Submitted to: Journal of Chromatography
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 28, 1998
Publication Date: N/A
Interpretive Summary: A variety of screening tests are used for detection of B-lactam antibiotics in milk and tissues. Testing of milk for B-lactam antibiotics is now mandatory in the United States. The screening tests cannot tell which B- lactam is present or how much. Specific confirmatory tests are needed to identify specific B-lactams and to determine how much is present. This information is useful to regulatory agencies as a check on the accuracy of screening tests, and to producers in identifying sources of residues. To be useful, a confirmatory procedure must equal or exceed the sensitivity of screening tests. It also must be able to detect any B-lactam or major metabolite thereof. The procedure described in this paper meets these rather stringent requirements and is the only one reported which has this capability.
Screening of milk shipments for B-lactam antibiotic residues is mandatory in the United States and is widely used in other countries. Interpretation of positive screening test results has been difficult. Only six B-lactam antibiotics are approved for use in food-producing animals in the United States but many others are used in other countries. A multiresidue procedure was developed for identification and quantitation of unknown B- lactam antibiotics. The residues were extracted with acetonitrile and tetraethylammonium chloride. The extract was concentrated by evaporation and filtered. The concentrated extract was then loaded onto an HPLC column in 100 percent 0.01M KH2PO4 and eluted with an acetonitrile gradient. Fractions corresponding to analytes of interest were collected and tested for antibiotics using rapid milk screening tests. Fractions testing positive were analyzed by HPLC. The identity of B-lactams was confirmed by treating a replicate with B-lactamase.