A Highly Efficient Method for the Accurate and Precise Determination of Zinc Isotopic Ratios in Zinc-rich Minerals Using MC-ICP-MS

This study proposes a highly efficient method for the direct determination of Zn isotopes in Zn-rich minerals, without the use of column chromatography, via multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). Experiments (with or without column chromatography) were performed to evaluate the feasibility of directly obtaining non-deviated Zn isotopic ratios by MC-ICP-MS. For Zn isotopes determined without the use of column chromatography, the instrumental mass bias was corrected using the standard sample bracketing with Cu as the internal standard. The effects of acidity and concentration mismatch and the matrix effect were strictly assessed in a wet-plasma mode. The Long-term reproducibilities of delta Zn-66 and delta Zn-67 better than +/- 0.03 parts per thousand (n = 42, 2 standard deviations (2s)) and +/- 0.05 parts per thousand (n = 42, 2s), respectively, were achieved by repeatedly measuring the NIST Standard Reference Materials (SRM) 682 solution doped with trace matrix elements over four months. Zn-rich minerals determined without employing column chromatography displayed little drift in delta Zn-66 and delta Zn-67 values compared with minerals determined using column chromatography, with Delta Zn-66(without-with) (Delta Zn-66(without-with) = delta Zn-66(without) - delta Zn-66(with)) ranging from -0.04 to +0.01 parts per thousand and Delta Zn-67(without-with) ranging from -0.06 to +0.01 parts per thousand. These results suggest that non-deviated Zn isotopic ratios in Zn-rich minerals can be achieved without column chromatography due to the low contents of undesired matrix elements.