Determination of ivermectin in bovine liver by optical immunobiosensor.

A rapid and sensitive biosensor immunoassay was developed for residues of the antiparasitic agent ivermectin in bovine liver. A detection limit of 19.1 ng g(-1) was achieved. The sensor employed was a Biacore optical instrument based on surface plasmon resonance. 5-O-succinoylivermectin-apo-transferrin conjugate was used to produce monoclonal antibody while a second derivative, ivermectin-oxime, was immobilised onto the surface of a sensor chip. A range of assay parameters (flow rate, injection time, temperature) and extraction techniques were investigated. In the final assay procedure, ivermectin was extracted with acetonitrile followed by C(8) SPE clean-up. Matrix effect was minimised by increasing the flow rate to 25 microl min(-1) and reducing the sample injection time to 2 min. The average value for liver samples spiked at 100 ng g(-1) (the MRL for the drug) and 50 ng g(-1) concentrations were 93.7 and 43.2 ng g(-1), respectively.