A rapid and reproducible method for the determination of residual sulfisoxazole (SFX), sulfamonomethoxine (SMM), sulfadimethoxine (SDM) and sulfaquinoxaline (SQX) in chicken tissues and egg by high-performance liquid chromatography was investigated. A sample was dried on Micro-cel E and homogenized with chloroform-acetic acid (98 : 2). The drugs were extracted from the organic solvent with 3N hydrochloric acid. The acidic solution was neutralized to suitable pH (6-7) with 12N sodium hydroxide. The extract was made acid again with 1.5N hydrochloric acid and injected into SEP-PAK C18 cartridge. The sulfonamides were eluted with methanol from the cartridge and the eluate was evaporated to dryness. The residue was dissolved in a mixture of methanol-0.03M phosphate buffer pH 5.0 (3 : 7)+0.005M tetra n-butylammonium bromide (TBA) and injected on a Li Chrosorb RP-18 column and eluted with a mixture of methanol-0.03M phosphate buffer pH 5.0 (7 : 13)+0.005M TBA. The effluent was monitored with ultraviolet detector at a wavelength of 260 nm. The recoveries of the sulfonamides added to chicken muscle, liver and egg at the 0.1 ppm level ranged from 77.0% to 103.0%. The detection limits were 0.005 ppm for SFX, SMM, SDM and SQX.
