Aromatherapy: A New Journey
Limitations in using GC/MS
to determine the quality of essential oils
by Hank Friedman
Note: For many of the themes on this page, I have relied heavily on a superb article on the subject by Alexis St-Gelais called "The Highs and Lows of GC-MS in Essential Oil Analysis"
A little bit of history: When I was in Neurochemistry graduate school, I took a course on the analysis of organic compounds using mass spectroscopy(the MS portion of GC/MS). It was the hardest course I've ever taken, and it showed me just how difficult it is to interpret MS graphs.
GC/MS is comprised of Gas Chromatography, which separates the substances in the sample, which are then passed along to the Mass Spectrometer, which breaks them down into smaller molecules and assesses their molecular weight and graphs the result.
GC/MS is excellent for detecting adulterants and contaminants, and for determining chemotypes (what components predominate in an oil). Expensive essential oils like Melissa are often counterfeited, and GC/MS can easily detect such tampering.
GC/MS is often touted as the "holy grail" of essential oil testing, but it has serious limitations that reduce its value considerably:
1. Alterations. Heat sensitive (thermally labile) and less volatile components of oils can be structurally altered, creating artifacts. "often neglected decomposition and rearrangement reactions may occur... due to high injector temperatures and hot and catalytically active liner or column surfaces." On Page 47 of the article
In other words, the process of separating an oil into its components using high temperatures can damage and alter them notably.
2. Misinterpretations. GC/MS analysis can have incorrect hits, i.e. misinterpreting one component for another. "Different compounds will yield quite similar mass spectra."
A prime example are stereoisomers, i.e. molecules that are chemically identical and only differ in their shape. As most aromatherapists know, for instance, S-linalool in coriander and R-linalool in basil are mirror images of the same molecule. Yet their scents and medicinal effects are quite different! And GC/MS is unable to distinguish between them.
3. Unknown substances. GC/MS cannot identify molecules that have not been isolated and cataloged before, and essential oils are very complex, and have many components that are not in any database, and so might be mis-identified or remain unlabeled.
Minor components can be crucial to the scent and therapeutic value of some essential oils and often cannot be properly determined. Vetiver, for example, has many compounds that have never been identified.
4. Variations. Essential oil constituents vary not only with the country of origin, but with the soil, weather, time of year, stage of the plant's cycle (e.g. flowering), sub-type, and many other factors, and so essential oils even from the same location do not have a consistent composition over time.
Just think of the variation in wines or teas from the same farm over different seasons or years.
Therefore there is no reference oil that GC/MS can use to measure other oils against.
Here's an example of the magnitude of the variations for Lemon Balm.
5. Rough measurements. The amount of each component in an oil can only be approximated using GC/MS, i.e. cannot be precisely measured, and can only be assessed if the MS is calibrated for each specific component. (Usually if any calibration takes place, it's for only a few components.)
6. Maintenance. MS detectors require frequent upkeep. "This means that, unless special care is taken to reproduce these parameters and the same calibration, chances are that some results will be skewed" ibid.
7. Oxidation. Many essential oils go rancid (become oxidized) over time. One of the main categories of oxidation products are called peroxides, and GC/MS breaks down peroxides and so can't measure their presence in an oil accurately.
8. Organic/Inorganic.Standard GC/MS cannot detect pesticides (or heavy metals) and therefore cannot distinguish between organic and non-organic oils.
9. Constituents lacking volatility. GC/MS cannot detect non-volatile components of an oil and is therefore of limited value in assessing CO2 extracted or solvent extracted oils.
10. Natural vs. Synthetic. GC/MS cannot even tell whether an oil is natural or synthetic, as they are chemically identical.
11. Nuances. GC/MS cannot evaluate the intangibles like aliveness or quality or therapeutic value the way that an aromatherapist's nose can.
Imagine trying to have a GC/MS detector distinguish between a gourmet hamburger and a Big Mac. It can't. Similarly, GC/MS cannot be used to determine which essential oil sample is of higher quality.
In my studies on the sense of smell, I've discovered that the human nose can detect trillions of different substances. That's one reason why the nose is such a better tool for evaluating essential oils than machines are.
End of Part Ten
(Note: Unlike many websites that "review" essential oils but are actually making a profit by selling oils via affiliations, I have no financial relationship with any aromatherapy company.)
Aromatherapy: A New Journey
Finding the best essential oils
The different methods of extraction
The Essential Oil Company
I didn't want to love
How to evaluate essential oils
A Phenomenally Great Essential Oil Company
Essential Oil Shootouts
and also, my blog on:
The Magical oil called Oud
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