Strategies to develop methods using ion-molecule reactions in a quadrupole reaction cell to overcome spectral overlaps in inductively coupled plasma mass spectrometry

Abstract

ICP-MS instruments that use ion-molecule reactions to overcome spectral overlaps are becoming more widely available. Strategies to develop methods that use ion-molecule reactions in a quadrupole reaction cell are systematically described. Ion-molecule reactions may be used to remove the spectral overlap ion so that the analyte elemental ion can be measured with little background. Alternatively, ion-molecule reactions can be used to produce a new analyte-containing product ion at a higher mass where the background is low. Considerations for each approach including selection of the reaction gas, adjustment of the reaction cell bandpass and optimization of the gas flow rate are discussed. Examples are given with available kinetic rate constants, thermodynamic data and experimental ICP-MS measurements to illustrate each consideration in development of methods using ion-molecule reactions. Rejection of reactant ions from the cell in order to prevent generation of undesired reaction product ions is quantitatively assessed.