Anion effects on storage and resonance ejection of high mass-to-charge cations in quadrupole ion trap mass spectrometry

The presence of negative charge created by an anion cloud in the center of a quadrupole ion trap is shown to be capable of affecting both the storage and the resonance ejection of high mass-to-charge cations. The attractive potential created by the presence of the anion cloud in the center of the ion trap can facilitate storage of high mass-to-charge cations under conditions that otherwise would allow the cations to escape. However, the presence of the anion cloud can interfere with the resonance ejection method for mass analysis due to the fact that the electric field created by the anion cloud can rival or exceed the influence of the quadrupole field on cation motion. Recognizing these phenomena allows for optimum conditions to be established for both ion storage and resonance ejection of high mass-to-charge ions formed via ion-ion reactions. The effect of high numbers of anions on the storage and resonance ejection of high mass-to-charge cations is illustrated with low charge state cations derived from ovalbumin and lysozyme formed via proton transfer reactions to anions derived from perfluoro-1,3-dimethylcyclohexane.