Conclusion
While it has been previously shown that using single protonating acids increases nicotine pharmacokinetics, data from this study demonstrate that while the nicotine concentration and the pattern of use (fixed vs ad libitum) affected nicotine delivery, varying the ratios that lactic, benzoic and levulinic protonating organic acids were combined in e-cigarette liquids was without significant effect on nicotine pharmacokinetics and did not notably impact product liking scores. This suggests that e-cigarette products designed within the range of protonating acid combinations assessed in this study would produce a similar nicotine delivery without negatively impacting product liking as a product designed with a single protonating acid. This can be used in designing e-cigarette products that more closely match nicotine delivery and sensorial performance of combustible cigarettes, and therefore more likely to have greater acceptance and are also likely to be more effective for adult smokers in providing a complete substitute for cigarette smoking.