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 precision measurement of ²⁰⁷Pb/²⁰⁶Pb and ²⁰⁸Pb/²⁰⁶Pb isotope ratios in solid samples, utilizing 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, provides a significantly simpler and more robust alternative to previous configurations. Advanced data collection and processing protocols enable accurate Pb isotope ratio measurements without calibration, achieving uncertainties (2σ) of 1% for zircon FC1 and NIST 610, and 2% for NIST 612. Remarkably, the isotope ratios remain stable despite variations in Pb⁺ signal intensity caused by the downhole fractionation. Semi-quantitative trace element sensitivities, determined using NIST 610, further underscore the method’s versatility. With an ablation spot size smaller than 2 μm, this technique is ideally suited for high-spatial-resolution applications, such as dating zoned zircons. The combination of precision, sensitivity, and robustness establishes VUV-TOF mass spectrometry as a powerful tool for advancing the isotopic analysis of Pb and other elements in geochronology and geochemistry.