ION KINETIC-ENERGY MODULATION FOR IMPROVED ION TRAPPING IN ELECTROSPRAY-IONIZATION FOURIER-TRANSFORM ION-CYCLOTRON RESONANCE MASS-SPECTROMETRY

A new technique for manipulating the kinetic energy distribution of el ectrospray ions that arrive at a Fourier transform ion cyclotron reson ance trapped-ion cell is presented. Narrow kinetic energy distribution s can complicate the selection of appropriate trapping conditions for electrospray ions and introduce charge discrimination in resulting mas s spectra. Modulation of the applied skimmer potential controllably br oadens the kinetic energy distribution, which improves the reproducibi lity of acquired spectra and eliminates charge discrimination. Mass sp ectra of horse heart cytochrome c are presented to demonstrate the uti lity of the technique. For example, applied static skimmer potentials of 12 and 9 V yield charge state distributions ranging from [M + 19H]19 to [M + 12H]+12 and [M + 15H]+15 to [M + 7H]+7, respectively. A 12 +/- 2 V, 100-Hz modulation of the skimmer potential yields an electros pray spectrum with charge states that range from [M + 19H]+19 to [M 7H]+7, which is more representative of the source distribution.