title: Separation of bound and free ligand by ethacridine (Rivanol) in thyroxin radioimmunoassay.
abstract: In this simple and low-cost radioimmunoassay (RIA) procedure for thyroxin (T4), ethacridine (6,9-diamino-2-ethoxyacridine lactate; Rivanol) is used to separate antibody-bound ligand and free ligand. This acridine dye precipitates free T4 not bound to antibody. At pH 8.6, it precipitates more than 90% of 125I-labeled T4. Precipitation is rapid and is constant over the concentration range of 1 to 3 g of ethacridine per liter; time of addition and temperature are not critical. The inherent yellow color of the dye gives it the advantage of a color-coded reagent. Analysis of 65 serum samples by the proposed method and by a procedure involving polyethylene glycol gave similar results: correlation coefficient, 0.988; slope, 0.981; y-intercept, -1.42. Within- and between-assay variations (CV) were less than 5 and 6%, respectively.
mesh_terms: D000166:Acridines; D004975:Ethacridine; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007457:Iodine Radioisotopes; D008024:Ligands / Q000302:isolation & purification; D011092:Polyethylene Glycols; D013223:Statistics as Topic; D013696:Temperature; D013974:Thyroxine / Q000097:blood / Q000302:isolation & purification*
chemical_list: D000166:Acridines; D007457:Iodine Radioisotopes; D008024:Ligands; D011092:Polyethylene Glycols; D013974:Thyroxine; D004975:Ethacridine