Herbicides phenoxyacetic acid type

Aliphatic hydrocarbons, triazine, substituted urea type and phenoxyacetic acid types of herbicides, Fluazifop and Fluazifop-butyl herbicides, ethylene diamine tetracetic acid salts in soil, aliphatic and polyaromatic hydrocarbons, phthalate esters, various organosulphur compounds, triazine herbicides, optical whiteners, mixtures of organic compounds and organotin compounds in non-saline sediments, aromatic hydrocarbons, humic and fulvic acids and mixtures of organic compounds in saline sediments and non-ionic surfactants and cobalamin in sludges. 

It is seen from Table 16.4, for example, that TCA a phenoxyacetic acid type of herbicide has a solubility exceeding 500000pg L 1 while chlorotoluron, a phenyl urea herbicide has a water solubility of 70mg L-1. Thus, due to rainfall over a period of time the concentration of TCA in soil will reduce considerably more rapidly than that of chlorotoluron. 

Gas chromatography has been used extensively for the determination of phenoxyacetic acid-type herbicides in soil extracts (Table 4.9). 

Larose and Chau [189] state that owing to the similar retention times of several common phenoxyacetic acid type herbicides the alkyl esters are subject to incorrect identification if several herbicides are present. Also, the sensitivity obtainable by means of electron capture detection of the alkyl esters by some herbicides, such as MCPA and MCPB is very poor and therefore the method is generally not suitable for the determination of these compounds in water. In addition, the methyl ester of MCPA has a very short retention time close to the solvent front and is prone to interference from sample coextractives, which usually appear in this region. In fact the MCPA methyl ester often cannot be detected even at higher levels because of overlapping with coextraction peaks when the same gas chromatographic parameters as for the determination of organochlorine pesticides are used. Hence other derivatives have been considered. 

The Frank and Demint [200] method is directly applicable to water samples. After addition of sodium chloride (340g IT1) and aqueous hydrochloric acid (1 1) to bring the pH to 1, the sample was extracted with ethyl ether and the organic layer was then extracted with 0.1M sodium bicarbonate (saturated with sodium chloride and adjusted with sodium hydroxide to pH8). The aqueous solution adjusted to pHl with hydrochloric acid was extracted with ether and after evaporation of the ether to a small volume, Dalapon was esterified at room temperature by addition of diazomethane (0.5% solution in ether) and then applied to a stainless steel column (1.5m/3mm) packed with Chromosorb P (60-80 mesh) pretreated with hexamethyldisilazane and then coated with 10% FFAP. The column was operated at 140°C, with nitrogen carrier gas (30mL muT1) and electron capture detection. The recovery of Dalapon ranged from 91 to 100% the limit of detection was O.lng. Herbicides of the phenoxyacetic acid type did not interfere trichloroacetic acid could be determined simultaneously with Dalapon. 

Applications of this technique are growing and include the analysis of mixtures of pesticides and herbicides, including oiganophosphorus, phenoxyacetic acid, caibamate, urea types, mixtures of various types of organic compounds, alkylbenzene sulphonates, polyethylene glycols, nonylphenyl ethoxylates, dioctadecylmethyl ammonium, ozonisation products and chlorination products. 

The derivatives of substituted phenoxyacetic acids are in practice the most important and most widely used of the hormone-type herbicides. 

During the short time of their application in the early 1980s, DLI interfaces were often applied for substance-specific analysis [60] of various types of pesticides and herbicides (triazines, carbamates, organophosphorus compounds) [61-67], chlorinated phenoxyacetic acids, phenylureas, analides (alachlor, propachlor and aldi-carb) [63]. 

We proposed a metabohc pathway of phosphonates with structure lo in plants when these compounds lo were initially designed. lo might be metabolized to substituted phenoxyacetic acids (lo-a) as auxin-type herbicide and acylphospho-nates (lo-c) as PDHc El inhibitors after the hydrolysis and oxidation by esterases and oxidases took place in plants (Scheme 1.21). 

The herbicidal activity of IC-IF including lA and IB were evaluated at different rates in the greenhouse. Substituted phenoxyacetic acid as an structure unit of auxin-type herbicide was contained in the stracture of lA-IF, therefore an auxin-type herbicide 2,4-D was used as a positive control for the test in the greenhouse. Considering 2,4-D against broadleaved weeds for post-emergence at a recommended rate of 0.2-2.0 kg ai/ha, a preliminary bioassay was first carried out at... 

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