Beyond the flask: Reactions on the fly in ambient mass spectrometry

Ionic reactions in bulk solution generally occur relatively slowly, and the course of reaction can be followed by on-line monitoring using, for example, electrospray ionization mass spectrometry (MS). In another approach, ionic reactions occurring in confined volumes can be studied with a focus on increasing reaction rates upon reduction in solution volume (e.g., by solvent evaporation from small droplets). Such a situation is encountered in ambient ionization MS, which involves the ionization of samples in their native state without significant sample preparation. Reagents can be included in the spray solvents used in ambient ionization and rapid derivatization reactions can accompany ionization. These latter experiments form the topic of this review. Emphasis is on their value in chemical analysis, but the products of these reactions can also be collected easily and form the basis for small-scale synthesis.