1
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Davankov V. 50 Years of Chiral Liquid Chromatography. How it started. J Chromatogr A 2022; 1668:462910. [DOI: 10.1016/j.chroma.2022.462910] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2022] [Revised: 02/14/2022] [Accepted: 02/16/2022] [Indexed: 11/27/2022]
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2
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Weerasekara D, Lunte S. Separation and detection of tyrosine and phenylalanine‐derived oxidative stress biomarkers using microchip electrophoresis with electrochemical detection. ELECTROANAL 2021; 34:1913-1927. [DOI: 10.1002/elan.202100580] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Affiliation(s)
| | - Susan Lunte
- University of Kansas College of Liberal Arts and Sciences UNITED STATES
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3
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Liu R, Du Y, Chen J, Zhang Q, Du S, Feng Z. Investigation of the Enantioselectivity of Tetramethylammonium L-hydroxyproline Ionic Liquid as a Novel Chiral Ligand in Ligand-Exchange CE and Ligand-Exchange MEKC. Chirality 2014; 27:58-63. [DOI: 10.1002/chir.22388] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2014] [Revised: 08/12/2014] [Accepted: 08/13/2014] [Indexed: 11/12/2022]
Affiliation(s)
- Ruijuan Liu
- Department of Analytical Chemistry; China Pharmaceutical University; Nanjing People's Republic of China
| | - Yingxiang Du
- Department of Analytical Chemistry; China Pharmaceutical University; Nanjing People's Republic of China
- Key Laboratory of Drug Quality Control and Pharmacovigilance (Ministry of Education); China Pharmaceutical University; Nanjing People's Republic of China
- State Key Laboratory of Natural Medicines; China Pharmaceutical University; Nanjing People's Republic of China
| | - Jiaquan Chen
- Department of Analytical Chemistry; China Pharmaceutical University; Nanjing People's Republic of China
| | - Qi Zhang
- Department of Analytical Chemistry; China Pharmaceutical University; Nanjing People's Republic of China
| | - Shuaijing Du
- College of Chemistry and Molecular Engineering; Peking University; Beijing People's Republic of China
| | - Zijie Feng
- Department of Analytical Chemistry; China Pharmaceutical University; Nanjing People's Republic of China
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4
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Zhang H, Qi L, Mao L, Chen Y. Chiral separation using capillary electromigration techniques based on ligand exchange principle. J Sep Sci 2012; 35:1236-48. [PMID: 22733505 DOI: 10.1002/jssc.201200067] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Over the last couple of decades, researchers have developed diverse chiral separation methods emerged from a few chiral separation principles. This review article is primarily focused on the application of chiral ligand-exchange (CLE) principle in capillary electromigration techniques, such as capillary electrophoresis (CE) and capillary electrochromatography (CEC). First, the most commonly used CLE-CZE separation mode by using different kinds of central ions, such as Cu(II), Zn(II), borate ion, and other metal ions, has been introduced. Meanwhile, several kinds of surfactants have been applied as the micelle-forming agents in the CLE micellar electrokinetic chromatography mode. The highlight of recent research of CLE-CEC is the exploitation of novel columns for chiral separation. Then, two kinds of capillary columns, packed capillary and monolithic capillary column, have been briefly described. Finally, the effective application of these chiral separation methods has been presented, including the application in life science and food analysis area.
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Affiliation(s)
- Haizhi Zhang
- Beijing National Laboratory for Molecular Sciences, Key Laboratory of Analytical Chemistry for Living Biosystems, Institute of Chemistry, Chinese Academy of Sciences, Beijing, China
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5
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Schmid MG. Chiral metal-ion complexes for enantioseparation by capillary electrophoresis and capillary electrochromatography: a selective review. J Chromatogr A 2012; 1267:10-6. [PMID: 22897866 DOI: 10.1016/j.chroma.2012.07.088] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2012] [Revised: 07/20/2012] [Accepted: 07/23/2012] [Indexed: 11/30/2022]
Abstract
This review gives an overview about chiral separation by capillary electrophoresis and capillary electrochromatography using different chiral metal-ion complexes. The topic enantioseparation is still of big interest for chiral drugs and natural compounds. Regarding chiral drugs it is often the case that the enantiomers differ in activity. The chiral separation principle of ligand-exchange (LE) can be enabled for liquid chromatography, capillary electrophoresis as well as for capillary electrochromatography. Ligand-exchange can be applied particularly for chiral amino acids, amino alcohols or α-hydroxy acids. Examples and applications are given along with the latest developments.
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Affiliation(s)
- M G Schmid
- Institute of Pharmaceutical Sciences, Department of Pharmaceutical Chemistry, Karl-Franzens-University, Graz, Austria.
