Coupling matrix-assisted laser desorption/ionization to liquid separations

Abstract

This review discusses the off-line and on-line coupling of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry to liquid chromatography (LC) and capillary electrophoresis (CE). Off-line methods involve collecting fractions or depositing a sample on a prepared target prior to MALDI analysis. Because LC fraction collection is straightforward, off-line MALDI LC-MS is relatively easy to implement and widely used. Collecting CE fractions poses a greater challenge due to the small sample volume and the high voltage electrical connection that must be maintained during separation. Methods for off-line MALDI CE-MS employing a porous glass joint, liquid sheath flow, low-volume buffer, or direct deposition are discussed. On-line coupling of MALDI to liquid separations involves introducing the sample directly into the mass spectrometer, using either a continuous-flow (CF) probe or an aerosol spray. With CF MALDI, liquid samples are delivered to the probe through a silica capillary. Aerosol MALDI relies on a pneumatic nebulizer to deliver samples to the mass spectrometer, where ions are formed through irradiation of the particles. CF MALDI and aerosol MALDI have both been coupled to LC separations, although further refinements in both techniques are needed. Future prospects for liquid separations and both off-line and on-line MALDI are discussed. © 1998 John Wiley & Sons, Inc., Mass Spectrom Rev 16, 283–299, 1997