CHARGE-STATE DISTRIBUTION AND ELECTRIC-DISCHARGE SUPPRESSION IN NEGATIVE-ION ELECTROSPRAY MASS-SPECTROMETRY USING CHLORINATED SOLVENTS

Solvent effects in electrospray mass spectrometry performed in the negative-ion mode have been examined, for a series of low-nucleophilicity chlorinated solvents. The charge-state distribution of a test analyte was observed to change radically with the nature of the solvent. Formation of anions of higher charge state was favored in solvents of higher polarity. The shift in the charge-state distribution has been largely attributed to improved solvation of charge sites by increasingly polar solvents. Evidence suggests that valence electrons of the chlorine atoms do not contribute significantly to solvation of acidic protons. Highly chlorinated solvents in the electrospray bath gas serve to suppress electrical (corona) discharge phenomena. The latter effect was magnified with increasing percent weight of chlorine in the solvent. The observed discharge suppression has been attributed to electron-capture processes. This solvent effect was muted when a highly efficient electron scavenger (i.e., SF6) comprised the electrospray bath gas.