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6
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Schmid MG, Gübitz G. Enantioseparation by chromatographic and electromigration techniques using ligand-exchange as chiral separation principle. Anal Bioanal Chem 2011; 400:2305-16. [DOI: 10.1007/s00216-011-4737-5] [Citation(s) in RCA: 65] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2010] [Revised: 12/21/2010] [Accepted: 01/27/2011] [Indexed: 11/24/2022]
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7
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Zheng ZX, Qu F, Lin JM. Investigation of Mixed Chiral Selectors of Different Metal Ion-L-Alanine Complex and β-Cyclodextrin on the Chiral Separation of Dansyl Amino Acids with Capillary Electrophoresis. CHINESE J CHEM 2010. [DOI: 10.1002/cjoc.20030211117] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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8
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Dimitrova P, Bart HJ. Non-ionic surfactant modified ligand exchange chromatography using copper (II) complex of N,N-dimethyl-l-phenylalanine as the chiral additive for enantioselective amino acids separation. Anal Chim Acta 2010; 663:109-16. [DOI: 10.1016/j.aca.2010.01.047] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2009] [Revised: 01/20/2010] [Accepted: 01/22/2010] [Indexed: 11/30/2022]
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9
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Kodama S, Aizawa SI, Taga A, Yamashita T, Kemmei T, Suzuki K, Honda Y, Yamamoto A. Metal(II)-ligand molar ratio dependence of enantioseparation of tartaric acid by ligand exchange CE with Cu(II) and Ni(II)-D-quinic acid systems. Electrophoresis 2010; 31:1051-4. [DOI: 10.1002/elps.200900596] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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10
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Zaher M, Ravelet C, Vanhaverbeke C, Baussanne I, Perrier S, Fize J, Décout JL, Peyrin E. Enantioseparation by MEKC using a ligand exchange-based chiral pseudostationary phase. Electrophoresis 2010; 30:2869-73. [PMID: 19637217 DOI: 10.1002/elps.200800832] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
In this paper, a new ligand-exchange -MEKC mode, based on the design of a unique lipohilic species (4'-octadecylneamine derivative), which served both as micelle-forming surfactant (by its hydrophobic part) and central ion-complexing ligand (by its hydrophilic part) is described. The CMC of the used lipophilic neamine derivative was first determined by surface tension measurements. Subsequent NMR experiments were performed in order to investigate the Cu(II) binding properties of the neamine micellar phase. The enantioseparation properties of both the octadecylneamine derivative-Cu(II) MEKC and the native neamine-Cu(II) CE systems were evaluated and compared using the tryptophan racemate as a probe analyte. The effects of several different electrophoretic conditions on the enantiomer migration behavior in the ligand-exchange-MEKC mode were examined. The developed methodology was also applied to the enantioseparation of other analytes such as 1-methyl-tryptophan, 3,5-diiodo-tyrosine and 1-naphtyl-alanine.
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Affiliation(s)
- Mustapha Zaher
- Département de Pharmacochimie Moléculaire UMR 5063 CNRS, Institut de Chimie Moléculaire de Grenoble FR 2607, Université Grenoble I (Joseph Fourier), UFR de Pharmacie, Grenoblex, France
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11
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Aït Adoubel A, Morin CJ, Mofaddel N, Dupas G, Desbène PL. Enantioseparation of underivatised amino acids by ligand exchange capillary electrophoresis in a counter-electroosmotic mode. Anal Bioanal Chem 2009; 394:597-608. [DOI: 10.1007/s00216-009-2694-z] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2008] [Revised: 02/04/2009] [Accepted: 02/09/2009] [Indexed: 10/21/2022]
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12
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WANG M, DING X, CHEN H, CHEN X. Enantioseparation of Palonosetron Hydrochloride by Capillary Zone Electrophoresis with High-concentration .BETA.-CD as Chiral Selector. ANAL SCI 2009; 25:1217-20. [DOI: 10.2116/analsci.25.1217] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Affiliation(s)
- Min WANG
- Department of Chemistry, Lanzhou University
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13
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Qi L, Chen Y, Xie M, Guo Z, Wang X. Separation of dansylated amino acid enantiomers by chiral ligand-exchange CE with a zinc(II) L-arginine complex as the selecting system. Electrophoresis 2008; 29:4277-83. [DOI: 10.1002/elps.200800064] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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14
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Ghosh A, Dey J. Enantiomeric separations of binaphthyl derivatives by capillary electrophoresis usingN-(2-hydroxydodecyl)-L-threonine as chiral selector: Effect of organic additives. Electrophoresis 2008; 29:1540-7. [DOI: 10.1002/elps.200700638] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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15
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Tang W, Ong TT, Ng SC. Chiral separation of dansyl amino acids in capillary electrophoresis using mono-(3-methyl-imidazolium)-beta-cyclodextrin chloride as selector. J Sep Sci 2007; 30:1343-9. [PMID: 17623477 DOI: 10.1002/jssc.200600461] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Enantioseparations of fourteen dansyl amino acids were achieved by using a positively-charged single-isomer beta-cyclodextrin, mono-(3-methyl-imidazolium)-beta-cyclodextrin chloride, as a chiral selector. Separation parameters such as buffer pH, selector concentration, separation temperature, and organic modifier were investigated for the enantioseparation in order to achieve the maximum possible resolution. Chiral separation of dansyl amino acids was found to be highly dependent on pH since the degree of protonation of these amino acids can alter the strength of electrostatic interaction and/or inclusion complexation between each enantiomer and chiral selector. In general, the chiral resolution of dansyl amino acids was enhanced at higher pH, which indicates that the carboxylate group on the analytes may interact with the imidazolium group of cationic cyclodextrin. For most analytes, a distinct maximum in enantioresolution was obtained at pH 8.0. Moreover, the chiral separation can be further improved by careful tuning of the separation parameters such as higher selector concentration (e.g. 10 mM), lower temperature, and addition of methanol. Enantioseparation of a standard mixture of these dansyl amino acids was further achieved in a single run within 30 min.
