Establishing the purity of an essential oil is of paramount importance when it is to be used in aromatherapy to treat physical or emotional conditions. At best, essential oils that have been adulterated or extended in any way will simply not deliver the health benefits that you expect. At worst, there is the risk of serious skin irritation or sensitisation due to an adverse reaction to the synthetic chemicals that have been used to adulterate the essential oil. Therefore, essential oils are never purchased in bulk by Quinessence until they been subjected to the most rigorous qualitative and quantitative analytical procedures to confirm their purity and authenticity. The practice of oil adulteration has now reached a very high level of sophistication, therefore a wide range meticulous checks must be made to ensure that the purity of every single essential oil has been confirmed.  Qualitative and Quantitative Analysis So what exactly what is the difference between qualitative and quantitative analysis? Put simply, qualitative testing helps to determine exactly what individual constituents are present in an essential oil, and quantitative testing provides information on how much of each component is present.  In the hands of experts, this information can be used to verify that the oil is indeed what it claims to be and originates from the stated country of origin. This is very important because it is well known by experts that for any given essential oil, there are several origins and the quality varies tremendously. Sensory evaluation  The first steps of essential oil testing usually begins with sensory evaluation, since this saves wasting precious time and money on more expensive analytical procedures and can identify inferior oils quickly. The viscosity, colour, clarity and odour of an essential oil can help to identify a poor quality oil right at the outset - provided you know precisely what to look for.  For example, a sample of Rose Otto which appears too mobile at a low temperature is a typical example of an oil which we would immediately regard as very suspicious. Genuine Rose Otto oil congeals at around 16 degrees centigrade because of the natural waxes that are present, therefore if it is still mobile at or below this temperature, it is likely that the oil has been adulterated or 'extended' in some way. Similarly, Geranium oil can be purchased in bulk from a wide range of geographical locations such as Egypt, China, Africa and Reunion at prices that vary considerably. Since Chinese Geranium oil is green and not a golden colour like the Egyptian material, it isn't difficult to spot the difference visually. It is not uncommon for unscrupulous traders to try and pass off one as the other, since at times of market fluctuations the purchase prices vary considerably. Odour evaluation An odour test can also help to determine if an oil is really what it purports to be, since certain adulterants can be identified in this way. Some essential oils such as Lavender are available from several geographical locations, and a trained nose will be able to detect if a so called 'French' Lavender is in fact from another, less desirable (or less expensive) origin. Sensory evaluation is a simple but effective method of identifying clumsily adulterated oils quite quickly, but remains only one of many procedures that must be conducted during the search for purity. Other, more sophisticated methods of analysis must be employed before a clearer picture can be formed of an oils authenticity. Physical parameters If an essential oil sample passes all of the sensory tests, the next stage is to test the physical parameters of the essential oil by means of measuring the Specific Gravity, Optical Rotation and Refractive Index. This is a more searching examination that will confirm or reject the authenticity of an oil’s declared botanical species and country of origin, whilst possibly revealing any adulteration with a foreign substance. The combination of these physical tests is usually sufficient to determine if it is worth proceeding to the final stage of testing an essential oil. If an oil successfully passes the first two stages it is then independently tested by a laboratory using Gas Chromatography/Mass Spectrometry (GC/MS). Gas chromatography When using Gas Chromatography to test an essential oil, a tiny sample of the oil is injected (pictured right) into the apparatus which contains a very thin coiled silica tube called a ‘capillary column’. This capillary column may measure up to 100 metres in length and is coated on the inside with a material that has an affinity to different chemicals at different temperatures.  The column is housed within a temperature regulated oven and is programmed to steadily increase in temperature over a period of time in a very precise manner. When the sample of oil is injected into the column it immediately vaporises, and an inert carrier gas (usually hydrogen or helium) moves the vapour along the column to a detector called a Flame Ionisation Detector which is situated at the end of the column. Component identification The flame ioniser detector responds quantitatively to the vaporised constituents of the oil and converts this information, via an integrator/computer, into proportional peaks printed onto computer listing paper. The height of every ‘peak’ on the graph corresponds proportionally to the level of that component within the oil.  Every individual component of the essential oil can be identified by the time at which the peak elutes on the trace. The data produced can then be compared to an established ‘profile’ or ‘fingerprint’ for that particular essential oil to finally determine the purity of the oil. Adulterants can usually be identified by this means of testing, although it does require the expertise of an organic analytical chemist who is a specialist in this area to fully and accurately interpret the results of the testing. Variations in climatic conditions, and the type of soil in which a plant was grown will produce natural variations in essential oils produced from the same species.	Gas Chromatograph