You will need to first derivative your sample,e.g methylation.

use the following protocol: column-length 30m,thickness 0.25,inner diameter 0.25. (use either a 5% diphenyl 95% dimethylpolysiloxane or PEG column)

Temperature program: 80oC-8oC/min-300oC,Detector FID 280oC,Injection Tempreture 250oC Injection mode:split

Gas Chromatography can be used to analyze fatty acids in fresh/used/waste oils either as free fatty acids or as fatty acid methyl esters. However fatty acids may be difficult to analyze in their free, underivatized form because these highly polar compounds tend to form hydrogen bonds, leading to adsorption issues. Reducing their polarity may make them more amenable for analysis. Also, to distinguish between the very slight differences exhibited by unsaturated fatty acids, the polar carboxyl functional groups must first be neutralized. This then allows column chemistry to perform separations by boiling point elution, and also by degree of unsaturation, position of unsaturation, and even the cis vs. trans configuration of unsaturation. As such you will need to first derivatize the fatty oil, constituent of the analyte i.e. oil through trans-esterification to get corresponding fatty acid methyl ester (FAME). The esterification of fatty acids to fatty acid methyl esters is performed using an alkylation derivatization reagent. Methyl esters offer excellent stability, and provide quick and quantitative samples for GC analysis. Protocil: Redisolve FAMEs in 100 μl hexane and inject 1 μl volume of sample five times into GC–FID for separation and quantification of the FAMEs. BPX-70 fused silica capillary column (30 M, 0.25 mm i.d., 0.2 μm film thickness, can be used. RUN GC under an optimized temperature programme as: initial column temperature 100 °C, programmed to increase at a rate of 10 °C min−1 up to 160 °C and then at 3 °C min−1 up to 220 °C. Maintain this temperature for 5 min, then at 10 °C min−1 up to final temperature of 260 °C and hold for 5 min. Keep Injector and detector temperatures at 260 °C and 280 °C, respectively. Use Nitrogen or Helium as the carrier gas at a flow rate of 1 ml min−1 with a split ratio of 30:1.

Thank you Doctor YOGESH CHANDRA TRIPATHI, your idea and explanation is good but can u provide me the method because there are some special methods for their analysis or just to prepare FAME by any catalyst and do the analysis

Dear Zahoor

For detailed procedure of FAME preparation and their analysis by GC, pl refer following link and a paper attached.

http://web.vscht.cz/~kohoutkj/ENG/LAB_FAMEs_Determination.pdf

Fatty acid analysis of cooking oils is not a simple thing, and you have to know what type of analysis (how in-depth) you want before you settle on a proceedure. See http://lipidlibrary.aocs.org/frying/frying.html

make esters and then analyse it on GC