Development of a monoclonal antibody-based cELISA for the analysis of sulfadimethoxine. 2. Evaluation of rapid extraction methods and implications for the analysis of incurred residues in chicken liver tissue

Several rapid extraction methods were evaluated for use with a monoclonal a ntibody-based competitive inhibition ELISA (cELISA) to detect sulfadimethox ine (SDM) in chicken liver tissue. These methods included extraction of the samples with (1) aqueous buffer with or without ultrafiltration, (2) aceto nitrile/water, (3) methanol/water, or (4) acetone. The organic extraction m ethods were evaluated with or without solvent evaporation prior to dilution into assay buffer for the cELISA. The aqueous-based extraction methods wer e compatible with the cELISA. However, of the organic extraction methods, o nly the acetone liver extract with solvent evaporation prior to analysis wa s compatible with the cELISA. The cELISA method coupled to aqueous- or acet one-based sample extraction as well as an HPLC method was evaluated for the analysis of chicken liver tissues fortified with SDM at levels from 0.2 to 0.025 ppm. Mean SDM recoveries for the HPLC method and for the cELISA meth od using samples prepared by aqueous extraction, aqueous extraction and ult rafiltration, or acetone extraction, evaporation, and reconstitution were 6 8.9, 95.7, 60.1, and 52.5%, respectively. For the analysis of samples obtai ned from an SDM incurred residue study, HPLC and cELISA analysis of the sam e organic extract gave results that were highly correlated (R-2 = 0.976; p < 0.0001). However, results obtained from the analysis of aqueous extracts by cELISA did not correlate well with those obtained by HPLC (R-2 = 0.61,p > 0.0006). This was attributed to the coextraction:of cross-reactive SDM-re lated residues that were not quantified by the HPLC method. The presence of these residues should be considered during data interpretation when ELISA methods coupled with rapid aqueous extraction of samples are used in SDM re sidue monitoring programs.