Residue analysis molinate

Table III summarizes the results of tissue residue analysis. It is evident that the amount of radioactivity in tissues was not directly related to the length of chemical exposure. The average accumulation in fish exposed from 1 to 14 days was 1.35%. In general, liver, kidney, intestine, and bile contained the most 1 C. C-labeled materials accumulated in the liver at levels 3 to 5 times greater than [111C]molinate concentration in the water. The maximum radiocarbon level in the bile was 14.5 ppm and was reached by the 7th day. On the 14th day, the radiocarbon decreased to 6.09 ppm which was 30-fold higher than the [ 1 C]molinate water concentration. Blood contained negligible amounts of radioactivity, and little of that was associated with the plasma. Twenty percent of total blood radioactivity was detected in the erythrocytes within 4 days after treatment and by the 14th day, 69% of the radiocarbon in whole blood was present in the erythrocytes.

Immunoassays offer much potential for rapid screening and quantitative analysis of pesticides in food and environmental samples. However, despite this potential, the field is still dominated by conventional analytical approaches based upon chromatographic and spectrometric methods. We examine some technical barriers to more widespread adoption and utilization of immunoassays, including method development time, amount of information delivered and inexplicable sources of error. Examples are provided for paraquat in relation to exposure assessment in farmworkers and food residue analyses molinate in relation to low-level detection in surface waters and bentazon in relation to specificity and sensitivity requirements built in to the immunizing antigen. A comparison of enzyme-linked immunosorbent assay (ELISA) results with those obtained from conventional methods will illustrate technical implementation barriers and suggest ways to overcome them. 

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. 

Applications of immunoassay to pesticide chemistry have been described which address some difficult problems in analysis by classical methods. These include stereospecific analysis of optically active compounds such as pyrethroids (38), analysis of protein toxins from Bacillus thuringiensis (5,37), and compounds difficult to analyze by existing methods, such as diflubenzuron (35) and maleic hydrazide (15 also Harrison, R.O. Brimfield, A.A. Hunter, K.W.,Jr. Nelson, J.O. J. Agric. Food Chem. submitted). An example of the excellent specificity possible is seen in assays for parathion (10) and its active form paraoxon (3). Some immunoassays can be used directly for analysis without extensive sample extraction or cleanup, dramatically reducing the work needed in typical residue analysis. An example of this is given in Figures 2 and 3, comparing the direct ELISA analysis of molinate in rice paddy water to the extraction required before GC analysis. 

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. 

A 50-mL Schlenk flask was charged with Pd(OAc)2 (22.2 mg, 0.33 mol%), cataCAlum A i.e., butyldi-1-adamantylphosphine) (108 mg, 1 mol%), and toluene (30 mL). Subsequently, hexadecane (1.5 mL, internal GC standard), tetramethylenetetramine (2.61 g, 3.40 mL, 22.5 mmol) and 4-bromoanisole (5.61 g, 3.77 mL, 30 mmol) were added. The resulting clear yellow solution was cannula-transferred to a 100 mL mini bench top reactor of the 4560 series from Parr Instruments (Moline, IL). After 16 h at constant 5 bar CO/Hj (1 1) and 100 °C, an aliquot was taken from the reaction mixture and subjected to GC analysis for determination of yield and conversion. The light yellow solution was separated from the solid tetramethylenetetramine-hydrobromide by filtration. The solvent was removed under reduced pressure and the residue was vacuum distilled to yield A-methoxybenzaldehyde (2.8 g, 71%) at 70 °C/0.15 mbar. ... 

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