Lipoxygenase products. A novel gas chromatographic-mass spectrometric assay for monohydroxy fatty acids

We present a novel mass spectrometric method for the profiling of monohydroxy fatty acids and illustrate its use for the analysis of lesional skin of patients with psoriasis. By combination of vapour phase hydrogenation and gas chromatography-mass spectrometry with selected ion monitoring the position of the substituted hydroxyl group of each fatty acid was determined in their methyl ester trimethylsilyl ether derivatives. Reduction was instantaneous and quantitative allowing detection of less than 100 picogram of each compound. Biological extracts, derivatised as methyl ester tert.-butyldimethylsilyl ethers, were purified by reversed-phase high-performance liquid chromatography. Separation was dependent on carbon chain length and degree of unsaturation, but not on the position of the silyl ether group. Subsequent conversion of the tert.-butyldimethylsilyl ethers to trimethylsilyl ethers facilitated detection of each of the positional hydroxyl isomers as described. Distinction between double bond isomers was possible when they were separated on gas chromatography prior to reduction.