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Enantioseparation
Kinds of Enantioseparation Selected AbstractsEnantioseparation of amino acids, ,-hydroxy acids, and dipeptides by ligand-exchange CEC using silica-based chiral stationary phasesELECTROPHORESIS, Issue 16 2009Elfriede Pittler Abstract This work deals with the application of silica-based ligand-exchange chiral stationary phases (CSPs) for the enantioseparation of underivatised amino acids, ,-hydroxy acids, and dipeptides with packed CEC. Two different possibilities of preparing silica-based CSPs are presented. One phase contains L -4-hydroxyproline chemically bonded via a spacer to 3,,m silica material. The other approach makes use of N -decyl- L -4-hydroxyproline dynamically coated on a reversed-phase packed capillary. Dynamical coating of reversed-phase material represents a simple alternative to prepare CSP. A comparison of the chemically bonded phase with the dynamically coated CSP by means of resolution of complex-forming analytes is presented. The chemically bonded phase was found to be superior to the dynamically coated phase in terms of resolution of amino acids and dipeptides. However, the dynamically coated CSP was found to be especially suitable for the separation of ,-hydroxy acids. Both techniques are applicable for enantiomer purity tests. [source] Cover Picture: Electrophoresis 11'09ELECTROPHORESIS, Issue 11 2009Article first published online: 10 JUN 200 Issue no. 11 is a regular issue consisting of 22 research articles distributed over 5 parts including: (i) Proteins and Proteomics, (ii) EKC and CEC, (iii) Detection and Preconcentration Approaches, (iv) Enantioseparation and (v) Methodologies and Assays. Selected articles are: Quantifying Western blots: pitfalls of densitometry ((10.1002/elps.200800720)) Light emitting diode-induced chemiluminescence detection for capillary electrophoresis ((10.1002/elps.200800708)) Double sample preconcentration by in-line coupled large volume single drop microextraction and sweeping in capillary electrophoresis ((10.1002/elps.200800759)) [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] 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] Fluorous "Racemic" Mixture Synthesis: Simultaneous Strategy for Demixing and Enantioseparation of Racemic Fluorous-Tagged ProductsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 11 2007Takayuki Tonoi Abstract Reported herein is the concept of fluorous "racemic" mixture synthesis (FRMS), which is applied to two types of proof-of-concept experiments. Mixtures of racemic O -benzoylmandelate derivatives and prochiral crotonamide derivatives, respectively, bearing different lengths of fluorous-cleavable tags are taken through a segmented reaction sequence to provide their enantiomers, as well as their individual derivatives, by virtue of chiral ,-cyclodextrin columns. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Enantioseparation with D -Phe- and L -Phe-imprinted PAN-based membranes by ultrafiltrationJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 4 2008Noaman Ul-Haq Abstract BACKGROUND: Solute rejection by a molecularly imprinted membrane was observed for the first time. Enantioselective poly[(acrylonitrile)-co-(acrylic acid)] membranes were prepared by a wet-phase inversion method using D -phenylalanine (D -Phe) and L -phenylalanine (L -Phe) as templates, separately, in order to compare the imprinting effects of these isomers using an ultrafiltration experiment. RESULTS: Recognition sites were successfully created in the prepared membranes, which had a nanoporous structure. The rejection selectivities of 0.13 and 0.28, adsorption selectivities of 2.25 and 2.40 and permselectivities of 1.94 and 2.08 were achieved for the D - and L -Phe-imprinted membranes, respectively, after 16 mL (34 min) of ultrafiltration. CONCLUSION: Solute rejection by a molecularly imprinted membrane was selective. The performance characteristics of both the D - and L -Phe-imprinted membranes were different. Thus, the selection of an appropriate stereoisomer as a template plays an important role in the imprinting of membranes with regard to chiral resolution by ultrafiltration. Copyright © 2008 Society of Chemical Industry [source] Enantioseparation via EIC-OSN: Process design and improvement of