Gas phase ion-molecule interactions in a collision reaction cell with QQQ-ICP-MS: Investigations with N2O as the reaction gas

Abstract:

Gas phase ion-molecule reactions have great potential in ICP-MS as a method for resolving difficult isobaric interferences with target analyte species. Nitrous oxide (N₂O) was used as a reaction gas to investigate gas phase ion-molecule interactions using the Agilent 8900 QQQ-ICP-MS. A multi-element standard containing 39 elements with masses ranging from 9 to 208 u was measured in the presence and absence of N₂O. The main product ion species observed were oxides and nitrides. Comparison of the N₂O reaction results with similar measurements conducted with O₂ revealed that N₂O was more effective at forming oxides: the elements Be, Cd and Pb were shown to produce oxides with N₂O where the reaction did not occur with O₂. Similarly, N₂O produced oxides in greater abundance than O₂ in elements such as Sr, Ba and the lanthanides. Nitrous oxide was also shown to produce a significant amount of nitride species in a few elements. Nitride formation showed a greater degree of selectivity, particularly amongst the lanthanides, which suggests that nitride formation may be a suitable product for mass shift method development. Nitrous oxide was also shown to be effective at suppressing plasma species such as ArN⁺. The results of this work are but one example of how creative selection of reaction gases can be effective for developing novel ICP-MS methods that enhance our analytical capability.