Fig. 4

a Boxplot showing mean nicotine concentration per puff at source from two products on two machines (n = 30/product/machine). The dotted line represents the published cigarette mean analytical target value. There was no significant difference between the same products tested on both machines: p = 0.105. The e-cigarette (mean) delivers 3.5 and 3.6 times lower nicotine concentration versus the cigarette (mean) on the RM20S and VC 10 respectively. b Individual nicotine values showing the puff-by-puff profile from two products on two machines (n = 3); p ≤ 0.01 for cigarette puffs 1–10 on both machines, p = 0.284 and p = 0.530 for ePen puffs 1–10 on the RM20S and VC 10 respectively