Development of an immunoassay for the beta-adrenergic agonist ractopamine

Antibody generated from ractopamine-hemiglutarate-KLH[ was used to develop a ractopamine ELISA. The antibody showed good sensitivity in phosphate buff er, with an IC50 of 4.2 ng/ml (ppb) toward ractopamine and 16.2 ng/ml towar d glucuronides of ractopamine conjugated to the phenethanolamine phenol of ractopamine. Phenylbutylamine phenol glucuronides of the (RS, SR) ractopami ne diastereoisomers showed about 4% cross-reactivity, but the glucuronide o f the (RR, SS) diastereoisomers conjugated at the same phenolic group showe d no detectable reactivity with the antibody. The antibody generally had cr oss-reactivity towards compounds with bis-phenylalkyl amine structures rath er than compounds with simple branched N-alkyl substituents. For example, t he antibody showed little or no cross reactivity towards clenbuterol, isopr oterenol, metaproterenol, and salbutamol, but cross-reacted with dobutamine , The system demonstrated a matrix effect similar to other enzyme immunoass ays, dilution of urine decreased but did not eliminate the matrix effect.