Zinc Isotopic Compositions of NIST SRM 683 and Whole-Rock Reference Materials

In this study the homogeneity of the zinc isotopic composition in the NIST SRM 683 reference material was examined by measuring the Zn isotopic signature in microdrilled sample powders from two metal nuggets. Zinc was purified using AG MP-1M resin and then measured by MC-ICP-MS. Instrumental mass bias was corrected using the "sample-standard bracketing" method and empirical external normalisation with Cu doping. After evaluating the potential effects of varying acid mass fractions and different matrices, high-precision Zn isotope data were obtained with an intermediate measurement precision better than +/- 0.05 parts per thousand (delta Zn-66, 2s) over a period of 5 months. The delta Zn-66(JMC-Lyon) mean values of eighty-four and fourteen drilled powders from two nuggets were 0.11 +/- 0.02 parts per thousand and 0.12 +/- 0.02 parts per thousand, respectively, indicating that NIST SRM 683 is a good isotopic reference material with homogeneous Zn isotopes. The Zn isotopic compositions of seventeen rock reference materials were also determined, and their delta Zn-66 values were in agreement with most previously published data within 2s. The delta Zn-66 values of most of the rock reference materials analysed were in the range 0.22-0.36%, except for GSP-2 (1.07 +/- 0.06 parts per thousand, n = 12), NOD-A-1 (0.96 +/- 0.03 parts per thousand, n = 6) and NOD-P-1 (0.78 +/- 0.03%, n = 6). These comprehensive data should serve as reference values for quality assurance and interlaboratory calibration exercises.