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Chiral Selector (chiral + selector)
Selected AbstractsEnantioselective, Potentiometric Memberane Electrodes Based on Different Cyclodextrins as Chiral Selectors for the Assay of S-FlurbiprofenELECTROANALYSIS, Issue 17 2006Raluca-Ioana Stefan-van, Staden Abstract Four enantioselective, potentiometric membrane electrodes (EPMEs) based on carbon paste impregnated with ,-, ,-, 2-hydroxyl-3-trimethylammoniopropyl-,-(as chloride salt) and ,-cyclodextrins, were proposed as a chiral selectors for assay of S-flurbiprofen raw materials and in its pharmaceutical formulation Froben 100 tablets. The best response was obtained when ,-cyclodextrin was used for the electrode design. The four EPMEs showed very low detection limits (of 10,8 to 10,9 mol/L magnitude orders). The surfaces of the electrodes are easily renewable by simply polishing on an alumina paper. [source] Enantioselective Recognition of Aspartic Acids by Chiral Ligand Exchange PotentiometryELECTROANALYSIS, Issue 11 2004Yanxiu Zhou Abstract Enantioselective resolution is realized by combining potentiometry with ligand exchange (CE) in a new method called chiral ligand exchange potentiometry (CLEP). A chiral selector, N -carbobenzoxy- L -aspartic acid (N-CBZ-L-Asp), preferentially recognizes D -aspartic acid (D-Asp) and undergoes ligand exchange with the enantiomeric labile coordination complexes of [Cu(II)(D-Asp)2] or [Cu(II)(L-Asp)2] to form a diastereoisomeric complex [(D-Asp)Cu(II)(N-CBZ-L-Asp)] (a) or [(L-Asp)Cu(II)(N-CBZ-L-Asp)] (b). Considerable stereoselectivity occurs in the formation of these diastereoisomeric complexes, and their net charges were ,2 (a) and 0 (b), respectively, resulting in different Nernst factor (electrode slope), thus enabling chiral D-Asp to be distinguished by potentiometry without any pre- or postseparation processes. [source] Determination of the binding constants of modafinil enantiomers with sulfated ,-cyclodextrin chiral selector by capillary electrophoresis using three different linear plotting methodsELECTROPHORESIS, Issue 17 2010Khaldun M. Al Azzam Abstract Binding constants for the enantiomers of modafinil with the negatively charged chiral selector sulfated-,-CD (S-,-CD) using CE technique is presented. The calculations of the binding constants employing three different linearization plots (double reciprocal, X -reciprocal and Y -reciprocal) were performed from the electrophoretic mobility values of modafinil enantiomers at different concentrations of S-,-CD in the BGE. The highest inclusion affinity of the modafinil enantiomers were observed for the S -enantiomer,S-,-CD complex, in agreement with the computational calculations performed previously. Binding constants for each enantiomer,S-,-CD complex at different temperatures, as well as thermodynamic parameters for binding, were calculated. Host,guest binding constants using the double reciprocal fit showed better linearity (r2>0.99) at all temperatures studied (15,30°C) and compared with the other two fit methods. The linear van't Hoff (15,30°C) plot obtained indicated that the thermodynamic parameters of complexation were temperature dependent for the enantiomers. [source] Heart-cutting 2D-CE with on-line preconcentration for the chiral analysis of native amino acidsELECTROPHORESIS, Issue 6 2010Suzanne Anouti Abstract The use of transient moving chemical reaction boundary (tMCRB) was investigated for the on-line preconcentration of native amino acids in heart-cutting 2D-CE with multiple detection points using contactless conductivity detection. The tMCRB focusing was obtained by using ammonium formate (pH 8.56) as sample matrix and acetic acid (pH 2.3) as a BGE in the first dimension of the heart-cutting 2D-CE. Different experimental parameters such as the injected volume and the concentration in ammonium formate were optimized for improving the sensitivity of detection. A stacked fraction from the first dimension was selected, isolated in the capillary, and then separated in the second dimension in the presence of a chiral selector ((+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid). This on-line tMCRB preconcentration coupled with heart-cutting 2D-CE was applied with success to the chiral separation of D,L -phenylalanine, and D,L -threonine in a mixture of 22 native amino acids. The sample mixture was diluted in 0.8,M of ammonium formate, and injected at a concentration of 2.5,,M for each enantiomer with a volume corresponding to 10% of the total capillary