enantiomers resolvability and separation performanceAICHE JOURNAL, Issue 4 2010Issara Sereewatthanawut Abstract This article presents a mathematical model to assess and optimize the separation performance of an enantioselective inclusion complexation-organic solvent nanofiltration process. Enantiomer solubilities, feed concentrations, solvent compositions, permeate solvent volumes, and numbers of nanofiltrations were identified as key factors for process efficiency. The model was first tested by comparing calculated and experimental results for a nonoptimized process, and then, calculations were carried out to select the best operating conditions. An important finding was that the optimal configuration varied with the objective function selected, e.g., resolvability versus yield, with a boundary on product optical purity. The model also suggested that the process efficiency could benefit from diafiltration of the distomer and from the use of higher feed concentrations. However, the latter strategy would result in higher losses of eutomer. To address this drawback, a multistage process was evaluated using the verified process model. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Enantioseparation of doubly functionalized polar norbornenes by HPLC and their ruthenium-catalyzed ring-opening metathesis polymerizationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 2 2010Yasushi Nishihara Abstract Doubly fuctionalized polar norbornenes bearing the cyano and ester groups in 2,3-positions are synthesized and enantiomers are separated by high performance liquid chromatography (HPLC) with a chiral stationary phase. These optically active monomers are polymerized by ruthenium carbene catalysts, and high yields of the polymers were obtained. The chiral monomer bearing ethyl ester gave an optically active polymer of lower, but opposite sign of optical rotation (monomer [,]D = +61.0°, polymer [,]D = ,3.1°). The circular dichroism (CD) of the obtained chiral polymers gave a Cotton effect. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 485,491, 2010 [source] Chiral stationary phases for separation of intermedine and lycopsamine enantiomers from Symphytum uplandicumJOURNAL OF SEPARATION SCIENCE, JSS, Issue 2 2010Rahul S. Pawar Abstract Enantioseparation of the pyrrolizidine alkaloid isomers intermedine and lycopsamine, isolated from Symphytum uplandicum, is discussed. The separatory power of two immobilized carbohydrate-based chiral HPLC columns, Chiralpak IA and IC, in different chromatographic conditions is compared. The study demonstrated the importance of solvent and column selection while developing such chiral HPLC separation methods. The baseline HPLC separation of the two alkaloid isomers in preparatory scale is reported for the first time. The optimized separations were achieved on a Chiralpak IA column with mobile phases of ACN/methanol (80:20) and methanol/methyl- t -butyl ether (90:10), both containing 0.1% diethylamine. [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] Enantioseparation of nuarimol by affinity electrokinetic chromatography-partial filling technique using human serum albumin as chiral selectorJOURNAL OF SEPARATION SCIENCE, JSS, Issue 18 2008Maria Amparo Martínez-Gómez Abstract The present paper deals with the enantiomeric separation of nuarimol enantiomers by affinity EKC-partial filling technique using HSA as chiral selector. Firstly, a study of nuarimol interactions with HSA by CE-frontal analysis was performed. The binding parameters obtained for the first site of interaction were n1 = 0.84; K1 = 9.7 ± 0.3×103 M,1 and the protein binding percentage of nuarimol at physiological concentration of HSA was 75.2 ± 0.2%. Due to the moderate affinity of nuarimol towards HSA the possibility of using this protein as chiral selector for the separation of nuarimol using the partial filling technique was evaluated. A multivariate optimization approach of the most critical experimental variables in enantioresolution, running pH, HSA concentration and plug length was carried out. Separation of nuarimol enantiomers was obtained under the following selected conditions: electrophoretic buffer composed of 50 mM Tris at pH 7.3; 160 ,M HSA solution applied at 50 mbar for 156 s as chiral selector; nuarimol solutions in the range of 