Quantitative analysis of propylene glycol in saliva of e-cigarette users by gas chromatography-mass spectrometry

A method was developed for the quantitation of propylene glycol in human saliva as a potentially useful biomarker for e-cigarette use. Saliva was collected from e-cigarette users, cigarette smokers, and non-users of any tobacco or nicotine product with approval from the University of Minnesota Human Research Protection Program Institutional Review Board. Two separate protocols, termed programmed and non-programmed, were used. In the programmed protocol, e-cigarette users (n = 20) and cigarette smokers (n = 20) brushed their teeth, waited 15 min, then used their product every 30 s for 5 min and collected a 2 mL saliva sample immediately after the last puff. In the non-programmed protocol, cigarette smokers (n = 30) and e-cigarette users (n = 21) came to the clinic and directly provided a saliva sample for analysis. Non-users (n = 29) of any nicotine or tobacco product served as controls. Propylene glycol in saliva was quantified by gas chromatography-mass spectrometry as its heptafluorobutyrate ester, using propylene glycol-d₈ as the internal standard. Accuracy and precision of the assay were established. Levels of salivary propylene glycol (mean ± S.D.) were 269 ± 319 and 8.04 ± 8.22 μg/mL saliva in e-cigarette users and cigarette smokers, respectively, in the programmed protocol, while the corresponding levels in the non-programmed protocol were 4.94 ± 8.68 and 1.91 ± 1.99 μg/mL. These amounts were all significantly greater than those found in non-users of any tobacco or nicotine product (0.39 ± 0.32 μg/mL). This straightforward validated assay is expected to be useful in future clinical studies of e-cigarette use.