore silica glass with a capacity of 0.213 mmol g−1. The sorption capacity of the solid phase was 0.42, 0.46, 0.53, and 0.49 mmol g−1 for AsV, CdII, HgII, and PbII respectively, whereas the preconcentration factor was 200. Chen et al.46 incorporated the solid phase, thiacalix[4]arene tetracarboxylate derivative modified mesoporous TiO2 coupled to ICP-OES for the preconcentration of V, Cu, Pb, and Cr. The ICP-OES detection limits were 0.09, 0.23, 0.50, and 0.15 μg L−1 for V, Cu, Pb, and Cr, respectively with a preconcentration factor of 20.
Peng et al.48 synthesised three novel solid phase extraction agents by functionalising sub-micron sized silica gel with organic functional moieties possessing {SN}-ligating atoms. Their capability of absorbing the ions FeIII, CuII, ZnII, CdII, CrVI, HgII, PbII, CoII, NiII, and AgI was described. The extractors demonstrated pH-tunable selectivity for AgI and PbII, with little or no interference by the other metal ions. At pH values <2, the solid phases became highly selective for AgI, with an adsorption capacity of 35 mg g.
1.1.1.2 Liquid–liquid extraction. There were several review articles discussing the merits of online liquid–liquid extraction techniques. Pena-Pereira, Lavilla and Bendicho49 critically reviewed liquid-phase microextraction (LPME) approaches combined with atomic spectrometric detection. They noted that LPME displays unique characteristics such as excellent preconcentration capability, simplicity, low cost sample clean-up and integration of steps. Theoretical features, possible strategies for these combinations, as well as the effect of key experimental parameters influencing method development were addressed. Finally, a comparison of the different LPME approaches in terms of enrichment factors achieved, extraction efficiency, precision, selectivity and simplicity of operation was provided.
In their review, Dadfarnia and Shabani50 discussed the historical development of miniaturised liquid-phase extraction methodologies, namely single drop microextraction (SDME), dispersive liquid–liquid microextraction (DLLME) and solidified floating organic drop microextraction (SFODME). The authors summarised some of the application of these methods in combination with various analytical techniques.
Anthemidis and Ioannou51 reviewed recent developments in homogenous liquid–liquid extraction (HLLE) and dispersive liquid–liquid microextraction (DLLME), and their potential use in inorganic analysis. Relevant applications to the determination of metal ions, metalloids and organometals were included. The authors discussed new trends in the fields of miniaturisation and automation, while proposing future trends and potential new areas for their application.
Lopez-lopez et al.52 presented an overview of recent developments in liquid-membranes for trace-metal speciation and determination in natural waters. Unpublished results from the author's own research illustrated new capabilities and applications.
Yamini et al.53 discussed a dispersive liquid–liquid microextraction technique based on the solidification of a floating organic drop (DLLME-SFO) and ICP-OES detection. Under optimal conditions, i.e., 140 μL of 1-undecanol extraction solvent, 2.0 mL of acetone disperser solvent, a ligand to mole ratio of 20, and pH of 6, the enhancement factor ranged from 57 to 96. The method was applied to the extraction of Co, Cr, Cu, and Mn ions in tap, seawater, and mineral water samples. The same group, with Rezaee as primary author,54 used the system for the preconcentration and determination of Al in waters, and with Ghambarian as primary author55 preconcentrated and speciated As in waters.
The following section will discuss liquid–liquid extraction applications, and to the aid the reader, techniques will be organised in the alphabetical order of the chemical symbol of the target analyte element.
Monasterio and Wuilloud56 described a highly efficient microextraction method for the determination of AsV, AsIII, and organic arsenic (DMA and MMA) preconcentration, and determination based on the novel use of tetradecyl (trihexyl) phosphonium chloride ionic liquid (CYPHOS®IL 101) as an ion-pairing reagent. AsV species was selectively separated by forming AsV-molybdate heteropoly acid [AsV-MHPA] complex with molybdenum, followed by ion-pairing reaction with CYPHOS®IL 101 and microextraction in chloroform. Under optimum conditions, the analyte extraction efficiency was 99% and yielded a preconcentration factor of 125 with only 5.00 mL of sample.
Jia et al.57 combined DLLME with FI-ICP-MS for the simultaneous determination of Cd, Pb, and Bi in water samples. The metals were complexed with sodium diethyldithiocarbamate, and the complexes were extracted into carbon tetrachloride by DLLME. The enrichment factors for Cd, Pb, and Bi were 460, 900, and 645 in 5 mL of a spiked water sample, respectively. Liet al.58 synthesised a novel hydrophobic task specific ionic liquid (TSIL) functionalised 2-mercaptobenzothiazole (MBT) for the selective separation and preconcentration of CdII. The TSIL-MBT was highly selective for CdII, and found to be more efficient in extracted Cd than the traditional extractants ammonium pyrrolidine dithiocarbamate (APDC) and diethyldithiocarbamate (DDTC).
Abdolmohammad-Zadeh and Ebrahimzadeh59 developed a method for Co preconcentration based on the application of 1-hexylpyridinium hexafluorophosphate [C6py][PF6] ionic liquid as an extractant solvent. 1-Phenyl-3-methyl-4-benzoyl-5-pyrazole (PMBP) was employed as a chelator forming a Co-PMBP complex to extract Co ions from aqueous solution into the fine droplets of [C6py][PF6]. With an enrichment factor of 60, the detection limit for Co was 0.70 μg L−1 by FAAS.
Sahin and Tokgoz60 used solidified floating organic microextraction (SFODME) and FI-FAAS to preconcentrate Cu ions. A free microdrop of 1-undecanol containing 1,5-diphenyl carbazide (DPC) as the complexing agent, was transferred to the surface of an aqueous sample containing the CuII ions. After complete extraction, the microdrop solidified on cooling. After warming at room temperature, the microdrop melted, and was diluted with ethanol. Under optimised conditions for 100 mL water, the preconcentration factor for Cu was 333. Mohammadi et al.61 proposed a ligandless(LL)-DLLME preconcentration method for Cu using 1,2-dichlorobenzene and ethanol as the extraction and dispersive solvents, respectively.
Bai et al.62 proposed the use of temperature-controlled ionic liquid-phase microextraction for the preconcentration of Pb from environmental samples prior to FAAS. Hydrophobic ionic liquid could be dispersed into infinite droplets at high temperature, and then could aggregate as big droplets at low temperature. Based on this phenomenon a new liquid-phase microextraction preconcentration of Pb was developed.
Najifi et al.63 employed dispersive liquid–liquid microextraction for the selective determination of TeIV and TeVI. Under acidic conditions, pH 1, only TeIV can form a complex with ammonium pyrrolidine dithiocarbamate (APDC) and therefore can be extracted into fine droplets of carbon tetrachloride, which are dispersed with ethanol into an aqueous solution. Under optimal conditions, the enrichment factor was 125.
1.1.1.3 Cloud-point extraction . Meeravali and Jiang64 presented a cloud-point extraction (CPE) approach using the cationic surfactant, Aliquat-336, for the separation and pre-concentration of chromium species in waters by ICP-DRC-MS. The non-ionic surfactant, Triton X-114 was found to induce the cloud point phase separation of Aliquat-336. The separation of anionic CrVI was enabled by the formation of ion associate with quaternary ammonium head group of Aliquat-336 at pH 2.
Chen et al.65 determined HgII and methylmercury by HPLC-ICP-MS after cloud-point extraction. The analytes were complexed with sodium diethyldithiocarbamate (DDTC) and pre-concentrated by a Triton X-114. The enhancement factors for 25 mL sample solution were 42 and 21, and the limits of detection were 4 and 10 ng L−1 for HgII and MeHg+, respectively. Depoi et al.66 preconcentrated Hg in honey using CPE with CV-ICP-OES. The enrichment factor for Hg was 13, with a limit of detection of 2.2 ng g−1Hg. Shah et al.67 detected Hg in the tissues of broiler chicken by using CPE and CV-AAS. Their CPE technique used ammonium o,o-diethyldithiophosphate (DDTP) as the complexing agent, and produced a detection limit of 0.117 μg kg−1Hg in tissue.
Gil et al.68 developed a method for the method for the determination of Pb by CPE coupled to USN-ICP-OES. The cloud point system was formed in the presence of non-ionic micelles of polyethyleneglycolmono-p-nonylphenyether (PONPE 7 5) and was retained in a minicolumn of PTFE. The use of CPE and ultrasonic nebulisation gave an enrichment factor of 150 with respect to the determination of Pb by conventional ICP-OES.
Garcia et al.70 characterised particles made by desolvation of monodisperse microdroplets of analyte solutions and particle suspensions for nanoparticle calibration in ICP-MS. The authors found that at desolvation temperatures of 150 °C, the particles from standard solutions are most often spherical and solid. They also found that drying diluted suspension of 250 nm Au at 200 °C produced stable concave balloons approximately 3 μm in diameter. The same group demonstrated the calibration of element line intensities in ICP-OES by introducing monodisperse droplets of diluted Au and SiO2 particle suspensions.71
Matusiewicz and Slachcinski evaluated a commercial ultrasonic nebuliser, the NOVA-DUO (ultrasonic nebuliser dual capillary system USN/DCS) for the simultaneous determination of transition (Au, Ag, Cd, Cu, Mn, Ni, Pb, Zn) and noble (Pd, Pt, Rh) volatile metals species by microwave induced-OES (MIP-OES).72 Simultaneous mixing and nebulization of the acidified sample and reductant solutions on the piezoelectric transducer, with the possibility of flow rate adjustment, permitted a wide variation of sensitivity. The authors employed a univariate approach and simplex optimisation procedure to achieve optimisation conditions and to derive analytical figures of merit. The accuracy of the method was verified by use of digested SRMs and CRMs (NRCC TORT-1, NIES CRM-13, NIST SRM 2710, and INCT SBF-4). The authors went on to evaluate the system for the classical hydride forming elements (As, Bi, Ge, Sb, Se, and Sn) and the conventional non-hydride forming elements (Ba, Ca, Fe, Li, Mg, and Sr),73 the volatile species Au, Ag, Pd, Pt, and Rh,74 and the hydride elements As, Bi, Ge, Sb, Se, and Sn along with vapour forming Hg.75
Asfaw and Beauchemin76 discussed the effect of replacing the desolvation system (heater/condenser and membrane desolvator) of an ultrasonic nebuliser with a pre-evaporation tube (PET) that is heated to 400 °C. Under optimal conditions the analytical performance of ICP-OES measurement was significantly improved (better sensitivity, detection limit and plasma robustness) with the USN-PET compared to that achieved with the un-modified USN system. The USN-PET approach also allows the determination of Hg, which appears to be otherwise lost in the heater/condenser component of commercially available USNs.
Grindlay et al.77 described a new fully microwave-assisted liquid sample introduction system (MASIS). The device employs a single TM010 microwave cavity for the simultaneous aerosol generation and desolvation. They found that the behaviour of the MASIS depends on the microwave power, the nebuliser nozzle inner diameter, the sample uptake rate, and the nature of the sample matrix. MASIS provided limits of detection up to 50 times lower than those obtained with a cyclonic spray-chamber and up to 8 times lower than those obtained from a microwave thermal nebuliser and microwave desolvation system.
Schroder and Zhang78 evaluated the use of the commercially available Multimode Sample Introduction System (MSIS) for the low level analysis of As and Se in waters. They lowered the quantification limits by approximately 100-fold for As and by 20-fold for Se compared with conventional nebulisation. Benzo et al.79 studied the operating characteristics of a number of ‘locally constructed’ dual sample introduction designs. Four cyclonic spray chamber arrangements with entrance slit angles of 0, 45, 90, and 180 degrees were tested. They found that the system with the 45° angled design gave the best analytical performance
Caumette et al.80 found the principle reason for signal suppression during the analysis of light petroleum matrices by ICP-MS was a decrease in the ionisation efficiency of the plasma. Consequently, they developed an interface based on a total consumption nebuliser and a heated spray chamber to alleviate the problem. A method based on flow-injection ICP-MS using this interface was developed for the direct multielement analysis of undiluted fuels (gasoline and kerosene).
