LIQUID-CHROMATOGRAPHIC DETERMINATION OF IVERMECTIN IN FEED

An analytical method for determining ivermectin in feed at 0.50-3 ppm is presented. The method is based on liquid chromatographic measuremen t after sample preparation by adsorption chromatography on alumina and solid-phase extraction. Two complete, final, finished medicated feeds and the corresponding control feeds used in their preparation were an alyzed. Recoveries from feeds fortified at 50-150% of the 2 ppm iverme ctin use concentration also were determined. Mean recoveries from repl icate analyses ranged from 90 to 100%, and coefficients of variation ( CVs) were less than 4.5%. No significant interferences were found in c ontrol feeds. The pooled distribution of individual analytical results (n = 100) gave a mean recovery of 100%, a recovery range of 90-111%, and an overall CV of 5.5%. Resolution of the total variance into its 2 components gave a within-laboratory CV of 4.1% and a between-laborato ry CV of 3.4%. There was no significant difference in recoveries among laboratories, days, concentrations, and feed base or between fortifie d and medicated feeds (P > 0.2).