Glass Reference Materials Research Articles

Preliminary Characterisation of New Glass Reference Materials (GSA-1G, GSC-1G, GSD-1G and GSE-1G) by Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry Using 193 nm, 213 nm and 266 nm Wavelengths

New glass reference materials GSA-1G, GSC-1G, GSD-1G and GSE-1G have been characterised using a prototype solid state laser ablation system capable of producing wavelengths of 193 nm, 213 nm and 266 nm. This system allowed comparison of the effects of different laser wavelengths under nearly identical ablation and ICP operating conditions. The wavelengths 213 nm and 266 nm were also used at higher energy densities to evaluate the influence of energy density on quantitative analysis. In addition, the glass reference materials were analysed using commercially available 266 nm Nd:YAG and 193 nm ArF excimer lasers. Laser ablation analysis was carried out using both single spot and scanning mode ablation. Using laser ablation ICP-MS, concentrations of fifty-eight elements were determined with external calibration to the NIST SRM 610 glass reference material. Instead of applying the more common internal standardisation procedure, the total concentration of all element oxide concentrations was normalised to 100%. Major element concentrations were compared with those determined by electron microprobe. In addition to NIST SRM 610 for external calibration, USGS BCR-2G was used as a more closely matrix-matched reference material in order to compare the effect of matrix-matched and non matrix-matched calibration on quantitative analysis. The results show that the various laser wavelengths and energy densities applied produced similar results, with the exception of scanning mode ablation at 266 nm without matrix-matched calibration where deviations up to 60% from the average were found. However, results acquired using a scanning mode with a matrix-matched calibration agreed with results obtained by spot analysis. The increased abundance of large particles produced when using a scanning ablation mode with NIST SRM 610, is responsible for elemental fractionation effects caused by incomplete vaporisation of large particles in the ICP. Les verres de reference fabriques recemment : GSA-1G, GSC-1G, GSD-1G et GSE-1G ont ete caracterises en utilisant un systeme prototype d'ablation laser, avec un laser solide capable de produire des longueurs d'onde de 193 nm, 213 nm et 266 nm. Ce systeme permet de comparer les effets des differentes longueurs d'onde d'ablation utilises dans les memes conditions d'ablation et d'operation de l'ICP-MS. Les longueurs d'onde 213 et 266 nm ont aussi ete testees a plus haute densite d'energie afin d'evaluer l'effet de ces plus hautes densites d'energie sur l'analyse quantitative. De plus, les verres de reference ont ete analyses avec un laser Nd-YAG commercial, de 266 nm de longueur d'onde et avec un laser Excimer ArF de 193 nm de longueur d'onde. Les analyses par ablation laser ont ete realisees en utilisant les modes d'ablation ponctuelle et en balayage. Les concentrations de cinquante huit elements ont ainsi ete determinees par calibration externe par rapport au verre de reference NIST SRM 610. Au lieu d'appliquer la procedure classique de standardisation interne, nous avons contraint la somme de tous les oxydes d'elements a 100%. Les concentrations en elements majeurs ont ete comparees avec celles determinees par microsonde electronique. Nous avons aussi utilise le standard BCR-2G de l'USGS comme autre standard de calibration externe, de matrice mieux adaptee, dans le but de comparer les effets de l'utilisation de standards externes de matrice adaptee ou non adaptee sur l'analyse quantitative. Les resultats montrent que les differentes longueurs d'onde et densites d'energie utilisees donnent des resultats similaires, a l'exception de l'ablation en mode balayage effectuee avec 266 nm de longueur d'onde et calibree avec un standard externe de matrice non adaptee, pour laquelle des deviations jusqu’a 60% ont pu etre observees. Neanmoins, les resultats acquis avec le meme mode operatoire, mais avec un standard externe de matrice adaptee, etaient en total accord avec les donnees obtenues par analyse ponctuelle. L'augmentation de la quantite de grosses particules produites durant le processus d'ablation par balayage du verre NIST SRM 610 est responsable des fractionnements elementaires observes, et dus a la vaporisation incomplete de ces grosses particules dans le plasma.

