PNNL

Abstract

Radio frequency (RF) multipoles are increasingly used in mass spectrometry as two-dimensional ion traps for ion accumulation and pre-selection. 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. The procedure can be very useful in removing singly charged species contributing chemical noise to mass spectra of complex bio-molecular samples, e.g. solvent contaminants in LC-MS or ampholytes in CIEF-MS experiments. We consider a physical mechanism and derive relationships that provide a quantitative description for the process of low charge state ejection. Experimental conditions for the efficient discrimination against lower charge states are evaluated. Initial experimental observations reported are in agreement with the theoretical treatment.