Introduction: Since its introduction more than 10 years ago, the e-cigarette has become a commonly used consumer product. This success has led in 2014 to the revision of the European Tobacco Product Directive (TPD) which came to force by the end of 2016, since then also containing mandatory rules to assure the quality and safety of electronic nicotine delivery systems. In this study, we investigate whether these regulatory changes had an impact on the quality of refill liquids (e-liquids) available on the Belgian market through analysis of their chemical composition.

Methods: By using in-house validated methods, a total of 246 e-liquids purchased prior (2013-2015), during (2016) and after (2017-2018) the implementation of the TPD revisions, were analyzed for the presence of nicotine, nicotine-related impurities, volatile organic compounds (VOCs), the additives caffeine and taurine, and the flavours diacetyl and acetylpropionyl.

Results: Although not all manufacturers manage to produce and label their products accurately, nicotine labelling discrepancies have decreased over time. Before the revised TPD came into force, almost half of the samples was not conform in contrast to less than 15% non-conformities observed in the period 2017-2018. Moreover, also the number of e-liquids, containing high risk VOCs (10% in 2016 versus none of the samples in 2017-2018), caffeine (16% in 2017 versus 5% in 2018) and diacetyl and acetylpropionyl (55% in 2017 versus 27% in 2018 of sweet flavoured samples) diminished over time.

Conclusion: Our results demonstrate that the overall quality of the e-liquids has improved after the implementation of the revised TPD. However, the results also show that periodic quality control might be required to ensure further compliance to the TPD.

Implications: This study clearly demonstrates that the implementation of the revised TPD has improved the quality of the e-liquids on the Belgian market. However, there are still e-liquids that are not in agreement with the TPD due to nicotine concentration label discrepancies, presence of e-liquid impurities and of the controversial flavours diacetyl and acetylpropionyl or the additive caffeine.