DETERMINATION OF 8-METHYL ETHER OF XANTHURENIC ACID IN HUMAN URINE BYHIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY

We developed a simple and sensitive assay for the urinary 8-methyl eth er of xanthurenic acid (XA-OMe) by high-performance liquid chromatogra phy with fluorescence detection (excitation at 340 nm; emission at 450 nm). Urine samples were diluted with 0.03 M potassium phosphate buffe r (pH 6.0) and applied to an octadecylsilane-bonded column (Nucleosil 5C(18), 150 x 4 mm I.D.). The mobile phase used was a mixture of this same buffer and acetonitrile (1000:140, v/v). Both direct injection of urine and solvent extraction prior to HPLC were tested and showed a g ood correlation and sensitivity, although the peak of XA-OMe was occas ionaly less distinguishable from close peaks in urine from normal cont rols by the direct injection method. The quantification limit was 5.10 (-14) mol which was sensitive enough to detect XA-OMe in urine from no rmal subjects. The method was applied to samples from patients with a deficiency in tryptophan catabolism, xanthurenic acid/3-hydroxykynuren ine-uria and showed a striking elevation in urinary XA-OMe excretion.