A Novel Bisquaternary Ammonium Compound as an Anion Sensor-ESI-MS and Fluorescence Study

Electrospray ionization mass spectrometry (ESI-MS) analysis is frequently associated with noncovalent adduct formation, both in positive and negative modes. Anion binding and sensing by mass spectrometry, notably more challenging compared to cation binding, will have major research potential with the development of appropriate sensors. Here, we demonstrated identification of stable bisquaternary dication adducts with trifluoroacetate (TFA^-), Cl^- and HSO₄^- in positive-mode ESI-MS analysis. The observed adducts were stable in MS/MS mode, leading to the formation of characteristic fragment ions containing a covalently bound anion, which requires bond reorganization. This phenomenon was confirmed by computational methods. Furthermore, given that anion detection and anion sensor chemistry have gained significant prominence in chemistry, we conducted an analysis of the fluorescent properties of bisquaternary ammonium compound as a potential anion sensor.