Collaborative study of assay method for erythromycin in pelleted feeds containing binding agents

A modified method for analysis of erythromycin in feeds containing the pelleting adjuvants bentonite and Masonex has been evaluated by collaborative study. Erythromycin is freed from the binding action of these adjuvants by an aqueous methanolic pH 8 buffer presoak before extraction with methylal. The recovery values for mash and pellets of 6 different sample types range from 86.6 to 103.0% of theory with a grand mean of 96.8%. This modification has been adopted as official first action.