Pesticides color reactions

Immunoassays, analytical procedures based on the specific binding of animal-derived antibodies to a target molecule (10), have been developed as rapid methods for detection of pesticides in soil and water samples. Field samples can be analyzed on site after water or solvent extraction using a visualization method, which generally involves reaction of the antibody-pesticide complex with an enzymatically derived colored product. The most sensitive and quantitative method for monitoring the color reaction is spectrophotometry. 

Organophosphorus (OP) insecticides containing phosphorus and sulfur atoms offer a large variety of chemical color reactions. There are also some corrunonly used methods based on the chlorine content of these insecticides, but these methods are not as specific for the OP pesticides. Further amine-specific reactions can also be applied for the visualization of these insecticides in certain cases. Comparing the sensitivities of these methods and enzyme inhibition (see Section V.B), the latter is two or three orders of magnitude better. 

A new method for the quantitative determination of pesticides is laser-pyrolysis scanning (LPS). No color reaction or visualization procedure is necessary simply the TLC plates are placed in a chamber after development and irradiated with an infrared laser to produce a high temperature at the location of the spot. The analyte is swept by a carrier gas to a gas chromatograph and analyzed by an appropriate sensitive GC detection method. 

Colorimetric agents, 938-939 Color reactions (pesticide detection system), 804-806... 

The 2,4-dinitrophenylhydrazone of patulin and other mono-2,4-dinitrophenylhydra-zones form red zones, 2-s c-butyl-4-amino-6-nitrophenol appears as a red-orange zone while dinitrophenols and their esters are colored yellow [14]. A whole range of organophosphorus pesticides do not give any reaction [12]. 

Absorbance- and reflectance-based measurements are widespread, as there are many enzymatic reaction products or intermediates that are colored or if not, can react with the appropriate indicator. Sensors using acetylcholinesterase for carbamate pesticides detection are an example of indirect optical fiber biosensors. This enzyme catalyses the hydrolysis of acetylcholine with concomitant decrease in pH41 ... 

As part of SW-846, the EPA has validated and approved many immunoassay and colorimetric screening methods for a wide range of contaminants, such as petroleum fuels, pesticides, herbicides, PCBs, and explosives. Immunoassay technology uses the property of antibodies to bind to specific classes of environmental pollutants allowing fast and sensitive semiquantitative or qualitative detection. Colorimetric kits are based on the use of chemical reactions that indicate the presence of target analytes by a change in color. Table 3.9 presents a summary of EPA-approved screening methods and their detection capabilities. 

Certain specialized reagents are used to visualize compounds based on their biological activity. Cholinesterase-inhibiting pesticides (e.g., organophos-phates, carbamates) are detected sensitively by treating the layer with the enzyme and a suitable suljstrate, which react to produce a colored product over the entire layer except where colorless pesticide zones are located due to their inhibition of the enzyme-substrate reaction. 

Pesticides are detected after development as colored, ultraviolet (UV)-absorbing, or fluorescent zones after reaction with a more or less selective re-... 

The sources of lipophilic/hydrophilic chemical exposure include environmental pollution (air, water, and soil contamination), pesticide, herbicide, and fertilizer residues in foods and drinking water, excipients (non-active additives such as colors, flavors, rheological agents, etc,) in foods and pharmaceuticals, industrial chemicals, household chemical products, personal care products, cosmetics, and environmentally synthesized chemicals that are formed from reactions with released chemicals with each other and with naturally present species. 

Dihydroxyphosphine oxide EINECS 237-066-7 Orthophosphorus Kid Phosphonic acid Phosphorous acid Phosphorus trihydroxide Trihydroxyphosphlne. Interm iate for manu ture of diphosphonic acids and phosphite salts used as pesticides, chelates, and plastic additives restricts color formation in esterification and condensation reactions (In small quantities) chemical reducing agent. Usually marketed as a 20% aqueous solution. White solid mp = 73° dj 1.65 soluble in H2O, EtOH. Albright Wilson Americas Inc. Asira Hassle AB CK Witco Corp. Janssen Chimica Lonzagroup Rasa. 

EIAs are most commonly used in pesticide analysis as they avoid the necessity of working with radioactive material and low DLs can be reached. Simple and cheap photometers which give an extremely rapid measurement capability and long-lasting stability of the colored product after the reaction has stopped make EIA superior to fluorimetry or luminometry, even though with these methods lower DLs may be reached. Enzymes... 

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