You can use solid phase extraction with C18 tube and eluation of organic compounds with methanol. SPE is the best procedure for extracting  organic compounds from water samples.

It is not clear what FA is?

Dear Soleya,

I am currently working on ethanol extract as well as water extract samples.My compound of interest are the fatty acids and sterol. I managed to detect in my ethanol samples but not yet on the latter sample. Thank you for your recommendation

You could use solid phase micro extraction and inject directly.

I think that the perfect solvents for dissolving fatty Acid are petroleum ether and n-hexane

I hope that good

Article Healthy cookies from cooked fish bones

Use n-hexane for extraction. Remove n-hexane. Apply esterification procedure using methanolic KOH and analyze using GC-FID.