Trace Element Analysis of Fused Whole-Rock Glasses by Laser Ablation-ICP-MS and PIXE

The concentrations of fifty trace elements, including relatively volatile elements and transition metal elements, in fused glasses of Geological Survey of Japan rock reference materials GSJ JR-2, JA-1, JA-2, JB-1a, JB-3, JGb-1 and JF-1 were determined by particle (proton) induced X-ray emission (PIXE) and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). The fused glasses were prepared by rapid fusion and subsequent quenching in welded platinum capsules and were found to be homogeneous for major elements and for trace elements with concentrations of more than 1 μg g^-1 within the observed precision (± 10% mean) on a 70 μm sampling scale. The values obtained by PIXE and LA-ICP-MS for the transition elements (Cr, Mn, Fe, Ni and Cu), the relatively volatile elements (Zn, Ga, Rb and Pb) and the refractory elements (Y, Zr, Nb and Th) with concentrations greater than a few μg g^-1 showed good agreement (within 10 % relative difference). The values for almost all the elements detected at concentrations higher than 1 μg g^-1 as determined by LA-ICP-MS also agreed well with the reference values (mean relative difference < ± 10%), except for B and Cu. The good agreement confirmed the appropriateness of the NIST SRM 600 series glass calibration reference material for LA-ICP-MS analysis of glasses with variable major-element compositions for almost all elements. The concentrations of Cu in all the samples were lower than the reference values, which was attributed to adsorption of the transition metals onto the platinum capsule during preparation.     

Characterisation of Two New Reference Materials: STL-1, the Stewart Lepidolite and ZA-1, the Zapot Amazonite

The analysis of granitic pegmatites still remains a challenge because suitable natural reference materials are scarce or not available. Two new reference materials were prepared at the Smithsonian Institution, to provide an avenue to pursue the geochemical analysis of micas and feldspars in granitic pegmatites: STL-1, the Stewart lepidolite (NMNH 174041) and ZA-1, the Zapot amazonite (NMNH 174042). STL-1 was prepared from lepidolite collected from the lithium-rich Stewart pegmatite, San Diego County, California (33°22'52'N, 117°03'41'W). ZA-1 was prepared from an amazonite from the topaz-bearing Zapot pegmatite, Mineral County, Nevada, (38° 41'N, 118 °33'W). The results of this study indicated that STL-1 and ZA-1 are homogeneous and could be used as reference materials that would allow the expansion of calibration curves in XRF analysis up to 16000 μg g⁻¹ for Rb, 2000 μg g⁻¹ for Cs and 100 μg g⁻¹ for Tl. STL-1 and ZA-1 also contain unusually high concentrations of Ga and Tl, and STL-1 of Nb.     

Determination of Chlorine in Nine Rock Reference Materials by Isotope Dilution Mass Spectrometry

A procedure for the determination of chlorine by the isotope dilution technique (ID) using negative thermal ionisation mass spectrometry (N-TIMS) is described. Silicate samples of about 10 mg were spiked and decomposed with hydrofluoric acid, and chlorine was isolated by precipitation of silver chloride after neutralisation with Ca(OH)₂. The ammonical solution of AgCl was then subjected to N-TIMS. Replicate analyses of rock reference materials, typically of JB-1 and JR-1, demonstrated the high quality of the analyses (precision for Cl was ± 1-2%). We present here the most precise data sets of chlorine concentrations in nine igneous rock reference materials, three basalts (JB-1, JB-2, JB-3), two andesites (JA-3, AGV-1), two rhyolites (JR-1, JR-2) and two granodiorites (JG-3, GSP-1). The chlorine concentrations found ranged from 152 μg g-1 in AGV-1 to 1008 μg g^-1 in JR-1. Our results presented here are partly (but not completely) in agreement with recommended values, where they are available. The N-TIMS ID technique can thus be used as a means of determining low chlorine contents in silicate materials to high precision.     

