Johann Moser

A simple procedure for the determination of platinum group elements and rhenium (Ru, Rh, Pd, Re, Os, Ir and Pt) using ID-ICP-MS with an inexpensive on-line matrix separation in geological and environmental materials

A simple and highly selective analytical procedure is presented here for the concentration determination of Ru, Rh, Pd, Re, Os, Ir and Pt via isotope dilution, which is suitable for the investigation of geological and environmental materials. Sample preparation consists of a sample digestion step in a high pressure asher (HPA-S) with concentrated HNO3 and HCl and drying down of the sample solution after the Os concentration was determined via sparging OsO4 into an ICP-MS. After drying and redissolution of the remaining solution the other PGEs are separated on-line from their matrix in a simple cation-exchange column that is coupled to a quadrupole ICP-MS. Through this technique it is possible to monitor in every sample the isotopes of the analytes as well as of those elements that cause isobaric interferences or that potentially cause interferences through molecular species. Concentrations of the two or more isotopic elements can be calculated through isotope ratios, whereas Rh is calculated via the peak area. Data for ultramafic reference materials UB-N and GP13 with concentrations lower than 8 ng g−1 show excellent reproducibilities (n = 9) for Re, Pd and Pt (2.5–3.9% RSD) and Pt, Ru, Rh, Os and Ir (4.5–7% RSD). It can be demonstrated that a large portion of the higher standard deviations is caused by sample heterogeneity. Road dust (BCR-723) was included to demonstrate the strength of this procedure for the determination of environmental samples. Reproducibilities (n = 5) for Re, Pt and Os were between 1.2 and 2.3% RSD, 5.2% RSD for Pd and 11% RSD for Rh. Data for Ru and Ir are presented for the first time.

Simplified method for the determination of Ru, Pd, Re, Os, Ir and Pt in chromitites and other geological materials by isotope dilution ICP-MS and acid digestion

A method for the determination of low Ru, Pd, Re, Os, Ir and Pt abundances in geological reference materials by isotope dilution inductively coupled plasma mass spectrometry (ICP-MS) after acid digestion in a high pressure asher (HPA-S) is presented. The digestion technique is similar to that using Carius tubes but easier to handle and reaches higher temperatures. Osmium can be determined as OsO4 with ICP-MS directly after digestion through a sparging technique. The remaining elements are preconcentrated by means of anion column chromatography. The resin is digested directly without elution leading to high yields but this causes problems if Zr is present at higher levels in the silicate rich materials. The analytical results for international platinum group element (PGE) reference materials, chromitite CHR-Bkg, basalt TDB-1 and gabbro WGB-1, are presented and compared with literature data, demonstrating the validity of the described method. Although higher in concentration, PGEs determined for reference material WGB-1 were worse than for TDB-1 indicating a more inhomogeneous distribution of the platinum group mineral phases. The low PGE abundance chromitite standard, CHR-Bkg, is likely to be homogeneous for Ru, Re, Os and Ir and is recommended as a reference material for the study of chromitites. Detection limits (3s x total procedure blank) range from 0.012 ng (Re and Os) to 0.77 ng (Pt), which could be further improved by applying higher quality acids.

Re–Os systematics of UB-N, a serpentinized peridotite reference material

The reference material (RM) UB-N is a typical representative of earths upper mantle. It is a serpentinized garnet and spinel-bearing peridotite (a metamorphosed lherzolite) from the Vosges mountains, France, that is well characterized for major and many trace elements. In order to test whether UB-N is a suitable Re–Os reference material, 32 digestions in three different laboratories (CRPG/CNRS, MPI (Mainz) and University of Leoben) with four different digestion techniques (low-temperature acid attack, Carius tube dissolution, high-pressure asher (HPA-S) acid attack and alkali fusion) were performed. The results show that the low-temperature acid attack is unsuitable for the study of the Re–Os systematics of UB-N. Surprisingly, the well-established Carius tube acid digestion technique also fails to completely digest all Os-bearing mineral phases. Only alkali fusion and HPA-S acid attack yield the highest Os concentrations. Though sample inhomogeneity has been recognized (approximately 6% RSD for 2-g sample aliquots), it is possible to determine a well-defined average Os concentration of 3.85±0.13 ng g−1 (95% confidence; 19 digestions, fusion and HPA-S only). Rhenium-bearing minerals are very homogeneously distributed and replicates within each laboratory yield highly reproducible results independent of the digestion technique. A value of 0.2095±0.0040 ng g−1 (95% confidence; n=24) is assigned to the Re concentration. The best estimate for the whole-rock 187Os/188Os is 0.1278±0.0002 (95% confidence; n=12). The UB-N reference material now has well-understood Re–Os systematics that are typical of fertile upper mantle rocks. Analysis of this standard is, thus, highly recommended for the validation of Re–Os analytical procedures.

Uncertainty of dead time estimation in ICP-MS

The dead time of the detection system of a quadrupole ICP-MS is estimated and the different calculation methods are rated for transparency and ease of use. They are optimised to yield minimum uncertainty of measurement and minimum bias. The dead time is calculated only from the count rates of the two isotopes and the precision of the count rates is governed by Poisson statistics. None of the investigated methods are biased, but differences between the methods concerning the uncertainty of the estimated dead times are visible. Nevertheless it is possible to rank one method as the best. This method allows us to estimate the uncertainty of the estimated dead time via error propagation following the CITAC-Eurachem-Guide.