Twelve monoclonal antibodies (MAbs) against the widely used herbicide 2,4-D were produced by hybridomas from two fusions of murine myeloma cells and spleen cells isolated from BALB/c mice immunized with hapten conjugated via the carboxyl group to thyroglobulin. To evaluate the sensitivity and selectivity of MAbs, competitive indirect ELISA was used. MAb E2/G2 exhibited the highest sensitivity toward 2,4-D (IC50 = 0.8 ng/mL) and a favorable selectivity toward 18 structurally related substances. Besides the expected high cross-reactivity with methyl ester 2,4-D (104.8 %), cross-reactivity with MCPA (13.8%) and with 2,4,5-T (9.5%) was found. Cross-reactivity with other structural analogs did not exceed 2.7%. Optimization studies showed that in competitive ELISAs for 2,4-D coating conjugates with hapten densities of 2.3 and 3.3 mol of 2,4-D/mol of BSA were more sensitive than conjugates with hapten densities of 15.9 and 26.5 mol of 2,4-D/mol of BSA. The best dose-response curves presented in this study were almost linear in the concentration range 0.2-10 ng/mL. 2,4-Dichlorophenoxyacetic acid (2,4-D) is a broadly used herbicide for controlling weeds which could potentially contaminate groundwater and the drinking water supply. The allowable limits for pesticide residues in drinking water are becoming lower and lower. In European Community (EC) countries, the maximum admissible concentration is 0.1 ng/mL of any one substance and 0.5 ng/mL for a sum of pesticides, including metabolites (Wittmann and Hock, 1991).Conventional methods of quantitation of polar phenoxyalkanoic acids include liquid-liquid extraction, acidbasic partitioning, chemical derivatization, and purification. This procedure is time-consuming, it involves toxic solvents and reagents, and the results are often inconsistent (Loconto, 1991). Therefore, quick, easy, and economical

Immunoanalytical techniques have found widespread use due to the characteristics of specificity and wide applicability for many analytes, from large polymer antigens, to simple haptens, and even single atoms. Electrochemical sensors offer benefits of technical simplicity, speed and convenience via direct transduction to electronic equipment. Together, these two systems offer the possibility of a convenient, ubiquitous assay technique with high selectivity. However, they are still not widely used, mainly due to the complexity of the associated immunoassay methodologies. A separation-free immunoanalytical technique is described here, which has allowed for the analysis of atrazine in real time and in both quasi-equilibrium and stirred batch configurations. It illustrated that determinations as low as 0.13 M (28 ppb) could be made using equilibrium incubation with an analytical range of 0.1-10 M. Measurements could be made between 1 and 10 mM within several minutes using a real-time, stirred batch method. This system offers the potential for fast, simple, cost-effective biosensors for the analysis of many substances of environmental, biomedical and pharmaceutical concern.

A highly sensitive immunoassay for sulphadimidine (SDM) is described, demonstrating the benefit of using spacer arms with different chemical compositions in the hapten immunogen and peroxidase tracer. The antiserum used in the optimized SDM assay exhibited 50% binding inhibition in buffer at approximately 0.15 m g l -1 , while the developed enzyme-linked immunosorbent assay (ELISA) exhibited approximately 100% cross-reactivity between SDM and its major metabolite N 4 -acetyl-SDM, relatively slight reaction with sulphamerazine (5.2%) and negligible reaction with 25 other related antimicrobials. The assay was evaluated using control and SDM-spiked milk, plasma, urine and edible tissue samples. The recovery of added SDM at the concentration of regulatory interest varied around 100%. The precision of the ELISA was below 5 and 15% for inter-and intra-assay variability, respectively. The highly sensitive method has been demonstrated to be an extremely effective way of overcoming problems caused by matrix interference, although care must be taken when using extremely high sample dilution.

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