NWU-GN and PY-FHP, two reference materials for in situ Pb isotope analysis of sulfide minerals by LA-MC-ICP-MS: an assessment of matrix effects

Abstract

Two new reference materials, NWU-GN and PY-FHP, have been developed and characterised for the calibration of in situ Pb analyses of sulfide minerals by LA-MC-ICP-MS. These two references exhibit homogeneous Pb isotopic compositions compared to existing reference materials. PY-FHP demonstrated excellent external precision of <0.06% for ^207,208Pb/²⁰⁶Pb and <0.10% for ^206,207,208Pb/²⁰⁴Pb (2RSD) when using a 100 μm beam size for spot analysis. Similarly, NWU-GN showed good homogeneity at the 9 μm scale, with external precision (2RSD) of Pb isotopes better than 0.01% for ^207,208Pb/²⁰⁶Pb and 0.025% for ^206,207,208Pb/²⁰⁴Pb. The in situ analytical results matched those values obtained using solution nebulizer MC-ICP-MS, suggesting NWU-GN and PY-FHP as potential reference materials for microbeam Pb isotopic analysis. Matrix effects were observed during nanosecond laser ablation system analysis when using silicate glass reference materials as the external standard to assess Pb isotopic ratios in sulfide samples, with deviations up to ∼0.17% for ^206,207,208Pb/²⁰⁴Pb. This necessitates matrix-matched reference materials for highly precise and accurate Pb isotope analysis of sulfide samples using a nanosecond laser ablation system. In comparison, both 266 nm and 206 nm wavelength femtosecond laser ablation systems, combined with MC-ICP-MS, can achieve accurate and precise Pb isotope ratios in sulfide minerals, even with non-matrix-matched silicate glass reference materials.