Synchrotron X-ray Fluorescence Microprobe Research Articles

Development and applications of an epifluorescence module for synchrotron x-ray fluorescence microprobe imaging

Synchrotron x-ray fluorescence (XRF) microprobe is a valuable analysis tool for imaging trace element composition in situ at a resolution of a few microns. Frequently, epifluorescence microscopy is beneficial for identifying the region of interest. To date, combining epifluorescence microscopy with x-ray microprobe has involved analyses with two different microscopes. We report the development of an epifluorescence module that is integrated into a synchrotron XRF microprobe beamline, such that visible fluorescence from a sample can be viewed while collecting x-ray microprobe images simultaneously. This unique combination has been used to identify metal accumulation in Alzheimer’s disease plaques and the mineral distribution in geological samples. The flexibility of this accessory permits its use on almost any synchrotron x-ray fluorescence microprobe beamline and applications in many fields of science can benefit from this technology.

Emissions and encapsulation of cadmium in CdTe PV modules during fires

Fires in residential and commercial properties are not uncommon. If such fires involve the roof, photovoltaic arrays mounted on the roof will be exposed to the flames. The amount of cadmium that can be released in fires involving CdTe PV and the magnitude of associated health risks has been debated. The current study aims in delineating this issue. Previous thermogravimetric studies of CdTe, involved pure CdTe and single-glass PV modules. The current study is based on glass–glass CdTe PV modules which are the only ones in the market. Pieces of commercial CdTe photovoltaic (PV) modules, sizes 25 � 3 cm, were heated to temperatures up to 1100 � C to simulate exposure to residential and commercial building fires. The temperature rate and duration in these experiments were defined according to standard protocols. Four different types of analysis were performed to investigate emissions and redistribution of elements in the matrix of heated CdTe PV modules: (1) measurements of sample weight loss as a function of temperature; (2) analyses of Cd and Te in the gaseous emissions; (3) Cd distribution in the heated glass using synchrotron X-ray fluorescence microprobe analysis; and (4) chemical analysis for Cd and Te in the acid-digested glass. These experiments showed that almost all (i.e., 99� 5%) of the cadmium content of CdTe PV modules was encapsulated in the molten glass matrix; a small amount of Cd escaped from the perimeter of the samples before the two sheets of glass melted together. Adjusting for this loss in full-size modules, results in 99� 96% retention of Cd. Multiplying this with the probability of occurrence for residential fires in wood-frame houses in the US (e.g., 10 � 4 ), results in emissions of 0� 06 mg/GWh; the probability of sustained fires and subsequent emissions in adequately designed and maintained utility systems appears to be zero. Published in 2005 by John Wiley & Sons, Ltd.

Quantifying trace elements in individual aquatic protist cells with a synchrotron X-ray fluorescence microprobe.

The study of trace metal cycling by aquatic protists is limited by current analytical techniques. Standard "bulk" element analysis techniques that rely on physical separations to concentrate cells for analysis cannot separate cells from co-occurring detrital material or other cells of differing taxonomy or trophic function. Here we demonstrate the ability of a synchrotron-based X-ray fluorescence (SXRF) microprobe to quantify the elements Si, Mn, Fe, Ni, and Zn in individual aquatic protist cells. This technique distinguishes between different types of cells in an assemblage and between cells and other particulate matter. Under typical operating conditions, the minimum detection limits are 7.0 x 10(-16) mol microm(-2) for Si and between 5.0 x 10(-20) and 3.9 x 10(-19) mol microm(-2) for Mn, Fe, Ni, and Zn; this sensitivity is sufficient to detect these elements in cells from even the most pristine waters as demonstrated in phytoplankton cells collected from remote areas of the Southern Ocean. Replicate analyses of single cells produced variations of <5% for Si, Mn, Fe, and Zn and <10% for Ni. Comparative analyses of cultured phytoplankton cells generally show no significant differences in cellular metal concentrations measured with SXRF and standard bulk techniques (spectrophotometry and graphite furnace atomic absorption spectrometry). SXRF also produces two-dimensional maps of element distributions in cells, thereby providing information not available with other analytical approaches. This technique enables the accurate and precise measurement of trace metals in individual aquatic protists collected from natural environments.

