Examination of Mass Spectra of Aroma Components in Essential Oils via GC/MS

Importance of the topic

Essential oils are complex mixtures of volatile aroma compounds widely analyzed by gas chromatography mass spectrometry. The growing demand for hydrogen as a carrier gas driven by helium shortages and decarbonisation efforts poses challenges, since conventional ion sources can alter mass spectra and compromise compound identification. Ensuring spectral fidelity when using hydrogen is critical for accurate profiling and library matching in research and quality control.

Objectives and overview of the study

This study evaluated mass spectral changes of key aroma components in 13 essential oils when using hydrogen carrier gas with a conventional ion source versus a HydroInert ion source designed for hydrogen. The aim was to characterise artefacts, elucidate reaction mechanisms, and assess the ability of the HydroInert source to maintain spectral integrity against existing helium based libraries.

Methodology and data analysis

Thirteen commercial essential oils including rose, peppermint, lemongrass and others were analysed by untargeted GC MS using both conventional and HydroInert ion sources with hydrogen carrier. Peak deconvolution and library searching against the NIST 20 database were performed using MassHunter Unknowns Analysis. Retention indices calibrated with n alkanes and refined by AromaOffice2D software were employed to narrow candidate lists and improve identification confidence.

Instrumentation

• Intuvo 9000 gas chromatograph with 5977B mass spectrometer
• DB HeavyWAX column 30 m × 0.25 mm ID, 0.25 µm film thickness
• Split injection 200 to 1, inlet at 250 °C, carrier flow 1.0 mL per min
• Oven ramp from 40 °C to 280 °C at 10 °C per min
• Transfer line at 300 °C, ion source at 300 °C
• HydroInert ion source optimised for hydrogen carrier gas

Main results and discussion

Using the conventional ion source with hydrogen led to significant spectral distortions for 20 to 40 percent of aroma components previously matching above 90 percent with HydroInert. Key affected classes included tertiary terpene alcohols, sesquiterpene alcohols, aldehydes, epoxides and esters. The predominant reaction was dehydration of tertiary alcohols, exemplified by terpinen 4 ol in peppermint being misidentified as its dehydration product. Ring opening of epoxides and other transformations were also observed. In contrast, spectra acquired with the HydroInert source remained consistent with helium based library spectra, preserving diagnostic fragment ions.

Benefits and practical applications

The HydroInert ion source enables laboratories to adopt hydrogen carrier gas for reduced cost and environmental impact without sacrificing identification accuracy. It supports seamless use of existing helium based mass spectral libraries for aroma profiling, flavor research and quality assurance in essential oil analysis.

Future trends and prospective applications

As global helium supplies tighten and sustainability gains priority, hydrogen carrier gas will see wider uptake in GC MS. Innovations in ion source design like HydroInert can be extended to other volatile and trace analyses. Integration with advanced deconvolution algorithms and expanded spectral libraries will further enhance throughput and reliability in complex sample matrices.

Conclusion

Mass spectral fidelity when using hydrogen carrier gas is compromised by conventional ion sources through dehydration and other artefacts. The HydroInert ion source effectively suppresses these reactions, maintaining spectra comparable to helium based analyses and ensuring accurate compound identification.

References

1. Agilent application note publication 5994-5751JAJP Evaluation of odor database via GC MS using HydroInert ion source with hydrogen carrier gas
2. Jakab et al Thermo oxidative decomposition of lime bergamot and cardamom essential oils Journal of Analytical and Applied Pyrolysis 134 2018 552–561
3. Chang et al Thermal degradation of linalool type essential oil and its stabilization by microencapsulation with beta cyclodextrin Molecules 26 2021 409