MULTIRESIDUE DETERMINATION OF BETA-LACTAM ANTIBIOTICS IN MILK AND TISSUES WITH THE AID OF HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHIC FRACTIONATION FOR CLEAN UP

Screening of milk shipments for beta-lactam antibiotic residues is man datory in the USA and is widely used in other countries. Interpretatio n of positive screening test results has been difficult. Only six beta -lactam antibiotics are approved for use in food-producing animals in the USA but many others are used in other countries. A multiresidue pr ocedure was developed for identification and quantitation of unknown b eta-lactam antibiotics. The residues were extracted with acetonitrile and tetraethylammonium chloride. The extract was concentrated by evapo ration and filtered. The concentrated extract was then loaded onto an HPLC column in 100% 0.01 M KH2PO4 and eluted with an acetonitrile grad ient. Fractions corresponding to analytes of interest were collected a nd tested for antibiotics using rapid milk screening tests. Fractions testing positive were analyzed by HPLC. The identity of beta-lactams w as confirmed by treating a replicate with beta-lactamase. (C) 1998 Pub lished by Elsevier Science B.V. All rights reserved.