INJECTION OF REAGENT IONS INTO THE SELVEDGE REGION IN FAST-ATOM-BOMBARDMENT MASS-SPECTROMETRY

A divided probe that incorporates a potassium aluminosilicate glass target and an analyte/glycerol matrix target, spatially separated, was used to inject potassium ions (K+) into the high-pressure ''selvedge'' region formed above the analyte/glycerol matrix target during fast-atom bombardment (FAB); [M + K]+ adduct ions that represent the types of gas-phase neutral molecules present in the selvedge region are observed. Computer modeling assisted in designing the divided target and an additional ion optical element for the FAB ion source to optimize interactions between K+ ions and the desorbed neutral molecules. The capability of injecting K+ ions into the FAB experiment has utility in both mechanistic studies and analyses. Experimental results here are consistent with a model for the desorption/ionization processes in FAB in which some types of neutral analyte molecules are desorbed intact and are subsequently protonated by glycerol chemical ionization. Unstable protonated molecules undergo unimolecular decomposition to yield observed fragment ions. The use of K+ cationization of analytes for molecular weight confirmation is demonstrated, as well as its utility in FAB experiments in which mixtures are encountered.