2,8×10,4 M injected hydrodynamically at 30 mbar for 2 s and the electrophoretic runs performed at 30°C applying 15 kV voltage. Resolution, accuracy, reproducibility speed and cost of the proposed method make it suitable for quality control of the enantiomeric composition of nuarimol in formulations and for further toxicological studies. The results showed a different affinity between nuarimol enantiomers towards HSA. [source] Influence of steric hindrance on enantioseparation of Dns-amino acids and pesticides on terguride based chiral selectors in capillary electrophoresisJOURNAL OF SEPARATION SCIENCE, JSS, Issue 7 2005Honzátko Abstract Three urea derivatives of ergoline-based chiral selectors (CSs), differing in the size of the urea side chain, i. e. dimethyl- (CSI), diethyl- (CSII), and diisopropylurea (CSIII), were used to study the effect of steric hindrance on the enantioseparation of dansyl amino acids (Dns-AAs), pesticides, and mandelic acid under condition of capillary electrophoresis (CE) in linear polyacrylamide coated capillaries. A mixture of organic modifiers (MeOH/THF, 4 : 1 v/v) in a BGE consisting of 100 mM ,-alanine-acetate was used to increase the solubility of CSs up to 25 mM. The capillary was filled with CS (high UV absorption), and the inlet and outlet vials contained buffer solutions only. The best enantioseparation of Dns-AAs was achieved on CSI. Increased steric hindrance of the chiral binding site led to reduction of both enantioselectivity and resolution. The opposite pattern was observed for the separation of mandelic acid enantiomers, where the best enantioseparation and resolution was obtained with CSIII. Most of the pesticides studied reached maximum selectivity on the diethylurea ergoline derivative (CSII). Enantioseparation of fenoxaprop was found to be independent of steric hindrance. [source] Enantioseparation of novel chiral tetrahedral clusters on an amylose tris-(3,5-dimethylphenylcarbamate) chiral stationary phase by normal phase HPLCCHINESE JOURNAL OF CHEMISTRY, Issue 10 2004Wen-Zhi Li Abstract Amylose tris(3,5-dimethylphenylcamate) (ADMPC) coated on a kind of small particle silica gel was prepared. On this ADMPC chiral stationary phase (CSP), the direct enantiomeric separation of six novel chiral transition metal tetrahedral clusters has firstly been achieved using n -hexane as the mobile phase containing various alcohols as modifiers. The effect of mobile phase modifiers and the structural variation of the solutes on their retention factors (k) and resolutions (Rs) were investigated. The result suggests that not only the structure and concentration of alcohol in mobile phase, but also the structural differences in racemates can have a pronounced effect on enantiomeric separation. ADMPC-CSP is a suitable CSP for the optical resolution of chiral tetrahedral cluster by HPLC. [source] Enantioseparation of benzazoles and benzanilides on polysaccharide-based chiral columnsCHIRALITY, Issue 4 2010Takateru Kubota Abstract The chiral recognition ability of the polysaccharide-based chiral columns (Chiralpak AD-RH, Chiralpak AS-RJ, Chiralpak IC, Chiralcel OD-RH, and Chiralcel OJ-RH) for the benzazoles and the benzanilides was evaluated under reversed phase conditions. The columns showed the high chiral recognition ability for a wide range of benzazoles and benzanilides. Twenty-one racemates were used for the evaluation, and 20 racemates were completely separated on at least one of the columns. In particular, AS-RH and OJ-RH showed the high chiral recognition ability for the benzazoles, and the AD-RH, IC, and OJ-RH were effective for the benzanilides. Chirality 2010. © 2009 Wiley-Liss, Inc. [source] Enantioseparation of extended metal atom chain complexes: Unique compounds of extraordinarily high specific rotationCHIRALITY, Issue 3 2007Molly M. Warnke Abstract Extended metal atom chains (EMACs) contain a linear metal chain wrapped by various ligands. Most complexes are of the form M3(dpa)4X2, where M = metal, dpa = 2,2,-dipyridylamide, and X = various anions. The ligands form helical coils about the metal chain, which results in chiral EMAC complexes. The EMACs containing the metals Co and Cu were partially separated in polar organic mode using a vancomycin-based chiral stationary phase. Under similar conditions, two EMACs