Characterization of e-cigarettes liquid contents and transformation products by LC-MS, GC-MS and ICP-MS techniques

Introduction While it is stated that e-cigarettes are less toxic than regular cigarettes, there are still safety and health issues that need to be clarified before they can be said to be safe and clean. The purpose of this study was to develop analytical MS methods to investigate both on chemical composition of e-liquids, characterize their quality and monitoring the aerosol composition during operation of e-cigarette. Final objective was the evaluation of toxic compounds, present in liquids and formed, as transformation products. Low-quality nicotine, glycerol, propylene glycol or flavours could greatly increase the toxicity. Quantitative determination involved nicotine contaminants as pro-carcinogen NOR-nicotine, toxic ethylene glycol and residues of volatile toxicants and metals present in e-liquids. Pyrolysis-originated aldehydes were also measured. Methods E-cigarette refill liquids were directly analyzed by LC-MS while their headspace was sampled by SPME in order to perform GC-MS VOC screening. A Borgwaldt RM 1/G-R58.02 smoking machine was used to operate commercial e-cigarettes. LC-MS analyses were accomplished on a Shimadzu Nexera LC system coupled with a Applied Biosystems 5500 Q-trap instrument, with ESI interface. C18 RP columns and ion pairing mobile phases were used for alkaloid separation. Agilent and Varian GC-MS systems were utilized for VOC determination and aldeydes quantification (after derivatization with pentafluorobenzoylhydroxylamine). Heavy metal residues were determined by ICP-MS after simple dilution on a Agilent 7700 instrument. Preliminary data In the first steps of method development we optimized the chromatographic separation of highly hydrophilic nicotine related compounds (nicotine, cotinine, anabasine, myosmine, nornicotine and N-nitroso-nornicotine) on an ion pair RP-HPLC chromatographic system. A full validation study was then completed to make possible quantitative determination on commercial e-liquid samples. Accuracy, precision, LLOQ, linearity, extraction recovery and stability were evaluated. Samples were acquired from Italian market in different cities. We analysed different e-liquids, from different producers, both produced in Italy, in China, in Poland and Germany. The nicotine concentration in samples analyzed is not constant. We found differences between declared and actual concentrations ranging from -70% to +20%. This has been observed by other authors too, indicating that it is a common problem in the e-cigarette market. By analyzing VOC fraction we could observe benzene, styrene and ethanol significant contamination in a number of cases. Solvent impurities are related to low-quality nicotine raw material used. Finally, we observed the formation of new products, like acetaldehyde and acrolein, during the vaporization. Glycols undergo pyrolysis during vaporization, and this process seems to be specific for liquids with different composition and for different vaporizer designs, and needs to be characterized. This brings us to the observation that inhaled “vapours” are not just vaporized e-liquids, but mixtures of new compounds that will necessarily have to be investigated and defined. For instance, acetaldehyde and the more chemically reactive acrolein are well-known thermal decomposition products of glycerol. Novel aspects Different MS approaches were developed to characterize e-liquids contaminants and pyrolytic formation of aldehydes was demonstrated with a smoking machine.