Imaging and quantification of trace metals in thin biological specimens using microprobe techniques: Synchrotron induced X-ray fluorescence microprobe and nuclear microprobe

The combination of Synchrotron X-Ray Fluorescence microprobe (SXRF) with other micro-analytical techniques based on accelerated particle beams, such as Rutherford Backscattering Spectrometry (RBS), and Particle Induced X-ray Emission (PIXE) enable to quantify SXRF results of thin biological specimens. The same specimens were analysed by both techniques. The average thickness calculated by RBS of discrete tissue regions in equivalent sample sections was used to normalise SXRF data. Analysing the same sample region with PIXE technique, simultaneously to RBS, can validate the methodology once it will enable to compare concentrations obtained for elements that are detected by both SXRF and PIXE. Major departures were found for the quantification of Ca and Ti. For Cr and Fe a good agreement was found between both micro-analytical techniques. Differences below 20% were obtained for the majority of the elements and samples analysed. The procedure can be applied to produce quantitative elemental maps and it will be advantageous to quantify toxic elements present at low concentrations in tissues, such as Cr, Ni and Pb, which can only be efficiently assessed by SXRF.

The 12 900 years BP Laacher See eruption: estimation of volatile yields and simulation of their fate in the plume

Abstract We estimated the volatile emissions of the 12 900 years BP eruption of Laacher See volcano (Germany), using a modified petrological method. Glass inclusions in phenocrysts and matrix glasses sampled over the Laacher See tephra profile were analysed by synchrotron X-ray fluorescence microprobe and electron microprobe to obtain the emitted masses of halogens, sulphur, and water. These data were used to initialize the numerical plume model ATHAM in order to investigate the fate of volcanic gases in the plume, and to estimate volatile masses injected into the stratosphere. The scavenging efficiency of each volatile component depends on its interactions with both liquid water and ice. We found a scavenging efficiency of c. 5% for the sulphur species, and of only c. 30% for hydrogen halides, despite their high water solubility. Our simulations showed that the greatest fraction of hydrometeors freeze to ice, due to the fast plume rise and great height of the eruption column. For the dry atmospheric conditions of the Laacher See eruption, the amount of liquid water was not sufficient to completely scavenge HCl and HBr, so that a large proportion could reach the stratosphere.

Interpretation of heterogeneity effects in synchrotron X-ray fluorescence microprobe data.

Heterogeneity effects often limit the accuracy of synchrotron X-ray fluorescence microprobe elemental analysis data to ± 30%. The difference in matrix mass absorption at Kα and Kβ fluorescence energies of a particular element can be exploited to yield information on the average depth-position of the element or account for heterogeneity effects. Using this technique, the heterogeneous distribution of Cu in a simple layered sample could be resolved to a 2 × 2 × 10 (x, y, z, where z is the depth coordinate) micrometer scale; a depth-resolution limit was determined for the first transition metal series and several other elements in calcite and iron oxide matrices. For complex heterogeneous systems, determination of average element depth may be computationally limited but the influence of heterogeneity on fluorescence data may still be assessed. We used this method to compare solid-state diffusion with sample heterogeneity across the Ni-serpentine/calcite boundary of a rock from Panoche Creek, California. We previously reported that Ni fluorescence data may indicate solid state diffusion; in fact, sample heterogeneity in the depth dimension can also explain the Ni fluorescence data. Depth heterogeneity in samples can lead to misinterpretation of synchrotron X-ray microprobe results unless care is taken to account for the influence of heterogeneity on fluorescence data.

Microfluorescence and Microtomography Analyses of Heterogeneous Earth and Environmental Materials