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Affiliation(s)
- Weihua Tang
- Department of Chemistry, National University of Singapore, Singapore
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16
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Tian K, Chen H, Tang J, Chen X, Hu Z. Enantioseparation of palonosetron hydrochloride by micellar electrokinetic chromatography with sodium cholate as chiral selector. J Chromatogr A 2006; 1132:333-6. [PMID: 16999973 DOI: 10.1016/j.chroma.2006.08.090] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2006] [Revised: 08/27/2006] [Accepted: 08/30/2006] [Indexed: 11/26/2022]
Abstract
The enantioseparation of four stereoisomers of palonosetron hydrochloride by micellar electrokinetic chromatography using sodium cholate as chiral surfactant was described. Sodium cholate was shown to be effective in separating palonosetron hydrochloride stereoisomers. For method optimization, several parameters such as sodium cholate concentration, buffer pH and concentration, the types and concentration of organic modifiers and applied voltage, on the enantioseparation were evaluated and the optimum conditions were obtained as follows: 30 mM borate buffer (pH 9.40) containing 70 mM sodium cholate and 20% (v/v) methanol with an applied voltage of 20 kV. Under these conditions, baseline separation of palonosetron hydrochloride stereoisomers was achieved within 18 min.
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Affiliation(s)
- Kan Tian
- Department of Chemistry, Lanzhou University, Lanzhou 730000, China
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17
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Kodama S, Yamamoto A, Iio R, Aizawa SI, Nakagomi K, Hayakawa K. Chiral ligand exchange micellar electrokinetic chromatography using borate anion as a central ion. Electrophoresis 2006; 26:3884-9. [PMID: 16167312 DOI: 10.1002/elps.200500327] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Three compounds having 1,2-diol structure (1-phenyl-1,2-ethanediol, 3-phenoxy-1,2-propanediol, and 3-benzyloxy-1,2-propanediol) were enantioseparated by ligand exchange MEKC using (5S)-pinanediol (SPD) as a chiral selector and borate anion as a central ion together with SDS. When (S)-1,2-propanediol, (S)-1,2,4-butanetriol, or (S)-3-tert-butylamino-1,2-propanediol were used as the chiral ligand instead of SPD, these three compounds were not enantioseparated. When borate was replaced with 2-aminoethane-1-sulfonate or N-cyclohexyl-3-aminopropanesulfonate, no chiral separation was achieved. Therefore, the hydrophobic interaction between the chiral selector and the chiral analytes within the transient diastereomeric complex may play an important role in the enantioseparation achieved by the proposed method.
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Affiliation(s)
- Shuji Kodama
- Toyama Institute of Health, Kosugi-machi, Toyama, Japan.
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18
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Koidl J, Hödl H, Schmid MG, Pantcheva S, Pajpanova T, Gübitz G. Chiral separation of halogenated amino acids by ligand-exchange capillary electrophoresis. Electrophoresis 2005; 26:3878-83. [PMID: 16217828 DOI: 10.1002/elps.200500130] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
The chiral separation of halogenated amino acids by ligand-exchange CE is described. Halogenated amino acids attracted increasing interest in recent years because of their physiological activities. Different chiral selectors, as there are L-4-hydroxyproline, L-histidine, and N-alkyl derivatives of L-4-hydroxyproline in form of their copper(II) complexes, are compared for their chiral recognition ability for halogenated amino acids. The influence of various parameters, such as selector concentration, pH, organic modifier, and field strength, on the resolution was investigated. All halogenated amino acids investigated were baseline-separated under optimized conditions.