volume. An LOD (S/N=3) of 2,,M was determined for L -threonine. [source] Glycogen: A novel branched polysaccharide chiral selector in CEELECTROPHORESIS, Issue 6 2010Jiaquan Chen Abstract Various chiral selectors have been employed in CE and among them linear polysaccharides exhibited powerful enantioselective properties. Different from linear polysaccharides, the use of branched polysaccharides as chiral selectors in CE has not been reported previously. In this study glycogen belonging to the class of branched polysaccharides was used as a novel chiral selector for the enantiomeric separations for the first time. Since glycogen is electrically neutral, the method is applicable to ionic compounds. Eighteen chiral compounds including 12 basic drugs and six acidic drugs have been tested to demonstrate the potential of this chiral selector. BGE and selector concentrations and buffer pH were systematically optimized in order to obtain successful chiral separations. Among the tested compounds, the enantiomers of ibuprofen, which is an acidic drug, were successfully recognized by 3.0%,w/v glycogen with 90,mM Tris-H3PO4 buffer (pH 7.0). The enantiomers of basic drugs such as citalopram, cetirizine and nefopam were also baseline-resolved with 50,mM Tris-H3PO4 buffer (pH 3.0) containing 3.0% glycogen. Amlodipine belonging to basic compound only gave partial enantioseparation under the above-mentioned condition. [source] Direct chiral analysis of primary amine drugs in human urine by single drop microextraction in-line coupled to CEELECTROPHORESIS, Issue 16 2009Kihwan Choi Abstract Three-phase single drop microextraction (SDME) was in-line coupled to chiral CE of weakly basic amine compounds including amphetamine. SDME was used for the matrix isolation and sample preconcentration in order to directly analyze urine samples with the minimal pretreatment of adding NaOH. A small drop of an acidic aqueous acceptor phase covered with a thin layer of octanol was formed at the tip of a capillary by simple manipulation of the liquid handling functions of a commercial CE instrument. While the saline matrix of the urine sample was blocked by the octanol layer, the basic analytes in a basic aqueous donor phase were concentrated into the acidic acceptor drop through the octanol layer by the driving force of the pH difference between the two aqueous phases. The enantiomers of the enriched amines were resolved by using (+)-(18-crown-6)-tetracarboxylic acid as a chiral selector for the subsequent CE separation. From 10,min SDME with the agitation of the donor phase by a small stirrer retrofit to the CE instrument, enrichment factors were about a 1000-fold, yielding the LOD of 0.5,ng/mL for amphetamine. This low LOD value as well as the convenience of in-line coupled SDME make the proposed scheme well suited for the demanding chiral analysis of amphetamine-type stimulants. [source] Enantioselective determination of thyroxine enantiomers by ligand-exchange CE with UV absorbance and ICP-MS detectionELECTROPHORESIS, Issue 10 2009Jianzhen Kang Abstract A simple CE method has been developed for the separation and determination of thyroxine (T4) enantiomers in pharmaceutical formulations. The method was based on ligand-exchange mechanism using a Cu(II)/L -proline complex as chiral selector. The effects of different parameters affecting separation such as chiral selector concentration, organic additive, buffer pH and temperature were investigated. A baseline separation of the two enantiomers was obtained at a Cu(II)/L -proline ratio of 1:8 in a borate buffer (15,mmol/L, pH 9.6) containing 10%,v/v acetonitrile. Under the optimized conditions, precision linearity range and detection limits of the developed enantioselective CE method were evaluated and compared using two different detection systems: conventional UV detection at 226,nm and iodine (127I)specific detection ("chiral speciation") with ICP-MS. Both methodologies show adequate analytical performance characteristics with detection limits around 0.30,,g/mL for each enantiomer of T4. Finally, a levothroid pharmaceutical formulation sample was successfully analyzed using both developed methods CE-UV and CE-ICP-MS. [source] Improved simultaneous enantioseparation of ,-agonists in CE using ,-CD and ionic liquidsELECTROPHORESIS, Issue 6 2009Lu Huang Abstract In this study, approaches to improve chiral resolutions in simultaneous enantioseparation of ,-agonists by CE via a CD inclusion complexation modified with ionic liquids (ILs) are described. Different