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The [M‐1] − ion in the negative chemical ionization mass spectra of diazepam and nordiazepam
Author(s) -
Garland W. A.,
Miwa B. J.
Publication year - 1983
Publication title -
biomedical mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.475
H-Index - 121
eISSN - 1096-9888
pISSN - 0306-042X
DOI - 10.1002/bms.1200100305
Subject(s) - chemical ionization , chemistry , ion , ionization , mass spectrum , ion source , electron ionization , mass spectrometry , analytical chemistry (journal) , organic chemistry , chromatography
The [M‐1] − ion sometimes observed in the methane electron capture/negative chemical ionization mass spectra of diazepam and nordiazepam is [M‐H] − . Generation of the [M‐H] − ion is caused by trace amounts of oxygen in the ion source. For nordiazepam the Hż lost from the [M] − ż ion is that on the amide nitrogen. For diazepam the Hż lost from the [M] − ż ion is that on the carbon adjacent to the amide carbonyl. The [M‐1] − ion generated by negative chemical ionization is structurally different from the [M‐1] + ion generated by positive electron ionization. At ion source temperatures greater than 150°C, the methane electron capture/negative chemical ionization mass spectra of diazepam and nordiazepam consist principally of [Cl] − ions. A comparison of the relative sensitivities of various analogs of diazepam and nordiazepam suggests that electron capture occurs at the imine bond.