Comparison of Different Sample Introduction Techniques for the Analysis and Characterisation of e-Liquids Using GC-MS
The last decade has seen an exponential increase in the consumption of electronic cigarettes (EC) amongst smokers. EC use a heated element to disperse a solution of propylene glycol (PG), glycerine (VG), water, flavouring and usually nicotine known as e-liquid. Since the 20th May 2016, a new European Legislation known as Tobacco Products Directive (TPD) came into force for the EC market requiring testing of these e-liquids to confirm regulatory compliance and enable risk assessments to be performed. The directive covers a diverse range of target compounds that may be present in a range of concentrations in the product. This presented a new challenge to analytical chemists responsible for performing the analysis, due to the variety of products and high level matrix components. The choice of sample preparation technique can be critical in obtaining the required information about a product. Five main sample introduction techniques were compared for the analysis of e-liquids with different PG/VG composition: standard liquid injection, Automated Tube Exchange (ATEX), Dynamic Headspace (DHS) as Fully Evaporative Technique (FET), Twister Headspace and Twister Liquid. Using the GERSTEL MPS platform, these can all be performed on a single system. Liquid injection via Agilent split/splitless injector, ATEX and FET DHS were comparable, with the advantage that the use of ATEX would reduce the need for inlet maintenance. Headspace approaches also can give a reduction in the PG/VG background. Direct immersion Twister enabled the detection of target compounds (e.g. nicotine) but also a reduction in matrix background and enrichment allowed the detection of peaks previously hidden by the noise. This work demonstrates the need for selection of appropriate sample preparation and the flexibility of the GERSTEL automated system to perform a number of options.
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