Matusiewicz et al.81 described the efficient atomisation principle of Flow Burring nebulisation with MIP-OES as the detector. The authors found that the flow burring nebuliser (FBN) used in the study, along with a D-DIHEN, gave rise to higher emission signals (Ba, Ca, Cd, Cu, Fe, Mg, Mn, Pb, and Sr) and slightly lower LODs than other nebulisers tested.
Kruger et al.82 employed a commercially available membrane desolvation system to study the lanthanide distribution in human placental tissue by ICP-MS. The desolvation increased the sensitivity of the target analytes, as well as decreasing oxide formation. The system was found to be robust for routine day-to-day analysis of digested tissue samples.
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000 ng ml−1. The RSD from ten replicate measurements of 10000 ng ml−1 for Cd was 0.85%. The method was successfully applied to the determination of Cd in Zn-based materials.
1.2. Chemical vapour generation
D'Ulivo85 attempted to clarify some of the most controversial aspects of the mechanism of volatile species generation from aqueous boranes. The review took into consideration the evidence, and literature data published in the last fifty years. The author proposed a “clarification of several controversial aspects and the ruling out of wrong concepts, among them the “nascent” hydrogen theory”.Kumar and Riyazuddin86 presented an overview of chemical interferences observed in the determination of As, Sb, Bi, Ge, Se, Te, and Sn by HG. The authors theorised on the mechanisms of liquid-phase and gas-phase interferences in light of recent studies reporting on the HG mechanism.
Wu et al.87 published a review discussing the applications of chemical vapour generation in non-tetrahydroborate media. The article discussed photochemical vapour generation (photo-CVG), borane complexes CVG, alkylation based on Grignard reactions and derivatisation with NaBEt4, cold vapour with SnCl2, halide generation, electrochemical hydride generation, oxide generation, and generation of volatile chelates. Special attention was given to two newly developed CVG approaches: photo-CVG and reduction in the presence of cyanoborohydrides.
Bendicho et al.88 discussed photochemistry-based sample treatments as greener approaches for trace-element analysis and speciation. The authors overviewed new interfaces for coupling chromatographic techniques with atomic and mass detectors based on photochemical VG, provided insight into new developments, and surveyed the main applications.
Sanchez-Rodas et al.89 presented atomic fluorescence spectrometry (AFS) as an ideal detection technique for speciation studies concerning hydride forming elements (mainly As, Se, and Sb) and Hg. The review commented on the instrumental couplings of chromatographic (HPLC and GC) and non-chromatographic (CE) with AFS. Other optional intermediate steps, i.e., online photo-oxidation, pyrolysis or microwave assisted direction for non-directly reducible compounds were discussed. Chen and Belzile90 focussed on the coupling of HPLC to AFS in their critical review. The review discussed the limitations of the technique; the necessity of post-column treatments, including the oxidation of organo-element compounds, and the pre-reduction to a suitable valence. Halko et al.91 also discussed the combination of LC with atomic spectrometry detection. The review discussed the various types of interface (hydride generators and nebulisers), potential utilisation, and their advantages and drawbacks.
Ferreira et al.92 critically overviewed the state-of-the-art of slurry sampling as an approach for the minimisation of sample preparation prior to the determination of metals and metalloids in complex matrices. Analytical applications of slurry sampling reported in the literature between 2004 and 2009 were comprehensively compiled. Relevant topics include CV-AAS, HG-AAS, and HG-AFS.
Sardans, Montes, and Penuelas93 presented an overview of recent advances and applications of ET-AAS for the determination of As, Cd, Cu, Hg, and Pb in biological samples drawn from studies over the last decade. The review includes a section discussing the incorporation of flow-injection analysis, and chemical vapour generation, specifically for the detection of As and Hg in environmental and food matrices.
Xiong and Hu99 described a new method by combining headspace PdII-coated graphite bar microextraction (GBME) with ETV-ICP-MS for the determination of trace Se, Te, and Bi (as hydrides) in seawater and human hair. Winkel et al.100 described a chemotrapping method with HNO3 for volatile Se species trapping. The recovery and speciation of dimethylselenide dimethyldiselenide entrained through both conc. HNO3 and H2O2 were compared by HPLC-ICP-MS and HPLC-HG-AFS.
Pohl and Broekaert101 studied the spectroscopic and analytical characteristics of an ICP combined with HG with or without simultaneous introduction of sample aerosol for OES. The effects of forward power, the presence of reducing agents [(NH2)2SC, KI, KBr and hot HCl], the occurrence of easily ionised elements (Ca, K, Mg, and Na) in the analyte solutions on the excitation temperature (as measured via Ar atomic lines) and the electron number density were investigated for both sample introduction modes.
Zhang et al.102 determined As, Bi, Ge, Sb, and Se by AFS following their electrochemical hydride generation. The effects of cathode material, shape and area of material, catholyte, sample flow rate, applied current, catholyte solution concentration and interference of transition metals on signal intensity were studied. Five kinds of materials including lead, graphite, copper, tungsten and platinum with different shapes were tested as cathode materials.
1.2.2.1 Silver . Musil et al.103 generated volatile Ag species in a FIA manifold from a nitric acid matrix in the presence of surfactants (Triton X-100 and Antifoam B) and permanent Pd deposits at the reaction modifiers. AAS with a multiple microflame quartz tube heated to 900 °C was used for atomisation. The study followed the hypothesis that the “volatile” Ag species were actually metallic nanoparticles formed upon reduction in the liquid phase and then released with good efficiency to the gaseous phase. Number/charge size distributions of dry aerosol were determined by Scanning Mobility Particle Sizer. Ag was detected in 40–45 nm particles holding 10 times more charge compared to Boltzman equilibrium. In a separate publication, the same group also studied the transport processes of Ag vapour generation, along with interferences.104Transport efficiency was studied by means of a 111Ag radioactive indicator. The interfering effect of hydride forming elements (As, Se) and transition metals (Cu, Co, Ni, Au) was examined.
1.2.2.2 Arsenic . Zhang et al.105 presented a method for the detection of As (and Sb) using electrochemical hydride generation under alkaline conditions. Compared to the traditional acid mode, the authors found the alkaline mode had better tolerance to interferences. The same group, with Yang as the primary author,106 evaluated the system for electrochemical hydride generation in the speciation of inorganic arsenic in salts and organic acid medium. An AF spectrometer was used to study the effects of a cathodic electrolyte in the performance of hydride generation with a Zn and Pb cathode. The results indicated that the presence of ZnII in the K2SO4 cathodic electrolyte could markedly increase the fluorescence intensity of AsIII, and reduce the impact of cathode erosion on the stability of the signal intensity.
Several papers have discussed hydride generation of various arsenic species post-column in HPLC systems. It should be noted that arsenic speciation is discussed in greater depth in the Elemental Speciation issues of the Atomic Spectrometry Updates.1 Chen et al.107 used HG to differentiate AsB from hydride forming species of As in urine. The paper emphasised the usefulness of complementary chromatographic separations (ion pairing, cation exchange, and anion exchange) in combination with HG-ICP-MS to quantitatively determine AsIII, DMA, MMA AsV and As in the sub μg L−1 range in human urine. Chung et al.108 employed HPLC-HG-AAS to study polymorphisms in As metabolism related genes. The biomonitoring project included the analysis of urine from 208 subjects collected from an arseniasis hyperdemic area in Taiwan. Jiang et al.109 studied the stoichiometry and affinity of arsenicals bound to human serum albumin (HSA) by using online microdialysis coupled to LC-HG-AFS. The results showed that AsIII reacted with HSA more readily than AsV, which provides a chemical basis for As toxicity. Choi and Korean co-workers110 studied the effects of repeated seafood consumption on urinary excretion of As species from Korean volunteers. The daily mean intake of total As in the Korean study group was 6.98 mg, comprising of 4.71 mg of seaweed (67%), 1.74 mg of flat fish (25%), and 0.53 mg conch (8%). Inorganic As, MMA and DMA in the urine were determined by HPLC-HG-ICP-MS. The increase in total urinary As metabolites was attributed to the increase in DMA, which is the more harmful metabolite of the arsenicals. Arbab-Zavar et al.111 developed a simple method for the fractionation of AsIII and AsV using an electrochemical HG technique. A graphite rod was used as a cathode to reduce AsIII to AsH3, the rod was replaced with a tin-lead wire for reducing AsV to AsH3. Macedo et al.112 applied a multivariate optimisation based on a Box-Behnken design to optimise a HG-AAS system for the determination of total As and AsIII in phosphate fertilisers and phosphate rocks. Slurry preparation with hydrochloric in an ultrasonic bath produced a method detection limit of 0.1 μg L−1 for AsIII.
Ito et al.113 evaluated three on-line oxidation methods for the determination of total As in urine by HG-AFS. Because the HG reaction is dependent on the species, AsIII, AsV, MMA, DMA, TMAO, and AsB were all ‘normalised’ to AsV prior to AFS detection. Three online oxidation systems were designed to convert the As in each species to AsV: (1) microwave-assisted heating (MW); (2) UV-photooxidation (UV-1); and (3) UV-photooxidation with post-reaction heating (UV-2). Each system used K2S2O8/NaOH as the oxidant, and was coupled to a commercial HG-AFS instrument. The authors found that matrix matching was required for the MW system, whereas aqueous calibrations could be used for the two UV systems, making the former less suitable for routine analyses. The UV-2 arrangement had some advantages with respect to a lower detection limit and shorter analysis times.
Sigrist et al.114 evaluated the influence of arsenical livestock drinking waters on total As levels in cow's raw milk from Argentinian dairy farms. A dry ashing procedure was used for the mineralization of the milk samples. The total As concentrations were determined by FI-HG-AAS. The mineralised milk samples and well water samples were pre-reduced with concentrated HCl and KI-C6H8O6 solutions.
Yuksel et al.115 collected hair samples from 94 Turkish volunteers ranging in age from 18 to 74 years. The samples underwent microwave-assisted acid digestion, and As was determined by electrothermal HG-AAS. The method showed linearity in the range 1–20 μg L−1, with a detection limit of 0.1 μg L−1. The assessed hair-As levels in the volunteers ranged from 21 to 367 μg kg−1, with an average value of 115 ± 6.12 μg kg−1.
Savio et al.116 optimised methods to assess levels of As, along with Bi, Sb, and Se in airborne particulate matter from urban and industrial areas of Argentina, by FI-HG-ICP-OES. The particulate matter was collected on ash-free glass-fibre filters, which were digested with HCl + HF. A pre-reduction with KI, and H3BO3 was necessary to avoid the interference of F− ions that would cause losses via volatile AsF3. Accuracy was assessed against NIST 1648 Urban Particulate Matter.
1.2.2.3 Bismuth . Xing et al.117 developed an atmospheric pressure dielectric barrier discharge (DBD) atomiser for Bi determination by HG-AFS. The characteristics of the atomiser, including observation height, discharge power, and flow rate of discharge gas were optimised. The method was applied to the determination of Bi in ore, soil and ash samples. Kula and Turkish co-workers118 studied the interferences on Bi when using a W-coil for on-line trapping of volatile Bi species using HG-AAS. Bi was trapped on the W-coil at 289 °C and released at 1348 °C. Interferences from Fe, Mn, Zn, Ni, Cu, As, Se, Cd, Pb, Au, Na, Mg, Ca, chloride, sulphate, and phosphate were examined. The Bi signal was enhanced 21 times compared to when using the system without the W-coil trap.
1.2.2.4 Cadmium . Feng and Liu119 utilised a new solid sampling device for the determination of trace Cd in food samples by AFS, which made use of a graphite fibre felt (GFF) as the vaporiser, and a tungsten-coil as the Cd trap. Cd was vaporised with the solid food matrix by GFF at about 1600 °C, then separated from the matrix by trapping on the W-coil at room temperature; finally Cd was released from the W-coil at 2000 °C and directly determined by a non-dispersive AFS. The detection limit of the procedure was 30 ng L−1. Lai et al.120 showed that appropriate amounts of ascorbic and sulphanilamide added simultaneously could improve the vapour generation efficiency of Cd. Meanwhile, Chen et al.121 used HG-AFS to determine Cd following preconcentrating as cadmium-dithizone complex extracted using a two-phase system formed by ionic liquid 1-isopentyl-3-methylimidazolium bromide and K2HPO4.
