T. Fodey, C. S. Thompson, I. Traynor
Feb 1, 2015
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Quality indicators
Journal
Food Analytical Methods
Abstract
Dicyclanil is a parasiticide used to combat myiasis (flystrike), the infectious infestation of sheep with fly larvae. The European Union has established maximum residue limits (MRLs) for the drug in sheep tissue of 200 μg kg−1 for muscle, 150 μg kg−1 for fat and 400 μg kg−1 for kidney and liver. It is therefore a requirement for regulatory laboratories to have reliable analytical methods at their disposal for the detection of the target analytes, dicyclanil and its major metabolite, 2,4,6-triamino-pyrimidine-5-carbonitrile (TPC). While physicochemical methods have been employed previously, this is the first report of an immunochemically based assay for dicyclanil and TPC. A structural analogue, 2-chloro-4, 6-diamino-5-cyanopyrimidine (CDC), was chosen as a hapten with potential to produce an antibody capable of binding both dicyclanil and TPC. Using homologous ELISA and biosensor assays (in buffer), superior sensitivity was displayed towards dicyclanil (IC50 = 2.1 and 5.0 ng mL−1 respectively) compared to TPC (IC50 = 34.3 and 48.7 ng mL−1, respectively). However, switching to a heterologous format (using a further analogue) for both technologies produced IC50 values of 1.5 ng mL−1 for both analytes by ELISA and 2.8 ng mL−1 (dicyclanil) and 3.7 ng mL−1 (TPC) by biosensor. The heterologous formats were employed to develop ELISA and biosensor methods for the analyses of ovine muscle samples using a simple acetonitrile extraction. Validation of both methods found them to be sufficiently reproducible and sensitive for the purpose of monitoring sheep muscle samples for the presence of non-compliant concentrations of dicyclanil. The detection capability of both methods was found to be less than 100 μg kg−1.