Nicotine levels in electronic cigarette refill solutions: A comparative analysis of products from the U.S., Korea, and Poland.

Background: Electronic cigarettes vaporize nicotine dissolved in glycerine and/or propylene glycol (e-liquid). Due to a lack of regulations, e-liquids may contain inaccurately labelled nicotine levels. Our aim was to test nicotine levels in samples of e-liquids from three countries.

Methods: We measured nicotine concentration in 32, 29 and 30 e-liquids purchased between 2013 and 2014 from locations in the United States (US), South Korea, and Poland, respectively.

Results: Nicotine concentration in the US products varied from 0 to 36.6 mg/mL. Traces of nicotine were found in three US products labelled as 'nicotine free'. Two-thirds of South Korean products did not contain detectable amounts of nicotine, whereas nicotine concentration in other products varied from 6.4±0.7 to 150.3±7.9 (labelled as 'pure nicotine') mg/mL. In products from Poland, nicotine concentration varied from 0 to 24.7±0.1 mg/mL. Overall, we found significant discrepancies (>20%) in the labelled nicotine concentrations in 19% of analysed e-liquids.

Conclusion: Most of the analysed samples had no significant discrepancies in labelled nicotine concentrations and contained low nicotine levels. However some products labelled as 'nicotine-free' had detectable levels of the substance, suggesting insufficient manufacturing quality control. We identified a single product labelled as 'pure nicotine' which contained significantly higher concentration of the drug, increasing the risk of accidental poisoning. The study reveals the need for quality standards of these new nicotine containing products.