Determination of trans-arachidonic acid isomers in human blood plasma.

Endogenous trans fatty acids originate from diet, but recent studies also suggest that cis-trans isomerization of fatty acids is possible by nitrogen dioxide radical, a product of NO and nitrite oxidation. We developed a method for quantitative analysis of four trans-arachidonic acids (TAA) in human plasma using isotopic dilution gas chromatography/mass spectrometry (GC/MS) with deuterium-labeled internal standard. Esterification of the plasma fatty acid extract with pentafluorobenzyl (PFB) bromide followed by high-performance liquid chromatography purification yielded a fairly pure fraction containing TAA-PFB esters that was analyzed by GC/MS.