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 δ82/76SeMERCK 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 1 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 δ82/76Se is − 3.54 ± 0.15; n = 7, 4 sessions) confirmed the value reported 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.] for this sample. Recalculated δ82/76Se relative to NIST for MERCK, CRPG and MH495 Se solutions are then respectively 1.54 ± 0.20‰, − 2.01 ± 0.15‰ and − 3.04 ± 0.50‰. ture values (δ82/76Se) were recalculated in the NIST 3149 scale. Troïlite from various iron meteorites yield zero per mil with a small variation of ± 0.39‰. Mafic terrestrial rocks also have a zero per mil composition on average, but with a larger variation of ± 0.72‰. Sediments (marine and continental) have a slightly positive average composition (0.39‰) with an even larger variation of ± 1.11‰. Sulfides from modern hydrothermal fields and various black shales yield rather negative average values of − 1.26‰ and − 0.57‰ respectively but with a relatively large range in composition (± 2.6‰ and ± 4.9% respectively). These large variations in δ82/76Se suggests that surface cycling may lead to significant isotopic fractionation, certainly due to Se phase transformations related to the different environmental conditions.