Scaling NIST SRM 3149 for Se isotope analysis and isotopic variations of natural samples

We report the isotopic composition of the Se NIST SRM 3149 (lot 992106) relative to a MERCK Se solution which was already used as reference by Rouxel et al. [Rouxel O, Ludden J.N., Carignan J., Marin L, Fouquet Y 2002. Natural variations of Se isotopic composition determined by hydride generation multiple collector inductively coupled plasma mass spectrometry. Geochim. Cosmochim. Acta., 66, 18, 3191-3199.]. The technique uses on-line, continuous flow, hydride generation coupled to a MC-ICP-MS Isoprobe, equipped with a collision cell, as described by Rouxel et al. [Rouxel O, Ludden J.N., Carignan J., Marin L, Fouquet Y. 2002. Natural variations of Se isotopic composition determined by hydride generation multiple collector inductively coupled plasma mass spectrometry. Geochim. Cosmochim. Acta., 66, 18, 3191-3199]. The delta Se-82/76(MERCK) measured for the NIST SRM 3149 is -1.54 +/- 0.20 (+/- is 2 times the standard deviation from the mean, n=43, 16 analytical sessions). Individual sessions comprised between I and 6 measurements of the NIST sample with standard deviations comparable to that of the sessions grand mean. Further analyses of the CRPG Se solution relative to MERCK (measured delta Se-82/76 is -3.54 +/- 0.15; n=7, 4 sessions) confirmed the value reported by Rouxel et al. [Rouxel 0, Ludden J.N., Carignan J., Marin L, Fouquet Y 2002. Natural variations of Se isotopic composition determined by hydride generation multiple collector inductively coupled plasma mass spectrometry. Geochim. Cosmochim. Acta., 66, 18, 3191-3199.] for this sample. Recalculated delta Se-82/76 relative to NIST for MERCK, CRPG and MH495 Se solutions are then respectively 1.54 +/- 0.20 parts per thousand, -2.01 +/- 0.15 parts per thousand and -3.04 +/- 0.50 parts per thousand. Literature values (682176 Se) were recalculated in the NIST 3149 scale. Troilite from various iron meteorites yield zero per mil with a small variation of +/- 0.39 parts per thousand. Mafic terrestrial rocks also have a zero per mil composition on average, but with a larger variation of +/- 0.72 parts per thousand. Sediments (marine and continental) have a slightly positive average composition (0.39 parts per thousand) with an even larger variation of +/- 1.11 parts per thousand. Sulfides from modem hydrothermal fields and various black shales yield rather negative average values of -1.26%o and -0.57%o respectively but with a relatively large range in composition (+/- 2.6 parts per thousand and +/- 4.9 parts per thousand respectively). These large variations in 682176 Se suggests that surface cycling may lead to significant isotopic fractionation, certainly due to Se phase transformations related to the different environmental conditions. (c) 2007 Elsevier B.V. All rights reserved.