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

Importance of Topic

Electronic cigarette liquids require precise measurement of nicotine and glycerin to ensure consumer safety and regulatory compliance.
Visible near-infrared spectroscopy offers a rapid, non-destructive approach without sample preparation, making it ideal for high-throughput quality control.

Objectives and Study Overview

The goal was to develop and validate a fast VIS-NIRS method for simultaneous quantification of nicotine and glycerin in e-liquids.
The study employed partial least squares regression with internal cross-validation to assess method performance.

Used Instrumentation

• Metrohm NIRS XDS RapidLiquid Analyzer covering 400–2500 nm
• 8 mm disposable glass vials
• Vision Air 2.0 Complete software for data acquisition and analysis

Methodology

24 e-liquid formulations containing 5–50% vegetable glycerin and 0–20 mg/ml nicotine were measured in transmission mode at 30 °C.
Spectral pretreatment included second derivative calculation and selection of optimal wavelength ranges (glycerin: 1120–1994 nm; nicotine: 1892–1994 nm).
Partial least squares models with three factors were built and validated internally.

Key Results and Discussion

Raw VIS-NIR spectra showed distinct differences between samples in 1400–1900 nm;
Second derivative spectra compensated baseline variability.
The glycerin model achieved SEC 1.53%, SECV 1.63%, R²=0.9877;
The nicotine model delivered SEC 0.58 mg/ml, SECV 0.69 mg/ml, R²=0.9893.
Correlation plots confirmed strong agreement with reference values.

Benefits and Practical Applications

• Analysis time of under one minute without chemical reagents
• Simultaneous, accurate multi-component determination
• Ideal for routine QC and regulatory monitoring
• Reduces labor and sample preparation costs

Future Trends and Potential Applications

Advances may include on-line process monitoring, expansion to flavor and propylene glycol content, portable VIS-NIR devices,
and integration with machine learning for automated spectral interpretation.
Stricter regulations will further drive adoption of rapid spectroscopic methods.

Conclusion

Visible NIR spectroscopy using the NIRS XDS RapidLiquid Analyzer and Vision Air software offers a robust, efficient solution
for simultaneous nicotine and glycerin quantification in e-liquids, supporting fast quality control and regulatory compliance.