Development of HPLC methods for the determination of cyadox and its main metabolites in goat tissues

Rapid and sensitive high-performance liquid-chromatographic methods were developed for the determination of cyadox, an antimicrobial growth-promoter, and its main metabolites (1,4-bisdesoxycyadox, quinoxaline-2-carboxylic acid) in goat muscle, liver, kidney and fat. Cyadox (CYX) and 1,4-bisdesoxycyadox (BDCYX) in fat were extracted with acetonitrile, and in other tissues with ethyl acetate. Quinoxaline-2-carboxylic acid (QCA) was isolated from tissue hydrolysates by solvent extraction, cleaned up with ion-exchange chromatography, followed by a final liquid-liquid extraction step. UV detections of CYX, BDCYX and QCA were performed at 305, 280 and 320 nm, respectively. The average recoveries of CYX, BDCYX and QCA in spiked tissues at levels of 25, 50, 100 microg/kg were 65 - 92%. The inter-day relative standard deviation for three compounds in different tissues was 5 - 16%. The quantitation limit was 25 microg/kg, and the detection limit was 15 microg/kg for three compounds in various tissues. Incurred goat tissues were analyzed to demonstrate the validity of the described methodologies. The present methods were highly selective and could be used in the metabolism and residue studies of cyadox.