Rapid Determination of Flavorings in e-Cigarette Liquid by Direct Analysis in Real Time (DART) Mass Spectrometry (MS) in the Quick Strip Mode

Electronic cigarettes (E-cigarettes) have become popular around the world. An important reason is the variety of available flavors. However, many countries have imposed restrictions on flavor substances in E-cigarettes due to their potential health risks. Therefore, it is necessary to develop an effective way to identify flavorings in E-cigarette liquids. In this work, direct analysis in real time-mass spectrometry (DART-MS) in the quick strip (QS) mode was developed and applied to determine flavorings in the E-cigarettes. Vanillin, ethyl vanillin, maltol, and ethyl maltol were quantified. Meanwhile, the ionization efficiency of flavorings in the different solvents was compared in the QS mode, which revealed that the solvent boiling point was related to the analyte ionization efficiency. The effect of endogenous matrix (propylene glycol and glycerol) on flavoring ionization was also investigated. Calibration curves with satisfactory linearity (R² > 0.99) were established from 1 to 1000 μg L⁻¹. Good sensitivity (limits of detection [LODs] < 0.3 μg L⁻¹), recoveries (92.6% to 104.7%), and acceptable repeatability (relative standard deviations < 14.6%, n = 5) were obtained. The limits of quantification (LOQs; 10–50 μg g⁻¹) for the E-cigarette liquid sample were much lower than the regulatory limits. The developed method provided a simple way for rapidly determining flavorings in E-cigarettes.