Zinc Isotope Measurement by MC-ICP-MS in Geological Certified Reference Materials

Abstract

Here we present an analytical method for Zinc (Zn) isotopic measurements using “standard-sample bracketing” on a Nu Sapphire multi-collector inductively coupled plasma-mass spectrometer. The effects of Zn mass fraction and HNO₃ molarity mismatch between the standard and the sample, as well as the presence of matrix elements have been evaluated. Long-term reproducibility of better than ±0.03‰ for δ⁶⁶Zn (2s) was routinely obtained. Accurate measurements were achieved when C_Ni/C_Zn < 0.001, C_Ti/C_Zn < 0.03, C_Ba/C_Zn < 0.05, C_Na/C_Zn and C_Al/C_Zn < 0.5, C_Mg/C_Zn < 0.1, C_Fe/C_Zn < 5 and C_Cu/C_Zn as well as C_Cd/C_Zn < 10. High-precision Zn isotopic determination were performed on twenty-one widely available geological certified reference materials, with an overall range of ~ 0.62‰ (0.15 to 1.07‰), which is nearly twenty times the current analytical precision (0.03), and the results are in agreement with most previously published data within 2s. Among them, δ⁶⁶Zn_{JMC 3-0749L} of eleven geological certified reference materials are reported for the first time: 0.22 ± 0.03‰ (dolerite, DR-N), 0.23 ± 0.02‰ (gabbro, GSR-10), 0.20 ± 0.04‰ (microgabbro, PM-S), 0.15 ± 0.02‰ (andesite, GSR-2), 0.22 ± 0.08‰ (diorite, GSR-9), 0.19 ± 0.07‰ (syenite, GSR-7), 0.30 ± 0.06‰ (granite, GSR-1), 0.25 ± 0.00‰ (rhyolite, GSR-11), 0.37 ± 0.01‰ (shale, GSR-5), 0.21 ± 0.03‰ (limestone, GSR-6) and 0.20 ± 0.03‰ (hornblendite, GSR-15). The novel Zn isotopic data from these certified reference materials can be used for future interlaboratory comparisons.