CEC enantioseparations on chiral monolithic columns: A study of the stereoselective degradation of (R/S)‐dichlorprop [2‐(2,4‐dichlorophenoxy)propionic acid] in soil

Abstract

For the study of the stereoselective degradation of the herbicide 2-aryloxipropionic acid dichlorprop (DCPP) in soil, a porous monolithic chiral column (100 microm id) was prepared by in situ copolymerization of glycidyl methacrylate, methyl methacrylate and ethylene glycol dimethacrylate in the presence of formamide and 1-propanol as the porogen solvents. Subsequently, the epoxide groups at the surface of the monolith were reacted with (+)-1-(4-aminobutyl)-(5R,8S,10R)-terguride as the chiral selector. Optimum conditions for the herbicide resolution by CEC were found using mobile phases consisting of acetic acid/triethylamine mixtures in ACN-methanol (9:1 v/v). Under these conditions fully separation of DCPP enantiomers in the presence of clofibric acid (internal standard) was achieved in about 5 min. Experiments on the incubation of rac-DCPP in soil at room temperature showed the herbicide undergone during 23 incubation days to a degradation to levels </=20% of the initial concentration, with rates for (R)-DCPP slower than (S)-DCPP. More interesting results were observed when herbicide enantiomers were individually incubated. In both the experiments, the formation of the opposite isomer in the presence of the initial one, and reversed enantiomeric interconversion in the case of (S)-DCPP was observed. (R)-DCPP was found to be the most persistent isomer after incubation.

Enantioselective capillary electrochromatography: Recent developments and new trends

“…The column showed stability towards external pressures up to 200 bar, indicating its mechanical stability. This study was continued for the determination of dichlorprop in soil samples [69]. Using this set-up, the degradation of this chiral herbicide could be followed.…”

Isomerization of chiral pesticides in the environment

“…The (S)-enantiomers of aryloxyalkanoic acid herbicides and their esters are favorably degraded in aerobic soils, [78][79][80][81][82][83][84][85][86][87] but with no enantiomerization reported for the esters. 79,81,[85][86][87] In most cases, the degradation of each enantiomer is faster than the chiral conversion in either direction, and the (S) (R) conversion rate (k SR ) is larger than the opposite one (k RS ); such as k SR /k RS =1.…”

Enantioseparation and Enantioselective Analysis of Chiral Herbicides

“…Under these conditions fully separation of DCPP enantiomers in the presence of clofibric acid (internal standard) was achieved in about 5 min. (Messina et al, 2007) A silica based monolithic capillary column derivatized with O-9-(tert-butylcarbamoyl) quinidine was prepared for CEC enantiomer separation of chiral 2-aryloxypropionic acid herbicides including inter alia DCPP, MCPP and fenoprop. Reasonable baseline separations of enantiomers were accomplished for all analytes after optimization of relevant mobile phase parameters in the anion-exchange CEC system, and the separations were comparable to such obtained on an optimized high density quinidine-carbamate modified organic polymer monolith column.…”

“…A large number of papers have discussed the enantioselectivity of DCPP and MCPP (Zipper et al, 1999, Rugge et al, 2002, Schneiderheinze et al, 1999, Zipper et al, 1998, Jarman et al, 2005, Garrison et al, 1996, Messina et al, 2007, Kurt-Karakus et al, 2010, Buser et al, 1997b, Muller et al, 1997, Wen et al, 2010), thereinto Bidleman et al (Kurt-Karakus et al, 2010 reviewed the concentrations and stereoisomer ratios of DCPP, MCPP and metolachlor. Mostly, the S-enantiomer of these herbicides degraded faster than the R-enantiomer (Zipper et al, 1999, Zipper et al, 1998, Garrison et al, 1996, Messina et al, 2007, Buser et al, 1997b, Muller et al, 1997. Enantioselective microbial degradation increased the enantiomeric ratio of R-to S-MCPP during groundwater passage of the landfill leachate (Zipper et al, 1998).…”