Analysis of organic acid content in e-liquids and e-cigarette aerosol by high performance liquid chromatography – ultraviolet detection (HPLC-UV)
Weak organic acids can be used as preservative agents, potentially affecting the stability of e-cigarette solutions. However, they can also impact characteristics like the aroma and taste of aerosols. The objective of this study was to develop and validate a simple analytical method for the analysis of 6 organic acids (formic, acetic, glycolic, lactic, benzoic and oxalic) possibly found in e-liquids.
Initially, one method was developed for the determination of benzoic acid. The aerosol was collected onto a filter pad and extracted with isopropyl alcohol, then diluted with a 0.1% phosphoric acid solution. The extract was then analyzed by HPLC-UV (230nm) using a Poroshell 120 EC-C18 column (2.7 µm, 100 x 4.6 mm). E-liquids were analyzed using the same chromatographic conditions as the aerosols. Limits of quantitation (LOQ’s) were 17.2 µg/collection for aerosol and 1.7 µg/g for e-liquids, with recoveries of 112% and 102% for laboratory fortified matrices, respectively. To extend the method to include additional organic acids, a Supelcogel C-610H column (9 µm, 300 x 7.8 mm) was used. Although satisfactory LOQ’s were obtained, ranging from 0.43 µg/g to 11.8 µg/g for e-liquids and 1.71 µg/collection to 47.3 µg/collection for aerosols, the method was hindered by the limited capacity of the column handle a higher organic content mobile phase required to elute the glycerol and propylene glycol sample matrix from the column. To overcome these long run times, a third chromatographic approach was developed using an Allure Organic Acids column (5 µm, 300 x 4.6 mm), able to utilize a mobile phase with up to 50% of acetonitrile (ACN), reducing the run time to 40 minutes.