FAST-ATOM-BOMBARDMENT MASS-SPECTRA OF THE BETA-BLOCKER NIPRADILOL WITH NITRATE ESTER GROUP TANDEM MASS-SPECTROMETRY (MS/MS) AND B/E CONSTANT LINKED SCANNING

Fast atom bombardment (FAB) or liquid secondary ion mass spectra (LSIMS) of nipradilol and its analogues exhibit intense [MH-45]+ ions corresponding to MH+ ions of those hydrolysis products. Although FAB low energy collision-activated dissociation (CAD)-tandem mass spectrometry (MS/MS) using a triple-stage quadrupole-type instrument indicates that both ions are identical, the FAB(LSIMS) B/E constant linked scanning spectra of the ions are different from each other. To elucidate the reason for the two methods used for the same purpose giving different results, FAB high energy CAD-MS/MS was carried out using an EBE sector-type instrument. Comparison between the results of the B/E constant linked scanning and those of the high energy CAD-MS/MS indicated that the discrepancy is due to the poor resolution of precursor ions in the linked scanning at the B/E constant. It was also found that the high energy CAD-MS/MS spectra differed from the low energy CAD-MS/MS spectra owing to the difference in CAD energy between the two instruments. Decomposition products of nipradilol under FAB conditions were identified by high performance liquid chromatography and confirmed that the structures of the [MH-45]+ ions were MH+ of the hydrolysis products. The reaction products by fast atom bombardment under FAB conditions turned out to be the corresponding hydrolysis products which are different from those obtained by heating in glycerol.