EXTRACTION AND LIQUID-CHROMATOGRAPHIC ANALYSIS OF SULFADIMETHOXINE AND 4-N-ACETYLSULFADIMETHOXINE RESIDUES IN CHANNEL CATFISH (ICTALURUS-PUNCTATUS) MUSCLE AND PLASMA

A simple and rapid method was developed for the simultaneous extractio n and liquid chromatographic (LC) determination of sulfadimethoxine (S DM) and 4-N-acetylsulfadimethoxine (N-acetyl SDM) in channel catfish m uscle and plasma. Tissues fortified at 0, 50, 100, 200, 400, and 1000 ppb were examined. Matrix solid phase dispersion (MSPD) was used for m uscle extraction. Plasma was extracted with a modified MSPD procedure in which 100 mu L plasma and 400 mg C-18 were blended by Vortex mixing in a disposable chromatographic column. Recovery of SDM based on radi oactivity was 79% for muscle and 67% for plasma. Standard curves based on extracted fortified samples were used for quantitation of N-acetyl SDM. LC run times of 12 min were obtained using a microbore analytica l column and an isocratic mobile phase of aqueous 0.017M phosphoric ac id-acetonitrile at ratios of 71:29 for muscle and 73:27 for plasma ext racts. Method detection limits were 26 ng SDM and 26 ng N-acetyl SDM/g muscle, and 33 ng SDM and 11 ng N-acetyl SDM/mL plasma. Intra-assay v ariation was <10% for both compounds at all concentrations examined. I nter-assay variation for SDM was 13% for muscle and 14% for plasma, an d for N-acetyl SDM was 11% for muscle and 10% for plasma.