Essential Oil Quality
Essential Oil Purity and Analytical Testing
When essential oils are used for health or therapeutic purposes, it is imperative that they are pure and of high-quality. At best, using adulterated or poor-quality essential oils may result in no therapeutic benefit, and at worst, may result in unexpected toxic reactions.
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Essential oils are complex mixtures of many different chemical constituents. The composition of a given oil can be affected by every step in production, including growing and harvesting conditions, distillation technique, essential oil handling and storage conditions. In addition, some unscrupulous distillers or sellers alter essential oils by diluting, cutting, or extending them, and then sell them as “pure.”
Even those oils that are produced and handled carefully will change over time as they age. Some oils, such as rose, patchouli, spikenard, and myrrh, improve as they age, but others, notably the citrus oils, oxidize and can become irritating and toxic with age.
Given all of these factors, it can be extremely difficult to ensure the quality of an essential oil, because it may have passed through many hands before it reaches the consumer. There are a few techniques for analyzing essential oil composition and purity, but bear in mind that there is no technique available which can analyze an oil so thoroughly as to absolutely guarantee its composition and purity.
Gas Chromatography / Mass Spectroscopy (GC/MS)
GC/MS is the most frequently used technique for analyzing essential oil composition. This method of testing requires an analytical component, a gas chromatograph, coupled with a detection component, a mass spectrometer.
A small sample of an essential oil is introduced into the GC, where it is heated to vapor and then carried along a column by an inert gas, such as helium. As the vaporized oil passes through the column, it separates into individual molecular constituents as it interacts with the stationary phase of the column. The separated constituents then pass into the MS. In the MS module, the constituents become charged, or ionized. The ionized constituents are then amplified and detected as current by the MS.
Each constituent is represented by a peak in a chromatograph, and the peaks can be compared to a library of molecules to identify the substance. Even though a GC/MS can produce a “fingerprint” of an oil, it can not detect some synthetic and natural diluents. It can, however, detect a mixture of two or more similar oils, an oil that has had the terpenes removed, an oil that has been rectified, and traces of solvents or mineral oils.
High Performance Liquid Chromatography (HPLC)
HPLC is another technique that may be used to analyze essential oils. HPLC may be used to separate an essential oil into fractions, as preparation for analysis by another technique. It can also be used by itself to analyze the non-volatile fractions of the essential oil.
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In liquid chromatography, a liquid solvent carries the essential oil through a column packed with tiny particles of a solid, stationary phase. The different components in the essential oil slow down and separate as they pass through the stationary phase, and each component is detected as a peak in the chromatograph.
What Consumers Can Do
Before purchasing essential oils from any seller, it’s wise to look into the seller’s background and practices. Ask questions, such as:
~ How do you ensure correct botanical sources of your essential oils?
~
Do you have your essential oils analyzed by an independent testing lab?
~
How do you store your essential oils before they are sold?
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Spend time developing familiarity with essential oils and learning to differentiate between natural essential oils and synthetic fragrance oils. Put one drop of an oil on a perfume test strip, a cotton swab, or a scrap of paper towel, and smell it periodically as it dries. An essential oil aroma is generally somewhat complex, and the aroma changes and develops as the essential oil evaporates.
Learn the top, middle, and base (dryout) notes for essential oils as a way to help differentiate an essential oil from a synthetic substitute. Though many essential oils will leave a discolored residue or stain on the dried test strip, a pure and undiluted essential oil should not leave an oily or greasy spot on the strip.
