Angular distribution of the ejecta in matrix-assisted laser desorption/ionization: Model dependence

The angular distribution of the ejecta in matrix-assisted laser desorption/ionizatiun (MALDI) was found to peak back toward the direction of illumination in the experiments of Aksouh et al. [Rapid Commun. Mass Spectrom. 9 (1995) 515]. It is shown here that such a result can be caused by a sample that is made up of crystallites with faces having a distribution of orientations relative to the substrate. The averaging of the yield over such a sample also affects the incident angle and threshold dependence of the yield, and it is shown that the results of Aksouh et al. can help differentiate between proposed models for MALDI. (Int J Mass Spectrom 177 (1998) 111-118) (C) 1998 Elsevier Science B.V.