[HPLC determination of oxacillin, cloxacillin and dicloxacillin in bovine muscle with automated cleanup by on-line solid phase extraction].

A high-performance liquid chromatographic (HPLC) method with automated cleanup by on-line solid phase extraction was developed for the determination of oxacillin, cloxacillin and dicloxacillin in bovine muscle tissue. The penicillins were extracted from the matrix with acetonitrile, transferred to phosphate buffer and automatically trapped on a RP-18 solid phase extraction column. After on-line elution onto the analytical HPLC-column, penicillins were quantified by UV (lambda = 225 nm) after isocratic separation. Mean recoveries at the MRL (0.3 mg/kg) were 92% for oxacillin, 92% for cloxacillin and 86% for dicloxacillin. The coefficients of variation for the three penicillins in the range of 0.15-0.6 mg/kg were 13.8%, 11.0%, and 7.3%, respectively. The applicability of this method for the determination of cloxacillin in milk was demonstrated.