Faster Qualitative Analysis of Essential Oils Using GC/MS with Hydrogen Carrier Gas and a Hydrogen Optimized EI Source

Significance of the Topic

Essential oils are complex mixtures of volatile compounds used extensively in flavor, fragrance and quality-control laboratories. Rising helium costs and supply constraints have driven interest in hydrogen as an alternative GC carrier gas. Demonstrating reliable, high-fidelity GC/MS analyses with hydrogen can enable faster runs, lower operating costs and sustainable workflows without sacrificing spectral quality or compound identification confidence.

Objectives and Study Overview

This study aimed to convert an established helium-based GC/MS method for identifying flavor and fragrance compounds in essential oils into a hydrogen-based workflow. Key goals included:

• Maintaining the original elution order and retention index (RI) calibration across carrier gases.
• Reducing total analysis time.
• Preserving or improving library match scores (LMS) against NIST23.
• Validating an EI source optimized for hydrogen to prevent in-source reactions.

Methodology and Instrumentation

Method conversion steps:

• Used Agilent’s Method Translation calculator to select a 20 m × 0.18 mm id × 0.18 µm HP-5MSUI column for hydrogen, achieving the same elution order as the 30 m helium column.
• Calibrated RIs using n-alkanes C5–C40 for accurate retention index comparison.
• Deconvoluted spectra via MassHunter Unknowns Analysis with RI filtering against NIST23.

Used Instrumentation

• GC: Agilent 8890 equipped with hydrogen supply and safety measures.
• MSD: Agilent 5977C single quadrupole detector.
• EI sources: 3 mm inert extractor for helium; 9 mm HydroInert optimized extractor for hydrogen to minimize in-source hydrogenation.
• Injection: split 25:1, 1 µL at 250 °C.
• Transfer line and source temperatures: 300 °C; quadrupole: 150 °C.
• Scan range: m/z 40–400; solvent delays adjusted to 0.88 min for H2 and 2.2 min for He.

Key Results and Discussion

The hydrogen method delivered a 2.5× faster total runtime while preserving chromatographic resolution and elution order. Retention indices measured under hydrogen matched helium values within ±6 units for most compounds.

HydroInert EI source performance:

• Carvone oxide library match score (LMS) with H2 + HydroInert: 95.8 versus 95.5 for helium.
• Standard 3 mm inert extractor under H2 showed decreased LMS (≈85) due to in-source reactions.

Overall, LMS values for a broad panel of essential-oil components remained within 2–5 points of the helium method, confirming spectral fidelity.

Benefits and Practical Applications

• Significant reduction in analysis time lowers per-sample cost and increases throughput.
• Hydrogen carrier gas reduces laboratory dependence on expensive helium cylinders.
• Maintained identification reliability through consistent RIs and high LMS values.
• Easy method migration using translation tools and standardized calibration mixtures.

Future Trends and Potential Applications

With hydrogen supply more accessible and cost-effective, broader adoption in GC/MS is anticipated. Future developments may include:

• Further optimization of column chemistries and flow rates to exploit hydrogen’s higher efficiency.
• Enhanced EI source designs to eliminate residual in-source reactions for sensitive analytes.
• Integration with tandem MS (GC/MS/MS) workflows using shared target ions for quantitative confirmation.
• Expansion to other volatile-compound analyses such as environmental screening and petrochemical profiling.

Conclusion

This work demonstrates that, with appropriate method translation, hydrogen carrier gas and a HydroInert EI source can replace helium in essential-oil analyses. Achieving a 2.5× faster run time with equivalent chromatographic performance and library match confidence highlights hydrogen’s viability as a cost-effective, high-throughput alternative.

References

1. Agilent EI GC/MS Instrument Helium to Hydrogen Carrier Gas Conversion Guide, 5994-2312EN, 2022.
2. Agilent GC Calculators and Method Translation Software, Agilent Technologies website.
3. Qualitative Analysis of Essential Oils Using GC/MS with Hydrogen Carrier Gas and the Agilent HydroInert Source, 5994-7058EN, 2024.
4. Examination of Mass Spectra of Aroma Components in Essential Oils via GC/MS, 5994-5818EN, 2023.