Abstract: Multiple-collector inductively coupled plasma mass spectrometry has been used for the precise measurement of the isotopic composition of Se in geological samples. Se is chemically purified before analysis by using cotton impregnated with thioglycollic acid. This pre-concentration step is required for the removal of matrix-interfering elements for hydride generation, such as transitional metals, and also for the quantitative separation of other hydride-forming elements, such as Ge, Sb, and As. The analyte is introduced in the plasma torch with a continuous-flow hydride generation system. Instrumental mass fractionation is corrected with a standard-sample bracketing approach. By use of this new technique, the minimum Se required per analysis is lowered to 10 ng, which is one order of magnitude less than the amount needed for the N-TIMS technique. The estimated external precision calculated for the Se-82/Se-76 isotope ratio is 0.25parts per thousand (2sigma), and the data are reported as delta notation (parts per thousand) relative to our internal standard (MERCK elemental standard solution). Measurements of Se isotopes are presented for samples of standard solutions and geological reference materials, such as silicate rocks, soils, and sediments. The Se isotopic composition of selected terrestrial and extraterrestrial materials are also presented. An overall Se isotope variation of 8parts per thousand has been observed, suggesting that Se isotopes fractionate readily and are extremely useful tracers of natural processes. Copyright (C) 2002 Elsevier Science Ltd.

Abstract: Multiple-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) has been used for the precise measurement of Sb isotopic composition in geological samples, as well as Sb(III) and Sb(V) species in aqueous samples. Sb is chemically purified prior to analysis by using cation-exchange resin and cotton impregnated with thioglycollic acid (TCF). Purification through cation-exchange resin is required for the removal of matrix interfering elements such as transitional metals, whereas TCF is required for the separation of other hydride-forming elements such as Ge and As. The analyte is introduced in the plasma torch using a continuous flow hydride generation system. Instrumental mass fractionation is corrected with a 'standard-sample bracketing' approach. Using this technique, the minimum Sb required per analysis is as low as 10 ng for an estimated external precision calculated for the 123Sb/121Sb isotope ratio of 0.4 [epsiv] units (2s).Sb isotope fractionation experiments reported here indicate strong fractionation (9 [epsiv] units) during Sb(V) reduction to Sb(III). Seawater, mantle-derived rocks, various environmental samples, deep-sea sediments and hydrothermal sulfides from deep-sea vents have been analyzed for their Sb isotope composition. We define a continental and oceanic crust reservoir at 2±1 [epsiv] units. Seawater [epsiv]123Sb values do not vary significantly with depth and yield a restricted range of 3.7±0.4 [epsiv] units. Sb deposited in hydrothermal environments has a significant range of Sb isotopic composition (up to 18 [epsiv] units). These variations may reflect not only contributions from different Sb-sources (such as seawater and volcanic rocks), but also kinetic fractionation occurring at low temperature in aqueous media through the reduction of seawater-derived Sb(V) in more reducing environment. Our results suggest that Sb isotopes can be extremely useful tracers of natural processes and may be useful as paleoredox tracers in oceanic systems.