1.2.2.5 Iodine . Zhu et al.122 described a novel vapour generation technique for iodide and iodate determination. The iodide and iodate are converted to volatile iodine vapour through solution cathode glow discharge induced advanced redox processes. It is achieved by in situ produced highly reactive chemical species in the discharge, thereby eliminating the need for externally supplied sources of any redox reagents. Iodine vapour is readily generated from a background electrolyte containing 0.01 M HNO3.
1.2.2.6 Mercury . Leopold et al.123 reviewed the current knowledge on Hg species and their distribution in natural waters. The review divided pre-concentration and separation techniques for Hg speciation into chromatographic and non-chromatographic methods. Derivatisation methods and the coupling of pre-concentration and/or separation methods to suitable detection techniques were also discussed. Dumarey et al.124 described the origin of the Dumarey equation and the validation of its accuracy. The authors described why the Dumarey equation remains superior to the use of the Hg vapour pressure in combination with the ideal gas law, for the purposes of calibrating instruments used to detect Hg vapour. Brown et al.125 presented a novel automatic method for in situ measurements of Hg vapour in ambient air using AFS, where calibration, sampling and analysis, are all performed fully automatically without manual intervention. Meanwhile, Thiebaud et al.126 reported their development of an in situ continuous emission monitor (CEM) for measuring Hg0 in the exhaust stream of coal-fired power plants. The instrument was based on atomic absorption of Hg vapour, and a light emitting diode (LED) background correction system.
Zhu et al.127 described a simple non-chromatographic approach for the determination of total and inorganic-Hg based on a dielectric barrier discharge (DBD) atomiser. In the absence of the DBD, only i-Hg was detected. Cai and Li128 claimed to increase the sensitivity of on-line Hg vapour AAS, by coating the inner wall of a T-shaped quartz tube with nanometer SiO2. This increased the residence time of the analyte atoms in the light path. Ramezani et al.129 tested the reliability of replacing quartz windows with a low density polyethylene (LDPE) windows with 65 nm thickness attached to the both ends of a glass cell for Hg determination by CV-AAS.
Jiang et al.130 described an electrochemical cold vapour system with polyaniline modified graphite electrode as the cathode material coupled with AFS. The system with the polyaniline/graphite electrode exhibited higher sensitivity, stability, and a lower Hg memory effect compared with a graphite electrode electrochemical system. Zhang et al.131 used a Pt/Ti cathode in the presence of formic acid catholyte. The authors reported that the introduction location for the carrier gas is probably the most important factor that influences the signal intensity of Hg from electrolytic vapour generation.
Cizdziel et al.132 coupled a commercially available Direct Mercury Analyzer (DMA) using a CV-AAS measurement with a Hg-specific CV-AFS instrument. The purpose was to evaluate combustion-AFS, a technique which is not commercially available. The two methods produced similar results for samples of hair, finger nails, coal, soil, leaves and food stuffs. However, for samples with Hg near the AAS detection limit (e.g. filter paper spotted with whole blood and segments of tree rings) the signal was still quantifiable with greater sensitivity of AFS.
Yin et al.133 accomplished Hg speciation by using a simple post HPLC column CV interface and AFS detection. Acetic acid and 2-mercaptoethanol in the mobile phase were used as a photochemical reagent. Optimised limits of detection were 0.53, 0.22, 0.18, and 0.25 μg L−1 for i-Hg, methyl-Hg, ethyl-Hg, and Phenyl-Hg, respectively. Chen et al.134 achieved a separation of HgII and MeHg+ on a ‘short-column’, a cation-exchange guard column, using a glutathione (GSH) containing eluent. Hg vapour was generated using an on-line photocatalyst-assisted technique, and the detection was made by ICP-MS. Wang and co-workers135 used L-cysteine-induced degradation of organic mercury as a novel interface in an HPLC-CV-AFS Hg speciation system. By adding L-cysteine to the mobile phase, the proposed system negated the use of a strong oxidant, UV or microwave interface, or organic solvent. Liu136 coupled Hg-cysteine ion chromatography to AFS, in this case the mobile phase contained 3% acetonitrile, 1% w/w L-cysteine, 20 nM pyridine, and 160 mM formic acid, at pH 7.
Among the environmental applications published for HG vapour analyses, Tseng et al.137 developed an online gaseous elemental mercury analyser (GEMA) for real time monitoring of gaseous elemental Hg over the northern South China Sea. The flow-injection based system incorporated Au amalgamation/preconcentration. The limit of detection was 0.1 ng Hg m−3 of air. Mousavi et al.138 incorporated a silver wool solid sorbent trap in their system used in the determination of Hg in water samples. Flores et al.139 used an anion exchange column to separate out organic and inorganic Hg species from urban landfill leachate, followed by preconcentration of the volatile organic species on an amalgam trap. Chen and Jiang140 used an ID-ICP-MS method for the determination of Hg and Pb in fuels. An emulsion of 10% v/v fuel, 2% m/v Triton X-100, and 1.0% m/v tartaric acid were injected into a nebuliser/vapour generation front-end.
Matusiewicz and Stanisz141 evaluated various sample pre-treatment methods for total and inorganic mercury determination in biological certified reference materials by CV-AAS. Microwave-assisted decomposition, and three ultrasonic extraction procedures based on acid leaching with HCl and HCOOH and solubilisation with TMAH were employed.
There were numerous publications reporting the determination of total Hg or mercury species in fish and marine mammals. Voegborlo and Adimado142 examined four classical wet digestion procedures for the determination of total Hg in fish tissue with CV-AAS detection. The effect of temperature and time on the digestion efficiency of the mixture of HCl, HNO3, HClO4, and H2SO4 were investigated to obtain optimum conditions. Pompte-Gotal et al.143 studied Hg (CV-AAS) concentrations in the tissues of bottlenose dolphins (Tursipos truncatus) and striped dolphins (Stenella coeruloalba) stranded on the Croatian Adriatic coast. Total Hg levels ranged from 1.51 mg kg−1 in muscle, from 2.04 to 143.1 in kidney, and from 10.35 to 1,833 mg kg−1 in liver tissues (expressed as wet weight). King and co-workers144 employed a commercially available Hg analyzer to determine total Hg in samples of fish and lobster obtained from various stores and markets in New York State. Of the total 177 samples analysed, 22 had Hg levels greater than the 1,000 ng g−1 limit set by the European Commission. De Carvalho et al.145 developed a method for determination of Hg species in fish tissues. Samples were first lyophilised and then extracted into a 25% (w/v) TMAH solution, extracts were analysed by FI-CV-AFS. Both inorganic and organic components were reduced with SnCl2 reductant, the organic component required pre-treatment with KMnO4. Saei-Dehkordi et al.146 studied the influence of season and habitat on the Hg concentration in commercially valuable fish species from the Persian Gulf. CV-AAS was employed after wet-ashing digestion.
Among the publications for which Hg was determined in a food matrix (other than fish), Liu147 proposed the use of photochemical vapour generation with acetic acid for the direct determination of ultra-trace Hg in white vinegars by AFS. Da Silva et al.148 developed a CV-AAS method for the determination of Hg in rice samples at the low ng g−1 concentration level. Samples were digested with HNO3 and H2O2, diluted with a KBr/KBrO3 and hydroxylamine solution, and reduced with SnCl2 in HCl.
Dos Santos et al.149 developed a method for the determination of Hg, present as thimerosal, in vaccines by photochemical vapour generation coupled to axial view ICP-OES. No sample treatment was necessary other than simple dilution and addition of 10% v/v formic acid. The detection limit (3 s, n = 10) was 0.3 μg L−1 of Hg or 0.6 μg L−1 of thimerosal in solution, or 0.03 μg of thimerosal per dose. Liu et al.150 described a method for the determination of Hg in Chinese herbs using CV-AFS, and a commercially available direct mercury analyzer (DMA) was employed by Jayawardene et al.151 to determine Hg and to study its bioaccessibility in selected traditional Indian medicines.
1.2.2.7 Lead . Ezer152 coupled continuous-flow hydride generation with laser induced fluorescence spectrometry (HG-LIF) for the determination of Pb in aqueous samples. Lead hydride was generated in K3Fe(CN)6–HCl medium using NaBH4 as the reducing agent. Parameters such as acid concentration, and concentrations of oxidising and reducing agents were studied in order to obtain the highest sensitivity. Popko et al.153 also used ferricyanide chemistry to determine Pb in dolomite samples. Afonso et al.154 studied the performance of K3Fe(CN)6 for the simultaneous generation of Pb, Bi, and Sn hydrides for determination by ICP-AES. Unlike BiH3 and SnH4, lead hydride (PBH4) generation, was not influenced from on-line or off-line addition of K3Fe(CN)6, nor did it show instability within 24 h. The method was applied to the analysis of calcium-rich biominerals, fish otoliths and NIST bone ash SRM 1400.
1.2.2.8 Rhodium . Duan155 used HG-ICP-AES for the determination of Rh in waste catalyst. Using sodium borohydride as reductant, and a nitric acid carrier stream, the study showed a two-fold increase in the efficiency of Rh compared to conventional nebulisation.
1.2.2.9 Antimony . Miravet et al.156 reviewed the development of coupling techniques used in the speciation of Sb in environmental matrices. They described current trends in Sb speciation, focusing mainly on methods because on HPLC and GC with AAS, AS, and ICP-MS detection. Yu and Zhang157 developed a method for the determination of water-soluble SbIII and SbV in soil by HG-AFS. The method was based on the different chemical reaction efficiency between SbIII and SbV with KBH4 in HCl-media.
1.2.2.10 Selenium . Liu158 used an on-line nano-TiO2 controlled volatilisation system for inorganic Se speciation based on irradiation of thiourea with UV light. Detection of was made by AFS. Zhao et al.159 developed a low volume microwave digestion (LVMWD) procedure to decompose all forms of selenium in biological samples to SeIV prior to HG-AFS determination. Between 0.3 and 0.4 mL of mixed digestion reagents consisting of concentrated 15.4 M HNO3, 18.5 M H2SO4 (v
:v = 10:1) and >5 to <40 mg sample, were found ideal systems with the optimised MW digestion program. Cuderman and Stibilj160 analysed antioxidant food supplements (coenzyme Q10, selenium as medical yeast, vitamin C and vitamin E) for Se and its species by HG-AFS. Martinez-Peinado et al.161 measured serum Se levels in patients suffering from cirrhosis, an oxidative stress-related disease. Blood samples from 30 healthy controls and 93 cirrhotic patients were analysed for total Se by HG-AAS. Significantly decreased serum Se levels in patients indicated that the Se component of the antioxidant system is severely impaired in cirrhosis.
1.2.2.11 Tin . Alp and Ertas162 developed a method for the in situ trapping of stannane on an iridium-coated tungsten coil. The coil could be used an on-line atomiser, or as a trapping surface. The interference effect of hydride forming elements, AsIII, SeIV, TeIV, and SbIII was investigated. The accuracy of the method was validated against fortified water TMDA 61 (NWRI) and Dogfish Liver DOLT-3 (NRCC) CRMs. Silva et al.36 employed HG-ICP-OES and SPE (with a baker's yeast solid phase) for the selective determination of tributyltin in the presence of SnIV in river water, seawater, and biological abstracts. Unal and Yalcin163 developed a continuous-flow HG laser-induced breakdown spectroscopy system for the determination of Sn in aqueous samples. The emission intensity from the neutral SnI line at 284 nm was measured at atmospheric pressure. The HG efficiency of the system was optimised using HG-ICP-MS.
1.2.2.12 Tellurium . Xi et al.164 described a method for the determination of trace tellurium after hydride trapping on a platinum-coated tungsten coil, and atomisation by electrically heated quartz tube. Tellurium hydride was transported to the tungsten coil in a mixture of Ar and H2, it was trapped at a temperature of 390 °C, and released at 1200 °C. A limit of detection of 0.08 ng mL−1Te was obtained with 1 min of trapping, and an enhancement factor of 28 compared to conventional HG-AAS. The Pt coating was stable for 300 firings without sensitivity loss.
