Variability and Quality of Essential Oils
The quality available on the market today is extremely variable. There doesn't exist strict regulations and quality control on oils imported and distributed, no regulations as to what a natural essential oil has to be.
More than 95% of the essential oils world-wide, are produced for the flavor, fragrance and toiletry industry. This industry is mainly interested in uniform batches of oil, less in differentiating between natural or synthetic constituents. Local merchants and diverse middlemen in the industry are often tempted to adulterate the oil in order to raise their profit or meet certain market demands.
Adulteration is done for example by mixing of the genuine oils with synthetic derivatives, or with other oils of lesser value. Oils like the Lavender ssp, Eucalyptus and Rosemary are often industrially required to contain a certain stable percentage of a certain compound, and since natural essential oils vary in their composition due to seasonal variations, these oils are adjusted, rectified by adding the desired compound from a synthetic source. Usually what is added is the synthetic equivalent to an oils major compound- such as synthetic linalool and linalyl acetate to a lavender oil. Industry, for example, requires an Eucalyptus oil to contain at least 80% 1.8 cineole. So, what can a producer or merchant do, if this years large production for the world market only contains 78% or even less of this compound? Just discard the entire production, or... rectify the oil.
From the petroleum industry we get today all kinds of synthetic volatile compounds at very low prices. Examples are limonene, nerol, linalool, cineole used in manufacture of soaps, detergents, shampoos, to fragrance tissues, candies etc. To detect synthetic compounds in essential oils is quite difficult. A simple gas chromatogram discerns not between synthetic or natural linalool for example, here chiral separation of the compound is necessary. More about that further down.
There was an interesting report published on bergamot peel oils, where some 53 commercial oils were tested. All of them were labeled 100% natural. However, thorough analysis showed 37 of them to be adulterated (Chiral GC), one was even 100% synthetic (labeled as 100% pure natural essential oil). A simple GC doesn't provide any guarantee. In the case of these bergamot oils, synthetic linalool and its acetate have been added.
Many essential oils are produced in so-called third world countries because of low labor costs. The stills used are in most cases not quite adequate and efficient, just like there exists no control on the use of pesticides and herbicides on the crops.
Another report, investigated 110 different essential oils for the presence of chlorine pesticides. The authors say, that the paucity of reports on pesticide residues in published scientific literature is due exclusively to the fact that detection is difficult because the physical and chemical characteristics are very similar to those of essential oils and present an analytic method (Schilcher and Habenicht 1997).
Organochlorine pesticides (OP's) were unequivocally found in 72 of the 110 samples, i.e. around two thirds of all the samples analysed. In 64 of these the levels were considerably greater than those permitted by the German residue limit ordinance (RHmV 1994).
In 62 samples more than 1 OP was found, alpha- hexachlorocyclohexane, lindane, hexachlorobenzene, alpha-endosulfan, and p,p ' DDE being the most common. Especially noteworthy was the presence of technical hexachlorocyclohexane (HCH) in 66 oils, the permitted limit being exceeded in 56 cases, while one sample contained some 50 times the limit permitted for this substance...
Highly significant also the finding of DDT contamination found in 21 samples. Both DDT and technical HCH are long since prohibited products in many countries. There was a tendency to higher concentration of OP's in oils from developing countries and Eastern Europe. All this is interesting in relation to the fact that OP's are regarded cancerous and especially linked to breast cancer. In Israel, breast cancer rate has fallen by 8% since these pesticides have been prohibited many years ago..
The market today is filled with essential oils called simply thyme oil, lavender oil etc. There exist many different thyme and lavender species with each their characteristic chemical composition. All to often the exact botanical species is not indicated, or the plant part distilled, nor the original origin of the oil.
Essential oils from the same species but of different origin show remarkable variation in their chemical composition. Sometimes these differences are so striking, that we speak of a chemo-type. That is when the main component is different. For example in the oils of thymus we can have a linalool, a carvacrol or a thymol chemotype. Of course each one of them has different therapeutic properties. Also the ratio of the components towards each other can differ significantly. That is why an oil of one origin most likely differs from others of other origins.
From the above, we can see, that the purchase of essential oils- especially when used therapeutically, is mainly a matter of confidence and trust. The close co-operation and communication between producer, merchant and customer is of great importance, and actually the only guaranty we can have on the quality of essential oils.