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Affiliation(s)
- Julia Koidl
- Department of Pharmaceutical Chemistry, Institute of Pharmaceutical Sciences, Karl-Franzens-University, Graz, Austria
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19
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Zheng ZX, Wei Y, Lin JM. Chiral separation based on ligand-exchange capillary electrophoresis using a copper(II)-L-ornithine ternary complex as selector. Electrophoresis 2005; 26:1007-1012. [PMID: 15714579 DOI: 10.1002/elps.200406133] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
A ligand-exchange capillary electrophoresis was explored, with L-ornithine as the ligand and copper(II) as the central ion. Its applicability was demonstrated with underivatized and dansyl amino acids, a dipeptide, and drugs with amino alcohol structure. The enantioselectivity was found to be strongly dependent on pH and copper(II)-L-Orn complex concentration. Due to the adsorption of the positively charged species onto the capillary inner walls, the chiral separation selectivity is very high while the efficiency is relatively low. Permanent 1,3-propanediamine-coated capillaries show an improved separation efficiency and theoretical plate numbers increasing from 10(4) to 10(5). Similar phenomena were observed when sodium dodecyl sulfate (SDS) micelles were added to the copper(II) complex solution. The poor separation efficiency of chiral compounds in uncoated capillaries may result from the low rate of the ligand-exchange reactions, and the high enantioselectivity may derive from the complexing process in the adsorbed phase.
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Affiliation(s)
- Zhi-Xia Zheng
- Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, China
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20
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Capillary Electrophoresis and Capillary Electrochromatography of Amino Acids as Dansyl Derivatives. ACTA ACUST UNITED AC 2005. [DOI: 10.1016/s0301-4770(05)80014-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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21
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Affiliation(s)
- Zilin CHEN
- Center for Micro-fluidics and Medical Diagnostics, Department of Chemical and Biomolecular Engineering, University of Notre Dame
| | - Hsueh-Chia CHANG
- Center for Micro-fluidics and Medical Diagnostics, Department of Chemical and Biomolecular Engineering, University of Notre Dame
| | - Toshiyuki HOBO
- Department of Applied Chemistry, Graduate School of Engineering, Tokyo Metropolitan University
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22
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Nakajima H, Kawata K, Shen H, Nakagama T, Uchiyama K. Chiral Separation of NBD-Amino Acids by Ligand-Exchange Micro-Channel Electrophoresis. ANAL SCI 2005; 21:67-71. [PMID: 15675519 DOI: 10.2116/analsci.21.67] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
The chiral separation of amino acid derivatives by ligand-exchange electrophoresis in a microchannel chip was performed for the first time. A Cu(II) complex with L-prolinamide was used as a chiral selector. The migration behaviors of eleven NBD-DL-amino acids were investigated by ligand-exchange capillary electrophoresis (LE-CE). The enantiomer of five NBD-amino acids (Ser, Thr, Val, Phe and His) could be separated by LE-CE using a 20 mM ammonium acetate buffer (pH 9.0) containing 10 mM copper acetate, 20 mM L-prolinamide and 1 mM SDS. NBD-His was eluted in the order D-form and L-form, while the elution order of another enantiomers was L-form and D-form. Under this condition, the enantioseparation of these five NBD-amino acids by ligand-exchange microchip electrophoresis (LE-ME) was investigated using a glass microchip. The enantioseparation of NBD-Ser, -Thr and -His could be successfully accomplished by LE-ME. LE-ME was superior to LE-CE in terms of the short migration time and a good enantiomeric separation.
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Affiliation(s)
- Hizuru Nakajima
- Department of Applied Chemistry, Graduate School of Engineering, Tokyo Metropolitan University, 1-1 Minamiohsawa, Hachioji, Tokyo 192-0397, Japan.
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23
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Chen Z, Uchiyama K, Hobo T. Chiral resolution of dansyl amino acids by ligand exchange-capillary electrophoresis using Cu(II)-l-prolinamides as chiral selector. Anal Chim Acta 2004. [DOI: 10.1016/j.aca.2004.07.024] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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24
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Electrochromatographic enantioseparation using chiral ligand exchange monolithic sol–gel column. Anal Chim Acta 2004. [DOI: 10.1016/j.aca.2003.09.012] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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25
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Zheng ZX, Lin JM, Qu F. Chiral separation of underivatized and dansyl amino acids by ligand-exchange micellar electrokinetic capillary chromatography using a copper(II)-L-valine complex as selector. J Chromatogr A 2003; 1007:189-96. [PMID: 12924564 DOI: 10.1016/s0021-9673(03)00960-9] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Ligand-exchange micellar electrokinetic capillary chromatography was used for the chiral resolution of underivatized and dansyl amino acid enantiomers simultaneously. The separation was achieved by chiral copper(II)-L-valine complexes incorporated in micelles of sodium dodecyl sulfate (SDS). The enantioresolution was strongly affected by SDS and a concentration of 20 mM SDS was shown to be necessary for the separation. Other impacting factors were investigated including pH, the molar ratio of copper(II) to L-valine and the total concentration of complex. Using the proposed method, 11 different dansyl amino acids and two underivatized amino acids were separated successfully with a running electrolyte of 20 mM NH4OAc, 4 mM CuSO4, 8 mM L-valine and 20 mM SDS at pH 9.0 in less than 25 min. Experiments were also performed with other amino acid ligands in order to vary the stability and the sterical arrangement of the copper(II) complexes and the possible chiral recognition mechanism was also discussed briefly.
