Spectrophotometric assay of xanthine oxidase with 2,2'-azino-di(3-ethylbenzthiazoline-6-sulphonate) (ABTS) as chromogen.

A new method for the determination of xanthine oxidase activity, based on the oxidation of 2,2'-azino-di(3-ethylbenzthiazoline-6-sulphonate) (ABTS) by use of uricase and peroxidase, is described. The absorbance increase of the oxidized form of ABTS, measured after 10 min at 410 nm is proportional to xanthine oxidase activity. The method is sensitive, precise (CV below 8.3%), and linear up to 20 U/l. The analytical recovery of the ABTS-method was quantitative. Comparison with the UV and colorimetric NBT-method gave good correlation (r greater than or equal to 0.984). Reference values for serum xanthine oxidase activities determined with the new ABTS-method on 83 healthy persons are 0 to 1.20 U/l.