Alcohol Determination of Sanitizer Gel Using Nexis GC-2060

Importance of the Topic

Accurate and repeatable quantification of ethanol in sanitizing gels is essential for regulatory compliance, product safety, and quality control. Methods that reliably handle high-water-content matrices and high analyte concentrations are particularly important for routine pharmaceutical, consumer-products, and manufacturing laboratories. This study demonstrates a GC-based approach that addresses common challenges in aqueous sample introduction and detector linearity when measuring ethanol in sanitizer gels according to USP <611> requirements.

Objectives and Study Overview

• Evaluate the performance of the Nexis GC-2060 equipped with a newly developed flame ionization detector (FID) for determining ethanol content in a commercially available sanitizing gel.
• Demonstrate sample-preparation and injection strategies that stabilize vaporization of aqueous samples and improve repeatability.
• Verify that the method meets the system suitability test (SST) criteria defined in USP <611> Method IIb (capillary GC).

Methodology

• Standards and samples: A standard solution was prepared by mixing 5 mL of 2 % (v/v) ethanol and 5 mL of 2 % (v/v) acetonitrile (internal standard) and diluting to 25 mL with water to yield 0.4 % (v/v). A commercial sanitizer (~80 % v/v ethanol) was diluted to ~2 % (v/v) and then prepared the same way to yield a ~0.4 % (v/v) measurement solution.
• Sample introduction: 0.2 µL injections in split mode (split ratio 1:5) using an autosampler with an Xtra Life Microsyringe (P/N 22735400-01) to ensure smooth aspiration/dispensing of aqueous samples.
• Quantification: Ethanol quantified relative to acetonitrile internal standard using calibration constructed from standard solutions; area ratios used for calculations and SST checks per USP <611> IIb.

Used Instrumentation

• Main unit: Nexis GC-2060 with AOC-30i autosampler.
• Detector: Newly developed FID offering high sensitivity and extended linearity for higher-concentration analytes.
• Column: SH-I-624Sil MS, 0.53 mm I.D. × 30 m, d.f. = 3 µm (P/N 227-36078-01).
• Special consumables: Liner for aqueous solutions (P/N 227-35015-01) to stabilize vaporization; Xtra Life Microsyringe (P/N 22735400-01) with flexible titanium-alloy plunger to improve repeatability for aqueous injections.
• Operating conditions (key): Injection unit 210 °C; carrier gas He (linear velocity control at 34 cm/s); oven program 50 °C (5 min) → 10 °C/min → 200 °C (4 min); detector 280 °C; detector gases — makeup N2 30 mL/min, H2 40 mL/min, air 170 mL/min.

Main Results and Discussion

• Chromatography: Ethanol and acetonitrile (internal standard) were baseline separated with reproducible peak shapes, indicating stable vaporization and good chromatographic resolution on the selected column and conditions.
• Calibration and linearity: The calibration curve for the ethanol/internal standard area ratio exhibited good linearity across the tested concentration range relevant for diluted sanitizer samples; the new FID contributed to extended linear dynamic range for higher analyte concentrations.
• System suitability: The method met USP <611> Method IIb SST criteria — tailing factor for ethanol below the threshold, resolution between ethanol and IS above the minimum (R ≥ 4), and repeatability of area ratios from replicate standard injections within the allowed limit (≤ 4.0 % RSD).
• Quantitative results and precision: Measured ethanol concentration in the sanitizing gel averaged 77.2 % (v/v) with excellent repeatability (n = 3, %RSD = 0.259). Six replicate standard injections returned area-ratio %RSD well below the USP limit, confirming instrument and method stability.
• Practical notes: Aqueous-sample-specific hardware (liner and syringe) mitigated common problems such as unstable vaporization, distorted peak shapes, and syringe plunger sticking, which often degrade quantitative precision in water-rich matrices.

Benefits and Practical Applications

• Regulatory compliance: Method meets USP <611> IIb SST requirements and is suitable for QC release testing of sanitizing gels and other alcohol-containing products.
• Improved throughput: Rapid oven heating/cooling of the Nexis GC-2060 reduces cycle times, increasing laboratory throughput for routine analyses.
• Robust handling of aqueous matrices: The combination of a special liner and a flexible-plunger microsyringe yields reproducible injections for water-rich samples, reducing rework and retests.
• Broader applicability: The approach is applicable to other volatile organics in aqueous formulations where detector linearity and stable vaporization are limiting factors.

Future Trends and Potential Applications

• Detector development: Continued improvements in FID linearity and sensitivity will expand dynamic ranges, reducing the need for extensive sample dilution for high-concentration samples.
• Automation and autosampler advances: Enhanced syringe materials and autosampler control will further improve repeatability for difficult matrices and support higher throughput workflows.
• Method extension: Similar configurations could be validated for other small alcohols, solvents, and volatile contaminants in formulation and environmental testing.
• Data analytics and compliance: Integration with advanced data-processing workflows and automated SST reporting will streamline regulatory reporting and batch release decisions.
• Greener operation: Optimization of carrier and detector gases, along with faster methods, can reduce laboratory resource consumption per analysis.

Conclusion

The Nexis GC-2060 equipped with the newly developed FID, a special aqueous-sample liner, and the Xtra Life Microsyringe provides a robust workflow for ethanol determination in sanitizing gels. The method delivered baseline separation, strong linearity, and excellent precision, meeting USP <611> Method IIb system suitability criteria and achieving accurate quantification (average 77.2 % v/v ethanol, %RSD 0.259). This configuration is well suited for routine QC of alcohol-based products and other applications requiring reliable analysis of aqueous matrices.

References

1. United States Pharmacopeia. General Chapter <611> Alcohol Determination, Method IIb (capillary GC) — system suitability and method criteria.
2. Shimadzu Corporation. Application note: Alcohol Determination of Sanitizer Gel Using Nexis GC-2060. First Edition: Apr. 2026.
3. Instrument and consumable part numbers referenced: Nexis GC-2060 / AOC-30i; SH-I-624Sil MS column (0.53 mm × 30 m, 3 µm); aqueous-sample liner (P/N 227-35015-01); Xtra Life Microsyringe (P/N 22735400-01).