Determination of lead isotope ratios in environmental matrices by quadrupole ICP-MS working at low sample consumption rates

Abstract

Measurement of lead isotope ratios in environmental matrices using inductively coupled plasma-dynamic reaction cell-mass spectrometry at low sample consumption rates was investigated. Two micro-sample introduction systems were evaluated, namely the PFA micronebuliser associated with a low-volume spray chamber, working at 150 μL min⁻¹ and the total-consumption sample introduction system TISIS, operating at 20 μL min⁻¹. In both cases, the dynamic reaction cell pressurised with ammonia was applied to improve the precision by collisional damping. Under optimal operating conditions, ²⁰⁸Pb/²⁰⁷Pb and ²⁰⁶Pb/²⁰⁷Pb ratios were accurately determined with an internal precision of 0.12–0.13% and 0.17–0.18% (%RSD, n = 10, c = 10 μg L⁻¹; t = 10 s). The sample consumption for the assessed sample introduction systems was less than 1.5 mL and 200 μL, allowing the precise analysis of limited-size samples and pre-concentrates. The developed method was characterised in terms of the analytical working range, in-cell interference, and uncertainty estimation. The applicability of the analytical method was demonstrated by the analysis of the lichen reference material CRM 482, as well as those of several environmental samples collected from polar regions, including atmospheric particulate, snow, marine suspended particulate matter and sediment. In particular, by combining a simple pre-concentration procedure with the application of TISIS, it was possible to perform the lead isotope analysis of Antarctic snow samples at the pg g⁻¹ concentration level.