Laser Ablation and Solution ICP-MS Determination of Rare Earth Elements in USGS BIR-1G, BHVO-2G and BCR-2G Glass Reference Materials

Data are reported for rare earth elements (REE) in three geological glass reference materials (BIR-1G, BHVO-2G and BCR-2G) using a UV (266 nm) laser ablation ICP-MS system and the classical (HF-HClO4) acid decomposition method, followed by conventional nebulisation ICP-MS. External calibration of laser ablation analyses was performed using NIST SRM reference materials with internal standardisation using 29Si and 44Ca. Replicate analyses of reference basaltic glasses yielded an analytical precision of 1-5% (RSD) for all the elements by solution ICP-MS and 1-8% (RSD) by laser ablation ICP-MS. The relative differences between the REE concentrations measured by solution and laser ablation ICP-MS compared with the reference values were generally less than 11 % for most elements. The largest deviations occurred for La determined by solution ICP-MS in BIR-1G. The results of both solution and laser ablation ICP-MS agreed well, generally better than 7%, with the exception of La, Pr and Sm in BIR-1G. The measured REE laser ablation data for BIR-1G, BHVO-2G and BCR-2G agreed with the previously published data on these basaltic reference glasses, within a range of 0-10% for most elements. No significant influences were observed for the predicted spectral interferences on some REE isotopes in the analysis of basaltic glasses.

Lithium Isotope Composition of Basalt Glass Reference Material

We present data on the lithium isotope compositions of glass reference materials from the United States Geological Survey (USGS) and the National Institute of Standards and Technology (NIST) determined by multicollector inductively coupled plasma mass spectrometry (MC-ICPMS), thermal ionization mass spectrometry (TIMS), and secondary ionization mass spectrometry (SIMS). Our data on the USGS basaltic glass standards agree within 2 per thousand, independent of the sample matrix or Li concentration. For SIMS analysis, we propose use of the USGS glasses GSD-1G (delta(7)Li 31.14 +/- 0.8 per thousand, 2sigma) and BCR-2G (delta(7)Li 4.08 +/- 1.0 per thousand, 2sigma) as suitable standards that cover a wide range of Li isotope compositions. Lithium isotope measurements on the silica-rich NIST 600 glass series by MC-ICPMS and TIMS agree within 0.8 per thousand, but SIMS analyses show systematic isotopic differences. Our results suggest that SIMS Li isotope analyses have a significant matrix bias in high-silica materials. Our data are intended to serve as a reference for both microanalytical and bulk analytical techniques and to improve comparisons between Li isotope data produced by different methodologies.

Determination of Lithium, Beryllium and Boron at Trace Levels by Laser Ablation‐Inductively Coupled Plasma‐Sector Field Mass Spectrometry

The analytical capabilities of laser ablation (LA)‐ICP‐MS in determining Li, Be and B at trace levels in geological samples have been tested on a series of glass reference materials and natural samples. The LA‐ICP‐MS instrument used consisted of a sector‐field ICP‐MS coupled with a laser ablation microprobe operating at either 266 or 213 nm wavelength. Reference glasses from NIST (SRM 612, 614 and 616) and MPI‐DING (KL2‐G, ML3B‐G, StHs6/80‐G, GOR128‐G, GOR132‐G, T1‐G and ATHO‐G) were selected to develop the analytical method and to assess the best instrumental configuration. A series of calcic amphiboles with different Li, Be and B concentrations were also analysed using both LA‐ICP‐MS and SIMS to test the applicability of the method to natural minerals. Results indicated that with a spot size of 40 μm the agreement between measured and reference values of Li, Be and B is generally better than 10% for NIST SRM 612 and 20% for NIST SRM 614. Average reproducibility at the 2s level was 10% for Li, 20% for Be and 15% for B. Limits of detection were approximately 100 ng g‐1 for Be and B and 200 ng g‐1 for Li. These results were confirmed by analyses carried out on natural amphiboles and compared well in terms of precision and accuracy with those commonly achieved by SIMS.

Sampling strategies for the analysis of glass fragments by LA-ICP-MS: Part II: Sample size and sample shape considerations

