Chlorinated phenoxy herbicides

There are many studies available concerning the characterization of interface and ionization performance for the thermospray LC-MS analysis of pesticides, herbicides and insecticides, the improvement of detection limits and information content of the mass spectra. Compound classes most frequently studied are the carbamates, organophosphorous pesticides, triazine and phenylurea herbicides, chlorinated phenoxy acetic acids, and sulphonylureas. 

Another case of high nitrosamine concentration in chlorinated phenoxy- and benzoic acid herbicides was resolved by the elimination by the manufacturer of nitrite salts in the formu-... 

Renberg [35] used an ion-exchange technique for the determination of chlorophenols and phenoxy acetic acid herbicides in soil. In this method the soil extracts are mixed with Sephadex QAE A-25 anion exchanger and the adsorbed materials are then eluted with a suitable solvent. The chlorinated phenols are converted into their methyl ethers and the chlorinated phenoxy acids into their methyl or 2-chloroethyl esters for gas chromatography. 

Di Corcia and Marchetti [160] determined chlorinated phenoxy acid and ester type herbicides in amounts down to lmg kg-1 or lower in soil by liquid chromatography combined with particle beam mass spectrometry and ultraviolet absorption spectrometry. 

Kim et al. [161] used particle beam mass spectrometry and ultraviolet absorption spectrometry as detectors in a method for the determination of down to lppm of chlorinated phenoxy and ester herbicides in soil. 

Polychlorinated Dibenzo-(p)-Dioxins and Dibenzo-Furans. Another group of compounds that we need to specifically address are the polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzo-furans (PCDFs) (Fig. 2.15). The PCDDs and PCDFs are not intentionally produced but are released into the environment from various combustion processes and as a result of their occurrence as unwanted byproducts in various chlorinated chemical formulations (e.g., chlorinated phenols, chlorinated phenoxy herbicides see Alcock and Jones, 1996). Because some of the PCDD and PCDF congeners are very toxic (e.g., 2,3,7,8-tetrachloro dibenzo-p-dioxin, see margin), there have been and still are considerable efforts to assess their sources, distribution, and fate in the environment. Similarly to the PCBs or DDT (see above), the PCDDs and PCDFs are highly hydrophobic and very persistent in the environment. It is therefore not surprising that they have also been detected everywhere on earth (Brzuzy and Hites, 1996 Lohmann and Jones, 1998 Vallack et al., 1998). Finally, we should note that polybrominated diphenylethers (PBDEs, see margin) that, like the PBBs (see above), are used as flame retardants, are of increasing environmental concern (de Boer et al., 2000). 

CDDs have been measured in all environmental media including ambient air, surface water, groundwater, soil, and sediment. While the manufacture and use of chlorinated compounds, such as chlorophenols and chlorinated phenoxy herbicides, were important sources of CDDs to the environment in the past, the restricted manufacture of many of these compounds has substantially reduced their current contribution to environmental releases. It is now believed that incineration/combustion processes are the most important sources of CDDs to the environment (Zook and Rappe 1994). Important incineration/combustion sources include medical waste, municipal solid waste, hazardous waste, and sewage sludge incineration industrial coal, oil, and wood burning secondary metal smelting, cement kilns, diesel fuel combustion, and residential oil and wood burning (Clement et al. 1985 Thoma 1988 Zook and Rappe 1994). 

An early chlorinated phenoxy acid herbicide (2,4-D) was first discovered in 1932. Although this compound rapidly breaks down in the environment, the seed fungicide hexachlorobenzene (HCB), introduced in 1933, was found to be far more persistent.2 The structurally similar insecticide hexachlorocyclohexane or... 

Tsyganok, A.I. and Otsuka, K. (1999) Selective dechlorination of chlorinated phenoxy herbicides in aqueous medium by electrocatalytic reduction over palladium-loaded carbon felt. Appl. Catal. B. Environ. 22, 15-26. 

Both underivatised and methylated samples are examined because uracil herbicides give a mixture of products on methylation and should be chromatographed in their underivatised forms, whereas carboxylic acid pesticides, e.g. chlorinated phenoxy acid herbicides, are best examined as methyl derivatives. 

