UTILIZATION OF ELECTROSPRAY-IONIZATION TO GAIN INFORMATION ON THE PROCESSES INVOLVED IN [M-H](+) FORMATION IN FAB LSIMS/

Some cyclic acetals and derivatized monosaccharides which yielded anom alous [M - H](+) in FAB/LSIMS were analyzed by electrospray ionization (ESI) to gain further information on the condensed phase processes su ggested to be responsible for the formation of [M - H](+) in FAB/LSIMS , For all compounds, [M + H](+) was the only significant ion present i n the molecular ion region in ESI. Since ionization in ESI is believed to reflect predominantly condensed phase equilibrium processes, the a bsence of [M - H](+) in ESI suggests that these processes are not resp onsible for hydride abstraction in FAB/LSIMS and that processes other than the pre-formation of ions in solution have to be invoked. Fast at om/ion-induced processes are thus considered the most likely origin of [M - H](+) in FAB/LSIMS and would explain the difference in ESI and F AB/LSIMS relative molecular ion intensities, The proposed occurrence o f particle-induced ionization processes in the condensed phase in FAB/ LSIMS is consistent with previous experimental evidence from this labo ratory, and many chemical reactions which take place in FAB/LSIMS have been explained in like manner. The [M + H](+) peak in ESI for the com pounds studied is attributed to the presence of NH4+ in solution as an impurity and the resulting condensed phase equilibrium processes. The presence of [M + NH4](+) in all ESI mass spectra is consistent with t his interpretation. An [M + Na](+) adduct is also observed in ESI for the derivatized monosaccharides which suggests that condensed phase eq uilibrium processes are responsible for this adduct when observed in F AB/LSIMS.