Analysis of high-precision vanadium isotope ratios by medium resolution MC-ICP-MS

We present and verify a new method to measure vanadium isotope ratios using a Thermo Scientific Neptune multi-collector inductively-coupled plasma mass spectrometer (MC-ICP-MS) operated in medium mass resolution mode. We collect masses 48 through 53 simultaneously using the L2, L1, Center, H1, H2 and H3 collectors. The Center cup is equipped with a 10(12) Omega resistor, H1 is equipped with a 10(10) Omega resistor, while the rest of the collectors have standard 10(11) Omega resistors. Unlike previous low-resolution methods, the use of medium mass resolution (Delta M/M similar to 4000) permits separation of V, Ti and Cr isotopes from all interfering molecular species representing combinations of C, N, O, S, Cl, and Ar. We show that the external reproducibility follows a power law function with respect to the number of V+ ions collected and achieve an external reproducibility of +/-0.15 parts per thousand with total V+ ion beam intensities of similar to 1 nA. The separation of interfering molecular species from the V mass spectrum reduces the V requirement for precise isotope data to as little as 200-300 ng V per analysis-a reduction of similar to 90% compared with previous methods-making several low-V matrices amenable to V isotope analysis.