Analytical techniques with high sensitivity and high spatial resolution are crucial for understanding the chemical properties of complex earth materials and environmental samples, and these so-called 'microprobes' have become workhorses of the geochemical community as well as important tools for environmental scientists. These microanalytical instruments are based on various forms of sample excitation and detection. They are complementary in terms of spatial resolution, element sensitivity, energy deposition and non-destructiveness. Several techniques fall in the class of methods employing charged particle excitation of X-ray fluorescence, including electron microprobe analysis (EMPA) and particle-induced X-ray emission (PIXE). EMPA is capable of {micro}m-sized spots with minimum detection limits near 100 mg kg{sup -1}. PIXE is well suited for analyses of relatively light elements with 10 mg kg{sup -1} sensitivity and {micro}m-sized spots. The relatively large energy deposited by the charged particle beam can complicate the analysis of volatile elements or induce valence state changes of redox sensitive elements. Sensitivity of these technologies is a relatively smooth function of atomic number. Other techniques are based on sample sputtering followed by mass spectrometry of the vaporized products, including secondary ion mass spectrometry (SIMS) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Beam sizes are inmore » the few to tens of {micro}m range. Elemental sensitivities for SIMS are highly variable depending on ion yield, and quantification can be difficult because of matrix effects in the ion production process. SIMS and LA-ICP-MS have very high sensitivities for some elements and low sensitivity for others. These and other microanalytical techniques used in earth science research are described in Potts et al. (1995). The subject of this chapter is synchrotron X-ray fluorescence (SXRF) microprobe analysis (Horowitz and Howell 1972) and microtomography.« less

Interpretation of heterogeneity effects in synchrotron X-ray fluorescence microprobe data

Interpretation of heterogeneity effects in synchrotron X-ray fluorescence microprobe data

Investigation of metal ion accumulation in Euglena gracilis by fluorescence methods

Single cell synchrotron X-ray fluorescence (SXRF) microprobe measurements as well as X-ray absorption near edge structure experiments have been done at Beijing Synchrotron Radiation Facility on Euglena Gracilis cells. Concentrations of the metal ions Mn 2+, Nd 3+, Ce 3+ and other trace elements, such as Ca, Fe, Zn, etc. have been measured both by single cell SXRF and bulk PIXE technique. It was found that the content of Ca, Fe and Zn was lower after the uptake of rare earths or Mn by the cells, while the valence states of Mn 2+, Ce 3+ and Nd 3+ were unaltered. The results related to cytochemistry are also discussed.

In Situ Synchrotron X-Ray Microprobe Studies of Passivation Thresholds in Fe-Cr Alloys

The dissolution of metal during the passivation of Fe-Cr alloys has been studied in situ as a function of alloy composition in order to investigate the critical Cr content required for corrosion protection. This is achieved using synchrotron X-ray fluorescence microprobe analysis on a sputter-deposited Fe-Cr thin film with a continuous lateral variation in composition. The technique can resolve the dissolution of less than one layer of atoms during electrochemical treatment of the graded alloy surface. The results show that there is a sharp change in behavior in the region of 17-18% Cr. Above 18% Cr, almost no metal dissolution occurs during passive film development, while below this composition there is continual dissolution. This result is consistent with the gelation model of passivation that uses an approach based on percolation theory. © 2001 The Electrochemical Society. All rights reserved.

Trace element diffusion in andesitic melts: an application of synchrotron X-ray fluorescence analysis

