DETERMINATION OF AMPICILLIN AND AMOXICILLIN IN MILK WITH AN AUTOMATEDLIQUID-CHROMATOGRAPHIC CLEANUP

A method is described for determination of ampicillin and amoxicillin in milk by using an automated liquid chromatographic (LC) cleanup. Mil k was deproteinated by adding tetraethylammonium chloride solution and acetonitrile. The filtrate was concentrated by evaporation, filtered, and loaded into a 4 mL autosampler vial. For LC cleanup, a Waters WIS P 712 autosampler, a Varian 9010 pump, a Supelcosil LC18 column, and a n ISCO FOXY fraction collector were used. The cleanup program, where A is 0.01M KH2PO4 and B is acetonitrile, was 100A + 0B for 0-3 min and then 70A + 30B for 24 min. Sample concentrate (2 mL) was loaded onto t he column for cleanup. Fractions containing amoxicillin and ampicillin were collected, partially acidified, and concentrated to 1 mL. Analys is was done on the LC-18 column, with a mobile phase of 0.015M H3PO4-[ 0.0075M sodium dodecyl sulfate-acetonitrile (70 + 30)] for amoxicillin and 0.0067M H3PO4-0.0033M KH2PO4-[0.005M sodium dodecyl sulfate-aceto nitrile (67 + 33)] for ampicillin. Recoveries were generally 80-90% at a concentration range of 1-0.01 ppm, with a detection limit of 2-5 pp b. By collecting appropriate fractions, the method can be applied to t he determination of any amphoteric beta-lactam.