Classification of N-Nitrosamines and Other Nitroso Compounds by Using Tandem Mass Spectrometry Experiments Based on...

A method is reported for the general detection of nitroso compounds by using MSn (n = 2 or 3) experiments based on collision-activated dissociation (CAD). The fragmentation reactions of 36 protonated nitroso model compounds, supplemented by the published fragmentation reactions of 46 additional protonated nitroso compounds, were examined. Four diagnostic reactions were identified: the elimination of •NO (general for nitroso compounds), H-N ═ O (for some N-nitrosamines), and a molecule containing the entire N-nitrosamino moiety (such as HN═N-OH; for some N-nitrosamines), all in MS2 experiments, and the elimination of an alkene in MS2 experiments followed either by the diagnostic elimination of HN═N-OH or the generation of the fragment ions H2N+═N-OH (m/z 47) or H3C-+NH═N-OH (m/z 61) in MS3 experiments (for some N-nitrosamines). The detection of one or more of these reactions upon MS2-3 CAD can be used to classify >80% (69/82) of the model compounds as nitroso compounds. This approach allowed all except one of the N-nitrosamines (N-nitroso-N-ethylurea) to be generally classified as nitroso compounds. However, only 19 out of 50 N-nitrosamines could be classified specifically as N-nitrosamines. The most difficult compound class to classify was the C-nitroso compound class, as only 57% of the protonated C-nitroso compounds studied underwent a diagnostic reaction upon CAD. Based on the model compound data, a decision tree was generated to facilitate the classification and structural characterization of unknown nitroso compounds.