Rapid liquid chromatographic determination of dimetridazole and ipronidazole in swine feed

A simple and rapid method is described for the determination of dimetridazole (DMZ) and ipronidazole (IPR) in swine feeds at various levels (0.11-110 ppm). The drugs are released from feed by prewetting with a buffer, followed by extraction with either methanol or methylene chloride, depending on the drug level; if necessary, an acid-base cleanup is used before the liquid chromatographic analysis. The analytes are separated on a C18 column and monitored at 320 nm for detection and quantitation. Recoveries of DMZ from several feed formulations averaged 108% at the 92.8 ppm level with a standard deviation (SD) of 4.00% and a coefficient of variation (CV) of 3.70%, 101% at the 11.2 ppm level with an SD of 11.9% and a CV of 11.8%, and 100% at the 0.112 ppm level with an SD of 9.27% and a CV of 9.25%. Recoveries of IPR averaged 77.1% at the 12.9 ppm level with an SD of 1.75% and a CV of 2.27%; IPR recoveries averaged 35.2% at the 0.129 ppm level with an SD of 3.39% and a CV of 9.63%.