with Ni metal and varying anions could be baseline separated. The polar organic mode was used because of the instability of the compounds in aqueous mobile phases. Also, these conditions are more conducive to preparative separations. Polarimetric measurements on the resolved enantiomers of Ni3(dpa)4Cl2 indicate that they have extraordinarily high specific rotations (on the order of 5000 deg cc/g dm). Chirality, 2007. © 2006 Wiley-Liss, Inc. [source] Enantioseparation by HPLC using phenylcarbonate, benzoylformate, p -toluenesulfonylcarbamate, and benzoylcarbamates of cellulose and amylose as chiral stationary phasesCHIRALITY, Issue 6 2005Tomoyuki Ikai Abstract Phenylcarbonate, benzoylformate, and p -toluenesulfonylcarbamate of cellulose and five new benzoylcarbamate derivatives of both cellulose and amylose were synthesized and their chiral recognition abilities were evaluated as chiral stationary phases (CSPs) for high-performance liquid chromatography (HPLC). Cellulose benzoylcarbamate has a higher chiral recognition ability compared to phenylcarbonate, p -toluenesulfonylcarbamate, and benzoylformate of cellulose. The benzoylcarbamate derivatives exhibited a characteristic chiral recognition for the racemates, which bear a hydrogen atom capable of hydrogen bonding to the carbonyl group of the benzoylcarbamates. The structures of the benzoylcarbamates were investigated by CD spectroscopy. Chirality 17:299,304, 2005. © 2005 Wiley-Liss, Inc. [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] Cellulose dimethylphenylcarbamate-immobilized zirconia for chiral separation in reversed-phase CECELECTROPHORESIS, Issue 22 2009Jurim Gwon Abstract Cellulose dimethylphenylcarbamate (CDMPC)-immobilized zirconia (CDMPCZ) was used as a chiral stationary phase for enantioseparation of a set of nine racemic compounds in reversed-phase CEC. Influences of the type and composition of organic modifier and the applied voltage on enantioseparation were examined. Separation data on CDMPCZ were also compared with those on CDMPC-immobilized silica (CDMPCS). Enantiomers of the analytes investigated are well separated in ACN/phosphate buffer mobile phases. Better enantioselectivity and resolution were obtained with ACN than MeOH as the organic modifier. Retention was longer but better enantioselectivity and resolution were obtained on CDMPCZ than CDMPCS. [source] Combined use of chiral ionic liquid and cyclodextrin for MEKC: Part I. Simultaneous enantioseparation of anionic profensELECTROPHORESIS, Issue 16 2009Bin Wang Abstract The enantiomers of five profen drugs were simultaneously separated by MEKC with the combined use of 2,3,6-tri- O -methyl-,-cyclodextrin and chiral cationic ionic liquid, N -undecenoxy-carbonyl- L -leucinol bromide, which formed micelles in aqueous buffers. Enantioseparations of these profen drugs were optimized by varying the chain length and concentration of the IL surfactant using a standard recipe containing 35,mM 2,3,6-tri- O -methyl-,-cyclodextrin, 5,mM sodium acetate at pH 5.0. The batch-to-batch reproducibility of N -undecenoxy-carbonyl- L -leucinol bromide was tested and found to have no significant impact in terms of enantiomeric resolution, efficiency, and migration time. Finally, this method was successfully applied for the quantitative determination of ibuprofen in pharmaceutical tablets. [source] Combined use of chiral ionic liquid and CD for MEKC: Part II.ELECTROPHORESIS, Issue 16 2009Determination of binding constants Abstract A competitive inhibition mechanism is proposed to investigate the interactions among 2,3,6-tri- O -methyl-,-CD (TM-,-CD), cationic ionic liquid type surfactants, N -undecenoxy-carbonyl- L -leucinol bromide (L -UCLB) and profens using affinity CE. The apparent binding constant of TM-,-CD to L -UCLB was estimated by nonlinear and linear plotting methods. The binding constants of one representative profen (e.g. fenoprofen) to TM-,-CD and L -UCLB were estimated by a secondary plotting approach. The R - and S -fenoprofens have different binding constant values, resulting in the enantioseparation due to the synergistic effect of the two chiral selectors, TM-,-CD and L -UCLB. [source] Enantioseparation of amino acids, ,-hydroxy acids, and dipeptides by ligand-exchange CEC using silica-based chiral stationary