Suppression of the lower charge state ions in the external accumulation RF multipole with a reduced trapping DC potential.

Radio frequency (RF) multipoles are increasingly used in mass spectrometry as two-dimensional ion traps for ion accumulation and preselection. It was reported recently that ions having lower charge states, in particular singly charged ions, can be efficiently removed from such an ion trap when reduced DC trapping voltages are applied. This procedure can be useful for removing singly charged species contributing chemical noise to mass spectra of complex biomolecular samples, e.g., solvent contaminants in LC-MS or relatively low MW ampholytes in CIEF-MS experiments. We consider a physical mechanism and derive relationships that provide a quantitative description for the low charge state ejection phenomenon. Experimental conditions for the efficient discrimination against lower charge states are evaluated. Initial experimental observations reported are in agreement with the theoretical treatment.