Pesticides carbamate types

Pesticides can be analyzed on a C18 column, the chlorinated hydrocarbon type (chlordane) at 80% An/water UV, 220 nm, the carbamate type (sevin) at 40% An/water UV, 254 nm, and the organic phospahate (malathion) at 50% An/water with UV, 192 nm or with a CAD. The organic phosphate types are hard to detect at low concentration and various phosphate analysis techniques have been evaluated. LC/MS, where available, is the technique of choice for analyzing all of these pesticides, but especially the organic phosphates, in a general gradient HPLC scheme. 

The term pesticide includes chemicals used to eradicate rodents (rodenticides), fungi (fungicides), weeds (herbicides) and insects (insecticides). These agrochemicals may be used directly on the medicinal plant crop itself, they may be used on crops growing adjacent to the herbs or they may occur as general environmental pollutants in soil, air or water. The presence of insecticide residues is of particular concern because those of the organochlorine type (DDT etc.) have been shown to cause cancers in animals and those of the organophosphate and carbamate types are potent cholinesterase inhibitors. 

Methode M.403-PEST4.0 Eaux — Determination des pesticides de types organophosphores, triazines, carbamates, urees substituees, phtalimides et pyrethrinoides. Extraction in situ avec dichloromethane dosage par chromatographie en phase gazeuse couplee a un... 

The contamination of fruits and vegetables with pesticides became a problem with the increased application of pesticides because of an intensified agriculture. So the comparison of APCI and ESI-LC-MS for the determination of 10 pesticides of carbamate type (pirimicarb, carbofuran, 3-hydroxycarbofuran, aldicarb, and its metabolites, the sulfoxide and the sulfone), besides others in fruits, met the... 

The reaction of [ CJacetyl chloride and sodium azide forms [ " C]acetyl azide, which upon heating rearranges to give methyl [ " C]isocyanate (34). The latter was used for the carbon-14 labeling of eserine 1351. a potent acetylcholinesterase inhibitor of the carbamate type, and of IBMU (36), a urea type pesticide . 

Carboxyhc acid ester, carbamate, organophosphate, and urea hydrolysis are important acid/base-catalyzed reactions. Typically, pesticides that are susceptible to chemical hydrolysis are also susceptible to biological hydrolysis the products of chemical vs biological hydrolysis are generally identical (see eqs. 8, 11, 13, and 14). Consequentiy, the two types of reactions can only be distinguished based on sterile controls or kinetic studies. As a general rule, carboxyhc acid esters, carbamates, and organophosphates are more susceptible to alkaline hydrolysis (24), whereas sulfonylureas are more susceptible to acid hydrolysis (25). 

Enzymes can be used not only for the determination of substrates but also for the analysis of enzyme inhibitors. In this type of sensors the response of the detectable species will decrease in the presence of the analyte. The inhibitor may affect the vmax or KM values. Competitive inhibitors, which bind to the same active site than the substrate, will increase the KM value, reflected by a change on the slope of the Lineweaver-Burke plot but will not change vmax. Non-competitive inhibitors, i.e. those that bind to another site of the protein, do not affect KM but produce a decrease in vmax. For instance, the acetylcholinesterase enzyme is inhibited by carbamate and organophosphate pesticides and has been widely used for the development of optical fiber sensors for these compounds based on different chemical transduction schemes (hydrolysis of a colored substrate, pH changes). 

In many applications nowadays it is essential to link a mass spectrometer to the gas chromatography in order to achieve positive identification and sensitivity of analysis. Some 12 types of compounds are listed in Table 1.11(a) which are based on the application of this technique, viz. polyaromatic hydrocarbons, polychlorobenphenyls, dioxins, chloro, carbamate and triazine types of herbicides and pesticides, Diazinon, Dicamba, Imidazoline and Cyperquat herbicides and herbicide pesticide mixtures. 

Estimated half-lives for chlorinated hydrocarbon pesticides vary widely [16, 22] Aldrin, 1-9 Dieldrin, 3-7 Chlordane, 1-8 Heptachlor, 1-4 and DDT, 3-10 years. Half-lives for PCBs range from one year to 16 years [23]. Other types of pesticides, e.g. organophosphates, triazines, carbamates and ureas, are generally less persistent [16, 24],... 

A preliminary cleanup procedure is often required for most food sample extracts before determination by HPLC. The goal of cleanup is to remove as much interfering coextracted material and as little analyte as possible. Due to the wide range of polarities of carbamate pesticides, it is difficult to develop one cleanup procedure equally effective for all of them. Therefore, the cleanup procedure will depend on the type of compound, the kind of sample to be analyzed, and the selectivity of the analytical equipment used in the determination. The use of selective detectors can reduce or even eliminate the need for cleanup procedures in some cases. 

