Electrospray ionization high-resolution ion mobility spectrometry-mass spectrometry.

A hybrid atmospheric pressure ion mobility spectrometer is described which exhibits resolving power approaching the diffusion limit for singly and multiply charged ions (over 200 for the most favorable case). Using an electrospray ionization source and a downstream quadrupole mass spectrometer with electron multiplier as detector, this ESI-IMS-MS instrument demonstrates the potential of IMS for rapid analytical separations with a resolving power similar to liquid chromatography. The first measurements of gas-phase mobility spectra of mass-identified multiply charged ions migrating at atmospheric pressure are reported. These spectra confirm that collision cross sections are strongly affected by charge state. Baseline separations of multiply charged states of cytochrome c and ubiquitin demonstrate the improved resolving power of this instrument compared with previous atmospheric pressure ion mobility spectrometers. The effects of electric potential, initial pulse duration, ion-molecule reactions, ion desolvation, Coulombic repulsion, electric field homogeneity, ion collection, and charge on the resolving power of this ion mobility spectrometer are discussed.