Qualitative Analysis of Essential Oils Using GC/MS with Hydrogen Carrier Gas and the Agilent HydroInert Source

Significance of the Topic

Quality control and compositional analysis of essential oils are critical in food, beverage, fragrance and industrial applications. Gas chromatography–mass spectrometry (GC/MS) is the gold standard for profiling hundreds of terpenoid and aromatic compounds. However, global shortages and rising costs of helium compel laboratories to seek alternative carrier gases. Hydrogen offers advantages─faster separations, lower costs and sustainable operation─but may induce in-source reactions that distort mass spectra and hinder reliable identification. This study demonstrates a robust method conversion from helium to hydrogen carrier gas, leveraging optimized chromatography and a novel hydrogen-compatible ion source to maintain spectral fidelity and accelerate essential oil profiling.

Objectives and Study Overview

The study aimed to transform a standard helium-based GC/MS method for qualitative analysis of flavor and fragrance components in essential oils into an equivalent hydrogen-based protocol that:

• Retains chromatographic resolution and analyte elution order
• Reduces total run time by a factor of 2.5
• Preserves mass spectral integrity to ensure high-confidence compound identification

The converted method was validated by analyzing Brazilian orange oil and Moroccan neroli oil in parallel using helium with a conventional EI source versus hydrogen with a new HydroInert source. MassHunter Unknowns Analysis software and the expanded NIST23 library enabled automated deconvolution, spectrum matching and retention index (RI) filtering.

Methodology and Instrumentation

Chromatography parameters were translated from helium to hydrogen using Agilent’s Method Translator tool. Key features included:

• Column selection: 30 m × 0.25 mm, 0.25 µm HP-5ms UI for He; 20 m × 0.18 mm, 0.18 µm HP-5ms UI for H₂ to achieve similar resolution and relative retention times.
• Constant flow control: 1.0 mL/min He versus ~0.96 mL/min H₂.
• Oven program adjustment: helium ramp of 3 °C/min changed to 7.5 °C/min for hydrogen to compress run time from 60 min to 24 min.

Mass spectrometric conditions were matched for optimal sensitivity (40–400 m/z scan, 300 °C source, 150 °C quadrupole). Automated spectral deconvolution and RI calculation used MassHunter Unknowns Analysis 10.0 linked to NIST23, which includes semistandard nonpolar RI entries. Calibration with C₅–C₄₀ alkanes enabled RI filtering (±10 s tolerance).

Key Results and Discussion

Conversion to hydrogen carrier gas with the HydroInert EI source yielded results comparable to helium while cutting analysis time by 60%. Chromatograms of orange and neroli oils showed:

• Maintained peak order and resolution despite reduced column phase ratio (36% of original capacity).
• High library match scores (LMS > 90) and consistent RIs within ±3 units of NIST23 references for most components.
• Signal-to-noise ratios with hydrogen ~2–5× lower than helium, reflected in slightly lower LMS for minor peaks.

Without the HydroInert source, using a standard inert extractor EI source with 3 mm or 9 mm lenses led to in-source hydrogenation and epoxide ring opening. Carvone oxide, for example, showed drastic spectral distortions and false identifications when analyzed with non-inert sources. The HydroInert design suppressed catalytic reactions on metal surfaces, preserving native mass spectra and ensuring accurate identification.

Benefits and Practical Applications

This hydrogen-based method offers laboratories a sustainable and cost-effective alternative to helium GC/MS analysis while preserving data quality. Advantages include:

• Reduced carrier gas cost and dependency on helium supply.
• Shorter analysis times, increasing sample throughput and productivity.
• Uncompromised spectral fidelity enabled by the HydroInert source, supporting reliable deconvolution and library searching.

Industries such as food flavor QC, fragrance development, environmental monitoring and pharmaceutical QA/QC can adopt this approach to maintain analytical performance while lowering operating expenses.

Future Trends and Potential Applications

Adoption of hydrogen carrier gas is expected to grow as GC instrument manufacturers and laboratories seek greener, more economical workflows. Ongoing developments include:

• Integration of hydrogen-optimized ion sources in future GC/MS instruments.
• Expansion of curated spectral libraries with experimental hydrogen-based spectra and retention indices.
• Use of artificial intelligence for predictive RI values and automated quality checks under variable carrier gases.
• Application to quantitative workflows and coupling with two-dimensional GC and high-resolution MS for complex mixtures.

Conclusion

The conversion of a helium GC/MS method for essential oil profiling to a hydrogen-based protocol with an optimized HydroInert source achieved comparable chromatographic separation, high-fidelity mass spectra and reliable compound identification, while reducing analysis time by 60%. This approach offers a viable alternative to helium, combining cost savings, increased throughput and spectral integrity. It supports laboratories in diverse sectors to transition toward sustainable carrier gas solutions without sacrificing data quality.

References

1. Agilent EI GC/MS Instrument Helium to Hydrogen Carrier Gas Conversion User Guide, 5994-2312EN, 2020.
2. Blumberg, L. M. Method Translation in Gas Chromatography, US Patent 6,634,211 B1, 2002.
3. Sparkman, O. D. NIST 23 Mass Spectral Library Enhancements for Flavor and Fragrance, Separation Science, July 2023.
4. Agilent HydroInert Source Technical Overview, 5994-4889EN, 2022.
5. MassHunter Unknowns Analysis Tutorial, Agilent Technologies, 2023.