Determination of Caffeine and Taurine in E-Liquid: An HPLC-MS/MS Approach
In the world of vaping, ensuring the safety of e-liquids is more important than ever. With regulations tightening around what can and can't be added to these products, substances like caffeine and taurine are strictly off-limits to protect users' health. But detecting both at the same time has been tricky because of their differing polarities. That's where our research comes in—we've developed a reliable method using high-performance liquid chromatography coupled with tandem mass spectrometry (HPLC-MS/MS) to measure these compounds simultaneously in e-liquids.
Abstract
To safeguard consumer health, e-liquids are prohibited from containing caffeine and taurine. However, simultaneously detecting these two compounds poses challenges due to their significant polarity differences. In this study, we screened and optimized chromatographic columns with various functional groups and separation conditions. By selecting a column that supports multiple separation modes, we established an HPLC-MS/MS method for the simultaneous determination of caffeine and taurine in e-liquids. Samples were extracted with a 50% acetonitrile aqueous solution, separated using acetonitrile and 0.1% formic acid aqueous solution (containing 10 mmol/L ammonium formate) as the mobile phase in gradient elution mode on a Phenomenex FMD Comixsil ACRP column (100 mm × 2.1 mm, 3.0 µm). Detection was performed via tandem mass spectrometry in multiple reaction monitoring (MRM) mode, with quantification by external standard method.
The results showed excellent retention and peak shapes for both caffeine and taurine, with no tailing. Caffeine exhibited good linearity in the range of 1.00–100 µg/L (r = 0.997), while taurine showed linearity from 10.0–1,000 µg/L (r = 0.998). The limits of detection (LOD) were 0.100 mg/kg for caffeine and 1.00 mg/kg for taurine, with limits of quantification (LOQ) at 0.250 mg/kg and 2.50 mg/kg, respectively. At three spiking levels (1×, 2×, and 10×), recoveries ranged from 88.2% to 99.0%, with relative standard deviations (RSD) of 2.2%–6.6% (n=6). This method is straightforward, rapid, and highly sensitive, providing valuable technical support for e-liquid quality regulation.
Sample Preparation
Getting the sample ready is a crucial first step, and we've kept it simple to make the process efficient. Weigh approximately 0.20 g of e-liquid sample (accurate to 0.001 g) into a container. Add 50 mL of 50% acetonitrile aqueous solution, vortex for 1 minute to mix thoroughly, then ultrasonicate for 15 minutes to extract the compounds. Filter the extract through a 0.22 µm polytetrafluoroethylene (PTFE) membrane, and the filtrate is ready for analysis. This approach ensures minimal hassle while maximizing extraction efficiency.
Analytical Conditions
Chromatographic Conditions
We used a Phenomenex FMD Comixsil ACRP column (100 mm × 2.1 mm, 3.0 µm) for separation—it's versatile and handles multiple modes well, which was key to our success. The mobile phase consisted of A: acetonitrile and B: 0.1% formic acid aqueous solution (containing 10 mmol/L ammonium formate). The gradient elution program was as follows:
0–2.0 min: 95% A
2.0–7.0 min: 95% A to 70% A
7.0–10.0 min: 70% A
Column temperature was maintained at 30°C, with a flow rate of 0.2 mL/min and an injection volume of 1 µL. These settings helped us achieve clean separations without any overlapping peaks.
Mass Spectrometry Conditions
For detection, we employed an electrospray ionization (ESI) source in positive ion mode, with multiple reaction monitoring (MRM). Nitrogen was used for nebulizer gas, drying gas, and heating gas. Key parameters included:
Curtain gas (CUR) pressure: 276 kPa (40.0 psi)
Nebulizer gas (GS1) pressure: 241 kPa (35.0 psi)
Auxiliary gas (GS2) pressure: 483 kPa (70.0 psi)
Electrospray voltage: 3.0 kV
Desolvation temperature (TEM): 350°C
Detailed mass spectrometry information for caffeine and taurine can be found in the original Table 1. This setup allowed for precise and sensitive detection, making sure we caught even trace amounts.
Conclusion
Through careful comparison and selection of a novel liquid chromatography column that offers multiple interaction modes, we've created an effective HPLC-MS/MS method for detecting caffeine and taurine in e-liquids. What stands out is how straightforward and quick it is, combined with impressive sensitivity and accuracy. We've validated it with real samples, and it shines in terms of low cost, ease of operation, excellent reproducibility, and high precision. This isn't just another lab technique—it's a practical tool that can help regulators and manufacturers keep e-liquids safe, ultimately contributing to better quality control in the vaping industry. If you're involved in product testing or research, this method could be a game-changer for ensuring compliance and protecting users.













