Liquid-chromatographic determination of vanillylmandelic acid in urine

Urinary vanillylmandelic acid (VMA) was determined by "high-performance" liquid chromatography with fluorometric (LC-F) and amperometric (LC-EC) detection. Urine samples were first purified on a small, open-bed, reversed-phase preparatory column. VMA and the internal standard (iso-VMA) were then separated by reversed-phase ion-pair liquid chromatography. Analytical recovery of VMA was high (98.3%, SD 3.3%, n = 8), and concentrations measured by LC-F and LC-EC were in excellent agreement (r = 0.996). The LC-F chromatograms of urine samples had fewer late peaks; however, detection limits were lower (15 vs 120 micrograms/L) for the LC-EC method. Typical concentrations of 1-10 mg/L in urine can be measured easily with either method.