A Novel Indirect Competitive Enzyme-Linked Immunosorbent Assay Format for the Simultaneous Determination of Ractopamine and Phenylethanolamine A Residues in Swine Urine

For monitoring ractopamine (RAC) and phenylethanolamine A (PA) with high efficiency, a novel indirect competitive enzyme-linked immunosorbent assay (ic-ELISA) format was developed. At first, two specific monoclonal antibodies (mAbs) against RAC and PA were prepared, respectively. Based on the finding that both mAbs RAC and PA could recognize the same coating antigen RAC-SA-OVA, a novel ic-ELISA format was constructed, in which the limit of detection (LOD), recoveries, and coefficient of variation of the ic-ELISA developed for RAC residues were 0.35 μg L−1, 96.7~108.6%, and less than 6.8%, and for PA residues, they were 0.11 μg L−1, 97.8~110.2%, and less than 9.4%, respectively. The developed method also exhibited a positive correlation with the results of HPLC-MS conducted on the samples. These data indicate that the developed novel ic-ELISA is reliable and could be used in a routine application for the simultaneous determination of RAC and PA residues in swine urine.