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Pure essential oils are subjected to a number of quality tests to establish their chemical composition and to determine their true quality; two of the most popular essential oil quality tests are GC-MS and GLC testing.

It may come as a surprise to some that an essential oil may not hold the therapeutic properties which it is supposed to have.  This is because, in today's world, many essential oils are often adulterated. The chemistry of essential oils is complex and there are number of quality tests which are available to find out if an essential oil is pure or is, in fact, a synthesized aromatherapy oil such as a fragrance oil.

The Chemistry of an Essential Oil

A pure essential oil will, by its very nature, have natural chemical differences between batches of the same essential oil due to a number of factors.  These factors include climate, soil, the country the plant was grown in and the altitude at which the plant was grown before the essential oil was extracted.   However, by quality testing essential oils, it is possible, to some extent, to determine if an essential oil has been tampered with.

Quality Testing of Essential Oils

There are a number of methods to test the quality of an essential oil; essential oil quality tests attempt to determine the components of the essential oil and if any suspicious elements have been added or removed. The quality tests for essential oils include:

–Gas Liquid Chromatography (GLC)
–Mass Spectrometry (GC-MS)
–Optical Rotation
–Infrared Test
–Refractive Index.

Gas Liquid Chromatography (GLC)  Quality Test for Essential Oils

Gas Liquid Chromatography separates the various components of the essential oil and produces a reading (in the form of a chromatogram) which makes it possible to compare to a “standard'” reading of what the essential oil components should be.  The essential oil passes through a long tube (and various “stages” of gas and liquid within the tube) and, on evaporation at the other end, the trace of essential oil is recorded; lighter essential oil molecules will pass through the tube faster than heavy essential oil molecules.

Essential oils are compared to a “standardized” reading for that particular essential oil.  It is only possible to compare essential oils generally to the “standard” reading as all pure essential oils are unique in their chemical make-up; however, certain chemical components should be present (or not present).

Mass Spectrometry Quality Test of Essential Oils

The Mass Spectrometry quality test is a more expensive test for essential oil quality; a gas chromatography-mass spectrometry (GC-MS) is an advanced version of the gas liquid chromatography quality test.  A reputable essential oil supplier should be able to provide the reports of the GC-MS analysis of an essential oil to demonstrate the quality and purity of the essential oils they are supplying.

The mass spectrometer is attached to the gas chromatograph and the emerging essential oil molecules are hit with high energy electrons to separate them. GC-MS testing separates the individual components of the essential oil and allows identification of each chemical component by comparison to the molecular mass spectrum of the essential oil. 

Optical Rotation, Infrared Testing and Refractive Index Quality Tests for Essential Oils

Optical rotation, infrared testing and refractive index quality testing for essential oils are less common methods and more complex, scientific methods of essential oil quality testing; however, it is possible to see signs of adulteration with the infrared quality test if the person is an expert in their field.  Refractive indexing produces consistent results for quality essential oil testing and optical rotation testing produces results which allow the physical characteristics of an essential oil to be recognized. 

Essential Oil Testing

Although it is possible to test essential oils for quality, purity and to try to identify the chemical components, pure essential oils will always vary in their chemical make-up slightly.  An essential oil extracted from a plant one year may be different to the next due to the external influences on the plant.  However, essential oil quality testing is a useful tool in an attempt in trying to eliminate the adulteration of essential oils and the attempts to pass off synthetic aromatherapy oils as pure essential oils.


- Price, Shirley, Price, Len 2002 Aromatherapy for Health Professionals UK: Churchill Livingstone
- Schnaubelt, Kurt 1998 Advanced Aromatherapy: The Science of Essential Oil Therapy USA: Healing Arts Press

This article was written by Sharon Falsetto and appeared in its original format on Suite101 as Essential Oil Quality Testing

It is expressively prohibited to copy or use this article in any way unless written permission is given by the author Sharon Falsetto.  If it is discovered that copyright laws have not been complied with, legal action will be pursued by the author Sharon Falsetto.

CopyrightSharonFalsetto2010 All Rights Reserved
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