Submitted to: Journal of Association of Official Analytical Chemists International
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 28, 1994
Publication Date: N/A
Interpretive Summary: The presence of antibiotic residues in milk is a topic of great concern to the general public, government regulatory agencies, and the dairy industry. For this reason, testing for B-lactam antibiotic residues in milk is now mandatory in the USA. Commercial kits that can detect B-lactams at concentrations equal to or lower than the "safe levels" established by the FDA are used to screen milk for the presence of B-lactams. Consequently, it is important to develop confirmatory methods for B-lactams that can identify and quantify all of the seven B-lactams that are commonly used. In this paper we have successfully integrated commercially available B- lactam screening kits with an HPLC method developed in our laboratory. This procedure considerably expedited and simplified the task of identifying and quantifying the violative B-lactams present in milk.
Technical Abstract: Testing for B-lactam antibiotic residues in milk is now mandatory in the USA, where the FDA has set safe levels that range from 5 to 50 ppb. Even though test kits, that are able to detect residues at or below these levels, are commercially available, they cannot identify or quantify the violative B-lactam(s). In this paper we describe a procedure for identifying and quantifying violative B-lactams in milk. This procedure integrates B-lactam residue detection kits with the multiresidue automated HPLC cleanup method developed in our laboratory. Spiked milk was deproteinized, extracted, and subjected to reverse-phase HPLC using a gradient program which concentrated the B-lactams. Amoxicillin, ampicillin, cephapirin, ceftiofur, cloxacillin, and penicillin G were thus separated into five fractions which were subsequently tested for activity using four kits. Quantification of the B-lactams in the positive fractions swas done using analysis HPLC methods developed in our laboratory. The HPL cleanup method separated B-lactam antibiotics from each other and from interferences in the matrix, and also concentrated the antibiotics, thus increasing the sensitivity of the kits to the above B-lactam antibiotics. The procedure facilitated the task of identifying and measuring the B- lactam antibiotics that may be present in unknown milk samples.