Atomic spectrometry update-X-ray fluorescence spectrometry

Contents

• 1 Introduction and reviews

• 2 Instrumentation
  • 2.1 General Instrumentation and excitation sources
  • 2.2 Detectors
  • 2.3 Spectrum analysis, matrix correction and calibration procedures
  • 2.4 X-ray optics and micro-fluorescence
  • 2.5 Synchrotron radiation
  • 2.6 TXRF
  • 2.7 Portable and mobile XRF
  • 2.8 On-line XRF

• 3 Applications
  • 3.1 Sample preparation and preconcentration techniques
  • 3.2 Geological
  • 3.3 Industrial minerals
  • 3.4 Environmental forensics
  • 3.5 Aerosols and particles
  • 3.6 Consequences of industrial activity
  • 3.7 Archaeological, cultural heritage and forensic
  • 3.8 Industrial
  • 3.9 Clinical
  • 3.10 Drugs
  • 3.11 Biological
  • 3.12 Thin films, coatings and nano-materials
  • 3.13 Chemical state and speciation

• Abbreviations

• References

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Abstract

This review offers the reader a wealth of information published between April 2010 and March 2011 concerning analytical endeavours using the range of conventional and hyphenated XRF techniques that encourage the user to ensure the potential for high spectral sensitivity and, where appropriate, spatial resolution is achieved. The development of advanced micro-beam set ups and new X-ray optics driven by third generation synchrotron based XRF techniques provide nano-imaging and the detection of nano-particles on single cells whilst TXRF coupled with GIXRF and GEXRF offer great potential for non-destructive investigations of thin layers on reflecting surfaces as well as depth profiling of implants. A new portable XRF system is described as an alternative for the traditionally applied K-X-ray fluorescence technology for in vivo measurements of lead in bone. Cryogenic cooling of heat sensitive biological samples is offered as a method to mitigate possible damage by the use of the more powerful μ-XRF technique. Other new preparation methods are also reviewed for the presentation and analysis of industrial, environmental and archaeological samples. One of the more unusual contributions available this year in the characterisation and use of industrial minerals showed that a semi-precious stone, amethyst, is more effective at shielding radiation than concrete.

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1 Introduction and reviews

This Update refers to papers published approximately between April 2010 and March 2011 and continues the series of Atomic Spectroscopy Updates in X-ray Fluorescence Spectrometry¹ that should be read in conjunction with other related reviews in the series.^2–6 A 25 year retrospective⁷ also described how atomic spectrometry has changed and how all the ASU reviews have developed with the passage of time. This year the XRF writing team offers a change in format to reflect the considerable developments in instrumentation that has lead to an increase in papers describing the ever expanding applications for the range of XRF techniques now available. The instrumentation section gives the reader an update on developments and innovations in XRF hardware and software whereas the applications section reflects XRF studies in existing and emerging fields of endeavour. Focused X-ray beams, X-ray optics and the spatially resolved characterisation of materials by μ-X-ray spectrometric techniques are now widely applied not only in large scale facilities but also in routine laboratory practice. A biennial review by Bedard and Linge⁸ also commented on the increase in the number of publications describing hyphenated XRF techniques including 3D μ-XRF for the investigation of sample heterogeneity. Block et al.⁹ described XRF mapping techniques to locate different chemical forms of sulfur in intact and damaged garlic and onion cells. Chainet et al.¹⁰ reviewed silicon speciation in environmental, biological and industrial matrices that has gained considerable importance due to its wide use in many consumer and personal care products. The writing team welcome feedback on this Update from readers via e-mail contact with the lead author.

2 Instrumentation

A few major trends were observed in the work published in the reviewed period, including development of advanced micro-beam set ups and new X-ray optics driven by synchrotron facilities.

2.1 General Instrumentation and excitation sources

The review year saw a resurgence of interest in the construction of a new type of X-ray tube described by Jyouzuka.¹¹ The design used novel materials for constructing heavy-duty X-ray tubes, in particular graphite nanospines which were encapsulated in the X-ray tube anode. The performance of the new tube was tested showing no degradation in the anode current after 100 h of continuous operation. The authors presented two applications of the new tube, namely: radiography and XRF analysis. More X-ray sources were discussed in two overview articles, one by Thomsen and Coutinho,¹² part II of a series of articles, on a general use of X-ray sources and the other by Economou¹³ summarising the use of radioactive sources in analytical instruments dedicated to planetary exploration. In the latter report, already accomplished, current and further space missions were discussed, and the topics covered included alpha proton X-ray Spectrometry radioisotope excited XRF spectrometry, Mössbauer spectrometry, as well as the use of ²³⁸Pu for power and heat generation. In another work related to planetary exploration, Blumers et al.¹⁴ described a new, miniaturised, combined Mössbauer/XRF spectrometer which was an improved version of the spectrometers found on-board the two Mars Exploration Rovers. The new spectrometer design utilised a silicon drift detector and incorporated new features and technological improvements.

In μ-SRXRF analysis an energy-dispersive detector is used for spectrum collection because it is efficient and fast. However, this method lacks energy resolution as compared with wavelength dispersive spectrometers. Szlachetko et al.¹⁵ reported the development of a WDXRF spectrometer for μ-XRF at ID 21 beamline, ESRF, Grenoble. The spectrometer was based on a polycapillary optic for the fluorescence collection and was operated in a flat crystal geometry. The achieved performance, in particular the energy resolution, was compared with that obtained by Monte-Carlo simulations. Further improvements were gained by using a double-crystal spectrometer. The main goal was to develop a system for characterising the samples where both spatial and spectral resolutions are of primary importance.

Advances were also made in construction of specialised laboratory instruments. Ingerle et al.¹⁶ proposed the use of grazing incidence XRF technique (GIXRF) to complement the results of SIMS used for depth profiling and characterisation of ultra-shallow junctions. A dedicated GIXRF instrument was constructed and tested for the characterisation of arsenic implants and Hf-based k-layers on silicon. In another report dedicated to materials research, Levy et al.¹⁷ presented a newly constructed XANES spectrometer combined with an ultra-fast laser-induced X-ray source dedicated to dynamic studies of Al and K absorption edges. A spectral resolution of 0.7 eV with fluctuations less than 1% rms were reported. Dicken et al.¹⁸ introduced a novel diffraction pattern detection technology that will be of interest in structural research studies. Their system was able to resolve diffraction patterns originating from different overlapping materials along the primary X-ray beam path. The authors predicted that the new technology could become very useful for rapid screening for illicit drugs distributed through the postal system. An advanced SRXRD instrument utilising a diamond-anvil cell heated by a pulsed laser beam was established by Goncharov et al.¹⁹ This instrument enabled time domain measurements to be made with a controlled temperature of up to 3000 K, by introducing a new and convenient method of maximum temperature fine tuning that involved changing the width of the laser pulse. Yet another new and significant development, this time in digital signal processing electronics, was reported by Clayton et al.²⁰ In their approach to pulse processing, the shaped and digitised waveform signal from a specialised Si-based X-ray detector was analysed by fitting with Gaussian functions in order to resolve pile-up events with good throughput and energy resolution. This signal processing system was used to measure Bremsstrahlung photons for plasma diagnostic purposes at the Madison Symmetric Torus, University of Wisconsin-Madison, Wisconsin, USA.

The efforts of scientists continued towards advancing existing or designing new instruments with conceptually new or seldom used but efficient analytical approaches. Two groups applied the known but rarely used concept of gamma-ray induced X-ray emission. The method was employed by Zhang et al.²¹ for the isotopic analysis of uranium using coincidence measurements of the gamma ray and X-ray fluorescence signals. The coincidence measurements were performed with two NaI(Tl) scintillator counters. The method enabled convenient “graphical fingerprinting” of ²³⁵U enrichment with possible application for the rapid isotopic verification of various nuclear materials based on a spectral fingerprint library. In similar research, Oh and Lee²² used gamma-rays emitted by a ⁵⁷Co source for the direct induction of X-ray fluorescence radiation. With this method, they obtained 2D maps of mixed materials with very high sensitivity. A new approach to high-resolution chemical imaging was proposed by Marcus,²³ who reported the basic ideas of X-ray chemical imaging with a sub-micrometre spatial resolution by using the so-called “photon-in/photon-out” approach. The details along with some examples were given in this work.

2.2 Detectors

In an excellent review of the development of thermoelectrically-cooled silicon PIN and Drift X-ray detectors, Pantazis and colleagues²⁴ used as an example a series of instruments produced by a commercial manufacturer to demonstrate the pivotal role that such detectors, along with low-power compact X-ray sources, played in enabling modern hand-held XRF systems to deliver analytical performance that has driven the dramatic growth in usage of this category of instrument in the past decade. The authors described the key developments in detector sensor chips, electronics and cooling technologies that delivered improvements in energy resolution from the original 1991 Si PIN prototype of around 850 eV at 5.9 keV through the 250 eV Si PIN model that drove the original growth in use to the modern SDD routinely delivering 135 eV. The 11th European Symposium on Semiconductor Detectors held at Wildbad Kreuth, Germany, in 2009 provided a valuable update on silicon drift detectors (SDD). In the first paper from that Symposium, Schlosser et al.,²⁵ described recent work aimed at improving detection efficiency of SDDs. New sensor entrance window technologies were reported that not only yielded high efficiency for low energy X-ray lines but also improved peak-to-background ratios and peak shape such that the effective detection of boron K lines was readily achieved. Thicker SDD chips were also reported, where the original thickness of 300 μm was increased to 500 μm or even 1 mm to improve stopping power for the higher energy K-line series. A number of larger area sensors and sensors with customised geometry were also described in which the solid angle of detection was substantially increased for specific applications. The specific use and advantages of large area SDDs were also reported by Bazzi et al.,²⁶ who deployed them for the high precision detection of low intensity kaonic ⁴He X-rays in the presence of very high background produced in the exotic, high energy physics collider experiment. The custom-made SDDs were each of 150 mm² active area and delivered an energy resolution of around 150 eV at 5.9 keV when cooled to 170 K. Three such detectors were arranged into a cell and 144 such cells were used in the experiment, which is surely a record both for the number of SDDs used in a single system and for the overall complexity of signal processing and timing. Of particular note by the authors was the first use of SDD in a collider and the excellent and robust performance in this rather extreme environment. In the second paper from the Wildbad Kreuth Symposium, Treis and co-workers²⁷ described very early results on a prototype SDD coupled with a DEPFET readout for use as an energy dispersive imaging detector for the MIXS instrument on the BepiColombo Mercury orbiter mission. This novel pixellated device was specified to deliver <250 eV energy resolution at 1 keV, an energy range of 0.05 to 10 keV and a pixel size of 300 × 300 μm² and to operate in the challenging thermal environment that will be experienced so close to the Sun. Early results from a device with 500 × 500 μm² pixel size readout were very promising and the device was able to operate at the very high count rates needed. An interesting multiple ring silicon-based 1D X-ray detector, which was not an SDD, was described by De Lurgio et al.²⁸ for use in small angle X-ray scattering experiments on the APS SR instrument at the Argonne National Laboratory. The large format device was fabricated on a 500 μm thick by 150 mm diameter high purity silicon wafer and comprised 128 concentric rings, each of which was connected to its own amplifier chain and a 12-bit, 20 MHz ADC allowing full parallel processing with a very impressive frame rate of 271 kHz. Although not designed specifically as an XRF detector, its energy range of 3.5 to 13.2 keV with 80% efficiency and interesting geometry and count rate performance could find use as a 1D energy-dispersive detector for WDXRF applications in similar SR instrumentation.

The use of position sensitive or pixellated X-ray detectors in a variety of imaging and high energy physics experiments was notable during the review period. However, there was little of real note in these publications for laboratory-scale XRF instrumentation. An interesting 2D position-sensitive monolithic Si(Li) detector was described in detail by Weber and co-workers,²⁹ who used the detector system for Compton X-ray polarimetry in a high energy atom-ion collision experiment on the ESR storage ring at GSI, Darmstadt. The novel Si(Li) detector was fabricated as a single detector of size 80 × 80 mm² and 7 mm thick that was then segmented into 32 strips of 2 mm width, separated by 50 μm grooves. The front and back-side grooves were perpendicular to each other, resulting in an effective array of 1024 “pseudo” pixels. Each of the strips was read out independently and an energy resolution of 2.5 keV at 100 keV was obtained at liquid nitrogen temperatures, in conjunction with a time resolution of around 100 ns. This unique and exotic Si(Li) detector is interesting and valuable for specific higher energy, exotic X-ray experiments but offers no direct benefits that could be applied to laboratory XRF imaging. A 2D array of silicon photodiode detectors comprising 185 × 194 pixels each of 110 × 110 μm² that was bump-bonded to an ASIC custom readout chip was described³⁰ as a precursor to the impressive full 1516 × 1516 pixel array being prepared for XRD studies at the X-ray Free Electron Laser facility at SLAC, Stanford, USA. Of particular note was the extremely high flux of 10¹⁷ photons sec⁻¹ pixel⁻¹ up to which the sensors needed to operate and any measures to improve the radiation hardness of the photodiodes that may prove useful for other silicon-based sensors. An ASIC 32-channel readout system³¹ designed for pixellated array detectors made from cadmium telluride (CdTe) or cadmium zinc telluride (CZT) and for use in medical X-ray systems may be of use in some industrial applications of X-ray absorption imaging where rates above 1 Mcps pixel⁻¹ are experienced but are unlikely to lead to the adoption of CdTe arrays for more general XRF imaging. A large, 1 × 5 cm², massively parallel, 96-element pixellated X-ray detector was also described by Etschmann et al.³² for direct, X-ray imaging of XANES and XAS at a micrometre-scale spatial resolution in an SR beamline. Again, such a device has little benefit for XRF but may be of some interest for energy dispersive XRD applications. Staying with SRXRD detectors, Aulchenko et al.³³ reviewed a series of multi-wire and micro-patterned high speed and high resolution gas proportional X-ray detectors capable of 10⁶ to 10¹⁰ cps and spatial resolution of 0.1 mm. Finally, a micropattern gas detector based on a new design combining Micro-Hole and Strip-Plate technologies was described by Veloso et al.³⁴ in which two-stage avalanche occurred in both the structures. The top and bottom surfaces of the anode strips of the detector were designed in an orthogonal arrangement, thereby providing a spatial resolution of around 125 μm, This interesting new detector had an attractive active area of 25 × 25 mm² and countrate of 500 kcps but a disappointing energy resolution of 850 eV at 5.9 keV, making it unattractive in practice for the target application of XRF imaging.

The review period saw a little activity in the area of cadmium telluride (CdTe) and cadmium zinc telluride (CZT) X-ray detectors with one particularly interesting publication³⁵ on the use of the audio input (microphone) channel in a standard personal computer for direct signal processing of the output from a commercially available CdTe detector. The preamplifier output was connected directly to the sound card ADC input and the recorded audio file was then processed by taking the first derivative of the signal and then performing a pulse height analysis of the resulting data. Results for an X-ray spectrum from a radium radioisotope source showed an energy resolution for the Bi Kα peak of 5.6 keV with the audio capture and processing compared to 5.3 keV when using a conventional shaping amplifier and MCA. Similar results were obtained for the K series of Dy and the authors concluded that not only was this simple approach suitable for CdTe X-ray detectors but that it could also be applied to other electronic signals. The powerful combination for PIXE X-ray spectrometry of a CdTe detector and a microcalorimeter was reported by Chavez and co-workers.³⁶ The high detection efficiency of the CdTe detector over the range 4 to 120 keV combined with its adequate energy resolution for the K lines in these higher energy regions was particularly well suited for many PIXE applications. However, the limited energy resolution below 20 keV presented a challenge for complex materials or where there were strong overlaps at lower energies. The authors chose perhaps the ultimate solution to this problem by incorporating in conjunction with the CdTe detector, a Polaris microcalorimeter X-ray detector to cover the energy range from a few eV up to 20 keV or so. The energy resolution of this cryogenic detector was an excellent 15 eV at 1.486 eV and only 24 eV at 10.55 keV. This unique combination of detectors provided important new data on the elemental ratios in Tb-Co-Fe thin films. In further, non-XRF reports, the potential advantages to be gained through the use of CdTe and CZT X-ray detectors were described for spectral CT³⁷ and direct monitoring of the operating kV of diagnostic X-ray tubes.³⁸ Finally, Prokesch et al.³⁹ described a technique that could lead to the reduction in the concentration of active hole traps in CZT detectors and result in much improved peak shapes and a faster response when used in high flux applications.

Notwithstanding the paper cited above in which a CdTe and a microcalorimeter were used for PIXE analysis, the activity in the field of cryogenic detectors was very low in the review period. In the single report available for review, the NIST transition edge sensor cryogenic detector with a claimed excellent energy resolution around 7 eV at a count rate of 130 cps was used to determine the relative line ratios of satellite lines in the K X-ray spectra of Al and Mg from a multielement glass sample excited by 12 keV electrons. As a result of this careful study, the authors showed that the Al K satellite intensity ratios were closer to those in metals than in oxides and they recommended the use of the high resolution X-ray detector for further in situ studies into the valence bonding of element.

Finally, the persistent team at Coimbra⁴⁰ reported a new variant of their Gas Proportional Scintillation Counter (GPSC) that incorporated a tertiary scintillation stage and resulted in a high and very stable gain. Early results from this new version of the GPSC showed an energy resolution of 8.2% at 22.1 keV, making it slightly worse than previous GPSC detectors but substantially better than conventional xenon-filled gas proportional detectors at this energy. That said, the relative operational complexity and bulk of the described device do not make it a compelling, practical or general EDXRF detector.

2.3 Spectrum analysis, matrix correction and calibration procedures

A large number of reports were devoted to the determination of fundamental parameters and the theoretical relationship between measured X-ray intensities and the concentrations of elements in a sample. Lα, Lβ, and total L-shell X-ray production cross-sections for Ag, Cd, I, In, Mo, Nb, Sb, Sn and Zr for photon energy 5.96 keV were determined experimentally by Han et al.⁴¹ The values obtained were in good agreement with those calculated using published data. Bennal et al.⁴² determined the K–L vacancy transfer probabilities for selected elements in the atomic range 42 ≤ Z ≤ 82 by using gamma ⁵⁷Co source excitation, also reporting good agreement with literature data. Mass absorption coefficients of selected semiconductor materials and biological matrices were determined experimentally at different X-ray energies by Ekinci et al.⁴³ Cengiz et al.⁴⁴ determined L-shell X-ray production cross-sections, fluorescence yields, and vacancy transfer probabilities for selected heavy elements by using ²⁴¹Am excitation. In another report by Cengiz and co-workers⁴⁵ K-shell X-ray production cross-sections, fluorescence yields, K–L shell vacancy transfer probabilities, and the natural line widths of selected heavy elements from the range 73 ≤ Z ≤ 81 were measured. Sidhu et al.,⁴⁶ determined the K-shell jump ratios for As, Co, Cu, Fe, Mn, Sr and Zn by utilising ²⁴¹Am excitation and a well-defined set of targets. In a similar direct empirical approach, Kahoul et al.⁴⁷ determined K-shell fluorescence yields for elements in the range 6 ≤ Z ≤99. Maillard et al.⁴⁸ employed high-resolution WDXRF spectrometry to estimate the natural level widths of K to N₅ and O₁ subshells and core binding energies of K to M₅ and O₁ subshells of liquid mercury with good accuracy and precision. Practical research was undertaken by Bansal and Mittal,⁴⁹ who developed a computer code for generating K-shell photoionisation cross-sections for elements in the range 5 ≤ Z ≤ 95 at photon energies up to 1500 keV. The code can be obtained from the authors upon request. Pursuing similar research on the experimental evaluation of X-ray interactions with matter, Sharanabasappa et al.⁵⁰ published a detailed study on the optimisation of measuring conditions for the precise estimation of mass-absorption coefficients of selected elements for three biological equivalent materials. They found that an optimum value of the transmission factor for this type of measurement lay in the range 0.02 ≤ T ≤ 0.5.

A smaller number of reports were devoted to chemo-physical effects in X-ray spectrometric data. Sogut⁵¹ observed variations in K-shell fluorescence yields of pure Ag, Ba, Cd, Ce, Co, Cr, Cu, Fe, La, Mn, Mo, Ni, and Zn, and compared the values obtained for their compound forms. The influence of heat annealing treatment on the Kβ/Kα ratios of 3d transition metals was observed by Han and Demir⁵² opening a possibility for quantitative use of the ratio to discriminate between thermally annealed and unannealed alloys of these elements. The same authors observed the alloying effect on K–L vacancy transfer probabilities in 3d transition metals.⁵³ The effect can be used for the quantitative determination of alloy composition. The influence of alloying effects was also reported by Aylikci et al.⁵⁴ in research on the K-series peak ratios of Al, Mo, and Ni excited using ²⁴¹Am radioisotope source. Cengiz et al.⁵⁵ studied the influence of chemical effects on the K- and L-series X-ray peak ratios in gold compounds. A good agreement with other results obtained from existing literature was observed.

In more fundamental research, Sharma and Mittal⁵⁶ observed angular anisotropy of the L-series characteristic X-rays emission from a tungsten target. The experimentally determined anisotropy was larger than the effect predicted theoretically using the non-relativistic dipole approximation in a point Coulomb field. In research that can also be regarded as fundamental, Vlasenko et al.⁵⁷ developed a theoretical quantum model to predict and interpret C-Kα, Mn-Lα, Mn-Kβ, and O-Kα XRF spectra emitted by dimeric manganese carbonyl. The predicted X-ray spectra were in good agreement with the experiment. Hayashi⁵⁸ developed a computer code for simulating resonant inelastic X-ray scattering spectra to derive theoretical XAFS profiles that reproduced the experimental data. Postavaru et al.⁵⁹ demonstrated the use of X-ray fluorescence spectra of highly charged relativistic ions in investigating atomic properties with extreme accuracy. The phenomenon of optical emission predominantly in the UV, which accompanies the emission of X-rays, gamma rays, and beta radiation from radioisotope sources and X-ray tubes was investigated by Rao.⁶⁰ It was the first work in which the emission of UV radiation was confirmed experimentally and a possible explanation for the mechanism of the UV emission was given by the author.

Despite many years of research and our deep understanding of X-ray interactions with matter, each year there are significant numbers of reports published dealing with the development of models and simulations of yet more aspects of these phenomena. Thus, Delgado⁶¹ took a different approach to the Sherman equation, treating, in a mathematically specific way, the problem of XRF excitation by a polychromatic source in a multielement target and concluded that only one physically acceptable solution of the problem existed. Li et al.⁶² proposed exponential and logarithm fitting equations for correcting interference effects in binary Ni–Cu, Ni–Zn, and Cu–Zn systems. The results were compared with binary influence coefficients calculated by using the Lachance-Trail algorithm and with corrections obtained by direct measurements. Four per cent accuracy was achieved with the fitting methods. Not a new, but an effective approach was used for the characterisation of X-ray tube spectra,⁶³ namely by measurements of the primary spectra scattered from a low-Z acrylic target. The accuracy of the approximation was confirmed by comparing the experimentally measured Pb-Lα/Pb-Lβ ratios with the ones obtained by applying a theoretical model employing the approximated X-ray tube spectrum. In another work on modelling X-ray tube spectra, Tirao et al.⁶⁴ developed a Monte-Carlo model dedicated to the simulation of Bremsstrahlung X-ray spectra generated by conventional X-ray tubes. The code was validated using experimental data. The results demonstrated a strong angular anisotropy of Bremsstrahlung radiation and this computer code can be used for educational purposes to perform virtual imaging. A computer model was also developed by Campbell et al.⁶⁵ to deal with the fitting of X-ray emission spectra and was based on the GUPIX approach (a software package for fitting PIXE spectra). The code was applied to fitting the X-ray spectra excited by a combined XRF/PIXE instrument installed on the Mars Exploration Rovers. Basic features of the proposed method were demonstrated using spectra originally calibrated from the MER mission. In a report concerning a similar area of planetary research, Banerjee and Vadawale⁶⁶ undertook a theoretical investigation into the possibility of detecting the surface emission of X-ray fluorescence of selected elements, induced by solar radiation, from a lunar orbit. The developed model could be applied for determining the abundances of Al, Fe, Mg, Si and Ti by analysing X-ray spectra collected during recent and future lunar missions. In a more practical application, Ogawa et al.⁶⁷ investigated the effect of X-ray filters placed in the primary beam path on the detection limits of elements by using a theoretical model validated with empirical data. The elaborated methodology proved useful for selecting an optimal filter for the determination of a given set of elements in specific types of sample. Aiming at achieving better accuracy, Elam et al.⁶⁸ proposed a new method of quantitative analysis by μ-XRF by combining X-ray peak intensities emitted by the same sample under different excitation conditions into a common fundamental parameter model. The method produced more accurate results for all investigated elements when compared to a model employing single excitation conditions. In a work which is of interest to analysts performing in situ element determination using portable equipment in conjunction with minimum samples preparation, i.e. valuable objects, Bertucci et al.⁶⁹ developed a method for calculating absorption correction factors and the thickness of pigment layers. In the case of thin layers, the method could also be used to calculate the pigment dilution ratio. The in vivo determination of Pb is a well established and approved method for the monitoring of workers exposed to this element. This method is usually operated close to the detection limit where measurement uncertainty is rather large. However Lamadrid-Figuero et al.⁷⁰ applied errors-in-variables regression models for reducing the bias caused by such measurement errors. The author demonstrated that the ordinary least-square methods produced strongly biased results, whereas the errors-in-variables model provided estimates of the Pb concentration with a significantly reduced bias. Another difficult analytical problem was tackled by Sun et al.⁷¹ who presented a method for the determination of element concentrations in single aerosol particles in which the diameter of the analysed particles was less than the beam spot diameter. The elemental sensitivities were modelled using a Gaussian function that corrected the effects of the polycapillary optics used in the detection channel.

Some really difficult problems cannot be solved analytically. In some cases it is more convenient, even if the analytical solution can be found, to approach the problem by numerical simulations. Such computer models can be a really useful tool when developing new instruments, predicting magnitudes of various effects, or even for solving real problems in chemo-physical analysis. In the current review period several reports addressed this area of research. Berlizoy et al.⁷² developed and experimentally validated a Monte-Carlo approach for simulating a hybrid K-edge/K-XRF densitometer instrument. The method could be used to minimise the effort in calibration in cases where such instruments were applied to the analysis of non-standard samples and in improving the accuracy of measurements. Hodoroaba et al.⁷³ elaborated an analytical, as well as a Monte-Carlo model of X-ray scattering based on systematic measurements carried out using SEM with an X-ray tube attachment. They used the model for predicting detection limits of elements and for determining the transmission probability of polycapillary X-ray lenses. Monte-Carlo simulations were used by Trojek et al.⁷⁴ to estimate the magnitudes of various surface- and measuring geometry-related interfering effects occurring during in situ XRF and μ-XRF analysis. The results facilitated the optimisation of the in situ measurements. Directed towards structural and imaging applications of X-rays, Happo et al.⁷⁵ proposed a new algorithm, based on the use of the Fourier transform, for separating the normal and inverse mode data from a mixed-mode hologram obtained by XRF holography. The algorithm efficiently removed normal mode interferences (spots) from the mixed-mode data, producing clear and properly reconstructed images of atomic positions. In an effort also devoted to improve X-ray imaging techniques, Miqueles and De Pierro⁷⁶ proposed a new method for XRF computed tomography based on the iterative use of a Radon transform. They iterated the solutions of the inverse Radon transform refining, at each step, the attenuation map of the sample using the emission data. The new method produced better images when compared to existing algorithms and was also much faster than arithmetic reconstruction methods.

