Identification of 9,10-epoxyoctadecanoic acid in human urine using gas chromatography-mass spectrometry

9,10-epoxyoctadecanoic acid has been detected in human urine. Two simple purification procedures were used; the one based upon liquid-liquid extraction and the other based upon sorbent extraction technology isolating the free fatty acid fraction. Prior to trimethylsilylation and gas chromatographic-mass spectrometric analysis, both the epoxy and carboxy functions were reduced to hydroxy groups. The shift in fragmentation of a deuterated sample verified the presence of intact epoxide prior to chemical reduction. Special attention was paid to the risk of false identification of the epoxide. The content of 9,10-epoxyoctadecanoic acid in human urine was estimated to be 2.1 nM/L.