Alcohol Levels Determination in Hand Sanitizers by FTIR

Importance of the Topic

Ensuring the correct alcohol concentration in hand sanitizers is essential for effective disinfection and consumer safety. Fourier-transform infrared spectroscopy (FTIR) with attenuated total reflectance (ATR) provides a rapid, non-destructive, reagent-free approach for both identification and quantification of ethanol and isopropanol. By implementing a robust FTIR method, laboratories can streamline quality control and comply with regulatory guidelines.

Study Objectives and Overview

This application guide outlines the development of a complete workflow—from preparing calibration standards to establishing a routine QC method—using the Agilent Cary 630 FTIR spectrometer paired with MicroLab software. The aim is to:

• Prepare representative standards following World Health Organization formulations.
• Develop individual quantification models for ethanol and isopropanol.
• Create a combined FTIR method that automatically identifies the alcohol type and calculates its concentration.

Methodology and Instrumentation

• Sample Preparation: Ten calibration standards and two independent verification samples are prepared for each alcohol type (ethanol 80% v/v and isopropanol 75% v/v) alongside hydrogen peroxide and glycerol, topped up with water. Glycerol and H₂O₂ are pre-mixed to simplify pipetting.
• Instrument Setup: Agilent Cary 630 FTIR with single-reflection diamond ATR module is connected to a PC running MicroLab. A background spectrum is collected after cleaning the ATR crystal.
• Data Collection: Spectra are acquired over the fingerprint region (800–1800 cm⁻¹) at defined resolution and scan count. A “Data Collect Only” method records raw spectra for all standards.
• Quantification Modeling: In MicroLab Quant, Simple Beer’s Law calibrations are built for each alcohol. Ethanol uses peak areas around 1080 and 1045 cm⁻¹; isopropanol uses bands near 1160, 1130, and 1105 cm⁻¹. Models achieve R² ≈ 0.99.
• Combined Identification/Quantification Method: A third quant model differentiates alcohols by the ratio of peak heights at ~950 cm⁻¹ (isopropanol) and ~879 cm⁻¹ (ethanol). A threshold ratio (~0.1) directs MicroLab to apply the correct quant model within one routine.

Key Results and Discussion

Calibration curves for both alcohols demonstrated linearity and precision across the working range. The identification model reliably distinguished ethanol from isopropanol in mixed samples. Routine QC runs delivered consistent concentration determinations within specified acceptance limits. The combined method reduced analysis time by eliminating manual method switching.

Benefits and Practical Applications

• Rapid turnaround for production in pharmaceutical and consumer goods laboratories.
• Non-destructive, minimal sample preparation and no consumable reagents.
• Automated reporting enforces compliance with quality and regulatory standards.
• Adaptable workflow for different sanitizer formulations.

Future Trends and Potential Applications

The approach can be extended to monitor additional active ingredients or contaminants. Integration with laboratory information management systems (LIMS) and automated sampling could further enhance high-throughput screening. Emerging miniaturized FTIR platforms and machine-learning-based spectral analysis promise field-deployable QC solutions and deeper insights into complex formulations.

Conclusion

FTIR-ATR combined with MicroLab software offers a versatile, efficient, and accurate method for identifying and quantifying ethanol and isopropanol in hand sanitizers. This protocol supports stringent QC requirements and can be readily implemented in research, manufacturing, and regulatory laboratories.

Reference

• Agilent Technologies. Alcohol Levels Determination in Hand Sanitizers by FTIR: Application Guide, Edition 1, November 2020, Document No. 5994-2827EN.
• World Health Organization. WHO-recommended handrub formulations.