Glass fragments recovered from crime scenes are usually very small and therefore the amount of sample available to conduct forensic analyses is limited. Elemental analysis using conventional digestion methods consumes at least 2–3 mg of glass per replicate. LA-ICP-MS requires 10,000 times less glass consumption per analysis (∼280 ng), and therefore the sample remains practically unaltered. Typically, the recovered fragments (unknowns) are 0.1–1 mm in length, while the “known” samples are usually larger, i.e. a broken fragment from a windshield (>3 mm). For bulk digestion analysis, the difference in fragment size does not present a problem for elemental comparisons – other than requiring at least 6 mg for triplicate analysis – because the sample is crushed and homogenized before weighing. Laser ablation sampling results in the creation of small craters (∼50 μm diameter and 80 μm deep) drilled into the sample due to the interaction of the laser with the glass target. This study aims to evaluate whether the quantitative elemental analysis using the LA sampling method is affected by the size of the glass fragment due to differences in heat dissipation and surface–laser interaction. The analytical method employed for the analysis of glass by LA-ICP-MS had previously shown to possess the same or better performance than dissolution ICP-MS methods in terms of accuracy, precision, limits of detection and discrimination power. A 266 nm Nd:YAG laser with a flat top beam profile was used in single point mode sampling a 50 μm spot size for 50 s at 10 Hz. Standard glass reference materials SRM 612 and SRM 610 were selected to conduct this work in order to account for different concentration ranges and different opacities of the samples. The set under study was comprised of seven fragments originating from each standard at different sizes and shapes ranging from 6 to 0.2 mm length. Analysis of variance (ANOVA) followed by the Tukey's honestly significant different test (HSD) was used for data analysis. The results show that there is no significant difference in the elemental composition of different sized fragments. The conclusions, however, cannot be generalized for fragments measuring less than 0.2 mm × 0.1 mm.

Improved in situ isotope analysis of low-Pb materials using LA-MC-ICP-MS with parallel ion counter and Faraday detection

A new analytical protocol is described allowing the measurement of Pb-isotope ratios, including the low abundance isotope 204Pb, in relatively small targets (∼100 micron) of low Pb content (1–10 ppm), such as might be encountered in the analysis of magmatic melt inclusions, for example. The analysis routine employed utilises multiple Faraday cups and two ion counters operated in static multi-collection mode. Concurrent analysis of the NIST 612 glass standard allows an external correction for mass bias, and simultaneous determination of ion counter gain, while Hg interference on 204Pb is corrected in real time by simultaneous acquisition of 200Hg in a second ion counter. Analytical precision approximates theoretical limits and it can be shown that analytical accuracy is limited primarily by ion counter gain for ratios involving 204Pb and the mass bias correction for all other ratios. We typically obtain precisions of <0.4% RSD (2 sigma) and accuracy of ≤0.2% on BCR2-g for ratios involving 204Pb. Two other glass reference materials (MPI-DING ATHO-G and KL2-G) were also analysed, and precision of ≤1.8% RSD (2 sigma) and accuracy of ≤0.9% were obtained for the glass with the lowest Pb abundance of approximately 2 μg g−1. These results provide an improvement on the accuracy and precision of laser ablation ratio determinations, attributable to stable instrument conditions and high sensitivity.

Secondary ion mass spectrometry for the determination of δ37Cl : Part I. Ion microprobe analysis of glasses and fluids

A detailed technique is presented for the determination of 37Cl/ 35Cl in natural glasses by Secondary Ion Mass Spectrometry (SIMS). This technique utilizes a large format high-resolution, high-transmission ion microprobe—the Cameca IMS 1270. The lateral spatial resolution achieved by the microprobe is 10–20 μm—providing the capability to measure δ 37Cl in very small objects, such as igneous melt inclusions, or in fine-scale zoning in other natural glasses. An overall reproducibility of individual analyses better than 1.5‰ (2 σ) is demonstrated for replicates of homogeneous glass reference material. This performance is achievable in samples with as little as 100–200 ppm total Cl. This technique has also been extended to the direct determination of 37Cl/ 35Cl in very small (1 μl) samples of natural fluids, containing only μg quantities of Cl. Using the simple approach of first integrating the dried fluids with graphite powder, these samples can also be analyzed with an overall reproducibility better than 1.5‰ (2 σ). This latter procedure is particularly advantageous in cases where the available sample supply is severely limited in quantity.

