*3.1. Quantitative Analysis: BTEX Contamination of the Investigated E-Liquids*

Single and total BTEX concentrations, expressed in μg/L, are reported in Table 2. As shown, most of the e-liquids investigated in the present study (85/97) were revealed to be affected, to a lesser or greater extent, by BTEX contamination. Only a few exceptions were observed with BTEX levels below the LOQ of the analytical methodology applied. Across all of the brands investigated (ID A-N, Table 1), concentration levels ranged from 2.7 μg/L to 30,200.0 μg/L for benzene, from 1.9 μg/L to 447.8 μg/L for ethylbenzene, from 1.9 μg/L to 1,648.4 μg/L for toluene and, finally, from 1.7 μg/L to 574.2 μg/L for m,p,o-xylenes. HS-SPME-GC-MS analysis of e-liquids with ID A (1-5), manufactured in China, highlighted a relevant contamination by BTEX with concentration levels up to four order of magnitude

higher than those determined in all the other investigated e-liquids, regardless of the manufacturing country and the chemical composition. More specifically, within brand A, benzene concentration levels ranged from 7,200.0 μg/L (sample 4-A) to 30,200.0 μg/L (sample 3-A), toluene concentration levels ranged from 764.4 μg/L (sample 1-A) to 1,648.4 μg/L (sample 4-A), ethylbenzene concentration levels ranged from 187.9 μg/L (sample 1-A) to 447.8 μg/L (sample 4-A) and, finally, m,p,o-xylenes concentration levels ranged from 201.8 μg/L (1-A) to 574.2 μg/L (sample 5-A). Moreover, making a comparison among samples ID A in terms of BTEX total concentration, it is possible to observe that 3-A shows the highest BTEX total concentration, equal to 32,151.1 μg/L. The comparison between samples ID A with all the other samples under investigation (ID B-N) revealed that benzene concentrations in 1-5 A samples were between one and four orders of magnitude higher than those determined in all the other e-liquids. Moreover, toluene concentrations in 1-5 A samples were up to three order of magnitude higher than those determined in all the other e-liquids, whilst ethylbenzene and m,p,o-xylenes were up to two order of magnitude higher. Benzene concentrations in 1–5 A samples were higher than toluene concentrations (from 4 to 22 times higher), a finding that was not observed for all the other samples characterized by toluene concentrations higher than benzene concentrations, with very few exceptions. To mention some examples, e-liquids with ID E and F manufactured in China showed toluene concentrations ranging from 20.7 μg/L to 96.2 μg/L and from 6.8 μg/L to 385.9 μg/L, respectively, in both cases one up to two order of magnitude higher than benzene concentrations. As already mentioned, some of the samples investigated were not affected by BTEX contamination. It is possible to observe that in most of the samples C (i.e., 1,2,3,8,10,12,14,15 and 17) and in samples 5D, G5, G6 the presence of BTEX was not detected at all with all concentration levels below the LOQ of the analytical methodology applied. Therefore the samples with ID C manufactured in Italy were revealed to be the highest quality e-liquids among all the tested samples. On the contrary, across samples with ID B-N, the highest BTEX total concentrations were associated with samples belonging to the batch with ID F (manufacture country China) with samples 12-F and 17-F showing the highest values, equal to 739.2 μg/L and 743.8 μg/L respectively. Therefore, it is possible to state that the highest BTEX contamination was observed in e-liquids belonging to two different brands (A and F), both of Chinese origin. Another important observation is that the highest BTEX total concentrations observed for most of the brands were associated with e-liquids characterized by mint flavor (brands B, F and L) and tobacco flavor (brands D, E, F and I).


**Table 2.** Benzene, toluene, ethylbenzene and xylenes (BTEX) concentration (expressed in μg/L) in the investigated e-liquids.


**Table 2.** *Cont.*
