LC-NSI-HRMS chromatograms resulting from the NNK-P450 2A13 incubations. For all sections, the top chromatogram is the accurate parent mass extracted from full scan for CH2-oxo-NNK and CH3-oxo-NNK. The middle and bottom chromatogram is the accurate product ion masses extracted from MS2 fragmentation for CH2-oxo-NNK and CH3-oxo-NNK, respectively. Sections are as follows: (A) CH2-oxo-NNK standard, (B) CH3-oxo-NNK standard, and NNK-P450 2A13 incubations containing all relevant enzymes and cofactors with incubation times of (C) 1 min, (D) 5 min, (E) 10 min, and (F) 60 min. RT = retention time; MA = Mass Area.