Rare-earth glass reference materials for near-infrared spectrometry: sources of x-axis location variability

The National Institute of Standards and Technology (NIST) recently introduced two optical filter standards for wavelength/wavenumber calibration of near-infrared (NIR) spectrometers. Standard Reference Material ®s (SRM ®s) 2035 and 2065 were fabricated in lots of ≈100 units each from separate melts of nominally identical rare-earth glass. Since individual filter certification is extremely time-consuming and thus costly, economic production of these SRMs required the ability to batch certify band locations. Given the specification that the combined uncertainty for the location of the bands in a given filter should be ≤0.2 cm −1, rigorous evaluation of material heterogeneity was required to demonstrate the adequacy of batch certification for these materials. Among-filter variation in measured band locations convolves any influence of material heterogeneity with that of environmental, procedural, and instrumental artifacts. While univariate analysis of variance established band-specific heterogeneity upper bounds, it did not provide quantitative descriptions of the other possible sources for the observed measurement variability. Principal components analysis enabled both the identification and isolation of the most important NIR band location variances among the SRM 2065 filters. After correction for these variance sources, the upper bound on the material heterogeneity was determined to be 0.03 cm −1 for all bands. Since this is a small part of the measurement uncertainty, we conclude that batch analysis provides an acceptable certification approach for these and similarly fabricated rare-earth glass reference materials.

A LASER PROBE COUPLED WITH ICP DOUBLE-FOCUSING SECTOR-FIELD MASS SPECTROMETER FOR IN SITU ANALYSIS OF GEOLOGICAL SAMPLES AND U Pb DATING OF ZIRCON

Quadrupole ICP–MS is currently the method of choice for laser-ablation applications, since sector-field instruments are generally considered too slow for the acquisition of rapidly varying signals. However, the new generation of double-focusing sector-field mass spectrometers is capable of rapidly scanning the mass spectrum both magnetically and electrostatically, and the combination of these two scan modes approaches the performance of quadrupoles for most practical applications. We present the instrumental configuration and operating conditions of a LA–ICP–MS system, assembled by coupling a 266 nm laser source to a double-focusing magnetic-sector mass spectrometer (“Element”, Finnigan MAT). The capability of the adopted configuration to furnish high-quality in situ trace-element analysis of minerals and U–Pb geochronological data is described. Concentrations of thirty geochemically relevant elements ( LILE , HFSE , REE , actinides) were determined on geological samples with good precision and accuracy (<10%), evaluated using two USGS basaltic glass reference materials, BCR–2 and BIR–1. The high sensitivity and low background allowed extremely low limits of detection (down to the ppb level) for the heaviest elements, and between 10 and 100 ppb for the lighter masses. The first results on U:Pb ratio determinations are also very positive. By adopting an external matrix-matched standard for corrections of mass bias and laser-induced fractionation of elements, precision and accuracy in age determinations to better than ~2% are attained on the zircon standard 91500.

Micro-heterogeneity study of trace elements in USGS, MPI-DING and NIST glass reference materials by means of synchrotron micro-XRF

Synchrotron μ-XRF (X-ray fluorescence analysis), a trace level micro analytical method, allows the quantitative study of the nature and degree of heterogeneity of inorganic trace constituents in reference materials with a homogeneous matrix. In the present study, glass materials of NIST, MPI-DING and USGS containing trace levels of heavy metals are considered. The measurements involve an extensive series of local analyses, performed in identical conditions at different locations on the material. This procedure is employed to measure the degree of micro-heterogeneity of several existing reference materials and to evaluate their suitability for calibration of trace-level micro-analytical methods. For a number of the trace elements present in the various reference materials, a minimum representative mass for homogeneous measurements is calculated.

Quality of determinations obtained from laboratory reference samples used in the calibration of X-ray electron probe microanalysis of silicate minerals

Nine simple minerals and oxides, traditionally used as laboratory reference samples in the electron probe microanalysis (EPMA) of silicate minerals, have been quantitatively evaluated. Three separate series of data, comprising the average concentration, standard deviation, relative standard deviation, confidence interval and the z-score of data quality, were calculated for 21 control samples derived from calibrations obtained from three sets of reference samples: (1) simple minerals; (2) oxides; and (3) certified glass reference materials. No systematic difference was observed between the concentrations obtained from these three calibration sets when analyzed results were compared to certified compositions. The relative standard deviations obtained for each element were smaller than target values for all determinations. The z-score values for all elements determined fell within acceptable limits (−2< z<2) for concentrations ranging from 0.1 to 100%. These experiments show that the quality of data obtained from laboratory reference calibration samples is not inferior to that from certified reference glasses. The quality of results obtained corresponds to the ‘applied geochemistry’ type of analysis (category 2) as defined in the GeoPT proficiency testing program. Therefore, the laboratory reference samples can be used for calibrating EPMA techniques in the analysis of silicate minerals and for controlling the quality of results.

