Methods for detecting and/or discriminating between variants of an antibody contaminating protein or multiple antibodies in a sample by a physical parameter, in which the method includes: separating protein components of a sample by molecular weight or charge in one or more capillaries using capillary electrophoresis; immobilizing the protein components of the sample within the one or more capillaries; contacting the protein components within the one or more capillaries with one or more primary antibodies that specifically bind to the antibody, the contaminating protein or multiple antibodies in the sample, thereby detecting and/or discriminating between variants in the sample.