Suppression of in-cell generated interferences in a reaction cell ICP-MS by bandpass tuning and kinetic energy discrimination

Abstract

The efficiency of kinetic energy discrimination and bandpass tuning for the suppression of potentially interfering product ions, formed by ion–molecule reactions in a dynamic reaction cell of an inductively coupled plasma mass spectrometer is compared. Suppression of the oxide ions from Sc⁺, Y⁺, La⁺ and Th⁺, formed in reactions with oxygen impurities in non-reactive gases, have been used as test system to determine the suppression efficiency of the in-cell generated ions in dependence of the operating parameters of a dynamic reaction cell. Kinetic energy discrimination was investigated by successively lowering the pole bias voltage of the reaction cell quadrupole below the pole bias of the analyser quadrupole to create a potential barrier of increasing height. For bandpass tuning, the transmission window of the reaction cell quadrupole was successively narrowed to determine the cut-off m/z, where precursors of the product ions are rejected. The efficiency of interference suppression and the elemental sensitivity are in all cases decreasing with m/z of the precursor ions. Both approaches allow the suppression of the in-cell generated ScO⁺ and YO⁺, while LaO⁺ and to a greater extent ThO⁺ cannot be fully eliminated without compromising elemental sensitivity significantly. LaO⁺ and ThO⁺ are observed at levels, which are by a factor of two and six higher than in standard operation of the ICP-MS. Elemental sensitivity is higher by approximately a factor of five and the abundance of the cell produced ions is reduced more effectively with the bandpass tuning approach when compared to kinetic energy discrimination.