A convenient equilibrium separation method for competitive protein-binding assay of corticosterone in rat serum

Competitive protein-binding assays for corticosterone have typically employed adsorption methods for separation of free and bound ligand. Such methods often impose inconveniently strict limits upon incubation time and temperature, due to the necessity of minimizing the progressive loss of bound ligand to the adsorbent. This paper describes a convenient equilibrium assay method in which a centrifugable ion-exchange medium, DEAE-cellulose, is used to separate the corticosteroid binding globulin of rat serum and ligand bound to it, from free ligand. This method allows great latitude in incubation time and temperature, and is therefore very convenient for processing large numbers of samples. An assay optimized for use over the 50-1000 pg range showed midrange precision averaging 12% c.v., an interassay variation of 15%, and high specificity.