1.3 Solids
Within a review of the potential of inorganic MS for characterisation at the nanoscale, Fernandez et al.167 consider techniques that allow direct solid analysis with spatial resolution capabilities. In this context, the present capabilities of widespread elemental MS techniques such as LA-ICP-MS, GD-MS and secondary ion/neutral MS are described and compared using selected examples. The evolution of high-irradiance laser ionization TOF-MS has progressed in recent years following significant improvements in the laser source, the TOF mass analyzer and in instrument construction geometries. Yu et al.168 review the main developments in the technique for direct elemental analysis including instrumentation and applications. The same authors169 have also described the successful determination of a number of analytes in several solid samples using this technique.
Feng and Liu119 describe a new solid sampling device and procedure for determination of trace Cd in food samples by AFS. The system incorporates a graphite fibre felt as the vaporizer and a tungsten-coil. The procedure was optimized by changing temperature and gas atmosphere at vaporizing, trapping and releasing steps, respectively. Under optimized conditions, Cd was vaporized with the matrix at 1600 °C, separated from the matrix by trapping at room temperature, released from the tungsten coil at 2000 °C and directly determined by non-dispersive AFS without an additional atomization step. The LOD was determined to be 0.3 pg with an RSD of less than 5% at 100 pg and no significant interference was found within a 10% error range. Some discussion of the mechanism was also provided.
Analysis using LA is often restricted to relatively small samples owing to the dimensions of conventional ablation cells. Carugati et al.172 used a comparatively large, rectangular, commercially-available sample cell to enable analysis over a 10.2 × 5.2 cm2 area. Comparison with conventional cells shows a small to moderate performance decrease for the large cell resulting from the dilution of ablated particles in a larger volume with a 4–31% lower signal output and longer signal tailings. The performance of the larger cell, however, was found to be sufficient for the determination of both major and trace elements in a number of samples. The applicability of the large cell LA-ICP-MS setup was demonstrated by the determination of several elements in sediment core sections at a resolution of 0.6 mm. LOD for sediment analysis were found to be 7, 68, 0.5, 20, 0.2, 0.3, 0.08 and 0.003 μg g−1 for Al, Si, Mn, Fe, Cu, Zn, Pb, and U, respectively. Element distribution patterns, which would have been overlooked in conventional analysis at cm resolution, were observed in analysed sediments. This study demonstrates the potential of the large sample cell setup for the analysis of a range of samples without sectioning.
2 Instrumentation and fundamentals
2.1 Instrumentation
Mao et al.173 have reviewed the potential for liquid electrode discharge atomic emission as an analytical tool, proposing that LODs for Cu, Hg, Ag, Na, K, and Mg of the order of μg L−1 were possible.Several workers describe detectors with the aim of coupling with chromatography for speciation studies. Quarles and Marcus174 have reported results of the development of a particle beam/hollow cathode AES device with a polychromator, to allow simultaneous multielement analysis. LODs for Pb, Ni, and Ag were 2.2, 0.17 and 0.19 ng respectively. Rogers et al.175,176 have published two reports on the development of an ESI/ICP-TOF-MS system. In the first, they detail results obtained with the ESI source, and in the second the simultaneous operation of both ESI and ICP sources for detection of molecular and atomic fragment ions of cyanocobalamin, myoglobin and superoxide dismutase. The same Hieftje group have also reported results of their third generation, Faraday-strip array detector for use with a Mattauch-Herzog geometry MS. This latest version has superior resolving power, lower LODs, IR precision of 0.07% and LDR of 5 orders of magnitude.
Some of the problems inherent in AMS have been addressed: Suter et al.177 have developed an ion optics program which includes small angle scattering and energy distributions caused by straggling in foils or stripper gas in transmission calculations. An example for 10Be measurements is discussed. Likewise, Eliades et al.178 have incorporated an rf quadrupole reaction cell, and evaluated it for the suppression of 36S interference on 36Cl.
2.2 Fundamentals
Ivokovic et al.179 have proposed a method for the determination of ne from line shapes of the He(I) 447.1 nm line and its forbidden component at high electron number density in He plasmas. The method was validated by comparison with other methods for plasma ne in the range 1–7 × 1023 m−3. D'Ammando et al.180 have produced a model to predict the emissivity and absorption coefficient of an atomic hydrogen plasma by incorporating a collisional-radiative model for the excited state population and the Boltzmann equation for the electron energy distribution function.The Hβ line is frequently used for plasma diagnostics. Palomares et al.181 have studied the asymmetry of this line profile in MIPs at high pressure, and have shown how this can be affected by inhomogeneities in the plasma.
Temperature measurement of diffusion flames has been performed using nonlinear regime two-line atomic fluorescence (NTLAF) thermometry,182 yielding results that agreed well with laminar flame calculations.
Rate coefficients and product distributions for the reactions between fourteen lanthanide cations and ammonia have been measured using ICP selected-ion flow tube MS. H2 elimination was observed in the reactions with La+, Ce+, Gd+, and Tb+, whereas NH3 addition was observed with Pr+, Nd+, Sm+, Eu+, Dy+, Ho+, Er+, Tm+, Yb+, and Lu+. The periodic trend in reaction efficiency along the lanthanide series reflected the periodic trend in the electron-promotion energy required to achieve a d1s1 or d2 excited electronic configuration in the lanthanide cation.
Grotti et al.183 have studied the time correlation between emission line intensities in axially viewed ICP-AES with several sample introduction systems, and when using internal standardization. The highest correlation was observed for ultrasonic nebulization with desolvatation—the noisiest system but with negligible uncorrelated shot-noise. For sample introduction systems with lower flicker-noise levels, shot-noise led to high, non-correlated RSD values, making the internal standardisation less efficient.
Katskov and Daranga184 propose a method for the simulation of transient sample vapor composition and release rate during vaporization of analytes in ETAAS. The approach is based on the Langmuir theory of evaporation of metals in the presence of a gas at atmospheric pressure, which advocates formation of mass equilibrium in the boundary layer next to the evaporation surface. The authors suggest that in ETA the release of atoms and molecules from the boundary layer next to the dry residue of the analyte is accompanied by spreading of the layer around the sample droplets or crystals. Thus, eventually, the vapor source forms an effective area associated with a monolayer of the analyte. In particular, for the case of a metal oxide analyte, the boundary layer contains the species present in thermodynamic equilibrium with oxide, which are metal atoms and dimers, oxide molecules and oxygen. Because of an excess of Ar, the probability of mass and energy exchange between the evolved gaseous species is low, this substantiates independent mass transport of each type of species from the boundary layer and through the absorption volume. Diffusion, capture by Ar flow and gas thermal expansion is considered to control vapor transport and release rate. Each specific flow is affected by secondary processes occurring in collisions of the evolved molecules and atoms with the walls of graphite tube. Diffusion of oxygen containing species out of the boundary layer is facilitated by annihilation of oxygen and reduction of oxide on the graphite surface, while interaction of metal vapor with graphite slows down transport of atomic vapour out of the atomizer. These assumptions are used as the basis of a description of the phenomenon as a series of first order differential equations describing mass and temperature balance in the atomizer. Numerical solution of the series of equations provides the simulation of temporal composition of the sample constituents in condensed and gas phase in the atomizer according to chemical properties of the analyte and the experimental conditions. The suggested approach avoids the description of atomization processes via kinetic parameters such as activation energy, frequency factor, surface coverage or reaction order.
A low resolution CCD spectrometer with continuum light source and a fast-heated graphite tube atomizer was employed for simultaneous multi-element determination by ETAAS.185 The sample vaporization pulse was monitored by fast scanning of vapour spectra within the 190–410 nm wavelength range; absorption was measured at the CCD pixels corresponding to atomic resonance lines; function absorbance vs. concentration of atomic vapour was automatically linearized, and the modified signals integrated. The setup consisted of a D2 or Xe arc lamp, a linear CCD array attached to a PC and a tube atomizer furnished with a carbon fibre collector. Simultaneous determination of 18 elements was performed at the mg l−1 to μg l−1 level within 4–4.5 orders of magnitude linear concentration range. About 1–2 min was required for measurement and calculation. LOD for individual elements were 1.5–2 orders of magnitude higher compared with single element ETAAS, but similar or lower than those obtained in flame AAS. Further reduction of LODs and correction of possible spectral and chemical interferences are associated with optimization of the light source and atomization programme and modification of the calculation algorithm.
The performance of a transversely heated filter atomizer (THFA) for the determination of inorganic As compounds was studied by Panichev et al.186 Increases in sensitivity with the THFA were found to be influenced by the length and internal diameter of the inserted filter, as noted by previous workers. Good agreement was found between determined and certified values in the analysis of several CRMs.
3 Laser-based atomic spectrometry
Lasers are often used when an intense energy source is required, but wavelength is not of primary importance, as in laser-induced breakdown spectroscopy (LIBS). Also, lasers are used as a bright radiation source of precise wavelength in laser excited atomic fluorescence, laser atomic absorption, and laser enhanced ionisation. This review will be divided in this way which is the same format as last year's AS review.187 The use of lasers for fundamental studies of the properties of atoms, atomic vapours, plasmas, and the applications to studies involving thin films will not be covered here. Also not covered in this section will be papers where lasers are used to vaporize a solid sample (laser ablation or LA) for detection with an ICP based instrument such as LA-ICP-MS or LA-ICP-AES.3.1 Lasers as energy sources
Laser energy may be used to generate a plasma and excite the emission spectrum of analyte atoms. The laser wavelength is not usually critical (many wavelengths from the ultraviolet to the infrared have been used) but matching wavelength to sample material is advantageous. Pulse energies are of the order of millijoules. Recently, the commercial availability of tunable diode and femtosecond lasers has allowed several advances in this area.The past several years has featured large developments in LIBS, and special issues and reviews are now dedicated to the topic in the major atomic spectroscopy journals. The use of LIBS is increasing, and is particularly attractive when non-contact sampling is required, or for remote sensing. Although the technique features high spatial resolution, it suffers from relatively poor detection limits compared to other elemental techniques. LIBS papers are often published in journals like Spectrochimica Acta Part B and the Journal of Analytical Atomic Spectrometry, but also are increasingly found in physics and medical, environmental, and industrial journals indicating this technique is rapidly expanding into wide scientific use. One particular area that has seen a large number of publications for the past several years is archaeological science and the analysis of objects of cultural heritage interest. The 5th Euro-Mediterranean Symposium on LIBS (EMSLIBS) took place in Rome.188 Also, during the last review period several LIBS reviews have been published which will be mentioned in the appropriate sections of this review, including an overview of the field outlining the capabilities and limitations of the technique.189
3.1.1.1 Fundamental studies. LIBS fundamental studies often focus on the physical processes taking place in the LIBS emission and how to best interpret the analytical measurements. Modelling and theoretical studies are often used to predict the experimental data that is easily generated by this technique. There are several groups working on the use of chemometrics, neural networks, and other advanced computational methods to improve the reliability of LIBS measurements. Tognoni et al.190 have written a critical review of calibration free (CF) LIBS, which is multi-elemental quantitative analysis using LIBS spectra using line intensities, plasma electron density, temperature, and assumes a Boltzmann population of excited states. As the name implies the method does not require calibration curves or matrix-matched standards. The literature suggests CF-LIBS is most accurate for the analysis of metals but more research is needed to delineate experimental effects.
Gornushkin and Panne191 have reviewed models based on a laser-induced plasma and overviewed plasma diagnostics. The emphasis was given to models relevant to spectrochemical analysis and special attention was paid to collisional-radiative and collisional-dominated plasma models where radiative processes play an important role. Also, calibration-free models were considered which allow for the possibility for standardless spectroscopic analysis. Image-based diagnostics (shadowgraphy, schlieren, and interferometry), absorption and fluorescence, Langmuir probe, and less frequently used cavity ringdown and Thomson scattering methods are also summarised.
