Practical screening procedure for chloramphenicol in milk at low parts per billion level.

A relatively simple screening procedure for the detection of chloramphenicol in cow's milk is detailed. The drug in 50 mL skim milk is adsorbed onto Chromosorb 102 and subsequently eluted; interfering impurities are removed by passing the effluent directly over one column containing small beds of alumina and cation exchange resin in the H+ form. After solvent is removed, the nitro group of the drug is reduced with zinc dust in HCl, and the drug is detected by diazotization and coupling to N-1-(naphthyl)ethylenediamine. Milk containing greater than or equal to 4 ppb chloramphenicol can be detected. A number of antibiotics and sulfa drugs permitted for use with dairy cows do not interfere with chloramphenicol detection, nor do some naturally occurring aromatic amino compounds. Nitromide (3,5-dinitrobenzamide) will interfere. It is estimated that approximately 50 samples of skimmed milk can be screened by one person during the working day. Cows secreted the drug into their milk for approximately 3 days following injection of chloramphenicol either intramuscularly or via infusion into the udder.