a lovely post by Julia Lawless @
http://www.aqua-oleum.co.uk/education_organic
The main method for testing essential oils for their precise chemical make-up is by gas chromatography (GCT). All essential oils & absolutes are volatile which means that they have a tendency to vaporize. Analysis by gas chromatography produces a trace, which shows the order in which the different constituents of an oil vaporize and the quantity of each constituent expressed as a percentage. For example, cineol and terpinen-4-ol in tea tree will always show up in the same place on the time axis of the graph. The trace for good tea tree oil will always show a similar pattern.
Some oils have so many constituents, rose has over 400, that many of them do not even have names but are referred to simply by co-ordinates (time and % quantity) on the trace. Many oils have constituents in common but the proportions differ which is why they have a different odour. This form of analysis is routinely used in the industry in an attempt to remove subjectivity. The large users of essential oils want a guaranteed repeatability so that their products are the same every year.
It was for this reason that the pharmaceutical industry in the UK laid down some standards for commonly used oils which they called B.P. (British Pharmacopeias). For example, eucalyptus, peppermint and clove are still sold in the UK as B.P. quality. However, since these tests were devised, extraction technology has evolved and improved to the extent that modern pure oils do not correspond to the former ‘set standards’. Today there are recipes which are used to make essential oils pass B.P standard tests, and these involve blending them with ‘nature identical’ chemicals. Consequently, many B.P quality oils are typically only 80% essential oil and contrary to what many pharmacists believe, they are very low quality.
However, there are also limitations to GCT’s as an indictor of quality. Although a gas chromatography trace will tell us the quantity of each constituent, it cannot tell us whether the oil is pure or not. For example, if some eucalyptus was also added into the still when tea tree oil is being distilled: the resulting oil will be higher in cineol (quality eucalyptus is at least 80% cineol). An analysis by gas chromatography will tell us how much cineol is in the oil but it will not tell us that the source of some of the cineol was eucalyptus. Spanish rosemary is sometimes distilled with camphorwood, unknown to the consumer, to make a cheaper oil.
Sticky substances (such as many pure absolutes and concretes) are not as volatile as oils and may clog up the equipment. Many providers of GC / MS analysis are reluctant (or refuse) to analyse materials of this type. The situation is made even more complex by the fact that so many of these constituents are available as natural isolates. It is an uncomfortable truth that there is no ‘fool-proof’ reliable test for the purity of essential oils. It is therefore important to always buy essential oils from a reputable supplier who source their products from precise botanical species, and where possible, organically grown plants.
The word ‘organic’ has become a very fashionable term in recent years and a growing number of beauty products are now being produced with organic ingredients. Unfortunately, unlike organic food, there are no legal standards for organic beauty products. So as a result, some companies choose to label a product as 'organic' even if it only contains 1% organic ingredients or if it contains potentially hazardous substances. To safeguard the consumer, the Soil Association provides a certification to products which fulfill their strict organic guidelines.