Fast and sustainable active pharmaceutical ingredient (API) screening in over-the-counter and prescription drug products by surface-assisted plasma-based desorption/ionization high-resolution mass spectrometry

Fast chemical analysis of pharmaceutical preparations is important for quality assurance, counterfeit drug detection, and consumer health. While quantitative methods such as high-performance liquid chromatography mass spectrometry (HPLC-MS) are powerful, there is a need for sustainable and environmentally friendly methods, which require less chemicals and produce less waste. Here, solvent-free ambient desorption/ionization (ADI) MS methods are attractive because they do not require time-consuming chromatography, produce little to no chemical waste, and, thus, contribute to green chemistry practice. In addition, sample throughput can be higher compared to HPLC-MS. In this study, a method for the direct analysis of single- and multi-agent drugs using a plasma-based ADI source (flowing atmospheric-pressure afterglow, FAPA) coupled to high-resolution (HR) MS was developed and optimized for best performance. The approach is rapid and requires analytes to be in solution (only a few μL) before application onto thin-layer chromatography (TLC) surfaces, specifically dimethyl (RP2-) and cyano (CN-) modified silica, for surface-assisted (SA) FAPA-HRMS measurements. No chromatographic separation was required, and the TLC plates served only as sample carriers. A broad variety of 19 active pharmaceutical ingredients (APIs) was carefully selected to cover analgesics, anesthetics, antibiotics, antiepileptics, calcium channel blockers, diuretics, expectorants, opioids, peripheral vasodilators, stimulants, and sympathomimetics. Fast screening and identification of APIs were performed by SA-FAPA-HRMS. Typically, the protonated molecular ion ([M + H]⁺) was the most abundant species, while some compounds (codeine, metamizole, phenoxymethylpenicillin, and torasemide) did show some degree of fragmentation. As a proof-of-principle application, benzocaine was directly detected in saliva samples post-intake of a lozenge. Time-resolved semi-quantitative screening was performed. The limit of detection for benzocaine in saliva was 8 ng mL^-1 (48.4 fmol) using internal standard calibration and CN-HPTLC plates. In addition, direct quantification of artificially spiked saliva was performed with minimal sample preparation. Here, SA-FAPA-HRMS with a CN-HPTLC sample substrate yielded the best performance (20.02 ± 0.52 μg mL^-1, RSD = 2.6%, and deviation of -1.9% from the theoretical value) compared to RP2-TLC (18.97 ± 1.37 μg mL^-1 and RSD = 7.2%, -7.0%), and HPLC-UV (18.51 ± 0.03 μg mL^-1 and RSD = 0.2%, -9.3%) results. In conclusion, SA-FAPA-HRMS is considered attractive for rapid and sustainable analysis of pharmaceuticals with potential in non-invasive patient monitoring.