Need for more research on e-cigarettes

E-cigarettes, which involve the vaporisation of a liquid by electronic heating, are increasing in popularity. Most of the liquids contain nicotine, although a few do not. There is controversy as to whether e-cigarettes encourage smokers to quit, and also whether they attract young people to smoking. Although most scientists in the field believe that e-cigarettes are less dangerous than ordinary cigarettes, there is still a lack of research about their contents and effects. The EU has limited the nicotine levels in e-cigarette liquids to a maximum of 20 mg/ml.

Italian researchers from the University of Bari and the National Centre for Chemicals in Rome examined a number of popular brands of e-cigarettes by LC-MS/MS (tandem MS), looking at the composition of the liquids and also the vapour in a test room where an e-cigarette is smoked. The latter is of interest due to the possible exposure of other people, including children, to nicotine from e-cigarettes.

LC-MS/MS on e-cigarette liquids shows impurities and inaccurate label assays

The researchers from Rome and Bari examined 95 refill liquids from 12 different brands. The liquid samples were diluted with methanol and injected into the HPLC system. The HPLC used a gradient elution programme, with acetonitrile and 20 mM aqueous ammonium carbonate making up the two mobile phases. The system was capable of separating nicotine from its closely-related analogues. A triple quadrupole mass spectrometer with an ESI (electrospray) source was used in MRM (multiple reaction monitoring) mode. The molecular ion was the most abundant in all cases for the initial (Q1) scan, while the subsequent scan (Q3) gave distinct breakdown ions.

The methods used were successfully validated using pure samples of the various species examined (nicotine and its analogues); the reproducibility and linearity were shown to be acceptable.

The values for nicotine concentrations from the e-cigarette liquids were found by the researchers to vary between 67% and 110% of the stated amount. About 47% of the samples were more than 10% out with regard to nicotine levels. Interestingly, traces of nicotine (1 to 254 μg/ml) were found in about 78% of the ‘nicotine free’ liquids examined, presumably due to cross-contamination during manufacturing.

Minor alkaloids (nicotine analogues) were found in total concentrations of up to 5.4% of the nicotine content, with an average value of 1.6%. For comparison, pharmaceutical grade nicotine (used in skin patches, etc.) has a limit of 0.8% for total minor alkaloids; 81% of the e-cigarette liquids exceeded this limit.

Vapours from the air near to a smoker were also collected using sorbent tubes and air pumps, with volunteers smoking either e-cigarettes or ordinary cigarettes. Desorption from the tubes was carried out with 9:1 ethyl acetate/methanol using ultrasound. This initial solvent was ‘swapped’ for neat methanol by evaporation under nitrogen and dissolving the residue, prior to HPLC (ethyl acetate was not miscible enough with the mobile phase to allow it to be used as an injection solvent). Examination of the vapour levels showed that the amount of nicotine produced from e-cigarettes (ca. 3 μg/m3 with 150 ‘puffs’) was significantly less than that from ordinary cigarettes (ca. 30 μg/m3 with 150 ‘puffs’).

Poor QC or storage for e-cigarette liquids exposed

The overall results from the study show that poor QC (or possibly poor storage leading to degradation) is a widespread problem with e-cigarette liquids. The amount of nicotine often bore little relation to that seen on the label, while significant amounts of minor alkaloids were often present. It was confirmed that e-cigarettes were a source of nicotine vapours in a room, possible leading to exposure to others, although the levels were much lower than those seen with normal cigarettes. Further research and possibly new legislation is needed in this field.

Author(s)

Ryan De Vooght-Johnson