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GC-MS and GC-FID Test Results: How to Understand and Use Them

What is GC-MS and GC-FID Testing?

GC-MS stands for Gas Chromatography and Mass Spectrometry. GC-FID stands for Gas Chromatography and Flame Ionization Detection. Labs that specialize in essential oil analysis combine Gas Chromatography with either Mass Spectrometry (the "MS" in GC-MS) and/or Flame Ionization Detection (the "FID" in GC-FID). There are technical differences and pros as well as cons with both Mass Spectrometry and Flame Ionization Detection.

To keep things as simple as possible in this guide, I won't go through the technical differences between each method. Both methods are considered to be reliable testing methods for essential oils provided that the lab conducting the testing is well experienced in testing essential oils.

Gas Chromatography is responsible for the actual seperation of the different constituents present in the essential oil.

Mass Spectrometry or Flame Ionization Detection is then used to identify and quantify the components that were separated out by Gas Chromatography.

The report, whether it is a GC-MS or a GC-FID report, typically includes a chromatogram (a graph with peaks and valleys). Generally speaking, each peak represents a different constituent (aromatic molecule) present in the essential oil. The size and position of each peak gives indication to the amount of the constituent present in the essential oil.

The chromatograms, on their own, are generally impossible for a typical person to interpret. Please be leery if you ask for a GC-MS / GC-FID report from a company and they only provide you with a chromatogram.

A complete GC-MS or GC-FID report also includes a detailed table that lists each component present in the essential oil and the percentage of the component present in the essential oil.

It's not uncommon for some essential oil GC-MS or GC-FID reports to show some components as being "unidentified." Vetiver, for example, has numerous constituents that are still unidentified.

Why are GC-MS and GC-FID Tests Conducted?

GC-MS and GC-FID testing results in a report that is useful in assessing the purity and composition of an essential oil.

GC-MS and GC-FID testing is also conducted for countless other substances, but for the purpose of this guide, I am only addressing the topic of essential oil testing.

The data collected during GC-MS or GC-FID testing can be used to compare the specific constituents and their percentages to those of a trusted known sample that possesses reliable purity and is of the optimal quality for the specific plant.

Gas Chromatography - Mass Spectrometry (GC-MS) and Gas Chromatography - Flame Ionization Detector (GC-FID) results are used in a multitude of ways including the following:

  • Reassuring customers of the purity and composition of the essential oil and allowing customers to determine if the composition of the essential oil is suitable for their needs.
  • For reputable vendors and manufacturers that have oils tested to ensure they are purchasing quality oils, the tests can reveal unusual levels of particular constituents that can flag that the oil is of inferior quality or has been adulterated.
  • Distillers often test their oils to compare them with previous distillations. This helps them assess quality between harvests and distillations.
  • If the GC-MS / GC-FID results determine that the oil contains an unsuitable level of certain constituents, some unscrupulous distillers/producers may adulterate the oil so that the oil appears to be of higher quality.
  • Manufacturers in other industries such as in the personal fragrancing and food/beverage industries where purity is not a concern use the results to identify whether the levels of key constituents are suitable and if not, they may use the GC-MS / GC-FID reports to potentially alter the oil until the constituent ratios are satisfactory.

How to Begin Using and Understanding GC-MS and GC-FID Reports

Taking a formal aromatherapy course or a course in essential oil chemistry is important to optimally learn what to look for and how to get the most out of GC-MS and GC-FID reports.

However, you can begin getting acquainted with GC-MS and GC-FID reports by making it a habit of reviewing, studying and comparing the reports from different essential oil vendors.

A growing number of essential oil companies are making many/most of their GC-MS / GC-FID reports readily available through each of their essential oil product detail website pages. If a company that you are interested in doesn't automatically offer their GC-MS / GC-FID reports on their website, you can try contacting the company to request the reports.

GC-MS / GC-FID report are especially helpful when used to verify that the key constituents present in an essential oil fall within the percentages that are considered normal or ideal for the particular essential oil.

Essential Oil Safety Edition 2 by Robert Tisserand and Rodney Young includes safety profiles for an extensive number of essential oils. Each profile includes a list of the key components with the typical percentages that are usually present in the essential oil. There are other sources for finding key constituent data, but Essential Oil Safety Edition 2 is an extensive single resource that also informs you of what components to be especially careful of in an essential oil and what the usage maximum recommendations are based on the content of certain components.

The more that you review GC-MS / GC-FID reports and the more that you work towards learning about essential oil chemistry, the more beneficial the reports will be to you.


This topic consists of several separate related articles. Use the links shown below to navigate through the series.

Next: Part 8: Organoleptic Testing of Essential Oils

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