Introduction:
This study aimed to identify and evaluate potential discrepancies in the reported vs. measured nicotine content of e-liquids.

Material and Methods:
Within the Horizon2020, EUREST-PLUS study, 122 of the most commonly sold e-liquids in 9 European Countries were randomly selected and purchased. A quantitative liquid chromatography - mass spectrometry based analysis was performed so as to assess nicotine concentrations.

Results:
Out of the 122 samples analyzed, differences in the concentrations of nicotine compared to the indicated levels on the vial were found. Refill vials from France had an increase in nicotine content between 3.7% up to 47.9% higher than the reported amount, while on the contrary samples from Romania were found to over report their nicotine content (-49.1% up to -9.9%). Samples from other countries identified both increased and decreased nicotine concentrations. Polish e-liquids had a range from -6.4% up to +37.2% in nicotine content, German samples (-71.7% up to +24.5%), Netherlands samples (-6.5% up to +23.6%), United Kingdom samples (-12.8% up to 22.9%), Spanish samples (-46.3% up to 7.2%), Hungarian samples (-41.9% up to 19,9%) and Greek samples (-34.5% up to 17.5%). Furthermore, out of all 122 samples, 12 samples exceeded the limit of 20 mg/ml based on the indicted nicotine levels of the vial and 3 samples were marketed to exceeded the limit.

Conclusions:
Results indicated that the regulations concerning nicotine content of the e-cigarette products are not yet fully adapted. Stricter strategies and surveillance necessary so that the products will be harmonized with the EU TPD.

Funding:
This work was supported by a grant from the European Commission (Horizon 2020 HCO-6-2015; EUREST-PLUS: 681109; Vardavas)