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Issue 9, 2006
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Ion formation mechanisms in UV-MALDI

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Matrix Assisted Laser Desorption/Ionization (MALDI) is a very widely used analytical method, but has been developed in a highly empirical manner. Deeper understanding of ionization mechanisms could help to design better methods and improve interpretation of mass spectra. This review summarizes current mechanistic thinking, with emphasis on the most common MALDI variant using ultraviolet laser excitation. A two-step framework is gaining acceptance as a useful model for many MALDI experiments. The steps are primary ionization during or shortly after the laser pulse, followed by secondary reactions in the expanding plume of desorbed material. Primary ionization in UV-MALDI remains somewhat controversial, the two main approaches are the cluster and pooling/photoionization models. Secondary events are less contentious, ion–molecule reaction thermodynamics and kinetics are often invoked, but details differ. To the extent that local thermal equilibrium is approached in the plume, the mass spectra may be straightforwardly interpreted in terms of charge transfer thermodynamics.

Graphical abstract: Ion formation mechanisms in UV-MALDI

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Article information

19 Apr 2006
27 Jun 2006
First published
27 Jul 2006

Analyst, 2006,131, 966-986
Article type
Critical Review

Ion formation mechanisms in UV-MALDI

R. Knochenmuss, Analyst, 2006, 131, 966
DOI: 10.1039/B605646F

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