Identification of Protonated Primary Carbamates by Using Gas-Phase Ion-Molecule Reactions Followed by Collision-Activated Dissociation in Tandem Mass Spectrometry Experiments

摘要

The levels of potentially mutagenic impurities (PMIs) in active pharmaceutical ingredients are highly regulated and must be below a critical safety threshold. One class of PMIs is primary carbamates, which are formed during drug manufacturing and formulation. To comply with safety regulations, it is critically important to develop analytical techniques that enable the identification of primary carbamates during the drug development process. In this study, tandem mass spectrometry combined with gas-phase ion-molecule reactions as well as collision-activated dissociation (CAD) is demonstrated to enable the identification of protonated primary carbamates. Primary carbamates were protonated via atmospheric pressure chemical ionization (APCI) in a linear quadrupole ion trap mass spectrometer, isolated, and allowed to react with trimethoxymethylsilane (TMMS) introduced into the ion trap via an external reagent mixing manifold. Protonated primary carbamates reacted with TMMS to form an adduct ion, [M + H + TMMS](+), and an adduct ion that had lost methanol, [M + H + TMMS - MeOH](+). Upon CAD, the [M + H + TMMS - MeOH](+) product ions generated a diagnostic fragment ion via loss of isocyanic acid. Quantum chemical calculations were employed to explore the possible mechanisms for the formation of the product ions upon ion-molecule reactions and for the fragmentation of the [M + H + TMMS - MeOH](+) product ion.