types of ILs, including tetraalkylammonium-based ILs, alkylimidazolium-based ILs and alkylpyridinium-based ILs, were examined and compared for controlling the EOF in order to improve resolutions of ,-agonists enantiomers. In this regard, tetraalkylammonium-based ILs were more effective because they could be used at much higher concentrations than other types of ILs. N -octylpyridinium hexafluorophosphate gave poor resolutions of ,-agonists enantiomers. In addition, when different ILs were mixed to use, they would present particular properties of their own. Moreover, the presence of ILs was essential in the chiral separations of (±) salbutamol, (±) cimaterol and (±) formoterol, which were reportedly not enantioseparated by using the buffer electrolytes containing only ,-CD as a chiral selector. [source] Fast derivatization of the non-protein amino acid ornithine with FITC using an ultrasound probe prior to enantiomeric determination in food supplements by EKCELECTROPHORESIS, Issue 6 2009Elena Domínguez-Vega Abstract An EKC method for the determination of ornithine (Orn) enantiomers has been developed after a fast pre-capillary derivatization with FITC. The derivatization step was needed to provide a chemical moiety to the Orn molecule, enabling a sensitive UV detection and the interaction with the CDs used as chiral selectors. To accelerate the derivatization reaction, an ultrasound probe was used. For the development of the chiral method, the influence of different experimental conditions (type and concentration of the chiral selector, temperature, and separation voltage) was investigated. Due to the anionic nature of the analyte (FITC-Orn), five neutral CDs were employed as chiral selectors. The native ,-CD showed the highest chiral separation power, observing that a low concentration of this CD (1,mM), using a working temperature of 25°C and a separation voltage of 20,kV, enabled to obtain the highest enantioresolution for Orn and its separation from other amino acids usually present in food supplements. After optimizing the method for the preconditioning of the capillary, the analytical characteristics of the chiral method were established. Linearity, LOD and LOQ, precision, and accuracy were evaluated previously to the determination of Orn enantiomers contained in ten commercial food supplements. No interferences from other amino acids present in these samples were observed. [source] Chiral separation of the plant lignan matairesinol by capillary electrophoresis,ELECTROPHORESIS, Issue 17 2008Ulrike Müller Abstract Lignans are dimeric phenylpropanoid compounds in plants that enjoy increasing medicinal interest because of their phytoestrogen activity. Lignans are chiral compounds and for most natural occurring lignans, chirality is not known. Separation of racemic matairesinol by CE in a non-coated silica capillary with carboxymethyl-,-cyclodextrin as chiral selector in phosphate buffer was successful. Electrolyte and selector concentrations and pH were systematically optimized in order to obtain baseline separation and short analysis times. Matairesinol from safflower fruit was determined as (,)-enantiomer. Quantitation results for matairesinol with the optimized method after calibration with authentic lignan were very similar to those by HPLC. The limit of detection is 2,,g/mL sample by DAD detection. [source] Determination of flurbiprofen enantiomers in plasma using a single-isomer amino cyclodextrin derivative in nonaqueous capillary electrophoresis,ELECTROPHORESIS, Issue 17 2008Anne Rousseau Abstract A nonaqueous capillary electrophoresis (NACE) assay was developed for the separation and determination of flurbiprofen enantiomers in plasma samples using 6-monodeoxy-6-mono(3-hydroxy)propylamino-,-cyclodextrin as chiral selector. The nonaqueous background electrolyte was made up of 40,mM ammonium acetate in methanol (MeOH), and flufenamic acid was employed as internal standard. Solid-phase extraction was used for sample cleanup prior to the NACE separation. The NACE method reproducibility was optimized by evaluating different capillary washing sequences between runs. After having tested various conditions, trifluoroacetic acid (1,M) in MeOH was finally selected. Concerning the solid-phase extraction procedure, good and reproducible analyte recoveries were obtained using MeOH for protein denaturation and a polymeric phase combining hydrophobic interactions with anion exchange properties (Oasis® MAX) was selected as extraction sorbent. The method selectivity was not