Attenuation of spectral interferences during laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) using an rf only collision and reaction cell

The reduction of spectral interferences in laser ablation inductively coupled plasma mass spectrometry was investigated using an rf only hexapole as a collision and reaction cell with H2 as the reaction gas and He as a buffer gas. Argon-based polyatomic ions (ArX+) were attenuated by between 1 and 6 orders of magnitude with H2 during laser ablation experiments whilst analyte transmission under the same parameters was maintained above 80%. The amount of ArX+ attenuation for a fixed volume of reactive H2 gas was proportional to the electronegativity of parent element X. Interferences were not significantly attenuated with He. However, a change from ‘dry’ to ‘wet’ conditions in the plasma led to reactions with water molecules in the cell giving an apparent reactivity for clean He buffer gas whilst reducing the efficiency of some reactions with H2. Improved accuracy and precision were demonstrated under optimised conditions for the analysis of trace elements in sulfide and carbonate standard reference materials as a result of background interference reduction. Multi-element analysis was possible with reactive gases in the reaction cell as demonstrated by the accurate analysis, to within 15% of the recommended values for most trace elements, of candidate glass reference materials using NIST SRM glasses for calibration.

Determination of Forty Two Major and Trace Elements in USGS and NIST SRM Glasses by Laser Ablation‐Inductively Coupled Plasma‐Mass Spectrometry

Forty two major (Na, Mg, Ti and Mn) and trace elements covering the mass range from Li to U in three USGS basalt glass reference materials BCR‐2G, BHVO‐2G and BIR‐1G were determined using laser ablation‐inductively coupled plasma‐mass spectrometry. Calibration was performed using NIST SRM 610 in conjunction with internal standardisation using Ca. Determinations were also made on NIST SRM 612 and 614 as well as NIST SRM 610 as unknown samples, and included forty five major (Al and Na) and trace elements. Relative standard deviation (RSD) of determinations was below 10% for most elements in all the glasses under investigation. Consistent exceptions were Sn and Sb in BCR‐2G, BHVO‐2G and BIR‐1G. For BCR‐2G, BHVO‐2G and BIR‐1G, clear negative correlations on a logarithmic scale exist between RSD and concentration for elements lower than 1500 μg g‐1 with logarithmic correlation coefficients between ‐0.75 and ‐0.86. There is also a clear trend of increasing RSD with decreasing concentration from NIST SRM 610 through SRM 612 to SRM 614. These suggest that the difference in the scatter of apparent element concentrations is not due to chemical heterogeneity but reflects analytical uncertainty. It is concluded that all these glasses are, overall, homogeneous on a scale of 60 μm.Our first results on BHVO‐2G and BIR‐1G showed that they generally agreed with BHVO‐2/BHVO‐1 and BIR‐1 within 10% relative. Exceptions were Nb, Ta and Pb in BHVO‐2G, which were 14‐45% lower than reference values for BHVO‐2 and BHVO‐1. Be, Ni, Zn, Y, Zr, Nb, Sn, Sb, Gd, Tb, Er, Pb and U in BIR‐1G were also exceptions. However, of these elements, Be, Nb, Sn, Sb, Gd, Tb, Pb and U gave results that were consistent within an uncertainty of 2s between our data and BIR‐1 reference values. Results on NIST SRM 612 agreed well with published data, except for Mg and Sn. This was also true for elements with m/z 85 (Rb) in the case of NIST SRM 614.The good agreement between measured and reference values for Na and Mg in BCR‐2G, BHVO‐2G and BIR‐1G, and for Al and Na in NIST SRM 610, 612 and 614 up to concentrations of at least several weight percent (which were possible to analyse due to the dynamic range of 108) indicates the suitability of this technique for major, minor and trace element determinations.

Trace Element Analysis of NIST SRM 614 and 616 Glass Reference Materials by Laser Ablation Microprobe‐Inductively Coupled Plasma‐Mass Spectrometry

Fifty elements in NIST SRM 614 and 616 glass reference materials were determined by laser ablation microprobe‐inductively coupled plasma‐mass spectrometry (LAM‐ICP‐MS). The values determined for NIST SRM 614 agreed well with the NIST‐certified and information values (mean relative difference ± 3.6%), except for B, Sc and Sb. The values determined for NIST SRM 616 agreed with the NIST‐certified and information values within a mean relative difference of ± 1.5%, except for B, Sc and Ga. In addition, at an 80 μm sampling scale, NIST SRM 614 and 616 glass discs were homogeneous for trace elements within the observed precisions of 5 and 15% (mean), respectively. Detection limits were in the range 0.01 ‐ 0.3 μg g−1 for elements of lower mass numbers (amu &lt; 80) and 1 ‐ 10 ng g−1 for heavy elements (amu &gt; 80). Detection at the sub ng g−1 level is possible for most of the heavy elements by using an ablation pit size larger than 10 0 μm.

