Determination of oxalate in urine using oxalate oxidase: comparison with oxalate decarboxylase.

The oxalate content of urine is determined by means of oxalate oxidase and simple pH measurement. The enzyme specifically decarboxylates oxalate, producing two moles CO2 per mole oxalate. The CO2 diffuses into an alkaline buffer solution (Hallson, P. C. & Rose, G. A. (1974), Clin. Chim. Acta 55, 29--39) in the closed reaction vessel, and reduces the pH value, which is measured with an electrode. Only 125 microliter native urine is required to measure oxalate concentrations in the range of 80 mumol/l to 1.6 mmol/l (corresponding to 7 to 144 mg anhydrous oxalic acid per liter). The limit of detection is 10 nmol oxalate, and the accuracy is 101% with a coefficient of variation of 6%. The method described is insensitive to various interfering factors, such as reducing and oxidizing substances, cloudy or colored samples. It is therefore also suitable for oxalate determination in food technology and plant breeding.