Noncompetitive flow injection immunoassay for a hapten, alpha-(difluoromethyl)ornithine

A noncompetitive flow injection immunoassay method has been developed to assay small haptens. In this assay the sample containing the hapten is incubated with excess enzyme-labeled monovalent antibody for a brief period. The excess antibody is then separated from the bound antibody by eluting through an antigen-immobilized immunoaffinity column. The enzyme label of the eluting antibody-hapten complex is fluorometrically detected. The applicability of the method is demonstrated by assaying alpha-(difluoromethyl)ornithine (DFMO), an anticancer drug in human plasma samples. The assay is sensitive enough to detect 200 amol of DFMO. Interferences from other similar endogenous amines have been eliminated by selective immunoaffinity purification of the antibodies.