Determination of Selenium Concentrations in NIST SRM 610, 612, 614 and Geological Glass Reference Materials Using the Electron Probe, LA-ICP-MS and SHRIMP II

A combination of EMPA, sensitive high resolution ion microprobe (SHRIMP II) and/or LA-ICP-MS techniques was used to measure the concentration of selenium (Se) in NIST SRM 610, 612, 614 and a range of reference materials. Our new compiled value for the concentration of Se in NIST SRM 610 is 112 ± 2 μg g⁻¹. The concentration of Se in NIST SRM 612, using NIST SRM 610 for calibration, determined using LA-ICP-MS (confirmed using SHRIMP II) was 15.2 ± 0.2 μg g⁻¹. The concentration of Se in NIST SRM 614, using LA-ICP-MS was 0.394 ± 0.012 μg g⁻¹. LA-ICP-MS determination of Se in synthetic geological glasses BCR-2G, BIR-1G, TB-1G and the MPI-DING glasses showed a range in concentrations from 0.062 to 0.168 μg g⁻¹. Selenium in the natural glass, VG2, was 0.204 ± 0.028 μg g⁻¹.     

Determination of Chlorine Contents in Geological Survey of Japan Reference Materials by Prompt Gamma Neutron Activation Analysis

We determined chlorine contents in nine GSJ (Geological Survey of Japan) reference materials (JB-1, 1a, 2, 3; JA-1, 2, 3; JR-1, 2) by prompt gamma neutron activation analysis, employing the standard addition method. Pressed powder disks of each reference material were used for neutron irradiation and gammaray measurement, after known quantities (25-200 μl) of sodium chloride solution were added. The influence of the nearby sodium peak overlap was checked, and fluctuations in the chlorine count rate were corrected using silicon as an internal standard. The slopes of calibration lines for seven reference materials (JB-1, 2, 3; JA-1, 2, 3; JR-2) and SiO₂ powders fall within 5% error, and their chlorine values were obtained from the intercepts. Chlorine contents in JB-1 a and JR-1 were also determined by using the calibration lines. Our chlorine values ranged from 26.1 to 934 μg g-¹, which agrees well with the previously reported values.     

Flotation Separation of Trace Elements from Alkaline-Earth Matrices by Co(III) Hexamethylenedithiocarbamate before ICP-AES Determination

A method for the selective separation of Ag, Cd, Cr, Cu, Ni, Pb and Zn in traces from solutions of calcite (CaCO₃), dolomite (CaMg(CO₃)₂) and gypsum (CaSO₄.2H₂O) before their determination by inductively coupled plasma-atomic emission spectrometry (ICP-AES) is presented. The expected interferences of Ca and Mg on intensities of trace analytes were removed by collecting the elements of interest with cobalt(III) hexamethylenedithiocar-bamate, Co(HMDTC)₃. The flotation of aqueous solutions (1 l) of calcite, dolomite and gypsum was performed at pH 6.0, by 1.5 mg l⁻¹ Co and 0.6 mmol l⁻¹ HMDTC⁻. To minimise the effect of the reaction between Ca/Mg, which restrains the function of the surfactant, careful selection of the most suitable foaming reagent was necessary. The accuracy of the method was established by analysing natural alkaline-earth minerals by the standard addition method as well as using the dolomite reference materials GBW 07114 and GSJ JDo-1. The ICP-AES limits of detection following flotation on different minerals were found to be 0.080 μg g⁻¹ for Cd, 0.105 μg g⁻¹ for Ag, 0.142 μg g⁻¹ for Cu, 0.195 μg g⁻¹ for Cr, 0.212 μg g⁻¹ for Ni, 0.235 μg g⁻¹ for Zn and 0.450 μg g⁻¹ for Pb.     