We label all our oils with the exact botanical species name, place of collection, and the chemotype if necessary. In addition we have analysed most of our oils by gas chromatography (GC) and mass spectroscopy (MS) for chemical composition analysis.
Analysis of Essential Oils
The analysis of essential oils has been greatly simplified in the last 20 years because of new and modern analytical techniques. Before that time chemists sometimes worked a whole life to elucidate a few structures. However, even today the analysis of the essential oil compounds is not a mere press on a button.
High technical equipment is necessary, such as a gas chromatography device, where the quantitative composition of an oil is revealed, and analytical detectors such as a mass spectroscopy detector, in order to identify the compounds separated by the former.
Gas chromatography is carried out by injecting the volatile sample into a thin column, of a certain length, typical around 50 meters. This column is coiled and fixed into an oven, which can be programmed to raise with for example 3°C per minute until the maximum temperature of the column is reached- typically around 240°C. The samples injected in the column are initially volatilised, and travel now through the column. The inside of the column is coated with a certain material, and helium or nitrogen serve as a carrier gas. According to their different volatility and the affinity the single compounds have with the coating material in the column, some compounds elute faster and some later from the column.
To obtain a gas chromatogram of a given essential oil sample, the column is at the outlet connected to a detector, e.g. a Fid (Flame ionisation detector).
Each time a certain compound reaches the detector, it is ionised- burned- and the electrical impulse is recorded.
The recorded data can be printed, and we obtain a chromatogram. This method will tell us how many compounds are found in a specific sample, and what quantitative relation they have towards each other.
But it will not tell us, what the compounds are, even though an experienced chemist can obtain quite some knowledge just by looking at a chromatogram. There also exist so-called retention time indices, retention time meaning, the time a certain compound need under standardised conditions, to elute from the column, these are useful for the comparison and suggestion of the identity of a component.
Simple rules for understanding a chromatogram are for example, that usually compounds with a low boiling point, such as simple monoterpenes will elute first, like the pinenes, myrcene, limonene etc., followed by their oxygenated derivatives, then the simple sesquiterpene hydrocarbons, followed by their oxygenated derivatives, and finally phenolic compounds, which have a high boiling point.
In order to positively identify a certain compound, other, more advanced detectors are needed, for example a mass spectroscopy detector.
Here each compound eluting is bombarded in the mass detector, braking it up into molecular ions and fragments. Since each compound has a specific arrangement of atoms, we can reconstruct its chemical structure from the fragments. Today usually a mass spectrometer is equipped with a 'library' of known compounds, with which the spectrums obtained are compared.
On of the most used libraries is the Wiley library which contains 140 000 known structures.
To analyse an essential oil and to identify its components is still a time and resource consuming procedure.
Concerning the detection of falsifications in essential oils by the use of Gas Chromatography/Mass Spectroscopy (GC/MS), we can obtain information on the adulteration of any given oil with an oil of different botanical origin, as the adulteration of bitter orange peel oil with sweet orange peel oil, or of cinnamon bark with cinnamon leaf oil. We can detect abnormal percentages of certain key compounds as indicators for an adulteration, and for some oils, studies have been done on the ratio of different compounds towards each other in the determination of the genuiness of the essential oil. Also the geographical origin can be verified. These detections, however, require excessive literature searches and careful interpretation of the obtained results by experienced analysts.
However, today falsifications of larger economic value oils have somehow co-advanced with the analytical techniques, and the detection of added synthetic major compounds as long as they do not occur in abnormal percentages or ratios, is still difficult. Most synthetic compounds, however, vary in their isomeric ratios from natural compounds. A new method, chiral chromatography (use of columns with a packing of a cyclodextrin derivative) is currently under investigation. By this method it is possible to separate the chiral isomers, and determine the ratios. In some natural oils, for example bergamot and rosewood only one linalool enantiomer (R-form) occurs, and the detection of the other (S-form) subsequently indicates adulteration with the synthetic equivalent which is a racemic mixture.
But the best, cheapest and surest guarantee is always to be in close contact with the producer, avoid all, or as many as possible middlemen. The purchase of essential oils- especially when used therapeutically, is mainly a matter of confidence and trust. The close co-operation and communication between producer, merchant and customer is of great importance, and actually the only guaranty we can have on the quality of essential oils.