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Affiliation(s)
- Zhi-Xia Zheng
- Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, P.O. Box 2871, Beijing 100085, China
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26
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Abstract
As a follow-up to a series of review articles on enantioselective ligand exchange chromatography, the present contribution critically evaluates achievements in this area of active and successful research which have been reported in the scientific since 1992. Also discussed is enantioselective ligand exchange in electromigration techniques which have developed especially fruitfully during the last decade.
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Affiliation(s)
- Vadim A Davankov
- Institute of Organo-Element Compounds, Russian Academy of Sciences, Vavilov Str. 28, Moscow 119991, Russia.
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27
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Chen Z, Niitsuma M, Uchiyama K, Hobo T. Comparison of enantioseparations using Cu(II) complexes with L-amino acid amides as chiral selectors or chiral stationary phases by capillary electrophoresis, capillary electrochromatography and micro liquid chromatography. J Chromatogr A 2003; 990:75-82. [PMID: 12685585 DOI: 10.1016/s0021-9673(02)01970-2] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
In this paper we report that Cu(II) complexes with L-amino acid amides were used as chiral selectors for enantioseparation by capillary electrophoresis, capillary electrochromatography (CEC) and micro liquid chromatography using chemically modified monolithic columns. The enantioselectivity, enantiomer migration order, and the performance have been compared when different chiral selectors were used in these modes. L-Enantiomers showed longer retention times than D-forms in both CEC and LC modes. However, it has interestingly been observed that the migration order of Dns-DL-Ser showed an exception in CEC using L-prolinamide-modified column that Dns-L-Ser was eluted as the first peak. On the basis of proposed structures of complexes in the chiral recognition, differences in migration orders and recognition mechanism were discussed.
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Affiliation(s)
- Zilin Chen
- Department of Applied Chemistry, Graduate School of Engineering, Tokyo Metropolitan University, 1-1 Minamiohsawa, Hachioji, Tokyo 192-0397, Japan.
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28
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Zhu C, Lin X, Wu J, Wei Y. Chiral separation of several drugs using electrophoresis with dual cyclodextrin systems. ANAL SCI 2002; 18:1055-7. [PMID: 12243405 DOI: 10.2116/analsci.18.1055] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Affiliation(s)
- Chenfu Zhu
- School of Chemistry, Shandong University, Jinan, PR China
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29
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Chen Z, Niitsuma M, Nakagama T, Uchiyama K, Hobo T. Enantioseparations of dansyl amino acids by capillary electrophoresis using Cu(II) complexes with L-amino acylamides as chiral selectors in electrolytes. J Sep Sci 2002. [DOI: 10.1002/1615-9314(20021101)25:15/17<1197::aid-jssc1197>3.0.co;2-2] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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30
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Lu X, Chen Y, Guo L, Yang Y. Chiral separation of underivatized amino acids by ligand-exchange capillary electrophoresis using a copper(II)-L-lysine complex as selector. J Chromatogr A 2002; 945:249-55. [PMID: 11860139 DOI: 10.1016/s0021-9673(01)01494-7] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
A ligand-exchange capillary electrophoretic method was explored, with L-lysine as the ligand and copper(II) as the central ion. Its applicability was demonstrated with underivatized aromatic amino acids, namely D,L-phenylalanine, D,L-tryptophan, D,L-tyrosine and D,L-beta-phenylserine. Optical resolutions of a single pair of amino acid enantiomers, and of mixed amino acids were obtained with a running buffer of 10 mM NH4Ac, 6.67 mM Cu(II) and 13.33 mM L-lysine, pH 7.0. Sodium dodecylsulfate (SDS) was shown to be necessary for simultaneous separation of the mixed amino acids. The resolution was found to increase with the concentration of the copper(II) complex at a copper(II)-to-lysine ratio of 1:2. If the total concentration of copper(II) and lysine was kept at 20 mM, decreasing the ratio of copper(II) to lysine caused a resolution loss of tryptophan, but a slight resolution improvement of the other three amino acids. The pH of buffer is another important factor controlling the separations. For all the studied amino acids, the optimum pH was 6.0. An interesting phenomenon was observed in this study. SDS induces precipitation at a concentration below 32 mM at room temperature (16+/-2 degrees C), possibly due to the formation of neutral substance from the SDS monomer and the copper(II)-lysine complex.
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Affiliation(s)
- Xiaoning Lu
- Center for Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing
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31
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Chen Z, Uchiyama K, Hobo T. Chemically modified chiral monolithic silica column prepared by a sol-gel process for enantiomeric separation by micro high-performance liquid chromatography. J Chromatogr A 2002; 942:83-91. [PMID: 11822400 DOI: 10.1016/s0021-9673(01)01381-4] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
In this work a new type of chiral monolith silica column was developed for the chiral separation by micro high-performance liquid chromatography (micro-HPLC). The chiral monolith column with a continuous skeleton and a large through-pore structure was prepared inside a capillary of 100 microm I.D. by a sol-gel process, and chemically modified with chiral selectors, such as L-phenylalaninamide, L-alaninamide and L-prolinamide, on the surface of the monolithic silica column. Based on the principle of ligand exchange, these chiral monolithic columns were successfully used for the separation of dansyl amino acid enantiomers, as well as hydroxy acid enantiomers by micro-HPLC. The chromatographic conditions, the enantioselectivity and the performance of columns are discussed.
