Use of Polyethylene Glycol to Separate Free and Antibody-Bound Peptide Hormones in Radioimmunoassays†

Aqueous polyethylene glycol causes precipitation of antibody-bound peptide hormones labeled with radioactive iodine with little or no precipitation of free hormones. Based on this finding, a method of separation has been developed and applied to radioimmunoassays of insulin, parathyroid hormone, growth hormone and arginine vasopressin. The new method provides several advantages over the double-antibody precipitation method. It appears particularly valuable in immunoassays of substances of low molecular weight.