Enhanced sensitivity in inductively coupled plasma sector field mass spectrometry for direct solid analysis using laser ablation (LA-ICP-SFMS)

Different hardware components in the interface region of an inductively coupled plasma sector field mass spectrometer (ICP-SFMS), like sample cone dimensions and material, the interface pressure and ion sampling position, were modified to study their contribution to ion extraction and transmission from a plasma operated under dry conditions as used for laser ablation. Analytical figures of merit, such as background levels, limits of detection and signal intensities, used to describe the effects in the interface were determined on two well-known standard reference materials, NIST SRM 612 and MPI-DING (GOR128-G). An aluminium cone with a sample cone orifice diameter of 0.8 mm and an aluminium skimmer with a cone diameter of 1.0 mm together with a second vacuum pump gave a vacuum pressure of 1.8 × 10−7 mbar. The blank level signals for elements in the lower mass region (e.g., Na, Si, Ca) decreased by a factor of 10, whereas the sensitivity for these elements increased 10 times. Thus, after incorporating such modifications, the limits of detection for elements suffering from elevated background intensities were improved by two orders of magnitude. For elements in the higher mass region (starting from mass 85), the limits of detection were in the low ng g−1 range for a 30 µm diameter laser spot. Modification to the sampling cones resulted in the reduction of oxide formation, which was demonstrated by monitoring the ThO+/Th+ ratio (0.01%). These interface changes made it possible to, for example, decrease the laser spot size down to 16 µm when directly sampling the geological glass reference material, MPI-DING (GOR128-G), while retaining trace element capabilities in the concentration range of 100 ng g−1. An agreement between the measured and the reported reference values of 5–10% was achieved, showing the potential for higher lateral resolution analyses when using sector field instruments for direct solid sampling.

Boron and Oxygen Isotope Composition of Certified Reference Materials NIST SRM 610/612 and Reference Materials JB‐2 and JR‐2

We present data on the concentration, the isotope composition and the homogeneity of boron in NIST silicate glass reference materials SRM 610 and SRM 612, and in powders and glasses of geological reference materials JB‐2 (basalt) and JR‐2 (rhyolite). Our data are intended to serve as references for both microanalytical and wet‐chemical techniques. The δ11 B compositions determined by N‐TIMS and P‐TIMS agree within 0.5% and compare with SIMS data within 2.5%. SIMS profiles demonstrate boron isotope homogeneity to better than δ11 B = 2% for both NIST glasses, however a slight boron depletion was detected towards the outermost 200 μm of the rim of each sample wafer. The boron isotope compositions of SRM 610 and SRM 612 were indistinguishable. Glasses produced in this study by fusing JB‐2 and JR‐2 powder also showed good boron isotope homogeneity, both within and between different glass fragments. Their major element abundance as well as boron isotope compositions and concentrations were identical to those of the starting composition. Hence, reference materials (glasses) for the in situ measurement of boron isotopes can be produced from already well‐studied volcanic samples without significant isotope fractionation. Oxygen isotope ratios, both within and between wafers, of NIST reference glasses SRM 610 and SRM 612 are uniform. In contrast to boron, significant differences in oxygen isotope compositions were found between the two glasses, which may be due to the different amounts of trace element oxides added at ten‐fold different concentration levels to the silicate matrix.

The preparation of uranium-doped glass reference materials for environmental measurements

Seven different uranium glass powders containing 5 mass% uranium with 235U abundances from natural to highly enriched have been prepared for the IRMM support programme to the International Atomic Energy Agency (IAEA) and for the IRMM external NUSIMEP quality control programme (Nuclear Signatures Interlaboratory Measurement Evaluation Programme). The particles will be primarily used, blended with (inactive) matrix glass powder in various ratios to simulate environmental samples containing “hot” particles in order to assess the performance of various separation and measurement techniques. High-purity borosilicate glass was prepared by blending of powders, melting and grinding by ball milling and jet milling to a powder of about 12 μm. A quantity of this glass was then blended with U 3O 8, melted and milled to powder. Laser diffraction measurements were made to ensure that the particle size distribution of the uranium glass matched that of the matrix glass in order to ensure homogeneous blending. The final yield was 30–40 g of each uranium glass and 1 kg of matrix glass. The glasses have been certified as reference materials for isotope abundances of uranium.

