Development of analytical methods for the detection and determination of kynurenic and xanthurenic acids

A survey was carried out on the techniques developed by numerous research workers in this important field since Liebig discovered the presence of kynurenic acid in the urine of dogs fed on meat and Musajo that of xanthurenic acid in the urine of rats on a fibrin diet. The survey starts with the old methods of assay by precipitation of kynurenic acid and goes on to include the more recent ones of colorimetric assay of xanthurenic acid with ferrous sulphate or ferric chloride and of kynurenic acid by means of transformation into a chloro-derivative of the type of Besthorn dyes. Chromatographic techniques including paper chromatography, thin-layer chromatography, column chromatography nad gas chromatography, enabled researchers to detect the slightest traces of the two quinolincarbonic acids in the biological fluids together with the other metabolites of tryptophan. Among the techniques adopted for this purpose electrophoresis, automatic analyzers, polarography and, finally, the use of labelled substances, in particular L-tryptophan-3-C14, are included.