you can detect that by using GC-Ms (gas chromatography - mass spectroscopy ) or even GC

Essential oils are generally volatile in nature that give fragrance or smell to the product. It can be quantified by simple hydrodistillation using clevenger apparatus. Chemoprofile of oil can be assessed by using GCMS or HPLC.

LCMS... C4 column

if you will use clevenger ,must detected sample amount as kg or gr and you can measure that obtained essentiol oil then you can calculated as percent.

Steam distillation followed by GS.MS analysis will give good results

You can extract oil by different solvents (hexane or chloroform: methanol, acetone) using soxhlet. and you can detect and identify by preparing FAME and analyze by GC-MS.

USING DISTILLATION METHOD.......