A Diagnostic Nitrosamine Detection Approach for Pharmaceuticals by Using Tandem Mass Spectrometry Based on Diagnostic Gas-Phase Ion-Molecule Reactions.

-Nitrosamines are strictly regulated in pharmaceutical products due to their carcinogenic nature. Therefore, the ability to rapidly and reliably identify the -nitroso functionality is urgently needed. Unfortunately, not all ionized -nitroso compounds produce diagnostic fragment ions and hence tandem mass spectrometry based on collision-activated dissociation (CAD) cannot be used to consistently identify the -nitroso functionality. Therefore, a more reliable method was developed based on diagnostic functional-group selective ion-molecule reactions in a linear quadrupole ion trap mass spectrometer. 2-Methoxypropene (MOP) was identified as a reagent that reacts with protonated -nitrosamines in a diagnostic manner by forming an adduct followed by the elimination of 2-propenol (CHC(OH)═CH]). From 18 protonated -nitrosamine model compounds studied, 15 formed the diagnostic product ion. The lack of the diagnostic reaction for three of the -nitrosamine model compounds was rationalized based on the presence of a pyridine ring that gets preferentially protonated instead of the -nitroso functionality. These -nitrosamines can be identified by subjecting a stable adduct formed upon ion-molecule reactions with MOP to CAD. Further, the ability to use ion-molecule reactions followed by CAD to differentiate protonated -nitroso compounds with a pyridine ring from analogous -nitrosamines was demonstrated This methodology is considered to be robust for the identification of the -nitroso functionality in unknown analytes. Lastly, HPLC/MS experiments were performed to determine the detection limit for five FDA regulated -nitrosamines.