Systematic Investigation into the Differences in the (+) APPI Efficiencies of Positional (Ortho, Meta, and Para) Isomers

Understanding the underlying principle behind the ionization technique is important for improving the sensitivity and selectivity of mass spectrometry (MS), and analyte–solvent interactions are important factors that affect the ionization process. In this study, analyte–solvent interactions were investigated using a series of ortho, meta, and para isomers, (+) APPI-MS, and computational chemistry. Experimental results reveal that isomers can have vastly different ionization efficiencies, despite their identical elemental formulas and functional groups. To better understand the reasons behind these observations, various analyte–solvent radical-ion complexes were investigated by quantum mechanical techniques, and the factors that contribute to the differences in the ion-formation behavior of these compounds were thoroughly investigated.