Cylinder Plate Assay for Lasalocid Sodium
Abstract A microbiological assay method is described for the determination of the coccidiostat lasalocid sodium in premixes and finished poultry feeds. Premixes are extracted with absolute methanol and diluted to assay range with 25% methanol in the final dilution. Feed samples are extracted with ethyl acetate and an aliquot is evaporated at 60°C. The residue is dissolved in hexane, the antibiotic is extracted with 75% methanol in water, and the extract is diluted to the assay range with a final methanol concentration of 25%. Microbiological activity by horizontal agar diffusion is measured by the cylinder plate technique with Bacillus subtilis ATCC 6633. Recoveries of drug from premix are quantitative. A correction is made for recovery from feeds which, in this laboratory, has averaged 82% for mash feeds and 75% for pellets at a level of 0.0075% lasalocid sodium. Bacitracin, lincomycin, 3-nitro-4-hydroxyphenylarsonic acid, ipronidazole, and a combination of sulf adimethoxine and ormetoprim at current use levels in feeds do not interfere.