Colorimetric determination of urinary xanthurenic acid using an oxidative coupling reaction with...

A simple enzymatic method for the spectrophotometric determination of xanthurenic acid (XA) in urine is described. The method is based on the formation of a pigment derived from an oxidative coupling reaction with XA and N,N-diethyl-p-phenylenediamine (DE-PPD) in the presence of hydrogen peroxide and horseradish peroxidase. The color of the reaction mixture was developed with a peak absorbance at 750 nm. The recoveries against XA added to urine ranged from 91.0 to 96.5%. With this method, XA can be determined within 5 min, without a time-consuming sample preparation. The detection range of this method was between 5 and 150 microM, with a coefficient of variation of 2.7% or less. The correlation between this and the fluorometric method was good.