Attenuation of metal oxide ions in inductively coupled plasma mass spectrometry with hydrogen in a hexapole collision cell

Some strongly bound metal oxide ions (MO+) can be attenuated in a hexapole collision cell with a mixture of helium and hydrogen gas. Various metal oxide ions with different dissociation energies, such as ZrO+, CeO+, LaO+, SmO+, HoO+, YbO+ and WO+, have been chosen to study the attenuation effect. By adjusting the collision conditions, especially the composition and flow rate of the collision gas and the hexapole dc bias voltage, the MO+/M+ signal ratio can be suppressed by a factor of up to 60 for CeO+ and LaO+ while maintaining approximate to 20% of the original signal for atomic analyte ions (M+). For the species studied, collisions with H-2 improve the MO+/M+ signal ratio more extensively for oxide ions with higher dissociation energies. The same collision conditions also serve to remove most of the ArO+, ArN+ and Ar-2(+) from the background spectrum.