The last but not least report cited in this section is that by a single author Il'in,⁷⁷ who postulated a rather revolutionary thesis that the past and present literature expressions that relate X-ray peak intensities to weight percentages of elements were based on completely the wrong concepts of density and Avogadro's constant and that instead X-ray peak intensity should be related to the elemental atomic percentages. By using existing published data, Il'in demonstrated in this report that the change from weight to atomic ratios resulted in much simpler formulas, a more linear behaviour of intensity versus the atomic concentration of an element, and even in some cases, in the absence of matrix effects. Your reviewer's curiosity being aroused, there will certainly be a follow up discussion-perhaps in our next review.

2.4 X-ray optics and micro-fluorescence

Focused X-ray beams, X-ray optics and the spatially resolved characterisation of materials by μ-X-ray spectrometric techniques are nowadays routinely applied not only in large scale facilities but also in routine laboratory practice. Still, there are many advances in this area of X-ray spectrometry being published. A good review of the status quo and recent advances in μ-XRF spectrometry was published by Janssens et al.⁷⁸ The work presented the development of instrumentation, calibration methods and gave a reliable comparison of the performance of the technique versus other micro-analytical methods. In another work, Gholap et al.⁷⁹ also compared the performance of elemental mapping of thin biological tissue cross-sections by μ-XRF spectrometry versus mapping by LA-ICP-MS. They concluded that μ-XRF was superior to LA-ICP-MS for mapping of sulfur whereas the latter was particularly sensitive for Zn, for which element the detection limit by μ-XRF was insufficient. Thus, both techniques were considered complementary. In a work by Patterson et al.⁸⁰ two X-ray based mapping techniques were put to test, namely the μ-X-ray computed tomography (CT) and confocal μ-XRF technique. A computer software programme “MATLAB” was developed for rendering data sets obtained by the two methods, yielding a volumetric image of a surface-mounted integrated circuit. The weaknesses and similarities of the two techniques were summarised in the report. Yet another comparative study was performed by an international team of scientists lead by Jimenez-Ramos.⁸¹ They compared the performance of synchrotron-based confocal μ-XRF technique with the nuclear micro-probe (PIXE) applied to the determination of Pu and U in individual grains of nuclear weapon-grade material originating from nuclear accident sites. Results obtained by both techniques showed very good agreement and were essential for assessing the long-term impact on the contaminated sites.

A significant number of articles dealt with development of specialised optics, construction of new instruments and advancement of existing apparatus with a majority of reports coming from synchrotron facilities. To advance the development of optics, as well as to determine the spectrometric properties of manufactured lenses, reliable and routine procedures were required. Such procedures for the characterisation of polycapillary X-ray half-lenses were proposed by Rackwitz et al.⁸² The method involved the use of an ED-SEM for the direct measurement of the lens transmission function, focal distance and full width at half maximum.

A couple of new optical devices and complete instruments were constructed. New tandem zone-plate optics capable of focusing hard X-rays (30 keV) was developed and tested by Kagoshima et al.⁸³ The tandem optics produced a 2.4 higher flux density as compared with a single zone-plate lens. These optics were used in a synchrotron μ-XRF facility for Sn mapping in float glass samples. Yamamura et al.⁸⁴ reported the fabrication of a doubly-curved crystal for a Johansson-type spectrometer produced by using numerically controlled wet etching. The reflectivity and the full width at half maximum (FWHM) of the rocking curve of the processed crystal surface were almost the same as those of the unprocessed one. Terada et al.⁸⁵ applied a long-working distance XRF microprobe, assembled at the 37XU Spring-8 beamline, for mapping of Cd in eggplant roots, thereby demonstrating the capability of the newly constructed instrument for heavy element mapping with micrometre spatial resolution. A description of a new, planned synchrotron nano-probe facility was presented by Schroer et al.⁸⁶ The XRF nano-probe at PETRA III, DESY, Hamburg, Germany will be based on a nano-focusing refractive X-ray lens. The facility was dedicated to elemental mapping, tomography and to coherent diffraction contrast measurements. The planned spatial resolution was approximately 50 nm with possible future improvement expected. Construction of a full-field imaging confocal XRF microscope at the 37UX Spring-8 synchrotron facility was reported by Takeuchi et al.⁸⁷ The microscope utilised a plane-like primary X-ray beam, irradiating a larger region of a sample. The X-ray fluorescence emission was received by a full-field X-ray microscope using a Fresnel zone plate and segmented (CCD-based) X-ray detector positioned at right angles to the primary beam. A 3D element distribution map was obtained from a single linear translation of the analysed object. A new, combined XRF/XAFS confocal instrument incorporating a diamond-anvil cell (DAC) was constructed by Wilke and collaborators.⁸⁸ In this set up, an X-ray half-lens with a very-long working distance effectively suppressed the unwanted scattering and fluorescence signals resulting from the interaction of the synchrotron beam with the body of the DAC.

In many applications of the μ-XRF technique, heat sensitive biological samples are prone to radiation damage during analysis. Matsuyama et al.⁸⁹ suggested cryogenic cooling of samples as a method to mitigate possible damage by the use of frozen-hydrated cells prepared by quick-freezing. Scans to visualise Ca, Cu, Fe, K, and Zn distributions with submicron resolution were obtained by a cryo-scanning X-ray nano-probe developed at the BL29XUL, SPring-8 synchrotron facility. Differences were observed between the results obtained using the frozen-hydrated cells and cells fixed with paraformaldehyde. With a similar aim, De Samber et al.⁹⁰ explored the capabilities of a synchrotron-based μ-XRF instrument equipped with a dual X-ray detector for the 2D mapping of elements in chemically fixed and cryogenically stabilised samples of Daphnia magna. This work also illustrated the potential of coupling a dual detector XRF cryo-measurements with a laboratory X-ray tube based μ-CT set up.

Due to the rather high costs involved, the development of micro-beam instrumentation was dominated by the synchrotron facilities. Despite this trend, advanced instrument construction was also carried out in smaller laboratories. Analytical performance of already constructed, laboratory-scale, confocal μ-XRF spectrometer was tested and the results presented by Nakano and Tsuji.⁹¹ The authors determined the depth sensitivity of the analysis of layered polymer standard samples, produced by spin coating, and reviewed the applications of the confocal μ-XRF spectrometry for characterisation of plastics, chemical microchips and biological samples. In a recent work Tsuji and Nakano⁹² constructed a confocal μ-XRF spectrometer utilising a fine-focus X-ray tube. As compared with their previous instrument, the new one offered a spatial resolution that was 3 to 4 times better. In their report, the performance of the two systems was compared by measurements of layered samples and a custom-designed 3D-structured material. A new concept for a full-field imaging-elemental mapping spectrometer was proposed by Yonehara et al.⁹³ in which the element distribution image was collected by a pixelated X-ray detector with two polycapillary lenses inserted in the X-ray radiation path between the sample and the detector. One of the lenses was fixed to the detector. The detector with the fixed lens could be tilted relative to the axis of the first lens thus preventing higher energy photons from entering the detector, the cutting energy being determined by the tilt angle. The authors demonstrated that the system was capable of producing images and discriminating objects made from Cu and Fe. In another paper, Yonehara et al.⁹⁴ provided details of a newly constructed, transportable XRF spectrometer, with a total mass of about 2 kg, that utilised a polycapillary half-lens attached to an X-ray detector for collecting signal. In this way, a small, spatially resolved region (spatial resolution of about 171 micrometres) could be selected out of the larger area irradiated by a compact X-ray tube source. The system could perform single, local determination of elemental concentrations as well as elemental mapping using the built-in scanning mode. The attached lens could easily be interchanged, as in an optical microscope, to adapt the system's sensitivity and spatial resolution to the current application. Selected applications of the spectrometer were presented in the report. Smolek et al.⁹⁵ extended the analytical capabilities of a laboratory μ-XRF instrument for the measurement of low-Z elements, down to Z = 6. The system could operate under vacuum conditions and the performance was evaluated by measurements of standard samples. The low-Z mapping capability was tested by scanning a microscopic NaF laser print pattern. The most advanced laboratory system was constructed by Rouziere et al.⁹⁶ who combined in one instrument a μ-XRD/XRF spectrometer capable of elemental and structural mapping with a spatial resolution of about 20 μm.

In a report by Sun et al.⁹⁷ that partially focused on the characterisation of specialised polycapillary optics but also devoted to practical aspects of μ-XRF analysis, the authors successfully applied a special polycapillary lens, with a uniform intensity around the central part of the beam spot (21.3 micrometres diameter) for source apportionment of air particulate matter. Also in an applied work, Patterson et al.⁹⁸ used a recently constructed confocal μ-XRF set up for investigating the differences in copper content in the near surface regions around the circumference of sputtered copper-beryllium capsules. The method proved much more sensitive to the changes in copper content as compared with an X-ray absorption CT technique, easily revealing inhomogeneity of copper distribution within a capsule and between capsules.

2.5 Synchrotron radiation

The main developments in SRXRF this year were concerned with imaging, reducing the resolution to the nano-metre scale and the adoption of new detectors. Rack et al.⁹⁹ described the outstanding scientific value of resolved imaging with penetrating high-energy radiation. Bending magnets and insertion devices of third generation synchrotron light sources offered a polychromatic flux density which was high enough for performing hard X-ray imaging with a micrometre spatial and temporal resolution in the microsecond range. Existing indirect X-ray imaging detectors were adapted for fast image acquisition by employing commercially available CMOS based high-speed cameras. In this publication, a few selected applications from life science and materials research were presented to underline the large potential of the high-speed hard X-ray micro-imaging techniques. Taibi et al.¹⁰⁰ theoretically modelled edge-enhanced (phase-contrast enhanced) imaging with the use of a very broad band X-ray source spanning the energy range from single keV up to 6 MeV. They confirmed the theoretical predictions in an experiment by using a “table synchrotron” source to image thin aluminium objects and by numerical Monte Carlo simulations.

Various applications of 3D elemental imaging using confocal SRXRS were reported within the review period. During the spring meeting of the European Material Research Society, Trushin et al.¹⁰¹ presented studies of the interaction between different impurities in intentionally contaminated block-cast multi-crystalline silicon by means of synchrotron-based microprobe techniques, such as XBIC (X-ray beam induced current), μ-SRXRF and μ-XAS installed at beamlines ID-21 and ID-22 of ESRF, Grenoble. It was found that Si₃N₄/SiC particles frequently observed in the upper part of multi-crystalline silicon blocks represented effective sinks for iron and copper impurities. The amount of precipitated iron was in the same order of magnitude for both nitride and carbide particles. The amount of copper precipitated at the SiC inclusions was significantly larger than that at Si₃N₄ rods. The state of copper was identified as copper-rich silicide Cu₃Si. Annealing at 950 °C enhanced the formation of nano-scale iron disilicide precipitates, both inside and at the grain boundaries. Bleuet et al.¹⁰² have shown the essential importance of chemical imaging, which in addition to the morphological information given by tomography, yielded a full 3D image of the elemental distribution within a sample and can be performed using the brilliant beams from third generation synchrotron sources. Their review highlighted synchrotron XRF tomography as a technique yielding spatial information by reconstructing the quantitative elemental distribution within samples down to sub-micrometre scale. Several applications were presented illustrating the power and importance of this method. Kashiv et al.¹⁰³ used SRXRF to measure trace element abundance in single presolar SiC grains. The authors determined the abundance of Zr and Nb in SiC size-separated grains that were most likely from carbon-rich main stream grains. Comparison of the data with s-process calculations suggested that the relatively short-lived isotope ⁹³Zr with a half-life T_1/2 of 1.5 million years condensed into the grains. The Nb/Zr ratios in the majority of the grains were higher than those predicted by the s-process, probably due to grains condensing from stellar gas that was depleted in zirconium but not in niobium. Still there remained the possibility of grain contamination with niobium that originated from the solar system. Upper limits on the initial ⁹³Zr/Zr ratios in the grains agreed with the ratios observed in late-type S stars. At the Shanghai Synchrotron facility, a study on metal inclusions distribution in fused silica with variations induced by UV laser pulses was carried out by Li et al.¹⁰⁴ The metal inclusions play an important role in laser induced damage for large fused silica optics. The spatial distributions of Al, Cu, Fe and Na were analysed by μ-SRXRF. The laser pulsed at a wavelength of 355 nm irradiated the fused silica samples followed by elemental mapping of the samples with up to 50μm spatial resolution. The obtained results indicated that the distribution of metals was closely associated with the fluence of laser pulses. Among the four elements Fe concentration had the most destructive effect on the optics lifetime, especially under high fluence irradiation.

The certification of reference materials is of great interest to the analytical community A group from the German Federal Institute for Material Research and Testing (BAM)¹⁰⁵ demonstrated how EDXRF, which was excluded until now from the final certification scheme, could be adopted by using energy dispersive SRXRF. It was shown that all the risks, such as the occurrence of strong peak interferences, and uncertainty in background subtraction, were no longer a reason for exclusion of this technique. Aided by synchrotron radiation and a combination of pure elements and stoichiometric compounds as comparator materials, all arguments against the EDXRF technique were eliminated, opening the doors for the use of this technique in the process of reference material certification. The measurements were performed at the hard X-ray beam line of the BAM, BESSY II facility, in Berlin.

2.6 TXRF

Meirer et al.¹⁰⁶ reviewed the results achieved with SR-TXRF where detection limits in the fg range for most elements could be achieved. In addition to measurements of analytical concentrations, SR-TXRF could provide additional information about the chemical state of elements by XANES. The authors gave a brief introduction of the method and a presentation of the XANES results by SR-TXRF in applications of industrial and environmental samples.

TXRF instrumentation appears to have reached a mature status as there were only two papers found within the review period dealing with instrumental developments. An exceptional design of a portable TXRF spectrometer fitting in a small aluminium suitcase was described by Kunimura et al.¹⁰⁷ using a low power 1W X-ray tube operated at 20 kV. Extreme short optical paths were realised as no monochromator was used and thus using the full polychromatic emission spectrum of this tube, extrapolated detection limits of 26 ng were achieved for cobalt. Sanchez et al.¹⁰⁸ studied the use of a monolithic polycapillary half lens to produce a near parallel X-ray beam for TXRF experiments. Recorded spectra showed an excellent signal-to-noise ratio with a low background, but lack of intensity in the fluorescent signal. This could be explained by losses inside the thin walls of the polycapillary X-ray optic, i.e., high energy cut off and low energy absorption in air due to the longer path to the sample. Nevertheless the detection limits were better than in conventional XRF. The authors suggest that further improvements in detection limits could be achieved by employing non-symmetrical polycapillaries.

Surface analysis was not a booming application of TXRF in this review period, as judged by the number of available publications. However, Takahara et al.¹⁰⁹ reported the work of ISO Technical Committee 201/Working Group 2 (ISO/TC201/WG2) that had been investigating the vapour phase treatment (VPT) method to determine 10⁹ atoms cm⁻² level of metallic contamination on silicon wafer surfaces. The VPT method involves the pre-treatment of the wafer surface with hydrofluoric acid vapour and is used to raise the sensitivity of TXRF. Although VPT could enhance the TXRF signal intensity from metallic contamination, it was found that the magnitude of the enhancement varied with the process conditions. Observations of the wafer surface by SEM and AFM showed that particles with a diameter of about 4 μm were formed and were unexpectedly dented from the top surface level. The TXRF technique was applied for investigating the sputtering of germanium targets by argon and nitrogen ions.¹¹⁰ The sputtered germanium was collected on silicon wafers which were subsequently examined by TXRF. The results obtained from TXRF measurements enabled fine tuning the model of ion penetration into the germanium target resulting in greater agreement between the model and experiments.

Two TXRF papers were applied to the analysis of low atomic number elements. Tarsoly et al.¹¹¹ studied the possibilities of determining the low Z elements from C to P by TXRF. In particular, the analytical performance of a TXRF spectrometer designed by the Atominstitut Vienna and equipped with a vacuum chamber, Cr-anode tube, multilayer monochromator and a SDD with an ultra thin window was investigated. The authors presented detection limits for F of 5 mg L⁻¹ equivalent to 10 ng absolute. Tests showed that the concentration range was linear between 15 and 500 mg L⁻¹ with a precision below 10%. Misra et al.¹¹² reported the determination of low Z elements at trace levels in a uranium matrix. Synthetic samples were prepared by mixing different volumes of low Z element solutions with a high purity uranium solution, to represent trace element concentrations of 100–300 μg g⁻¹ with respect to solid uranium. The analysis was undertaken with the same instrument described in the previous reference. An average deviation of 14% from the calculated concentrations of these low Z elements was achieved and showed that this TXRF spectrometer design offered promising performance for the determination of trace elements in uranium, thereby avoiding the need for a chemical separation. Dhara et al.¹¹³ also applied the TXRF technique for the determination of trace amounts of cadmium in a uranium matrix. A simple linear calibration between the Cd-Ka intensity and cadmium concentration was used, enabling determination of Cd with 2% precision and accuracy better than 4%.

Techniques related to TXRF have seen some significant developments during the present review period. One of the major applications of grazing incidence XRF (GIXRF) is the determination of layer thickness and the concentration profiles of implants. Measurements are made by varying the angle of incidence from almost zero degree to values above the critical angle for total reflection. This results in a change of the pattern of nodes and antinodes within the interference region between incidence and reflected beam. Thus the thickness of layers as well the concentration profile can be determined. In the work by Sanchez et al.,¹¹⁴ the surface oxidation of copper layers of thickness 19 nm, 40 nm and 80 nm deposited on a silicon wafer substrate were presented. Different measurements were taken immediately after evaporation and after 0.5 h, 1 h, 4 h and finally after 0.5 h in an oven at 65 °C. The results showed significant variations for the first measurement after evaporation and after heating in the oven with surface oxidation taking place immediately after exposure to air and progressing only after the sample was heated. The authors concluded that oxidation started immediately after exposure to air because the stratified model developed for a two layer system showed inconsistencies when applied to the experimental data. In conventional applications, a multilayer structure is used to monochromatise the primary radiation or is used as the analyser when measuring the characteristic radiation of low atomic number elements in a WD spectrometer. Tiwari et al.¹¹⁵ used the strong X-ray field intensity generated over a multilayer surface during Bragg reflection conditions to analyse the particulate matter deposited on its surface, to determine the average particle size distribution and detection sensitivity of various elements. The elemental sensitivities achieved at the Bragg reflection condition were compared with those obtained under total reflection conditions. Results indicated that fluorescence yields deteriorated by 15% to 18% in the case of TXRF when particles with a size greater than 1μm were distributed over a large surface area, due to strong sample absorption effects. Under Bragg reflection conditions greater fluorescence yields and thus improved detection limits were achievable. The reviewer is in doubt about the economic benefit of this approach as a multilayer is rather expensive and it may not be possible to reuse it after cleaning, unlike a standard quartz reflector. The same authors¹¹⁶ also characterised trace impurities, unintentionally embedded in thin multilayer structures during the deposition process, using synchrotron XSW. The XSW field generated under Bragg reflection conditions in a periodic Mo/Si multilayer structure was used to determine the concentration and location of these contaminants. The authors observed impurities containing Cr, Fe, Ni and W and the consequences of such impurities on the optical properties of the multilayer structure were discussed in the hard and soft X-ray regions. These measurements were found to be important, firstly to optimise the deposition methods and secondly to better correlate the measured optical properties of a multilayer structure with theoretical models.

2.7 Portable and mobile XRF

Technological advances, especially in the development of hand-held instrumentation have led to a substantial growth in the use of portable and hand-held XRF instrumentation, exemplified by the significant number of publications available for review this year and to justify a Special Issue of X-ray Spectrometry.¹¹⁷

However, by far the largest number of portable XRF applications this year, cover archaeological and cultural heritage artefacts demonstrating the widespread adoption of the technique in this area. Obsidian artefacts at two Classic Maya archaeological sites in southern Belize were studied by Nazaroff et al.¹¹⁸ whose main interest was in evaluating the validity and reliability of PXRF in geochemical source provenancing. They concluded that although PXRF data were internally consistent, they are not statistically equivalent to other XRF instruments and PXRF cannot, therefore, be regarded as a reliable technique; a rather surprising conclusion when related to other contributions in this area.

Notwithstanding these concerns, Sheppard et al.¹¹⁹ used PXRF to classify a large number of obsidian artefacts transported following colonisation of New Zealand in the late 13th century. Classification tree analysis was judged to be superior to discriminant analysis when attributing these artefacts to sources which originated from rhyolitic volcanism in North Island, New Zealand. A portable XRF instrument was used by Jia et al.¹²⁰ to source 440 volcanic glass artefacts from 18 Late Palaeolithic sites located in Northeast China. To avoid the use of classical intrusive techniques, Goren et al.¹²¹ evaluated portable XRF for the provenancing of cuneiform tablets from Hattusa (Turkey) and el Amarna (Egypt) and concluded that the technique had high potential for the non-destructive study of well-defined ‘closed’ assemblages of clay-derived, delicate artefacts, such as cuneiform tablets, bullae and fine-ware pottery. Donais et al.¹²² used portable XRF to analyse ancient mortars and hydraulic cements at an excavation site at Orvieto, Italy and found that Ca, Fe, Pb, Rb, Zn and Zr were useful in distinguishing different mortars. Cesareo and colleagues¹²³ undertook a detailed evaluation of pre-Colombian metal artefacts from the Royal Tombs of Sipan, now held in Lambayeque, northern Peru. As part of their study, a detailed assessment was made of the composition of gold, silver and copper artefacts and in the case of gilded items, accurate measurements were made of the Cu-Kα/Kβ and Au Lα/Cu-Kα ratios to determine the thickness of the gilding (on gold gilded copper) or the equivalent gilded thickness (on tumbaga-a poor quality gold alloy in which the surface had been enriched in gold by the removal of copper and silver). Further details of this study were published in a related paper.¹²⁴ A gilded bronze relief (Lorenzo Ghilberti, Gate of Paradise, Baptistery, Florence, Italy) was analysed by Migliori et al.¹²⁵ using an innovative portable XRF spectrometer and Liu et al.¹²⁶ used the technique to illuminate the technical origin and development of Chinese glass.

Continuing the theme of characterising objects of cultural heritage, portable XRF systems are finding an increasing role in the in situ analysis of paintings and pigments. Bonizzoni et al.¹²⁷ evaluated the performance of three portable instruments for this application, highlighting the advantages and limitations of each instrument. Continuing an instrumentation theme, Buzanich et al.¹²⁸ described a portable focused-beam XRF spectrometer designed for the study of works of art at the Kunsthistorisches Museum, Vienna. This innovative instrument was equipped with a vacuum chamber fitted with a kapton window, to allow determinations from Na upwards in the periodic table. The excitation source was either a Mo- or Cr-anode tube with a point focus of about 180 μm, which when coupled to a polycapillary lens, could achieve a spot size of 150 μm, for example to access details from individual brush strokes. Hocquet et al.¹²⁹ presented new developments in a mobile EDXRF instrument and UV-VIS-NIR coupled spectrometer designed for the 2D imaging of paintings, presenting the discovery of a hidden painting under an anonymous oil painting on a wood panel claiming the first example of a 2D large scan image recorded with a mobile instrument. Demonstrating that portable XRD can make an impact as great as XRF in this area of application, Eveno et al.¹³⁰ reported a combined portable XRD/XRF instrument, providing examples of the analysis of the paintings of several masters. Sil et al.¹³¹ described a portable XRF system for the study of Mexican cultural heritage. The red (Fe) and black (Mn) pigments in Levantine rock art at the Valltorta Gorge, Castellon, Spain were characterised by Roldan et al.¹³² using a portable XRF system. Particular interest was shown in the Fe/Ca ratio in assessing the degree of preservation of the pictorial layer, noting the presence of Ca in the underlying bedrock. Pages-Camagna and colleagues¹³³ used portable XRD and XRF systems for the non-destructive in situ analysis of Egyptian wall paintings from the New Kingdom. This combination of techniques allowed identification of the mineralogy of individual pigments and elucidated the unexpected presence of arsenic compounds. In a rather more modern, but related field, Grieten and Casadio¹³⁴ used two portable XRF systems (one a portable microfocus instrument and the other a conventional hand-held system) for the rapid assessment of photographic images in one of the highest profile collections in the world-that of Alfred Stieglitz. The study was designed to identify the chemical process used to produce the photograph to aid conservation, exhibition conditions and scholarly research and this scientific approach proved to be more reliable than conclusions drawn from a visual or microscopic examination of the photographs. And to conclude this paragraph, there is an on-going and sometimes overlooked requirement to ensure the education and training of both students in natural science and those who will work in the field of conservation, for which Sianoudis et al.¹³⁵ have developed an educational package incorporating details of portable EDXRF to demonstrate the basic principles of XRF, calibration of instrumentation and the application to metal artefacts and the pigments of wall paintings.

Portable XRF systems are being applied to an ever widening range of applications of industrial, environmental and medical relevance. Thus, Kunimura and Kawai¹³⁶ applied a portable TXRF instrument to the determination of trace elements in wine. The elements Fe, K, Mn, Rb and S were detected in the sub- to several hundred μg ml⁻¹ range and although the organic residue from dried wine caused a significant scattering of X-rays, detection limits of several tens of ng ml⁻¹ could be achieved. The technique was proposed for the screening of trace elements in wine before the accurate and precise analysis using other techniques. Using a more conventional approach, Anderson¹³⁷ used a hand-held tube excited XRF analyser to determine As, Cd, Hg and Pb in beverages. Accurate results (within measurement uncertainties) were obtained when analysing spiked beverages through the wall of the original polyethylene terephthalate container, after application of a container wall correction factor with detection limits expected to be above 20 mg kg⁻¹. Figi et al.¹³⁸ reported that hand-held EDXRF was an efficient screening tool for the reliable assessment of elements in automotive brake linings and reported quantitative measurements for Cd, Co, Cr, Mn, Mo, Ni, Pb and Sb. Other elements that could be determined qualitatively were Bi, Cu Sn, Sr, V and Zn. A review of another important hand-held XRF application-Pb in paint-was presented by DeKosky,¹³⁹ emphasising the contribution in the development of instrumentation by an individual manufacturer. The feasibility of developing portable XRF instrumentation for the determination of Pb in bone was discussed by Nie et al.¹⁴⁰ who made comparisons with the conventional KXRF method. They concluded that portable XRF technology could be used for in vivo Pb measurement with a sensitivity comparable to the KXRF technology and good correlation with KXRF results. Martin et al.¹⁴¹ proposed a concept of a portable probe utilising a CdZnTe detector for intraoperative screening of radiopharmaceuticals during cancer surgery by counting gamma ray excited X-ray fluorescence emitted by a secondary target installed in the probe. They considered the method to be effective for detection of radionuclides with gamma ray energies greater than about 88 keV (e.g. Tc-99m, Ga-67, I-123, In-111, F-18 and I-124).

