Analysis of Ethanol in Liquors Using Nexis™ GC-2030

Significance of the Topic

Accurate measurement of ethanol content in alcoholic beverages is essential for regulatory compliance, quality assurance and taxation. The Japanese National Tax Agency (NTA) prescribes a gas chromatography (GC) method, but conventional isothermal analysis at 50 °C faces challenges in eluting water and high-boiling-point components. This study addresses these limitations and delivers a rapid, precise ethanol assay.

Objectives and Study Overview

The goal was to develop a fast GC method conforming to the NTA official protocol, optimize sample introduction and column cleaning, and apply it to beer, liqueur and Japanese sake. Key aims included shortening analysis time and improving repeatability.

Methodology and Instrumentation Used

Sample preparation and quantification employed internal standard calibration:

• Standard solutions: ethanol diluted in water to 5, 10, 15 and 20% (v/v).
• Internal standard (IS): 2% (v/v) isopropyl alcohol in water; 0.9 mL IS added to 0.1 mL of sample or standard.

Instrument configuration and GC conditions:

• Main unit: Shimadzu Nexis GC-2030 with AOC-20i auto-sampler.
• Column: SH-Rtx-1 (0.53 mm × 30 m, df 3 µm).
• Detector: FID-2030; make-up He 24 mL/min, H₂ 32 mL/min, air 200 mL/min; detector temp. 250 °C.
• Injection: split mode 1 µL, split ratio 1:40, injector temp. 250 °C.
• Carrier gas: He, pressure program 28 kPa (3 min) → 300 kPa/min → 90 kPa (6.79 min).
• Oven program: 50 °C (3 min) → 40 °C/min → 200 °C → 25 °C/min → 245 °C (1.45 min).
• Insert optimization: 10 mg silica wool packed 22 mm from top; elastic titanium-plunger syringe (P/N 221-49548).

Key Results and Discussion

Calibration and precision:

• Calibration curve over 5–20% ethanol showed R² = 0.9995.
• Repeatability for ten injections: RSD < 0.1%.

Actual sample analysis:

• Beer: 4.697% ethanol, RSD 0.073%.
• Liqueur: 8.780% ethanol, RSD 0.096%.
• Japanese sake: 15.445% ethanol, RSD 0.048%.

The temperature ramp effectively eluted high-boilers after ethanol and IS peaks, ensuring column cleanliness within a short run time (< 9 min).

Benefits and Practical Applications

Highlights of the optimized method:

• Compliance with NTA official method while reducing analysis duration.
• Improved repeatability through optimized silica wool packing and syringe design.
• Applicability to routine QA/QC in breweries, distilleries and regulatory laboratories.

Future Trends and Opportunities

Emerging opportunities include integration with automated online sample preparation, use of smaller-bore or micro GC columns for faster runs, coupling to mass spectrometric detection for enhanced selectivity, and extension to other complex alcoholic matrices.

Conclusion

The Nexis GC-2030 method with optimized temperature programming and sample handling delivers rapid, accurate ethanol quantification in various liquors. Excellent linearity and precision make it a valuable tool for regulatory and industrial applications.

References

• Shimadzu Corporation. Analysis of Ethanol in Liquors Using Nexis GC-2030. Application Note No. G315, First Edition November 2019.