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Affiliation(s)
- Zilin Chen
- Department of Applied Chemistry, Graduate School of Engineering, Tokyo Metropolitan University, Hachioji, Japan.
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32
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Chen Z, Yamada K, Niitsuma M, Uchiyama K, Hobo T. Separation selectivity in micellar electrokinetic chromatography using different anionic surfactants as pseudo-stationary phases. Chromatographia 2001. [DOI: 10.1007/bf02492190] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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33
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Kodama S, Yamamoto A, Matsunaga A, Hayakawa K. Direct chiral resolution of tartaric acid in food products by ligand exchange capillary electrophoresis using copper(II)-D-quinic acid as a chiral selector. J Chromatogr A 2001; 932:139-43. [PMID: 11695859 DOI: 10.1016/s0021-9673(01)01228-6] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Chiral resolution of native DL-tartaric acid was performed by ligand-exchange capillary electrophoresis using copper(II)-D-quinic acid as a chiral selector. Factors affecting chiral resolution, migration time, and peak area of tartaric acid were studied. The running conditions for optimum separation of tartaric acid were found to be 1 mM copper(II) sulfate-10 mM D-quinic acid (pH 5.0) with an effective voltage of -15 kV at 30 degrees C, using direct detection at 250 nm, and resolution of racemic tartaric acid was approximately 1.3. With this system, chiral resolution of DL-tartaric acid in food products was conducted successfully.
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Affiliation(s)
- S Kodama
- Toyama Institute of Health, Kosugi-machi, Japan.
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34
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Chen Z, Hobo T. Chemically L-prolinamide-modified monolithic silica column for enantiomeric separation of dansyl amino acids and hydroxy acids by capillary electrochromatography and mu-high performance liquid chromatography. Electrophoresis 2001; 22:3339-46. [PMID: 11589299 DOI: 10.1002/1522-2683(200109)22:15<3339::aid-elps3339>3.0.co;2-5] [Citation(s) in RCA: 89] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
A silica-based chiral monolithic column prepared by sol-gel process and chemical modification of chiral selector was used for enantioseparation of dansyl amino acids and hydroxy acids by capillary electrochromatography (CEC) and mu-high-performance liquid chromatography (mu-HPLC). L-Prolinamide was modified as a chiral selector. The chiral stationary phase (CSP), the chiral complex of Cu(II) with L-prolinamide, provides an anodic electroosmotic flow (EOF) in CEC. The EOF was found to be dependent on applied electric field strength, the pH, and the composition of mobile phases. Scanning electron micrograph showed that monolithic columns have the morphology of continuous skeleton and large through-pore. D-Enantiomers migrated before L-enantiomers except for dansyl-(Dns)-DL-Ser. The separation efficiencies of up to 17600 (D) and 13,200 plates m(-1) (L) were achieved for the separation of DL-indole-3-lactic acid.
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Affiliation(s)
- Z Chen
- Department of Applied Chemistry, Graduate School of Engineering, Tokyo Metropolitan University, Japan.
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35
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Kodama S, Yamamoto A, Matsunaga A, Soga T, Hayakawa K. Direct chiral resolution of malic acid in apple juice by ligand-exchange capillary electrophoresis using copper(II)-L-tartaric acid as a chiral selector. Electrophoresis 2001; 22:3286-90. [PMID: 11589292 DOI: 10.1002/1522-2683(200109)22:15<3286::aid-elps3286>3.0.co;2-j] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Chiral resolution of native DL-malic acid was achieved by ligand-exchange capillary electrophoresis using copper(II)-L-tartrate as a chiral selector. Factors affecting chiral resolution, migration time, and peak area of malic acid were studied. The running conditions for optimum separation of malic acid were found to be 1 mM copper(II) sulfate-1 mM L-tartrate (pH 5.1) with an effective voltage of -20 kV at 30 degrees C, using direct detection at 280 nm, and resolution (Rs) of racemic malic acid was approximately 4. With this system, D- and L-malic acids in apple juice were analyzed successfully.
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Affiliation(s)
- S Kodama
- Toyama Institute of Health, Japan.
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36
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Schmid MG, Grobuschek N, Lecnik O, Gübitz G. Chiral ligand-exchange capillary electrophoresis. ACTA ACUST UNITED AC 2001; 48:143-54. [PMID: 11356484 DOI: 10.1016/s0165-022x(01)00145-2] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
This review summarizes the application of capillary electrophoresis and capillary electrochromatography for the chiral separation of various substance classes using the principle of ligand exchange. The application of this principle to various substance classes is reported.
