Is transmission Surface-enhanced Raman spectroscopy a good alternative to separative technique for the nicotine dosage in-liquid boosters?

During the last decade, the use of electronic cigarettes grew in popularity. They became an alternative for smokers especially for young people due to their attractive various flavours1,2. Since 2014, electronic cigarettes must follow the European Directive on tobacco products. This new legislation called for the development of new analytical tools to control the quality of these products and more especially to determine the nicotine dosage in the e-liquid boosters since the nicotine concentration must not exceed 20 mg/mL. Chromatography techniques are commonly used in this context but the development of alternative techniques being faster, greener and compatible with in-field analyses are required. In this study, the feasibility of using surface enhanced Raman spectroscopy (SERS) as an alternative analytical tool was evaluated through the development and the validation of new methods. A transmission Raman scattering (TRS), enabling to improve the sample representativity, and a handheld Raman system were used to perform acquisitions aiming to compare the analytical performances of both instruments. As pioneers in surface-enhanced transmission Raman scattering (SETRS), a robust method validation, ICHQ2 (R2) compliant, was performed to evaluate the analytical performances. The SERS samples were prepared using lab-made gold nanoparticles in suspension (AuNps) as SERS substrate, diluted reconstituted e-liquid booster spiked with different nicotine concentrations and nicotine-d4, added as an internal standard. To reach a SERS signal stabilisation, the SERS samples were analysed after 15 minutes. The methods developed on both equipment were successfully validated involving 6 series using a total error risk-based approach for a range of concentration from 100 to 300 ppb. To answer to the main question, these promising results could pave the way to the implementation of SETRS in laboratory routine analysis while handheld Raman systems combined with SERS could be considered for in field analyses.
1 S. Barhdadi et al., Nicotine Tob. Res., 23 (2021) 227