Abstract
Procedures for the separation, purification, and high-precision analysis of mass-independent isotopic variations in molybdenum (Mo) using negative thermal ionization mass spectrometry are reported. Separation and purification of Mo from silicate and metal matrices are achieved using a two-stage anion exchange chromatographic procedure. Molybdenum is ionized as the MoO
species using a double filament assembly. The MoO
ion beams are collected using Faraday cup detectors equipped with a mixed array of amplifiers utilizing 10
and 10
Ω resistors, which allows for
measurement and correction of oxygen isobars. The long-term external reproducibility of
Mo/
Mo, the most precisely measured Mo isotope ratio, is ±5.4 ppm (2SD), based on the repeated analyses of the
Mo plasma standard and using
Mo/
Mo for fractionation correction. The long-term external reproducibilities of 92Mo/
Mo,
Mo/
Mo,
Mo/
Mo, and
Mo/
Mo are ±107, 37, 23, and 32 ppm (2SD), respectively. With this precision, smaller differences in Mo isotopic compositions can be resolved than have been previously possible.