Quantitative determination of 3-methoxy-4-hydroxy-mandelic acid (VMA) in urine

A relatively simple but specific method is described for the quantitative determination of 3-methoxy-4-hydroxymandelic acid (VMA) in urine. The procedure employs a Dowex-1 anion exchange resin column for removal of VMA from urine. VMA is eluted with 3 N NaCl and oxidized with periodate to vanillin. Quantitation is accomplished by reacting vanillin with an indole-phosphoric acid reagent to yield a colored compound which absorbs maximally at 495 mμ. Urinary VMA excretions for 60 normal subjects were determined by this, method. A mean daily excretion of 5.2 mg with a range of 1.8 to 7.6 mg was obtained. Also studied were 3 patients with surgically confirmed pheochromocytoma. Preoperative VMA values were all elevated, ranging from 17 to 43 mg per day, whereas post-operative values were within the normal range. The influence of various compounds structurally related to VMA was studied with respect to possible interference in the method. Of 44 compounds tested, only p-hydroxymandelic acid interfered but only at levels above that normally present in urine.