Sources of Inaccuracy in Boron Isotope Measurement Using LA-MC-ICP-MS

Laser ablation multi-collector-inductively coupled plasma-mass spectrometry (LA-MC-ICP-MS) has become a valuable tool for the in situ measurement of the boron isotope composition of geological samples at high (tens to hundreds of mu m) spatial resolution. That said, this application suffers from significant analytical challenges. We focus in this study on the underlying processes of two of the main causes for inaccuracies using this technique. We provide empirical evidence that not only Ca ions (Sadekov et al. 2019, Standish et al. 2019, Evans et al. 2021) but also Ar ions, that are reflected within the flight tube of the mass spectrometer, are the source for previously reported issues with spectral baselines. We also address the impact of plasma conditions on the instrumental mass fractionation as a source for matrix- and mass-load-related analytical biases. Comparing experimental data with the results of a dedicated release and diffusion model (RDM) we estimate that a close to complete (similar to 97%) release of boron from the sample aerosol is needed to allow for consistently accurate LA boron isotope measurement results without the need for corrections.

Automated summary

Laser ablation multi-collector-inductively coupled plasma-mass spectrometry (LA-MC-ICP-MS) is a valuable tool for in situ measurement of boron isotope composition in geological samples, but it faces significant analytical challenges. This study focuses on the underlying processes causing inaccuracies in this technique, including the contribution of Ca and Ar ions to spectral baselines and the impact of plasma conditions on analytical biases. Experimental data and a release and diffusion model (RDM) suggest that a nearly complete release of boron from aerosol samples is necessary for consistently accurate measurement results without corrections.