—We have investigated the diffusivity of trace elements in hydrous iron-free andesitic melts containing 4.5 to 5.2 wt.% water at a pressure of 500 MPa and at temperatures between 1100 and 1400°C using the diffusion couple technique. The studied elements can be combined in several groups of particular geochemical interest: low field strength elements (LFSE: Rb, Sr, Ba), transition elements (Cr, Fe, Ni, Zn), rare earth elements (REE: La, Nd, Sm, Eu, Gd, Er, Yb, Y), and high field strength elements (HFSE: Zr, Nb, Hf). The diffusion profiles of the trace elements were measured using the synchrotron X-ray fluorescence (SYXRF) microprobe. H 2O distribution in the samples was analyzed by IR microspectroscopy. Diffusion profiles are excellently reproduced, assuming concentration-independent diffusion coefficients. For all trace elements, the temperature dependence of diffusion in the hydrous melt can be described by a simple Arrhenius law. In general, the diffusivity decreases from the LFSE, to transition elements, to REE, and to the HFSE, a trend that can be correlated to the increase of charge in the same order. The activation energy shows a similar trend, increasing from 129 kJ/mol for Rb to 189 kJ/mol for Zr. For the transition elements Cr and Fe, the activation energy is relatively high (228 and 193 kJ/mol, respectively), which can be explained by increasing contributions of divalent cations to the diffusion flux with increasing temperature. Higher diffusivity of Eu compared to its neighbor elements also is attributed to contributions of divalent cations. Modeling Eu-diffusivity using data of Sr as representative for Eu 2+, and of Sm and Gd as representative for Eu 3+, shows that at all temperatures Eu 3+ is clearly dominating in the hydrous melt. To quantify the effect of water, an additional experiment was performed at 1400°C using a nominally anhydrous melt. The obtained diffusion coefficients are (for most of the elements) by one and a half orders of magnitude lower than for a melt containing 4.5 wt.% H 2O. Chemical diffusion coefficients D η, which were calculated from the viscosity data of Richet et al. (1996) using the Eyring equation, and which assumed a jump distance of 3 Å, are in excellent agreement with the diffusivity of the HFSE for both dry and hydrous melt. Most of the investigated elements show a linear relation between log diffusivity and log viscosity, enabling the prediction of diffusivities in hydrous andesite systems at various conditions. Provided viscosity data are available, we suggest that this relation can be a useful tool to estimate trace element diffusivities for silicate melts with different compositions. The new diffusion data show that water strongly enhances diffusivity of trace elements in andesitic melts. After 10,000 yr at 1200°C, diffusion produces in the dry melt relatively short profiles with lengths (defined as x=( Dt) 1/2) between 0.8 and 0.07 m (for Sr and Zr, respectively), whereas in hydrous melts (5 wt.% water), profiles are much longer with lengths between 3.9 and 0.92 m (for Sr and Zr, respectively).

Cathodoluminescence in Calcite Cements: New Insights on Pb and Zn Sensitizing, Mn Activation, and Fe Quenching at Low Trace-Element Concentrations

ABSTRACT The role of Pb and Zn as sensitizers of cathodolumines (CL) in sedimentary carbonates is still speculative, as is the relationship between Mn, Fe, and CL intensity at low concentrations of Mn and Fe. We address these questions using calcite cements from the Lower Oligocene Suwannee Formation of Florida, which have mean Mn, Pb, Zn, and Fe concentrations less than 45 ppm. Only a small fraction of these cements exhibit visible CL, but when present, the luminescence is orange to reddish orange. Trace-element contents were measured using a synchrotron x-ray fluorescence microprobe, and CL intensity was approximated by spot-metered photomicrograph exposure times. Based on Mn and Fe contents, four cement populations can be defined. Group I is luminescent calcite with Mn > 25 ppm and molar Mn/Fe > 1.8. Group II contains both luminescent and nonluminescent cements, all with Mn > 25 ppm, molar Mn/Fe 25 ppm, molar Mn/Fe 100 ppm. Group IV is nonluminescent calcite with Mn < 25 ppm and variable Fe. These groupings and statistical analyses of the data (Mann-Whitney tests and factor analyses) confirm that 25 ppm Mn is necessary to initiate visible CL, and that Mn is the sole control on CL intensity when Mn and Fe contents are very low (<100 ppm). The data also establish 100 ppm Fe as a new minimum for the quenching of CL when Mn is below 200 ppm. There is no evidence in our data that Pb or Zn concentrations in tens of parts per million either activate or sensitize CL. The Mann-Whitney test shows that there is no statistical evidence at the 95% confidence level to indicate that luminescent and nonluminescent cements reflect different populations of Pb and Zn, except for Group II cements that have more Pb in nonluminescent cements than in otherwise chemically equivalent luminescent cements. Factor analysis shows that CL intensity in all luminescent cements is unrelated to Pb or Zn concentrations. Given that Pb or Zn sensitizing is lacking in low-Mn calcites like the Suwannee cements, it is hard to imagine how these elements could play a significant role in calcites containing even more Mn, as is typical of most sedimentary carbonates.

Characterization of Quaternary Metal Oxide Films by Synchrotron X-ray Fluorescence Microprobe

A synchrotron X-ray fluorescence microprobe has been used to study the composition and microstructure of pulsed-laser ablation-deposited films of calcium–nickel–potassium oxides that have applications in heterogeneous catalysis. The films, whose individual metal oxide components have widely varying boiling points and thus prevent a solid-phase synthesis with the use of standard thermal techniques, represent a new quaternary metal oxide phase containing the three elements. Experimental conditions for preparing the films are given. The X-ray fluorescence microprobe data are discussed with respect to both the distribution of the three metals in the films at the micrometer lateral spatial resolution level and the presence of trace amounts of metals that were introduced into the films as contaminants in targets made of the parent three-metal oxide.

