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E-cigarettes: an evidence update <br /> <br />68 <br />poorly labelled products are now less common and overall the labelling accuracy has <br />improved. For instance in the latest study which sampled 263 liquids from 13 <br />manufacturers, the correlation between the declared and measured concentrations was <br />r=0.94 with the samples ranging from -17% to +6% of the declared value [85]. In <br />another study testing the five most popular EC brands, the consist ency of nicotine <br />content across different batches of nicotine cartridges of the same products was found <br />to be within the accuracy required from medicinal nebulisers [100]. Given the generally <br />adequate labelling accuracy and the fact that the actual nicotine intake by vapers is <br />dictated by a host of other factors discussed below, the accuracy of labelling of common <br />e-liquids poses no major concerns. <br /> <br />Is there is a risk from e-liquids inaccurately labelled as containing 0 nicotine? <br />All samples labelled as containing 0 nicotine were nicotine free in the newer studies, but <br />three early studies found nicotine in some samples of ‘0 nicotine’ e-liquids. One sample <br />reported in 2011 was clearly mislabelled [87] but in all other cases, only trace <br />contamination was detected (below 1mg/ml). This would have no central effect on <br />users. <br /> <br />Summary <br />Poorly labelled e-liquid and e-cartridges mostly contained less nicotine than declared <br />and so posed no risk to users. The accuracy of product labelling currently raises no <br />major concerns. <br /> <br />Nicotine in e-vapour <br />A number of studies evaluated nicotine in EC vapour generated by puffing machines. A <br />recent experiment [101] has shown that parameters of puffing topography, especially <br />puff duration and puff frequency, have a major influence on nicotine delivery. This poses <br />a serious problem in interpreting the existing studies. The key parameters used by <br />puffing machines differ widely across studies, and may not correspond well or at all with <br />vapers’ behaviour generally and especially with the way individual EC products are <br />used. To illustrate the point, Table 7 below, from Cheng et al. 2014 [84], shows the wide <br />range of settings used in different studies. (Table 7 includes some unpublished studies). <br /> <br />Table 7. Settings of EC puffing parameters. From Cheng et al 2014 [84]. <br /> <br />Study Puff volume <br />(mL) <br />Puff interval <br />(s) <br />Puff duration <br />(s) <br />Puffs/session Smoking <br />machine <br />Goniewicz et al [100] 70 10 1.8 15 Palaczbot* <br />Pellegrino et al [89] 498 8 3 16 Aspiration