Characterisation of gas cell reactions for 70+ elements using N2O for ICP tandem mass spectrometry measurements

Abstract

One widely utilised method to reduce spectral interferences for measurements using inductively coupled plasma mass spectrometry (ICP-MS) is to employ the use of a reaction cell gas. Nitrous oxide (N₂O) is a highly reactive gas typically used for mass-shifting only target analytes to a higher mass-to-charge ratio with increased sensitivity (e.g. +16, +32, +48 amu for monoxide, dioxide, and trioxide product ions respectively). Traditionally, the use of N₂O was limited to selected applications due to the creation of new interferences that also interfere with the detected masses of interest. However, with the advent of inductively coupled plasma tandem mass spectrometry (ICP-MS/MS), the use of N₂O has gained more traction, with a growing number of publications in recent years. Here, a comprehensive study of the use of N₂O for the determination of 73 elements has been conducted, with a comparison to the most widely used mass-shift method using oxygen (O₂) as a reaction gas. In total, 59 elements showed improved sensitivity when performing mass-shift with N₂O compared to O₂, with 8 elements showing no reaction with either gas. Additionally, N₂O demonstrated a collisional focusing effect for 36 elements when measuring on-mass. This effect was not observed using O₂. Monitoring asymmetric charge transfer reactions with N₂O highlighted 14 elements, primarily non-metals and semi-metals, that enter the gas cell as metastable ions and could be used as an alternative mass-shift option. The results from this study highlight the high versatility of N₂O as a reaction cell gas for routine ICP-MS/MS measurements.