Galbacs et al.192 characterised multiple pulse LIBS in the collinear configuration with time-integrating detection on metallic samples in ambient air. The goal was to clarify the processes involved for the signal enhancement observed compared to single-pulse LIBS. Laser bursts of up to seven ns pulses from Nd-YAG lasers operating at 1064 nm were separated by 8–50 microsecond gaps. The plasmas were investigated using light profilometry, microscopy, plasma imaging, emission mapping, time-resolved emission, and plasma temperature. The results show that two contributing processes responsible for the signal enhancement are plume reheating and the increased material ablated.
A search algorithm193 has been used for automatic element identification in LIBS. The method is inspired by techniques which have been applied to text retrieval where text documents and queries are represented as weighted vectors. Documents are ranked by relevance to a query. For application to LIBS spectra, elements and samples as are represented as vectors of weighted peaks from their spectra. The presence of an element in a sample is computed by comparing the corresponding vectors of weighted peaks. The method requires a database containing the peaks of all elements to be recognised, where each peak is represented by a wavelength and relative intensity. This approach is tested on metallic alloys to show for future studies that automatic element identification by LIBS should be possible. A partial least squares algorithm194 was used to compare the quantitative analysis of brass samples by LIBS using traditional calibration curves. Major and trace elements (Cu, Zn, Sn, Pb, Fe) were analyzed, and predicted concentrations of major elements obtained by rapid partial least squares algorithms are in very good agreement with the nominal concentrations from standards of known composition and also unknowns analysed by XRF.
Asgill and Hahn195 have performed LIBS on silica particles 2.5 to 4 micrometers in diameter with an emphasis on the temporal evolution of the emission signal. Discrete delay times of 15 to 70 microseconds were used and the analyte signal profile was recorded. The ratio of analyte signals was observed to be approximately constant with plasma decay time. Thus further vaporization and enhanced analyte response do not continue with increasing delay times.
Ben Ahmed and Cowpe196 used formulas for radiative transfer to predict the spectral profile of self-absorbed Ca2+ 393.4 nm in a laser induced plasma. This theoretical plasma study divided a LIBS plasma into five layers with a thickness 0.5 mm, and each was characterized by an electron density, temperature. The model was successfully compared with experimental data from a Nd:YAG laser on a calcium solution.
A new method for determining self-absorption coefficients197 for emission lines in LIBS experiments has been put forward. The approach does not require, providing some conditions are fulfilled, plasma parameters such as temperature, electron number density, and emission transition probability. The method is applied to emission lines measured at different delay times after LIBS of a silver target material. Also, a stagnation layer may form at the interface between two colliding, dense laser-induced plasmas. Time-resolved emission imaging was used to determine the size and shape of the stagnation layer between plasmas for a variety of target shapes and materials.198 The target geometry and elemental composition strongly influence the collision process and degree of stagnation. Wedge-shaped targets, as compared to flat, and aluminium targets, instead of calcium, both decrease the degree of stagnation.
Continuum radiation in laser induced plasma emission spectra dominates immediately after the laser pulse, and the understanding of the spectral details is important for determining the initial mechanisms of the plasma. This was accomplished by a qualitative interpretation of the plasma continuum during initial expansion and improved atomic temperature measurements using Boltzmann and Planck plots. Results show that it is important to consider non-equilibrium effects in the initial stages of laser induced plasma expansion.199
Cristoforetti et al.200 have suggested that the well known McWhirter criterion should be discontinued from use in assessing the existence of local thermodynamic equilibrium (LTE). This has been one of the main ways to relate fundamental plasma parameters to the concentration of analyte species, but the application to a transient, non-homogeneous plasma such as in LIBS has been shown to be problematic. Theoretical expressions should include relaxation times and diffusion coefficients, as well as space and time-resolved measurements that could be used to calculate electron number density. These approaches should provide a better representation of LTE and improved quantitative results. Pietanza et al. have also performed a modelling study using a collisional-radiative approach at conditions typical of a LIBS experiment on a metallic sample.201 Estimates of the hierarchy of the various plasma expansion processes and possible deviations from local thermodynamic equilibrium conditions were made. The experimental and theoretical results agree but also raise questions on the correct use of the McWhirter criterion and other assumptions in LIBS.
The popular Boltzmann plot method was theoretically tested for an inhomogeneous non-isothermal laser-induced plasma to assess performance of calibration-free LIBS202 for the analysis of minor and trace element determinations. Synthetic spectra were generated assuming minimal Stark broadening, spectral overlap, self absorption, and all possible sources of error were minimised. Plasmas were investigated at a range of temperature and density gradients, and the spectra were analysed with software that calculated plasma temperature and concentrations using the Boltzmann plot approach. Despite this best case scenario, calibration-free LIBS was only capable of providing accurate concentrations for main plasma components (major elements) but failing for minor and trace elements. This might be acceptable for many industrial and environmental monitoring purposes.
Wester and Noll203 have modelled the emission of a LIBS plasma using heuristics with the assumption that the composition of the plasma and the plasma state is known. The model takes into account a stationary spherical shell model that is surrounded by ambient gas and partially absorbs the emitted radiation. Fine structures of experimental multiline spectra are reproduced by the simulation but the degree of agreement varies, which is attributed to a lack of precise Stark broadening data and also the simplified plasma model.
3.1.1.2 Instrumentation. Recent developments in LIBS instrumentation include improving detection limits by use of improved lasers, dual pulse techniques, improving standoff LIBS204 and sophisticated data processing approaches. Also, there are trends toward smaller, more capable systems for portable instruments and also combined Raman and LIBS instruments that provide molecular and elemental information simultaneously. Hoehse et al.205 have presented an instrument with Raman and LIBS integrated into a single system for molecular and elemental microanalyses. The spectrometer system is a high resolution dual arm Echelle spectrograph with a broad spectral range of 200–6000 cm−1 without moving the dispersive element. In Raman mode the instrument shows similar or better sensitivity and resolution to a dedicated scanning Raman microscope. LIBS detection limits are in the ppm range with 15
000 resolution and spectral range of 290–945 nm.
A major limitation to LIBS performance is the continuum background radiation in the early stages of plasma formation, which interferes with atomic and ionic emission lines. The lifetime of the continuum is shorter than that of the spectrum, and it may be suppressed using an intensified charge-coupled device camera to delay and gate the fluorescence measurement. However, waiting for the continuum emission to subside has a downside that performance is sacrificed and each experiment must be optimized. It has been shown that the background of the LIBS of an Al target material using an 800 nm femtosecond laser is strongly polarized.206 A polarizer may be used to filter out the background and improve signal/background ratios for analyte emission, and be a solution for other LIBS systems.
Windom and Hahn207 have presented a novel use of LIBS by first performing laser ablation on metallic samples and the ablated material carried to a second laser for LIBS measurement as a means for reducing matrix effects. Laser-ablation LIBS (LA-LIBS) should improve analyte response, minimize matrix effects, and allow the use of non-matrix matched standards. Compared to a traditional LIBS system, LA-LIBS produces an improved analytical response, and with a single calibration curve accurately analysed samples of varying composition. Also, helium was shown to be a better carrier gas when compared to nitrogen.
Neural network prediction208 has been used with LIBS for the quantitative analysis of minor element impurities in a tin alloy. Ag, Cu, Pb were evaluated by artificial neural networks and compared to an external calibration curve approach. Results using both approaches agreed, and detection limits ranged from 29 to 213 ppm. Glass samples of forensic interest have been identified correctly based on a method that correlates only essential spectral information and ignores empty spectral fragments. This linear correlation method via spectral filtering has improved on the traditional approach for forensic glass analysis which can be prone to errors in identification.209
Resonance-enhanced LIBS210 was investigated to improve the detection limits of trace elements in aluminium alloys. A Q-switched Nd:YAG laser (7 ns, 1064 nm) was used to ablate the samples. After a delay, a second laser pulse at 396.15 nm resonates the aluminium host atoms. The Mg(I)285.21 nm and Si(I) 288.16 nm lines were observed. At low ablation fluences of 1 J cm−2, the Mg 285.21 nm line achieved this resonance enhanced approach was significantly enhanced when compared to LIBS. At laser fluences higher than 8 J cm−2, similar results were observed for both approaches.
As nanotechnology develops, the requirement of nanoscale microanalysis will increase. Zorba et al.211 used a femtosecond laser on a silicon target at 400 and 800 nm while tightly focusing the laser beam in the far-field to produce sub-micrometer craters. Sub-wavelength apertures produced sub 30 nm craters. Even at such small crater sizes, LIBS emission was possible, and are among the smallest reported for femtosecond LIBS.
There are further developments on the LIBS instrument to be included on the missions to Mars212 and other planets, or moons such as Jupiter's Europa. The instrument will be installed on a rover for the in situ geochemical analysis of surface rocks materials. Due to the strict requirements for space travel, the 1 kg instrument features a laser with an energy of 1.8 mJ but is able to analyse for 14 major and minor elements. Detection limits are >400 ppm for the prototype laser, and agreed within 10–20% compared to a larger laboratory LIBS instrument. Lanza et al.213 have developed a calibration technique using a LIBS instrument for carbonate minerals on Mars. Both chemical composition and rock type are determined using multivariate data analysis techniques. LIBS has also been demonstrated as a quantitative technique for bulk geochemical elemental analysis of igneous rock powders on Mars.214 The method used the LIBS spectra of 100 igneous rocks with varying compositions acquired at 9 m standoff distance under Mars atmospheric conditions. Partial least squares regressions were used to predict major element compositions. The 1-sigma errors were 2 wt% for SiO2, Al2O3, TiO2, Fe2O3, MgO, MnO, CaO, Na2O, P2O5, K2O, and the totals were near 100%.
Gottfried et al.215 used principal components analysis and partial least squares discriminant analysis of LIBS chemical signatures for geomaterial classifications. A suite of natural carbonate, fluorite and silicate geological materials were tested by single and double pulse LIBS using benchtop and standoff systems. Good discrimination was achieved using the partial least squares approach, and the double-pulse system did not provide any advantage for sample classification over single-pulse, except for soil samples. The standoff LIBS system provided comparable results to the benchtop system.
Popov et al.216 have constructed an emission confinement chamber to enhance LIBS sensitivity. The 4 mm diameter chamber features polished brass walls and high efficiency collecting optics. The optimal position of the focus was found below the sample surface. The LIBS intensity is enhancement for several major (Fe, Mg, Si) and trace elements (As, Ba, Cr, Hg, Mn, Ni, P, Pb, Ti, V) but there is a decrease in signal-to-noise ratio due to slightly worse reproducibility of single-shot spectra inside the chamber. The LOD for As, Hg, Pb, Mn, V and Ba in soil were 30, 25, 90, 140, 1 and 50 ppm, respectively, which is 2–5 times lower than the same system without the chamber.