Studies of LA-ICP-MS on quartz glasses at different wavelengths of a Nd:YAG laser.

The capability of LA-ICP-MS for determination of trace impurities in transparent quartz glasses was investigated. Due to low or completely lacking absorption of laser radiation, laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) proves difficult on transparent solids, and in particular the quantification of measurement results is problematic in these circumstances. Quartz glass reference materials of various compositions were studied by using a Nd:YAG laser system with focused laser radiation of wavelengths of 1064 nm, 532 nm and 266 nm, and an ICP-QMS (Elan 6000, Perkin Elmer). The influence of ICP and laser ablation conditions in the analysis of quartz glasses of different compositions was investigated, with the laser power density in the region of interaction between laser radiation and solid surface determining the ablation process. The trace element concentration was determined via calibration curves recorded with the aid of quartz glass reference materials. Under optimized measuring conditions the correlation coefficients of the calibration curves are in the range of 0.9-1. The relative sensitivity factors of the trace elements determined in the quartz glass matrix are 0.1-10 for most of the trace elements studied by LA-ICP-MS. The detection limits of the trace elements in quartz glass are in the low ng/g to pg/g range.

Quasi ‘non-destructive’ laser ablation-inductively coupled plasma-mass spectrometry fingerprinting of sapphires

A homogenized 193 nm excimer laser with a flat-top beam profile was used to study the capabilities of LA-ICP-MS for ‘quasi’ non-destructive fingerprinting and sourcing of sapphires from different locations. Sapphires contain 97–99% of Al 2O 3 (corundum), with the remainder composed of several trace elements, which can be used to distinguish the origin of these gemstones. The ablation behavior of sapphires, as well as the minimum quantity of sample removal that is required to determine these trace elements, was investigated. The optimum ablation conditions were a fluency of 6 J cm −2, a crater diameter of 120 μm, and a laser repetition rate of 10 Hz. The optimum time for the ablation was determined to be 2 s, equivalent to 20 laser pulses. The mean sample removal was 60 nm per pulse (approx. 3 ng per pulse). This allowed satisfactory trace element determination, and was found to cause the minimum amount of damage, while allowing for the fingerprinting of sapphires. More than 40 isotopes were measured using different spatial resolutions (20–120 μm) and eight elements were reproducibly detected in 25 sapphire samples from five different locations. The reproducibility of the trace element distribution is limited by the heterogeneity of the sample. The mean of five or more replicate analyses per sample was used. Calibration was carried out using NIST 612 glass reference material as external standard. The linear dynamic range of the ICP-MS (nine orders of magnitude) allowed the use of Al, the major element in sapphire, as an internal standard. The limits of detection for most of the light elements were in the μg g −1 range and were better for heavier elements (mass >85), being in the 0.1 μg g −1 range. The accuracy of the determinations was demonstrated by comparison with XRF analyses of the same set of samples. Using the quantitative analyses obtained using LA-ICP-MS, natural sapphires from five different origins were statistically classified using ternary plots and principal multi-component analysis.

Preparation of two uranium glass reference materials for fission-track dating of geological samples

The European Commission produced and certified uranium glass for fission-track dating in 1996 (Reference Material IRMM-540). This material is now out of stock and a project for the preparation of two new reference glasses is underway. The new glasses, containing nominally 15 and 55 mg kg −1 uranium, were prepared from blended oxide powder, and cast using an improved method, which minimised micro-scale defects and optimised the yield. Glass rods were produced which were then cut into discs of 2 mm thickness and 15 mm diameter and subsequently polished. Uranium homogeneity and fission-track stability are critical properties of the glass. An extensive study was carried out to verify the homogeneity by fission-track counting, investigating both within-disc and between disc effects, and to investigate potential track fading due to thermal annealing. No evidence of uranium heterogeneity was detected. The stability study, using an “isochronous” method, in which all measurements are made at the end of exposure to artificial ageing, is still underway. The reference material will be certified for isotopic composition (natural), uranium mass fraction and neutron fluence (one disc out of each set of three will be irradiated, together with a mica foil, to induce fission tracks in a certified fluence). The reference materials will be released as IRMM-540R ( 15 mg kg −1 U) and IRMM-541 ( 55 mg kg −1 U).