phasesELECTROPHORESIS, Issue 16 2009Elfriede Pittler Abstract This work deals with the application of silica-based ligand-exchange chiral stationary phases (CSPs) for the enantioseparation of underivatised amino acids, ,-hydroxy acids, and dipeptides with packed CEC. Two different possibilities of preparing silica-based CSPs are presented. One phase contains L -4-hydroxyproline chemically bonded via a spacer to 3,,m silica material. The other approach makes use of N -decyl- L -4-hydroxyproline dynamically coated on a reversed-phase packed capillary. Dynamical coating of reversed-phase material represents a simple alternative to prepare CSP. A comparison of the chemically bonded phase with the dynamically coated CSP by means of resolution of complex-forming analytes is presented. The chemically bonded phase was found to be superior to the dynamically coated phase in terms of resolution of amino acids and dipeptides. However, the dynamically coated CSP was found to be especially suitable for the separation of ,-hydroxy acids. Both techniques are applicable for enantiomer purity tests. [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] On-line preconcentration and enantioseparation of thalidomide racemates by CEC with the hyphenation of octyl and norvancomycin monolithsELECTROPHORESIS, Issue 4 2009An-Na Tang Abstract A method was developed for simultaneous preconcentration and chiral separation of thalidomide enantiomers in human urine by CEC in combination with self-concentration and solvent gradient effects. A 4,cm long octyl (C8) monolithic column was hyphenated with a 15,cm long norvancomycin (NVC)-bonded monolithic column via a fluorinated ethylene,propylene interface. Sample solution was injected into the C8 monolithic column, the two thalidomide enantiomers were first preconcentrated on the C8 monolithic column, and then separated with a further concentration on the NVC-bonded monolithic column by CEC. Injection of 34.8,mm plug of sample solution gave 278- and 298-fold enhancement in sensitivity, and detection limits of 90 and 94,,g/L for the two thalidomide enantiomers. Peak areas of the two isomers were linear in a range of 0.5,50,mg/L. The precision for five replicate injections of 10,mg/L were 0.8,0.9 and 1.1,2.3% for the migration time and peak height, respectively. The developed method was applied to the determination of racemic thalidomide in spiked human urine samples. [source] Simultaneous enantioseparation and sensitivity enhancement of basic drugs using large-volume sample stackingELECTROPHORESIS, Issue 19 2007Nerissa L. Deńola 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] Influence of microemulsion chirality on chromatographic figures of merit in EKC: Results with novel three-chiral-component microemulsions and comparison with one- and two-chiral-component microemulsionsELECTROPHORESIS, Issue 17 2007Kimberly A. Kahle Abstract Novel microemulsion formulations containing all chiral components are described for the enantioseparation of six pairs of pharmaceutical enantiomers (atenolol, ephedrine, metoprolol, N -methyl ephedrine, pseudoephedrine, and synephrine). The chiral surfactant dodecoxycarbonylvaline (DDCV, R - and S -), the chiral cosurfactant S -2-hexanol, and the chiral oil diethyl tartrate (R - and S -) were combined to create four different chiral microemulsions, three of which were stable. Results obtained for enantioselectivity, efficiency, and resolution were compared for the triple-chirality systems and the single-chirality system that contained chiral surfactant only. Improvements in enantioselectivity and resolution were achieved by simultaneously incorporating three chiral components into the aggregate. The one-chiral-component microemulsion provided better efficiencies. Enantioselective synergies were identified for the three-chiral-component nanodroplets using a thermodynamic model. Additionally, two types of dual-chirality systems, chiral surfactant/chiral cosurfactant and chiral surfactant/chiral oil, were examined in terms of chromatographic figures of merit, with the former providing much better resolution. The two varieties of two-chiral-component microemulsions gave similar values for enantioselectivity and efficiency. Lastly, the microemulsion formulations were divided into categories based on the number