Determination of Lithium Contents in Silicates by Isotope Dilution ICP-MS and its Evaluation by Isotope Dilution Thermal Ionisation Mass Spectrometry

A precise and simple method for the determination of lithium concentrations in small amounts of silicate sample was developed by applying isotope dilution-inductively coupled plasma-mass spectrometry (ID-ICP-MS). Samples plus a Li spike were digested with HF-HClO₄, dried and diluted with HNO₃, and measured by ICP-MS. No matrix effects were observed for ⁷Li/⁶Li in rock solutions with a dilution factor (DF) of 97 at an ICP power of 1.7 kW. By this method, the determination of 0.5 μg g^-1 Li in a silicate sample of 1 mg can be made with a blank correction of < 1%. Lithium contents of ultrabasic to acidic silicate reference materials (JP-1, JB-2, JB-3, JA-1, JA-2, JA-3, JR-1 and JR-2 from the Geological Survey of Japan, and PCC-1 from the US Geological Survey) and chondrites (three different Allende and one Murchison sample) of 8 to 81 mg were determined. The relative standard deviation (RSD) was typically < 1.7%. Lithium contents of these samples were further determined by isotope dilution-thermal ionisation mass spectrometry (ID-TIMS). The relative differences between ID-ICP-MS and ID-TIMS were typically < 2%, indicating the high accuracy of ID-ICP-MS developed in this study.     

Boron Isotopic Composition and Concentration of Ten Geological Reference Materials

We present boron isotope and concentration data from magmatic (komatiitic to rhyolitic) and sedimentary geological silicate and artificial glass reference materials that cover a wide spectrum of boron isotope compositions and boron concentrations. Boron isotope compositions were determined by TIMS (Cs₂BO₂⁺ -graphite and BO₂^- method) and boron concentrations by ICP-AES. Boron concentrations ranged from 7 to 159μ g^-1 and agree within 14% with published values. Based on replicate analyses of individually prepared sample aliquots an overall external reproducibility of better than 10% was determined. The obtained δ¹¹B values ranged from -12.6 to +13.6% and were reproducible within 1.1 % (2 RSD; excluding NTIMS) on the basis of individually prepared sample aliquots. The δ¹¹B values of JA-1 (+5.3%), JB-3 (+5.9%) and JR-2 (+2.9%) overlap the published data within analytical uncertainty. For the first time δ¹¹B values for the TB (-12.6%) and the MPI-DING glasses GOR-128-G (+13.6%), GOR-132-G (+7.1 %) and StHs6/80-G (-4.5%) are reported. The δ¹¹B values obtained by the Cs₂BO₂⁺ -graphite and the BO₂^- method as well as the majority of δ¹¹B values obtained using different sample preparation methods agree within analytical uncertainty. Therefore, we conclude that none of these analytical methods introduce any systematic error on the obtained δ¹¹B values.     

High Sensitivity Analysis of Trace Element-Poor Geological Reference Glasses by Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS)

Fifty-two trace elements in NIST SRM 614, 616 and MPI-DING BM90/21-G glass reference materials as well as in NIST SRM 612, USGS BCR2-G and other MPI-DING reference glasses (KL2-G, GOR132-G, GOR128-G, ATHO-G, Tl-G, StHs6/80-G and ML3B-G) were determined by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). Accurate ultra-low trace element abundances in the NIST SRM 614, 616 and BM90/21-G reference glasses down to lower ng g⁻¹ levels were determined with relative standard deviations (RSD) of less than 10%. Limits of detection using He as carrier gas were up to two times lower than with Ar and were 0.004 to 0.12 μg g⁻¹ for elements of lower mass numbers (amu < 85) and 0.002 to 0.06 μg g⁻¹ for elements having amu < 85. The measured concentrations generally agree within 15% with previous studies except for B in NIST SRM 614 and 616, which appears to be heterogeneously distributed, and Co, Zn, Ga and Ag in NIST SRM 616 for which the existing data set is too small to evaluate the discrepancies. New values for As (0.593 μg g⁻¹), Ag (0.361 μg g⁻¹) and Cd (0.566 μg g⁻¹) in NIST SRM 614 and new values for Na (94864 μg g⁻¹) and As (0.276 μg g⁻¹) in NIST SRM 616 are reported.     