Chlorinated phenoxy acid (CPA) herbicides can analysed by GC-MS only after derivatization. For LC-MS, negative-ion ESI is the method of choice. Deprotonated molecules are detected as the most abundant ions under these conditions, often next to a phenolate fragment ion due to the loss of the acid side chain. Next to the deprotonated molecule, weak formic acid adducts [M+HCOO] were observed for MCPA, 2,4-D, MCPP, andMCPB [41]. 

Graphitized carbon black (GCB) materials are frequently used for off-line SPE as well. GCB behaves as a nonspecific sorbent, but because positively-charged adsorption sites are present, it also acts as an anion exchanger, which is useful for the enrichment of acidic compounds [75]. Examples involve the enrichment of chlorinated phenoxy acids [42], aryloxyphenoxypropionic herbicides [45], sulfonylurea herbicides [50], and imidazolinone herbicides [65]. 

Kim, I.S., F.I. Sasins, R.D. Stephens, J. Wang, and M.A. Brown. 1991. Determination of chlorinated phenoxy acid and ester herbicides in soil and water by liquid chromatography particle beam mass spectrometry and ultraviolet spectrophotometry. Anal. Chem. 63 819-823. 

Takino, M., Daishima, S., and Nakahara, T., Automated online in-tube solid-phase microextraction followed hy liquid chromatography/electrospray ionization-mass spectrometry for the determination of chlorinated phenoxy acid herbicides in environmental water. Analyst, 126, 602-608,... 

Further recent developments in fiber SPME have extended applications to compounds with low volatilities and/or low thermal stability. Thus, fiber-(or tube-) based SPME-LC has a considerable future potential, particularly as it has been recognized that GC capillary columns (available with a very wide range of internal coatings) can be used for this purpose. Samples are pumped through the tube using a micropump and then eluted onto the EC column using appropriate solvents. Applications of in-tube SPME (in combination with LC) include phthalates, chlorinate phenoxy acid herbicides, tributyl tin compounds, polyaromatic hydrocarbons (PAEIs), and polar aromatic compounds in water. 

Chlorinated phenoxy acids are used extensively as herbicides in agriculmre, as algaecides in paints, and as coating agents. These are the main sources of their introduction in to the aquatic system. Their removal efficiency using... 

In sludge anionic and non-ionic surfactants carboxylic acids hhydroxybutyrate hydroxy valerate chloroaliphatic compounds chlorophenols polychlorobiphenyls 4-nitrophenol mixtures of organic compounds chlorinated insecticides, phenoxy acetic acid type herbicides and organotin compounds. 

Dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) dominated the herbicide market up to the late 1960s. These are sometimes called phenoxy herbicides. Phenol is the starting material for 2,4-D. Chlorination via electrophilic aromatic substitution (know the mechanism ) gives 2,4-dichlorophenol. The sodium salt of this compound can react with sodium chloroacetate (Sn2) and acidification gives 2,4-D. 

Numerous studies on the metabolism of 2,1t-dichlorophenoxy-acetic acid (2,1+-D) and related herbicides in animals have shown that these chemicals are absorbed and distributed rapidly in the body, and are excreted, undegraded, relatively quantitatively in the urine within a week after administration (M Pharmacokinetic studies with 2,1+,5-T in rats and dogs (5.) and in humans (6J supported these findings, and demonstrated that rates of clearance from plasma and elimination in urine depend on dosage level, animal species, and chemical structure of the phenoxy acid being studied ( + ). Corresponding chlorinated phenol metabolites were detected only in ruminants (M or in trace amounts in urine of rats fed very high doses of phenoxy herbicides (7.) ... 

Chlorinated [407,408] and 2,4-dinitrophenoxy acid herbicides [409] have been determined. liquid chromatography particle beam mass spectrometry has been used as an analytical finish [408]. Crescenzi et al. [410] evaluated the feasibility of selectively and rapidly extracting herbicide residues in soils by hot water and collecting analytes with a Carbograph 4 solid-phase extraction cartridge set on-line with the extraction cell. Phenoxy acid herbicides and those non-acidic and acidic herbicides that are often used in combination with phenoxy acids were selected for this study. Five soil samples were... 

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