only demonstrated toward a blank plasma sample but also toward other non-steroidal anti-inflammatory drugs. The method was then successfully validated with respect to response function, trueness, precision, accuracy, linearity and limit of quantification. [source] Simultaneous enantioseparation and sensitivity enhancement of basic drugs using large-volume sample stackingELECTROPHORESIS, Issue 19 2007Nerissa L. Deñola Abstract Simultaneous enantioseparation with sensitive detection of four basic drugs, namely methoxamine, metaproterenol, terbutaline and carvedilol, using a 20-,m ID capillary with native ,-CD as the chiral selector was demonstrated by the large-volume sample stacking method. The procedure included conventional sample loading either hydrodynamically or electrokinetically at longer injection times without polarity switching and EOF manipulation. In comparison to conventional injections, depending on the analyte, about several hundred- and a thousand-fold sensitivity enhancement was achieved with the hydrodynamic and the electrokinetic injections, respectively. The simple method developed was applied to the analysis of racemic analytes in serum samples and better recovery was achieved using hydrodynamic injection than electrokinetic injection. [source] Evaluation of enantioselective binding of antihistamines to human serum albumin by ACEELECTROPHORESIS, Issue 15 2007María Amparo Martínez-Gómez Abstract The drug binding to plasma and tissue proteins is a fundamental factor in determining the overall pharmacological activity of a drug. HSA, together with ,1 -acid glycoprotein, are the most important plasma proteins, which act as drug carriers, with implications on the pharmacokinetic of drugs. Among plasma proteins, HSA possesses the highest enantioselectivity. In this paper, a new methodology for the study of enantiodifferentiation of chiral drugs with HSA is developed and applied to evaluate the possible enantioselective binding of four antihistamines: brompheniramine, chlorpheniramine, hydroxyzine and orphenadrine to HSA. This study includes the determination of affinity constants of drug enantiomers to HSA and the evaluation of the binding sites of antihistamines on the HSA molecule. The developed methodology includes the ultrafiltration of samples containing HSA and racemic antihistaminic drugs and the analysis of the free or bound drug fraction using the affinity EKC-partial filling technique and HSA as chiral selector. The results shown in this paper represent the first evidence of the enantioselective binding of antihistamines to HSA, the major plasmatic protein. [source] Enantioselective analysis of ketamine and its metabolites in equine plasma and urine by CE with multiple isomer sulfated ,-CDELECTROPHORESIS, Issue 15 2007Regula Theurillat Abstract CE with multiple isomer sulfated ,-CD as the chiral selector was assessed for the simultaneous analysis of the enantiomers of ketamine and metabolites in extracts of equine plasma and urine. Different lots of the commercial chiral selector provided significant changes in enantiomeric ketamine separability, a fact that can be related to the manufacturing variability. A mixture of two lots was found to provide high-resolution separations and interference-free detection of the enantiomers of ketamine, norketamine, dehydronorketamine, and an incompletely identified hydroxylated metabolite of norketamine in liquid/liquid extracts of the two body fluids. Ketamine, norketamine, and dehydronorketamine could be unambiguously identified via HPLC fractionation of urinary extracts and using LC-MS and LC-MS/MS with 1,mmu mass discrimination. The CE assay was used to characterize the stereoselectivity of the compounds' enantiomers in the samples of five ponies anesthetized with isoflurane in oxygen and treated with intravenous continuous infusion of racemic ketamine. The concentrations of the ketamine enantiomers in plasma are equal, whereas the urinary amount of R -ketamine is larger than that of S -ketamine. Plasma and urine contain higher S - than R -norketamine levels and the mean S -/R -enantiomer ratios of dehydronorketamine in plasma and urine are lower than unity and similar. [source] Electrokinetic partial filling technique as a powerful tool for enantiomeric separation of DL -lactic acid by CE with contactless conductivity detectionELECTROPHORESIS, Issue 11 2007zslav Maier Dr. Abstract A modified partial filling method for chiral separation of DL -lactic acid as the model chiral compound with vancomycin chloride