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

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 mlz, where precursors of the product ions are rejected. The efficiency of interference suppression and the elemental sensitivity are in all cases decreasing with mlz 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.