H-ATOM TRANSFER FOLLOWING ANALYTE PHOTOIONIZATION IN MATRIX-ASSISTED-LASER-DESORPTION IONIZATION PROCESSES/

As recently shown in Fourier transform ion cyclotron resonance mass sp ectrometry studies (Rapid Commun. Mass Spectrom. 11, 1602, 1997), phot ochromic systems can be used as molecular probe for the study of matri x-assited laser desorption ionization (MALDI) processes inducing the t ypical formation of the triply hydrogenated molecules [M + 2H + H](+) simultaneously with the color change. In this paper, a novel photochro mic system blocked in its open form allows the proposal of a possible mechanism for protonated ions. The results suggest that hi-atom transf er from a matrix molecule to an analyte plays an important role in the ionization step. The transferring H-atom may be derived from electron ically excited states of matrix and analyte molecules via the triplet states. Among several ionization processes described in the literature , we observe that H-atom transfer following analyte photoionization is a possible ionization mechanism in MALDI. (C) 1998 John Wiley & Sons, Ltd.