as the chiral selector was developed by CE with contactless conductivity detection. Electrokinetic partial filling technique (EK-PFT) was used as an alternative method to the conventional hydrodynamic partial filling method. EK-PFT, in contrast to the hydrodynamic partial filling technique, allowed the removal of the chloride counterions from the chiral selector which otherwise led to poor sensitivity in conductivity detection. The baseline separation of DL -lactic acid as the model analyte was achieved in 5,min in a polyacrylamide-coated capillary. The best resolution was achieved by electrokinetic partial filling of vancomycin cations from the injection solution containing 5,mmol/L oxalate L -histidinium at pH,4.5 with 10,mmol/L vancomycin chloride. Computer simulation was used to explain the observed phenomena in the boundary between the inject vial and the capillary during the EK-PFT of vancomycin cations. [source] Effect of alkali metal hydroxides on the enantioseparation of amines using di- O -isopropylidene-keto- L -gulonic acid as the selector in NACEELECTROPHORESIS, Issue 22 2006Ylva Hedeland Dr. Abstract The present work demonstrates the importance of the ionic composition in the BGE for enantioseparation. (,)-2,3:4,6-di- O -Isopropylidene-2-keto- L -gulonic acid ((,)-DIKGA) has been used as the chiral selector in methanolic and ethanolic BGEs. The influence of added alkali metal hydroxides on the EOF and the chiral separation of amines (atenolol, isoprenaline, pindolol and propranolol) have been studied. The ion-pair formation constants in ethanol were determined by precision conductometry for the enantiomers of pindolol with (,)-DIKGA, for Li+, Na+ and Cs+ with (,)-DIKGA, and also for the corresponding alkali metal hydroxides. The effective mobilities and the enantiomeric mobility differences were affected by the type of alkali metal hydroxide (LiOH, NaOH, KOH, RbOH or CsOH) added to the BGE. The effective mobility and mobility difference were increased with decrease in solvated radius of the alkali metal cation. These differences could partly be correlated to the ion-pair formation constants of the alkali metal cations with the chiral selector, affecting the equilibrium concentration of the free selector. The electroosmosis was also affected by the alkali metal hydroxide added to the BGE. The cathodic electroosmosis decreased with decreasing solvated radius of the alkali metal cation added to the BGE. Interestingly, the cathodic EOF was even reversed, i.e. became anodic in the ethanolic BGEs containing KOH, RbOH or CsOH and the methanolic ones with RbOH and CsOH. [source] ,-Cyclodextrin as novel chiral probe for enantiomeric separation by electromigration methodsELECTROPHORESIS, Issue 21 2006Dorothee Wistuba Abstract Native ,-CD has been employed as chiral selector in CE and MEKC. To investigate the potential of the enantiodiscriminating properties of ,-CD, negatively charged 5-dimethylamino-1-naphthalene-sulfonyl (dansyl)-, 2,4-dinitrophenyl (DNP)- and FMOC-derivatives of several amino acids, 1,1'-binaphthyl-2,2'-diylhydrogenphosphate, flavanones and three positively charged drugs have been selected as testing samples. Enantioresolution factors up to 4.82 have been observed. The results were compared with those achieved by the conventional running buffer additives ,-, ,- and ,-CDs. For several examples a steady increase of enantioresolution with increasing degree of oligomerization has been detected. [source] Optimization of capillary electrophoretic enantioseparation for basic drugs with native ,-CD as a chiral selectorELECTROPHORESIS, Issue 12 2006Nerissa L. Deñola Abstract This study presents the advantages of the 20,µm inner diameter (id) capillary for the enantioseparation of ten basic drugs with native ,-CD as the chiral selector. The apparent binding constants of each enantiomeric pair were determined to calculate the optimum ,-CD concentration ([,-CD]opt) and the optimization was subsequently carried out. Comparison of the 20,µm id with 50,µm id were made in terms of the results obtained in the optimization and detection limits. Applying the optimum conditions for each compound, reproducible results (RSD from 0,3; n>5) were obtained for the 20,µm id capillary. Although the sensitivity is lower in the 20,µm id capillary, the LOD determined using this capillary is still found to be acceptable for the ten basic drugs studied. Enhanced resolution and faster analysis times were the main advantages observed with the use of this capillary in