Ion-pair reverse-phase liquid chromatographic determination of amprolium in complete feeds and premixes

Amprolium is extracted with methanol-water (2 + 1) containing 5mM dioctylsulfosuccinate (DOSS) and 10mM CaCl2. The analyte is separated from coextracted materials by isocratic ion-pair reverse-phase liquid chromatography, following removal of late-eluting materials on an acid alumina cleanup column, and is detected at 270 nm. The mobile phase contains 4mM DOSS with 0.3% diethylamine and 1% acetic acid in 40% acetonitrile. Linearity is satisfactory over the range of 2.5-50 micrograms/mL. Mean recovery, as determined by standard addition to commercial samples, is 100.1%. Accuracy was further tested in studies comparing the LC method to the official AOAC colorimetric method, using commercial samples, and was found to be satisfactory. Studies show that common poultry feed additives, grass meals, and some pelletization aids do not interfere with the analysis; however, when bentonite is present, recovery is decreased. The precision of the method, measured over several experiments on commercial samples, is satisfactory as indicated by coefficients of variation ranging from less than 1 to 4.5. A ruggedness test resulted in an overall CV of 3.2%, indicating the probable success of the method in a collaborative study.