High precision Pb isotope ratio analysis of wet depositions with low Pb concentration using multi-collector type inductively coupled plasma mass spectrometry and solid phase extraction

Abstract

Lead in wet deposition samples collected from remote mountainous areas in Japan, which exhibited low Pb concentrations (0.0020–1.94 µg L⁻¹) comparable to those found in Antarctic snow, was preconcentrated and separated from interfering components using a solid-phase extraction (SPE) procedure with a chelating resin under non-clean-room conditions. Subsequently, Pb isotope ratios were measured by MC-ICP-MS equipped with a desolvating nebulizer, applying mass discrimination correction based on Tl isotope ratio as an external standard. For snow samples, the relative standard deviation (RSD) of ²⁰⁸Pb/²⁰⁶Pb improved slightly from 0.0037% without the SPE to 0.0028% with the SPE. In contrast, the RSD of ²⁰⁷Pb/²⁰⁶Pb showed an improvement from 0.014% to 0.0017% with the SPE. Notably, the RSD of ²⁰⁴Pb/²⁰⁶Pb improved significantly from 0.19% without the SPE to 0.032% with the SPE. For rain samples, the RSDs were 0.0042% for ²⁰⁸Pb/²⁰⁶Pb, 0.0019% for ²⁰⁷Pb/²⁰⁶Pb, and 0.024% for ²⁰⁶Pb/²⁰⁴Pb. Without the SPE, the ²⁰⁶Pb/²⁰⁴Pb ratio exhibited a large error, making it difficult to distinguish between potential sources. However, with the SPE, the ²⁰⁶Pb/²⁰⁴Pb ratio was measured with sufficient precision to enable source discrimination.