enantioseparation. [source] On-line sample preconcentration with chemical derivatization of bacterial biomarkers by capillary electrophoresis: A dual strategy for integrating sample pretreatment with chemical analysisELECTROPHORESIS, Issue 21 2005Adam S. Ptolemy Abstract Simple, selective yet sensitive methods to quantify low-abundance bacterial biomarkers derived from complex samples are required in clinical, biological, and environmental applications. In this report, a new strategy to integrate sample pretreatment with chemical analysis is investigated using on-line preconcentration with chemical derivatization by CE and UV detection. Single-step enantioselective analysis of muramic acid (MA) and diaminopimelic acid (DAP) was achieved by CE via sample enrichment by dynamic pH junction with ortho -phthalaldehyde/N -acetyl- L -cysteine labeling directly in-capillary. The optimized method resulted in up to a 100-fold enhancement in concentration sensitivity compared to conventional off-line derivatization procedures. The method was also applied toward the detection of micromolar levels of MA and DAP excreted in the extracellular medium of Escherichia coli bacterial cell cultures. On-line preconcentration with chemical derivatization by CE represents a unique approach for conducting rapid, sensitive, and high-throughput analyses of other classes of amino acid and amino sugar metabolites with reduced sample handling, where the capillary functions simultaneously as a concentrator, microreactor, and chiral selector. [source] Enantioseparation in capillary electrophoresis using 2- O -(2-hydroxybutyl)-,-CD as a chiral selectorELECTROPHORESIS, Issue 20 2005Xiuli Lin Abstract The resolving ability of 2- O -(2-hydroxybutyl)-,-CD (HB-,-CD) with different degrees of substitution (DS,=,2.9 and 4.0) as a chiral selector in CZE is reported in this work. Fourteen chiral drugs belonging to different classes of compounds of pharmaceutical interest such as ,-agonists, antifungal agents, ageneric agents, etc., were resolved. The effects of the DS of HB-,-CD on separations were also investigated. The chiral resolution (Rs) was strongly influenced by the concentrations of the CD derivative, the BGE, and the pH of the BGE. Under the conditions of 50,mmol/L Tris-phosphate buffer at pH,2.5 containing 5,mmol/L HB-,-CD, all 14 analytes were separated. The very low concentration necessary to obtain separation was particularly impressive. The DS had a significant effect on the resolution of the chiral drugs and the ionic strength of the separation media; hence, the use of a well-characterized CD derivative is crucial. [source] Chiral capillary electrophoresis applied to the determination of phenylglycidol enantiomers obtained from cinnamyl alcohol by asymmetric epoxidation using new titanium(IV) alkoxide compounds as catalystsELECTROPHORESIS, Issue 16 2004Sonia Morante-Zarcero Abstract A capillary electrophoresis method for the simultaneous determination of phenylglycidol enantiomers in the presence of an excess of cinnamyl alcohol was developed. The effects of the nature, pH and concentration of the buffer, the nature and concentration of chiral selector, the addition of methanol or acetonitrile, and the capillary temperature on the chiral resolution of phenylglycidol enantiomers were studied. Separations were achieved using 20 mM succinylated ,-cyclodextrin dissolved in a 10 mM borate buffer (pH 10.0). Chiral resolution for the phenylglycidol enantiomers in the optimized electrophoretic conditions was higher than 2.0 with an analysis time less than 7 min. The method developed was validated in terms of selectivity, linearity, precision (instrumental repeatability, method repeatability, intermediate precision), the limits of detection and quantitation, and accuracy. Limits of detection of 6.5 mg/L and 8.3 mg/L for (2S,3S)-(,)-3-phenylglycidol ((S,S)-PG) and (2R,3R)-(+)-3-phenylglycidol ((R,R)-PG), respectively, were obtained. The method was applied to study the asymmetric epoxidation of cinnamyl alcohol with titanium(IV) alkoxide compounds as catalysts in order to evaluate their catalytic activity and stereoselectivity of the epoxidation processes. [source] Polymeric alkenoxy amino acid surfactants: II.,Chiral separations of ,-blockers with multiple stereogenic centersELECTROPHORESIS, Issue 6 2004Syed A. A. Rizvi Abstract Two amino acid-based (leucine and isoleucine) alkenoxy micelle polymers were employed in this study for the separation of multichiral center-bearing ,-blockers, nadolol and labetalol. These