Concerning the development of innovative portable XRF instrumentation, Economou¹³ reviewed the impact made in planetary exploration, with a particular emphasis on the use of radioactive excitation sources and the alpha proton spectrometer that has flown on several successful missions to Mars. Although portable XRF is one of the most widely used techniques for element determination in the field, laser induced breakdown spectroscopy also has significant potential, so it is of interest to review the publication by Colao et al.,¹⁴² who used both techniques to provenance historic building materials to the originating quarries in the Seville region, Spain. Their conclusion was that laser induced breakdown spectroscopy on a relatively small set of elements was a fast and effective method in this provenancing application. Laser induced breakdown spectroscopy was also used in conjunction with Raman spectroscopy, XRF, ED-SEM and ion analysis by Ciupinski et al.¹⁴³ in a study of the effect of environmental pollution on copper roofing from the Wilanow Palace in Warsaw, Karol Poznanski Palace in Lodz and other bronze/copper alloy artefacts. The aim of this work was to evaluate the contribution of these techniques in the characterisation of the chemical composition and stratigraphy of corrosion products.

2.8 On-line XRF

Although the on-line contribution section is normally the shortest section in this review, we continue to regard this area as having substantial potential for XRF and it is pleasing to be able to report a few developments here. Thus, Pilz et al.¹⁴⁴ described an XRF instrument for the on-line determination of Zn in converter dust in a challenging environment where XRF instrumentation was shown to offer stable results despite high temperatures, mechanical vibration and external magnetic fields. Volkov and Alov¹⁴⁵ investigated the effect on X-ray fluorescence intensity of the distance between spectrometer and test sample relevant to the continuous XRF analysis of iron ore mixtures on a conveyor belt. Their approach accounted for the absorption of X-rays in air and changes in the surface area of analysed material and they claimed the proposed method could be applied to various loose materials. Tuo et al.¹⁴⁶ described an on-line analyser for monitoring Ti in a titanium ore concentration plant. Instrumentation was based on a ²³⁸Pu excitation source and a proportional counter detector and was shown to be reliable over a two year period of operation. And finally, Fleming et al.¹⁴⁷ were interested in monitoring the filtration of arsenic in the decontamination of drinking water using an absorbent column of granular ferric hydroxide. These authors presented trial results using water containing 1000 μg l⁻¹ As at a flow rate of 1.5 l hr⁻¹ with a miniature X-ray tube coupled to a Si-PIN detector to detect characteristic As X-rays.

3 Applications

3.1 Sample preparation and preconcentration techniques

This review offers the reader a wealth of information concerning analytical endeavours using XRF techniques that encourage the user to develop sample preparation methods that ensure the potential for high sensitivity and, where appropriate, spatial resolution is achieved. Carter et al.¹⁴⁸ described the use of silicon nitride as a versatile substrate for μ-XRF and μ-XANES mapping of individual cells. Their protocol offered an opportunity to gather information on the intracellular biochemistry of metabolic processes, diseases and their treatment to further the understanding of cell and tissue biology at the molecular level. The cells adhered strongly to Si₃N₄ membranes and visually displayed normal growth with the additional benefit that the rapid alcohol fixation of the cells did not affect their structural integrity for subsequent analysis. Khuder et al.¹⁴⁹ offered a dry ashing method for elemental analysis of bee honey as an alternative to the wet ashing approach. Dry ashing was shown to improve the limits of detection by an order of magnitude. A molybdenum secondary target was used for the measurement of Cu, Fe, Ni, Rb, Sr and Zn whereas Ca, Cr, K, Mn and Ti were measured with a copper secondary target. Jastrzebska et al.¹⁵⁰ considered the effects of sample pre-treatment for the simple and rapid determination of phosphorus in meat samples by WDXRF. Meat samples spiked with phosphate were used for the calibration procedure and CRMs confirmed the validity of the curve. This proposed method was compared with the standard spectrophotometric method (PN-ISO 13730, 1999) for the determination of total phosphorus confirming that this new approach offered a satisfactory alternative. Tateishi et al.¹⁵¹ published a simple analytical method for the determination of bromine in fruits and grain by WDXRF. Five gram samples of fresh, dried or frozen fruit and grain products were extracted twice with distilled water and diluted to 25 mL with distilled water. The sample solution (0.5 mL) was then dripped onto filter paper which was allowed to dry prior to analysis. The method was successfully compared to a gas chromatography method using an electron capture detector. A copolymer of acrylonitrile, butadiene and styrene (ABS) is a tough, light, economical, heat and stain resistant plastic used in the manufacture of telephones, boat hulls and medical equipment. Ohata et al.¹⁵² evaluated CRMs made from ABS resin disk for the determination of heavy metals by EDXRF. Sensitivities for Cd, Cr and Pb were measured within and between discs to confirm homogeneity. It was interesting to note that those discs that contained mercury were stable after long-term X-ray irradiation. Porwal et al.¹⁵³ published a method for the determination of rare earth impurities in aqueous media that also contained uranium. To satisfy the required lower limit of detection, a novel method based on polyvinyl alcohol films was established and tested using four uranium oxide samples containing Dy, Eu, Gd and Sm. The results were reported to be in good agreement with ICP-AES after separation of uranium. As mentioned above, mercury offers an analytical challenge. Margui et al.¹⁵⁴ recognised these difficulties due to the high vapour pressure and low boiling point of this element that produce evaporation and high loss of mercury from the surface of reflectors during the drying process that is commonly used in the preparation of samples for TXRF analysis. The authors developed a fast and simple chemical strategy to avoid mercury volatilisation during the analysis of wastewater samples. Three different procedures were tested; a) increasing the viscosity of the sample by a non-ionic surfactant (Triton(R) X-114), b) immobilisation of the mercury on the quartz reflectors using the extractant tri-isobutylphosphine (Cyanex 471X) and c) the formation of a stable and non-volatile mercury complex into the wastewater sample. The best strategy was reported to be the formation of a Hg-complex with thiourea (pH 10) before the deposition of 10 μL of sample on the reflector. Analytical figures of merit such as linearity, limits of detection, accuracy and precision were also reported. Their chosen method was then tested for the determination of mercury in different types of wastewater samples (industrial effluent, municipal effluent from conventional systems and municipal effluent from constructed wetlands). It is good to read a paper that described all the procedures tested rather than just reporting the adopted method. Mirashi et al.¹⁵⁵ reported EDXRF studies for the determination of thorium, in the range 7–137 mg mL⁻¹, in phosphoric acid solutions after dissolution of thoria in an autoclave. Yttrium was added to the solution as an internal standard. Solution aliquots of approximately 2–5 μL were deposited on thick absorbent sheets which were then analysed. The authors compared the EDXRF method with the more time consuming gamma ray spectrometry. Readers may be interested to read a paper on inter-particle porosity in polycrystalline zeolite and the authors' work¹⁵⁶ to reduce inter-particle voids, a problem well known to those analysing pressed powder pellets. The zeolite was mixed with a sub-colloidal aluminium hydroxide binder that was effective in reducing the voids.

This year saw an increase in papers devoted to sample deposition systems for TXRF analysis. A system capable of delivering picolitre droplets of analyte solution onto the surface of Si wafers for the semiconductor industry was presented by Sparks et al.¹⁵⁷ The droplets of the liquid sample could be formed in an array defined by the user with a device similar to an ink jet printer. Due to the small volume, the droplets were found to dry almost immediately on the surface and individual droplets were typically spaced 100 μm or less apart with an overall pattern that matched the area viewed by the detector (80 mm²). This is a promising technique for studying the possible effects of self absorption associated with sample thickness or shadow effects caused by individual droplets, both of which can cause deviations from linearity in calibration curves required for quantification. Tavares et al.¹⁵⁸ used TXRF to evaluate minor and trace elements in water during different water purification stages of a deionised water production plant. Gallium was used as an internal standard for the quantification of As, Br, Co, Cr, Cu, Fe, Ge, Mn, Ni, Rb, Se and Zn at concentrations in the range 40–100 mg L⁻¹ and for Ca, K, Sc, Sr, Ti and V at sub mg L⁻¹ levels. This work will be of interest to those using deionised water as a blank. The selenium content of soil is of great interest due to the narrow range between nutritious requirement and toxic effects. Because complex matrix effects hamper most analytical techniques, Margui et al.¹⁵⁹ studied several rapid and simple analytical approaches that reduced matrix effects and improved detection limits. They explored new sample preparation methods for TXRF analysis, including a dispersive liquid–liquid micro-extraction procedure that achieved a concentration value of 1.4 ± 0.27 mg kg⁻¹ of Se, which is in good agreement with the certified value 1.32 ± 0.23 mg kg⁻¹. Fernandez-Ruiz¹⁶⁰ presented the quantitative determination of Zr in quartz microspheres functionalised with two kinds of organometallic compound. Two approaches were followed-acid leaching and direct analysis of the microspheres. For acid leaching, a validation of the TXRF results was performed by ICP-MS. Results by the direct analysis TXRF procedure agreed with both acid leaching TXRF and ICP-MS data, providing an important improvement in analysis time, and a reduction in reagent costs and demonstrating the versatility of TXRF to solve analytical problems in an easy, quick and accurate way. The same group¹⁶¹ studied the quantification of the rare earth elements, Eu and Tb in γ-ZrP organometallic compounds which are important as dopants in this highly efficient luminescent system. They developed a procedure that allowed the analysis of very low quantities (5 mg) of the compound and reported an expanded uncertainty of 8% and detection limits lower than 0.002% m/m for Eu and Tb. The described direct solid procedure was tested against the usual quantitative analysis by acid digestion of the samples by TXRF and ICP-MS. After a thorough optimisation of the digestion procedure to eliminate unanticipated chemical effects leading to strong losses of Eu and Tb, the validity of the TXRF procedure was confirmed so avoiding a time-consuming sample digestion approach. Shapovalov et al.¹⁶² used TXRF for the quantification of DNA bound to lipid monolayers at an air–water interface. To use TXRF in this case, DNA from salmon testes was labelled with covalently bound bromine and formed a Langmuir monolayer at an air–water interface. Detection limits of 10–20 μg were achieved and it was found that the pH of the solution had a strong influence on the yield of brominated DNA with much higher degrees of bromination observed at pH 5 than at pH 7. Another important result of these studies was the finding that higher salt concentrations (representing physiological conditions) led to an increased amount of adsorbed DNA. A TXRF procedure for the determination of metal trace elements in petrochemical end products or intermediates for surfactant synthesis was developed by Cinosi et al.¹⁶³ The method combined the fast deposition of the sample on the reflector and evaporation of the sample matrix with an efficient addition of the internal standard which was an organic gallium compound. During the study, 15 elements (Ca, Cd, Co, Cr, Cu, Fe, Mn, Mo, Ni, Pb, Rh, Sn, Sr, V and Zn) were determined in matrices such as paraffins, n-olefins, linear alkylbenzenes, long chain alky alcohols and esters with typical metal contents of 1μg g⁻¹. Detection limits achieved were impressively low and ranged from 0.05 to 0.005 μg g⁻¹. Results of the TXRF measurements were compared with results from the reference method ASTM D5708 (ICP-OES) and critically evaluated.

Many preconcentration methods were developed long ago, so Margui et al.¹⁶⁴ offered a review of multi-element and single-element preconcentration procedures prior to XRF analysis of liquids. The publication included some new efficient variations of those methods and new techniques that extended the possibilities for liquid solution analysis. In addition, the authors comment on trends and future perspectives for this valuable sample preparation technique. Aranda et al.¹⁶⁵ described a new simple and selective method for preconcentration and determination of Cr^VI in drinking water. After adsorption in “batch mode” on Aliquat 336-AC, XRF measurements were made directly on the solid 16.7 mm diameter discs thereby avoiding an elution stage of the retained chromium. The preconcentration factor was calculated as 71 fold. Heiden et al.¹⁶⁶ developed an in-field preconcentration technique using a cation-exchange resin, Amberlite IRC748, for the analysis of metals in surface waters, ground water, acid leach and aqueous soil extracts encountered during on-site environmental assessments. Operational parameters such as flow rate and the mass and chemical form of the resin were tested to maximise analyte recovery. The authors proved their method on extracts from landfill soils and surface waters from a derelict metal mine. The method was shown to recover Cu, Pb and Zn accurately with Fe and Ni at concentrations deemed satisfactory for screening purposes. This work will delight those responsible for controlling finances to support field assessment studies in that it will now be possible for a transportable EDXRF spectrometer to measure many toxic elements in the 1–10 μg L⁻¹ range, reducing the amount of equipment that needs to be purchased, transported and operated in remote locations. Spalding et al.¹⁶⁷ presented a method for the preparation of polyacrylamide hydrogel-encapsulated soils and ground waters that contained uranium. Barros et al.¹⁶⁸ determined arsenic in water samples by TXRF after a preconcentration stage using alumina substrates. The method was tested using Al Kα and Co Kα lines as internal standards. The 50 mL samples were mixed with 10 mg of alumina with pH, time and temperature carefully controlled. The alumina was then separated from the slurry by centrifuge, washed with deionised water and analysed on the sample holder. The authors reported a preconcentration factor of 100 and a detection limit of 0.7 μg L⁻¹ with 98% recovery for As^III and 95% for As^V. Tikhomirova et al.¹⁶⁹ found that Cu^II, Fe^III, Pb^II, Ti^IV, V^V and Zn^II could be adsorbed on alumina modified with Tiron. The adsorption of Fe^III was accompanied by a violet colouration of the adsorbent which indicated the formation of a 1 : 2 complex on the adsorbent surface whilst copper formed a 1 : 1 yellowish green complex. The adsorbent surface was found to be suitable for analysis by XRF.

3.2 Geological

There have been a number of contributions in the development of techniques and applications, including the work of Pret et al.¹⁷⁰ who exploited the capability of a number of modern instruments to scan and record X-ray maps of geological thin sections to develop a method of quantitative petrology based on a ‘mineral thresholding’ approach that accommodates mixtures and solid solutions. They demonstrated the capabilities of their method in the analysis of a bentonite test sample at a spatial resolution of a few μm, an area of 0.1 to 1 cm² and with the opportunity to undertake full modal analysis of the sample. The approach has relevance to microanalytical techniques, including μ-SRXRF. Carbone et al.'s¹⁷¹ interest was in the application of SR-based techniques in the analysis of iron-rich hardpans within sulfide-rich waste rock deposits (eastern Liguria, Italy). They promoted the combined use of μ-XRD, μ-XRF and μ-XANES to demonstrate that iron-rich phases generally contain significant amounts of As, Cu, Mo, Se and Zn with goethite-rich assemblies showing a high affinity for Cu and Zn and hematite-rich assemblies concentrating As, Cu, Mo, Se and Zn. Ene et al.¹⁷² developed an XRF technique for the determination of heavy metals in soils, specifically As, Cr, Cu, Ni, Pb, V and Zn in the vicinity of an iron and steel works (Galati, Romania). Their study was undertaken with a handheld XRF instrument. When analysing soils to contribute to regional geochemical surveys, effective quality assurance procedures have high importance, as emphasised by Maritz et al.¹⁷³ who described the approach taken by the Council for Geoscience (South Africa) in the use of simultaneous XRF and ICP-MS data in contributing to the South African regional geochemical mapping programme. Wu et al.¹⁷⁴ reviewed applications of XRF for the determination of the REEs in China, covering samples prepared as pressed powders, glass disks, liquid thin films and solid pieces. Periodically, further work is reported on the use of XRF to determine the FeO/Fe₂O₃ ratio, covered this year by Chubarov and Finkel'shtein¹⁷⁵ who evaluated the uncertainties associated with measurement of the Kβ_2,5/Kβ_1,3 and Lβ/Lα_1,2 ratios and evaluated the precision of the determination in various rock types. Viswanathan et al.¹⁷⁶ used WDXRF to determine Ta in columbite-tantalite using the Ta Kα line and a LiF-420 crystal to avoid spectrum overlap problems from the Nb K-lines on Ta L. Test portions prepared by mixing powdered samples 1 : 1 with cellulose, with a boric acid backing, and were excited at 100 kV with a Rh anode tube-precisions of 0.4 to 2.4% were reported. Smirnova et al.¹⁷⁷ determined Hf, Nb, REE, Ta, Th, U and Y in two candidate reference materials, a spinel lherzolite (LSHC-1) and an amphibolite (Amf-1) evaluating data by solution ICP-MS with INAA and XRF results. Rate et al.¹⁷⁸ were interested in the geochemical analysis of soils using partial extractions and investigated the bulk cyanide extraction approach, which reduces the nugget effect for gold and can provide a higher contrast in anomalies of interest in geochemical exploration than total elemental determinations. To evaluate this approach further, the authors undertook bulk cyanide extractions, elemental determinations by INAA and XRF and aqua regia digests on samples from exploration prospects in Namibia and Australia. They found that multielement anomaly contrast was improved by (i) normalising bulk cyanide extraction data to the carbonate content (if present), (ii) normalising data to the amorphous iron and manganese oxide content or total Al, K or Mg (at some prospects), (iii) adjusting bulk cyanide extraction data using a simple adsorption model (more limited success).

XRF continues to make a significant contribution to a range of geochemical investigations, although often in supporting the use of more specialised techniques. However, a rather more sophisticated approach was followed by Boone et al.¹⁷⁹ who employed X-ray microcomputed tomography (μ-CT), μ-XRF and μ-XRD to generate a 3D phase identification of the mineralogical structure of a Precambrian granite. The μ-XRF and μ-XRD contributions were required to provide positive identification of phases, recognising that μ-CT only provides X-ray attenuation contrast. XRF with XRD contributed to an investigation by Meneghini et al.¹⁸⁰ of earthquakes recorded as complex crystalline microlayers in black fault rocks on Kodiak Island, Alaska. XRF and ICP-MS were used by Marion and Sylvester¹⁸¹ to contribute to a study of the composition and heterogeneity of anorthositic impact melts found at the Mistastin Lake crater, Labrador. Again using a multi-technique approach that included XRF, Nishimoto and Yoshida¹⁸² investigated the mineralogical changes associated with hydrothermal alteration at depth in a granite from a drill core sampled from Gifu, Central Japan. Their study was designed to advance the understanding of granite alteration processes in an orogenic belt, such as the Japanese island arc. Sandstones from Paraguay were of interest to Facetti-Masulli et al.,¹⁸³ who interpreted spidergrams derived from major and trace element data by XRF to interpret the geological provenance. Mangili et al.¹⁸⁴ used μ-XRF, XRD and micro-facies studies, with ¹⁸O isotope data to investigate the effect of detrital carbonate on the stable oxygen and stable carbon isotope data from varved sediments (i.e., sediments with annual layering) of the interglacial Pianico palaeolake in the southern Alps in Italy. Their overall conclusions were that micro-facies analysis can provide a quick way of reducing detrital contamination in bulk carbonate samples to obtain more reliable stable isotope measurements.

During the current review period, XRF has made a significant contribution to climate change studies over geological time scales generally in scanning geological sediment cores. Ingram et al.¹⁸⁵ used XRF in this way to evaluate biogenic calcium and siliciclastic titanium sediment inputs in a study of Late Pleistocene-Holocene sedimentation associated with an active seafloor gas-hydrate and cold-seep field on the northern slope of the Gulf of Mexico. XRF data complemented radiocarbon dating by accelerator mass spectrometry and foraminiferal and nanofossil biostratigraphy. Kujau et al.¹⁸⁶ used XRF core scanning to estimate the concentrations of siliclastic elements in bulk sediment samples in a study of the sediment input into the Gulf of Mexico from the River Mississippi. The authors used the element, K, as a proxy for river sediment influx and their interest was in evaluating changes over the last 560,000 years covering the last six glacial-interglacial cycles. Transient global warmings during the Upper Paleocene and lower Eocene periods were of interest to Zachos et al.¹⁸⁷ who used XRF core scanning to measure Fe intensities in a pelagic sediment core sample from an Ocean Drilling Programme (ODP) site in the Southeast Atlantic. These data were required to better understand carbon isotope excursions that occurred during this period and were associated with orbital forcing (i.e., the effect on climate of small changes in the Earth's axis and orbit). A range of other studies have incorporated XRF core scanning, exemplified by high resolution Ti determinations in a laminated lake sediment from Laguna de Juanacatlan, Mexico; the variability of climate over the last two Millennia in the North American monsoon region;¹⁸⁸ the basin stratigraphy from a coastal lake in the Lofoten Islands, Norway to evaluate the impact of sea-level change;¹⁸⁹ changes in status of the Les Echets, France sedimentary sequence, linked to climate change over the last 40 ka in which XRF core scanning provided multielement major and trace element data¹⁹⁰ and the 20th century impact on sediments of the Haverstraw Bay section of the Hudson River Estuary.¹⁹¹ Although XRF is widely used for core scanning, Davids et al.¹⁹² expressed a word of caution in respect of its non-destructive capabilities. In particular, laboratories that use optically stimulated luminescence to date clastic deposits should be aware that the radiation dose imparted during XRF (or X-ray radiography) studies will affect the luminescence signal, a discrepancy investigated by these authors. Cuven et al.¹⁹³ investigated the variability of grain size in sediment cores from two Arctic lakes using a commercial XRF core scanner that offered a spatial resolution of 100 μm and compared results with standard geochemical methods, including ICP-AES of bulk samples and ED-SEM. Grain sizes were characterised using a laser particle size analyser and thin section image analysis and the authors concluded that the boundaries between core facies could be identified by the XRF core scanner using elemental abundance or ratio data of which the K/Ti ratio was the best marker for the upper varve boundary.

XRF was also widely used for the more conventional analysis of soils and sediments. Andrist-Rangel et al.¹⁹⁴ were interested in the reserves of potassium in the northern temperate grassland soils of Scotland using XRD, XRF and aqua regia leachable potassium data to rank eight contrasting soils on the basis of their potential to release potassium. Dantu¹⁹⁵ undertook a geochemical survey of both top-soil (0–25 cm) and subsoil (70–95 cm) in and around Siddipet, Andhra Pradesh, India, reporting that the regional parent materials and pedogenisis were the primary factors influencing trace element patterns with anthropogenic activities having a secondary influence. In assessing the sources of heavy metals in soils freshly deposited from the Seyhan River, Turkey, Yalcin et al.¹⁹⁶ used XRF data and a multivariate statistical approach to identify the three most important influencing factors: lithology, local industrial activity and a ‘natural’ factor. Moros et al.¹⁹⁷ used a partial least squares approach to evaluate the XRF spectra of estuarine sediments from the Nerbiol-Ibaizabal River, Spain, to predict the concentration of a wide range of trace elements. In a study with more practical applications, Stamatakis et al.¹⁹⁸ used XRD, SEM, XRF and optical microscopy to investigate opaline silica-rich sedimentary rocks on the Island of Milos, Greece. Their study demonstrated that the diatomite and porcelanite deposits both improved the pozzolanic properties of cement compared with that currently produced using glassy tuffs. Wang et al.¹⁹⁹ investigated a rapid method for the analysis of major and trace elements in salt lake clay minerals prepared as compressed powder pellets using a WDXRF with polarising excitation geometry. They made a particular study of inter-element interferences and presented details of detection limits, precisions and accuracies in the analysis of clay mineral species. XRF and XRD were used by Saeedi et al.²⁰⁰ to examine the heavy metal concentration of natural sediments of the Jajrood River, Iran, demonstrating that absorbabilities varied in the order Pb>Cu>Zn>Cd>Ni>Cr with heavy metal sorption being mainly associated with the organic matter in the river sediments. Han et al.²⁰¹ examined the concentrations of eco-toxic elements by XRF in the sediments of Lake Chaohu, eastern China covering 150 years of sedimentation in a study designed to elucidate the impact of the industrialisation of China. Statistical analysis showed an increase since 1978 in As, Pb, Zn associated with the use of chemical fertilisers and pesticides, and Cr, Cu, Mn, Ni from industrial and mining activities, with clustering of Ca, Co, Fe, K, Rb and Ti associated with post-depositional processes and land exploitation and of Sr and Zr from soil.

The weathering of rock surfaces is an area that continues to attract XRF interest, not only for terrestrial studies. Thus, Altheide et al.²⁰² used XRF, XRD and SEM to investigate the hypothesis that the association observed on Mars between phyllosilicates, amorphous silica and sulfates results from acid weathering of older philosilicate deposits. The authors undertook laboratory experiments to investigate the reaction products after sulfuric acid leaching of nontronite, montmorillonite and kaolinite and largely confirmed the hypothesis, and noted differences in reaction rate and products between these minerals. Turning now to a more conventional terrestrial study, Ferrier et el.²⁰³ calculated the mineral-specific chemical weathering rates at two field sites in the Rio Icacos, Puerto Rica, with the aim of demonstrating that presence of cosmogenic nuclides can provide weathering rates of abundant, soluble mineral phases in actively eroding terrains to an accuracy of better than 20%. The authors used XRF-based geochemistry and XRD-based mineralogy to quantify measurements. XRF was used by Brinatti et al.²⁰⁴ to support the Rietveld Method in the mineralogical characterisation of highly weathered soil from the Ponta Grossa region, Parana, Brazil, with a particular interest in quantifying the mineralogy of the finer clay fraction. McFarlane et al.²⁰⁵ undertook a 128 m surface weathering profile in the Kalahari, Northwest Ngamiland, Botswana, using XRF, ICP-AES, XRD and the electron microscope to characterise the 15 m of Aeolian sand, overlying 14 m of residual sand, overlying a saprolite profile. The project was designed to evaluate the origin of the Kalahari Sediments, suggesting an autochthonous rather than an allochthonous origin. Turning to archaeological applications, Xu et al.²⁰⁶ studied the weathering crusts on outdoor stone artefacts in the Kylin area, Nanjing, China using a range of techniques, including XRF to demonstrate the presence of gypsum, kaolinite, calcium oxalate and phosphate on sheltered or partially exposed areas, with an extensive network of fissures on surfaces directly exposed to rainwater; their observations indicated that atmospheric pollution was the main cause of deterioration. Ciccioli et al.²⁰⁷ used XRF and other techniques to examine surface and structural decay of rock-cut cliff tombs in the Etruscan necropolis of Norchia, Northern Latium, Italy, where volcanic tuffs are susceptible to weathering, plant root infiltration and microclimatic conditions, leading to rock falls.

