Matrix independent and interference free in situ boron isotope analysis by laser ablation MC-ICP-MS/MS

The accuracy of boron isotope analysis by laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS), particularly when the mass bias correction utilises non-matrix-matched reference materials, is compromised by matrix- and mass-load induced biases and an interference from scattered Ca and Ar ions which can induce bias in excess of 20‰. Here we explore the first application to in situ boron isotope analysis of the Thermo Scientific Neoma MS/MS mass spectrometer, which combines a traditional MC-ICP mass spectrometer with a collision/reaction cell and pre-cell mass filtering technology. While operating in full transmission mode, i.e. without using the collision/reaction cell, the pre-cell mass filter successfully eradicates the interference from scattered ions seen on some pre-existing models of MC-ICP-MS and exhibits good analytical sensitivity (∼6-14 mV per μg per g of total boron is typically achieved here). Furthermore, when matching laser operating parameters for samples/secondary reference materials and bracketing reference materials, and limiting the mass of ablated material introduced to the plasma, matrix- and mass-load induced biases can be prevented without the need for instrument tune conditions that severely limit sensitivity. Mean values of 14 reference materials, varying in bulk chemical composition (carbonates and silicates) and boron concentration (c. 2-150 μg g^-1), are within uncertainty of reference values when instrumental mass bias is normalised using bracketing analyses of NIST SRM612 glass, demonstrating the accuracy and utility of this approach. Internal precision and external reproducibility are primarily controlled by boron signal intensity and both are typically better than 1‰ when the ¹¹B intensity is at least ∼40 mV. LA-MC-ICP-MS/MS therefore offers a new and exciting opportunity for accurate and precise matrix independent, in situ, boron isotope analysis of geological materials.