polymers include polysodium N -undecenoxy carbonyl- L -leucinate (poly- L -SUCL) and polysodium N -undecenoxy carbonyl- L -isoleucinate (poly- L -SUCIL). Detailed synthesis and characterization were reported in our previous paper [26]. It was found that poly- L -SUCIL gives better chiral separation than poly- L -SUCL for both nadolol and labetalol isomers. The use of 50,100 mM poly- L -SUCIL as a single chiral selector provided separation of four and three isomers of labetalol and nadolol, respectively. Further optimization in separation of both enantiomeric pairs of nadolol and labetalol was achieved by evaluation of type and concentration of organic solvents, capillary temperature as well type and concentration of cyclodextrins. A synergistic approach, using a combination of poly- L -SUCIL and sulfated ,-CD (S-,-CD) was evaluated and it showed dramatic separation for enantiomeric pairs of nadolol. On the other hand for labetalol enantiomers, separation was slightly decreased or remain unaffected using the dual chiral selector system. Finally, simultaneous separation of both nadolol and labetalol enantiomers was achieved in a single run using 25 mM poly- L -SUCIL and 5% w/v of S-,-CD in less then 35 min highlighting the importance of high-throughput chiral analysis. [source] Role of the charge in continuous beds in the chiral separation of hydroxy acids by ligand-exchange capillary electrochromatographyELECTROPHORESIS, Issue 17 2003Oliver Lecnik Abstract This paper deals with the chiral separation of hydroxy acids using diallyl-dimethylammonium chloride as a positive charge-providing agent in the continuous bed. The chiral continuous bed was prepared by in situ copolymerization of monomers, including an L -4-hydroxyproline derivative as a chiral selector. This phase was applied to the chiral separation of hydroxy monocarboxylic acids and hydroxy dicarboxylic acids, respectively. The influence of both the selector concentration and the charge-providing agent on retention and separation was investigated. [source] Enantioseparation of warfarin and its metabolites by capillary zone electrophoresisELECTROPHORESIS, Issue 15 2003Qingyu Zhou Abstract A capillary zone electrophoresis (CZE) method with direct ultraviolet (UV)-absorbance detection is presented for the simultaneous enantiomeric separation of warfarin and its main metabolites, including warfarin alcohols, 4'-, 6-, and 7-hydroxywarfarin, using highly sulfated ,-cyclodextrin (HS-,-CD) as the chiral selector. This chiral separation method was optimized in terms of the electrophoretic parameters, which included the concentration of HS-,-CD used, the type and composition of organic modifier added to the background electrolyte (BGE) buffer, and the BGE buffer pH. Chiral separation of warfarin and its major metabolites was achieved with high resolution, selectivity, efficiency, repeatability, and reproducibility. This optimized chiral analysis of warfarin along with its metabolites was completed within a satisfactory electrophoresis time of 20 min. [source] Quantitation of talinolol and other ,-blockers by capillary electrophoresis for in vitro drug absorption studiesELECTROPHORESIS, Issue 15 2003Bilal Awadallah Abstract A capillary zone electrophoresis method is described for the enantioseparation of talinolol using heptakis(2,3-diacetyl-6-sulfo)-,-cyclodextrin (HDAS-,-CD) as a chiral selector. After liquid-liquid extraction of talinolol from physiological solution, electrokinetic injection was employed to improve the sensitivity. The use of a coated capillary was necessary to achieve stable and reproducible enantioseparations. A baseline separation of the talinolol enantiomers was achieved in less than 10 min using 100 mM phosphate solution as background electrolyte and pH 3.5, at the presence of 3.0 mM HDAS-,-CD and at 20°C. In addition, this analytical condition proved to be useful for the enantioseparation of a number of other ,-blocking agents such as alprenolol, atenolol, bisoprolol, celiprolol, metipranolol, oxprenolol, and sotalol. For determing talinolol, the method could be validated in terms of precision, accuracy and linearity, and was found to be suitable in determination of talinolol enantiomers in highly diluted samples obtained from in vitro experiments. [source] Optimization of the chiral resolution of baclofen by capillary electrophoresis using ,-cyclodextrin as the chiral selectorELECTROPHORESIS, Issue 12-13 2003Imran Ali Abstract The chiral resolution of baclofen was achieved by capillary