Bound residues, labeled pesticides

Xenobiotics are frequently metabolized in plants by mechanisms that lead to the incorporation or inclusion of the xenobiotic into biological polymers or tissue residues that are not soluble in commonly used nonreactive solvents. These residues are frequently refered to as bound, insoluble, or nonextractable residues (2 ). Bound residues in plants have most commonly been detected in plant tissues treated with radloactlvely-labeled pesticides. These residues were an important topic of a symposium held in Vail, Colo, in 1975 (17) they have been discussed in mauiy more recent papers (11,154-1577"and they were discussed at a symposium at the l88th ACS National Meeting, 1984 "Non-extractable Pesticide Residues Characteristics, Bioavailability and Toxicological Significance". 

Figure 4.3 Sandwich-immunoassay for the determination of bound pesticide residue. Schematic view. Antibody 1 (Ab 392) is immobilized on a polystyrene surface. Incubation of the analyte (bound residue). Addition of antibody 2 (Ab K1F4) detection by use of a third enzyme-labelled antibody 3. (From Ulrich, M.G.,. Anal. Chem., 354, 352, 1996. With permission.)... 

Immunochemical methods have also been applied to the detection of bound pesticide residues in soil. These are formed by binding of pesticides to the organic matter of the soil, mainly humic and fulvic acids, and cannot be analyzed using common extraction and assay methods. Hahn et al. used Fab fragments labeled with a fluorescent dye to detect nonextractable residues of atrazine in soil from corn fields. The fluorescence signal obtained was related to the amount of bound atrazine in native soil samples determined by GC after supercritical methanol extraction. A noncompetitive sandwich lA for the analysis of bound residues based on HA-Ab and triazine Ab was developed by Ulrich et HA was extracted from soil, bound to the plates by the HA-Ab and the nonextractable triazine residues were detected by... 

Noncompetitive assays can only be apphed for high-molecular-mass analytes with more than one antigenic determinant (i.e. Ag) or low-molecular-mass analytes (haptens) bound to a solid phase, exposing the antigenic determinant. They work with an Ab excess. Noncompetitive lAs have been employed for the detection of soil-bound pesticides. In this case the soil particles, to which the pesticide residues have bound, form the sohd phase, and the residues can be detected by a labeled Ab specific to the analyte. 

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