Essential Oil Analysis

Gas Chromatography

Good essential oil testing includes analysis of the chemical makeup of an essential oil. This testing is crucial to verify the potency of the oil and the oil’s medicinal quality. Chemical analysis will also reveal when oils have been adulterated by impurities like; synthetic additives, extraction chemicals, pesticides, and other contaminants. Test results should be made publicly available by an oil manufacturer to ensure transparency and trust.

Chemical analysis of essential oils is performed using an instrument called a gas chromatograph, or GC. The analysis creates a ‘chemical fingerprint’ for the essential oil called a test chromatogram. A chromatogram is a type of chart with many sharp vertical spikes or peaks in a row, each peak representing a separate chemical compound present in the essential oil. The height of each peak on the chromatogram is proportional to how much of each compound is present in the oil.

Reference Standard Chromatograms

Each test chromatogram for an essential oil is compared against a reference standard. Reference standards are made using historical samples of essential oil of known quality, potency and purity. These reference standards are like a standard yardstick by which all new batches of essential oil are measured during GC analysis.

Chromatograms By Themselves are Meaningless

It is important to understand that a chromatogram by itself is useless without a known reference standard to compare it to. Without a reference standard, the individual peaks cannot be identified. The individual peaks in the chromatogram must be precisely matched against a reference standard to identify the chemical compound responsible for making each peak. Because some peaks are causes by impurities and adulterants, the use of an accurate reference standard is essential to determine if these peaks are present or not.

The quality of the reference standard is also of vital importance. The relative size of each peak in a chromatogram is a crucial marker of purity and therapeutic effectiveness. The reference standards used to judge a test chromatogram must therefore be of the highest possible quality from the best historic source of the essential oil. For example, if a particular peak on the chromatogram is unnaturally high compared to the reference standard, this usually means that a synthetic source of the compound was artificially spiked into the essential oil. Likewise, if a particular peak is too low, it often indicates a lesser quality source of the oil with less medicinal benefit.

How Chromatograms Work

How chromatograms work - the mixed drink analogy
How chromatograms work - the mixed drink analogy

Let’s use an analogy of a mixed drink to better understand how chromatograms work. Consider a drink, such as a Fuzzy Navel, that has several ingredients mixed together to make a single liquid. To keep things simple, let’s assume that each ingredient we use in this analogy are all single chemical substance (not made from other ingredients).

Once the drink is mixed, there’s no easy way to separate the ingredients again. However, if we use a gas chromatograph (GC), we could separate the ingredients for a small sample of the drink. The GC makes the individual ingredients of the drink separate from each other and they come out of the GC at different times. As each ingredient comes out of the GC, it is recorded on the chromatogram as a sharp peak.

Each peak on the chromatogram represents a different ingredient, and each ingredient always shows up on the chromatogram at the exact same horizontal position, or RRT. If there’s a lot of an ingredient inside the mixed drink, it’s peak will be larger and taller on the chromatogram. The exact identity of each ingredient and how much of each ingredient is in the mixed drink is therefore revealed on the chromatogram.

In our mixed drink, we see that there are 4 main ingredients, with alcohol being the biggest one. The next most concentrated ingredient in the drink is the peach flavoring. The smaller the peak, the less of that ingredients is in the mixed drink. Note that there’s a very small peak for soap residue, which was probably left on the glass after cleaning. Extremely small amounts of residues and impurities can be detected by the GC, even if you can never see of taste them in the mixed drink.

How Essential Oils are Adulterated

Example of a pure essential oil with 1 primary ingredient of constituent
Example of a pure essential oil with 1 main ingredient of constituent

The chromatogram at left shows a pure essential oil with nothing added or taken away, exactly as it should be from its natural source. In this example, the main ingredient or constituent has it’s peak at position of 1.00 on the chromatogram. All of the other smaller peaks on the chromatogram are from the many other natural ingredients found in this particular essential oil. For this example, the main constituent is the active ingredient used to measure the potency of the essential oil.


Example of an isolated or synthetically made artificial constituent
Example of an isolated or synthetically made artificial constituent

The chromatogram shown here represents a sample of an synthetically made or chemically extracted constituent. In this example, the artificial constituent is the same as the main ingredient in the pure essential oil above. Notice that there are two unique impurity compounds in this artificial constituent, left over from the extraction process or from the synthesis process when it was made.



Example of the essential oil spiked with the artificial constituent.
Example of the essential oil spiked with the artificial constituent.

The chromatogram at left is the final essential oil product, after the artificial constituent has been added to artificially increase the concentration of the primary ingredient. The main peak is noticeably larger than in the pure essential oil, which on the surface make the essential oil look more potent and higher quality. However, the two impurity peaks from the artificial constituent are clearly present. The presence of these impurities is proof that an artificial constituent was added to the oil.


The Power of Good Testing

Each artificial ingredient usually has a unique set of impurities that can identify it, just like a fingerprint. When the artificial ingredient is added to an essential oil, these unique impurities often show up as a clear sign of adulteration. Quite often too much of an artificial ingredient is added, producing a main constituent peak on the chromatogram that is unnaturally high and not found in nature. This is another common way that adulteration is identified in GC testing of essential oils.

Of course, to correctly identify artificial ingredients and unnatural levels of ingredients takes the combination of a very experienced technician plus a library of standards to compare results against. For this reason, GC testing by itself is not sufficient to guarantee and essential oil’s quality, potency and its purity.

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