Pb isotope ratio and trace element analysis using VUV-TOF mass spectrometry: applications to NIST 610/612 and zircon FC1†

Abstract

We present a novel method for measurement of ²⁰⁷Pb/²⁰⁶Pb and ²⁰⁸Pb/²⁰⁶Pb isotope ratios in solid samples, employing vacuum ultraviolet (VUV) laser ablation/ionization coupled with a time-of-flight reflectron mass spectrometer (VUV-TOF). The 125.5 nm VUV laser, generated via four-wave mixing in an Hg cell driven by a YAG-pumped two-dye laser system, offers a simpler and more robust alternative to previous configurations. Advanced data collection and processing protocols enable calibration-free Pb isotope ratio measurements with accuracies better than 1.6% (2 times the relative standard deviations) for reference materials NIST 610, NIST 612 and zircon FC1. Notably, isotope ratios remain stable despite variations in Pb⁺ signal intensities caused by downhole fractionation. Semi-quantitative trace element sensitivities, determined using NIST 610, further highlight the method's versatility. With an ablation spot size smaller than 2 μm, this technique is ideally suited for high-spatial-resolution applications, including the dating of zoned zircons. The combination of precision, sensitivity, and robustness establishes VUV-TOF mass spectrometry as a powerful tool for advancing isotopic analysis in geochronology and geochemistry.