Biogeochemistry has attracted some interest this year, with Totsche et al.²⁰⁸ demonstrating the importance of research into biogeochemical interfaces in soil, justifying funding of 22 individual research projects by the German Research Foundation. Ali-Bik et al.²⁰⁹ used XRD, XRF and FTIR to explore gypsum and dolomite biomineralisation in a perennial saline basin characterised by a microbial bloom in Fayium, Egypt. Baines et al.²¹⁰ used μ-SRXRF to show that diatom cells from the cold, high-silicic acid waters of the Antarctic zone of the Southern Ocean had six times more Si per unit volume than samples from the warm low-silicic acid waters of the Eastern Equatorial Pacific, concluding that ecological processes may cause much larger systematic regional and temporal differences in cell stoichiometry than was currently accommodated by ecosystem models. Hasegawa et al.²¹¹ also used μ-SRXRF in mapping mode to measure Ba, Br, Cd, I, Mn, Mo, Sn and Zn (as well as Ca and Sr) in precious corals from Japanese waters, detecting relatively high contents of Ba and Cd, elements that are expected to act as good marker elements. Both μ-SRXRF and LA-ICP-MS were used by Munsel et al.²¹² in laboratory experiments to measure the heavy metal incorporation into foraminiferal calcite, setting concentrations of Cu, Ni and Mn at level of 5-, 10- and 20-times higher than filtered natural North Sea waters. Partition coefficients were measured providing an opportunity to reconstruct past concentrations of these elements in sea water. Iodine in biocarbonates of the Callovian-Oxfordian deposits of the eastern part of the Paris basin were measured by Lerouge et al.²¹³ using EPMA and μ-SRXRF and μ-XRD. Samples were provided by the French Radioactive Waste Agency. Pena et al.²¹⁴ applied EXAFS to find that nickel sorption by a bacteriogenic birnessite occured through two dominant coordination environments. The results of EXAFS analysis agreed well with a model based on density functional theory.

The geochemistry of water courses and bodies has been the subject of a number of studies, including that of Asta et al.,²¹⁵ who combined XRF with XRD, SEM and XAS to evaluate the natural attenuation of As in the acid waters and sediments of the Tinto Santa Rosa acid stream, Iberian Pyrite Belt, Spain. Some of their results demonstrated that As was present predominantly in the pentavalent state, and that upstream As was sorbed onto the mineral schwertmannite, whereas downstream, this association was with goethite and jarosite. Guo et al.²¹⁶ used SRXRF to demonstrate the role of organics and iron colloids in the partition and transport of As in groundwaters of the Hetao basin, Inner Mongolia. In the same region, Hagiwara et al.²¹⁷ used XRF and XRD to investigate the high concentrations of As found in groundwater in the village of Ershe, Jianshe, Inner Mongolia. Their results indicated that in highly reducing environments, As absorbed on iron oxyhydroxides is released. The presence of iron oxyhydroxides was associated with extremely black sand formed from a greigite (iron sulfide) coating on sand grains and evolved from the iron oxyhydroxides and most probably associated with bacterial activity. In the southern Choushui River alluvial fan, XRD, XPS and XRF were used by Lu et al.²¹⁸ to study the source and mobility of As, demonstrating that iron oxyhydroxides and sulfides were likely to be the major sinks of As, whereas the reductive dissolution of iron oxyhydroxides (caused by high levels of bicarbonate and ammonium ions) was likely to be the release mechanism for As. Of more geochemical relevance, James-Smith et al.²¹⁹ used SRXRF, XANES and EXAFS to characterise the speciation of As in natural fluid inclusions from a typical orogenic gold deposit, in brines from a Proterozoic Fe–Cu–Au deposit and in an As-rich magmatic fluid in a study designed to elucidate the role of arsenic chemistry in ore-forming fluids. Heath and Plater²²⁰ investigated the impact on floodplain wetland sedimentation from damming the Pongolo River, KwaZulu-Natal, South Africa using XRF to provide a geochemical record of sediment with depth (>1 m). In sediments deposited after the construction of the Dam, the authors observed an increase in fine-grained mineral sedimentation with an increase in biogenic productivity at one site, both associated with a reduced frequency of flooding and a reduced average water flow velocity. Facetti-Masulli and Kump²²¹ were interested in the minor and trace element composition of water bodies from western Paraguay, using XRF to analyse bottom sediments. The Sargasso Sea was of interest to Twining et al.,²²² using SRXRF to analyse Fe, Mn, Ni, P and S in individual Synechococcus cells collected from the surface and deep chlorophyll maximum layers of three mesoscale eddies; the data demonstrated the dynamic response of the elemental composition of phytoplankton to physical and chemical environmental gradients. Laboratory experiments were undertaken by Rango et al.²²³ to assess the effect of leaching on pyroclastic glassy ash deposits collected from the central Main Ethiopian Rift, where surface and groundwater resources are affected by fluorine pollution which causes fluorosis in the local population. Using XRF, XRD and SEM, the authors showed that very fast leaching of F⁻ occurred from a column containing the fine fraction with a strong accumulation of F⁻, in comparison with columns containing raw (unsieved) and coarse powder.

3.3 Industrial minerals

One of the more unusual contributions available this year in the characterisation and use of industrial minerals was the work of Korkut et al.²²⁴ who used WDXRF to evaluate the radiation shielding properties of amethyst and showed that this semi-precious stone is more effective at shielding gamma rays than concrete. Following a similar theme, Kurudirek et al.²²⁵ used WDXRF to analyse clinoptilolite-rich natural zeolite, which is generally used as a mineral admixture in Portland cement to produce high performance concrete, and concluded that due to the natural radioactive content of clinoptilolite, the resultant material had poorer X-ray attenuation properties compared with Portland cement. SRXRF was used by Cabral et al.²²⁶ to determine the iodine content of alluvial platinum-palladium aggregates from Minas Gerais, Brazil, in a study of the role of this element in biogenic fixation of these precious metals. Lignite will be the main coal source for the next generation of power stations in northern Greece, so it was timely for Koukouzas et al.²²⁷ to use XRF and XRD to investigate the relevant deposits especially to evaluate their slagging and fouling properties which were related to the palaeoenvironments in which they were formed. Dai et al.²²⁸ used XRF as one of the techniques for undertaking a detailed assessment of the geochemistry and mineralogy of a high pyrite semi-anthracite coal from the Late Permian in the Songzao coalfield, southwestern China. Hayati-Ashtiani et al.²²⁹ undertook a range of tests, including XRF analysis, on natural and activated bentonites for both swelling and non-swelling categories, with a particular interest in their industrial applications as barriers, drilling mud, plethorapy, filtering agents and in the pharmaceutical industry. Gougazeh and Buhl²³⁰ used a range of techniques, including XRF to characterise the kaolin deposits at Jabal-Al-Harad, southern Jordan, with a view to industrial exploitation. Other studies included the separation and purification of montmorillonite from Vietnamese bentonite deposits,²³¹ iron-bentonite interactions in the Kawasaki bentonite deposit, Japan²³² and firing tests on clay-rich materials from the Algarve basin, Portugal.²³³ Ferromanganese nodules from the Gulf of Cadiz attracted some interest²³⁴ with XRF contributing to a comprehensive study that concluded that the growth of nodules was affected by diagenetic-hydrogenetic processes influenced by fluids venting from deep-seated hydrocarbon reservoirs, bio-mineralisation processes and erosion and chemical influences of bottom currents. Ferromanganiferous sediments were also studied by Cronan et al.²³⁵ whose interest lay in material from the Penrhyn Basin, South Pacific Ocean. The authors used an automatic XRF core scanner, calibrated by laboratory WDXRF to characterise underlying dark brown ferromanganese clays to understand the environmental impact before any major disturbance caused by nodule mining activities. The diamond potential of the Yakutian kimberlite fields, Russia, was studied by Vasilenko et al.²³⁶ through the XRF analysis of core samples. The presence of diamonds showed a positive correlation with the K₂O content and a negative correlation with TiO₂. The authors results confirmed the hypothesis that the kimberlite parent melts are selective melts of lithospheric peridotites that are saturated with water and carbon dioxide. Zarasvandi et al.²³⁷ studied the Sar-Faryab bauxite deposit in the Zagros Mountains, Iran, using XRF to show that Al and Ti were immobile during the bauxitisation process and undertook a detailed geochemical provenancing. And finally, Cevik et al.²³⁸ characterised phosphate rocks from the Mardin-Mazidagi deposit, Turkey, using XRF and XRD to characterise their geochemistry and mineralogy. This was extended to an assessment of radioactive properties, concluding that the annual dose derived from a radiation model would fall below international limits in the industrial use of this material as a fertiliser.

3.4 Environmental forensics

The literature this year continues to reflect the ability of XRF techniques to contribute to an understanding of mechanisms for the accumulation and distribution of elements between different parts of plants. Desideri et al.²³⁹ used polarised XRF to investigate elements in Italian medicinal plants with measurements of leaves, fruits, seeds, roots, flowers, barks, berries and thallus to show the dependence on soil composition and climate in which the thirty five investigated plants were grown. Chuparina and Aisueva²⁴⁰ determined concentrations of Ba, Cr, Cu, Fe, Mn, Ni, Sr, Ti and Zn in the medicinal plant Hemerocallis minor Miller to show differences between rhizome, stalk, leaves and flowers with respect to toxic levels reported to be a threat to human health. In India Behera et al.^241,242 compared in vitro root tissues of a medicinal herb to naturally grown in vivo plants to show that the elemental content of in vitro roots was equal to that of naturally grown plants of the same species. This work demonstrated the possible exploitation of in vitro root culture as a viable alternative and renewable source of phytochemicals and provides a means for conservation of valuable natural resources. Tahkokorpi et al.²⁴³ used XRF to measure the uptake of Ni from soil to the rhizome and aerial shoots of bilberry to show that Ni translocation from rhizome to aerial shoots did not occur. Trees are recognised as important plants for the restoration of soil due to their high biomass. Harada et al.²⁴⁴ examined the cadmium tolerance and growth rate of six willow species common in Japan. Cadmium accumulated at the tips of serrations in leaves and the phelloderm under the stem surface was measured by μ-SRXRF. Straczek et al.²⁴⁵ measured differences in uranium root to shoot translocation of four plant species differing in their cation exchange capacity of roots following hydroponic exposure for seven days to100 μmol L⁻¹ U. Luo and Zhang²⁴⁶ recognised that synchrotron-based XRF techniques would play a significant role in the understanding of geo and bio-chemical processes as they provided a combination of spectral and spatial resolution for studies into reaction mechanisms for various environmental processes. Banuelos et al.²⁴⁷ used μ-XRF and XANES to map the accumulation, distribution and speciation of selenium in spineless prickly pear cactus, to assist in the understanding of the health benefits of this fruit. Lombi et al.²⁴⁸ also used high definition SRXRF to investigate the distribution and association of essential elements in barley grain at the micro scale. The complexity of spatial distribution and associations was shown to have implications for improving the nutritional content of cereal crops such as barley. Evidence of bio-magnification of gold nano-particles within the food chain was reported by Judy et al.²⁴⁹ who used μ-XRF and LA-ICP-MS to demonstrate that nano-materials may accumulate in sludge derived from wastewater treatment and ultimately in soil following land application as biosolids. Tobacco hornworm was used to investigate plant uptake and trophic transfer of 5, 10 and 15 nm diameter gold particles to highlight risks associated with nano-technology that your reviewer expects to find in future literature reviews. Yigit and colleagues²⁵⁰ reported a WDXRF comparative study of 14 elements in white, red and black mulberry leaves and fruits. Among the various macro-nutrients in the mulberry species, potassium was found in the highest quantity in fruit samples, whereas calcium was predominant in the leaves. Characteristics of the Turkish delicacy, Mulberry Pekmez with 0, 10 and 20% Cornelian cherry fruit were measured by Cakmakci and Tosun²⁵¹ using XRF for Ca, Fe, K and Zn and panellists for sensory quality to show that Ca, Fe and K concentrations were increased in the favoured addition of 20% cherry to the Pekmez. Another Turkish research group was interested in the influence of progesterone and beta-estradiol on the germination velocity in chickpea²⁵² and maize²⁵³ seeds. The seeds were germinated in hormone solutions of various concentrations (10⁻⁴, 10⁻⁶, 10⁻⁹, 10⁻¹² and 10⁻¹⁵ M) for 5 days then analysed by WDXRF to show that Cl, K, Mg, P and S levels were augmented by all levels of both hormones. The highest germination ratio, in terms of root to coleoptyle lengths, was recorded at 10⁻⁹ M and 10⁻¹² M solutions of both steroids in both studies. Ibrahim²⁵⁴ subjected fenugreek seeds to acid treatment in order to activate their surface. XRF data showed there was no change in the level of metals and metal oxides following the treatment and FTIR showed no change in the characteristic bands and/or structure of the fenugreek. Molecular modelling suggested that metal oxides such as Al₁₆O₂₄ offered its surface for adsorption of gases indicating that fenugreek could be used safely to control the level of gases in the stomach.

Several papers used XRF techniques to investigate cultivation effects in plants. Janik et al.²⁵⁵ used TXRF to measure the elemental composition of spores, peridium walls and lime nodes of Physarum compressum sporocarps cultivated on rabbit dung as a natural growing environment and on artificial agar medium. Whole fruiting bodies and samples of both media were extracted with nitric acid or Parr digest bomb, respectively. Biological and geological reference materials were used in the quantification procedure to show that the agar medium yielded lower concentrations of Ca, Cr, Fe, K and Mn in relation to fruiting bodies from the dung. An EDXRF study by Gupta et al.²⁵⁶ compared elemental uptake in cauliflower grown on farms near the main dumping site for municipal waste in the city of Kolkata, India and uncontaminated farms some 50 km away from the city. The same instrumental scattering constants were used for quantification of both soil and plant from a calibration derived from NIST-SRMs. The results showed that elemental concentrations in the root soils and leaves of the samples varied from farm to farm whereas concentrations of Cu, Pb and Zn in contaminated root soils were higher by almost an order of magnitude compared with uncontaminated farms. However, an interesting feature of the study is the strikingly similar elemental concentrations in the edible flower part of all samples irrespective of soil type. Demir et al.²⁵⁷ examined the effects of poultry manure on the growth of tomatoes. Yields of fruit and vegetative material were studied in plants grown in soil with 0, 10, 20 and 40 g kg⁻¹ added poultry manure. Concentrations of Ba, Br, Ca, Cl, Cu, Fe, K, Mg, Mo, Mn, N, P, Rb, S, Si, Sr and Zn in leaves at flowering and at final harvest and in fruits were determined by polarised EDXRF. The poultry manure fertiliser was found to improve both tomato shoot growth and fruit yield. Concentrations of P in the leaves and fruit were increased as the application rate of manure was increased whereas fruit Ca and Mg were significantly reduced but not to the extent to cause the calcium deficiency disorder, blossom end rot. The manure treatment increased the concentrations of Rb and Zn in the fruit but decreased Br levels. This increase in fruit yield and Zn (an element required in the human diet) combined with the lowered concentration of potentially harmful Br in the fruit make poultry manure a valuable growing medium for tomato production. Kaymak et al.²⁵⁸ investigated the relationship between endogenous element content determined by WDXRF and the development of hollowing in four radish root cultivars (Siyah, Beyaz, Antep and Iri Kirmizi). The results showed that Ba, Br, Ca, Cl, Mn, N, Sn and Zn may affect development of hollowing with the Siyah cultivar being most resistant to the defect. Parra²⁵⁹ compared TXRF and HG-AAS for the determination of total arsenic in onion plants grown in contaminated and control substrates in Venezuela. The contaminant was added to the plants three weeks after transplanting the plantlets. The green leaves, bulbs and roots together with the stems were separated 45 days after transplant and analysed by TXRF and for total arsenic. Good agreement between the two techniques was reported, demonstrating the accuracy of the TXRF procedure. Quantitative XRF measurements were reported by Camarillo-Ravelo et al.²⁶⁰ on lead-contaminated plant tissue. The calibration procedure, which used the ratio of Rayleigh to Compton scattered radiation, investigated using Monte Carlo simulation. Experimental data with low-energy photons (14 KeV) and simulations showed very good linearity of the fluorescence-to-Compton ratio as a function of metal concentration. Lead, iron and zinc were measured in bean seeds that had been grown in a nutritive solution with different Pb dopings. The authors reported that the calibration must be prepared for fixed conditions of X-ray energy and scattered angle, while the beam intensity and detector-to-sample distance may change with sample. The linearity was shown to be preserved even in the presence of other heavy elements in the periodic table. However, the calibration was restricted to similar matrices as it affected the slope of the curve.

Quality control of commercial food products using 3D polarised EDXRF was reported by Otaka et al.²⁶¹ with the measurement of heavy elements at sub-μg g⁻¹ levels in 63 wheat flour samples produced in Japan and imported from overseas. Measurements of 17 elements were subjected to multivariate analysis to discriminate the domestic and imported wheat flours. Arsenic contamination of rice was investigated by Zheng et al.²⁶² whose paper described ICP-MS and HPLC-ICP-MS methods for the determination of total arsenic concentration and speciation. However, SRXRF was used to investigate in situ arsenic distribution in the leaf, inter-node, node and grain. Total arsenic concentrations in the vegetative tissues were found to increase two weeks after flowering. The concentration of dimethylarsinic acid (DMA) in the caryopsis decreased progressively with its development, whereas inorganic arsenic concentration remained stable. SRXRF revealed that the arsenic content between neighbouring leaves or neighbouring inter-nodes was 0.6 with arsenic accumulation in the centre of the caryopsis during its early development and then in the ovular vascular trace. This study showed that there were different controls on the unloading of inorganic arsenic and DMA. Work by Seyfferth et al.²⁶³ also investigated the widespread arsenic contamination of rice. They looked at the iron plaque around the rice roots as it is thought to be a barrier to arsenic uptake. The authors used a combination of μ-XANES, transmission X-ray microscopy and tomography to show that the dominant species were As^V and As^III with minor amounts of DMA and arsenic triglutathione. Viable iron plaque formation was found to affect arsenic entry into the rice roots but did not coat many of the younger roots that were important for solute uptake. Mihucz et al.²⁶⁴ used synchrotron-based confocal micro X-ray fluorescence analysis and ICP-MS to study the washing and cooking effects on the removal of trace elements (As, Cd, Cu, Mn, Ni and Ti) from two white and one brown rice species. Sector field ICP-MS was used to study the extraction of the elements after the samples were subjected to cold and hot water extraction where the ratio of the rice mass to the deionised water volume were 1 : 6 and 1 : 3, respectively. The liquid washed-out fractions were freeze dried and digested in a microwave oven. About 50% of the investigated elements could be extracted from the white rice. In the case of the brown rice the boiling water contained As, Cd, Ni and Ti in significant percentages. A surprising discovery was made with synchrotron radiation confocal μ-SRXRF. The technique revealed that the surface layer having the thickness of roughly 80 μm, was the region most abundant in elements. Titanium was only detectable in the skin region. A strong correlation was found between the water extracted levels of As, Mn, Ni and Ti. The authors concluded that in regions with heavy metal or toxic element pollution, rice grains should undergo thorough washing followed by cooking with abundant amounts of water. The understanding of elemental uptake and the accumulation mechanism of cadmium and other essential elements in rice was studied by Yamaoka et al.²⁶⁵ The stems of rice plants “Nipponbare” and “Milyang 23” were analysed by μ-SRXRF and μ-XANES. The latter was used to determine the chemical form of cadmium and to reveal the mechanisms of cadmium transport in rice. The results showed that the Cd concentration of Nipponbare was higher than that of Milyang 23 in the root, although there were no significant differences in the shoots of these two cultivars. It was also found that cadmium was localised at the bundle. From XANES measurements it was found that cadmium was bound to sulfur in the root of both rice plants. The content of Cd-S in the stem of Nipponbare became 1.5 times higher after exposure to cadmium, while only a slight change was observed in the stem of Milyang 23. In contrast the leaves of Nipponbare showed lower values of Cd than Milyang 23. In conclusion, the different chemical state of cadmium in the shoots affected the different accumulation behaviours of both investigated plants. The regional classification of foods is important to growers in terms of reputation, quality and price. Akamine et al.²⁶⁶ developed a rapid and easy method for the analysis of trace elements in coffee beans in order to differentiate their region of origin and identify product mislabelling. Beans from 6 different regions (Brazil, Colombia, Vietnam, Indonesia, Tanzania and Guatemala) were analysed by 3D polarised EDXRF to measure Ba, Fe, Mn, Ni, Rb and Sr levels. The analytical data was assessed using PCA to classify the coffee beans according to geographical origin. The authors also found that roasted beans may similarly be classified as their green bean counterparts. Sweets, including chewing gum and candies are not strictly a food but nonetheless are eagerly consumed by children, the most vulnerable age group to any kind of metal contamination in the food chain. Martinez et al.²⁶⁷ used TXRF to determine Br, Cr, Cu, Fe, Mn, Ni, Pb, Rb, Sr, Ti and Zn in six different flavours of candy sold in Mexico. Triplicate samples of the various candies were digested in 8 ml of a supra-pure HNO₃ and H₂O₂ (6 ml:2ml) in a microwave oven. Lead concentrations were found to fluctuate in the range 0.102 to 0.342 μg g⁻¹. The authors offered their data for discussion on the risks associated with the consumption of the candies.

Two papers published during this review period offered analytical data on wines. Pessanha et al.²⁶⁸ measured heavy metals in vine leaves, grapes, must and wine in order to assess the influence of vineyard age on the elemental content of samples collected throughout several stages of wine production. Samples were collected from two vineyards, aged 6 and 14 years, in the Douro region, Portugal. The elemental content in the vine leaves and grapes was determined by EDXRF, whereas TXRF was used for the must and wine. The authors found that almost all elements present in the wine and must samples did not exceed the recommended values found in literature on wines. Bromine was present in wine from the six year old vines in a concentration an order of magnitude greater than that usually detected. The copper content in vine leaves from the older vineyard was found to be “extremely high”, probably due to the excessive use of Cu-based fungicides used to control vine downy mildew. A higher content was also detected in the grapes from the older vineyard although the level was not found to exceed the recommended value. Kunimura and Kawai¹³⁶ used a portable TXRF spectrometer to measure Fe, K, Mn, Rb and S in wines. This work is reviewed in section 2.7 devoted to developments in portable X-ray spectrometers.

Mosses are often used as bio-accumulators near roads with high density traffic and in industrial areas where pollution is expected. Ozdemir et al.²⁶⁹ used AAS and EDXRF to determine 11 elements accumulated on nine moss species near a copper and zinc mine and local roads in Cayeli, Turkey. Another group²⁷⁰ at the same Turkish institution analysed 12 lichen species living in 12 different habitats to assess pollution in two geographical regions. Radulescu et al.²⁷¹ evaluated essential elements and heavy metal concentrations in wild mushrooms to show they were good bio-accumulators for Ca, Cu, Mg, Se and Zn with a smaller affinity for Bi, Sr and Ti. Tan et al.²⁷² determined spatial imaging and speciation of lead in sedum by μ-SRXRF and EXAFS. Lead was found to be predominantly restricted to the vascular bundles of both leaf and stem in the accumulator suggesting low lead mobility.

Fish migration using otolith micro-chemistry was investigated by Lochet and co-workers^273,274 using SRXRF to measure Hg, Se and Sr in the otoliths and surrounding water. A third study by the group²⁷⁵ measured bromine in otoliths of Norwegian coastal cod reared under known conditions and moved from one environment to another. The relocation caused marked changes in some otolith elemental concentrations with bromine being continuously accumulated along certain growth axes as revealed by 2D elemental mapping. It was thought that bromine uptake may be under physiological and genetic control and, as such, may prove useful as a stock identification tool. Espinoza-Quinones²⁷⁶ used SR-TXRF for the evaluation of trace element concentrations in the muscles, liver and gonads of fish species from the Sao Francisco River in the Parana state of Brazil. Chromium ion values were found to be above the limits defined in the Brazilian legislative norm on food. Numerous studies have addressed methyl-mercury toxicity in fish but the detailed mechanisms underlying its transport and accumulation, especially during early developmental stages, remained unclear until Korbas et al.²⁷⁷ used SRXRF to show that mercury was redistributed from the original target tissue to the eye lens. This work identified the developing lens as a major sink for methyl-mercury in the early embryonic and larval stages.

High altitude soils constitute a long-term cumulative record of atmospherically deposited elements from both natural and anthropogenic sources. Bacardit and Camarero²⁷⁸ used WDXRF to measure major and trace elements in “top” (i.e. first 10 cm) and “bottom” (i.e. below 10 cm) soil samples along an altitude transect (1,520–2,880 m above sea level) in the Central Pyrenees. The study produced a spatial pattern of accumulation of trace elements in soils as a function of altitude and an indication of background contamination in SW Europe. Time-dependent changes of zinc speciation in soils were reported by Voegelin et al.²⁷⁹ who used XAFS to assess four types of soil, ranging from strongly acidic to calcareous, spiked with 2000 mg kg⁻¹ Zn using either ZnO or ZnS as the contaminant source. The soils were incubated under aerated conditions in a moist state for up to 4 years. The extractability and speciation of zinc were then determined after 1, 2 and 4 years. After 4 years, more than 90% of the added ZnO was dissolved in all the soils, with the fastest dissolution occurring in the acidic soil. With the exception of the calcareous soil, ZnS dissolved more slowly than ZnO, reaching only 26–75% of the added ZnS after 4 years showing that the type of Zn-bearing contaminant has a significant influence on the formation of pedogenic zinc species in soils. Gardeners amongst our readership will be aware that the availability of phosphorus fertilizer to plants is decreased in acid soils. This is due to phosphate sorption onto solid-phase binding sites as demonstrated by Schefe et al.²⁸⁰ who used μ-XRF and μ-XANES to investigate the degree to which the sorption was determined by reaction with aluminium compounds and the extent to which carboxylic acid-addition may influence these reactions. This research highlighted the value of the μ-X-ray mapping techniques to add new knowledge about phosphorus chemistry in soils. Each year, this review comments on the contribution that portable XRF systems offer in survey programmes of play-areas intended for children. This year is no exception, with a report by Mielke et al.²⁸¹ on arsenic in New Orleans soils and chromated-copper-arsenate-treated wood in residential and public spaces. The consequence of rapid urbanisation and industrialisation that has taken place in China over recent decades is now reflected in the publication of assessments of heavy metal contamination in urban topsoil. Yang et al.²⁸² conducted an extensive soil survey in Changchun City to evaluate the current status of heavy metal contamination that pose a threat to human health. The authors reported topsoil enrichment with Cd, Cu, Hg, Pb and Zn. Principal component analysis identified vehicle emissions as a source of Cu, Pb and Zn with zinc primarily from vehicle tyres. Coal combustion was linked to As and Hg, whereas Cd was mainly associated with industrial sources. According to the pollution index in China, the overall levels of metal pollution were not especially high, but there were clearly contaminated sites concentrated in the central and NE districts.

