Quantitative analysis of fatty acid precursors in marine samples: direct conversion of wax ester alcohols and dimethylacetals to FAMEs.

To apply fatty acid analyses to the study of foraging ecology and diet determination, all compounds that may be deposited as fatty acids in a predator must be quantified in the prey. These compounds include the usual fatty acids in acyl lipids, but also the alcohols of wax esters and the vinyl ethers of plasmalogens. In routine fatty acid analysis, samples are extracted and transesterified (methylated), resulting in the formation of fatty acid methyl esters (FAMEs); however, fatty alcohols and dimethylacetals (DMAs) are also generated if wax esters or plasmalogens are present. Here, we present a new method using a modified Jones' reagent to oxidize these alcohols and DMAs to free fatty acids (FFAs). These FFAs are then easily methylated and quantitatively recombined with FAMEs from the same sample. This generates a fatty acid signature of prey that is equivalent to that which the predator has available for deposition upon digestion of that prey. This method is validated with alcohol and DMA standards. Its application to typical marine samples is also presented, demonstrating the change in effective fatty acid signature after inclusion of fatty acids derived from wax esters and plasmalogens.