3.1.1.3 Applications. Table 1 summarizes some recent applications of LIBS. This list is not comprehensive and includes work selected for novelty, special significance, or to illustrate the variety and flexibility of the technique. In addition to those listed in the table, the following papers show significant advances in the application of LIBS. There have been two reviews of LIBS applications, one covering analysis of aerosol particles217 and another for single shot LIBS.218 Additionally, the use of LIBS in industrial and security applications shows how the technique can be used for rapid analysis, and also in applications looking for lead in paint and children's toys, analysis of electronic and solder materials, quality control of fibreglass panels, discrimination of coffee beans from different vendors, and identification of generic versus brand-name drugs.219
| Matrix | Analyte | Comments | Reference |
|---|---|---|---|
| Archaeological pottery | Si, Al, Fe, Ca, K, Mg, Ti and Na | Application to the analysis of a ceramic glaze and comparison to other atomic spectroscopic techniques | 220 |
| Biological tissue | Multielement spectral analysis | Identify various types of body tissue from a chicken | 221 |
| Concrete | Cl | Monitoring concrete content for elements corrosive to steel | 222, 223 |
| Cotton | Al, Ba, Ca, Cr, Cu, Fe, Mg, and Sr | Study to determine geographical source of cotton fibers using principal component analysis | 224 |
| Crude Oils | Co, Fe, V, Ni, Pb, P, Mo, Ca, Si, Ti, Mn, Cd, Cu | A rapid and high throughput method for monitoring trace elements in oil refining and also exploration studies | 225 |
| Fertilizer | K, Na, Mg | Process monitoring for quality control | 226 |
| Fuel Cells | H | Imaging hydrogen leaks from fuel cells | 227 |
| Ground water | B | 10 ppb detection limit, graphite solid support used for water samples | 228 |
| Human Tissue | Ca, Mg | To identify and characterize some types of malignant tumors and tissues | 229 |
| Lipstick | Pb, Cr, Cd, Zn | Screening for toxic elements in lipstick as a tool for safety monitoring | 230 |
| Obsidian tools | Multi element | Fingerprinting archaeological objects from the southwestern USA | 231 |
| Paper swipes | Ag, As, Ba, Be, Cd, Cr, Cu, Hg, Mn, Ni, Pb, Sr, Sn | Using post it note paper to swipe surfaces and analyse the samples for contamination elements | 232 |
| Potatoes | Na, Al, Si, Ca, Fe | Measure elemental composition of fresh vegetables | 233 |
| Soils | Cd | Screening for contaminated soils | 234 |
| Speleothem | Na, Mg, Al, Si, K, Fe and Sr | Palaeoclimate elemental mapping | 235 |
| Sugar cane leaves | P, K, Ca, Mg, B, Cu, Fe, Mn, Zn | Chemometric method for analysis of nutrients in pellets, compared to ICP-OES | 236 |
| Surfaces | U | Detecting weapons of mass destruction, LOD 0.26% | 237 |
| Tall Fescue | Ca, Cd, Mg, Fe, Mn, Cu, Ni, Zn | Forage analysis and phytoremediation studies | 238 |
| Teeth | Mg, Ca, Sr | Determining element ratios in anthropological samples | 239 |
| Zinc alloys | Zn | Investigating microscale inhomogeneities | 240 |
LIBS was used to determine the elemental concentration of cerium oxide (a surrogate for plutonium oxide) for the monitoring of glasses that will be used for nuclear waste storage.241 Multivariate calibration was applied to LIBS data to predict the concentrations of Ce, Cr, Fe, Mo, and Ni. A total of 18 different surrogate samples were prepared and analysed using LIBS with principal component regression and partial least squares. Accuracy and precision both improve using the multivariate methods or data analysis compared with a traditional LIBS approach. Multivariate and univariate calibration strategies were also compared for the analysis of plant materials by Braga et al.242 Plant materials were cryogenically frozen, ground, and pressed into pellets for LIBS analysis, and the results calculated using partial least squares regression of carefully chosen spectral regions to improve the analytical accuracy for complex natural samples in agricultural and environmental analysis.
LIBS analysis on metal samples on a conveyor belt, replicating a metal recycling facility, was tested for statistical uncertainty.243 A Nd:YAG laser operating at 532 nm was used for the purpose of sorting shredded scrap metal. Samples were tested in motion and varied in size, shape, and cleanliness. Flat, clean scrap samples exhibited acceptable reproducibility and repeatability. By contrast, samples with an irregular shape or a dirty surface exhibited a poor relative standard deviation.
Boron has been measured in photovoltaic grade silicon using LIBS with a UV laser.244 Varying the laser wavelength had a small effect, but comparing helium and argon atmospheres showed a significantly higher signal-to-background ratio (SBR) for boron emission using argon.
Laser ablation has been combined with a high voltage spark to increase the sensitivity of LIBS for soil samples.170 The technique uses a fast pulse discharge circuit to enhance the laser induced plasma emission. The optical emission spectroscopy of soil was compared with single pulse LIBS, and relative standard deviation and also signal to noise ratios were both improved by a factor of 2 to 3. Also, LIBS has been assisted by microwaves245 for the analysis of alumina ceramics. Signal enhancements for some spectral lines were found to be up to 33 times higher when microwaves were used, and was more effective in air compared to argon atmosphere.
Alvey et al.246 used LIBS for geochemical fingerprinting of 157 natural garnet samples from 92 global locations Statistical signal processing and classification techniques were applied to single-shot, broadband LIBS spectra. Partial least squares analysis was applied to 25 LIBS spectra for each garnet sample and used to classify the garnet samples by composition and geographic origin. In a related application, LIBS was used as an alternative to slow and costly laboratory based techniques for monitoring on-line mineralogical ore production for the multi-element and mineralogical analysis of iron, nickel and lead/zinc mineral ores.247 The resulting LIBS spectra was evaluated with chemometric analysis. Principal components regression was used on selected emission bands, and relative errors for Fe, Al, Si, K, P were on the order of 3–6%. Principal components analysis of the LIBS spectra was used to determine ore mineralogy, and the technique shows potential to monitor the quality of ore production.
3.2 Lasers as sources of intense monochromatic radiation
Ribiere and Cheron249 used absorption spectroscopy to analyse atmospheric LIBS formed on aluminum, magnesium, copper, nickel and silicon targets. The use of absorption spectroscopy allowed the use of a very small delay after the LIBS plasma when the continuum spectrum still dominates. The plasmas were characterized by size, free electron and absolute atomic densities against distance from the target and delay time after laser firing. All parameters employed in determining the spectra were either calculated or found in standard databases. This calibration-free method does not require the local thermodynamic equilibrium assumption and shows good agreement with model predictions and experimental findings for metallic and non-metallic elements.
4 Chemometrics
Chemometric procedures are typically used for three main purposes: optimisation; instrumental calibration and/or interference correction; and pattern recognition when applied to datasets. Very few novel developments have been published over the review period.Barwick and Wood251 have published a tutorial article on traceability in chemical and bioanalytical measurement, in which they outline the role of metrology in achieving traceable results. Part of this process is the estimation of uncertainty contributions to analytical measurements, and is becoming more important with several publications on this topic with relevance to FAAS252 and the exact matching technique used in ICP-AES.253 Mermet254 has published a tutorial review on calibration in atomic spectrometry, concentrating on the basics of linear regression and the influence of weighting.
Mahani et al.255 have used PLS algorithm to resolve 235U and 238U emission lines in ICP-AES and achieved good agreement with TIMS measurements of isotope ratios.
Pattern recognition methods have been widely applied to food authentication or place of origin studies. Gonzalvez et al.256 have reviewed (84 refs.) the literature on authentication of foods with Protected Designation of Origin (PDO) using atomic spectrometry and chemometric methods of data treatment. There has been the usual crop of papers describing chemometric methods applied to food authenticity257–268 and environmental forensics,269–275 but without any significant new developments.
5 Isotope analysis
The biennial IUPAC review of the atomic weights of the elements276 has resulted in changes for the standard atomic weights of 11 elements. Text from the abstract is quoted directly below:To emphasize the fact that these standard atomic weights are not constants of nature, each atomic-weight value is expressed as an interval. The interval is used together with the symbol [a; b] to denote the set of atomic-weight values, Ar(E), of element E in normal materials for which a ≤ Ar(E) ≤ b. The symbols a and b denote the bounds of the interval [a; b]. The revised atomic weight of hydrogen, Ar(H), is [1.007 84; 1.008 11] from 1.007 94(7); lithium, Ar(Li), is [6.938; 6.997] from 6.941(2); boron, Ar(B), is [10.806; 10.821] from 10.811(7); carbon, Ar(C), is [12.0096; 12.0116] from 12.0107(8); nitrogen, Ar(N), is [14.006 43; 14.007 28] from 14.0067(2); oxygen, Ar(O), is [15.999 03; 15.999 77] from 15.9994(3); silicon, Ar(Si), is [28.084; 28.086] from 28.0855(3); sulfur, Ar(S), is [32.059; 32.076] from 32.065(2); chlorine, Ar(Cl), is [35.446; 35.457] from 35.453(2); and thallium, Ar(Tl), is [204.382; 204.385] from 204.3833(2).
5.1 Reviews
A large number of reviews, of varying length, have been published over the last year. These are both of a general nature, such as reviews by Beauchemin277,278 (181 and 342 refs. respectively) and Bings279(315 refs.); and directed toward specific applications. De Laeter280 has reviewed the application of inorganic mass spectrometry in the nuclear field (87 refs.), with particular emphasis on metrological protocols that are necessary to obtain valid data. Similarly, Yang281 has reviewed the use of MC-ICP-MS (174 refs) to obtain accurate and precise isotope ratio measurements. Linge and Jarvis282 have authored a tutorial review (124 refs.) on the use of ICP-MS for geological applications; Resano et al.283 have reviewed the use of LA-ICP-MS in archaeometric research (118 refs.); Vajda284 has reviewed methods for the determination of 241Am; and Bullen285 has authored a primer on the determination of the fractionation of metal stable isotopes in low temperature systems. Boulyga286 has reviewed the current status of calcium isotope analysis, with a discussion of biological isotope fractionation in medical studies, paleoclimatic and paleoceanographic, and other terrestrial as well as extraterrestrial investigationsThere is increasing interest in the use of inorganic mass spectrometry for the absolute and relative quantification of biological molecules, as reflected in reviews by Mi and Wang287 (30 refs) and Tholey288 wherein both discuss the advantages and disadvantages of labelling with specific isotopes. Related to this general area of biological research, Fernandez167 has reviewed the use of mass spectrometry for nano-scale measurements, including assays of biomolecules tagged with nano-particles.
The use of AMS is growing rapidly. Steier et al.289 have reviewed its use for the measurement of heavy isotopes in the environment, with emphasis on the actinides. Garner290 has reviewed the role of AMS for 14C measurements in translational medicine.
5.2 Isotope dilution analysis (IDA)
Isotope dilution analysis is a method used for quantification whereby an isotopically enriched spike of the analyte is added to the sample, and the modified isotopic ratios can be measured and used to determine the concentration of the analyte. When the detector is a mass spectrometer (as is often the case) the technique is referred to as isotope dilution mass spectrometry (IDMS). This review will cover advances in IDA for determination of total concentrations of elements using atomic emission, absorption, fluorescence and mass spectrometry, but not including radiochemical techniques. The developing field of species-specific IDA (which typically involves coupling between LC or GC and ICP-MS), is covered in the separate AS Update ‘Elemental Speciation’.1Mana et al.291 have developed a method for the determination of the molar mass of Si, enriched with 28Si, using a new equation linking measurement results to the ratio of amount of substance for 28Si and 30Si. In related papers292,293 they discuss the uncertainty of the Si molar mass measurement and the calibration factors required for the determination of absolute isotope amount ratios respectively.
Inductively coupled plasma mass spectrometry (ICP-MS) has been used extensively for IDMS measurements, particularly for measurements in biological applications. In this context, Bettmer294 has reviewed (55 refs.) the use of ID-ICP-MS in quantitative proteomics. The main stated advantage of this approach is the ability to perform quantitative measurements of proteins, or other biomolecules, through use of isotopically enriched spikes or tagged molecules. In a second paper by the same group,295 the use of p-hydroxymercuribenzoic acid (pHMB) as a labeling reagent for cysteine-containing proteins, using the complementary techniques of MALDI-TOFMS and ICP-MS and isotopically labeled 199HgpHMB, is described for the absolute quantitation of insulin. Martinez-Sierra et al.296 have evaluated various methods, including IDMS, for the quantification of biomolecules containing sulphur in 34S labelled yeast using post-HPLC IDMS. They used 33S to successfully determine sulfate, cysteine, glutathione and methionine by developing a procedure that discriminated between ‘natural abundance’ and 34S-enriched' sulfur species in the labelled yeast. Sar et al.297 have used cisplatin, isotopically enriched in 194Pt, to perform IDMS of cisplatin-DNA adducts generated in Drosophila melanogaster larvae and in head and neck squamous cell carcinoma cultures. Zheng et al.97 generated volatile species of Ni, Fe and Se using on-line UV photochemical vapour generation coupled with ID-ICP-MS for determination of these elements in biological CRMs TORT-2 and DORM-3. They achieved LODs of 0.18, 1.7, and 1.0 pg g−1 using external calibration.