Several papers were published during this Review period describing mechanisms for the removal of metal ions from aqueous solutions. Rice husk ash featured in three papers as a low cost novel adsorbent; Fan et al.²⁸³ studied the characteristics for Cu^II removal and in a second paper²⁸⁴ described its use for the removal of Cr^VI whilst Zhao et al.²⁸⁵ reported the removal of elemental mercury by iodine-modified rice husk ash sorbents. These studies were supported by XRF, XRD, SEM and FTIR analyses. Baraka et al.²⁸⁶ used XRF to show that Na-modified seashells (aragonite) were also effective for the removal of Cu^II from aqueous solutions. A mix of pulverised oyster shells and fumed silica was used by Yu et al.²⁸⁷ in a multi-technique investigation to assess the removal of phosphate from wastewater. The mix was calcined to produce hydrated calcium silicate that reacted with phosphate ions in the water to form hydroxyapatite precipitate. The developed mix showed 74% or 92% phosphate removal after 2 or 4 h respectively. Paper mulberry, Broussonetia papyrifera, leaf powder was used by Nagpal et al.²⁸⁸ to remove Cd^II, Cu^II and Pb^II from aqueous solutions. EDXRF data confirmed the sequestration of the metal ions to demonstrate that this abundantly available natural biosorbent could be effectively developed. Shomar et al.²⁸⁹ assessed whether water from waste treatment plants could be safely used for irrigation of crops such as alfalfa, oranges and lemons. XRF and ICP-OES were used to measure 26 elements in waters, sludges, soil and produce to show that treated wastewater could be reused for agricultural purposes in areas where water is at a premium. A study by Twining and colleagues²⁹⁰ demonstrated the ability of μ-SRXRF to determine the elemental content of individual cells and cellular stoichiometry. The cells in question were four functional groups (diatoms, autotrophic flagellates, heterotrophic flagellates and autotrophic picoplankton) collected from the Pacific Ocean using trace-metal clean techniques during transects across the equator at 110° W and along the equator between 110° W and 140° W. Phosphorus normalised Fe, Mn, Ni and Zn ratios were found to be significantly higher in diatoms than other cell types, while cobalt stoichiometries were highest in the autotrophic flagellates. A wealth of additional data was reported to demonstrate the substantial biogeochemical insight that could be gained from metal quotas in individual function groups. Conventional XRF and SEM techniques were used by Joseph et al.²⁹¹ to measure Ca and P concentrations in surface sediments from three mangrove systems off the SW coast of India. One of the sampling stations is a site for breeding birds with an accumulation of guano. The excreta and carcass of birds in this sanctuary was thought to be the reason for the formation of monetite, a thermodynamically metastable calcium phosphate mineral that was not found at the other two sites. Lake sediment composition determined by XRF in addition to results of core sediment experiments were reported by Lehman²⁹² to assist in the understanding of cyclic nuisance cyanobacteria in fishing lakes in Michigan, USA. The data indicated that phosphorus-release was governed by an ion trap mechanism such that phosphate and iron were released when oxygen and nitrate were depleted.

3.5 Aerosols and particles

Literature during this review period reflects a surge in analytical investigations of aerosols and particles using TXRF, a technique that until recently was mainly employed for quality control in the electronics and semiconductor industry. The technique's capability to analyse environmental samples was recognised by Borgese et al.,²⁹³ who being familiar with ICP and AAS techniques, found that TXRF offered greater sensitivity for trace heavy metal detection and was practical, accurate and reliable in occupational settings such as the analysis of air filters. Osan et al.²⁹⁴ studied the composition and speciation of aerosols with the even higher sensitivity offered by combined SR-TXRF-XANES facility at the HASYLAB Beamline L. Atmospheric aerosol particles were collected at different urban and rural locations using a 7 stage May cascade impactor adapted from its initial use for sampling Si wafers. The thin stripe geometry formed by the particulate matter deposited on the May-impactor plates was ideally suited to SR-TXRF. Information on Cu and Zn speciation was reported for elemental concentrations as low as 140 pg m⁻³. Fine particles were found to contain the metals of interest in sulfate and nitrate forms. Another convert to the ability of SR-TXRF to detect many elements in nano-gram quantities was a group in Italy,²⁹⁵ who collected filter samples in Brescia,Italy for TXRF analysis and subsequent μ-XRD at the Daresbury Laboratoies, Cheshire, UK, on the same intact filters. Richard et al.²⁹⁶ offered a method for quantitative size and time-resolved trace element evaluation in ambient aerosols with a rotating drum impactor and SRXRF. The impactor collection efficiency curves and size segregation characteristics were investigated in an experiment with oil and salt particles. Cut-off diameters were determined from the ratio of size distributions measured from two particle fractions. The calibration was based on elemental reference samples applied with an ink-jet printer on thin films; a novel approach recognised in last year's review. Wagner and Mages²⁹⁷ applied the technique of cold plasma ashing on polycarbonate filters as a preparative step for subsequent elemental analysis of aerosol particles by TXRF. Their procedure was validated by analysing filter blanks, chemicals used as additives as well as CRMs. The authors were satisfied that their technique was superior to conventional digestion methods offering a simple, contamination-free procedure. A PIXE cascade impactor was used to collect 9 size-fractionated particulates ranging from 16 to 0.06 μm aerodynamic diameter at urban and suburban sites in Goteborg, Sweden. Loaded filter segments were cut out and fixed on quartz carriers. After the addition of 10 ng of Ga as internal standard, the samples were dried, digested by cold plasma ashing and analysed by TXRF. Another study in Sweden by Boman et al.²⁹⁸ concentrated on PM2.5 particles and the ability of TXRF to offer more information on the composition of particles rather than the legal focus on sample mass. The information obtained was related to possible health effects associated with the elemental content of the particles as well as support for source apportionment. The particles were collected using a cyclone that separated PM 2.5 from the air stream for collection on polycarbonate filters.

The literature continues to reflect the plethora of activity associated with source apportionment surveys, with the majority of laboratories using WD or ED spectrometers fitted with sample changes to accommodate the large numbers of samples involved. Cuccia et al.²⁹⁹ reported an alternative method to determine size distribution in samples collected in Genoa, Italy. Their methodology was found to have two main advantages; requiring only standard semi-automatic sampling equipment and compositional analysis to provide size-segregated information averaged over periods of several months as opposed to the use of generally laborious cascade impactors that are limited to short campaign periods. A sampler designed by the Norwegian Institute of Air Protection was used by Samek and Lankosz³⁰⁰ to assess seasonal variations in three particle size fractions collected in Warszawa, Poland. Pekey et al.³⁰¹ adopted a variation on conventional data analysis by using varimax rotated factor analysis to identify possible heavy metal sources of PM2.5 and PM10 particle fractions in urban and industrial areas of Kocaeli City, Turkey. Orru et al.³⁰² determined the origin of air masses in Tartu, Estonia by computing 96 h back trajectories of air masses with a model that divided the air into four sectors according to geographical patterns; Russia, Eastern Europe, Western Europe and Scandinavia. Source apportionment surveys in China included those in Changsha by Li et al.,³⁰³ in Shanghai by Waheed et al.³⁰⁴ and in Shaanxi provice by Cao et al.³⁰⁵ Surveys continue in Belgium,^306,307 building on the wealth of data collected over the years by the renowned group at the University of Antwerp. Moving indoors, Horemans and Van Grieken³⁰⁸ reported speciation and diurnal variation of thoracic, fine thoracic and sub-micrometre airborne particulate matter in naturally ventilated office environments. Zitnik et al.³⁰⁹ measured elemental concentrations in aerosols with a 2 h time resolution in two different working environments; a chemistry laboratory dealing with the processing of advanced nano-particulate materials and a medium-sized machine workshop. Clougherty et al.³¹⁰ noted that data on PM2.5 urban matter was often modelled using land-use regression and factor analysis, however, most people spend more time indoors, where these methods were less explored. The authors developed land use regression predictive models using GIS-based outdoor source indicators and questionnaire data on their indoor sources. This approach to validating source interpretations provided direction for future studies to characterise indoor and outdoor source contributions to indoor concentrations thereby reducing misclassification and improving the relationship between particle constituents and health effects.

Other work of interest to readers of this section of the review included a characterisation of particulate exposure during firework displays by Joly et al.³¹¹ PM2.5 samples were collected during nine launches at the 2007 Montreal International Firework Competition. This study confirmed that persons in the plume and in close proximity to the launch site may be exposed to extremely high levels of PM2.5 for the duration of the display but little is known of the cardio-respiratory toxicity of the specific elements contained in such plumes. Brown et al.³¹² compared EDXRF and LA-ICP-MS analyses of ambient particulate matter. The uncertainty of each data set was estimated and compared with the data quality objectives for uncertainty specified in the relevant European air quality legislation. This has tentatively shown that approximately 75% of the analyses using both techniques met the legislative requirements. However, the authors thought that improvements in repeatability and calibration methods for both EDXRF and LA-ICP-MS would be needed before these methods were truly applicable for routine air quality measurements of this type.

3.6 Consequences of industrial activity

Heavy metals in the soils adjacent to abandoned mining areas are known to affect the ecosystem with consequences for animal and human health. Gutierrez-Gines et al.³¹³ measured As, Cd, Cr, Cu, Ni, Pb and Zn in forage crops used as human food sources or components of fodder grown on soils polluted with Al, Fe and Mn from old mines in Central Spain. The analytical data measured by XRF and ICP-OES provided the rural population, political leaders and administrators with evidence needed to encourage investment to deal with the polluted soils. In South Korea, Ok et al.³¹⁴ measured the effectiveness of natural and calcined oyster shells to remediate Cd and Pb contamination in soils around an abandoned mine. XRD, XRF and SEM data showed that the calcined shells were more effective in immobilising Cd and Pb than natural oyster shell powder. The same combination of analytical techniques was used by Recio-Vazquez et al.³¹⁵ to study elevated arsenic concentrations in groundwater in the catchment of the Madrid detrital aquifer, Spain. Although natural arsenopyrite was found in the region encapsulated in pegmatite bodies and quartz veins, mining wastes from outcropping activities had been dumped and exposed to weathering. The more soluble secondary phases of scorodite, FeAsO₄.2H₂0 and jarosite KFe₃(SO₄)₂.OH₆ were found in this waste with adverse consequences from additional arsenic release to the Madrid water supplies. Terzano et al.³¹⁶ used μ-SRXRF, μ-XANES and μ-XRD to characterise mercury species that had formed from the slow weathering of a previously inert Hg-containing waste material dumped several years ago. The newly formed Hg-species was shown to be a more dangerous source of pollution than that originally discarded. Beauchemin et al.³¹⁷ used μ-SRXRF and μ-XANES to measure the effectiveness of lime treatment of acid mine drainage that generated large volumes of neutralised sludge often stored under water. The sludge consisted mainly of calcite, gypsum and a ferrihydrite-like phase with several associated species of metalloid contaminants. The synchrotron studies indicated that arsenic was associated with iron in the sludge. Manganese and As K-edge XANES analyses showed that manganese was the redox-active element in the solid phase while arsenic was stable. After 9 months of anoxic treatment, As^V was still reported to be the dominant species in all the water covered sludge provided that organic matter accumulations were negligible. Perez-Lopez et al.³¹⁸ also benefited from synchrotron based X-ray studies to measure iron oxide transformations in terraces from the Tinto-Odiel river system, Spain. Simultaneous μ-XRD and μ-XRF analyses on the iron terrace samples that were formed during oxidation and precipitation of dissolved iron along riverbeds impacted by acid mine drainage, showed that fresh precipitates at the surface were primarily metastable schwertmannite, which was gradually transformed at depth over short-time scales into goethite. However, on a century-time scale, goethite is known to partially re-crystallise to hematite as a consequence of diagenetic processes. This transformation is accompanied by an increase in grain size and a decrease in surface area of hematite and a concomitant decrease in arsenic trapped in the solid. The authors considered that this corresponding increase in arsenic mobility should be recognised in the development of conceptual and analytical models used to describe long-term fate, transport and bioavailability of arsenic in environmental systems. Also in Spain, Gonzalez-Fernandez and Queralt³¹⁹ reported fast elemental screening of soil and sediment profiles using a small spot EDXRF spectrometer to measure the distribution of heavy metals. Cores were obtained from upstream sediments of a mining creek, from the lowland sedimentation plain and from a mine tailing dump. The 600 μm focal spot generated a core mapping of heavy metals present that was verified by a more powerful wavelength dispersive spectrometer. Oram et al.³²⁰ published μ-SRXRF measurements to monitor the influence of hyporheic exchange on selenium bio-geochemistry and mobility in sediments of East Mill Creek, Idaho, USA. Pore water redox profiles indicated that a transition to sub-oxic conditions began at approximately 6 cm. The μ-SRXRF data showed reduced elemental selenium or selenides throughout the profile and selenite in surface sediments. Field geochemical measurements and the micro-scale analysis support the hypothesis that reduction in the hyporheic zone promoted sequestration of surface water selenium. Chromium speciation in marsh soils developed in weathered chromite ore processing residue was characterised by Elzinga and Cirmo³²¹ using sequential extraction and μ-SRXRF and bulk XAS techniques. The X-ray maps and XAS data indicated the presence of micro-sized chromite particles scattered throughout the samples. These particles have relatively high resistance to weathering and therefore persisted even after prolonged leaching. The authors proposed further studies on chromium speciation to assist in the understanding of the complex weathering of the chromite ore residue. Concentrations and speciation of molybdenum together with Cu, Fe and Zn in Nver River sediments impacted by molybdenum mining activities in western Liaoning, NE China, were investigated by Yu and colleagues.³²² XRF and XRD were used to characterise metals in the tailing ponds situated on the river bank. The alkaline condition in sediments and tailing ponds was found to be a significant factor governing the chemical speciation of the analytes of interest. Molybdenum in the sediments was thought to pose a high risk to the local environment. Dusty surfaces of post-flotation wastes containing high concentrations of toxic compounds may be contained by appropriate vegetation. It has been established that effective restoration of such waste areas are best met with xerthermic, mycorrhiza-assisted plants. Turnau et al.³²³ used TXRF to evaluate elemental concentrations in the leaves of 23 plant species growing in the wild and on Pb-Zn waste. Higher levels of As, Cu, Pb, Y and Zn in plants from tailings were found to be associated with calcium, suggesting a role of this element in detoxification mechanisms. The authors also found that plants from the tailings exhibited potassium deficiency when compared to grassland specimens. Hence, it was thought that potassium supplementation of the waste substrata should be considered to improve plant growth. Of the plants investigated, three grass species (Melica transilvanica, Bromus inermis and Elymus hispidus) and one legume (Anthylis vulneraria) were reported to be most suitable for phytostabilisation.

Interest continues in the use of field portable instrumentation for the analysis of soil and other environmental materials. A topical contribution was made by Chou et al.³²⁴ who used the capability of portable XRF systems for the rapid collection of data in the field to monitor As and Pb contamination in the greater New Orleans area resulting from the devastation caused by Hurricane Katrina. They produced a map of Pb contamination that showed areas where Pb concentration exceeded EPA allowable levels. The interest of Kenna et al.³²⁵ was in improving the quality of the calibration of a field portable XRF spectrometer for use as a bench top unit in the analysis of siliciclastic soils and sediments. Their approach was to use certified reference materials as calibrators with a least squares regression that allowed for uncertainty in both x and y axes. Results for the Hudson River estuary sediments agreed very well with independent laboratory analyses. Jang³²⁶ used portable XRF instrumentation to determine heavy metals in the soil from crop-fields near abandoned mine sites. Results were compared with concentrations determined by the Korean Standard Test (a method based on extraction) and the author concluded that in situ PXRF field-screening based on a zig-zag sampling pattern was effective in achieving an economical survey. Contaminated soil in an abandoned mining area (Rodalquilar, SE Spain) was of interest to Peinado et al.,³²⁷ who used an in situ PXRF approach to measure the spatial distribution of As, Cu, Pb and Zn, which exceeded background values. The authors concluded that the main mechanism of dispersion of these elements was water and wind erosion. Lu and colleagues³²⁸ used field portable XRF to determine the total concentrations of As, Cr, Cu, Pb and Zn in soil samples from various provinces in China. The authors presented results demonstrating the effect of soil particle size and moisture content on analytical results. A decrease in particle size from 420 to 180 μm caused the relative standard deviation of XRF results to decrease from 15.6 to 6.9%. Results were also presented for the influence of moisture content compared with oven dried samples. Other environmental applications of portable XRF available in the current review year include the work of Chou et al.,³²⁹ whose interest was in the toxic element content of oyster shells to provide a rapid, quantitative, non-destructive and cost effective method of assessing oyster shell contamination from Pb, and Melquiades et al.,³³⁰ who used portable XRF to determine various metals in water, claiming that four hours of field work was adequate for preparing, measuring and analysing 14 membranes.

Readers will appreciate that other industries also benefit from studies to ameliorate their impact on the environment. Gao and Schulze³³¹ reported As, Cd, Cr and Pb measurements by synchrotron based micro-X-ray techniques to characterise metal-contaminated soil from a site that was once occupied by a lead smelter. Their studies were used to support remediation strategies in the locality. A steel plant in Nova Scotia, Canada is acknowledged to have emitted toxic pollutants into the neighbourhood for almost 100 years. Although no paper record exists of the amount and spatial variability of the pollutants emitted, MacDonald et al.³³² demonstrated that a natural record exists locked in the annual growth of native tree species in the region offering a record of their environment. Two species, white birch and eastern larch, were sampled within a 5 km radius of the steel plant site, to produce samples for EDXRF measurements of Pb and Zn in the hardwood birch and softwood larch tissues. Sracek et al.³³³ used XRF, XRD, SEM and Raman spectroscopy combined with geochemical modelling to demonstrate the impact of efflorescent salts at a Cu–Co chemical leaching plant in Zambia. Dissolution experiments using the collected efflorescent salts indicated a rapid dissolution associated with an instantaneous drop in pH to ∼4.0 and a fast increase of dissolved species concentrations. Such behaviour was thought to have a serious environmental impact at the beginning of the rainy period in November and December, when seepage through the impounded dam was recorded. Zhang et al.³³⁴ offered a μ-SRXRF method for the measurement of lanthanum eco-toxicity in China. Their elemental maps of metal distribution in single nematodes demonstrated the extent of the polluted water-bodies sampled. Vespa et al.³³⁵ used μ-SRXRF, μ-EXAFS and μ-XRD to monitor zinc pollution in soil near a smelter showing that the zinc sequestration was potentially irreversible. The Lerma River is reported to be the most polluted body of water in Mexico. For this reason, only highly resistant organisms such as water hyacinth are able to reproduce in this river. Tejeda et al.³³⁶ used TXRF to measure 14 elements in the roots of water hyacinth sampled from the river at five sites. Their data reported the average metal concentrations found and the bio-concentration factors that reflected the high pollution encountered.

Readers of earlier XRF reviews will recall that the construction industry has embraced waste materials from other sectors as it strives to reduce costs of incoming raw materials. Rodriguez et al.³³⁷ evaluated the suitability of spray-dried sludge from a water treatment plant as a prime material in the manufacture of clinker. A control product (limestone, clay and sand) was compared with the proposed alternative material, where clay was substituted with the candidate sludge, by grinding to the same fineness before heat treatment. Clinkers produce at 1450 °C for 30 min were characterised by XRF, XRD, FTIR and SEM. Granite sludge wastes were assessed by Marmol et al.³³⁸ for use in the production of coloured cement-based mortars. The sludges, characterised by XRF, XRD and SEM were found to be an effective filler in the mortars. The reddish pigment, produced by calcining at 700–900 °C also offered a coloured component to the mortar that had good compressive strength. Kurudirek et al.³³⁹ used WDXRF to assess trommel sieve waste, formed during boron ore production, for possible use as an additive in the production of Portland cement. Geopolymers are a class of versatile materials that not only find use as cement replacements and fireproof barriers but also as biological implants. Williams and van Riessen³⁴⁰ used XRF and XRD to characterise geopolymers made with fly ash from coal-fired power stations. The X-ray data was then used to formulate a mixture with a high compressive strength for a number of applications.

Other industrial sectors have assessed material previously considered as waste. Empty palm fruit bunches, a by-product of the palm oil industry, was characterised by Konsomboon et al.³⁴¹ using XRF and XRD for potential use as biomass in Thailand. Kaolinite was used to capture alkali metal vapour that evolved during combustion of the palm co-product in an attempt to minimise fouling and corrosion problems previously encountered. Premixing 8% kaolin with the empty palm fruit bunches was reported to be sufficient to capture the potassium compounds at 700 and 800 °C but at 900 °C combustion, 16% kaolin-addition was needed to capture the volatiles. At the higher melting temperature, potassium-alumino-silicates were formed from the premixed feed thereby reducing boiler corrosion. Pratt and Shilton³⁴² used steel slag as a reactive substrate for the removal of phosphorus from water effluent. SEM, XRD, XRF and chemical extractions revealed that P-sequestration was achieved by adsorption onto iron oxyhydroxides on the surface of the slag. This study raised the prospect of developing a technology for both the removal and recovery of phosphorus from the effluent. High metal containing wastes from the aluminium, tannery and electroplating industries were tested by Sushil et al.³⁴³ as precursors for catalysts. X-ray data and information from other analytical techniques showed that the catalyst obtained from a combination of red mud with tannery shavings mixed in high ratio followed by thermal treatment was the most active. Margui et al.³⁴⁴ reported the accuracy, precision and limits of detection obtained from a bench-top TXRF spectrometer for the analysis of inlet and outlet waters from metallurgical and leather tanning factories. The data were compared with measurements obtained by ICP-OES and ICP-MS after microwave digestion. The authors considered the possibilities and drawbacks of the bench-top spectrometer for rapid and routine determination of inorganic impurities such as As, Ba, Cd, Cr, Cu, Fe, Mn, Ni, Pb, Se, Sn and Zn.

3.7 Archaeological, cultural heritage and forensic

The large number of papers available for review this year reflects the continuing high level of interest in the application of XRF in the current areas of application, no less in the characterisation of paints and pigments. Indeed the non-destructive and portable properties of the XRF approach continue to make a substantial impact in this area, as reviewed by Janssens et al.,³⁴⁵ who evaluated the capabilities of a range of infrared and X-ray techniques that could provide imaging information on hidden layers in painted cultural heritage artefacts. This information was of particular value in identifying the state of conservation of old masters and in postulating the original manufacturing technology of metallic and other sculptures. Trentelman et al.³⁴⁶ evaluated instrumental parameters relevant to the measurement of X-ray line and area scans to optimise the signal from various categories of works of art. The advantages and application of a range of portable instrumentation, installed in a mobile laboratory (MOLAB), was described by Miliani et al.³⁴⁷ emphasising applications in the in situ, non-invasive study of works of art. Application of the XRF approach in the characterisation of the artist's palette of pigments were reported for the paintings of ‘Gioventu’ (Eliseu Visconti),³⁴⁸ James Ensor,³⁴⁹ painted enamel objects from the Limoges School³⁵⁰ and Brazilian artists from the 19th century.³⁵¹ In extending X-ray techniques for art conservation beyond the more traditional approach, Cotte et al.³⁵² reviewed the principles and capabilities of SR-based X-ray absorption spectroscopy in the chemical analysis of works of art, emphasising the capability of this approach to provide data on local composition and chemical states. These data can provide information on craft skills as well as alteration reactions that may change an object's visual appearance. Although pigment composition is important in all these studies, the thickness of paint layers can also be a parameter of interest as demonstrated by Trojek et al.³⁵³ who demonstrated the use of Kα/Kβ and Lα/Lβ ratios illustrated by the distribution of cinnabar in medieval manuscripts. In terms of more innovative applications, a number of authors evaluated the degradation of pigments. Alberghina et al.'s³⁵⁴ area of interest was degradation caused by soluble salts on the wall matrix and graffiti at the inquisition jails of Chiaramonte Palace (Palermo, Italy), These authors included XRF as one of the techniques to demonstrate the deleterious effect of soluble chloride, nitrate and sulfate salts. Monico et al.'s³⁵⁵ research was more specific-the process of degradation of lead chromate in paintings by van Gogh. These authors used a number of SR techniques (μ-XANES, μ-SRXRF, μ-SRXRD) complimented by EELS (electron energy loss spectroscopy), μ-Raman and μ-FTIR to show that the darkening of chrome yellow was caused by the reduction of PbCrO₄ to Cr₂O₃·2H₂O (viridian green) and another Cr^III compound; an aging process confirmed by the analysis of paint samples from two of van Gogh's paintings. The work of Sotiropoulou et al.³⁵⁶ demonstrated the prehistoric relevance of pigment studies with the use of portable XRF and XRD to analyse tools used for the preparation of pigments at Akrotiri on Thera, Greece during the period 3000–1600 BC. These studies revealed the presence of lead oxides on stone tools. As in previous years, a significant number of authors have demonstrated the value of XRF in combination with a number of complementary techniques (often Raman spectroscopy) especially where elemental and mineral identity are important objectives of the work. Such an approach has been used to characterise the paintings of Alberto Burri (1915–1995),³⁵⁷ the Wyts triptych,³⁵⁸ paintings in Antwerp Cathedral,³⁵⁹ 20th century Japanese colour sticks,³⁶⁰ Chinese funerary lacquer ware of the West Han Dynasty³⁶¹ and pigments decorating a leather screen and illuminated title pages of books of ordinances (from 1605 and 1658) owned by the Worshipful Company of Barbers where XRF was particularly useful in identifying green paints that could not be uniquely identified by Raman microscopy.³⁶²

The characterisation of pottery and ceramics continue to be objects of significant interest in the application of XRF, sometimes combined with complementary techniques. A substantial number of contributions on this topic were provenancing studies to classify artefacts by source material and if possible to identify or speculate on the source. Thus, Burley and Dickinson³⁶³ were interested in pottery sherds from the earliest archaeological site in Polynesia (Nukuleka) and suggested that ceramic vessels did not have a local origin but were brought on founding canoes. Freitas et al.³⁶⁴ classified fragments of Marajoara ceramics held at the National Museum (Rio de Janeiro). Having divided Roman pottery from the Caudium area (southern Italy) into two main groups, De Bonis et al.³⁶⁵ used mineralogical analysis and SEM observations to evaluate the firing temperature (800 to 1200 °C). Facetti-Masulli et al.³⁶⁶ used a ²⁴¹Am-excited XRF instrument to classify Neolithic Amazonian pottery sherds. Trojek et al.³⁶⁷ evaluated three configurations of a portable XRF instrument constructed at the Czech Technical University for an investigation of post-medieval pottery from southern Moravia. Other studies covered 6th century BC pottery fragments from Potenza, Italy,³⁶⁸ Roman pottery from Granada, Spain³⁶⁹ and 2nd to 1st century BC red-slipped fine ware from Cassope, Greece.³⁷⁰ A novel combination of techniques was used to characterise the medieval (6th to 13th centuries AD) production of ceramics from the Phlegrean area of southern Italy. Terenzi et al.³⁷¹ combined EDXRF with proton nuclear magnetic resonance. The EDXRF data demonstrated the elemental homogeneity of two groups of ceramic fragments, indicating continuity of source clay raw material and manufacturing methods. NMR data revealed structural differences in pore space topography and the magnetic properties of pore walls that gave further insight into the manufacturing technology. Bardelli et al.³⁷² combined non-destructive portable EDXRF with SR-XAS to provide spatially resolved data on the decorated coating of 12th to 13th century ceramic fragments of ‘protomajolica’ pottery from Sicily. An interpretation of the XAS data led the authors to propose a mixture of hydrated iron and manganese oxides as the pigmenting agent. Yang et al.³⁷³ contributed to the resolution of a mystery concerning the decline of the Fanchang kiln (Anhui Province, China), important because it was the earliest kiln to fire bluish-white porcelain (907–960 AD). WDXRF results, supported by INAA data and a glaze study showed a significant change in elemental composition of the porcelain indicating a change in raw material or production technology that led to a decline in quality and a collapse of production at the kiln. The characterisation of glazes on 12th to 15th century Byzantine pottery from two archaeological sites in Cyprus by Charalambous et al.³⁷⁴ revealed the presence of Pb and sometimes Sn with Co, Cu, Fe and Ni contributing to decorative colours. Guilherme et al.³⁷⁵ took advantage of a recent exhibition at Coimbra, Portugal to analyse locally produced polychrome lead-glazed faiences. Their results indicated a unique production centre with blue pigments containing As, Co, Fe and Mn and yellow pigments containing Pb and Sb. Their study is also of interest due to the improvements made to the non-commercial μ-EDXRF instrument, whereby the use of a capillary X-ray lens, low power X-ray tube and drift chamber detector allowed the authors to make measurements with a few tens of picometres lateral resolution.