Total Sulfur Concentration in Geological Reference Materials by Elemental Infrared Analyser

Total sulfur is an analyte for which there are few determinations published, despite the fact that it is a very important element (e.g., a major element in most ores, an important gas constituent in global warming, an active participant in acid drainage). Most geological reference materials have very poor quality sulfur results, that is with relative standard deviations (RSD) in the range of 30–50%, even for concentrations over 100 μg g⁻¹ S, which compromises their use as calibrators. In order to provide modern results with low RSD, sulfur was determined in twenty-nine geological reference materials with a state-of-the-art elemental S/C analyser using metal chips (certified reference materials with a traceability link) and analytical grade sulfur for high concentration samples. Analytical parameters (sample mass, crucible degassing, calibration strategy, etc.) were optimised by testing. Our results agreed with reference material values provided by issuing bodies. Results for CCRMP SY-2 (129 ± 13 μg g⁻¹ S), which has been proposed as a sulfur reference material, were in agreement with the proposed modern value of 122 ± 3.7 μg g⁻¹ S.     

Ion Chromatographic Determination of Fluorine and Chlorine in Silicate Rocks Following Alkaline Fusion

A simple and accurate method to determine fluorine and chlorine contents in small amounts (∼ 30 mg) in rock has been developed using ion chromatography after extraction by alkaline fusion. Powdered sample was mixed with sodium carbonate and zinc oxide at a mass ratio of 1:3:1, and was fused in an electric furnace at 900 °C for 30-40 minutes. An aqueous solution obtained by dissolving the fused silicate rock was diluted to the appropriate concentration of sodium carbonate (< ∼ 24 mmol l^-1) to minimise the tailing effect on F^- during ion chromatography caused by the large amount of carbonate species originating from the flux. Fluorine and chlorine contents were then determined by a standard additions method. Based on the relative standard deviation of the backgrounds, detection limits of both fluorine and chlorine were ∼ 4 μg g^-1, when 30 mg test portions were fused and diluted by a factor of 1200. We also report new fluorine and chlorine contents in nine GSJ (Geological Survey of Japan) reference materials, including peridotite (JP-1), granite (JG-1a), basalts (JB-1b, 2 and 3), andesites (JA-1 and 2) and rhyolites (JR-1 and 2). Fluorine and chlorine contents in the reference materials in this study were consistent with previously reported values. Reproducibilities were < 10 % for samples with F and Cl concentrations of > 20 μg g-1 and < 20 % with F and Cl < 20 μg g^-1.     

Trace Determination of Strontium and Barium in River Waters by Inductively Coupled Plasma-Atomic Emission Spectrometry Using an Ultrasonic Nebulizer

Inductively coupled plasma-atomic emission spectrometry in conjunction with an ultrasonic nebulizer was employed for the determination of Sr and Ba in river waters at parts per billion (μg l⁻¹) levels without pre-concentration. The ultrasonic nebulizer, equipped with a desolvation system, enhanced the analytical sensitivity by ten to twenty fold compared to conventional pneumatic nebulizers. The detection limits for Sr and Ba, ascertained from blanks and reference samples made in 0.05% NaCl solution, were 0.045 μg l⁻¹ and 0.16 μg l⁻¹ respectively. The accuracy of measurements, based on analyses of solutions of reference materials (G-2 and W-1) and multielement commercial standards (Merck®), was ± 10%. Replicate analyses of samples and reference samples showed measurement precision to be to be better than ± 5%, which is adequate considering that the concentration of Sr and Ba in river waters varies by one to two orders of magnitude.     

Preliminary Investigation into the Use of a High Resolution Inductively Coupled Plasma-Mass Spectrometer with Laser Ablation for Bulk Analysis of Geological Materials Fused with Li2B4O7

The paper presents preliminary results of the use of a high resolution double-focussing, magnetic sector inductively coupled plasma-mass spectrometer (HR-ICP-MS) with ultraviolet laser ablation (LA) for the bulk analysis of geological materials fused with Li₂B₄O₇. Detection limits are based on data from precision measurements of a fused SiO₂ sample of high purity, and sensitivity data (cps/μg g^-1) obtained on the Reference Material (RM) Syenite SY-2. For many trace elements, the detection limits are better than 0.05 μg g^-1 using a sample to flux weight ratio of 1:7.
Calibration curves, which are based entirely on RMs, are established for Hf, Ta, Tb, Tm and Lu. They indicate that, even at this early stage in the development of the technique, data accurate to ˜ 25% can be collected. It is concluded that the method may prove to be a valuable supplement to XRF for low level element concentration measurements; it is also very practical, as the same sample discs can be used for both XRF and LA-ICP-MS analyses.     

