Simultaneous chromatographic purification of Si and Mg for isotopic analyses using MC-ICPMS

This study presents a chemical protocol for simultaneous purification of silicon and magnesium from a single aliquot of rock sample. The procedure is based on a new silicate digestion technique in Teflon vial and a combination of two-step cation exchange chromatography using AG 50W-X8 (200-400 mesh) resin. The robustness of the protocol has been established by checking the accuracy of Si and Mg isotopic values in seven USGS rock reference materials. All isotopic analyses have been carried out in the interference free plateau of pseudo high-resolution mode of a Thermo Neptune MC-ICPMS to resolve Si-30 and Mg-26 peaks from their (NO)-N-14-O-16 and (CN+)-C-12-N-14 interferences respectively. The total variation of delta Si-30 among all terrestrial rock samples analyzed in this study lies in a limited range from - 0.28& to - 0.21%. The long-term reproducibility assessed by repeated measurements of Si standard solutions and reference materials is better than +/- 0.09& (+/- 2 sigma) for d30Si. The Mg isotopic ratios of the analyzed rock samples range from - 0.12 to - 0.87 and the external precision is better than +/- 0.08% (+/- 2 sigma) for delta Mg-26(DSM-3). The level of precision achieved allows us to distinguish the limited fractionation of Si and Mg that occurs at high temperature. Simultaneous determination of Si and Mg isotopic patterns from a single aliquot of rock sample has the potential to open up a range of new studies in widely different fields of science including geological, cosmo-chemical, bio-geochemical and environmental studies.