Secondary ion-molecule reactions in matrix-assisted laser desorption/ionization

Ion-molecule charge- and proton-transfer reactions in the desorption plume are considered for the case of matrix-assisted laser desorption/ionization (MALDI) with ultraviolet laser excitation, and it is proposed that they are major determinants of the observed mass spectrum, Specific MALDI phenomena which are discussed include the dominance of singly charged ions and analy te-matrix or analyte-analyte signal suppression, Should any be formed, high ly charged products can be reduced by reaction with neutral matrix, yet sin gly charged ions cannot generally be neutralized in the same manner, Ion su ppression effects can also be explained by similar reactions, which in some cases involve interconversion of dissimilar ion types, The plume is propos ed often to be more under thermodynamic rather than kinetic control owing t o these secondary reactions, UV/MALDI mass spectra should therefore be larg ely predictable, given sufficient thermodynamic information, and appropriat e experimental conditions of sufficient analyte and plume density. Copyrigh t (C) 2000 John Wiley & Sons, Ltd.