#Id: 4617
#Unit 13. Methods in Biology
Scatchard plots are based on repeated equilibrium dialyses with a constant concentration of antibody and varying concentration of ligand.
If all antibodies have the same affinity, then a Scatchard plot yields a straight line with a slope of Ka. The x intercept is n, the valency of the antibody, which is 2 for IgG and other divalent Igs. For IgM, which is pentameric, n 10, and for dimeric IgA, n 4. In this graph, antibody #1 has a higher affinity than antibody #2.