Photoionization Features of Mobile Phase Components in Supercritical Fluid Chromatography–Mass Spectrometry

Supercritical fluid chromatography with mass spectrometric detection (SFC–MS) represents a rapidly evolving analytical method that offers an alternative to conventional mass spectrometric chromatography techniques. This approach boasts notable advantages, such as high efficiency, flexibility, rapidity, and environmental friendliness. One field of development within this methodology involves the integration of various ionization techniques, notably atmospheric pressure photochemical ionization (APPI). In this study, the component composition of negatively charged ions generated under APPI conditions for the systems carbon dioxide–organic modifier (methanol, isopropanol, acetonitrile)–dopant (toluene, acetonitrile, anisole) was studied. The impact of mobile phase composition and ion source temperature on the generated ions was explored. The results obtained demonstrate the pivotal role of carbon dioxide as both a direct precursor of the formation of reactive particles (including carbonate radical anions, hydrocarbonate and percarbonate anions) and a reagent capable of forming compounds with the organic modifier (resulting in alkyl alcohol anions for alcohols and adducts with deprotonated acetonitrile molecules) and the dopant (yielding acetoacetic acid in the case of acetone). As a result, a plethora of reactive particles capable of participating in the ionization processes of analytes in SFC-APPI–MS was observed.