Preparation of 18O-labelled standards of hydroxy-eicosatetraenoic acids and thromboxanes for quantitative measurement by gas chromatography/mass spectrometry.

A study on the extent of 18O incorporation into various hydroxy-eicosatetraenoic acids, thromboxane B2 and 2,3-dinor-thromboxane B2 by base-catalysed hydrolysis of their methyl ester derivatives is presented. The amount as well as the position of the inbuilt 18O atoms were determined by gas chromatography/mass spectrometry, utilizing electron impact and positive and negative ion chemical ionization.