An electrostatic focusing ion guide for ion mobility-mass spectrometry

An electrostatic focusing ion guide ion mobility-mass spectrometer (IM-MS) is described. The apparatus consists of a MALDI ion source coupled to an ion drift cell operating at pressures of 1-10 Torr and a small linear time-of-flight (TOF) mass spectrometer. The electrostatic focusing IMS drift cell acts as an ion guide, thus increasing ion transmission while maintaining high resolution. The drift cell is composed of a series of focusing and defocusing electrostatic fields superimposed on the potential drop applied across the drift cell. Calculated ion trajectories for several drift cell configurations, which include Monte Carlo simulations to model ion-neutral collisions, show significantly higher ion transmission and these results are supported by preliminary experimental results. A mobility resolution of similar to100 and detection levels of <10 fmol is demonstrated for peptides ionized by MALDI. (C) 2004 Elsevier B.V. All rights reserved.