The oils were obtained from soft-gel capsules of evening
primrose oil, flax seed oil, black currant oil, and borage oil. The
fats were initially in the form of triglycerides. They were
saponified into their free acids and esterified for better volatility
and inertness by GC. To do this, 5mL of hexane and 250μL of
2N KOH were added to 0.24g oil. The mixture was shaken for
2 minutes in a closed 20mL vial. After settling, the supernatant
was injected.