Pesticides ELISA tests

Current work Is aimed at developing prototype antibody kits for use by the grain Industry. Considerable stability testing and collaborative trialling Is, however, required before this can be done. Assay validation of pesticide ELISAs has also been reviewed elsewhere(20. While quantitative ELISA kits... 

Lopez-Avila, V., C. Charan, and J.M. Van Emon (1996). Quick determination of pesticides in foods by SFE-ELISA. Food Testing Anal., 2 28-37. 

ELISA could potentially be used advantageously in many types of exposure and monitoring situations, for paraquat and other pesticides amenable to ELISA analysis. An obvious use of ELISA is the detection of pesticide residue levels in plant and animal tissues, or food extracts. Biological specimens such as plasma and urine currently analyzed by RIA seem particularly amenable to analysis by ELISA. Portable field kits could be developed to determine safe worker re-entry times into treated fields. Environmental samples such as soil, water, and air, can be analyzed by the ELISA. Pesticide conjugates have been proposed for skin testing of individuals suspected of sensitivity to pesticides (fi.) the ELISA could be used to detect specific antibodies in these individuals and aid in exposure studies. 

Antibodies have been raised against representative compounds from the major classes of pesticides. Although the ELISA will be useful for individual analysis of a wide variety of compounds, if one needed to analyze several different compounds simultaneously in one matrix immunoassay may not be the method of choice, due to the large amount of controls and standards needed. However, it could be successfully used for the rapid screening of a large number of samples for the presence of specific types of pesticides and for confirmatory tests (Ji). The work reported here with paraquat,... 

Immunochemical methods are rapidly gaining acceptance as analytical techniques for pesticide residue analysis. Unlike most quantitative methods for measuring pesticides, they are simple, rapid, precise, cost effective, and adaptable to laboratory or field situations. The technique centers around the development of an antibody for the pesticide or environmental contaminant of interest. The work hinges on the synthesis of a hapten which contains the functional groups necessary for recognition by the antibody. Once this aspect is complete, immunochemical detection methods may take many forms. The enzyme-linked immunosorbent assay (ELISA) is one form that has been found useful in residue applications. This technique will be illustrated by examples from this laboratory, particularly molinate, a thiocarbamate herbicide used in rice culture. Immunoassay development will be traced from hapten synthesis to validation and field testing of the final assay. 

The sample workup necessary for pesticide residue analysis will vary with each combination of analyte and antibody, each of which may have a different tolerance for the matrix and other factors. The effects of these factors must be considered as with the development of any other analytical technique. Matrix effects for one ELISA system are summarized in Figure 4. While the effect of the matrix on the antibodies in Figure 4 is different for each antibody-solvent-matrix combination, the competitive ELISA standard curves for most of these combinations are similar when expressed as percent of the appropriate control. Some systems may not require extensive adjustment, but this must be tested with each individual system. For example, our molinate assay performs equally well in a variety of water types at high concentrations of molinate (Figure 5). The small difference seen between the buffer and water standard curves in Figure 5 was eliminated by the addition of small amounts of concentrated buffer to water samples to equalize them to the buffer composition. 

The evaluation of a number of immunoassay diagnostic kits was undertaken to determine their usefulness in a regulatory analytical laboratory environment in the food, feed and pesticide areas. Four rapid enzyme immunoassay tests for the detection of aflatoxin residues at the 20 ppb level in animal feeds were compared to the official HPLC procedure. In the pesticide area, a commercial pentachlorophenol competitive inhibition assay for residues in water was investigated as to its applicability to poultry and pork liver matrices. In addition, an ELISA screening procedure for the herbicide fusilade was developed. Modifications were incorporated into the rapid immunoband 1-2 Test procedure for the detection of motile Salmonella in various food and animal feed products resulting in quicker analysis than the standard culture method. Also, a comparative evaluation of a Quik-Card Test for sulphamethazine drug residues in pork urine, liver and muscle tissue, is described. 

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