A sensitive double isotope modification of the Farr assay using beta-particle emitters

A sensitive modification of the ammonium sulfate precipitation assay for antibody affinity is described. The assay combines small reaction volumes and a 32P volume marker to determine the average relative affinity of small amounts of antibody to DNP hapten. The assay is relatively safe since two beta-particle emitters are utilized instead of two gamma-ray emitters. The assay has proven useful for the determination of small amounts of antibody such as might be found in secretions and column fractions.