Beam-induced dehalogenation in LSIMS: Effect of halogen type and matrix chemistry

Article abstract of DOI:10.1002/jms.1190300125

The LSIMS beam-induced dehalogenation of several 4-halo-phenylalanine methyl esters (I, Br, Cl, F) was investigated and compared to that of atrazine using 12 different matrix compounds including diethyl phthalate for which the empirical electron affinity was known. The extent of dehalogenation, induced by a one-electron reduction process, is in agreement with the leaving group ability of the corresponding halogens (I > Br > Cl > F) and the dehalogenation inhibiting efficiency of the matrices. The latter is rationalized in terms of electron scavenging capacity and matrix structural features relating to that capacity. The extent of dehalogenation observed for 4-I-phenylalanine methyl ester is similar to that of atrazine, a chlorinated compound, which indicates that the halogen effect is not overwhelming in determining the extent of dehalogenation. The bracketing of matrix reduction potential was attempted based on the propensity of the matrices to induce M^+. formation from analytes of known oxidation potentials. The ability of matrices to induce M^+. formation parallels their dehalogenation and reduction inhibiting efficiencies. The last observation underlines the importance of matrix redox properties in effecting or inhibiting beam-induced processes, be they reductive or oxidative.