Rapid screening test for sulfamethazine in swine feeds.

A simple, 10-min qualitative screening test for sulfamethazine (SM) in swine feeds is detailed. The method, which can be run in the field, uses 2 plastic tubes arranged piggyback style. The upper tube contains, from top to bottom, the feed sample (about 1 g), partially deactivated alumina, and an anion exchange resin buffered at pH 5.7. The bottom tube contains a small bed of anion exchanger buffered at pH 7.9, which traps the SM. After percolation of solvent from the pH 7.9 resin and is reacted with Bratton-Marshall reagents to give a pink-to-lavender color. Feeds containing less than or equal to 0.15 ppm can be detected. A simple, additional dye concentration step allows for detection of 0.02 ppm, if desired. Only amphoteric primary aromatic amino-containing compounds with a pKa close to that of SM can theoretically interfere. Preparation of permanent color solutions using cobalt and copper acetates in glacial acetic acid is described for the optional establishment of the minimum concentration of SM in the feed. The method offers a simple way to detect some cross-contaminated withdrawal feeds containing greater than 2 ppm SM, which can lead to violative (greater than or equal to ppm) residues in swine liver.