N-ALKYLNICOTINIUM HALIDES - A CLASS OF CATIONIC MATRIX ADDITIVES FOR ENHANCING THE SENSITIVITY IN NEGATIVE-ION FAST-ATOM-BOMBARDMENT MASS-SPECTROMETRY OF POLYANIONIC ANALYTES

The addition of some surfactants to the fast-atom bombardment (FAB) ma trix previously has been demonstrated to enhance analyte signals in fa st-atom bombardment mass spectrometry. In particular, cationic surfact ants appear to enhance the negative ion FAB detectability of analytes that exist as anionic species in the matrix solution. It has been prop osed that the charged surfactant concentrates the oppositely charged a nalyte near the surface, which results in larger signals for the analy te. Cationic surfactants that contain a fixed positive charge and an a dditional basic site were prepared with different hydrophobic moieties and were evaluated for their effectiveness as FAB matrix additives. T he compound N-octylnicotinium bromide (ONBr) is shown to improve great ly the analyte-related signals in negative ion fast-atom bombardment m ass spectrometry for a variety of polyanionic analytes, relative to ot her surfactants (e.g., cetylpyridinium salts). This surfactant not onl y enhances detectability, but also simplifies the pseudomolecular ion region of the resulting spectra by reducing or eliminating metal catio n adduct peaks. The simple mechanism of enhancement via surface activi ty, is evaluated, and alternative mechanisms are considered. It is cle arly shown that ONBr, as a FAB matrix additive, will allow mass spectr ometry to be used for the analysis of anionic compounds that normally exhibit very low responses.