Quantification of cephalexin as residue levels in bovine milk by high-performance liquid chromatography with on-line sample cleanup.

A multidimensional, selective and precise high performance liquid chromatography (HPLC) method based on direct injection of biological samples has been developed for the determination of cephalexin in skimmed and whole bovine milk. The cephalosporin antibiotic was extracted from bovine milk using an octyl restricted access medium bovine serum albumin column (C(8)-RAM-BSA) and analyzed on an octadecyl column using phosphate buffer (pH 7.5, 0.01M): ACN (92:8, v/v) and ultraviolet detection at 260nm. The calibration graph was linear in the concentration range of 25-1600ng/mL and this is in accordance with the tolerance level of 100ng/mL set by the FDA (Food and Drug Administration) and EU (European Union) for cephalexin as residue in bovine milk. The intra- and inter-day coefficients of variation for the replicate analysis at the quality control levels were less than 15% while the transfer efficiency was in the range of 90.2-92.3%. The limits of detection and quantification were 10 and 20ng/mL, respectively.