Abstract: An improved immunoassay method, reagent means, test kit, and test device for determining an iodothyronine, e.g., thyroxine (T-4), in a biological fluid, usually serum or plasma, wherein 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid (HMS), or a salt thereof, is employed as a blocking agent for the binding of iodothyronines to thyroxine binding protein (TBP). The present invention is particularly advantageous as applied to homogeneous competitive binding iodothyronine immunoassays employing labels which are participants in enzyme-catalyzed reactions. Such labels include enzyme substrates, coenzymes, enzyme inhibitors, enzyme prosthetic groups, and enzymes.

Abstract: An apoglucose oxidase preparation having a residual glucose oxidase activity of less than 0.05%, and preferably less than 0.005%. The preparation is obtained by incubation of glucose oxidase in aqueous solution at a pH of less than about 2 and in the presence of about 20 to about 40, preferably about 30, percent by volume glycerol, and separating resulting dissociated prosthetic group, flavin adenine dinucleotide, from apoglucose oxidase by column chromatography, preferably on cross-linked dextran gel. The purified apoglucose oxidase is useful as a reagent in specific binding assays employing flavin adenine dinucleotide as a label.