Reading GCMS

Reprinted with permission from Harvest to Hydrosol

Reading the GC/MS Report

First we need to have analyses, and then we need to learn how to read them. Most aromatherapists have a general understanding of how to read a GC/MS report of an essential oil. However, you must understand that reading the GC/MS report of a hydrosol is not the same as reading that of an essential oil. GC/MS is an abbreviation for Gas Chromatography–Mass Spectrometry. Currently the GC/MS is our least expensive analysis to measure the percentage of volatile components in a hydrosol.
Let’s start with a GC/MS report of an essential oil. It only takes one extraction to analyze an essential oil because it is 100% volatile. In simple terms, the MS—or Mass Spectrometry—is the part of the analysis that identifies or names the peaks of the GC—Gas Chromatography. These components are listed as percentages of the sample. The percentages are of the entire sample. So, if an essential oil lists 4.65% nerol, it means that the nerol accounts for 4.65% of the entire essential oil sample, whether it is 1ml or 30 ml in quantity.
A GC/MS report of a hydrosol differs from the GC/MS report of an essential oil because it identifies a percentage of the volatiles, which are a fraction of a percent of the hydrosol. Hydrosols contain only a small percentage of volatile components; less than 1% of a hydrosol solution is volatile. The chemist must first extract the volatile components from the aqueous, non-volatile sample. He then runs that sample for analysis. Therefore it takes two extractions for one hydrosol analysis. This is one of the reasons that a hydrosol is more expensive to analyze than an essential oil and less accurate.
A good hydrosol GC/MS report will list the percentage of volatile components in a hydrosol. This percentage can then be converted into a measurement of mg/L; mg/L (milligrams/Liter) is essentially the same as ppm (parts per million). A milligram is 1/1,000,000 th of a liter of water. If a hydrosol report indicates that the hydrosol contains 0.1% (1/10th of a percent) essential oil that is equal to 1000 mg/L. A hydrosol that has 1000 mg/liter is a highly saturated hydrosol; most run less than 0.05% (5/100th of 1%).
After the chemist has run the analysis, the GC/MS report looks almost identical to that of an essential oil. The difference now is that if the analysis says the hydrosol contains 4.65% nerol, and the hydrosol had 1000 mg/L of volatiles, it has 4.65% of 1/10 of a percent of the hydrosol or 0.00465%!
To understand my hydrosol GC/MS report more clearly, I find it easier to convert the component’s percentages to mg/L (ppm) or to a percentage of the entire hydrosol. I use a spreadsheet to easily convert to ppm and percentage of the entire hydrosol.

To convert the percentage of a component to mg/L (ppm) of entire hydrosol, you would follow these steps:
{Formula: P(ppm)= mg/L of volatiles x P(%) of component}
1. Take the total mg/L of essential oil (for this example I am using 1000 mg/L)
2. Multiply the total mg/L of volatiles by the percentage (4.65%) of component
(1000 x 4.65%) = 46.5 mg/L(ppm)


The next time you read a GC/MS report of a hydrosol, try to understand the miniscule amount of individual named components. Perhaps this is one of the reasons why hydrosols are so gentle.
Not all labs are qualified to analyze essential oils and hydrosols. There is something called the library which is a reference library that identifies the peaks of the GC. A chemist’s ability to name the peaks of the GC is only as good as his library. The price range of these analyses is quite broad and you don’t always get what you pay for. I have seen analyses that cost $300 and only named a few peaks. Another lab charged $90 and had named over 100 peaks. It is imperative that you find a lab who specializes in essential oils. The field is narrowed even further when you search for a lab that will analyze hydrosols. Remember you are analyzing a small percent of volatile components in a large solution of non-volatile components. It is a tedious process and much more time consuming than analyzing essential oils.

Comments are closed.