Rapid screening for monensin residues in poultry plasma by a dry reagent dissociation enhanced lanthanide fluoroimmunoassay

Monensin, a carboxylic acid ionophore, is commonly fed to poultry to contro l coccidiosis. A method for rapid analysis of unextracted poultry plasma sa mples has been developed based on a novel immunoassay format: one-step all- in-one dry reagent time resolved fluorimetry. All assay specific components were pre-dried onto microtitration plate wells. Only addition of the serum sample diluted in assay buffer was required to perform analysis. Results w ere available one hour after sample addition. The limit of detection (mean + 3s) of the assay calculated from the analysis of 23 known negative sample s was 14.2 ng ml(-1). Intra- and inter-assay RSD were determined as 15.2 an d 7.4%, respectively, using a plasma sample fortified with 50 ng ml(-1) mon ensin. Eight broiler chickens were fed monensin at a dose rate of 120 mg kg (-1) feed for one week, blood sampled then slaughtered without drug withdra wal. Plasma monensin concentrations, as determined by the fluoroimmunoassay ranged from 101-297 ng ml(-1). This compared with monensin liver concentra tions, determined by LC-MS, which ranged fi om 13-41 ng g(-1). The fluoroim munoassay described is extremely user friendly, gives particularly rapid re sults and is suitable for the detection and quantification of plasma monens in residues. Data from medicated poultry suggest that analysis of plasma ma y be useful in predicting the extent of monensin liver residues.