The application of perfluorotributylamine (PFTBA) ions/analyte molecule reaction ionization for the selective determination of tobacco pyridine alkaloids by ion trap mass spectrometry (IT-MS) is reported. The main three PFTBA ions (CF 3 ϩ , C 3 F 5 ϩ , and C 5 F 10 N ϩ ) are generated in the external source and then introduced into ion trap for reaction with analytes. Because the existence of the tertiary nitrogen atom in the pyridine makes it possible for PFTBA ions to react smoothly with pyridine and forms adduct ions, pyridine alkaloids in tobacco were selectively ionized and formed quasi-molecular ion [M ϩ H] ϩ and adduct ions, includingϩ , and [M ϩ 264] ϩ , in IT-MS. These ions had distinct abundances and were regarded as the diagnostic ions of each tobacco pyridine alkaloid for quantitative analysis in selected-ion monitoring mode. Results show that the limit of detection is 0.2 g/mL, and the relative standard deviations for the seven alkaloids are in the range of 0.71% to 6.8%, and good recovery of 95.6% and 97.2%. The proposed method provides substantially greater selectivity and sensitivity compared with the conventional approach and offers an alternative approach for analysis of tobacco alkaloids. (J Am Soc Mass Spectrom 2007, 18, 1774 -1782
The methyl migration between the protonated N,N-dimethylisopropylamine and other neutral aliphatic amines in the gas phase has been investigated by a hybrid external chemical ionization source ion trap mass spectrometer. Similar reactions have been found in the aqueous solution by Callahan and Wolfenden (J. Am. Chem. Soc. 2003; 125: 310). At the same time, density functional theory (DFT) calculations show that in contrast with the neutral N,N-dimethylisopropylamine, protonated N,N-dimethylisopropylamine is a better methyl donor. These results indicate that protonation promotes the methyl migration between aliphatic amines both in the gas phase and in the aqueous solution. In addition, methyl transfer also exists between the protonated N,N-dimethylisopropylamine and some other nitrogen-containing compounds.
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