One of the areas of application of XRF that is attracting increasing interest is the analysis of buildings and building materials of archaeological significance. In this context, archaeological mortars have featured in a number of contributions. Thus, Miriello et al.³⁷⁶ used a range of techniques, including XRF to characterise the composition of Roman, proto-Byzantine and Medieval mortars from Kyme (Turkey), a city founded in the middle of the 11th century BC by the Greeks. The hydraulic mortars developed during Roman and Byzantine periods were superior to the lower quality friable mortars used during the medieval period. Similarly, two houses at Pompeii were found to have employed three main construction phases and the use of pyroclastic deposits from Vesuvius as aggregate. Blumich et al.³⁷⁷ characterised the layer structure of historic walls and wall paintings on two buildings in Volterra, Italy, using a combination of a mobile ¹H NMR instrument and portable XRF and discriminated between paint and mortar layers and differences in the moisture content of the adhesive used to fix the wall painting to its support. XRF was one of the techniques used to characterise Iron Age hydraulic plaster from Tell es-Safi (Gath), Israel,³⁷⁸ and also renders, joint mortars and adobes (mud sun-dried blocks) from Aveiro (Portugal) by Coroado et al.,³⁷⁹ particularly to evaluate the effects of weathering, lack of maintenance or effect of a coastal environment. The decay of historic mortars by atmospheric pollution causing the sulfation of lime mortars to gypsum and the blackening of gypsum mortar was the justification of a study by Sanchez³⁸⁰ in which both XRF and SEM made a contribution. Brai et al.³⁸¹ used XPS, XRD and XRF to investigate the degradation of stone materials in the Ancient Theatre of Taormina, Sicily. Artificial stone materials in various states of conservation, and efflorescence from brick walls and mortars were analysed with results indicating that efflorescence samples contained chlorides, sulfates and nitrates from the degradation of stone materials while mortars suffered decomposition by sulfate attack. Ortiz et al.³⁸² used a range of techniques, including XRF to investigate the effect of weathering in an urban atmosphere on stone monuments in Seville, Spain. Gypsum was identified as the main weathering product from sulfur originating from automobile exhausts, but deposits of atmospheric particles were found over this alteration layer containing Al, Ba, Ca, K, Mg, Na, Si, Ti, V (from LIBS) and Fe, Mn, P and S (from XRF) of both anthropomorphic and terrigenous origin. Serra et al.³⁸³ used μ-XRF to provenance marble from the central-northern Apennines in Italy, reporting that Mn, Sr and Ti were the most useful elements for provenancing ancient statues and artefacts. The interest of Wadley³⁸⁴ went back 58 000 years to the use of cemented ash as a work surface or receptacle for red and yellow ochre powder at Sibudu, South Africa, with XRF data suggesting that the ochre was derived from different geological sources.

Obsidian is one of the geological materials of interest in the study of archaeological artefacts, exemplified by the work of Giesso et al.³⁸⁵ in provenancing of 428 artefacts from the province of Mendoza, Argentina and from Central Chile, and of Poupeau et al.³⁸⁶ who evaluated the relative capabilities of the ED-SEM and PIXE as well as EDXRF in the analysis of Anatolian obsidians and correlated them with two sources. Jia et al.¹²⁰ undertook a survey of the long-distance transport of obsidian from the Paektusan volcano (on the China-North Korea border) to eastern Russia and Korea using portable XRF for the rapid non-destructive analysis of samples from 18 Late Paleolithic sites in Northeast China. These studies revealed three other sources of obsidian and it was suggested that a two-way movement of volcanic glass occurred between Primorye and Northeast China. XRF and ED-SEM were used by Tripati et al.³⁸⁷ to undertake a geochemical and mineralogical analysis of stone anchors recovered from the west coast of India, which revealed that the anchors were made from a wide range of rock types. The authors inferred that these were sourced from rock formations in Gujarat, Goa, Karnataka and the Maharashtra regions and used in ancient and medieval periods in maritime trading activities. Tijani et al.³⁸⁸ undertook a provenancing study of sandstone from the Anambra Basin, South East Nigeria and Odriozola et al.³⁸⁹ were interested in trade patterns involving the mineral variscite from the Pico Centeno mining district of Spain in which XRD and FTIR data were combined with XRF. Their studies indicated that the P/Al atomic ratio could be used as a strong indicator of provenance. And, to exploit the full potential of aerial photography and high resolution magnetometry of ancient (Neolithic) settlements in southern Italy, XRD, XRF and optical analysis were used to characterise the soil infill in ditches and the calcareous substrate, with a particular interest in identifying magnetic minerals (pyroxenes, monometric magnetite, haematite).

As in previous years, XRF has been used extensively in the analysis of metallic artefacts, many routine in nature. One category of relevance is bronze artefacts and Valerio et al.³⁹⁰ used a number of non-invasive micro-analytical techniques (EDXRF, μ-EDXRF, ED-SEM, optical microscopy) to elucidate the metallurgical technology revealed by the analysis of 54 bronze artefacts from the inland settlement of Castro dos Ratinhos, Portugal (9th-8th century BC). Their results demonstrated the use of binary alloys with a narrow range of tin content and the authors speculated that this technology was inherited from the Late Bronze Age and indicated that Phoenician interaction with inland indigenous communities was a slow and selective process. A second study from Portugal by Figueiredo et al.,³⁹¹ in this case of the Late Bronze Age site at Viseu, used similar techniques to analyse selected artefacts and metallurgical debris including slag to show that bronze production involved smelting and recycling. The authors supported earlier proposals concerning the exploitation of tin resources in the Late Bronze Age and that bronze was widely produced on a domestic scale in this Western extreme of Europe. Melo et al.³⁹² used μ-EDXRF to analyse nine fibulae from the Iron Age Castro de Praganca site on the western Portugal coast. The fact that five of the fibulae were made of bronze with the other four being polymetallic (bronze and iron) had important implications for the very early development of metallurgical technology. A funerary gold mask from the Museum of Sican, Peru was analysed in detail using portable EDXRF by Cesareo et al.³⁹³ with results demonstrating that the majority of this artefact was made of tumbaga (low quality gold enriched at the surface by depletion gilding). Figueredo et al.³⁹⁴ were interested in Late Bronze Age gilding technology, based on the analysis (EDXRF,μ-EDXRF and ED-SEM) of artefacts at the Crasto de So Romo site, Central Portugal. The excitement in this work was a report of the first diffusion-gilded artefact identified in Portuguese territory dated to the Late Bronze Age. Constantinescu et al.³⁹⁵ applied μ-SRXRF to Carpathian gold and Romanian museum objects with the object of identifying trace elements that characterise Carpathian gold where Pb, Sb, Sn and Te were the elements of interest. In a second contribution,³⁹⁶ the authors used in addition μ-PIXE and XRF to characterise trace element tracers in primary and alluvial native gold from Transylvanian mines and placer deposits to contribute to the provenance of Romanian archaeological gold artefacts. Cannonballs were the artefact of interest to Mentovich et al.,³⁹⁷ specifically originating from the wreck of a small Mediterranean naval vessel discovered in Akko harbour, Israel. Historic and archaeological evidence obtained by optical microscopy, ED-SEM, XRF and microhardness, including a petrographic study of casting sand remaining in the voids of the cast iron, dated the vessel to circa 1840.Warmlander et al.³⁹⁸ undertook a metallurgical investigation of metal objects found at a Viking-age chieftain's farmstead located just outside Iceland's present day capital of Reykjavik. The authors identified evidence of the reuse of materials and second grade metal in some objects interpreted as Iceland's colonisers having to improvise because of shortage of materials. Chirikure et al.³⁹⁹ used a range of techniques, including WDXRF to analyse slags and refractory ceramics from two archaeological sites (ca. 1650 and ca. 1850 AD) in the Rooiberg Valley, Limpopo Province, South Africa. A comparison of slag chemistry with ore deposit mineralogy suggested that one of the sites used alluvial cassiterite, the other cassiterite from hard rock mining.

The analysis of coins continues to attract significant XRF interest as illustrated by a number of publications over the current review period. After a LA-ICP-MS and XRF study of Egyptian bronze coins from the 6th or 7th centuries AD, Torrisi et al.⁴⁰⁰ proposed the existence of a local mint in Antinoupolis, never considered before in Egyptian numismatics. In a related work, this research group⁴⁰¹ extended this study to Egyptian bronze coins from the same period, which were attributed to production sites at Alexandria and Antinoupolis. ICP-MS and EDXRF with multi-target polarising excitation geometry was used by Epstein et al.⁴⁰² to analyse first century corroded coins from Judea, in which lead isotope ratios were used to contribute to an attribution to Herod Agrippa I, noting the biblical significance of this work. Martins and Martins⁴⁰³ used EDXRF with SEM, optical microscopy and XRD to analyse a medieval silver coin of D. Afonso IX of Leon (1155–1188 AD) found at a site in Torre de Moncorvo, Portugal, with a particular interest in the corrosion products and their relationship to the burial environment. They detected the presence of cuprite, atacamite, native silver, silver oxide and silver sulfide on the outer layers of the coin. Rizzo et al.⁴⁰⁴ used portable alpha PIXE, XRF and Deep Proton Activation Analysis to characterise late Roman nummi coins (308–311 AD) minted at Carthago. The main aim of this investigation was to determine the silver content in coins produced over different periods of time and to infer manufacturing techniques. Pitarch and Queralt⁴⁰⁵ evaluated the use of EDXRF in the screening of silver coins produced by Greek colonizers who arrived in the Iberian Peninsula at the beginning of the sixth century BC. These coins had an average silver content of over 98% m/m. SRXRF was used by Rodrigues et al.⁴⁰⁶ to analyse silver-copper coins from the Ottoman Empire (16th-17th centuries), adding to previous investigations in a study designed to confirm the fineness of the coinage as well as the provenance of the alloy. Buccolieri et al.⁴⁰⁷ experimented with laser cleaning to remove ambient contamination from silver artefacts. The work was designed to optimise the laser fluence and led to the successful cleaning of a King Carlo II silver coin of 1689. EDXRF and XRD were used to measure the reduction in sulfur surface contamination. As part of a wider study, Drakaki et al.⁴⁰⁸ laser-cleaned late Roman coins and demonstrated an increase in the measured silver content after the corrosion products had been removed. Kudryashov et al.⁴⁰⁹ advised that XRF can also be used to monitor progress in laser-cleaning of the surface of historic monuments.

Glass is another archaeological artefact widely analysed by XRF as demonstrated by the study of Arletti et al.,⁴¹⁰ who characterised glass from three Italian archaeological sites dating from the 3rd century BC to the 6th century AD onwards. All samples were soda-lime-silicate glasses and Fe, Mn and Ti were found to be the principal discriminatory elements with the main differences in composition being related to chronology. Cavalieri and Giumlia-Mair⁴¹¹ presented an analysis of data of materials from the excavation of a Lombardic glassworking site in the Siena region of Italy to provide a reconstruction of glass working processes. Alberta et al.'s⁴¹² interest lay in the use of WDXRF, EPMA, SEM and XRD in the analysis of the stained glass window of the southern transept of St Anthony's Basilica, Padova, Italy. In addition to contributing to an understanding of 19th century stained glass windows, this study was designed to contribute to a combined conservation and restoration strategy. Ramli et al.⁴¹³ used XRF to evaluate whether Indo-pacific glass beads from archaeological sites in Kedah, Malaysia were manufactured locally in Sungai Mas, or imported from Arikamedu, India. Results supported local production in the 6th to 13th century AD. Portable XRF analysis of Chinese ancient glass from Xinjiang Province by Liu et al.¹²⁶ demonstrated good agreement with PIXE data and PIXE/PIGE data were compared with XRF analyses of 13th to 20th century AD glasses from different Spanish provinces by Carmona et al.,⁴¹⁴ reporting that PIXE/PIGE spectrometry was useful for heavy and light (sic) oxides as well as minor components. Because of the scope of the study, XRF was combined with XPS, SEM and UV-VIS-NIR reflectance analysis by Croveri et al.⁴¹⁵ to characterise glass tesserae from the mosaics of the Villa del Casale, Enna, Italy in a study designed to elucidate production technology and state of preservation. The authors reported the chromophore ions and opacifiers in the various tesserae and indicated that pale blue tesserae showed the greatest signs of degradation. In contrast to studies of soda-lime-silicate glass, Kato et al.⁴¹⁶ reported on Islamic plant ash glass from the 9th to 11th centuries AD from South Sinai in Egypt. On-site portable XRF data was used to divide samples into three compositional types and the authors used their results to speculate on social and commercial trading networks in the Middle East, post 9th century. Mantouvalou et al.⁴¹⁷ applied a laboratory, confocal micro-beam XRF spectrometer for qualitative investigations of historical glasses. Their results provided evidence of different manufacturing techniques used in the production of the samples investigated.

A remarkable array of other artefacts qualify for inclusion in this section. Treasure et al.⁴¹⁸ undertook a review of relics associated with the sinking of HMAS Sydney by a German raider in 1941. This review, which studied relics recovered from an unmarked grave of a potential victim, included XRF, SEM, Raman, FTIR and X-ray tomography of a metal fragment recovered from the man's skull. In contrast, Cross et al.⁴¹⁹ described the use of portable XRF in museums to monitor As and Hg levels in artefacts treated in earlier times with pesticides containing these elements. Their study was designed to demonstrate the effectiveness of a concentrated aqueous reduced-lipoic acid solution for the removal of these toxic elements. The treatment process was effective for the removal of sodium arsenate from simulated artefacts, and for the removal of mercuric chloride from cotton and paper, but not from sulfur-bearing materials such as wool and feathers. FTIR combined with EDXRF for the detection of fillers was used by Doncea et al.⁴²⁰ for the analysis of historic papers from books of the 19th to 20th centuries. The results provided information on manufacturing technology, age and approaches to preservation. Historical and modern Italian paper was studied by Manso et al.⁴²¹ using XRF, XRD and SEM with XRF contributing to the identification of fillers comprising calcite, gypsum, kaolin, talc, magnesite and dolomite. WDXRF was successfully used by Da Silva et al.⁴²² to resolve all the lines of interest in the Au–Br–Hg region of the spectrum in characterising 21st century Daguerreotype photographic paper in a study designed to evaluate the effectiveness of cleaning prints by electro-cleaning or by treatment with thiourea. Yan et al.⁴²³ used μ-XRF to analyse archaeological animal bone, of importance in elucidating the dietary habits of the creature. One of their conclusions was that enamel constitutes an excellent barrier to diagenetic influences such that Sr in bone is not susceptible to contamination from the burial environment. As a contribution to the broader field of geoarchaeology, Schmidt-Wygasch et al.⁴²⁴ used in situ XRF to measure the heavy metal content of fluvial deposits of the Inde River, Germany in a study designed to elucidate man-made contamination of the flood plain going back to, at least 2800 BC. This study was integrated with an archaeo-botanical investigation of pollen and an evaluation of historic accounts. They found significant differences in Cu, Pb and Zn concentrations related to the age of the deposit.

XRF has an important and continuing role in the analysis of samples in a wide range of forensic investigations. At the criminal end of the business, Reid et al.⁴²⁵ evaluated two techniques for the collection of gunshot residues and used SEM and EDXRF to demonstrate that the carbon coated adhesive stubs technique was superior to the alcohol swabs approach based on the number of particles collected that contained Ba, Pb and Sb. Perdekamp et al.⁴²⁶ conducted experiments to demonstrate that gunshot residues were deposited along the length of a wound channel when firearms are discharged in contact with a subject. Experiments were conducted with a composite model comprising pig skin and 25 cm gelatine blocks and XRF was used to detect primer elements (Ba, Pb, Sb or Ti, Zn depending on the primer). Kasamatsu et al.⁴²⁷ used SRXRF for the forensic discrimination of small (1 mm²) fragments of aluminium foil. Element peak intensities, effective for discrimination were Cu, Fe, Ga, Zn and Zr. Comparative measurements were made by ICP-AES and results showed that a comparison of normalised X-ray intensity data was nearly as good in the discrimination of foils as quantitative ICP-AES results. Jones et al.⁴²⁸ conducted an investigation of commercially available white powders used for the development of latent fingerprints on adhesives, using XRF, TEM, XPS and laser particle size analysis. Differences in effectiveness appeared to be largely associated with aluminosilicate anti-caking agents used in the various formulations. DeYoung and colleagues⁴²⁹ reported that PIXE offered increased sensitivity for several higher atomic number elements compared with XRF in the characterisation of glass fragments. XRF in combination with μ-Raman was used by Duran et al.⁴³⁰ to demonstrate that an Arabic illuminated manuscript supposed to be from the 14th century was a forgery, and had been repainted or retouched after the 19th century, based on the detection of titanium oxides, barite and organic synthetic colourants. Pessanha et al.⁴³¹ showed that EDXRF is suitable for the forensic analysis of manuscripts using quantification of paper and inks of books and documents based on an analysis of historic documents from the 18th and 19th century and an early 20th century book. Dhara et al.⁴³² showed that TXRF could be used to differentiate tagged and untagged inks, by evaluating the amounts of REE in painted papers and single REE-tagged inks and comparing TXRF results with ICP-MS data. XRF together with XRD and an isotope-dating test were used by Horak and Emery⁴³³ to undertake a forensic investigation of the premature failure of an asphalt surface layer on a major road in South Africa. The investigation focused on the absence of the prescribed quantity of lime and the reduced thickness of the filler binder mastic.

3.8 Industrial

Ahmed and Selim focussed their research, published in two reports, on the development of new anticorrosive pigments in paint for protection of steel. In the first contribution,⁴³⁴ the anticorrosive effects of a pigment based on bulk of talc and covered with a surface layer of titanium oxide, were investigated and XRF was used to elucidate the concentration of the different elements present. An increased thickness layer of titanium oxide enhanced the anticorrosive properties of the new pigment. Secondly,⁴³⁵ anticorrosive hybrid pigments were prepared by depositing a surface layer of an expensive efficient anticorrosive pigment (ferrite) on a bulk of cheap extender pigment (kaolin). EDXRF was used to estimate the concentration of each element in the pigments. The results showed that these eco-friendly pigments could replace hazardous pigments such as chromates.

EDXRF was shown to be a valuable technique to verify contaminants when recycling plastic material. Romao et al.⁴³⁶ developed a model to predict the weight percent of post-consumption bottle-grade PET in commercial PET samples. Indeed, recycled PET showed Fe K alpha emission lines with higher intensities than those presented by virgin bottle-grade PET. Therefore, iron could be assigned as the intrinsic contaminant after the recycling process and could be used to indicate class separation of bottle-grade PET samples. Driven by the presence of Sb contamination in drinking water from PET bottles, Martin et al.⁴³⁷ examined the elemental distribution and chemical form of residual Sb used as a catalyst in the manufacture of PET bottles. Micro-SRXRF analysis revealed clusters of Sb^III having dimensions of the order of tens of micrometres. Bezati et al.⁴³⁸ used EDXRF to detect rare earth oxides added into the polymer matrix as tracers in order to increase sorting selectivity of polypropylene during end-of-life recycling. The XRF test system was evaluated by analysing several samples containing rare earth oxides (CeO₂, Dy₂O₃, Er₂O₃, Nd₂O₃, Y₂O₃ and Yb₂O₃) in different concentrations. It was possible to detect 5 of the 7 tracers tested for 1 min. exposure time and at a concentration level of 1000 mg kg⁻¹.

During this review period the research performed in the framework of Restriction of Hazardous Waste (RoHS) and Waste from Electrical and Electronic Equipment (WEEE) was dedicated to the sample preparation procedures prior to analysis. Wienold et al.⁴³⁹ investigated the influence of the sample pretreatment of PCBs from personal computers on the precision and reproducibility of Cd, Hg and Pb results obtained by ICP-OES, XRF and CV-AFS (for Hg). A size reduction of the particles down to 1.5 mm could already be sufficient for decision-making with respect to RoHS compliance. However, to ensure analytical results with relative standard deviations of less than 20%, as recommended by the EN 62321, further particle size reduction might be required; but this was strongly related to the mass fraction of the element under investigation. In a preliminary study by Martin et al.,⁴⁴⁰ the EDXRF results clearly showed that the applied sample preparation as well as the measurement location on the PCB had a significant impact. Comparative analyses were performed on individual parts of the PCB and subsequently on the same parts ground up into a fine powder with a cryogenic laboratory grinding mill. Generally, higher concentrations of metals were observed in the ground samples. This meant that spot checking of various locations on a PCB with a hand-held EDXRF device might produce misleading results, whilst on the other hand the preparation of a homogeneous sample might yield a more representative result for the overall composition of the PCB.

An interesting guide with practical advice and methodology for the chemical analysis of glass making sands was presented by West. The first part⁴⁴¹ addressed sampling and physical testing, including the determination of moisture, inspection for contamination and particle size analysis. Part 2⁴⁴² focussed on chemical analysis describing both the conventional wet chemical techniques and the XRF technique. With respect to XRF, a clarification was given about the benefits of the XRF technique in combination with hints regarding the proper selection of the required sample preparation method (fused glass beads, pressed powder pellets and loose powders). Smolders and Krystek⁴⁴³ used the WDXRF technique to set up a quantitative method to control the chemical composition of recycled glass, in order to guarantee a high and constant level of production quality. The sampling procedure for recycled glass including TV glass and subsequent sample preparation steps up to the melting of the fused glass beads were described. A WDXRF method was developed and validated for the determination of the concentration of 18 elements using a multiple point calibration set up with both certified and in-house prepared reference materials. During the collection of recycled TV glass, two main streams were produced, meaning Pb-free panel glasses (clear screen glass) and high-Pb containing funnel glass (mixture of screen and cone glass), which could clearly be identified using WDXRF. The developed protocol could elucidate the different composition of the collected samples and allowed accurate determination of the relevant inorganic components, minor components and contaminants of various types of recycled glass. Yoshida et al.⁴⁴⁴ used WDXRF to evaluate the antimicrobial effect of porcelain glaze with silver-based clay antimicrobial agent. The results showed that the negative activity could be correlated with the disappearance of the Ag in the glaze.

Tests on the stabilisation and solidification of lead in cement matrices were performed by Gollman et al.⁴⁴⁵ The leaching behaviour was monitored by GF-AAS, whilst the metal mobility along the cement block was monitored by XRF. Complementary techniques were employed in the characterisation of the modified matrices. Lead incorporated matrices have shown that a long cure time was more suitable for avoiding metal leaching. Moreover, XRF analyses showed that the Ca concentration was lower in matrices where Pb was added. An interesting study was reported by Margui et al.⁴⁴⁶ that dealt with the determination of water-soluble Cr^VI in clinker samples. The application of a simple and low-cost Cr^VI isolation procedure on activated thin layers (a commercial polyvinylidene difluoride impregnated with an organic solution) was followed by WDXRF analysis. Results showed that the analytical performance of the proposed methodology was similar to that of the reference spectroscopic method commonly applied for water-extractable Cr^VI determination at cement-industries laboratories. The calculated detection limit of 0.3 mg kg⁻¹ was suitable for the intended purpose and was almost ten times lower than the maximum Cr^VI content permissible in commercial cements (according to the 2003/53/EC Directive). WDXRF spectrometry combined with a multivariate least-squares calibration method and reflection colorimetry were successfully used for rapid monitoring the Fe₂O₃/FeO ratio in calcium aluminate cement.⁴⁴⁷ The chemical composition of a range of building materials used in Turkey was examined by Cevik et al.⁴⁴⁸ using EDXRF. Generally, the most abundant oxides in all samples were Al₂O₃, CaO, Fe₂O₃, K₂O, MgO, SiO₂ and SO₃. While the main chemical component of gas concrete, cement, sand and marble samples were SiO₂ and CaO, brick and roofing tiles consisted mainly of Al₂O₃ and SiO₂. Calcium oxide and SO₃ were the major components of lime and gypsum samples, respectively.

To gain insight into the chemical alteration and its effect on the mobility patterns of chemical species in coal fly ash weathered in stockpiles, the chemical and mineralogical composition of these samples were investigated by Akinyemi et al.⁴⁴⁹ using IC, ICP-OES, FTIR, XRD and XRF. The XRF results showed major oxides, such as Al₂O₃, Fe₂O₃, SiO₂, while CaO, K₂O, MgO, MnO, P₂O₅, SO₃ and TiO₂ occurred in minor concentrations. The major elements Fe, K, Mg, Mn and Si and the trace elements P and Zn, reflected an increasing trend down the depth of the core (20-year-old coal fly ash), while Al and Ti and traces of Ba, Cr, Ni, Pb, Sr and V showed the opposite pattern. The trace metal distribution patterns in 1-year-old ash showed increasing trends down the depth of the core for Cr, Ni, Pb, P, S and Y while Ba and Sr decreased.

In an attempt at understanding the problem of severe slag formation in biomass-fired boilers, Niu et al.⁴⁵⁰ successfully characterised slags formed at the different superheater stages in a 12 MW biomass-fired grate furnace using XRF and XRD. A quantitative XRF method for the determination of F in slags produced in the stainless argon-oxygen decarburization process, was proposed by Jung et al.⁴⁵¹ using the pressed pellet method. Synthetic standards were prepared in order to set up and validate the calibration curves for Al₂O₃, CaO, Cr₂O₃, F, MgO and SiO₂. Although the authors considered the precision and accuracy of the method as satisfactory, one can wonder whether the pressed pellet method was suitable and sufficient to determine F in real slag samples due to particle size influences and critical depth.