Method 1 (cellulose layers). The cellulose powder is washed twice with isopropanol-ammonium hydroxide-water (6 3 1), washed once in isopropanol and dried at 10S °C for 8 h. The plates (thickness, 0.25 mm) are prepared with a commercial TLC applicator. The slurry consists of 15 g of prepared cellulose in 85 ml of water which has been homogenized in a blender. The plates are dried at room temperature, and then eluted with diethyl ether in order to remove organic impurities. The plates are dried in air immediately before use. The pesticides are spotted and developed with appropriate solvent systems. The chromatoplate is dried in air and sprayed lightly with a 0.05% solution of fisetin in isopropanol. The separated spots are observed visually under a UV light at 365 nm (excitation, 370 nm emission, 533 nm). This method has been examined for several types of pesticides including carbamates, organophosphates, triazines and chlorinated hydrocarbons. 

A series of multielectrode sensors were developed based on Drosophila mutant AChE immobilised via photocrosslinking onto screen-printed carbon electrodes [8]. Four different mutant and wild-type AChE were evaluated for their sensitivity to the organophosphate paraoxon and the carbamate pesticide carbofuran. The response of the electrodes in thiocholine before and following a 15-min exposure to solutions of the pesticides was compared. The data was then processed using a feed-forward neural network generated with NEMO 1.15.02 as previously described [8,9]. Networks with the smallest errors were selected and further refined. This approach together with varying the AChE led to the construction of a sensor with capability to analyse the binary pesticide mixtures. 

The structure of urea type pesticide is similar to carbamate, except the terminal oxygen atom is replaced by a nitrogen atom. 

Analysis of Pesticides. Organophosphates, carbamates, atrazine derivatives, and other types of compounds are receiving expanded use in comparison to classical organochlorine pesticides. Many of these compounds are not amenable to GC analysis due to thermal instability or other factors. HPLC holds promise for analysis of such substances. HPLC procedures for selected pesticide analyses are presented in the following. 

Pesticides include a broad range of substances most commonly used to control insects, weeds, and fungi. Insecticides are often subclassified by chemical type as organophosphates, organochlorines, carbamates, and pyrethroids [110]. Some studies have indicated that pesticide exposure is associated with chronic health problems or health symptoms such as respiratory problems, memory disorders, dermatologic conditions, cancer, depression, neurologic deficits, miscarriages, and birth defects [111]. 

As Table I illustrates, the chemical classes represented by the pesticides studied include thiophosphates [0,0-diethyl-o-p-nitrophenyl phos-phorothioate], carbamates [1-naphthyI-N-methylcarbamate], dinitrophe-nols [2,4-dinitro-o-sec-butylphenol and 2,4-dinitro-o-cyclohexylphenol], and chlorophenoxy acids [2,4-dichlorophenoxyacetic acid, 2,4,5-trichloro-phenoxyacetic acid, and 2-(2,4,5-trichlorophenoxy)propionic acid]. In addition, a number of molecularly related nitrophenols have been studied to establish the effects of molecular geometry and substituent groups on adsorption of pesticide-type materials. 

Pesticide is used to control pests of different kinds, such as target insects, vegetation, and fungi. Pesticides are known poisons used specifically for the control of crop pests and rodents. Some are very poisonous, or toxic, and may seriously injure or even kill humans. Others are relatively nontoxic. Pesticides can irritate the skin, eyes, nose, or mouth. The health effects of pesticides depend on the type of pesticide. The organophosphate and carbamate pesticides affect the nervous system. Others cause irritation to the skin, eyes, and mucous membranes. Several pesticides are carcinogens and some others cause disturbances to the hormone or endocrine system in the body. 

Hydrolytic Reactions. Many pesticides possess bonds that are susceptible to hydrolytic attack. These reactions are most easily characterized according to the type of bond hydrolyzed carboxjlic acid ester, carbamate, oiganophosphate, urea, or chlorine (hydrodechlorination). In many instances the specific hydrolytic enzymes have been purified and characterized and the genes encoding for the enzymes isolated and cloned. It is commonly observed that there are multiple forms of the enzymes catalyzing a particular hydrolytic reaction, which suggests that these catalytic functions have evolved independendy in different bacteria (19). 

A further negative influence on the possible limit of detection of residue analysis is given by the type of residue under investigation. There is a marked difference in detector sensitivity in analysis of, e.g., carbamates and DDT-type pesticides. The general diflBculties of each class have to be considered, as is demonstrated in Table III. 

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