Quantification of nicotine and glycerin in e-liquids using visible near-infrared spectroscopy

Importance of the Topic

The rapid and accurate quantification of nicotine and glycerin in e-liquids is essential for regulatory compliance and quality control in the booming e-cigarette industry. VIS-NIR spectroscopy enables non-destructive, preparation-free analysis, reducing turnaround time and operational costs.

Study Objectives and Overview

• Develop a fast VIS-NIR method for simultaneous determination of nicotine and glycerin in e-liquids.
• Validate the method across a range of sample compositions provided by a customer.

Methodology and Instrumentation

The study employed transmission-mode visible near-infrared spectroscopy covering 400–2500 nm. Twenty-four e-liquid formulations with glycerin content between 5.00–50.00 % and nicotine between 0–20 mg/mL were measured at 30 °C using 8 mm glass vials. Data preprocessing included second-derivative transformation and selection of specific wavelength ranges. Partial least squares regression with internal cross-validation (SECV) was applied to model both analytes.

Instrumentation Used

• Metrohm NIRS XDS RapidLiquid Analyzer (400–2500 nm)
• NIRS 8 mm disposable glass vials
• Vision Air 2.0 Complete software

Main Results and Discussion

Raw and second-derivative spectra exhibited clear sample-dependent features. For glycerin (1120–1994 nm), a 3-factor PLS model yielded SEC of 1.53 %, SECV of 1.63 %, and R² = 0.9877. For nicotine (1892–1994 nm), a 3-factor PLS produced SEC of 0.58 mg/mL, SECV of 0.69 mg/mL, and R² = 0.9893. High correlation between VIS-NIR predictions and reference values confirms method reliability.

Benefits and Practical Applications

This VIS-NIR approach allows simultaneous, non-destructive analysis of multiple e-liquid components with minimal sample preparation, making it ideal for routine quality control in manufacturing and regulatory labs.

Future Trends and Applications

Further expansion may include additional analytes such as propylene glycol and flavor compounds. Integration into inline process analytics and adaptation to stricter regulatory frameworks will enhance real-time monitoring and quality assurance.

Conclusion

VIS-NIR spectroscopy coupled with multivariate calibration provides a fast, accurate, and preparation-free method for quantifying nicotine and glycerin in e-liquids, supporting efficient quality control workflows.

References

1. Metrohm NIR Application Note NIR-070, Version 1, February 2019.