Chemicals & Petrochemicals

Seeing Through the Smoke with NMR

NMR brings transparency to e-cigarette analysis

The popularity of e-cigarettes has risen phenomenally since they were first introduced in 2005. It is estimated that, in 2015, the global market for these products will reach US $3.5 billion. However, this rapid rise to prominence has been set against a backdrop of uncertainty around the safety of e-cigarettes.

Touted as smoking cessation devices, e-cigarettes have been marketed as healthier alternatives to traditional cigarettes and a means to circumvent indoor smoking restrictions.

But, because time is the only way to know the long-term consequences of using these products, policymakers have had to base their regulatory decisions on a handful of studies of composition analysis and exposure estimates. As a result, there is no clear consensus on how e-cigarettes should be regulated, with some countries opting for outright bans and others choosing to classify them as either medical devices or tobacco products.

But what is in an e-cigarette? The devices usually use aerosolised nicotine to produce a vapour, which manufacturers’ claim contains fewer toxins than tobacco cigarettes. Alongside nicotine, they typically include ingredients such as propylene glycol, glycerol, ethylene glycol and polyethylene glycol mixed with concentrated flavours.

A 2014 study by Hahn et al. showed that NMR spectroscopy could be used to quickly detect the composition of e-cigarette liquids. The researchers analysed 54 samples of e-cigarette liquids using a Bruker Avance device coupled to a Bruker Automatic Sample Changer. Data were automatically acquired using Bruker ICON-NMR software.

The researchers found that the average nicotine content of the samples was 11 mg/mL. However, their findings revealed that nicotine contents were not always accurately represented on product packaging. For example, of 23 samples that claimed to be nicotine-free, only 18 could be confirmed as such. Meanwhile, one sample that claimed to contain nicotine did not.

The team were also able to use their NMR data to estimate the levels of exposure to various compounds to users. By converting these figures using the margin of exposure (MOE) method, they could then estimate the risk posed by the different components.

The researchers found that nicotine was the only detectable compound with an MOE value indicating high risk (defined as below 0.1). No other substance – including glycerol, 1-2-propanediol, ethylene glycol, 1,3-propanediol, thujone and ethyl vanillin – had a median MOE below the safety threshold of 100.

The researchers note that they were unable to detect tobacco-specific impurities using NMR, and say that this is likely due to them being present at trace concentrations, which NMR cannot detect. Previous studies have indicated that such levels are unlikely to cause harm.

Nevertheless, the researchers use their findings to recommend that e-cigarettes should be subject to greater regulation, in order to improve the consistency of nicotine delivery. They say that deviations between labelling and content revealed in their study highlight the need for external quality control, as is currently enforced for tobacco and alcohol products.

They add that, in contrast to traditional methods, such as gas and liquid chromatography, the NMR spectroscopy provides a rapid method to simultaneously detect the multiple components of e-cigarette liquids.


Fleck, F. Countries vindicate cautious stance on e-cigarettes. Bulletin of the World Health Organization 2014; 92: 856-857.

Geiss O, et al. Characterisation of mainstream and passive vapours emitted by selected electronic cigarettes. International Journal of Hygiene and Environmental Health 2015; 218: 169-180.

Hahn, J et al. Electronic cigarettes: overview of chemical composition and exposure estimation. Tobacco Induced Diseases 2014; 12: 23.

Ranasinghe, D. E-cigarettes: Smoking hot among these consumers. Available at: http://www.cnbc.com/id/102521988. Date accessed: 17th May 2015.