Methods for Determining Ronnel in Feeds and Mineral Mixtures

Abstract The official first action GLC method (electron capture detector) for ronnel in feeds, 38.126–38.129, is rapid and dependable but has been found to give low ronnel recoveries with stored samples. A major study was made to determine whether the low results are due to decomposition or binding of the ronnel. Ronnel and trichlorophenol (TCP) analyses were made by GLC on a feed sample stored for 9 months; results showed that 29–33% of the added ronnel and 29–54% TCP (reported as ronnel) were recovered under various conditions, accounting for 58–87% of the original ronnel. Analyses for TCP made by hydrolysis gave similar results. The ronnel not accounted for was probably lost through degradation, followed by volatilization and/or sublimation on the container walls. This study indicates conclusively that degradation of the ronnel is a major cause for the low recoveries in stored feeds. A biological (housefly killing) assay was made on another sample of the stored feed and showed 41% of the ronnel remaining. Agreement between the GLC analyses and the biological assay, plus proof of ronnel decomposition in stored samples, are convincing evidence that the first action method determines the true ronnel content of the feed. The official first action GLC method for ronnel in feeds has been adopted as official final action.