Alcohol Determination of Sanitizer Gel in accordance with USP<611>

Significance of the Topic

Alcohol-based hand sanitizers must contain an adequate ethanol concentration to ensure antimicrobial efficacy and comply with regulatory standards such as the United States Pharmacopeia (USP) <611>. Gas chromatography offers accurate, sensitive, and robust quantitation of ethanol in complex matrices like gels, making it an essential tool in pharmaceutical quality control and industrial analytics.

Objectives and Overview

This study presents a quantitative analysis of ethanol in commercial sanitizer gel following USP <611> Method II b. The aim is to validate the method using a capillary column and internal standard technique, ensuring compliance with system suitability criteria and demonstrating its suitability for routine quality control.

Methodology and Instrumentation

Standard Solution Preparation:

• Mix 5 mL of 2% (v/v) ethanol and 5 mL of 2% (v/v) acetonitrile internal standard, dilute to 25 mL with water to yield 0.4% (v/v) ethanol.

Sample Preparation:

• Dilute commercial sanitizer gel (approximately 80% (v/v) ethanol) with water to ~2% (v/v) ethanol, then mix 5 mL of this solution with 5 mL of 2% acetonitrile and dilute to 25 mL for a final ~0.4% (v/v) ethanol concentration.

Instrumental Setup:

• Gas chromatograph: Shimadzu Nexis™ GC-2030 with AOC-20i Plus autosampler
• Detector: FID-2030 flame ionization detector
• Column: SH-Rtx™-624 capillary (30 m × 0.53 mm i.d., 3 µm film)
• Temperature program: 50 °C (5 min) to 200 °C at 10 °C/min (24 min total)
• Injection: split mode (split ratio 1:5), injection volume 0.2 µL at 210 °C
• Carrier gas: helium, linear velocity 34 cm/s
• FID flows: H₂ 32 mL/min, air 200 mL/min, make-up gas (He) 24 mL/min
• Modified split insert: 20 mg deactivated glass wool at 20 mm depth to meet USP system suitability.

Main Results and Discussion

System Suitability Test (n=6) Results:

• Resolution between ethanol and acetonitrile >10 (requirement ≥4).
• Tailing factor of ethanol peak ~1.5 (≤2.0 required).
• RSD of ethanol/internal standard area ratio 0.4% (≤4% required).

Calibration:

• Linear response for ethanol concentration ratios up to 0.4% (v/v).

Sample Analysis (n=3):

• Measured ethanol in diluted gel: average 78.9% (v/v) with RSD 0.24%.

These results confirm the method’s accuracy, precision, and compliance with USP <611> for routine ethanol determination in sanitizer gels.

Benefits and Practical Applications

The capillary GC method provides high sensitivity and reproducibility, rapid analysis (24 min runtime), and straightforward sample preparation. It is ideal for pharmaceutical QC laboratories, sanitizer manufacturers, and regulatory testing to ensure product compliance and public safety.

Future Trends and Applications

Further developments may include automation of sample handling, faster temperature programs, miniaturized or high-throughput columns, and extension to other alcohol types or complex formulations. Real-time or at-line monitoring in production environments can enhance process control and product consistency.

Conclusion

This application of USP <611> Method II b using a capillary column and the Shimadzu Nexis GC-2030 system effectively quantifies ethanol in hand sanitizer gels. The method meets all system suitability requirements, delivers robust repeatability, and is well-suited for regulatory and quality control environments.

Reference

• United States Pharmacopeia. USP <611> Alcohol Determination. USP–NF, 2020.
• Shimadzu Corporation. Application Note No. G333: Alcohol Determination of Sanitizer Gel; August 2020.