Ion formation in MALDI mass spectrometry

TLDR

The origin of ions in MALDI mass spectrometry remains an active research area, with multiple proposed pathways such as photoionization, ion–molecule reactions, disproportionation, excited‑state proton transfer, energy pooling, thermal ionization, and desorption of preformed ions. Understanding these ionization pathways can improve ion yields, control analyte charge states and fragmentation, and enable new analyte classes. The authors critically review these pathways and discuss their varying roles across diverse MALDI experiments. © 1999 John Wiley & Sons, Inc.

Abstract

The origin of ions in matrix-assisted laser desorption/ionization (MALDI) mass spectrometry is currently a matter of active research. A number of chemical and physical pathways have been suggested for MALDI ion formation, including gas-phase photoionization, ion–molecule reactions, disproportionation, excited-state proton transfer, energy pooling, thermal ionization, and desorption of preformed ions. These pathways and others are critically reviewed, and their varying roles in the wide variety of MALDI experiments are discussed. An understanding of ionization pathways should help to maximize ion yields, control analyte charge states and fragmentation, and gain access to new classes of analytes. © 1999 John Wiley & Sons, Inc. Mass Spec Rev 17: 337–366, 1998