Obviously you need to separate and identify. LC-MS, GC-FTIR, LC-FTIR, etc. first come to mind.

I would suggest you to use GC-MS or GC-MS/MS as you have to separate and identify biodiesel. I think using Gas chromatography it would not be easy and accurate, therefore, it is the best option to use gas chromatography tandem mass spectrometry. I am giving you a link in below, I hope it will be useful for you

"GC/MS Analysis of Methyl Esters of Biodiesel Produced from Cotton Seed Oil."

With regards,

Dr. Dalower

Find out in your country if your normalization Institute did not have already a norm about it.

This type of method are already normalize by ISO, EN, ASTM, etc.

In your case I think that ISO 17037:2016 will help you, it establishes a method for determining the total methyl ester content in fatty acid methyl ester (FAME) by gas chromatography and using an external standard. The method is suitable for biodiesel which contains esters between C6 and C26. This method allows verifying that the total ester content is greater than 96,5 % (m/m).

NOTE 1 The method also allows determination of the total ethyl ester content in FAEE, but precision for this has not been established.

This Technical Specification does not determine the linolenic nor the poly-unsaturated alkyl ester content. Alternative techniques, such as EN 14103[1] and EN 15779[2], respectively, are available for this.

NOTE 2 For the purposes of this Technical Specification, the term "% (m/m)" is used to represent the mass fraction, µ.

Best regards

Both are good but is more accurate by GC-MS. For qualitative analysis I mean.

For quantitative determination GC is good enough by determining peak areas. If you have well identified all peaks representing Fame, GC by using FID detector is good enoung.

GC-MS can be considered as more accurate