Puff-By-Puff Analysis of E-Liquid Components, Flavor Compounds and HPHC in E-Cigarette Vapor Using the Vocus PTR-TOF

puff-by-puff analysis

Alessandra Paul1, Devon O’Regan1, Jeremy Nowak1, Luca Cappellin2, Nadja Heine1
1 JUUL Labs, San Francisco, California; 2Tofwerk, Thun, Switzerland
ASMS 2020 Poster

Real-Time Analysis of Vapor Products Using Proton Transfer Reaction Time-Of-Flight Mass Spectrometry (PTR-MS)

This poster presented at the ASMS 2020 conference demonstrates the use of the Vocus PTR-TOF for the real-time analysis of e-cigarette vapor products. Additionally, e-liquid analysis and aerosol characterization are possible employing different sampling strategies prior analysis with the Vocus PTR-TOF.

In recent years Electronic Nicotine Delivery Systems (ENDS) such as e-cigarettes are showing a tremendous increase in popularity and they are forecasted to overcome traditional tobacco products in the future. E-liquids are typically constituted by main components (including propylene glycol, glycerol, and nicotine) and flavor compounds which might be added even at very low concentrations. Vaporized e-liquid by vapor products produces aerosols that are inhaled by the consumer. Such aerosol, besides containing volatilized main components and flavors, might also contain harmful and potentially harmful compounds (HPHCs) such as degradation products of e-liquids which are caused by the high temperature (about 200 °C or more) used to produce the vapor in the devices.

The consistent delivery of main components by vapor products is of utmost importance, and in some cases it is regulated by legislation. For instance, in the European Union, the Tobacco Product Directive (TPD, 2014/40/EU) requires electronic cigarettes to deliver nicotine doses at consistent levels. However, this legislation does not specify which measurement approach should be used to demonstrate consistent delivery. Using a methodology capable of puff-by-puff analysis in real-time would provide a direct assessment of nicotine delivery consistency.       

E-liquids are characterized by a specific flavor. Flavor perception by the consumer is mediated by flavor compounds in the aerosols inhaled. Puff-by-puff determination of flavor compounds delivered by ENDS therefore offers a tremendous insight useful to characterize the products. Off-line measurement techniques such as chromatographic methods (e.g., GC-MS) miss the real-time capability and therefore fail to provide such insight.

HPHCs determination is fundamental for risk assessment of ENDS. High concentrations of HPHC (e.g., aldehydes such as acrolein) might pose serious risk to consumers. The behavior of ENDS in terms of HPHC formation might vary during a puff series. For instance, the present study demonstrates that the chemical profile changes as the e-liquid depletes. The inconsistent performance of some ENDS devices likely contributes to the varying profiles. It is a standard practice to use off-line techniques to determine HPHCs on the aerosol of a few puffs (e.g. 50) trapped in filters and/or using impingers. However, such methods might not provide a complete picture of HPHC formation and their aerosol concentrations, as only a real-time puff-by-puff analysis offers a more comprehensive characterization of HPHC and of the acute risks posed by their inhalation.    

The present research demonstrates the possibility to perform real-time analysis of main components, flavor compounds, and HPHCs with the Vocus PTR-TOF.

The soft chemical ionization offered by the Vocus PTR-TOF allows to simultaneously quantify many organic compounds, making it especially suitable for the determination of small molecules in ENDS aerosol. It is a direct injection method which avoids aerosol collection, extraction, and derivation steps. E-liquid can also be directly analyzed by headspace analysis or via a liquid calibration system (LCS) which evaporates the sample before introduction into the Vocus inlet.

Complete puff series are studied for various ENDS. Consistent delivery of nicotine is shown on a single puff basis. Moreover, for specific ENDS, a very peculiar emission of HPHC is reported with, for instance, acrolein, crotonaldehyde, nicotine-n-oxide, acrylonitrile increasing markedly during the last puff before e-liquid depletion. For acrolein a comparison was carried out with a characterization of selected puffs by a standard off-line GC-MS method on the same ENDS type, cross-validating the results obtained by the Vocus PTR-TOF. The phenomenon discovered in this case is known as “dry puff” and is characterized by high levels of aldehydes and other harmful compounds which give a strong negative perception and health impact to the consumer.

The study indicates that a puff-by-puff analysis is necessary and that a traditional approach of collecting a few puffs is not sufficient in some very relevant cases. It also shows that the unique features of the Vocus PTR-TOF make it suitable for such measurements.

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