Abstract

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 ≈20% of the original signal for atomic analyte ions (M⁺). For the species studied, collisions with H₂ 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 Ar₂⁺ from the background spectrum.