EXTRACTION AND ENZYME-IMMUNOASSAY OF SULFADIMETHOXINE RESIDUES IN CHANNEL CATFISH (ICTALURUS-PUNCTATUS) MUSCLE

Four commercially available enzyme immunoassays were evaluated for the detection of sulfadimethoxine (SDM) residues in channel catfish muscl e. Matrix solid-phase dispersion (MSPD) extracts of samples (n = 60, 0 .5 g) fortified with SDM at 0, 25, 50, 100, and 250 ng/g were used in all assays. Intra-assay variations for 2 MICROTITER well-based quantit ative assays, SIGNAL sulfamethazine test and IDS SDM One-Step ELISA (e nzyme-linked immunosorbent assay), were 5.6 and 7.7%. Interassay varia tions for these tests were 7.9 and 16.6%. The agreements between evalu ators for 2 membrane-based, visually determined assays, CITE Sulfa Tri o and EZ-SCREEN: SDM, were 77 and 95%. Performance values, as indicate d by sensitivity, specificity, efficiency, and positive and negative p redictive values, were 100, 92, 95, 89, and 100%, respectively for the SIGNAL test; 100, 94, 97, 92, and 100% for the IDS test; 98, 71, 82, 69, and 98% for the CITE test; and 98, 94, 96, 92, and 99% for the EZ- SCREEN assay. Eight sulfonamides cross-reacted in the SIGNAL test; EC- 50 values (concentrations causing 50% inhibition of color development compared with blanks) varied from <0.1 to 45 mug/mL. The EC-50 value f or SDM was 0.25 mug/mL. The CITE test cross-reacted with sulfachloropy ridazine at 10 mug/mL. The IDS and EZ-SCREEN tests had no significant cross-reactivity with other sulfonamides. -Acetyl SDM reacted like the parent SDM in all assays. Performance results indicated that MSPD ext racts of catfish muscle may be used in these immunoassays to screen ca tfish muscle samples for violative levels of SDM residue.