Development of pressed sulfide powder tablets for in situ sulfur and lead isotope measurement using LA-MC-ICP-MS

Abstract

Controlling the accuracy and precision of sulfur and lead isotopic compositions in natural sulfide minerals requires the use of well-characterized reference materials with matrices similar to those of the unknown samples being analyzed. However, it is often a challenge to prepare natural or synthetic reference materials with homogeneous isotope compositions on a micro-scale. Herein, we report a novel method to synthesize homogeneous sulfide reference materials in the form of nano-particulate pressed sulfide powder tablets (PSPTs). Non-matrix-matched external calibration was used to obtain accurate and precise lead isotopic ratios, while mass bias was corrected using a standard-sample bracketing method and a thallium standard solution doping process. In situ analysis of lead isotopic ratios of PSPTs using laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) yielded good external precisions of <0.026% for 207,208Pb/206Pb and <0.057% for 206,207,208Pb/204Pb (2RSD). Meanwhile, the standard deviations of results afforded by LA-MC-ICP-MS were better than 0.41‰ for 34S/32S (2SD). The in situ analytical results of PSPTs were consistent with the values obtained using solution nebulizer MC-ICP-MS, thus demonstrating the reliability and robustness of our analytical protocol. This method can also be used to synthesize different material matrices with homogeneous sulfur and lead isotopes to correct mass bias when using standard-sample bracketing for in situ analysis.