Which detector do you use?

For MS detection you should use external calibration for each FAME and for FID detection there is a correlation between C-atoms and signal intensity, hence the use of your internal standard can be sufficient.

yes,, you can use internal standard, but depend of king sample because if serum plasm is not posible 

I agree with Etienne up to a point.  The FAME reaction MAY not be quantitative, so you will only get a fingerprint.  But this depends on your sample matrix and its complexity.  Your best bet is to include a CRM (certified reference material with a known fatty acid composition) in each run, which is close in complexity to your samples.

It is a common analysis.  See articles below.

https://www.nrel.gov/bioenergy/microalgae-analysis.html

http://journal.frontiersin.org/article/10.3389/fenrg.2015.00015/full

i agree with Bruce Neagle

Dear 

As mentioned by Bruce and Etienne you should get standard if FANE and I inject it to your GC/MS . And then define each fatty acids by retention time and after you put your samples and you define them. This qualitative analysis.

For quantitative analysis you should make different standard with different concentrations and draw the standard curve and then put your samples to measure it.

For internal standard it's only to check as mentioned by Etienne.

Regards

thank you all for your answers and advises.