Determination of caffeine and taurine in electronic cigarette oil by high performance liquid chromatography- tandem mass spectrometry

Electronic cigarette refers to electronic delivery systems designed to generate aerosols for human inhalation. In recent years， the global electronic cigarette market has experienced rapid expansion， drawing widespread international attention to its potential health impacts. To protect consumer health， China's mandatory National Standard for electronic cigarettes issued in 2022 explicitly prohibits the addition of additives and stimulants associated with energy and vitality in electronic cigarette oil. However， to attract consumers， many illicit manufacturers illegally incorporate various stimulating substances into e-liquids. While detection methods have been reported for some illegal additives such as industrial cannabinoids and sweeteners in electronic cigarette oil， there is no fast and reliable detection method for the determination of caffeine and taurine in electronic cigarette oil available to this day. In order to ensure human health， a method was developed for the simultaneous determination of caffeine and taurine in electronic cigarette oil using high performance liquid chromatography-tandem mass spectrometry （HPLC-MS/MS） with a mixed-functional column. Sample preparation involved a simple dilution and filtration step， which was optimized prior to analysis. The analytes were separated on a FMD Comixsil ACRP column （100 mm×2.1 mm， 3.0 μm）. The column temperature was maintained at 30 ℃. The mobile phase consisted of acetonitrile and a 0.1% formic acid solution containing 10 mmol/L ammonium formate with gradient elution. The flow rate was 0.2 mL/min and the injection volume was 1μL. Mass spectrometric detection was carried out using electrospray ionization in positive mode （ESI⁺） with multiple reaction monitoring （MRM）. Under the optimized conditions， both caffeine and taurine were well retained on the chromatographic column， exhibiting excellent， tailing-free peak shapes. The method demonstrated that the limits of detection of caffeine and taurine were 0.100 and 1.00 mg/kg， and the limits of quantification were 0.250 and 2.50 mg/kg， respectively. The linear correlation coefficient （<i>r</i>） was ≥0.997. The average recovery of each component was 88.2%-99.0%， with relative standard deviation （RSD， <i>n</i>=6） between 2.2% and 6.6%. These results indicate that the method is simple， rapid and accurate. It has been successfully applied to the detection of caffeine and taurine in real electronic cigarette oil samples.