Electrospray LC/MS response differences from equimolar quantities of drugs using a compact mass spectrometer equipped with atmospheric pressure ionization

The purpose of this study was to evaluate the positive and negative electrospray (ESI) and atmospheric pressure chemical ionization (APCI) LC/MS ion current response from a representative synthetic mixture of standard pharmaceutical compounds. The selected drup compounds were prepared as an equimolar mixture and analyzed by an optimized gradient LC/MS procedure using a novel compact mass spectrometer. The total and extracted ion current chromatographic peaks were compared between ESI and APCI in both positive and negative ionization modes. The results from this study shed some light on the relative merits of APCI vs ESI as well as the importance of the optimal ionization polarity for the LC/MS determination of the selected acidic and basic small molecule drugs. We also note some differences in adduct formation between these two API techniques.