ICP-QMS for lead isotopic analysis: Method development and key parameters

Abstract

This technical note demonstrates the potential of inductively coupled plasma mass spectrometry with a quadrupole analyzer (ICP-QMS) for lead isotope ratio determination offering a step-by-step guide for laboratories aiming to achieve reliable precision without access to multi-collector instrumentation. Key instrumental parameters such as dwell time, number of replicates, sweeps per replicate, pump speed and nebulizer gas flow were systematically optimized. Special attention was given to the influence of detector mode selection (Auto vs. Analog) and its impact on low-abundance isotopes such as ²⁰⁴Pb. The optimized procedure yielded precision of 0.08–0.10 % RSD for ²⁰⁶Pb/²⁰⁷Pb and ²⁰⁸Pb/²⁰⁶Pb ratios and 0.10–0.12 % RSD for ²⁰⁶Pb/²⁰⁴Pb as a minimum, which is sufficient for selected applications. The optimized method was validated using NIST SRM 981 and archaeological metal samples previously analyzed by MC-ICP-MS. Results show good agreement in isotope ratios between ICP-QMS and MC-ICP-MS, with deviations expressed as delta values <0.3 % in most cases, for ²⁰⁶Pb/²⁰⁴Pb < 1.5 %. Although the method does not aim to replace MC-ICP-MS for high-precision work, it offers a robust and cost-effective alternative for applications requiring moderate precision, especially in laboratories without access to multi-collector instrumentation.