Yttrium zoning in metamorphic garnets

Yttrium zoning has been measured in garnets from The Straits Schist, Connecticut, USA, using the Synchrotron X-ray fluorescence (SXRF) microprobe. SXRF compositional maps for Mn and Fe show that the major elements are concentrically zoned about the gannet core in the classic bell-shaped profiles considered indicative of growth zoning. Yttrium, however, displays oscillatory zoning which varies three orders of magnitude in abundance, from about 3 to 4000 ppm, and is correlated with textural zoning in garnet. The major element abundances, by contrast, display no visible inflection related to textural zoning. At this time it is not possible to unequivocally identify the mechanism which has produced this oscillatory zoning. Most likely this reflects either the breakdown of Y-enriched phases, changes in the rate of garnet growth with time, or changes in the effective Y concentration of matrix phases due to breakdown and reprecipitation of garnet as the equilibrium reactions involving gannet change. This study demonstrates that the SXRF microprobe provides excellent, spatially resolved compositional maps for trace elements in porphyroblasts, something other analytical techniques have been unable to do. It also suggests that the diffusion rates for Y in garnet are probably significantly slower than those for major cations such as Mn, Fe, Mg, and Ca. As a result trace element mapping potentially provides a clearer record of the reaction history of the rock, provides details of how chemical zoning in garnet is produced, and allows evaluation of assumptions about chemical equilibrium between minerals.

Distribution of moderately volatile trace elements in fine-grained chondrule rims in the unequilibrated CO3 chondrite, ALH A77307

The concentrations of Ni, Cu, Zn, Ga, Ge, and Se in five, fine-grained chondrule rims in the highly unequilibrated CO3 chondrite ALH A77307 (3.0) have been determined for the first time by synchrotron X-ray fluorescence (SXRF) microprobe at Brookhaven National Laboratory. These elements are especially useful for tracing the role of condensation and evaporation processes which occurred at moderate temperatures in the solar nebula. Understanding the distribution of moderately volatile elements between matrix and chondrules is extremely important for evaluating the different models for the volatile depletions in chondritic meteorites. The data show that the trace element chemistry of rims on different chondrules is remarkably similar, consistent with data obtained for the major and minor elements by electron microprobe. These results support the idea that rims are not genetically related to individual chondrules, but all sampled the same reservoir of homogeneously mixed dust. Of the trace elements analyzed, Zn and Ga show depletions relative to CI chondrite values, but in comparison with bulk CO chondrites all the elements are enriched by ∼ 1.5 to 3.5 × CO. The abundance patterns for moderately volatile elements in ALH A77307 chondrule rims closely mimic those observed in the bulk chondrite, indicating that matrix is the major reservoir for these elements. The close matching of the patterns for the volatile depleted bulk chondrite and enriched matrix is especially striking for Na, which is anomalously depleted in ALH A77307 in comparison with average CO chondrite abundances. The depletion in Na is probably attributable to the effects of leaching in Antarctica. With the exception of Na, the volatile elements show a relatively smooth decrease in abundance as a function of condensation temperature, indicating that their behavior is largely controlled by their volatility.

Synchrotron x-ray fluorescence microprobe: Quantification and mapping of mixed valence state samples using micro-XANES

The synchrotron x-ray fluorescence microprobe is a valuable instrument for quantification and mapping of mixed valence state samples with high spatial resolution and elemental sensitivity. A method has been developed for quantifying the proportions of Fe2+ and Fe3+ with 100 μm spatial resolution and better than 100 ppm sensitivity using x-ray absorption near-edge structure (XANES). Applications of valence state mapping have been made to selenium in water-saturated sediments and manganese associated with wheat roots attacked by the take-all fungus.

