Screening of closantel and rafoxanide in animal muscles by HPLC with fluorescence detection and confirmation using MS

A sensitive and selective LC-FLD method was described for determination of closantel and rafoxanide in bovine and ovine muscles. Bovine and ovine muscles were extracted with ACN and acetone mixture (80:20, v/v). After cleanup with Oasis MAX SPE cartridges, the sample was analyzed by LC-FLD using the control point approach. No false-negative result was observed at or below maximum residue limits and the false-positive rate was below 5%. Suspected positive sample was confirmed by LC-MS/MS. This method was suitable for screening of large batch of samples and hence considerably reduced the time and cost required for quantitation and confirmatory analyses.