of chiral microemulsion reagents and the average results for each pair of enantiomers were analyzed for trends. In general, enantioselectivity and resolution were enhanced while efficiency was decreased as more chiral components were used to create the pseudostationary phase (PSP). [source] Effect of alkali metal hydroxides on the enantioseparation of amines using di- O -isopropylidene-keto- L -gulonic acid as the selector in NACE (vol. 27, issue 22, pp.ELECTROPHORESIS, Issue 24 20064469-4479) No abstract is available for this article. [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] Enantioselectivity of basic analytes in CZE enantioseparation under reversed-polarity mode using sulfated ,-cyclodextrins as chiral selectors: An unusual temperature effectELECTROPHORESIS, Issue 21 2006Chen-Hsing Lin Abstract Temperature effects on the enantioselectivity of basic analytes in CZE enantioseparation were studied under reversed-polarity mode using randomly sulfate-substituted ,-CDs (MI-S-,-CD) as chiral seletors. Two catecholamines (epinephrine and isoproterenol) and two structurally related compounds (octopamine and norephedrine) were selected as test compounds in an electrophoretic system at low pH. The mobility differences between the (+)-enantiomers and the (,)-enantiomers of the two catecholamines and dopamine at 40°C are greater than those at 25°C with MI-S-,-CD, even at a concentration as low as 0.3%,w/v. Thus the enantioselectivity of these three basic analytes increases with increasing temperature. This phenomenon results from the inequality of the temperature effect on the mobility of the two enantiomers. In contrast, norephedrine behaves differently. The (+)-enantiomers of these basic analytes were found to migrate faster than the (,)-enantiomers. Consequently, the unusual temperature effect on the enantioselectivity can be observed when the mobility difference of the (+)-enantiomer between 40 and 25°C is greater than that of the (,)-enantiomer using MI-S-,-CD at a concentration greater than about 0.7%,w/v for enantioseparation of isoproterenol, 0.4%,w/v for epinephrine, and 0.3%,w/v for octopamine. This unusual temperature effect offers the advantages to enhance enantioselectivity, to improve enantioseparation, and to reduce migration times. [source] Optimization of capillary electrophoretic enantioseparation for basic drugs with native ,-CD as a chiral selectorELECTROPHORESIS, Issue 12 2006Nerissa L. Deńola 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] Application of polymeric surfactants in micellar electrokinetic chromatography-electrospray ionization mass spectrometry of benzodiazepines and benzoxazocine chiral drugsELECTROPHORESIS, Issue 5-6 2006Jingguo Hou Abstract Chiral micellar EKC (CMEKC) coupled to ESI-MS using polymeric surfactants as pseudostationary phases is investigated for simultaneous enantioseparation of two benzodiazepines, (±)-oxazepam ((±)-OXA) and (±)-lorazepam ((±)-LOR), and one benzoxazocine, (±)-nefopam ((±)-NEF). First, enantioselectivity and electrospray sensitivity of six chiral polymeric surfactants for all three chiral compounds are compared. Second, using poly(sodium N -undecenoyl- L -leucinate) as pseudostationary phase, the organic modifiers (methanol (MeOH), isopropanol, and ACN) are added into the running buffer to further improve chiral resolution (RS). Next, a CMEKC-ESI-MS method for the simultaneous enantioseparation of two benzodiazepines is further developed by using a dipeptide polymeric surfactant, poly(sodium N -undecenoxy carbonyl- L,L -leucyl-valinate) (poly- L,L -SUCLV). The CMEKC conditions including nebulizer pressure, capillary length, ammonium acetate concentration, pH, poly- L,L -SUCLV concentration, and capillary temperature were optimized to achieve maximum chiral RS and highest sensitivity of MS detection. The spray chamber parameters (drying gas temperature and drying gas flow rate) as well as sheath liquid conditions (MeOH content, pH, flow rate, and ionic strength) were found to significantly influence MS S/N of both (±)-OXA and (±)-LOR. Finally, a comparative study between simultaneous UV and MS detection showed high plate numbers, better chiral RS, and enhanced detectability with CMEKC-MS. However, speed of analysis was faster using CMEKC-UV. [source] | |||||||||||||