For quality control of SiC-based grinding tools, Gazulla et al.⁴⁵² described extensively the development of a chemical characterisation method. Silicon carbide grinding tools were selected from the different tile polishing steps, thus involving grinding tools containing different SiC grain sizes. Different steps might be distinguished in the chemical characterisation of the SiC-based grinding tools, ranging from sample preparation to the determination of each grinding tool component by various techniques. WDXRF was applied for the determination of Al, Ca, Cl, Fe, K, Mg, Mn, Na, P, Si and Ti in pressed pellets and fused bead samples while crystalline phases were characterised by XRD and the different forms of carbon were determined using a series of elemental analyses. For the elemental analysis of C a sample below 150 μm particle size was used, while for the XRD and XRF analyses a sample below 60 μm was used. The method was validated with synthetic mixtures or reference materials, as there are no specific reference materials of SiC grinding tools available. Moreover, the same research group developed a methodology for the determination of minor and trace elements in petroleum cokes by WDXRF in order to develop a rapid and reliable control method, because these elements determine coke end-uses.⁴⁵³ To fulfil the required detection limits and to cover all the elements of interest, the method described in ASTM D6376 was optimised with respect to the sample preparation as well as the measurement conditions. Pressed pellets were prepared under conditions of high cleanliness of the mills, crushers, presses, and dies, and of the laboratory itself. Reference materials were used for both the calibration and the validation of the WDXRF method. In addition, a series of materials were analysed by WDXRF and ICP-OES, and the results were compared. The developed WDXRF methodology achieved very low detection limits and measurement uncertainties were obtained for the following elements: Al, Ba, Ca, Cr, Cu, Fe, Ge, K, Mg, Mn, Mo, Na, Ni, P, Pb, S, Sb, Se, Si, Sn, Sr, Ti, V, and Zn. Zhang et al.⁴⁵⁴ investigated the sulfur content in 235 samples of vehicle fuel from urban areas and highway service stations in northern China using EDXRF. The results showed that 41% of the gasoline samples had a S content below 150 mg kg⁻¹, consistent with the China III gasoline standard that became effective from January 1st, 2010. At that time, the China national standards for vehicle emissions were similar to Euro III. For diesel fuel, only 13% of samples contained S concentrations below 350 mg kg⁻¹, appropriate for the China III vehicle diesel standard, which is effective from July 1st, 2011. About 72% of the diesel samples contained S concentrations ranging from 500 to 2000 mg kg⁻¹, only appropriate for pre- Euro II diesel vehicles to use. The high S levels in both gasoline and diesel fuel diminish the performance of vehicle emission controls. A coordinated systematic approach in implementing emission standards together with appropriate fuel standards would lower vehicle induced pollution.

A method for the simultaneous determination of As, Co, Cr, Cu, Fe, Ni, Pb and Zn in liquid chemical waste using EDXRF was evaluated by Almeida et al.⁴⁵⁵ A small sample volume (200 μL) was dried on a 6.35 μm thick Mylar film at 60 °C and the analyses were carried out using an EDXRF spectrometer operated with an X-ray Mo tube (Zr filter) at 30 kV and 20 mA. The acquisition time was 300 s and the element Ga was utilised as internal standard at 25 mg L⁻¹ for quantitative analysis. The method trueness was assessed by spiking and the detection limit for those elements ranged from 0.39 to 1.7 mg L⁻¹.

Finally, it's always a pleasure to notice how well the XRF technique in combination with other complementary analytical techniques, is established for the chemical characterisation of materials such as catalysts, modified zeolites and clays, mesoporous silicate molecular sieves and steel slags. As these contributions are more dedicated to the performance of the material itself rather than to the analytical XRF measurement, they are not incorporated in this section. Interested readers should refer to our companion ASU review on Industrial analysis: metals, chemical and advanced materials.⁵

3.9 Clinical

Trace metal imaging in biomedical research is definitely an emerging field as shown by the number of published reviews and new applications. In a review by Qin et al.⁴⁵⁶ experimental studies on the nano-meter scale were highlighted using metal-imaging techniques, including LA-ICP-MS, SIMS and SRXRF in order to demonstrate the sensitivity, the spatial resolution, specificity and quantification ability of these techniques. Moreover, Petibois⁴⁵⁷ showed in his review that imaging instruments, which includes μ-XRF, are able to provide interesting information about a cell, from high spatial and time resolution. When grown sufficiently, it is possible to envisage quantitative analysis of chemical species inside subcellular compartments. Pascolo et al.⁴⁵⁸ demonstrated the potential of advanced synchrotron-based X-ray imaging and microspectroscopy techniques for studying the response of human lung tissue to the presence of asbestos fibers. The X-ray absorption and phase contrast images with simultaneously monitored XRF maps of tissue samples, had revealed the location, the distribution and elemental composition of asbestos bodies and associated nanometric structures. These results provided clear evidence that Mg, in addition to Fe, was involved in the formation mechanism of asbestos bodies. Kinoshita et al.⁴⁵⁹ used μ-SRXRF to determine the Fe distribution in the lobules of human livers. Iron deposits were distributed predominantly in periportal hepatocytes in a normal liver, in a decreasing gradient from the periportal area to the perivenous area. On the other hand, Fe deposits in the periportal area were more intense than those in the centrilobular area in both a liver with chronic hepatitis C and a cirrhotic liver.

Several contributions presented the powerful combination of gel electrophoresis and XRF for the analysis of protein metal binding. Zahler⁴⁶⁰ described in general the benefits of combining gel electrophoresis with SRXRF imaging for simultaneously examining multiple proteins and metal ions of interest. Finney et al.⁴⁶¹ used this approach for identifying metal protein adducts in complex samples using native- or SDS-PAGE, blotting, and rapid SRXRF with μ-XANES. The identification and quantification of each metal bound to a protein spot was demonstrated and the technique was applied to the in vitro speciation of Cr in blood serum proteins and the in vivo Fe speciation in Shewanella oneidensis. Lima et al.⁴⁶² investigated the presence of Ca, Fe and Zn in protein spots in samples of Nile tilapia liver tissue, obtained after protein separation by 2D-PAGE and subsequent qualitative and quantitative evaluation by SRXRF and FAAS, respectively. The measurements indicated the presence of Ca, Fe and Zn in 12, 6 and 8 liver protein spots, with concentration ranges from 1.08 to 5.80 mg g⁻¹, 2.02 to 8.03 mg g⁻¹ and 1.60 to 8.55 mg g⁻¹, respectively.

A study of trace element behaviour in cancerous and healthy tissues from colon, breast and stomach was performed by Magalhaes et al.⁴⁶³ using TXRF. The elemental distribution of Br, Cl, Ca, Cr, Cu, Fe, K, Mn, Ni, P, Pb, Rb, S, Se, Sr and Zn in these samples showed that the behaviour of the elements was tissue dependent. Some elements, such as K and P exhibited the same behaviour in all the analysed tissue types with increased concentrations in all cancerous tissues. Other elements such as Br showed completely different behaviour depending on the tissue. A similar Br concentration was observed in tissues from both a healthy and a cancerous stomach, while decreased levels in colon cancerous tissues and enhanced concentrations in breast tissues were measured. Moreover, cancer tissues presented decreased Se concentrations in those from the colon and increased concentrations in those from the breast. Al-Ebraheem et al.⁴⁶⁴ reported the determination of Cu, Fe, and Zn oxidation states in invasive ductal carcinoma from breast tissue and from normal surrounding tissue using XANES. Twenty-two normal and 23 tumour regions, spread over 30 formalin-fixed, paraffin-embedded tissue samples of human primary invasive breast cancer were investigated. A micro-mapping analysis of the metal distribution in the tissue was performed prior to XANES analysis to identify and localise the metals in the tumour and normal tissue regions. The aim was to identify the oxidation states of Cu, Fe and Zn in order to correlate them with the carcinogenesis process. The authors concluded that in order to estimate the best target for therapy, more information was required about the relative abundances of Cu, Fe, and Zn binding proteins, their oxidation states and their localisation at the subcellular level. Zaichick and Zaichick⁴⁶⁵ developed a procedure for radionuclide-induced ¹⁰⁹Cd EDXRF, to estimate the Zn content together with those of Br, Rb and Sr in both fresh and dry needle-biopsy specimens of human prostate, as well as in samples made of lyophilised and homogenised tissues of resected prostate. The EDXRF facility was compact and could be located in close proximity to the site carrying out the biopsy procedure. Crossley et al.⁴⁶⁶ studied the uptake and distribution of a Pt^II-carborane complex within a tumour cell using SRXRF imaging. Although a significant cellular uptake of Pt existed, there was no significant accumulation of the element within the cell nuclei. Other statistically significant changes from the XRF data included an increase in Cl, Cu and K levels, and a decrease in Fe within the treated cells. Lewis et al.⁴⁶⁷ reported intracellular synchrotron nano-imaging and DNA damage/genotoxicity screening of novel lanthanide-coated nano-vectors. In cancer therapy, research has focused on the development of nano-carriers that could aid diagnosis, deliver therapeutic agents, and progress monitor treatments. The authors introduced high-resolution synchrotron X-ray fluorescence microscopy (SR-XFM) to investigate intracellular localisation of novel lanthanide-coated nanoparticles in human cells. They were able to demonstrate the unprecedented capability of SR-XFM for extremely sensitive nano-imaging and intracellular elemental mapping of noble metal nano-particles in cells. They concluded that the variable genotoxic impact of newly designed nano-vectors emphasised the need for careful and comprehensive testing of biological responses of all new nano-constructs intended for future clinical applications. This could be greatly facilitated by SR-XFM nano-imaging of nano-particles in cells at very low concentrations.

Several contributions used SRXRF to determine elemental concentrations and mapping in tissues in order to correlate these results with a disease profile. Chwiej et al.⁴⁶⁸ used μ-SRXRF for topographic and quantitative elemental analysis of tissue from rat brains suffering from pilocarpine-induced epilepsy and neuroprotection with FK-506. In a second contribution⁴⁶⁹ μ-SRXRF was used to elucidate long-term changes in the levels and distributions of trace elements such as Ca, Cl, Cu, Fe, K, P, S and Zn in nerve tissue from rats with neocortical brain injury. The authors noted that identical changes in the same areas were observed for animals with pilocarpine-induced seizures described in the previous contribution. In the last contribution,⁴⁷⁰ cluster and discriminant statistical methods were applied for grouping the results of synchrotron-based microbeam XRF analysis of substantia nigra tissue samples representative of Parkinson's disease, finding statistical differences between the control and disease affected groups. Leskovjan et al.⁴⁷¹ quantified the brain Fe content and found that elevated Fe concentration coincided with early plaque formation in a mouse model of Alzheimer's disease. Using SRXRF and EXAFS spectroscopy, George et al.⁴⁷² demonstrated the presence of phosphate-bound Gd in autopsy skin tissues from patients with nephrogenic systemic fibrosis, a disease associated with exposure to Gd-based contrast agents used in magnetic resonance imaging. Chronic exposure to manganese results in neurological symptoms referred to as manganism which is a risk factor associated with Parkinson's disease. Carmona et al.⁴⁷³ showed that manganese was accumulated within “Golgi” apparatus in dopaminergic cells by applying SRXRF nano-imaging at the undulator beamline at ESRF, Grenoble. The manganese causes cell death in the dopaminergic cells. The mechanism of the manganese cytotoxicity is unexplained. It was found that manganese was located in the Golgi apparatus of PC12 dopaminergic cells at physiological concentrations. Manganese was accumulated at increasing levels of concentrations within the Golgi apparatus until cytotoxic levels were reached and the storage capacity was exceeded. Cell exposure to manganese and brefeldin-A caused the collapse of the Golgi apparatus resulting in an intercellular redistribution of manganese which accumulated in the cytoplasm and the nucleus. These results showed that the Golgi apparatus plays an important role in the manganese detoxification in the cell. Additionally, manganese exposure leads to a decrease in the total iron content, contributing to an overall neurotoxicity.

As an alternative for the traditionally applied K-X-ray fluorescence (KXRF) technology for Pb in bone measurements, Nie et al.¹⁴⁰ investigated the methodology and feasibility of developing a portable XRF to quantify Pb in bone in vivo. The detection limit of the portable XRF device was 8.4 μg g⁻¹ with 2 mm tissue thickness. Comparable sensitivity and good correlation with KXRF measurements were obtained. The entrance skin dose delivered to the human subject was about 13 mSv and the total body effective dose was about 1.5 μSv that should pose minimal radiation risk. A study dedicated to radiation dose measurements when performing proposed measurements of As and Se in human skin with a portable XRF instrument comprising a miniature X-ray tube and a silicon PIN diode detector, was carried out by Gherase et al.⁴⁷⁴ The effective dose for a 1 cm × 1 cm skin area was estimated to be 13.2 mSv, while the effective dose corresponding to a proposed As and Se skin measurement was estimated to be 0.13 μSv for a 2 min. irradiation. Research studies using the KXRF technology for bone lead measurements strengthened the evidence that cumulative lead exposure increases the risk of Parkinson's disease⁴⁷⁵ and might be an important risk factor for age-related hearing loss.⁴⁷⁶ Wright et al.⁴⁷⁷ found that changes in DNA methylation within white blood cells might represent a biomarker for past lead exposure.

Thin sections of articular cartilage affected by osteoarthritis were examined by Bradley et al.⁴⁷⁸ using low energy μ-SRXRF, μ-PIXE and μ-PIGE, primarily to investigate the distribution of essential cations and anions. The authors pointed out that the combination of these techniques offered the ability to make a comprehensive assessment of the elemental content of such issues and simultaneous mappings of a range of relatively low atomic number ions being obtained over quite large areas. In two contributions the influence of strontium ranelate therapeutic treatment for osteoporosis is investigated. Busse et al.⁴⁷⁹ studied the effect on biphosphonate-altered hydroxyapatite using quantitative backscattered electron imaging and energy-dispersive X-ray analysis combined with μ-XRF to observe any mineralisation changes. The data showed that strontium ranelate treatment led to an increased Sr content within the biphosphonate-altered hydroxyapatite nanocomposites and was accompanied by changes in mineralisation and microstructure. Secondly, Roschger et al.⁴⁸⁰ provided evidence that the investigated bone quality determinants at tissue level were preserved in postmenopausal osteoporotic women after 3 years of strontium ranelate treatment, using multiple complementary techniques among which μ-SRXRF elemental mapping. Meirer et al.⁴⁸¹ performed chemical speciation of lead accumulated in tidemarks of human articular cartilage by XANES. A highly specific accumulation of the toxic lead was measured in the transition zone between non-calcified and calcified normal human articular cartilage. This transition zone, the so-called ‘tidemark’, was considered to be an active calcification front of great clinical importance. Using spatially resolved μ-XANES at the Pb L₃-edge, the chemical species of lead in the osteochondral region were investigated. The feasibility of the μ-XANES set-up at the SUL-X beamline (ANKA synchrotron light source) was tested and confirmed by comparing XANES spectra of bulk Pb-reference compounds recorded at both the XAS and the SUL-X beamlines at ANKA. The μ-XANES set up was then used to investigate the tidemark region of human bone. The spectra recorded at the tidemark and at the trabecular bone were found to be highly correlated with the spectra of synthetic Pb-doped carbonated hydroxyapatite, suggesting that in both of these very different bone tissue locations, lead was incorporated into the hydroxyapatite structure.

Elemental characterisation and speciation of human nails using synchrotron-based techniques was thought to be useful in order to detect illness-related changes. In a first contribution, Katsikini et al.⁴⁸² collected XRF maps of human nails, recorded with a lateral resolution of 5 μm, and revealed that Ca, S and Zn were distributed homogeneously while Fe tended to cluster. In the Fe-rich clusters, which had a diameter in the range from 15 to 30 μm, the Fe concentration was 10 times higher than in the matrix. The Zn-K EXAFS spectra revealed that Zn, in the nails from healthy donors and patients suffering from lung diseases, was four-fold coordinated with N and S and the Zn-N and Zn-S distances were equal to 2.03 Å and 2.25 Å, respectively. In a second contribution,⁴⁸³ the distribution and the spatially-resolved bonding environment of Fe in human nails of healthy and ill donors affected by lung cancer were further investigated. Pearce et al.⁴⁸⁴ explored the uptake of arsenic in toenail clippings of children living in a historic gold mining area using synchrotron-based X-ray microprobe techniques. In clipping thin sections (n = 2), the XRF mapping showed discrete layering of As consistent with nail structure, and irregular As incorporation along the nail growth axis. Arsenic concentrations were heterogeneous at 10 μm × 10 μm microprobe spot locations investigated. XANES spectra suggested the presence of two distinct arsenic species: a lower oxidation state species, possibly with mixed sulphur and methyl coordination and a higher oxidation state species. Depth profiling suggested that surface contamination was unlikely (n = 4), and XRF and XANES analyses of thin sections of clippings incubated in dry or wet mine waste, or untreated, suggested that direct diffusion of arsenic occurred under moist conditions.

An interesting study related to the maternal-fetal distribution of Ca, Cu, Fe and Zn in pregnant teenagers and adults was conducted by de Moraes et al.⁴⁸⁵ using SR-TXRF. The levels of Ca, Cu and Zn in maternal and cord plasma from teenagers were not significantly different than those from adults, whilst Fe levels in the teenagers were higher than in the adults. All of the minerals measured were present at higher levels in the placentas from adults than those from teenagers. However, the low quantities of placental Ca, Cu, Fe and Zn in the teenagers did not compromise the levels of these minerals in the cord plasma. Future research regarding the placental transport of these minerals was recommended to investigate the efficiency of mechanisms of transfer of these minerals in pregnant teenagers. Abraham et al.⁴⁸⁶ used the SR-TXRF technique to investigate the influence of smoking on the elemental composition of oral fluids. Two sets of patients, smokers and non-smokers, were selected and the elemental concentrations were measured in their saliva and gingival crevice fluid. The results revealed significant differences between both groups in the elemental concentration of Ca, K and S in saliva, while only a few differences, related to the concentration of Cl, were observed in gingival crevice fluid.

A toxicological study of injuries of rat's hippocampus after lead poisoning was performed by Liang et al.⁴⁸⁷ using μ-SRXRF. The Pb concentrations in blood, bone and hippocampus collected from rats subject to lead poisoning were quantified by ICP-OES, while morphological information and elemental distributions in the hippocampus were obtained with SR- X-ray phase contrast imaging and μ-SRXRF, respectively. Analysis revealed that some essential elements such as Cl, K, P and S increased in the regions with high Pb content in the treated hippocampus. The study proved that synchrotron radiation methods are very powerful for investigating structural injury caused by heavy metals in the nervous system. The influence of chronic arsenic uptake on the association between As and Cu renal cortex accumulation and physiological and histological alterations was studied by Birri et al.⁴⁸⁸ using 9 male Wistar rats. The As and Cu mapping was carried out by μ-SRXRF using a collimated white synchrotron spectrum (300 μm × 300 μm) on kidney slices (2 mm thick) showing As and Cu co-distribution in the renal cortex. Then, renal cortical slices (100 μm thick) were scanned with a focused white synchrotron spectrum (30 μm × 30 μm). Peri-glomerular accumulation of As and Cu at 60 and 120 days of arsenic consumption was found. The effects of 60 days of arsenic consumption were seen in a decreased Bowman's space as well as a decreased plasma blood urea nitrogen/creatinine ratio. Major deleterious effects, however, were seen on tubules at 120 days of exposition. Guerra et al.⁴⁸⁹ determined the elemental distribution of Ca and Pb in different regions of primary incisor of children living in a notoriously contaminated area (Santo Amaro da Purificacao, Bahia State, Brazil). The measurements were performed in standard geometry of 45 degrees incidence, excitation with a white beam and using a conventional system collimation (orthogonal slits) in the XRF beamline at the Synchrotron Light National Laboratory (Campinas, Brazil). Cox and Green⁴⁹⁰ performed a study to verify the Pb content in 1500 pieces of jewellery using XRF followed by laboratory verification. They noticed a significant reduction in the prevalence of lead-containing jewellery compared to previous measurements in the past in California. Moreover, only about 4% of the analysed samples failed to comply with California lead standards.

3.10 Drugs

In a study by Weekley et al.⁴⁹¹ the uptake, distribution and speciation of selenomethionine (SeMet) and Se-methylselenocysteine (MeSeCys) supplements by human cancer cells were investigated. X-ray absorption spectroscopy of bulk cell pellets treated with the selenoamino acids for 24 h showed that while Se was found exclusively in carbon-bound forms in SeMet-treated cells, a diselenide component was identified in MeSeCys-treated cells in addition to the carbon-bound selenium species. X-ray fluorescence microscopy of single cells showed that Se accumulated with S in the perinuclear region of SeMet-treated cells after 24 h, but μ-XANES mesurements in this region indicated that Se was carbon-bound rather than sulfur-bound. X-ray absorption and X-ray fluorescence studies both showed that the Se content of MeSeCys-treated cells was much lower than that of SeMet-treated cells. In a study by Chadha et al.⁴⁹² the influence of zinc supplements on chemically-induced colonic carcinogenesis was evaluated. Rats were segregated into four groups: normal control, dimethylhydrazine (DMH) treated, zinc treated and combined DMH and zinc treated group. EDXRF studies of the colonic samples revealed that the concentrations of the elements Cr, Cu, Mn and Zn were decreased, whereas the concentration levels of Fe were found to be increased in the colon tissues following 8 and 16 weeks of DMH treatment. However, zinc supplementation to DMH-treated rats significantly improved the altered levels of elements when compared with DMH-treated animals indicating the chemopreventive role of zinc. Stosnach⁴⁹³ tested TXRF regarding its suitability for Se analysis in different medical, food basics and dietary supplement samples applying the most simple sample preparation techniques. The reported results indicated that accurate analysis of Se in all sample types was possible with acceptable detection limits in the range from 7 to 12 μg L⁻¹ for medical samples and 0.1 to 0.2 mg kg⁻¹ for food basics and dietary supplements. Da Silva et al.⁴⁹⁴ used WDXRF spectrometry for the quantification of Al and Sr in calcium supplements, required for the maintenance of dialysis patients. The use of readily available oyster shell-based calcium was found potentially to increase the total amount of ingested strontium substantially with concentrations reaching 2.26 ± 0.05 mg Sr (g Ca)⁻¹, while the use of antacids or chewable supplements was found to contain concentrations reaching as high as 1.2 ± 0.3 mg Al (g Ca)⁻¹ in the supplements analysed within this work. It was recommended that the choice of calcium supplement prescribed to individuals undergoing haemodialysis should be closely regulated and noted as a possible factor in the prevalence of bone disorders reported in these patients.

The EDXRF technique was used by Saha et al.⁴⁹⁵ for the determination of trace element profiles during different developmental stages of somatic embryogenic callus of an economically important medicinal plant, Plantago ovata Forssk. Subsequent experiments showed significant alteration in the concentration of Br, Ca, Cu, Fe, K, Mn, Sr and Zn in both the embryogenic and non-embryogenic callus. A higher Ca, Cu, Fe, K and Zn accumulation was observed in the embryogenic tissue stage as compared to the other stages, suggesting these elements are crucial for successful embryogenesis. Lin et al.⁴⁹⁶ described 4 cases of paediatric lead intoxication from imported Indian spices and cultural powders, and therefore, determined Pb concentrations in these products and predicted the effects of ingestion on paediatric blood Pb levels. XRF measurements showed that 22 of the 86 spices and food products, and 46 of 71 cultural products contained more than 1 μg g⁻¹ of Pb, while 3 Sindoor products contained more than 47% m/m of Pb. Chronic exposure to these spices and cultural powders might cause elevated blood Pb levels. The authors suggested, and with reason, that clinicians should routinely screen for exposure to these products. For the evaluation of heavy metal poisoning due to improper use of a traditional ayurvedic drug, Borgese et al.⁴⁹⁷ used the TXRF technique. For this analysis, a 1 cm cut of the patient's hair was directly deposited onto the quartz glass sample carrier, then 10 μL of nitric acid (65%) were added and dried in air. TXRF showed high versatility, rapid and simultaneous element detection, and short analysis time, thus supporting its wider use in emergency medicine and in forensic analyses. Finally, Arzhantsev et al.⁴⁹⁸ introduced a rapid limit test for the determination of metal impurities in pharmaceutical materials by hand-held XRF using continuous wavelet transform filtering. In this limit test the wavelet domain signal-to-noise ratios at the energies of the elements of interest were compared to an empirically determined signal-to-noise decision threshold. The limit test was evaluated in a collaborative study that involved 5 different hand-held XRF spectrometers used by multiple analysts in 6 separate laboratories across the United States. In total, more than 1200 measurements were performed. The detection limits estimated for As, Cr, Hg and Pb were 8, 150, 20, and 14 μg g⁻¹, respectively.

Melquiades et al.⁴⁹⁹ determined inorganic elements in sunscreen using a portable EDXRF device. Fifteen commercial samples with different sun protection factors (SPF) from different brands were analysed without any sample preparation. The measured TiO₂ and ZnO concentration values were related to their respective SPF values, and the presence of Br, Ce, K and Sr in the sunscreen samples was verified.

3.11 Biological

Confocal μ-SRXRF using a fast dynamic scanning approach was employed by De Samber et al.⁵⁰⁰ to unravel the tissue-specific 3D distribution of metals down to trace concentration levels in a non-destructive manner within the crustacean Daphnia magna. The analytical characterisation of the employed confocal μ-XRF set-up was investigated, together with specific areas of metal accumulation in different cross-sections of interest within the organism. Coupling the obtained elemental information with microscopic morphological data obtained by laboratory absorption microtomography, full 3D element-to-tissue correlation could be derived, allowing a more detailed interpretation of the obtained results with respect to metal accumulation within this model organism. De Jonge et al.⁵⁰¹ demonstrated submicron resolution XRF tomography of a whole unstained biological specimen, quantifying 3D distributions of the elements Ca, Cl, Cu, Fe, K, Mn, P, S, Si and Zn in the freshwater diatom Cyclotella meneghiniana with 400 nm resolution, improving the spatial resolution by over an order of magnitude. The resulting maps faithfully reproduced cellular structure revealing unexpected patterns that might elucidate the role of metals in diatom biology and of diatoms in global element cycles. With anticipated improvements in data acquisition and detector sensitivity, such measurements could become routine in the near future.

In several biological applications TXRF or SRXRF were used as analytical techniques. The effects of parasitism on the concentration of inorganic elements in the fat bodies of larvae of Diatraea saccharalis during the development of the parasitoid Cotesia flavepes was evaluated by Pinheiro et al.⁵⁰² using TXRF. Overall, the concentration of inorganic elements was higher early in parasitoid development (1 and 3 days after parasitism) compared with non-parasitised larvae, but much lower towards the end of parasitoid development (7 and 9 days after parasitism). Calcium, K and S were reduced after the fifth day of parasitism, which affected the total abundance of inorganic elements observed in the fat bodies of the parasitised hosts. The observed variation of the host's inorganic elements could also be related to the known effects of parasitism on the host's immune response. Fernandez-Ruiz et al.⁵⁰³ successfully used TXRF to study the kinetic behaviour of the Cr^VI bioaccumulation process in Acinetobacter beijerinckii type bacterium. The results demonstrated that this new strain of Acinetobacter bacterium was able to reduce the chromium present in the culture medium. As a consequence, it might be used as a promising micro-organism for Cr^VI bioremediation from polluted wastewaters. Ducic et al.⁵⁰⁴ reported elemental mappings with high spatial resolution using a multimodal synchrotron spectromicroscopy on the sub-cellular level of myelinated sciatic neurons isolated from wild-type mice. The distribution of Cl, Cu, Fe, K, Mn, Na, P and S was imaged in freeze-dried as well as cryo-preserved specimens, using the recently developed cryogenic sample environment at beamline ID21 at the European Synchrotron Radiation Facility (ESRF). In addition, SR-FTIR spectro-microscopy was used as a chemically sensitive imaging method. Single fibre diffraction in highly focused hard X-ray beams, and soft X-ray microscopy and tomography in absorption contrast were demonstrated as novel techniques for the study of single nerve fibres. A study of single cell elemental composition was carried out by Nunez-Milland et al.,⁵⁰⁵ who described the quantification of phosphorus in single cells using SRXRF. Phosphorus can serve as a proxy for total cell biomass. By exposing single cells to bright synchrotron radiation, quantitative and qualitative analysis of cell elemental composition could be carried out with high sensitivity. The basic problem with the determination of phosphorus was the lack of appropriate standards. However, the authors derived empirical phosphorus conversion factors by analysing certified thin film standards and used the factors to quantify phosphorus in the model diatom Thalassiosira pseudonana. The results obtained from single cells were compared with bulk measurements by spectrophotometry. The mean cellular phosphorus quotas, quantified with SRXRF for cells mounted on Au, Ni and nylon grids, were in good agreement with the data measured by spectrophotometry. It was found that the nylon grids created the lowest background as compared to the other supports. A detailed discussion of advantages and disadvantages of the grid types was given for use in the elemental analysis of individual phytoplankton cells. Finally, Yuan et al.⁵⁰⁶ applied XRF analysis for the determination of minor and trace elements in silks produced by spiders and silkworms confirming relatively high contents of K and Na suggesting the important role of these elements in the silk forming mechanism.

