# Carbonyl Composition and Electrophilicity in Vaping Emissions of Flavored and Unflavored E-Liquids
## 3 Results and Discussions
### Levels of Target Carbonyls in _E-Liquids' Vaping Emissions_  
The 2,4-DNPH method was used to estimate the amount of seven target carbonyls in vaping emissions of PG-VG and four flavored e-liquids. Carbonyls can react with 2,4-DNPH to form hydrazone derivatives [57; 58], which can be identified by their EICs \(m/z\) of [M-H]\({}^{-}\) from LC/ESI-Q-TOFMS analysis. The \(m/z\) values of hydrazone derivatives of target carbonyls are 209 (formaldehyde), 223 (acetaldehyde), 235 (acrolein), 237 (acetone and propionaldehyde), 251 (butylraldehyde), and 285 (benzaldehyde). As shown in Figure 2, formaldehyde, acetaldehyde, and acetone/propionaldehyde were detected in emissions samples from PG-VG and flavored e-liquids. In the case of formaldehyde, the amounts per puff were as follows (ranking from the highest to the lowest): 22,717 \(\pm\) 4036 ng/puff (PG-VG), 1072 \(\pm\) 319 ng/puff (_trans_-2-hexenol), 1248 \(\pm\) 142 ng/puff (I-(-)-menthol), 399 \(\pm\) 64 ng/puff (benzyl alcohol), and 126 \(\pm\) 44 ng/puff(linalool). For acetaldehyde, PG-VG and _trans_-2-hexenol had two highest amounts of 4082 \(\pm\) 42 ng/puff and 85 \(\pm\) 3 ng/puff, respectively. The rest of the e-liquid emissions had <20 ng/puff of acetaldehyde detected. As for acetone and propionaldehyde, their amounts in vaping emission samples were combined, as they have the same EIC of \(m/z\) 237 and close retention times that could not be separated by our LC method. The order of acetone/propionaldehyde ranking from the highest to the lowest amount was 401 \(\pm\) 152 ng/puff (l-(-)-menthol), 382 \(\pm\) 104 ng/puff (_trans_-2-hexenol), 360 \(\pm\) 95 ng/puff (benzyl alcohol), 314 \(\pm\) 138 ng/puff (linalool), and 216 \(\pm\) 33 ng/puff (PG-VG). Carbonyls not detected in all e-liquids' emission samples were acrolein, butyraldehyde, and benzaldehyde. Acrolein was detected in emission samples of PG-VG (12 \(\pm\) 2 ng/puff) and _trans_-2-hexenol (2 \(\pm\) 1 ng/puff). Butyraldehyde was detected in emissions of _trans_-2-hexenol (35 \(\pm\) 6 ng/puff), benzyl alcohol (1 \(\pm\) 0.1 ng/puff), and l-(-)-menthol (0.4 \(\pm\) 0.1 ng/puff). On the other hand, benzaldehyde (0.7 \(\pm\) 0.1 ng/puff) was only detected in emission samples of benzyl alcohol. The levels of formaldehyde, acetaldehyde, and acrolein were lower in vaping emissions of alcohol-flavored e-liquids. The addition of alcohol flavoring chemicals in e-liquids (with PG-VG as the base solvent) could potentially lead to competing reactions during thermal decomposition [59; 60]. For example, intermediates produced from the vaping of flavored e-liquids might interact with each other and shift the product distribution when compared to the vaping of PG-VG e-liquid alone. However, the detailed mechanism needs further investigation. Figure 2: Levels of target carbonyls per puff (ng/puff) in PG-VG and flavored e-liquids (_trans_-2-hexenol, benzyl alcohol, 1-(-)-menthol, and linalool). Target carbonyls measured are formaldehyde, acetaldehyde, acrolein, acetone/propionaldehyde, butyraldehyde, and benzaldehyde. Error bars represent one standard deviation of triplicate measurements. E-liquid constituents, among many parameters, affects carbonyl concentrations and chemical composition in vaping emissions. Figure 2 shows presence of formaldehydehyde, acetaldehyde, acrolein, acetone, propionaldehyde, and butyratedehyde in vaping emission samples, which are consistent with published findings [10; 11; 12; 13]. In addition, composition of emitted carbonyls may be largely contributed to their parent compounds. [PERSON] et al. [51] examined acrolein that was mostly produced from VG degradation, while formaldehyde was produced from both PG and VG degradation. Our results show higher concentrations of formaldehyde emitted compared to acrolein. In addition, presence of benzaldehyde in benzyl alcohol e-liquid's emission samples may explain primary production of benzaldehyde from benzyl alcohol degradation. Addition of flavoring chemicals in e-liquids can also affect carbonyl production.