Herbicides chlorophenoxy acid

Chlorophenols, manufacture of, 23 654 Chlorophenoxy acid herbicides, 73 304 (E) -(RS) -1 -(4-Chlorophenyl) -4,4-dimethyl-2-(lH- l,2,4-triazol-l-yl)-pent-l-en-3-ol, 73 47—48. See also 4-Chlorophenyl-4,4- dimethyltriazol pentenol 4-Chlorophenyl-4,4-dimethyltriazol pentenol, 73 40t, 47 48 Chlorophosphazenes, 19 55, 56 in silicone polymerization, 22 556... 

HMSO (1986) Chlorophenoxy acid herbicides, trichlorobenzoic acid, chlorophenols, triazines and glyphosate in water. HMSO, London... 

Gomez, ]., Bruneau, C., Soyer, N., and Brault, A. Thermal degradation of chlorophenoxy acid herbicides. J. Agric. Food Chem., 36(3) 649-653, 1988. 

Yu, L., Qin, W., and Li, S. F. Y, Ionic liquids as additives for separation of benzoic acid and chlorophenoxy acid herbicides by capillary electrophoresis. Anal. Chim. Acta, 547,165-171,2005. 

Methods for Organochlorine Pesticides and Chlorophenoxy Acid Herbicides in Drinking Water and Raw Source Water Environmental Monitoring and Support Laboratory. U.S. Environmental Protection Agency Cincinnati, OH EPA 600/4-81-053. 

Some Common Chlorophenoxy Acid Herbicides Table 2.13.1... 

This is applied to separate acidic or basic organics from neutral organics. The solvent extract is shaken with water that is highly basic. The acidic organics partition into the aqueous layer whereas, the basic and neutral compounds stay in the organic solvent and separate out. After this, the aqueous layer is acidified to a pH below 2, and then extracted with methylene chloride. The organic layer now contains the acid fraction Phenols, chlorophenoxy acid, herbicides, and semivolatile organic pollutants are cleaned up by the procedure described above. 

Some of the common chlorophenoxy acid herbicides are listed in Table 2.11.1. 

Analysis for 2,4-D and 2,4,5-T in the air may be performed using NIOSH Method 5001. Other chlorophenoxy acid herbicides such as 2,4,5-TP, 2,4-DB, and MCPA can be analyzed in a same general way. The method involves HPLC determination of herbicides in the form of acids or salts but not their esters. 

Sherma, J (1986). Determination of triazine and chlorophenoxy acid herbicides in natural water samples by solid phase extraction and quantitative thin layer chromatography. J. Liquid Chromatog., 9(16) 3433-3438. 

Chlorophenoxy acid herbicides are also widely used to control broadleaf weeds and grass plants. Several immunoassays have been reported for 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T).246 247 Several immunosensors have been described using a transducing principle similar to the RIANA system already described in this chapter. Thus, Meusel et al.248 reported the use of monoclonal antibodies in a sensor chip to analyze river and lake water samples, obtaining detection limits of 0.1 ig L 1. Moreover, monoclonal antibodies, produced by Cuong et al.,249 were used in a dipstick immunoassay format to analyze pond water samples. When applied to the 2,4-D compound, this semiquantitative method yielded for an IC50 of 6 ug I. and an LOD of 0.5 pg L-1. 

Occupational Exposure. Exposures to 2,3,7,8-TCDD, one of the most potent of the CDD congeners, have occurred occupationally in workers involved in the manufacture and application of trichlorophenols and the chlorophenoxy acid herbicides 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichloro-phenoxyacetic acid (2,4,5-T). Holmstedt (1980) has reviewed the history of industrial exposures that have occurred between 1949 and 1976, and Kogevinas et al. (1997) summarized recent data on these cohorts. 

A procedure might be for the, Preparation of an extract of chlorophenoxy acidic herbicides from water using Cl8 solid phase cartridge . The procedure will contain a set of instructions, for the analyst to follow, on how to obtain the extract solution. Another procedure will be required to explain how to analyse the extract solution using gas chromatography. 

These herbicides are highly selective for hroadleaved weeds. 2,4-D was the first chlorophenoxy acid herbicide developed. There are several compounds that belong to this group in addition to 2,4-D and they include 2,4-DB, Di-chlorprop, MPCA, MPCB, MCPP, 2,4,5-T, and 2,4,5-TP (Silvex). 

Analysis of Chloronhenoxv Herbicides. Many important target environmental pollutants can only be detected via conventional GC methods by first converting them to derivatives that are less polar and more volatile, e.g., the chlorophenoxy herbicides. A standard EPA method (SW-846 8150) specifies soil extraction and alkaline hydrolysis of any esters present followed by (re) esterification via diazomethane and detection and confirmation by GC/MS. The methylation step is required because the free carboxylic acids will not pass through conventional GC analytical columns. Reversed phase chromatography functions equally well to resolve free carboxylic acids or the corresponding esters and thus can eliminate the diazomethylation step. An interlaboratory check sample provided by the EPA of soil spiked with the chlorophenoxy acid herbicides Silvex and 2,4-D was obtained by our laboratory to demonstrate that LC/MS can offer a simpler and effective method for these compounds. 

Hopper, M.L. 1987. Methylation of chlorophenoxy acid herbicides and pentachlo-rophenol residues in foods using ion-pair alkylation. /. Agric. Food Chem. 35 285-289. 

