DETERMINATION OF PENICILLINS IN ANIMAL-TISSUES AT TRACE RESIDUE CONCENTRATIONS .1. DETERMINATION OF BENZYLPENICILLIN IN MILK BY REVERSED-PHASE LIQUID-CHROMATOGRAPHY WITH SOLID-PHASE EXTRACTION AND LIQUID-CHROMATOGRAPHIC FRACTIONATION CLEANUP

A liquid chromatographic (LC) method for the determination of benzylpe nicillin (penicillin G) in milk has been developed. Milk was decreamed by centrifugation and deproteinised using sulphuric acid/sodium tungs tate. Initial clean-up was achieved using C-18 solid phase extraction (SPE). The SPE eluate was cleaned-up by reversed-phase LC fractionatio n at neutral pH. Final determination was by reversed-phase LC at acidi c pH with post-column derivatisation with imidazole/mercury(II) chlori de reagent followed by UV absorbance determination at 320 Mm. Average recoveries at 2 and 10 mu g kg(-1) were 70-73%. The lower limit of qua ntification was 2 mu g kg(-1).