The GC-MS (gas chromatography – mass spectrometer) is two machines/instruments that are attached to give the ultimate results of identifying an essential oil. Less than one drop of an essential oil is required to find results of a genuine or an adulterated oil.
Once the small droplet of essential oil is in the instrument, it is vaporized and is forced into and long, flexible column that is 60 meters long. The thickness of the column is .25 micrometers and it is so tiny that individual molecules need to be pushed through one at a time with the help of helium gas.
The instrument starts at 40C (104F) and ends at 310C (590F) making the GCMS a scientific oven. The molecules are able to further separate the heat and by bouncing in and off the thin coating of polymer in the column.
Source: Dr Cole Woolley PhD, August 18, 2015
The GCMS signal is a continuous trace within the time vs abundance axis. When no molecules are being detected by the GCMS, the GCMS trace is at the bottom – we call it the “baseline”.
When a molecule is separated in the 60m column and detected by the GCMS instrument, the GCMS trace rises until it reaches a “peak” (level of highest abundance for the molecule group), then drops back to the baseline indicating the molecule has passed through the mass spectral detector.
Each “peak” represents one (sometimes two or more) molecule. Each molecule possesses its own aroma and biological activity. So when you look at the chromatogram you can count the number of molecular components within the essential oils.
In general, the higher the peak the higher the percentage of that molecule in the essential oil. Some peaks pass beyond the displayed abundance range in the chromatogram.
In addition, such abundant peaks are wider so they continue for more time than molecules of lower abundance. These wide, tall peaks represent the molecules with the highest abundance in the essential oil.
Source: Dr Cole Wooley, PhD, May 15, 2015
The Light Notes are composed of the lighter Monoterpene components of the essential oil. The Monoterpenes do not mix with water or hydrosol. Monoterpenes help the molecules from the Medium and Heavy Notes flow through the plant. When a drop of essential oil is placed on the skin, the Monoterpenes act as “skin penetration enhancers” to move the Medium and Heavy Notes into the skin. The majority of the Monoterpenes evaporate from the skin surface – these are the main molecules that you smell during the first 1-5 minutes. These volatile molecules create a “personal aroma cloud”. After an hour, the Monoterpenes are either in the skin or in the air around you.
The Medium Notes are the Oxygenated Monoterpenes – they have at least one oxygen atom added to the Monoterpenes or similar sized molecules. The Oxygenated Monoterpenes are divided into the organic structure classes: ketones, aldehydes, alcohols, diols, oxides, organic acids, and esters. These components are some of the most “sweet, floral, tasty” aromas in essential oils. The Medium Notes linger on your skin and in the air for hours.
The Heavy Notes are the prize molecules of essential oils – they are the most bioactive molecules. Heavy Notes are composed to larger Sesquiterpenes, Oxygenated Sesquiterpenes, and Diterpenes.
The Heavy Notes are the aromas that last and last and last! When you put a drop of essential oil on your skin, the Heavy Notes are the molecules you can smell after one hour! You may still be able to detect their aroma after 24 hours. Sesquiterpenes usually have a “woody, earthy” aroma. The aroma of each essential oil is a combination of Light, Medium, and Heavy Notes – a combination of the aromas of each molecule
Source: Dr Cole Wooley, PhD, May 16, 2015
Chemistry of Aromatic Notes
As an example, I listed some of the Light Note, Medium Note, and Heavy Note molecules detected by GCMS in Sacred Frankincense essential oil.
Note that the names of the Monoterpenes end in “-ene”. The Medium Note Oxygenated Monoterpenes endings signify their organic classes:
- Aldehydes – “-al or aldehyde”
- Ketones – “-one or ketone”
- Alcohols – “-ol or alcohol”
- Diols – “-diol”
- Oxides – “-oxide”
- Esters – “-ate”
This just gives you an idea about organic nomenclature. Later I’ll share the properties of these classes of Oxygenated Monoterpenes.