Catalina, M. I., Dalliige, J., Vreuls, R. J. J., and Brinkman, U. A. Th., Determination of chlorophenoxy acid herbicides in water by in situ esterihcation followed by in-vial liquid-liquid extraction combined with large-volume on-column injection and gas chromatography-mass spectrometry, J. Chromatogr. A, 877, 153-166, 2000. 

Luque-Garcia, J. L. and Luque de Castro, M. D., Coupling continuous subcritical water extraction, filtration, preconcentration, chromatographic separation and UV detection for the determination of chlorophenoxy acid herbicides in soils, J. Chromatogr. A, 959, 25-35, 2002. 

Chlorophenol metabolites of chlorophenoxy acid herbicides were successfully extracted from water and soils by SPME. The optimization of the derivatization-SPME in water for these metabolites (among 30 phenohc compounds), showed that CW-PDMS (85 fim) was the most suitable fiber, with quantification limits ranging from 1 to 15... 

In the case where liquid chromatography is not available, acidic herbicides need to be derivatized because they can dissociate in water and are not usually volatile to be analyzed by gas chromatography. The basic methods used for chlorophenoxy acid herbicides are esterification, silylation, and alkylation, as described in a recent exhaustive review.The derivatization step is performed after preconcentration and cleanup. The step consists of the formation of esters and ethers from the carboxyl and phenol groups of the acidic herbicides. A lot of reagents and chemical mechanisms can be used to perform derivatization reactions. The most employed derivatization reagents are diazomethane, methyliodide, trimethylsulfonium (or anilinium) hydroxide, bis (trimethylsilyl) trifluoroacetamide (BSTFA), pentafluorobenzyl bromide, and anhydride acetate. It should be noted that explosive and hazardous diazomethane was replaced by safer agents. Authors also underline that surface water generally contains humic substances, which can interfere with the derivatization reaction. ... 

Rosales-Comado, N., Leon-Gonzalez, M. E., Perez-Arribas, L. V., and Polo-Diez, L. M., Determination of chlorophenoxy acid herbicides and their esters in soil by capillary high performance liquid chromatography with ultraviolet detection, using large volume injection and temperature gradient. Anal. Chim. Acta, 470, 147-154, 2002. 

Chlorophenoxy acid herbicides, such as, 2,4-D, silvex, or 2,4,5-T — In these compounds, the alkyl group of a lower carboxylic acid usually acetic or propionic acid is attached to a chlorophenoxy moiety as follows ... 

Chlorophenoxy acid herbicides, such as acids, or as their esters or salts, are first converted into acids, which are then extracted with solvent ether. The solvent extract is treated with a methylating agent, then converted to their methyl esters. The acids are converted into their methyl esters. The esters are extracted with toluene or benzene and determined by a GC, using an ECD, or by a GC/MS. 

Herbicides are conveniently analyzed by instrumental techniques GC, HPLC, and GC/MS. For GC analysis, selection of the detector should be based on the structure of the herbicides. Chlorinated compounds, including the chlorophenoxy acid herbicides in potable water or wastewater, can be analyzed by GC-ECD. Chlorophenoxy acids (e.g.,... 

It is used in organic synthesis as a methylating agent to methylate acidic compounds such as carboxylic acids and phenols. It is used in trace environmental analysis to methylate chlorophenoxy acid herbicides. 

Liquid-liquid extraction (LLE) LLE is the classical method used for herbicide isolation, especially from water and biological fluid samples. Ethyl acetate, dichloromethane, and their mixtures are among the preferred extraction solvents for phenylureas, triazoles, amides, carbamates, benzimidazoles, and chlorotriazines. The extraction efficiency is modified by adjustment of pEI and ionic strength in the aqueous phase. In situ derivatization of the target analytes is also used as an effective tool (e.g., chlorophenoxy acidic herbicides are derivatized with dimethyl sulfate prior to their extraction by n-hexane). The classical way of performing LLE is the separation funnel extraction. Some continuous LLE extractors or steam distillers are also available. 

Mobile phases Eor RP-LC, mixtures of an aqueous component and organic solvents are invariably used. The aqueous component is eventually buffered (e.g., phosphate buffers l-10mmoll for triazines and phenylureas) or acid additivated (e.g., 0.1% phosphoric acid for chlorophenoxy acidic herbicides or 0.1-0.4% for phenoxyacetic herbicides). The organic solvents are mainly methanol, acetonitrile, or their mixtures. For NP-LC, hexane, dichloromethane, ethanol, and iso-propanol are frequently used. 

Herbicides are the most widely used type of pesticides, and triazines, N-arylcarbamates, and chlorophenoxy acids are among the most important classes of herbicides. Herbicides are used to control unwanted grasses and weeds in a variety of crops, such as cotton, alfalfa, sunflower, sorghum, rice, and a variety of fruits and vegetables. The following experiment involves the analysis of atra-zine as an example of the triazines, 2,4-D for the chlorophenoxy acid herbicides, and chlorpropham for the carbamates. 

Ding, W.-H., Liu, C.-H., and Yeh, S.-P., Analysis of chlorophenoxy acid herbicides in water by large-volume online derivatization and gas chromatography-mass spectrometry, /. Chromatogr. A, 896, 111, 2000. 

Qin, W. and Li, S.F.Y., Determination of chlorophenoxy acid herbicides by capillary electrophoresis with integrated potential gradient detection. Electrophoresis, 24, 2174, 2003. 

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