Analytical method development and preformulation stability studies of L-665,871 (a beta-agonist) in swine feed

An analytical procedure for the determination of the beta-agonist L-665,871 by LC with fluorescence detection has been developed. The mobile phase consists of acetonitrile-phosphate buffer (pH 3.0) with ion-pairing reagent hexanesulphonic acid sodium salt for the analysis of swine feed samples with 1 and 20 microgram g-1 L-665,871. Storage of feed samples at room temperature, however, indicated that the stability L-665,871 and its analogue L-674,239 were greatly compromised by the presence of moisture in the feed. Acidification with maleic acid and/or freezing the feeds were found to significantly improve drug stability.