Yan et al.298 have used a sectional power law for correction of 176Lu:175Lu ratios in geological samples using MC-ICP-MS. Other developments of note include an uncertainty analysis for the determination of 137Ba, the stable decay daughter of 137Cs, from a sealed radioactive source;299 a microchip-based solvent extraction system, with ID-ICP-MS, for the determination of Cu in JSS601-10 steels,300 which involved extraction of Cu into o-xylene using 8-hydroxyquinoline at pH 7 and back extraction with 0.1 mol L−1nitric acid.
There have been few novel developments on the use of TIMS for IDMSper se (but see Section 5.3). Ghidan and Loss301 have developed a method for the determination of low levels of Zn in geological and biological reference materials and water samples by double spiking IDMS using 67Zn and 70Zn isotopes.
5.3 Isotope ratio analysis (IRA)
Isotope ratio analysis (IRA) covers a group of related techniques used for the measurement of isotope ratios in a variety of sample types and for a range of applications. When used in conjunction with mass spectrometric detection the technique is referred to as isotope ratio mass spectrometry (IRMS). The primary focus of this review will be IRMS confined to advances in the measurement of isotope ratios of relatively heavy isotopes (i.e., of elements traditionally associated with atomic spectrometry), and will not cover the literature pertaining to IRMS of C, N, H, and O.:238U isotope ratios varying from 10−4 to 10−9, suitable for TIMS, ICP-MS, TIMS and AMS analyses. A subsequent paper by the same authors304 reported on new average values for 238U:235U isotope ratios in NBS SRM 960 and IRMM-184. Another study by the same group305 reported on isotope fractionation as a result of the redox reaction between Zn0 and ZnII in a pyrometallurgical biphase extraction between liquid zinc and molten chloride. The effect on Zn isotope ratios, measured using MC-ICP-MS, of nuclear mass volume were evaluated using first-principles quantum calculations and correlated with the Gibbs free energy change in the redox reaction.
An electrochemical separation method for Pu, prior to isotopic determination by ICP-MS, has been developed by Liezers et al.,306 wherein Pu is concentrated on a glassy carbon anode by redox conversion of Pu(III) to Pu (IV and VI) in 2% HNO3. The system allows separation of UIV from PuIV, thereby eliminating uranium hydride interferences. The half life of 10Be has been determined307 using a combination of MC-ICP-MS and liquid scintillation counting, and a half-life of 1.386 ± 0.016 My (standard uncertainty) was calculated. An independent study determined a half-life of 1.388 ± 0.018 My, so the authors propose that the combined half-life and uncertainty of 1.387 ± 0.012 My be used in nuclear studies and in studies that make use of cosmogenic 10Be in environmental and geologic samples. Fujii et al.308 have studied the fractionation of Cd isotopes during liquid–liquid extraction, and measured precise ratios using MC-ICP-MS. Interestingly, they found that the odd atomic mass isotopes (111Cd and 113Cd) showed excesses of enrichment comparing to the even atomic mass isotopes (110Cd, 112Cd, 114Cd and 116Cd). They ascribed this to the nuclear field shift effect (an isotope shift in orbital electrons resulting from the difference in nuclear size).
The use of LA-ICP-MS for the measurement of Li isotope ratios has been reported y le Roux,309 who used an instrument fitted with a ‘low-mass, high abundance’ skimmer cone and a 213 nm laser operating in a He atmosphere. Simultaneous measurement of 7Li and 6Li was achieved with <1 permil precision at 3–35 ppm concentration.
Improvements in the measurement of actinide isotopes using AMS has been effected310 by using a fast switching electrostatic system based on a pair of deflector plates, deflecting in the orbit plane, set at the entrance and exit of the analysing magnet.
A number of developments in the use of TIMS for IRA have been published over the review period. In particular, Berger311 have reported on application of the GUM (Guide to the expression of Uncertainty in Measurement) to calculate standard uncertainties for routine uranium IR measurements. Detailed examples of uncertainty calculations are presented for the most common types of uranium isotope measurements, with the main contributions to uncertainty discussed. Cavazzini312 has studied the relationship between Rayleigh's distillation law and linear models of instrumental isotopic fractionation. It was found that the fractionation factor per amu was a function of the residual mass fraction of the sample on the filament, and the rate of change of the vapour/residue distribution coefficient with mass. Experimental results of instrumental isotopic fractionation of Sr in NIST SRM-987 tended to confirm a linear model of isotope fractionation, and hence Rayleigh's distillation law. Kraiem et al.313 have investigated the vaporisation and ionisation of U from a rhenium filament and found it to be consistent with the formation of UO2 on the surface. In a related paper the same group314 have investigated the ionization mechanism of U in the presence of carbon and found that the uranyl nitrate sample turned into a uranium carbide compound, independent of the type of carbon used as ionization enhancer; and on further heating this led to formation of uranium metal ions and a small amount of uranium carbide ions. Staying with the uranium theme, Suzuki et al.315 have reported a ‘continuous heating method’ for IRA of U by TIMS to determine accurate isotope ratios of U ranging from sub-pg to several dozen pg. An improvement in precision compared to the ‘total evaporation method’ was cited.
Isnard et al.316 have undertaken a comparison of TIMs and MC-ICP-MS for IRA of Cs. Results obtained by the two techniques showed good agreement, with only between 0.2% to 0.5% relative difference for 133Cs:137Cs and 135Cs:137Cs ratios for two nuclear samples. Similarly, de Oliviera et al.317 have performed a metrological comparison of GSMS, TIMS, and MC-ICP-MS for IRA of U.
Ludwig318 has studied the errors in isotope ratios associated with cyclic peak jumping, and observed that isotope-ratio uncertainties for a single spot are usually underestimated by factors of 1.2–1.3 when performing IRA with ion microprobe MS.
A novel use of laser ablation and laser atomic absorption spectroscopy has been reported,248 wherein diode lasers were tuned to specific isotopes in two different atomic transitions for 152Gd (at 405.9 nm) and 160Gd (at 413.4 nm), directed collinearly through the laser ablation plume, separated on a diffraction grating, and detected with photodiodes to monitor transient absorption signals on a shot-by-shot basis. 152Gd:160Gd ratios of between 0.01 to 0.43 were measured in river sediment particles doped with isotopically enriched GCCl3. Lastly, ICP-AES has also been used for isotope ratio measurements of U by the application of a PLS multivariate calibration model to resolve the 235U and 238U atomic emission lines.
000 y using the U-series approach. Douville et al.321 have applied the U-Th dating technique to marine aragonite skeletons by separating U and Th from the matrix on UTEVA resin and simultaneously quantifying their isotopic compositions using Q-ICP-MS. They were able to process up to 50 samples day−1 and achieved δ234U and δ230Th reproducibility (2 sigma) of 3–4 and 10 permil. Another publication on U-Th dating using ICP-MS describes322 a method for calibration of in-house Th isotopic standards, and an evaluation of mass fractionation which the authors ascribe to a linear-law fractionation model.
Acclerator mass spectrometry (AMS) is being used increasingly in geological applications. Several papers have been published on the optimisation of AMS for the determination of 36Cl:Cl323–327 and 10Be328–332 ratios, though few have got as far as real applications. Fifield and Morgenstern333 have reviewed the field 32Si dating, with particular reference to AMS. They conclude that the chronometric potential of this isotope is close to being realised as a result of improvements in detection techniques. In a later paper334 the same group report the application of the 32Si dating technique using AMS for ice cores, with comparable results to the radiometric technique. They conclude that chronology of ice cores is now possible using this method.
:Se measurement, which makes it possible to use the probe as a tracer in biological studies. They demonstrated its applicability for 79Se:80Se measurements in a subsequent paper,336 in which they reported a relative standard uncertainty of 4.7% for the ratio.
Amrani et al.339 have developed a coupled GC-MC-ICP-MS for determining δ34S values in volatile organics in crude oils. They minimized isobaric O2+ interference by using a dry plasma and achieved 0.1 and 0.5 per mil precision for samples containing >40 pmol and 6 pmol S respectively.
6. Glossary of abbreviations
Whenever suitable, elements may be referred to by their chemical symbols and compounds by their formulae. The following abbreviations may be used without definition. Abbreviations also cover the plural form.| AA | atomic absorption |
| AAS | atomic absorption spectrometry |
| AB | arsenobetaine |
| AC | arsenocholine |
| ac | alternating current |
| AE | atomic emission |
| AEC | anion exchange chromatography |
| AED | atomic emission detection |
| AES | atomic emission spectrometry |
| AF | atomic fluorescence |
| AFS | atomic fluorescence spectrometry |
| AMS | accelerator mass spectrometry |
| ANOVA | analysis of variance |
| ANSI | American National Standards Institute |
| APDC | ammonium pyrrolidine dithiocarbamate |
| APPI | atmospheric pressure photoionization |
| APS | advanced photon source |
| ASE | accelerated solvent extraction |
| ASTM | American Society for Testing and Materials |
| ASU | Atomic Spectrometry Update |
| ASV | anodic stripping voltametry |
| BCR | Community Bureau of Reference |
| BFR | brominated flame retardants |
| CC | collision cell |
| CCA | copper chromium arsenic |
| CCD | charge coupled detector |
| CCP | capacitively coupled plasma |
| CE | capillary electrophoresis |
| CEC | cation-exchange chromatography |
| CE-ICP-MS | capillary electrophoresis inductively coupled plasma mass spectrometry |
| CFC | chlorofluorocarbon |
| CID | collision induced dissociation |
| CL | confidence limits |
| CMOS | complementary metal oxide semiconductor |
| CMP | capacitively coupled microwave plasma |
| CPE | cloud point extraction |
| cps | counts per second |
| CRM | certified reference material |
| CRS | cavity ringdown spectroscopy |
| CV | cold vapour |
| CV-AAS | cold vapour atomic absorption spectrometry |
| CV-AFS | cold vapour atomic fluorescence spectrometry |
| CVD | chemical vapour deposition |
| CVG | chemical vapour generation |
| CW | continuous wave |
| Cys | cysteine |
| CZE | capillary zone electrophoresis |
| DBT | dibutyltin |
| dc | direct current |
| DCP | direct current plasma |
| DDTC | diethyldithiocarbamate |
| DDTP | o,o-diethyldithiophosphate |
| DEtHg | diethylmercury |
| DIBK | diisobutyl ketone |
| DIC | dissolved inorganic carbon |
| DIHEN | direct injection high efficiency nebulizer |
| DMA | dimethylarsinic acid |
| DMAA | dimethylarsinoylacetic acid |
| DMDTAv | dimethyldithioarsinic acid |
| DMT | dimethyltin |
| DMTAv | dimethylthioarsinic acid |
| DNA | deoxyribonucleic acid |
| DNPH | 2,4-dinitrophenylhydrazine |
| DNTC | diffuse neurofibrillary tangles with calcification |
| DOTA | 1,4,7,10-tetraazacyclododecane-1.4.7.10-tetraacetic acid |
| DPAA | diphenylarsinic acid |
| DPhT | diphenyltin |
| DRC | dynamic reaction cell |
| DU | depleted uranium |
| DVB | divinylbenzene |
| EDL | electrodeless discharge lamp |
| EDTA | ethylenediaminetetraacetic acid |
| EI | electron impact |
| EIE | easily ionizable element |
| EIMS | electron ionization mass spectrometry |
| EPA | Environmental Protection Agency |
| EPMA | electron probe microanalysis |
| ES | electrospray |
