| Abstract: | Mechanisms are proposed for the formation of M+, M + 2H]+ and M + 3H]+ ions in the fast atom bombardment (FAB) mass spectra of 4-(2,2,6,6-tetramethyl-1-oxyl)-piperidol and its carboxylates. Free radical quenching induced by the fast atom beam has been observed. The effects of temperature on the radical quenching and of acid on the FAB mass spectra are discussed. The experiment showed that the volatile liquid samples with vapour pressures higher than that for glycerol produced M+ even-electron molecular ions, and the FAB mass spectra were similar to the corresponding electron ionization mass spectra. For the solid samples, it was found that the free radicals were quenched during the FAB process so that the mononitroxide and dinitroxide compounds produced M + 2H]+ and M + 3H]+ ions, respectively. Further experiments showed that the intensities and stabilities of M + 2H]+ and M + 3H]+ ions could be improved by addition of acids. |