Readers seeking additional information regarding clinical and biological applications are advised to consult our companion ASU review on Clinical and biological materials, foods and beverages.²

3.12 Thin films, coatings and nano-materials

Several authors reported the application of GIXRF using SR as the excitation source. Carvalho et al.⁵⁰⁷ investigated the effect of the doping depth profile on the degradation of methylene blue on the photocatalyst TiO₂-Co. Two thin film layers of TiO₂ (200 nm) and Co (5 nm), respectively, were deposited by physical evaporation on a glass substrate. These films were annealed for 1 s at 100 and 400 °C and the Co layer was removed by chemical etching. The SR-GIXRF measurements indicated that the thermal treatment caused migration of Co atoms to below the surface-the depths found were between 19 and 29 nm. Von Bohlen et al.⁵⁰⁸ reported experiments combining X-ray standing waves and ED-SEM to study gold nano-particles. A systematic characterisation was performed of mono-dispersed nano-particles with nominal diameters of 25 nm, 46 nm, 73 nm, 100 nm, 115 nm, and 250 nm. The samples were prepared on Si-wafer pieces and analysed at the DELTA synchrotron facility in Dortmund under grazing incidence geometry. In addition, ED-SEM inspections of single particles as well as population-density checks were conducted. Particles with smaller diameters could be characterised by XSW whilst the larger ones were not completely covered by the interference field produced by the 15 keV monochromatic, synchrotron radiation. The results of the measurements were compared with those of numerical simulations and the extension of the interference field perpendicular to the silicon wafer reflector was determined to be 83 nm. Tiwari et al.⁵⁰⁹ applied the ‘CATGIXRF’ computer programme to the GIXRF and X-ray reflectivity characterisation of thin films and surfaces. Dopant depth profiling and dose determination are essential for the development of ultra shallow junction technology, thus Honicke et al.⁵¹⁰ applied SR-GIXRF in the soft X-ray range for the depth profile characterisation of ultra shallow junction implants. They used an energy-dispersive detector with an absolute efficiency calibration for the acquisition of the B Kα and As Lα spectra and determined the total retained dose. The concentration profile was obtained by an ab initio calculation and comparison with the measured angular dependence of the X-ray fluorescence emissions. However, these measurements pose a challenge to the widely used dynamic SIMS technique because of uncertainties due to an initial transient width comparable to the dopant depth distribution. Pepponi et al.⁵¹¹ combined GIXRF and SIMS to characterise the distribution of arsenic in ultra shallow junctions to overcome the limitations of SIMS for the study of the topmost few nanometres. A polynomial variation of the sputtering rate was applied in the first sputtering stage of the SIMS analysis and the parameters that regulate the magnitude of such corrections were determined by a least squares fitting of the angle dependent fluorescent signal. The total retained fluence was also measured by INAA and SR soft X-ray GIXRF showing good agreement. Furthermore, it was clearly shown that the GIXRF profile correction was very sensitive to the SIMS profile in the very first nano-metres. Streeck et al.⁵¹² performed elemental depth profiling of Cu(In,Ga)Se⁻² (CIGSe) thin films by reference-free GIXRF analysis. The semiconductor band gap of the CIGSe compound can be varied by adjusting the In to Ga ratio, which determines the photovoltaic properties of the thin film. Their composition depth profile must be optimised to maximise efficiency in solar cell applications. The general suitability of SR-GIXRF for determining depth gradients in CIGSe thin films was first shown by calculations. Reference-free XRF test measurements were carried out at the focused crystal monochromator beamline in the PTB laboratory at the BESSY II. Synchrotron. X-ray fluorescence was induced by photon excitation at energies of 4.0 keV and 10.5 keV, respectively, using various shallow incident angles. The calculations and experimental measurements showed that even small differences in the Ga/In profile might be distinguished, indicating that GIXRF was a promising tool for the non-destructive characterisation of compositional depth profiles. Kayser et al.⁵¹³ reported the determination of depth profiles of Al impurities implanted in silicon wafers by means of the high-resolution grazing exit XRF (GEXRF). Aluminium ions were implanted in silicon wafers with a dose of 10¹⁶ atoms cm⁻² and energies ranging between 1 and 100 keV. The depth distributions of these implanted ions were deduced with nanometre-scale precision from the measured angular profiles of the Al Kα line. Good agreement between experiment and theory was found, which showed that the presented high-resolution GE-XRF was well suited to perform depth profiling measurements of impurities located within the extinction depth, provided the overall shape of the distribution could be assumed a priori.

New instrumental developments were described by several authors during the review period. Faenov et al.⁵¹⁴ studied the homogeneity of wide field of view nano-thickness foils by conventional and phase contrast soft X-ray imaging using a tabletop ultra-bright femto-second-laser-driven cluster-based plasma soft X-ray source, which emitted more than 10¹² photons per sr-pulse in the spectral range 1–10 nm within a 4 pi solid angle. A spatial resolution of 700 nm was reported and the authors demonstrated that the high precision of their techniques could distinguish inhomogeneity of measured intensities in the order of ± 3%. A CdTe detector was used for PIXE characterisation of TbCoFe thin films by Chaves et al.³⁶ Cadmiun telluride detectors can accommodate K X-rays lines instead of the usually used L-series. The advantages and disadvantages of the proposed methodology were reported.

Queralt et al.⁵¹⁵ determined the thickness of semiconductor thin films by an EDXRF benchtop instrument and applied the method to GaN epilayers grown by molecular beam epitaxy. The authors presented results for samples with thickness layers in the range from 400 to 1000 nm that exhibited a good correlation with the layer thickness determined by optical reflectance. They claimed it was possible to precisely evaluate layer thickness from 5 nm, with a low relative standard deviation <2%. Trojek and Wegrzynek⁵¹⁶ successfully compared measurements and Monte Carlo calculations for layered samples. The Monte Carlo N-Particle eXtended (MCNPX) computer code was applied to calculate the Kα/Kß ratios of elements distributed heterogeneously in an analysed specimen. Experiments were performed on specimens made of thick substrates covered by one or two mono-elemental layers (Ti, Ni, and Cu) of intermediate thickness. The Kα/Kß ratios of the elements present in the substrate and in the layers were measured and then compared with the ratios obtained with the MCNPX computer code and with simple analytical calculations. The authors demonstrated that the MCNPX code made it possible to predict the Kα/Kß ratios for a specimen composed of both layers and a substrate. A possible application was suggested for the investigation of sample homogeneity or the depth heterogeneity of a specimen. In addition, the depth distribution of elements and the coating thicknesses in layered samples could also be determined.

Several experiments using μ-XRF for layer characterisation were described within the review period. Segura-Ruiz et al.⁵¹⁷ reported a direct observation of elemental segregation in InGaN nano-wires by X-ray nano-probe. Perez et al.⁵¹⁸ applied a new quantification algorithm for confocal μ-XRF, an iterative procedure valid for thin intermediate layers. The new algorithm was used to analyse a sample of a paint layer on a glass substrate. To test the accuracy of the proposed algorithm, the present results were compared with conventional XRF analysis. Lewis et al.⁴⁶⁷ described intracellular synchrotron nano-imaging and DNA damage/genotoxicity screening of novel lanthanide-coated nano-vectors. Macdonald et al.⁵¹⁹ reported scanning XRF micro-spectroscopy measurements of metallic impurities in solar-grade silicon. The authors found that the spatial spread of metallic impurities in the material were several millimetres in size, allowing scans across several grains. Relatively high concentrations of Cu, Fe and Zn were observed, with traces of Mn and Ni. The metals were mostly present as discrete particles up to 60 μm in size, however, Cu was found to be more uniformly distributed. More than 50% of the detected Fe was present as large particles at the grain boundaries, probably due to diffusion and precipitation during cooling. In contrast, less than 5% of the Cu resided in such large particles. The particles contained multiple metallic elements, with strongly varying proportions of their metal constituents. Mino et al.⁵²⁰ presented a selective area growth method to quantitatively extract from a SRXRF map, the variation of the thickness and chemical composition of a In_1-xGa_xAs ternary semiconductor film. The purposed method was based on a theoretical influence coefficient algorithm using only a few reference materials coupled with the fundamental parameter approach and was optimised for intermediate thickness samples. The authors showed that reported values agreed quantitatively with independent high resolution XRD analysis within 1%.

Several publications were offered this year using XRF in conjunction with other techniques such as photoluminescence, Raman scattering or XRD for thin film characterisation. Martinez-Criado et al.⁵²¹ reported the analysis of impurities in unintentionally doped ZnO nano-wires. Using the multi-element capability of XRF they determined the contribution of residual elements in the ZnO nano-wires growth. In a report by Mezdrogina et al.,⁵²² XRF along with photoluminescence and infrared spectroscopy were used to study Fe, Cu, and Si impurities in p-type ZnO crystals.

Leon et al.⁵²³ investigated the nature of marbled Terra Sigillata slips from the largest Gallic workshop, La Graufesenque, that was famous for a special type of terra sigillata. Produced exclusively at this site, this pottery was characterised by a surface finish made of a mixture of yellow and red slips. Because the two slips were intimately mixed, it was difficult to obtain the precise composition of either constituent. Combined EPMA, μ-XRF and μ-XRD analyses were performed on cross-sectional samples to show that the yellow component of marbled sigillata was made from a titanium-rich clay preparation. The colour was due to the formation of a pseudobrookite (TiFe₂O₅) phase in the yellow part of the slip, considered nowadays as a main mineral for the fabrication of stable yellow ceramic pigments. De Nolf and Janssens⁵²⁴ used μ-XRD and μ-XRF tomography in a study of multilayered automotive paints. This tomography is a recently developed method that enabled the visualisation of the distribution of chemical elements and associated crystalline phases inside complex, heterogeneous materials of thickness in the millimetre range. Ahmed and Selim⁴³⁴ investigated the anticorrosive effects of a new pigment based on a bulk of talc covered with a surface layer of titanium dioxide. EDXRF was used to confirm the presence of titanium dioxide on the talc surface and to elucidate the concentration of different elements in the prepared pigments. The results of this work showed that as the layer of titanium dioxide was increased in thickness, enhanced anticorrosive properties of the new pigments were obtained. Abe et al.⁵²⁵ reported quantitative analysis of calcium phosphate layers deposited on metallic titanium substrates in order to evaluate the ostrogenic capability of metallic biomaterials. The authors achieved a quantification of the layers with good accuracy validated by other methods. Dubent et al.⁵²⁶ characterised corrosion behaviour of tin-20% m/m zinc coatings electroplated from a non-cyanide alkaline bath. Tin-zinc alloy electroplated coatings were recognised as a potential alternative to toxic cadmium as corrosion resistant deposits because they combine the barrier protection of tin with the cathodic protection afforded by zinc. The authors showed that the corrosion resistance of tin-20% m/m zinc alloy coating was superior to that of cadmium and zinc-12% m/m nickel coatings using various techniques such as SEM, EDS, XRF and GD-OES. Diso et al.⁵²⁷ investigated the growth of CdS layers to develop all-electrodeposited CdS/CdTe thin-film solar cells by voltammetry, XRD, XRF, optical absorption, photo-electrochemical studies, and SEM. The continuous process of electro-deposition of CdS was investigated with the aim of using it instead of the batch process of chemical bath deposition currently used in solar cell production. A comparison of initial solar cell devices showed that electrodeposited CdS layers had similar or superior performance in thin-film CdS/CdTe solar cells.

3.13 Chemical state and speciation

Unrine et al.⁵²⁸ studied the effects of particle size on chemical speciation and bioavailability of copper to earthworms (Eisenia fetida) exposed to copper nano-particles. Effects on growth, mortality, reproduction and expression of a variety of genes associated with metal homeostasis, general stress, and oxidative stress were investigated. The authors claimed that oxidised copper nano-particles might enter food chains from soil but that adverse effects in earthworms were likely to occur only at relatively high concentrations (> 65 mg Cu kg⁻¹ soil).

The combination of SRXRF and XAS for comprehensive characterisation of samples was reported by several authors. A specialised 96-element prototype Maia detector was used for SRXRF and SR-XAS studies by Etschmann et al.³² It provided rapid collection of fully quantitative maps of the distributions of major and trace elements at micrometre spatial resolution over areas as large as 1 × 5 cm². Fast data acquisition rates opened the way to XANES imaging, in which spectroscopic information was available at each pixel in the map. The authors reported imaging of thin sections of an oxidised pisolitic regolith and a metamorphosed, sedimentary exhalative Mn–Fe ore. In both cases, As K-edge XANES imaging revealed localised occurrence of reduced arsenic in parts of these oxidised samples. Tirez et al.⁵²⁹ discussed nickel speciation and fractionation using a multidisciplinary approach for different particulate matter samples collected in industrial and rural atmospheres. XANES and XRD were compared to a wet chemistry sequential leaching assay. Nickel speciation and fractionation results on the PM samples confirmed the good agreement between the modified Zatka sequential leaching procedure and the XANES data. For PM collected in and close to a stainless steel factory, nickel included in a spinel structure (NiFe₂O₄) was identified as the principal nickel species. The rural PM showed a 50 : 50 distribution between soluble and oxidic nickel species. Bozzini et al.⁵³⁰ successfully showed that scanning transmission electron microscopy combined with XAS and μ-XRF could be used to explore corrosion processes in iron and nickel electrodes in contact with a hydrated Nafion film in a thin-layer cell. Nafion contamination by ferrous-alloy corrosion products, resulting in dramatic drops of the Ohmic potential, is a suspected major failure mode of polymer electrolyte membrane fuel cells that make use of metallic bipolar plates. The authors provided XRF maps and absorption spectra, sampled at different locations. They showed diffusion of corrosion products within the Nafion film only in the case of the iron electrodes, whereas the nickel electrodes appeared corrosion resistant. Selenium speciation in whole sediment using XAS and μ-XRF imaging was reported by Wiramanaden et al.⁵³¹ Whole sediment, pore water, surface water, and chironomid larvae were analysed in an attempt to link whole sediment selenium speciation to various environmental factors, including selenium availability to benthic macro-invertebrates, a trophic level through which selenium can enter the diet of higher trophic level organisms. The authors claimed this link to be established successfully. Finch et al.⁵³² presented barium EXAFS in Ba-rich standard minerals to explore the potential for determining barium structural state in calcium carbonate. Ba L₃- XAFS data from a suite of barium carbonates, hydroxides, sulfate and a Ba-bearing organic compound were used to explore whether the technique could be used for fingerprinting structural states in biominerals such as celestite, aragonite and calcite. The authors were able to show that the combination of XANES and EXAFS enabled phases to be identified, with the exception of the two hydrated barium hydroxides, which could not be distinguished from each other due to the proximity in energy of Ca Kα secondary radiation to the Ba L-line, which overloaded the X-ray detector. Legros et al.⁵³³ investigated copper speciation in pig slurry by a multi-technique approach. The motivation for the study was the assumption that the mobility and bioavailability of copper from pig slurry spreading could be better predicted by determining the speciation of this element in addition to its total concentration. Size fractionation and chemical characterisation of each size fraction were performed to complement results obtained in raw samples. The results of μ-XRF analysis highlighted the co-localisation of copper and sulfur. Using XANES the authors could show that copper speciation in raw pig slurry and its size fractions could be described by Cu₂S and that its oxidation state was Cu^I. In addition, geochemical calculations demonstrated that chalcocite (Cu₂S) was the major copper species found in the pig slurry lagoon. Micro-spectroscopic investigation of aluminium and sulfur speciation in hardened cement paste (HCP) was reported by Wieland et al.⁵³⁴ The authors used μ-XRF and μ-XANES to determine the spatial distribution of Al and S and to identify the Al- and S-bearing species in compact HCP hydrated at 50 °C. The same research group⁵³⁵ also determined the uptake and speciation of U^VI in hardened cement paste. A sample was prepared by in-diffusion of U^VI into HCP over 9 months. Micro-XRF maps revealed a heterogeneous distribution of U^VI in a 10 μm thick layer on the surface of the HCP disk. Micro-XAS measurements on a U^VI hot spot showed that the coordination environment of U^VI was similar to that in U^VI doped HCP samples. Pinakidou et al.⁵³⁶ performed μ-XRF and μ-XAFS studies of an Al matrix Fe–Ni composite. Nagoshi et al.⁵³⁷ reported μ-XRF and Fe–K Edge XAFS on a cross section of the rust layer formed on a weathering steel. Chromium distribution, including layered patterns in the rust layer, was clearly observed. The combination of both techniques on identical analytical points showed that the crystallinity of alpha-FeOOH was strongly related to the Cr concentration.

Some authors combined XAS with other X-ray techniques such as GIXRF, TXRF or GEXRF to investigate depth information. Pagels et al.⁵³⁸ investigated buried ZnO/Si interfaces as a thin film model of solar cells with GIXRF-NEXAFS to detect changes of the chemical state due to annealing. The authors proved that GIXRF-NEXAFS could be used for the non-destructive, depth-dependant chemical speciation of layered systems in the range of a few to several hundred nano-meters. Baake et al.⁵³⁹ reported the analytical characterisation of BC_xN_y films generated by low pressure chemical vapour deposition (LPCVD) with triethylamine borane. The authors used TXRF-NEXAFS as well as XPS. Shinoda et al.⁵⁴⁰ performed non-destructive depth-resolved chemical state analysis of (La, Sr) MnO₃ films under high temperature using fluorescence yield XAS experiments with a grazing-exit geometry for detection of the emitted fluorescence. The observed XAFS spectra provided information about depth-resolved chemical states in the surface layer of the film materials through the dependence of the escape depth of XRF radiation emitted from the sample on the take-off angle. Giubertoni et al.⁵⁴¹ reported ultra-low energy boron implants in silicon by non-oxidising SIMS and soft X-ray GIXRF. Boron energy (0.2–3 keV) high dose (1 × 10¹⁵ cm⁻²) implants in single crystalline silicon were characterised by SIMS using an energy (0.35–0.5 keV) O²⁺ ion primary beam and collecting positive secondary ions. The measured dose values were compared with results of soft X-ray SR-GIXRF. Dopant depth profiling and dose determination are essential for ultra-shallow junction technology development. Pepponi et al.⁵⁴² described a combined approach of GIXRF and SIMS for the characterisation of ultra-shallow arsenic distribution in silicon. SIMS suffers from large uncertainties due to an initial transient width. The authors reported the application of GIXRF for arsenic-in-silicon dose and profile determination with SIMS in order to overcome the limitations of the latter in the topmost nano-metres. The first sputtering stage of the SIMS analysis was modelled with a polynomial sputtering rate function and the parameters for the rate of sputtering were determined by least-square fitting of the angle dependent XRF signal. The total retained fluence was also measured by INAA and by soft X-ray SR-GIXRF. The total retained fluence determinations showed a good agreement among the techniques. Furthermore it was clearly shown that the GIXRF profile correction is very sensitive to the SIMS profile in the very first nanometres. The authors concluded that if, in addition to the sputtering rate changes, matrix effects were present in the SIMS analysis, the tested sputtering rate corrections could not produce reliable profiles.

Another method to gain information about the chemical speciation is to investigate intensity ratios within fluorescence line families. Porikli et al.⁵⁴³ reported measurements using ¹⁰⁹Cd radioisotopes source excitation on Kß₁/Kα, Kß₂/Kα, Kß₂/Kß₁and Kß/Kα X-ray intensity ratios. The Kα and Kß_1,2 emission spectra for compounds of 4d transition metals Y, Zr, Nb, and Mo were measured using a Si(Li) solid-state detector. Modenes et al.⁵⁴⁴ described the Cr^VI reduction by activated carbon and non-living macrophytes roots assessed by K beta spectrometry. The high-resolution XRF technique was used to study the adsorption process, as well as Cr^VI reduction and removal from metal solutions. Chromium K beta satellite lines were characterised for all K beta spectra of chromium ions on the treated samples and reference material. The authors reported that activated carbon and non-living aquatic macrophytes roots were found to act mainly as good adsorbents, first reducing Cr^VI to Cr^III followed by Cr^III adsorption. Although cationic-exchange resin was treated with Cr^VI solution, no evidence of any Cr Kß spectral satellite lines was found, suggesting that Cr^VI was not removed in a cationic-exchange process. De Oliveira et al.⁵⁴⁵ combined XRF and chemometrics for direct chromium speciation. The authors obtained spectra of several solutions containing different concentrations of Cr^III and Cr^VI. The data underwent principal component analysis and partial least squares regression. The authors claimed that direct speciation using a conventional X-ray spectrometer was possible, with calculated limits of detection for Cr^III and Cr^VI being lower than 17 and 50 mg kg⁻¹, respectively. Tochio et al.⁵⁴⁶ reported XRS analysis of Cr^VI species in mixtures of Cr₂O₃ and K₂CrO₄. Baydas and Oz⁵⁴⁷ used WDXRF spectrometry to investigate the speciation of cobalt compounds by registering the shift in X-ray peak position and changes in peak widths. The results were strongly correlated with cobalt oxidation states as larger changes were observed for Kβ peaks as compared with Kα.

Abbreviations

AAS	Atomic absorption spectrometry
ABS	Acrylonitrile, butadiene and styrene
AD	Anno domini
ADC	Analog-to-digital converter
AFM	Atomic force microscopy
ASIC	Application specific integrated circuit
ASTM	American Society for Testing and Materials
ASU	Atomic Spectrometry Updates
BC	Before Christ
BUN	Blood urea nitrogen
CCD	Charge coupled device
CMOS	Complementary metal oxide semiconductor
CRM	Certified reference material
CT	Computer tomography
CV-AFS	Cold vapour atomic fluorescence spectrometry
CZT	Cadmium zinc telluride
2D/3D	2 Dimensional/3 Dimensional
2D-PAGE	2 Dimensional-polyacrylamide gel electrophoresis
DAC	Diamond-anvil cell
DEPFET	Depleted P-channel field effect transistor
DMA	Dimethylarsinic acid
DMH	dimethylhydrazine
DNA	Deoxyribonucleic acid
ED	Energy dispersive
EDS	Energy dispersive spectrometry
ED-SEM	Energy dispersive-scanning electron microscopy
EDXRF	Energy dispersive X-ray fluorescence
EELS	Electron energy loss spectroscopy
EPA	Environmental Protection Agency
EPMA	Electron probe microanalysis
ESRF	European Synchrotron Radiation Facility
EXAFS	Extended X-ray absorption fine structure
FAAS	Flame atomic absorption spectrometry
FP	Fundamental parameter
FTIR	Fourier transform infrared spectroscopy
FWHM	Full width at half maximum
GD-OES	Glow discharge-optical emission spectrometry
GF-AAS	Graphite furnace-atomic absorption spectrometry
GEXRF	Grazing exit X-ray fluorescence
GIS	Geographic information system
GIXRF	Grazing incidence X-ray fluorescence
GPSC	Gas proportional scintillation counter
HCP	Hardened cement paste
HG-AAS	hydride generation atomic absorption spectrometry
HPLC-ICP-MS	High performance liquid chromatography-inductively coupled plasma -mass spectrometry
IC	Ion chromatography
ICP-AES	Inductively coupled plasma-atomic emission spectrometry
ICP-MS	Inductively coupled plasma-mass spectrometry
ICP-OES	Inductively coupled plasma-optical emission spectrometry
ICP-SF-MS	Inductively coupled plasma-sector field-mass spectrometry
INAA	Instrumental neutron activation analysis
ISO	International Organization for Standarization
KXRF	K-line X-ray fluorescence
LA-ICP-MS	Laser ablation-inductively coupled plasma-mass spectrometry
LIBS	Laser induced breakdown spectroscopy
LPCVD	Low pressure chemical vapour deposition
MCA	Multichannel analyser
MCNPX	Monte Carlo N-Particle eXtended
MER	Mars Exploration Rovers
MW	Megawatt
NE	North east
NEXAFS	Near-edge X-ray absorption fine structure
NIST	National Institute of Standards and Technology
NMR	Nuclear magnetic resonance
ODP	Ocean drilling programme
PCA	Principle component analysis
PCB	Printed circuit board
PET	Polyethyleneterephthalate
PIGE	Particle induced gamma ray emission
PIXE	Particle-induced X-ray emission
PM	Particulate matter
PXRF	Portable X-ray fluorescence
REE	Rare earth elements
RoHS	Restriction of Hazardous Substances
SDD	Silicon drift detectors
SDS-PAGE	Sodium dodecyl sulfate-polyacrylamide gel electrophoresis
SEG	Selective area growth
SEM	Scanning electron microscopy
SIMS	Secondary ion mass spectrometry
SPF	Sun protection factor
SRM	Standard reference material
SR	Synchrotron radiation
SR-FTIR	Synchrotron radiation-Fourier transform infrared spectroscopy
SR-GIXRF	Synchrotron radiation-grazing incidence X-ray fluorescence
SR-TXRF	Synchrotron radiation-total reflection X-ray fluorescence
SR-TXRF-XANES	Synchrotron radiation-total reflection X-ray fluorescence-X-ray absorption near edge structure
SR-XAS	Synchrotron radiation-X-ray absorption spectroscopy
SR-XFM	Synchrotron radiation-X-ray fluorescence microscopy
SRXRD	Synchrotron radiation X-ray diffraction
SRXRF	Synchrotron radiation X-ray fluorescence
SRXRS	Synchrotron radiation X-ray spectrometry
SW	South west
TEM	Transmission electron microscope
TXRF	Total reflection X-ray fluorescence
TV	Television
UK	United Kingdom
USA	United States of America
UV	Ultraviolet
UV-VIS-NIR	Ultraviolet-visible spectroscopy-near infrared
VPT	Vapour phase treatment
WDXRF	Wavelength dispersive X-ray fluorescence
WD	Wavelength dispersive
WEEE	Waste of electrical and electronic equipment
XAFS	X-ray absorption fine structure
XANES	X-ray absorption near edge structure
XAS	X-ray absorption spectroscopy
XBIC	X-ray beam induced current
XPS	X-ray photoelectron spectrometry
XRD	X-ray diffraction
XRF	X-ray fluorescence
XSW	X-ray standing waves
Z	Atomic number

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