Liquid Chromatographic Determination of Ivermectin in Feed at the 2-PPM Level: Interlaboratory Study

Abstract

Abstract An analytical method for the determination of ivermectin in feed at the 2 ppm level was evaluated in an interlaboratory study involving 4 laboratories. The method is based on liquid chromatographic measurement following sample preparation by adsorption chromatography on alumina and solid-phase extraction techniques. Each laboratory analyzed 2 complete, final, finished medicated feeds and the corresponding control feeds used in their preparation. In addition, they also measured recoveries in fortified feeds covering 50–150% of the 2 ppm ivermectin use concentration. The mean recoveries from the replicate analyses reported by the laboratories ranged from 90 to 110% and all coefficients of variation (CVs) were less than 4.5%. No significant interferences were found in the control feeds. The pooled distribution of all the 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 withinlaboratory CV of 4.1% and a between-laboratories CV of 3.4%. There was no significant difference in recoveries among laboratories, days, concentrations, and feed base or between fortified and medicated feeds (P > 0.2).