Gas chromatographic-mass spectrometric characterisation of unsaturated dicarboxylic acids in urine.

Drcarboxylic aciduria is a condition sometimes encountered during routine urine screening for inborn errors of metabolism [l] and may be due to ketosrs, a transient condition m some neonates [2] or a number of enzyme deficiencies mainly involving fatty acid metabolism or transport. Unsaturated dicarboxylic acids have also been reported m some of these conditions. These compounds are usually detected using gas chromatography (GC) and/or gas chromatographymass spectrometry (GC-MS). Unfortunately, little information regarding the position of unsaturation in these dicarboxyhc acids IS obtained with these techniques. With non-polar columns, many isomeric unsaturated organic acids will co-elute and may not be adequately separated from other fatty acid metabohtes, usually 3-hydroxydrcarboxylic acids. The mass spectra of the isomeric unsaturated compounds are often very similar and the double bond position is not apparent. Although some detailed structural studies have been undertaken in isolated cases [3-61 there is generally little information available regarding the structure or occurrence of unsaturated dicarboxyhc acrds. This report describes a technique suitable for the identification of unsaturated organic acids in urine and its application to the identification of a series of unsaturated dicarboxylic and 3-hydroxydicarboxylic acids in the urine of subjects with abnormal fatty acid metabolism.