Analysis of selected organic acids in e-liquids by ion chromatography
At the 2021 CORESTA Smoke-Techno Conference, we presented a novel method for the quantitation of four organic acids (formic acid, acetic acid, propionic acid and lactic acid) by ion chromatography in e-vapor products. Herein, and following from that work, we present a method with modified chromatography for the analysis of additional organic acids in e-liquids by ion chromatography. The modified method is suitable for the quantitative analysis of oxalic acid and benzoic acid which require stronger eluent. The method uses isocratic condition (35 mM KOH) and thus requires no equilibrating time with the run time of 9.5 minutes. The calibration range is 0.02 to 2 µg/mL for oxalic acid and 0.1 to 10 µg/mL for benzoic acid. The method LOQ is 2 µg/g for oxalic acid and 10 µg/g for benzoic acid. The recoveries are 90-100% for e-liquids containing either nicotine or nicotine salts. We have analyzed a range of commercial e-vapor products obtained from the local market by this new method. Oxalic acid was widely present in the commercial e-vapor products we analyzed, but generally not exceeding the level of about 200 µg/g. Benzoic acid was found at two extreme levels: either <90 µg/g, or >20,000 µg/g. There was an additional peak in some samples which has been identified as citric acid by comparing the retention time with the reference material. In terms of the qualitative analysis of citric acid associated with this new method, the comparison of peak area in the samples with the solution from reference material at known concentration indicates the levels of citric acid are all at about 1000 µg/g or less.