electrophoresis using a fused-silica capillary (60 cm×75 ,m ID). The background electrolyte (BGE) was phosphate buffer (pH 7.0, 50 mM)-acetonitrile (95:5 v/v) containing 10 mM ,-cyclodextrin. The applied voltage was 15 kV. The values of , and Rs were 1.06 and 1.00, respectively. The electrophoretic conditions were optimized varying the pH and the ionic strength of the BGE, concentrations of ,-cyclodextrin and acetonitrile and the applied voltage. [source] Enantioseparation of dansyl amino acids by ligand-exchange capillary electrophoresis with zinc(II)- L -phenylalaninamide complexJOURNAL OF SEPARATION SCIENCE, JSS, Issue 18 2009Li Qi Abstract A novel method of chiral ligand-exchange CE was developed with L -amino acylamides as a chiral ligand and zinc(II) as a central ion. It has been demonstrated that these chiral complexes, such as Zn(II)- L -alaninamide, Zn(II)- L -prolinamide, and Zn(II)- L -phenylalaninamide, are suitable for use as chiral selectors for the enantioseparation of either individual pair of or mixed dansyl amino acids. The optimal separation running buffer consisted of 5 mM ammonium acetate, 100 mM boric acid, 4 mM ZnSO4·7 H2O, and 8 mM L -amino acylamides at pH 8.2. The experiments showed that apart from the effect of the concentration of the complexes on the resolution and the migration time, the buffer pH also had a sharp influence on resolution. The employed chiral ligands exhibited different enantioselectivities and enantiomer migration orders. D -Amino acids migrate faster than L -amino acids when Zn(II)- L -alaninamide and Zn(II)- L -phenylalaninamide are used as chiral selectors, but it was observed that the migration order is reversed when Zn(II)- L -prolinamide is used as the chiral selector. Furthermore, the amount of dansylated amino acids is found to be highly dependent on the labeling temperature. [source] Quantification of D -Asp and D -Glu in rat brain and human cerebrospinal fluid by microchip electrophoresisJOURNAL OF SEPARATION SCIENCE, JSS, Issue 17 2009Yong Huang Abstract A microchip electrophoresis (MCE) method with LIF detection was presented for quantification of D -aspartic acid (D -Asp) and D -glutamate (D -Glu) in biological samples. D -Asp and D -Glu were determined after precolumn derivatization with FITC. The chiral separation was performed on a glass/PDMS hybrid microfluidic chip using ,-CD as chiral selector in the running buffer. High sensitive detection was obtained by the LIF detection. The LODs (S/N = 3) for D -Asp and D -Glu were 6.0×10,8 and 4.0×10,8 M, respectively. Using this method, the levels of D -Asp and D -Glu in rat brain and human cerebrospinal fluid (CSF) were determined. [source] HPLC enantioseparation of ,2 -homoamino acids using crown ether-based chiral stationary phaseJOURNAL OF SEPARATION SCIENCE, JSS, Issue 7 2009Róbert Berkecz Abstract RP high-performance liquid chromatographic methods were developed for the enantioseparation of eleven unusual ,2 -homoamino acids. The underivatized analytes were separated on a chiral stationary phase containing (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid as chiral selector. The effects of organic (alcoholic) and acidic modifiers, the mobile phase composition and temperature on the separation were investigated. The structures of the substituents in the ,-position of the analytes substantially influenced the retention and resolution. The elution sequence was determined in some cases: the S enantiomers eluted before the R enantiomers. [source] Enantioselective separation of chiral vicinal diols in capillary electrophoresis using a mono-6A -aminoethylamino-,-cyclodextrin as a chiral selectorJOURNAL OF SEPARATION SCIENCE, JSS, Issue 1 2009Peng Liu Abstract This paper describes an improved access to mono-6A -aminoethylamino-,-CD (,-CDen), a very efficient cationic chiral selector for CZE in the separation of eight chiral aromatic vicinal diols. The ,-CDen concentration has a strong influence on the efficiency of enantioseparation. The effects of the pH and concentration of the BGE, the capillary temperature, and the applied voltage on the resolution and separation selectivity have been studied. Excellent chiral resolution was achieved under the optimal conditions of ,-CDen 10 mM, pH 10, 200 mM borate buffer at 15 kV and 20°C within 20 min. Moreover, the developed method was successfully applied to the determination of the enantiomeric purity of the catalytic asymmetric dihydroxylation (AD) reaction products. 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