Simultaneous determination of six penicillins in cows' raw milk by a multiresidue high-performance liquid chromatographic method

A high-performance liquid chromatographic method based on C-18 solid-phase extraction and ultraviolet detection at 323 nm of analytes derivatized with benzoic anhydride and 1,2,4-triazole mercuric chloride solution was developed for the simultaneous determination of amoxicillin, penicillin G (benzylpenicillin), ampicillin, oxacillin, cloxacillin and dicloxacillin residues in raw milk. The detection limit of the method was 1.3 mu g/l for penicillin G; 1.4 mu g/l for amoxicillin, oxacillin and cloxacillin, 1.5 mu g/l for ampicillin and 2.7 mu g/l for dicloxacillin. The mean recovery was 95-102% for amoxicillin, penicillin G and ampicillin, 92-98% for oxacillin and cloxacillin and 87-94% for dicloxacillin, measured by using an internal standard. The relative repeatability standard deviation was 4-9% on level 4-15 mu g/l, respectively, 2-7% on level 30-40 mu g/l. (C) 1997 Elsevier Science B.V.