Phenoxy acid herbicides resolution

CE has been used for the analysis of chiral pollutants, e.g., pesticides, polynuclear aromatic hydrocarbons, amines, carbonyl compounds, surfactants, dyes, and other toxic compounds. Moreover, CE has also been utilized to separate the structural isomers of various toxic pollutants such as phenols, polyaromatic hydrocarbons, and so on. Sarac, Chankvetadze, and Blaschke " resolved the enantiomers of 2-hydrazino-2-methyl-3-(3,4-dihydroxyphenyl)propanoic acid using CD as the BGE additive. The CDs used were native, neutral, and ionic in nature with phosphate buffer as BGE. Welseloh, Wolf, and Konig investigated the CE method for the separation of biphenyls, using a phosphate buffer as BGE with CD as the chiral additive. Miura et al., used CE for the chiral resolution of seven phenoxy acid herbicides using methylated CDs as the BGE additives. Furthermore, the same group resolved 2-(4-chlorophenoxy) propionic acid (MCPP), 2-(2,4-dichlorophenoxy) propionic acid (DCPP), (2,4-dichlorophenoxy) acetic acid (2,4-D), 2-(4-chlorophenoxy) propionic acid (2,4-CPPA), [(2,4,5-... 

Crego and Marina [1] and Giibitz and Schmid [16] reviewed the chiral resolution of environmental pollutants by CE, and they described phosphate, borate, acetate, CHES and carbonate as suitable BGEs. Welseloh et al. [17] used a pH 2.4 30 mM phosphate buffer as the BGE for the chiral resolution of biphenyls. Mechref and El Rassi [40] resolved phenoxy acid herbicides using 175 mM phosphate (pH 6.5) [40] and 200 mM borate (pH 10.0) buffers [37] as BGEs. Furthermore, Tsunoi et al. [20] used a mixture of 0.1 M borate and 0.05 M phosphate buffers (pH 9.0) as BGE for the chiral... 

Figure 9.2 The effect of pH on the chiral resolution of phenoxy acid herbicides, using 100 mM sodium phosphate-sodium acetate buffers containing 60 mM OM as BGE. Other conditions as in Figure 9.1 [37],...

Figure 9.4 The effect of the cyclodextrin concentration on the chiral resolution of phenoxy acid herbicides, using 25 mM sodinm phosphate and 600 mM borate buffers (pH 5.0) containing different concentrations of (a) fi-CD, (b) DM-jS-CD, (c) HP-yJ-CD and (d) TM-jS-CD as BGEs. 1 = dichlorprop, 3 = mecoprop, 4 = 2,3-CPPA, 5 = 2,4-CPPA, 6 = silvex, 8 = 2, 2-CPPA, 9 = 2-PPA [34],...

The chiral resolution of environmental pollutants by CE depends on the formation of diastereomeric complexes and, therefore, the stmctures and sizes of the chiral pollutants are responsible for their enantiomeric resolution. To study this aspect, phenoxy acid herbicides (see Table 9.4) may be considered as the best class of chiral pollutant. Mechref and El Rassi [40] studied these herbicides using cyclodextrins as chiral selectors. It has been reported that the chiral resolution of these herbicides was in the order 2-PPA > 2,2-CPPA > 2,3-CPPA. 2-PPA has no chlorine atom on the phenyl ring, while 2,2-CPPA and 2,3-CPPA have chlorine atoms in the ortho- and meta- positions, respectively. Therefore, it may be concluded that the chlorine atom creates some sort of hindrance in the formation of diastereomeric complexes. Furthermore, it may be observed that the ortho- position creates a greater strain in comparison to the meta- position in the formation of diastereoisomeric complexes, and hence the above-mentioned order of resolution is observed. Briefly, the steric effect due to... 

Additional peaks and improved resolution of peaks were obtained after cleanup and column chromatography separations. The method of analysis is described by the flow diagram shown in Figure 3. An aliquot of the air-dried dust was slurried with water, adjusted to pH 3 with sulfuric acid, and then repeatedly extracted in a Waring blendor with a solvent mixture of hexane and diethyl ether, 1 + 1 (v./v.). A portion of the extract was used for herbicide analysis in which methylation with diazomethane and gas chromatography were employed for the detection of the methyl ester of the chloro-alkyl phenoxy compounds. 

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