Finally, we get to the Heavy Notes. The Sesquiterpenes also contain the ending “-ene” (even though they are larger molecules. The Oxygenated Sesquiterpenes have similar endings as the Oxygenated Sesquiterpenes. The Diterpenes usually end in “-ene”.
Wow, that’s a lot of chemistry!
Source: Dr. Cole Wooley, PhD, May 18, 2015
Above is the GCMS total ion chromatograms of Young Living Peppermint. Let’s look at our examples of Young Living essential oils. The most abundant component of Young Living Peppermint is the molecule menthol depicted as a tall, wide peak at about 19 minutes in the chromatogram.
The molecule with the second highest abundance is menthone (the peppermint plant converts menthone into menthol) which is located at 18 minutes in the Peppermint chromatogram.
The third most abundant molecule in Peppermint is 1,8-cineole (also known as eucalyptol) locate at 14 minutes in the chromatogram. This peak is “split” designating two components – 1,8-cineole is the first, taller peak, while limonene is the second, shorter peak.
The fourth most abundant component of Peppermint essential oil is menthyl acetate located at nearly 23 minutes in the total ion chromatogram.
Source: Dr Cole Wooley, May 19, 2015
Monoterpenes (light notes), Oxygenated Monoterpenes (medium notes), and Sesquiterpenes (heavy notes) of Sacred Frankincense Essential Oil
beta-myrcene, alpha-thujene, alpha-pinene, camphene, sabinene, beta-pinene, myrcene, alpha-phellandrene, p-cymene, limonene, cis-beta-ocimene, terpinolene, psuedolimonene, cis-4-carene, delta-3-carene, neo-allo-ocimene, perillene,
eucalyptol, fencholenic aldehyde, beta-linalool, , myrcenol, octanyl acetate, limonene oxide, trans-pinocarviol, pinocampone, alpha-phellandrene-8-ol, borneol, terpinen-4-ol, myrtenol, verbenone, cis-piperitol, carveol, cis-geraniol, cuminaldehyde, carvone, carvotanacetone, piperitone, linalyl formate,
delta-elemene, alpha-cubebene, alpha-copaene, alpha-muurolene, alpha-ylangene, alpha-bourbonene, sativene, alpha-gurjunene, gamma-guaiene, aristolene, beta-copaene, tamariscene, isoledene, alpha-humulene, allo-aromadendrene, gamma-muurolene, d-germacrene, beta-selinene, delta-amorphene…
230 components in Sacred Frankincense identified by GCMS
Source: Dr Cole Wooley, May 21, 2015
Peaks in a GCMS Total Ion Chromatogram are Molecules Peppermint Essential Oil-2
While the USA was the major grower of peppermint, India is where nearly 80% of the world’s supply of peppermint is grown and distilled.
The growing region has a small effect on the components in peppermint essential oil. The GCMS can detect these small variances.
The remaining components that constitute the complex Peppermint essential oil are represented by shorter peaks – all being in lower abundance than menthyl acetate.
When you look close to the “baseline” you may be able to see numerous small peaks, we call this collection of molecules the “grass” – because it looks like grass growing on a flat lawn. There are approximately 30 major peaks in the chromatogram, with an additional 80-90 small peaks in the “grass”.
Let me illustrate in other terms what a GC-MS chromatogram can be compared to. I think of essential oils like a movie with many lead actors, supporting actors, and background actors (extras).
Every actor plays a valuable role in the movie, while only 20-30 of them have speaking parts. The lead actors have the highest number of speaking and camera moments, while the supporting actors also have speaking parts and appear often, but are not the main focus of the story. The background actors (extras) usually have no speaking parts, but their appearance in the movie makes it real, (Check out the picture of the movie scene from 7 brides for 7 brothers, wouldn’t the movie be different without the background characters or the main characters).
Take out the background actors and you will have an “unrealistic” movie. Whether essential oil components are the 20-30 major peaks or are minor components (80-90) in the “grass” of a chromatogram, each component adds aroma and bio activity to the essential oil.
Source: Dr Cole Wooley, May 21, 2015