Capillary Electrophoresis Of Chiral Pollutants

Capillary electrophoresis(CE) is a relatively recent instrumental separation technique,which is of high efficiency,low sample\reagent consumption,flexible modes.Separation of the analytes is achieved by their different velocities in the capillary driven by the high voltage.Enantiomers of a chiral compound can be separated in the presence of chiral selector(s) by capillary electrophoresis.A continuous increase in the interest for capillary electrophoresis concerning the enantiomeric separation is accelerated by the various chiral selectors and separation modes.With significant progress in chemical industry and environmental science,more attention has been paid on the pollutants,foods and pharmaceuticals.As far as chiral compound is concerned,more light should be shed on the analyte from the enantiomer level. Thus,there is urgent need for the robust chiral analysis method to obtain the unknown information masked by the achiral method.In this thesis,chiral separation of pollutants(imazalil and esbiothrin) was achieved by capillary electrophoresis.The chiral analysis method of Rotigotine and its structurally-related impurities was developed.The enantiospecific binding of Rotigotine and its antipode to serum albumin was studied by affinity capillary electrophoresis.1.A scheme was demonstrated to elucidate the degradation behaviors of fungicide imazalil enantiomers in soil using cyclodextrin-modified capillary zone electrophoresis.The separation buffer was 5 mmol/Lβ-cyclodextrin,50 mmol/L NaH₂PO₄,5 mmol/L(NH₄)H₂PO₄,pH 3.0.LODs of this method were 0.24 and 0.26μg/mL for(-)-and(+)-imazalil,respectively.The degradation rate of imazalil in soil under the five different sets of conditions decreased in the order:UV irradiation＞sunlight＞wheat planted＞sterilized＞in darkness. Imazalil in slightly alkaline soil(pH 8.2) collected in the suburbs showed non-enantioselective degradation.2.A comparison between chiral cyclodextrin-modified microemulsion electrokinetic chromatography(CD-MEEKC) and cyclodextrin-modified micellar electrokinetic chromatography(CD-MEKC) for the enantiomeric separation of esbiothrin was carried out.For both methods,the separation conditions were optimized by varying CD types and concentration,running buffer pH and compositions,organic modifiers,and temperature.The optimal CD-MEEKC conditions were 0.8%n-heptane,2.3%SDS,6.6%n-butanol, 90.3%10 mM sodium tetraborate containing 3%(w/v,the ratio of CD mass to microemulsion volume) methyl-β-cyclodextrin,pH 10,25℃.The optimized CD-MEKC conditions were 3.3%SDS,96.7%10 mM sodium tetraborate containing 5%(w/v)β-CD,pH 10,25℃.Both methods provided excellent separation(R_s≈3) with similar migration time(ca.15 min).The LODs for CD-MEEKC and CD-MEKC were 4.7 and 3.2μg/mL,respectively.Both the demonstrated CDMEEKC and CD-MEKC methods provided high efficiencies, low LODs,and reproducible enantioseparations of esbiothrin.3.A dual cyclodextrin(CD) system consisting of sulfatedβ-CD(S-β-CD) and methyl-β-CD(M-β-CD) based capillary electrophoresis method was proposed to separate the antiparkinsonian drug Rotigotine and its related chiral impurities.The method was optimized by varying the CD type,the buffer pH, individual CD concentration of the dual system and the ionic strength of background electrolyte.Under the optimum conditions,i.e.2%(w/v) S-β-CD and 2%(w/v) M-β-CD in 100 mM sodium phosphate,pH 2.5 as the running buffer,-20 kV,200 nm,20℃,a satisfactory separation of the six analytes was accomplished.The relative standard deviation for migration time was less than 0.58%,and 3.78%for peak area ratio.The linearity ranged from 0.005 to 0.25 mM.The recovery ranged from 95.9%to 108.3%.The LODs and LOQs for each enantiomer were 0.003 and 0.01 mM,respectively.This method was utilized for evaluating the chiral impurities of five batches of Rotigotine.4.Anionic polysaccharide dextran sulfate(DxS) was successfully employed as chiral selector for the enantioseparation of two antiparkinsonian drugs,including Rotigotine and trihexyphenidyl,by electrokinetic chromatography(EKC).The enantioseparation was performed under normal and reversed polarity modes and reversed enantiomer migration order was achieved under two modes.The parameters including buffer pH,DxS concentration,organic additive,and temperature were investigated and optimized.The optimized conditions for the enantioseparation under reversed polarity mode were 2.0%(w/v) DxS,10 mM phosphate buffer,pH 2.5,-30 kV, 25℃,200 nm.Under the optimal conditions,Rotigotine and trihexyphenidyl enantiomers were enantioresolved in 40 min with the resolution of 2.0 and 5.8, respectively.The analytes could be enantioseparated using DxS of molecular mass 1 000 000 or 500 000.It was inferred that the electrostatic,hydrophobic, and steric interactions may be involved in the chiral separation mechanism in this study.5.Enantiospecific binding of antiparkinsonian medication Rotigotine (S-enantiomer) and its antipode to human serum albumin(HSA) or bovine serum albumin(BSA) was demonstrated employing partial-filling affinity capillary electrophoresis(PF-ACE) under near-physiological conditions(50 mM phosphate,pH 7.4,37℃).The enantioseparation of the enantiomers was achieved by PF-ACE,subsequently the binding constants were obtained.It revealed that Rotigotine had weaker affinity for the two serum albumins,and both enantiomers showed stronger affinity for HSA than BSA.The presence of either site marker(warfarin or ketoprofen) had adverse effect on the enantioseparation due to the competitive binding,or even eliminated the enantioselective binding of the enantiomers to the albumin when the molar ratio of the site marker to the albumin was at certain level.Although there might be a synergistic binding between the drug and the albumin,it was suggested that siteâ…¡and siteâ… were the preferential binding site of the drug on HSA and BSA,respectively.