Fingerprinting of e-liquids by the determination of untargeted compounds using two modern analytical approaches
To better elucidate characteristic compounds present in e-liquids, and monitor potential changes to a product that occur during storage or between lot preparations, the determination of untargeted analytes is a valuable tool. The aim of this study was to apply two analytical techniques for the untargeted analysis of selected e-liquids using Headspace - Solid Phase Microextraction - Gas Chromatography – Mass Spectrometry (HS-SPME-GCMS) and Liquid Chromatography coupled with Time-of-flight Mass Spectrometry (LC-ToF-MS). A 1 cm Stableflex DVB/CAR/PDMS fiber was used in the HS-SPME-GCMS analysis, providing the pre-concentration of volatile and semi-volatiles compounds. The mass spectrometer operated in scan mode, monitoring a range of 35-400 m/z. The ToF-MS was operated with electrospray and atmospheric pressure chemical ionization (ESI; APCI), both in positive and negative modes. Operating parameters included an acquisition mass range of 70-750 m/z, typical of most small molecules. Both techniques used 100 mg of e-liquid. Each method used isotopically labelled compounds as internal standards (or a fiber performance check in the case of SPME). For this study five replicates of four different e-liquids were evaluated. HS-SPME-GCMS analysis indicated the presence of over 120 different flavour compounds including mono- and sesquiterpenes, higher alcohols, esters, pyrazines, lactones and aldehydes. LC-ToF-MS identified 60 to 400 features, or distinct compounds, depending on the mode of operation, including isomeric compounds typical of modified sugars such as sugar alcohols and acids, as well as, C6 - C18 fatty acids. The combination of compounds identified in the different e-liquids by both techniques, present at different levels, create a unique and distinguishable fingerprint of each e-liquid.