From liquid to aerosol: an innovative HPLC method sheds light on nicotine salt dynamics of e-cigarettes

Nicotine salts-formed through the reaction of nicotine with organic acids-are widely used in e-liquids due to their enhanced sensory properties. Consequently, there is a growing need for a simple, robust, accurate, and rapid analytical method capable of simultaneously determining multiple nicotine salts in e-cigarette liquids and aerosols. In this study, we developed a novel high-performance liquid chromatography with diode array detection (HPLC-DAD) method for the simultaneous quantification of nicotine and six organic acids (benzoic acid, D,L-tartaric acid, malic acid, citric acid, lactic acid, and levulinic acid) in e-liquids and aerosols. Chromatographic and extraction parameters were fully optimized to ensure analytical reliability. Under optimal conditions, the method exhibited excellent linearity over the range of 0.005-2.5 mg/mL (R² > 0.9999), low limits of detection (0.1-3.0 μg/mL), and satisfactory recoveries (96.6-105.9%). The proposed method was successfully applied to quantify nicotine and the six acids in 60 commercial e-liquids, yielding results consistent with GC-FID and LC-MS/MS analyses. Among the tested products, three nicotine salts-nicotine benzoate, nicotine lactate, and nicotine levulinate-were identified, with nicotine benzoate being the most prevalent (found in 25 e-liquids as the sole salt). Finally, analysis of aerosol emissions revealed the differential release behavior of nicotine salts from e-liquids, explaining the selective use of particular salts in commercial formulations.