Determination of ractopamine in monkey plasma and swine serum by high-performance liquid chromatography with electrochemical detection

A high-performance liquid chromatographic (HPLC) method is described for the determination of ractopamine (LY031537) in monkey plasma and swine serum. Plasma or serum (0.5 ml) was diluted with phosphate buffer pH 7.0. Ractopamine was isolated from the plasma matrix using ion exchange on a polymeric carboxylic acid solid-phase extraction cartridge followed by partitioning with ethyl acetate. An isocratic HPLC method using electrochemical detection at +700 mV was used to separate and measure ractopamine in the purified extract in 6.5 min of run time. Standard area response was linear with respect to concentration of ractopamine over the range of 0.5 to 40 ng/ml. Validation data were collected using rhesus monkey plasma and swine serum. The method precision and accuracy were evaluated in the range 1.0 to 20 ng/ml using fortified samples of monkey plasma. The method limit of quantitation was estimated at 2 ng/ml as determined in monkey plasma.