| ESD | element specific detection |
| ESI | electrospray ionisation |
| ESI-MS | electrospray ionisation mass spectrometry |
| ES-MS | electrospray mass spectrometry |
| ETA | electrothermal atomization |
| ETAAS | electrothermal atomic absorption spectrometry |
| EtHg | ethylmercury |
| ETV | electrothermal vaporization |
| ETV-AAS | electrothermal vaporization atomic absorption spectrometry |
| ETV-ICP-MS | electrothermal vaporization inductively coupled plasma mass spectrometry |
| EU | European Union |
| FAAS | flame atomic absorption spectrometry |
| FAES | flame atomic emission spectrometry |
| FAFS | flame atomic fluorescence spectrometry |
| FANES | furnace atomic non-thermal excitation spectrometry |
| FAPES | furnace atomization plasma excitation spectrometry |
| FES | flame emission spectrometry |
| FF | flame furnace |
| FFF | field flow fractionation |
| FI | flow injection |
| FI-CV-ICP-MS | flow injection cold vapour inductively coupled plasma mass spectrometry |
| FI-HG-QF-AAS | flow injection hydride generation quartz furnace atomic absorption spectrometry |
| FI-ICP-MS | flow injection inductively coupled plasma mass spectrometry |
| FILM | fluorescence lifetime imaging |
| FP | fundamental parameter |
| FPD | flame photometric detector |
| FPGA | field programmable gate array |
| fs | femto second |
| FT | Fourier transform |
| FWHM | full width at half maximum |
| GC | gas chromatography |
| GC-AAS | gas chromatography atomic absorption spectrometry |
| GC-AFS | gas chromatography atomic fluorescence spectrometry |
| GC-C-IR-MS | gas chromatography combustion isotope ratio mass spectrometry |
| GC-EIMS | gas chromatography electron ionization mass spectrometry |
| GC-FPD | gas chromatography flame photometric detector |
| GC-ICP-MS | gas chromatography inductively coupled plasma mass spectrometry |
| GC-IR-MS | gas chromatography isotope ratio mass spectrometry |
| GC-MIP-AES | gas chromatography microwave induced plasma atomic emission spectrometry |
| GC-MS | gas chromatography mass spectrometry |
| GC-TOF-MS | gas chromatography time-of-flight mass spectrometry |
| GD | glow discharge |
| GD-MS | glow discharge mass spectrometry |
| GE | gas electrophoresis |
| GF-AAS | graphite furnace atomic absorption spectrometry |
| GFC | gel filtration chromatography |
| HCL | hollow cathode lamp |
| HDPE | high density polyethylene |
| hf | high frequency |
| HG | hydride generation |
| HG-AAS | hydride generation atomic absorption spectrometry |
| HG-AFS | hydride generation atomic fluorescence spectrometry |
| HG-ICP-MS | hydride generation inductively coupled plasma mass spectrometry |
| HG-QT-AAS | hydride generation quartz tube atomic absorption spectrometry |
| HPLC | high-performance liquid chromatography |
| HPLC-DF-ICP-MS | high performance liquid chromatography double focusing inductively coupled plasma mass spectrometry |
| HPLC-HG-AAS | high performance liquid chromatography hydride generation atomic absorption spectrometry |
| HPLC-HG-AFS | high performance liquid chromatography hydride generation atomic fluorescence spectrometry |
| HPLC-ICP-MS | high performance liquid chromatography inductively coupled plasma mass spectrometry |
| HR | high resolution |
| HR-CS-AAS | high resolution continuum source atomic absorption spectrometry |
| HR-ICP-MS | high resolution inductively coupled plasma mass spectrometry |
| IAEA | International Atomic Energy Agency |
| IAG | International Association of Geoanalysts |
| iAs | inorganic arsenic |
| IBMK | isobutyl methyl ketone |
| IC | ion chromatography |
| IC-HG-AFS | ion chromatography hydride generation atomic fluorescence spectrometry |
| IC-ICP-MS | ion chromatography inductively coupled plasma mass spectrometry |
| ICP | inductively coupled plasma |
| ICP-AES | inductively coupled plasma atomic emission spectrometry |
| ICP-MS | inductively coupled plasma mass spectrometry |
| ICP-OES | inductively coupled plasma optical emission spectrometry |
| ICP-QMS | inductively coupled plasma quadrupole mass spectrometry |
| ICP-TOF-MS | inductively coupled plasma time-of-flight mass spectrometry |
| ICR | ion cyclotron resonance |
| id | internal diameter |
| ID | isotope dilution |
| IDA | isotope dilution analysis |
| ID-ICP-MS | isotope dilution inductively coupled plasma mass spectrometry |
| ID-MS | isotope dilution mass spectrometry |
| iHg | inorganic mercury |
| IMF | instrumental mass fractionation |
| INAA | instrumental neutron activation analysis |
| IP | ionization potential |
| IR | infrared |
| IRA | Isotope ratio analysis |
| IRMM | Institute for Reference Materials and Measurements |
| IRMS | isotope ratio mass spectrometry |
| iSb | inorganic antimony |
| iSe | inorganic selenium |
| iTe | inorganic tellerium |
| ISO | International Organization for Standardization |
| IUPAC | International Union of Pure and Applied Chemistry |
| LA | laser ablation |
| LA-ICP-MS | laser ablation inductively coupled plasma mass spectrometry |
| LA-MC-ICP-MS | laser ablation multi collector inductively coupled plasma mass spectrometry |
| LA-SF-ICP-MS | laser ablation sector field inductively coupled plasma mass spectrometry |
| LC | liquid chromatography |
| LC-HG-AFS | liquid chromatography hydride generation atomic fluorescence spectrometry |
| LC-ICP-MS | liquid chromatography inductively coupled plasma mass spectrometry |
| LC-MS | liquid chromatography mass spectrometry |
| LC-MS-MS | liquid chromatography mass spectrometry mass spectrometry |
| LCSM | laser confocal scanning microscopy |
| LDA | linear discriminant analysis |
| LEAFS | laser-excited atomic fluorescence spectrometry |
| LED | light emitting diode |
| LEI | laser-enhanced ionization |
| LIBS | laser induced breakdown spectroscopy |
| LIF | laser induced fluorescence |
| LINAC | linear accelerator |
| LIPS | laser induced plasma spectroscopy |
| LLE | liquid–liquid extraction |
| LLLME | liquid–liquid–liquid microextraction |
| LOD | limit of detection |
| LOQ | limit of quantification |
| LPME | liquid phase microextraction |
| LREE | light rare earth element |
| LTE | local thermal equilibrium |
| MA | methylarsonic acid |
| MALDI | matrix-assisted laser desorption ionization |
| MALDI-TOF | matrix-assisted laser desorption ionization time-of-flight |
| MBT | monobutyltin |
| MC | multicollector |
| MC-ICP-MS | multicollector inductively coupled plasma mass spectrometry |
| MCN | microconcentric nebuliser |
| MDL | method detection limit |
| Me2Hg | dimethyl mercury |
| MeSeCys | methylselenocysteine |
| MeHg | methyl mercury |
| MIP | microwave induced plasma |
| MIP-AES | microwave induced plasma atomic emission spectrometry |
| MMA | monomethylarsonic acid |
| MMAv | monomethylarsinic acid |
| MMDTAv | monomethyldithioarsinic acid |
| MMSe | monomethylselenium |
| MMT | monomethyltin |
| MMTAv | monomethylthioarsinic acid |
| MOctT | monooctyltin |
| MOCVD | metal organic chemical vapour deposition |
| MPhT | monophenyltin |
| MPT | microwave plasma torch |
| MRI | magnetic resonance imaging |
| MS | mass spectrometry |
| MSFIA | multi-syringe flow injection analysis |
| MS/MS | tandem mass spectrometry |
| m/z | mass to charge ratio |
| NAA | neutron activation analysis |
| NASA | National Aeronautics and Space Administration |
| Nd:YAG | neodymium doped:yttrium aluminum garnet |
| ne | electron number density |
| NIES | National Institute for Environmental Studies |
| NIOSH | National Institute of Occupational Safety and Health |
| NIST | National Institute of Standards and Technology |
| NMR | nuclear magnetic resonance |
| NRCC | National Research Council of Canada |
| ns | nano second |
| NTIMS | negative thermal ionisation mass spectrometry |
| od | outer diameter |
| OES | optical emission spectrometry |
| PAGE | polyacrylamide gel electrophoresis |
| PAR | 4-(2-pyridylazo)resorcinol |
| PB-HC-OES | particle beam hollow cathode optical emission spectrometry |
| PCA | principal component analysis |
| PCB | polychlorinated biphenyl |
| PCR | polymerase chain reaction |
| PDB | Pee Dee Belemnite |
| PDMS | polydimethylsiloxane |
| PEEK | polyetheretherketone |
| PET | polyethyleneterephthalate |
| PGE | platinum group element |
| PGM | platinum group metal |
| PhHg | phenylmercury |
| PLE | pressurised liquid extraction |
| PLS | partial least square |
| PLS-DA | partial least squares discriminant analysis |
| PMT | photomultiplier tube |
| ppb | parts per billion (10−9) |
| ppm | parts per million (10−6) |
| ppq | parts per quadrillion (10−15) |
| ppt | parts per trillion (10−12) |
| ps | pico second |
| PT | proficiency testing |
| PTFE | poly(tetrafluoroethylene) |
| PVC | poly(vinyl chloride) |
| PVD | physical vapour deposition |
| Q | quadrupole |
| QC | quality control |
| RDA | regularised discriminant analysis |
| REE | rare earth element |
| rf | radio frequency |
| RI | refractive index |
| RIMS | resonance ionization mass spectrometry |
| RM | reference material |
| RMM | relative molecular mass |
| rms | root mean square |
| RP | reversed phase |
| RSD | relative standard deviation |
| RSE | relative standard error |
| RSF | relative sensitivity factor |
| SARM | South African Reference Material |
| S/B | signal-to-background ratio |
| SD | standard deviation |
| SEC | size exclusion chromatography |
| SEM | scanning electron microscopy |
| SF | sector field |
| SFC | supercritical fluid chromatography |
| SF-ICP-MS | sector field inductively coupled plasma mass spectrometry |
| SF-MS | sector field mass spectrometry |
| SHRIMP | sensitive high mass resolution ion microprobe |
| SI | système international d'unités |
| SIMAAC | simultaneous multi-element analysis with a continuum source |
| SIMCA | soft independent modelling of class analogy |
| SIMS | secondary ion mass spectrometry |
| SIRMS | stable isotope ratio mass spectrometry |
| SLNL | Synchrotron Light National Laboratory |
| SMT | Standards, Measurement and Testing |
| S/N | signal-to-noise ratio |
| SPE | solid phase extraction |
| SPF | sun protection factor |
| SPME | solid phase microextraction |
| SRM | standard reference material |
| STP | standard temperature and pressure |
| STPF | stabilized temperature platform furnace |
| TBT | tributyltin |
| TD-GC-ICP-MS | thermal desorption gas chromatography inductively coupled plasma mass spectrometry |
| TD-GC-IR-MS | thermal desorption gas chromatography isotope ratio mass spectrometry |
| Te | electron temperature |
| TEL | tetraethyllead |
| Tgas | gas temperature |
| THF | tetrahydrofuran |
| THFA | transversely heated furnace atomiser |
| TIMS | thermal ionization mass spectrometry |
| Tion | ionization temperature |
| TLC | thin layer chromatography |
| TMA | tetramethylarsonium ion |
| TMAH | tetramethylammonium hydroxide |
| TMAO | trimethylarsine oxide |
| TML | tetramethyllead |
| TMT | trimethyltin |
| TOC | total organic carbon |
| TOF | time-of-flight |
| TOF-MS | time-of-flight mass spectrometry |
| TOF-SIMS | time-of-flight secondary ion mass spectrometry |
| TPhT | triphenyltin |
| TPrT | tripropyltin |
| TS | thermospray |
| uhf | ultra-high frequency |
| US | United States |
| USGS | United States Geological Survey |
| USN | ultrasonic nebuliser |
| USN-ICP-MS | ultrasonic nebulisation inductively coupled plasma mass spectrometry |
| UV | ultraviolet |
| UV-VIS | ultraviolet-visible spectrophometry |
| VG | vapour generation |
| VOC | volatile organic carbon |
| VPDB | Vienna Pee Dee Belemnite |
| VPD-DC | vapour phase decomposition droplet collection |
| v/v | volume per volume |
| WHO | World Health Organisation |
| w/v | weight per volume |
| XRD | X-ray diffraction |
| XRF | X-ray fluorescence |
| YAG | yttrium aluminium garnet |
| z | atomic number |
| ZAAS | Zeeman atomic absorption spectrometry |
| Ar | relative atomic mass |
| Mr | relative molecular mass |
| λ | wavelength (symbol lambda) |
| τ | pulse duration (symbol tau) |
| r | correlation coefficient |
| s | standard deviation of sample |
| σ | population standard deviation |
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