Discussion
Within both cigarette smoke and e-cigarette vapour, the alkaloid nicotine is initially distributed in both the gas and particulate phases and deposition of nicotine mostly occurs either directly from the gas phase or following the evaporation of nicotine from the particulate phaseA number of different acids have been used to protonate nicotine in e-liquids, though the most commonly used organic acids are lactic, levulinic and benzoic acidIt was found that nicotine absorption was higher in all e-cigarette products evaluated than the usual brand cigarettes during ad libitum use. It was also observed that participants when smoking their usual brand cigarettes took approximately half the number of puffs in the session compared to e-cigarette products. Furthermore, it was found that the TInterpretation of data from this study is subject to some limitations. Firstly, it was carried out among combustible cigarette and e-cigarette dual users in the UK and as such our findings may not be generalisable to other groups such as other geographic populations, smokers using e-cigarettes for the first time, a group whose nicotine delivery is different compared with accustomed e-cigarette users