Preparation and Certification of Re-Os Dating Reference Materials: Molybdenites HLP and JDC

Two Re-Os dating reference material molybdenites were prepared. Molybdenite JDC and molybdenite HLP are from a carbonate vein-type molybdenum-(lead)-uranium deposit in the Jinduicheng-Huanglongpu area of Shaanxi province, China. The samples proved to be homogeneous, based on the coefficient of variation of analytical results and an analysis of variance test. The sampling weight was 0.1 g for JDC and 0.025 g for HLP. An isotope dilution method was used for the determination of Re and Os. Sample decomposition and pre-concentration of Re and Os prior to measurement were accomplished using a variety of methods: acid digestion, alkali fusion, ion exchange and solvent extraction. Negative thermal ionisation mass spectrometry and inductively coupled plasma-mass spectrometry were used for the determination of Re and ¹⁸⁷Os concentration and isotope ratios. The certified values include the contents of Re and Os and the model ages. For HLP, the Re content was 283.8 ± 6.2 μg g⁻¹, ¹⁸⁷Os was 659 ± 14 ng g⁻¹ and the Re-Os model age was 221.4 ± 5.6 Ma. For JDC, the Re content was 17.39 ± 0.32 μg g⁻¹, ¹⁸⁷Os was 25.46 ± 0.60 ng g⁻¹ and the Re-Os model age was 139.6 ± 3.8 Ma. Uncertainties for both certified reference materials are stated at the 95% level of confidence. Three laboratories (from three countries: PR. China, USA, Sweden) joined in the certification programme. These certified reference materials are primarily useful for Re-Os dating of molybdenite, sulfides, black shale, etc.     

Boron Determination in Twenty One Silicate Rock Reference Materials by Isotope Dilution ICP-MS

The concentration of boron was determined in twenty one geochemical reference materials (silicate rocks) by isotope dilution inductively coupled plasma-mass spectrometry. Boron was extracted from the rocks using HF digestion, suppressing boron volatilisation through boron-mannitol complexation. Sample solutions, in a diluted HCl matrix, were analysed by ICP-MS without any separation of boron from the matrix elements. The results obtained were in agreement with the literature data and indicate that using the described procedure, trace amounts of boron can be very easily determined in complex matrices with rapidity and precision. With the instrumentation and reagents used in this study, this procedure can be used for the determination of 0.5 μg g⁻¹ boron in a 15 0 mg silicate rock sample. Replicate analyses of the twenty one geochemical reference materials (GRM), ranging in boron concentration from 1.35 to 15 7 μg g⁻¹, yielded precisions (relative standard deviation) varying between 0.9 and 9.8%.     

Determination of Selenium Concentration in Sixty Five Reference Materials for Geochemical Analysis by GFAAS after Separation with Thiol Cotton

Selenium has been determined in sixty five geological reference materials of different origins by graphite furnace atomic absorption spectrometry. Samples were decomposed with a mixture of nitric and hydrofluoric acids. Selenium was reduced to Se^IV with hydrochloric acid, and then fixed and separated from the matrix on thiol cotton. After digestion of the thiol cotton in hot nitric acid, the Se concentration was measured using palladium and magnesium nitrates as a matrix modifier. The limit of determination was 0.02 μg g⁻¹, the precision of the results (relative standard deviation of 3 to 8 replicates) varied from 2.6 to 17.7% with an average of 7.9% in the range 0.02-42.7 μg g⁻¹ and was similar to the value obtained for synthetic samples. Our results are in good agreement with available literature values.     

