Method Translation and Evaluation to Implement Nitrogen Carrier Gas in the Dual-Flame Ionization Detector Configuration for Blood Alcohol Analysis

Significance of the Topic

Helium shortages and cost fluctuations pose significant challenges for laboratories performing headspace gas chromatography (HS-GC) analyses. Substituting helium with nitrogen as the carrier gas can reduce operational costs, conserve helium for critical applications, and enhance supply security without compromising analytical performance.

Objectives and Overview

This study aimed to translate an established dual-column HS-GC/flame ionization detector (FID) method for blood alcohol analysis from helium to nitrogen carrier gas. Key goals included:

• Maintaining matching retention times for target analytes.
• Preserving chromatographic resolution.
• Verifying equivalent calibration linearity and repeatability.

Methodology and Instrumentation

The method translation used the Agilent Method Translator tool within the GC data system to calculate nitrogen carrier parameters from the original helium method. The instrumentation comprised:

• Agilent 8890 GC with split/splitless inlet and dual FIDs.
• Agilent 8697 headspace sampler.
• Precolumn (0.5 m × 530 µm) split into two analytical columns: 30 m × 0.32 mm, 1.8 µm (DB-BAC1 UI) and 30 m × 0.32 mm, 1.2 µm (DB-BAC2 UI).
• Gas Identity Test built into the 8890 GC to confirm correct carrier gas configuration.

Main Results and Discussion

Ethanol calibration over 20–400 mg/dL produced linear curves (R² ≥ 0.9995) under both helium and nitrogen. Tenfold repeatability injections of a 50 mg/dL QC mix yielded relative standard deviations below 3% for all analytes, with nitrogen often matching or exceeding helium performance. USP resolution values for critical pairs remained above acceptance criteria, confirming minimal impact on separation quality. The Gas Identity Test reliably detected mismatches between configured and actual gases, ensuring method integrity.

• Linearity: correlation coefficients ≥ 0.9995 for nitrogen carrier.
• Repeatability: RSD ≤ 2.7% for key analytes under nitrogen.
• Resolution: USP Rs > 1.0 for all critical separations.

Benefits and Practical Applications

Transitioning to nitrogen carrier gas delivers several advantages:

• Reduced dependence on scarce helium supplies.
• Lower operational costs and improved sustainability.
• Unchanged method robustness and data quality for blood alcohol testing in forensic and clinical settings.

Future Trends and Opportunities

As GC systems become more intelligent, further opportunities include:

• Automated gas translation for diverse methods and analytes.
• Broader adoption of gas verification diagnostics to prevent setup errors.
• Extension of helium-free workflows to environmental, flavor–fragrance, and petrochemical analyses.

Conclusion

The study demonstrates that nitrogen can effectively replace helium as the carrier gas in dual-column HS-GC/FID blood alcohol methods using Agilent instrumentation and software tools. Analytical performance metrics—including linearity, repeatability, and resolution—remain equivalent, offering laboratories a reliable, cost-effective alternative during helium shortages.

References

• Fausett A. Blood Alcohol Analysis with the Integrated 8697 Headspace Sampler on 8890 GC-Dual FID System. Agilent Technologies application note 5994-3126EN, 2021.
• GC Calculators and Method Translation Software. Agilent Technologies website, accessed 2022-11-07.
• Agilent 8890 Browser Interface Diagnostics. Agilent Technologies YouTube video, Apr 14, 2022; accessed 2022-11-07.