Interference of eluates from octadecyl cartridges with an angiotensin II radioimmunoassay

Variable values for angiotensin II were obtained when a radioimmunoassay was performed after extraction of biological samples on octadecyl cartridges. Dried residues of eluates from the cartridges were found to decrease the binding of the tracer to the antibody in assay tubes, causing high blank values. When the tubes used for the standard curve contained dried residues of eluates extracted in the same fashion as the unknowns, the interference and the high blanks were eliminated.