Simultaneous Determination of Total Carbon, Nitrogen, Hydrogen and Sulfur in Twenty-seven Geological Reference Materials by Elemental Analyser

The contents of total carbon, hydrogen, nitrogen and sulfur in twenty-seven geological reference materials, issued by five producer organisations (USGS, CCRMP, ANRT, NIST and GSJ) were determined using an automated simultaneous elemental analyser following combustion. In order to complete gasification of C and N in some geological materials, the combustion temperature needed to be greater than 1150 °C. The calibrator prepared from known amounts of reagent material was not adopted for more than 1.2% m/m of H. Unrealistically high values in certain materials supposed to contain less than 1000 μg g⁻¹ S may be due mainly to memory effects. The limit of detection was 50 μg g⁻¹ for C and N, 500 μg g⁻¹ for H and 1000 μg g⁻¹ for S. Although the blank value of C and N was always stable and less than one third of the detection limit, it had a slightly higher value for N and S. By repeating long-term analysis, high reproducibility for each of the four elements was verified. The method has been applied satisfactorily to a variety of geological reference materials, and recommended values for C, H and N for most of the reference materials studied have been tabulated.     

Determination of Major/ Minor and Trace Elements in Seamount Phosphorite by XRF Spectrometry

In this paper, a method developed to determine the major, minor and trace elements, including carbon and the four halogens, in seamount phosphorite involving a modern XRF spectrometry technique is described. Ultra-fine (99% v/v < 40 μm) powder samples (4 g) were directly pressed into pellets (Φ= 30 mm). For elements having an analytical line lower in energy than the energy of Fe Kα line absorption edge, the inter-element absorption-enhancement effects were corrected using an influence coefficient method. For the other elements, the matrix effects were corrected using the ratio of element peak to Rh Kα Compton peak (for I, Rh K|3 Compton peak was used instead). The relative standard deviation was smaller than 1.0% for the major elements (except C, Na and Cl). The detection limit levels of C, F, Cl, Br and I were 30, 20, 0.8, 0.2 and 0.3 (μg g⁻¹ respectively for 100 s count time of background. The accuracy of this method was tested by evaluating determinations on three certified reference materials. The direct analysis of major and minor elements in geological materials by pressed pellet without any chemical procedures makes XRF spectrometry a particularly environment-friendly analytical technique.     

DETERMINATION OF SULPHUR AT LOW LEVELS IN STANDARD REFERENCE MATERIALS BY PYROHYDROL YSIS/LON CHROMATOGRAPHY

The determination of sulphur in rocks, soils and sediments by pyrohydrolysis/ion chromatography has been modified to reach lower detection limits of the order of 2 μg g⁻¹. Thirty-one standard reference materials containing sulphur at levels ranging from 3 to about 900 μg g⁻¹ have been analysed in triplicate. In general, the comparison of the results with those published is favorable. The method is also applicable to organic-rich samples as demonstrated by the analysis of NBS samples (citrus leaves, tomato leaves, bovine liver).     

Suppression of Matrix Effects in ICP-MS by High Power Operation of ICP: Application to Precise Determination of Rb, Sr, Y, Cs, Ba, REE, Pb, Th and U at ng g-1 Levels in Milligram Silicate Samples

We found that the suppression of signals for ⁸⁸Sr, ¹⁴⁰Ce and ²³⁸U in rock solution caused by rock matrix in ICP-MS (matrix effects) was reduced at high power operation (1.7 kW) of the ICP. To make the signal suppression by the matrix negligible, minimum dilution factors (DF) of the rock solution for Sr, Ce and U were 600, 400 and 113 at 1.1, 1.4 and 1.7 kW, respectively. Based on these findings, a rapid and precise determination method for Rb, Sr, Y, Cs, Ba, REE, Pb, Th and U using FI (flow injection)-ICP-MS was developed. The amount of the sample solution required for FI-ICP-MS was 0.2 ml, so that 1.8 mg sample was sufficient for analysis with a detection limit of several ng g^-1. Using this method, we determined the trace element concentrations in the USGS rock reference materials, DTS-1, PCC-1, BCR-1 and AGV-1, and the GSJ rock reference materials, JP-1, JB-1, -2, -3, JA-1, -2 and -3. The reproducibilities (RSD %) in replicate analyses (n=5) of BCR-1, AGV-1, JB-1, -2, -3, JA-1, -2, and -3 were < 6 %, and typically 2.5%. The difference between the average concentrations of this study for BCR-1 and those of the reference values were < 2%. Therefore, it was concluded that the method can give reliable data for trace elements in silicate rocks.