Quantitative analysis of an N-oxide metabolite by fast atom bombardment tandem mass spectrometry

An assay for the N‐oxide metabolite of a benzazepine drug by fast atom bombardment ionization with tandem mass spectrometric analysis on a triple quadrupole mass spectrometer has been developed and validated for urine and plasma samples. This methodology allows analysis of this metabolite directly in crude sample extracts, without the need for extensive chromatography or sample derivatization. Quantification was accomplished with the use of a stable isotope analog of the analyte as an internal standard, using the selected reaction monitoring mode of operation.