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Affiliation(s)
- M G Schmid
- Institute of Pharmaceutical Chemistry, Karl-Franzens University, Universitätsplatz 1, A-8010, Graz, Austria
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37
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Chen Z, Hobo T. Chemically L-phenylalaninamide-modified monolithic silica column prepared by a sol-gel process for enantioseparation of dansyl amino acids by ligand exchange-capillary electrochromatography. Anal Chem 2001; 73:3348-57. [PMID: 11476235 DOI: 10.1021/ac010243p] [Citation(s) in RCA: 116] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
A new type of chiral monolithic column was successfully developed for the enantioseparation of dansyl amino acids by ligand exchange-capillary electrochromatography (LE-CEC) in this work. The monolithic column matrix was prepared by a sol-gel process and then chemically modified with the spacer (3-glycidoxypropyl)trimethoxysilane and the chiral selector L-phenylalaninamide. After being conditioned with Cu(II) aqueous solution, the ligand exchange-chiral stationary phase (LE-CSP) possesses positive charges. When the external electric field was applied in CEC, electroosmotic flow (EOF) was generated on the surface of LE-CSP in the direction from the cathode to the anode. The EOF was found to be dependent on the applied electric field strength and the composition of the mobile phase. With the increase of pH of the mobile phase, the EOF showed a tendency to decrease. Scanning electron microscopy showed that the chiral monolithic column has a continuous skeleton and large through-pore structure. The separation efficiency (theoretic plate numbers) for the separation of Dns-DL-Leu reached up to 9.0 x 10(4) plates m(-1) for the D-enantiomer and 6.6 x 10(4) plates m(-1) for the L-enantiomer, by using pH 5.5, acetonitrile/0.50 mM Cu(Ac)2-50 mM NH4Ac (7:3) as mobile phase. The reproducibility and lifetime were satisfactory. CEC was carried out with conventional capillary electrophoresis equipment without pressurizing the ends of the capillary. No bubble was formed during the operation, after degassing the mobile phase and conditioning the column.
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Affiliation(s)
- Z Chen
- Department of Applied Chemistry, Graduate School of Engineering, Tokyo Metropolitan University, Hachioji, Japan.
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38
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Chen Z, Uchiyama K, Hobo T. Interaction between 18-crown-6-tetracarboxylic acid and positional substituents of enantiomers and simultaneous separation of positional enantiomers of methyl-DL-tryptophans by capillary electrophoresis. Electrophoresis 2001; 22:2136-42. [PMID: 11504044 DOI: 10.1002/1522-2683(20017)22:11<2136::aid-elps2136>3.0.co;2-z] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
18-Crown-6-tetracarboxylic acid (18C6H4) is a chiral selector with high selectivity for the enantioseparation of solutes bearing the primary amine function. This work presents the simultaneous separation of positional enantiomers of methyl-DL-tryptophans by using 18C6H4 as an additive to the background electrolyte. Separation conditions such as pH, the concentration of 18C6H4, and the applied voltages have critical inference on the simultaneous separation. The addition of cyclodextrins as anionic surfactants to the background electrolyte did not improve the separation. The selector-selectand interactions between 18C6H4 and the positional enantiomers have been investigated. It was observed that both the position and type of substituents contribute to the enantioselectivity. The migration order and resolution depended on the distance from the substituents to the asymmetric carbon of the enantiomers.
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Affiliation(s)
- Z Chen
- Department of Applied Chemistry, Graduate School of Engineering, Tokyo Metropolitan University, Japan.
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39
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Lin JM, Hobo T. Inspection of the reversal of enantiomer migration order in ligand exchange micellar electrokinetic capillary chromatography. Biomed Chromatogr 2001; 15:207-11. [PMID: 11391678 DOI: 10.1002/bmc.63] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Enantiometers of D,L-phenylalanine were separated by capillary electrophoresis based on the principle of ligand exchange. Copper (II) complex of 4-hydroxy-L-proline was used as chiral selector. The separation and the migration order of D- and L-phenylalanine were strongly affected by adding an anion surfactant sodium dodecylsulfate (SDS). Without SDS in the electrolyte, the separation was also carried out but the resolution was very small. With SDS added into the electrolyte, the resolution decreased with increasing concentration of SDS until 5.0 mM. When the concentration of SDS in the electrolyte was over 5.0 mM, inversion of the migration order of DL-phenylalanine was observed and the resolution was also increased with increasing concentration up to 20 mM. It was interesting to find that the inversion of the migration order took place not only in the enantioscparation but also in the positional isomers. A family of a fluorinated amino acid, o-, m- and p-fluoro-D,L-phenylalanine was separated and the inversion of the migration order is discussed.
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Affiliation(s)
- J M Lin
- Department of Applied Chemistry, Graduate School of Engineering, Tokyo Metropolitan University, Hachioji, Tokyo 192-0397, Japan.
