AN IMPROVED COLOR REAGENT FOR THE SERUM URATE DETERMINATION

An improved procedure for preparation of the final stage reagent containing 3,5-dichloro-2-hydroxybenzenesulfonic acid/4-aminoantipyrine chromogenic system, for enzymatic assay of urate in human serum is described. The improvement was achieved in preparing a very stable aqueous reagent solution with the chromogen which was dispersed in micellar form by the use of ethylene glycol and stabilized in HEPES buffer, pH 7.5. Ethylene glycol was found to possess many advantages over Triton X-100 which had originally been used to dissolve the chromogen. Apart from the improved stability of the reagent from 1 to 30 days, ethylene glycol does not affect the chromogen oxidation, and consequently does not increase the reagent blank. The data on the test linearity, reproducibility and accuracy of the modified procedure were similar to those of the original procedure. It was also found that the incubation temperature of 25-degrees-C was preferable to 37-degrees-C since the color intensity at the end of the reaction is on the average over 10% higher in favour of the lower temperature.