Electronic cigarettes are widely used as alternatives to conventional cigarettes. However, the relationships among e-liquid formulation, nicotine volatility, and nicotine delivery remain insufficiently investigated due to limited data on nicotine vapor pressure in e-liquid systems. This study aimed to investigate the effects of e-liquid formulations on nicotine vapor pressure, explore the underlying mechanisms, and establish correlations with nicotine delivery and pharmacokinetics. A headspace method was applied to measure nicotine vapor pressure at 37 °C, with variables including nicotine concentration, PG/VG ratio, organic acid type and ratio, and water content. The results showed that nicotine vapor pressure increased linearly with free-base nicotine fraction and decreased monotonically with increasing PG/VG ratio, acid-to-nicotine molar ratio, and water content. In addition, nicotine vapor pressure followed the order: free-base e-liquids > nicotine salt e-liquids > conventional cigarettes. Then, a correlation analysis was conducted between nicotine vapor pressure and nicotine pharmacokinetics. Lower vapor pressure correlated with deeper lung deposition, higher plasma nicotine, and greater potential toxicity, while higher vapor pressure correlated with more deposition in the upper respiratory tract and potential local irritation. Overall, nicotine vapor pressure can serve as an indicator for predicting nicotine delivery, supporting the rational regulation of e-liquid formulations and health risk assessment.
Wang et al. (Thu,) studied this question.