A quantitative model of ultraviolet matrix-assisted laser desorption/ionization including analyte ion generation.

A quantitative model of ionization in ultraviolet matrix-assisted laser desorption/ionization (Knochenmuss, R. J. Mass Spectrom. 2002, 37, 867) is extended to include secondary ion-molecule reactions. Matrix-to-analyte charge-transfer reaction kinetics are described by a hard-sphere Arrhenius expression. The activation energy is derived from the reaction exoergicity using a nonlinear free energy relationship. The approach is applied to the specific case of proton-transfer reactions. With no adjustable parameters, the model correctly predicts the existence and characteristics of the matrix and analyte suppression effects, the shapes of the two-pulse time-delayed yield curves, and the dependence of analyte yields on laser fluence, molecular weight, relative concentrations, and reaction exoergicity.