MAPPING OF SELENIUM CONCENTRATIONS IN SOIL AGGREGATES WITH SYNCHROTRON X-RAY FLUORESCENCE MICROPROBE

The possible occurrence of reducing microsites in synthetic soil aggregates and their influences on the distribution of selenium species with redox-dependent mobilities was tested using the synchrotron X-ray fluorescence microprobe (SXRFM). Synthetic, effectively two-dimensional soil aggregates of diameters ranging from 10 to 30 mm were constructed, with and without inclusion of sections of Scirpus robustus and S. californicus root sections. Each aggregate was uniformly wetted with a saline solution containing 240 g m{sup {minus}3} Se [98% as Se(VI), and 2% as Se(IV)]. Gas-phase porosities varied between individual aggregates from 0.00 to 0.40 and were maintained relatively constant during the incubation period of up to 17 days. Exchanges of soil gases with atmospheric air occurred only along the periphery of the aggregates. Scanning of the aggregates using SXRFM demonstrated that Se was essentially homogeneously distributed in soils without Scirpus root sections, suggesting that Se remained primarily as the soluble Se(VI) species. The SXRFM results revealed large accumulations of total Se was measured in water-saturated soils within 1 to 4 mm of decomposing roots. These observations provide support for a model of localized reducing zones in which Se(VI) is reduced to less mobile Se(IV) and to insoluble Se(0), resulting in local accumulationmore » of total Se. The measured Se accumulation in one microsite compared reasonably well with a simple transient Se(VI) diffusion model. It is postulated that such mechanism may account for similar heterogeneities observable in some Se-contaminated soils at Kesterson Reservoir. Such heterogeneities in concentrations of Se and other constituents within individual soil aggregates have important implications with respect to reactivity and need to be included in any detailed mechanistic modeling of chemical cycling within soils. This work provides an example of the substantial capabilities of SXRFM in studies of soils. 45 refs., 11 figs.« less

X-ray microprobe analysis of iron oxidation states in silicates and oxides using X-ray absorption near edge structure (XANES)

Initial results are reported on a new microprobe technique for determining Fe 3+ ∑Fe ratios in Fe-bearing minerals. The technique is based on the energy shift of a pre-edge peak in X-ray absorption near-edge structure (XANES) spectra obtained using the synchrotron X-ray fluorescence microprobe. A linear relationship between pre-edge peak energy and iron oxidation state was observed for oxide and silicate standards. Reasonable iron oxidation state results were obtained for pallasitic olivine, acmite, altered magnetites and synthetic wüstite. Direct measurements of Fe 3+ ∑Fe in coexisting phases is feasible using this technique.

Synchrotron X-ray fluorescence microprobe: A microanalytical instrument for trace element studies in geochemistry, cosmochemistry, and the soil and environmental sciences

The availability of high-brightness synchrotron radiation sources has permitted the development of X-ray microprobe instrumentation for trace element studies at high spatial resolution based on the X-ray fluorescence technique. The X-ray microprobe at beamline X26A at the National Synchrotron Light Source (Brookhaven National Laboratory) has been applied to a wide variety of problems in the earth, planetary, soil and environmental sciences, including: volatile element contents of micrometeorites, oxidation state heterogeneity of uranium in contaminated sediments, elemental compositions and speciation of flyash particles and the compositions of hydrothermal fluids based on inclusion analyses.

Geochemical applications of synchrotron x-ray microspectroscopy

The synchrotron x-ray fluorescence microprobe at bending magnet beamline X-26A at the National Synchrotron Light Source has been used for a number of years for geochemical trace element microanalysis using collimated white radiation. More recently an incident beam monochromator and 8:1 focusing mirror have been added. These optics permit the formation of a small (30-100 micron) intense beam of monochromatic radiation suitable for use in x-ray absorption spectroscopy, including both near edge (XANES) and extended fine structure (EXAFS) techniques. This system has been used to study a number of problems in the earth and environmental sciences, including: oxidation state of uranium in contaminated waste sites; oxidation state of Cr in olivine inclusions in diamonds from the Earth's mantle; oxidation state of Mn in wheat roots infected with the take-all disease. We report here some recent results obtained on studies of the oxidation state of Fe in cosmochemical systems.Oxygen fugacity is one of the most important parameters in determining the cosmochemical and geochemical evolution of a system.