Zinc isotope fractionation analyses by thermal ionization mass spectrometry and a double spiking technique

The aim of this work was to develop thermal ionization mass spectrometry (TIMS) isotopic procedures to measure Zn isotope fractionation (delta Zn) in natural materials. This work represents the most recent development of Zn isotope measurements and the first delta Zn identification in terrestrial materials using TIMS and a double spike technique. The developed procedures evaluate and solve several critical analytical issues involved in TIMS Zn isotope analysis. For example, no more than 1 mu g Zn was used for isotopic analyses which, considering the high ionization potential and low thermal ionization of Zn, represents a useful breakthrough in Zn isotope TIMS analysis. The effect of the ion exchange process on delta Zn was assessed and found equal to +0.07 +/- 0.02 parts per thousand amu(-1) per column. The ionization efficiency of Zn was enhanced to 0.22 +/- 0.07%, which is four times more than what was achieved previously. The magnitude of delta Zn accompanied by the 95% confidence associated uncertainties were calculated relative to the IRMM 3702, using a Monte Carlo approach for each individual analysis, while the calculated average of delta Zn for number of analysis was accompanied by a 95% confidence calculated using GUM Workbench software. delta Zn values where always calculated using two different sets of isotopes which always agreed within uncertainty. These developments enabled sub-per mil delta Zn to be revealed relative to delta Zn zero for natural materials. Most of the samples measured are Standard Reference Materials SRMs, where, except for BCR-1 and BIR-1, this is the first time Zn isotopic fractionation has been measured in these samples. No previously published results for Zn isotopic fractionation have been published on these samples using double spiking. Consistent delta Zn of similar to+ 0.3 parts per thousand amu(-1) was found in 5 sediments from a range of localities. delta Zn in two metamorphic samples is similar to that found in igneous rocks but different to that found in sedimentary rocks, which is consistent with our understanding that high temperature and pressure processes do not fractionate the composition of chalcophile elements. The isotope fractionation of Zn in a clay sample is within uncertainties the same as the sediments. The isotope fractionation of Zn of -0.088 +/- 0.070 parts per thousand amu(-1) was also measured in a standard rice sample. delta Zn in Antarctic Krill of +0.21 +/- 0.11 parts per thousand amu(-1) was found to be similar to the average delta Zn of +0.281 +/- 0.083 parts per thousand amu(-1) for marine sediments. River water was fractionated by -1.09 +/- 0.70 parts per thousand amu(-1), while restrained tap water yielded the maximum isotope fractionation of -6.39 +/- 0.62 parts per thousand amu(-1). delta Zn in high pure Zn standard materials ranged from 5.11 +/- 0.36 parts per thousand amu(-1) for AE 10760 to +0.12 +/- 0.16 parts per thousand amu(-1) for Zn IRMM 10440 with some evidence for a relationship between Zn isotope fractionation and its purity. All of the measured isotope fractionation yields an atomic weight within the IUPAC atomic weight of Zn. (C) 2011 Elsevier B.V. All rights reserved.