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 oxi de 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 ra te 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 ma intaining approximate to 20% of the original signal for atomic analyte ions (M+). For the species studied, collisions with H-2 improve the MO+/M+ sign al ratio more extensively for oxide ions with higher dissociation energies. The same collision conditions also serve to remove most of the ArO+, ArNand Ar-2(+) from the background spectrum.