The determination of hypoxanthine and xanthine with a PO2 electrode

A simple and rapid method for determination of the hypoxanthine and xanthine concentration in plasma and urine is described. The method is based on the principle that oxygen is consumed quantitatively when hypoxanthine and xanthine are oxidized to urate by xanthine oxidase. By using Henry's law a direct measure of the hypoxanthine and xanthine concentration is obtained. The method determines these oxypurines in volumes of 200 mul in concentrations less than 5 mumol/liter in about 5 min. The average precision in the range of 0-50 mumol/liter is 2.6 mumol/liter. Of the added hypoxanthine, 99-102% is recovered in plasma. Even though xanthine oxidase is a rather nonspecific enzyme, experiments show that this method is highly specific during physiologic conditions.