The separation efect depends on the type of stationary phase.

On non polar column the elution order according to their boiling point is generally obtained. If you use polar stationary phase changes in retention take place - depending on the number and position of double bonds.

best regards,

G

PS if you post something you should give a list of all parameters of your method otherwise we're guessing/assuming a lot of conditions.

I agree with Grzegorz. On a non-polar column the elution order is roughly according to their boiling point (which for straight chain, saturated acids is generally determined by the chain length) with longer acids having higher boiling points. However separation does not only depend on volatility but on a physical affinity between the stationary phase in your column and the fatty acids (or any other analytes). This means that different isomers - branched-chain, unsaturated, hydroxy etc. - will behave differently, often because the physical shape of the molecule is different which changes how easily it 'sticks' to the stationary phase. This is true for all types of stationary phase which is why it's so important to get the right one for your analytes and/or derivatise your analytes appropriately. For FAMES for example, on a non-polar column, most (not all) of the unsaturated acids will elute before the saturated acids. On a polar column, most elute after the saturated acids. This is due to the differing affinities between the FAMES and the different stationary phases, not to the volatility as unsaturated acids are generally more volatile than saturated acids. See the link below for more information.

http://lipidlibrary.aocs.org/Analysis/content.cfm?ItemNumber=40379

for FAMES the expected elution order of fatty acids are from short to branched long carbon chain and so you can order from short carbon to longest chain. for the degree of saturation and unsaturation you can use Proportion (mg/100 g), SFA, MUFA, PUFA and UFA:SFA. for further check please read this article

Melese Temesgen., et al. “Chicken Amino Acid and Fatty Acid: Effect of Feeding Taro Leaf in the Diet”. Acta Scientific Nutritional Health 2.1 (2018):

12-18.

the GC-MS result is from short chain carbon to long chains. so the chain elongation is also depending on the degree of volatility and the final result tell you the class of fatty acids basically obtained after FAME and just use two ways to explain

1, absolute concentration or relative concentration calculation.