Abstract: A specific binding assay method, and a test device and test kit for use therein, for determining a liqand, such as an antigen or antibody, in, or the ligand binding capacity of, a liquid medium, particularly a body fluid such as serum, wherein the unknown ligand competes with a labeled component, such as a radiolabeled form of the ligand or of a binding analog of the ligand, for binding with a binding partner, and wherein separation of the resulting bound-species and free-species of the labeled component is accomplished by allowing the liquid reaction mixture to be drawn by capillary action into a column comprising a bed of an adsorbent material selective for one of the two species. The improvement comprises using a column containing at least one additional bed of capillarily absorbent material disposed above said adsorbent bed and which is substantially nonadsorbent relative to the one of said two species which said adsorbent bed selectively binds.

Abstract: A specific binding assay method and test kit for determining a ligand, such as an antigen or antibody, in, or the ligand binding capacity of, a liquid medium, particularly a body fluid such as serum, wherein the unknown ligand competes with a labeled component, such as a radio labeled form of the ligand or of a binding analog of the ligand, for binding with a binding partner, with the improvement that separation of the resulting bound-species and free-species of the labeled component is accomplished by drawing the liquid reaction mixture into a column of an adsorbent material selective for one of the two species. Separation results by immobilization of the selected species at the beginning portion of the adsorbent column while the other species is transported farther along the column by advance of the reaction mixture.