1.) Best if you buy straight from the grower and/or distiller.

2.) Have a great nose for the oils you purchase.

3.) Do a GC-Ms (gas chromatography mass spectrum) cross referenced with your own retention library, with other chemical libraries, with published data on the specific oil on a period of years from various sources, chemotypes and origins.

4.) Run as many known origin - distillation samples as possible to judge against.

5.) Look for the ratio % of a number of chemicals within the oil, including very small peak chemicals and look for the chemicals that shouldn't be there and should be there.

6.) If you are using a split less injection with Pentane, Acetone or Ethanol carrier in the test sample to increase column life (acetone doesn't help column life) you must do a Head Space Analysis ( heat vile of pure oil and vapors get vacuumed into the GC-Ms.)

7.) If after all this you even slightly suspect adulteration, synthetic or not, put sample in suspect archive and don't waste any more time. Make a note of who sent you the sample and watch them carefully. They may or may not have done this intentionally.

Or get to know me and my company and realize all these things have already been done for you.

Whew!