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40
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Lin X, Li G, Jiang W, Chu Y, Wu P, Yafeng G. Chiral separation of lobeline and benzhexol by capillary electrophoresis using the reaction mixture of β-cyclodextrin, phosphorous-pentoxide and l-glutamic acid as chiral selector. Anal Chim Acta 2001. [DOI: 10.1016/s0003-2670(00)01295-2] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
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41
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Xu W, Uchiyama K, Shimosaka T, Hobo T. Fabrication of polyester microchannels and their applications to capillary electrophoresis. J Chromatogr A 2001; 907:279-89. [PMID: 11217035 DOI: 10.1016/s0021-9673(00)01074-8] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Inexpensive and disposable polyester microchips were fabricated through photolithographic and wet-chemical etching procedure, followed by replication using an imprinting method at room temperature. Laboratory-scale laser-induced fluorescence equipment was employed as a detection system. The generation of electroosmotic flow (EOF) on the polyester channels was discussed in this paper. Surfactants in the running buffer had a significant effect on the EOF depending on their types. The epsilon potential of the electric double layer formed by adsorbing sodium lauryl sulfate molecules on the wall of polyester channels seemed to be constant within the buffer pH investigated. EOF could also be suppressed to zero by adding polyoxyethylene 23 lauryl ether into the running buffer. The separation of two laser dyes was obtained using polyester chips through both micellar electrokinetic chromatography and capillary zone electrophoresis. The polyester channels modified with 10-undecen-1-ol exhibited a dramatically high-separation efficiency compared with the conventional fused-silica capillary tubes.
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Affiliation(s)
- W Xu
- Department of Applied Chemistry, Graduate School of Engineering, Tokyo Metropolitan University, Hachioji, Japan
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42
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Abstract
This review summarizes recent developments in the field of chiral separations by electromigration techniques including capillary zone electrophoresis (CZE), capillary gel electrophoresis (CGE), isotachophoresis (ITP), electrokinetic chromatography (EKC), and capillary electrochromatography (CEC). This overview focuses on the development of new chiral selectors and the introduction of new techniques rather than applications of already established selectors and methods. The mechanisms of the different chiral separation principles are discussed.
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Affiliation(s)
- G Gübitz
- Institute of Pharmaceutical Chemistry, Karl-Franzens University, Graz, Austria.
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43
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Abstract
Chiral separation of amino acids and peptides by capillary electrophoresis (CE) is reviewed regarding the separation principles of different approaches, advantages and limitations, chiral recognition mechanisms and applications. The direct approach details various chiral selectors with an emphasis on cyclodextrins and their derivatives, antibiotics and chiral surfactants as the chiral selectors. The indirect approach deals with various chiral reagents applied for diastereomer formation and types of separation media such as micelles and polymeric pseudo-stationary phases. Many derivatization reagents used for high sensitivity detection of amino acids and peptides are also discussed and their characteristics are summarized in tables. A large number of relevant examples is presented illustrating the current status of enantiomeric and diastereomeric separation of amino acids and peptides. Strategies to enhance the selectivity and optimize separation parameters by the application of experimental designs are described. The reversal of enantiomeric elution order and the effects of organic modifiers on the selectivity are illustrated in both direct and indirect methods. Some applications of chiral amino acid and peptide analysis, in particular, regarding the determination of trace enantiomeric impurities, are given. This review selects more than 200 articles published between 1988 and 1999.
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Affiliation(s)
- H Wan
- Department of Chemistry, Karlstad University, Sweden
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44
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Schmid MG, Lecnik O, Sitte U, Gübitz G. Application of ligand-exchange capillary electrophoresis to the chiral separation of alpha-hydroxy acids and beta-blockers. J Chromatogr A 2000; 875:307-14. [PMID: 10839150 DOI: 10.1016/s0021-9673(99)01333-3] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The application of the principle of ligand-exchange capillary electrophoresis to two substance classes is described. As chiral selector N-(2-hydroxyoctyl)-L-4-hydroxyproline-copper(II) complex was used. This principle was applied to the chiral separation of alpha-hydroxy acids and drugs containing amino alcohol structure such as beta-blockers. The enantioselectivity was found to be strongly dependent on pH corresponding to the optimal conditions for complex formation for each structure class.
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Affiliation(s)
- M G Schmid
- Institute of Pharmaceutical Chemistry, Karl-Franzens University, Graz, Austria
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45
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CHEN Z, LIN J, UCHIYAMA K, HOBO T. Reversal Behaviors of the Enantiomer Migration Order and the Stereo-selectivity of Cu(II) Complex with Amino Acid Enantiomers in Ligand Exchange-Micellar Electrokinetic Chromatography. ANAL SCI 2000. [DOI: 10.2116/analsci.16.131] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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46
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CHEN Z, UCHIYAMA K, HOBO T. Estimation of Formation Constants of Ternary Cu(II) Complexes with Mixed Amino Acid Enantiomers Based on Ligand Exchange by Capillary Electrophoresis. ANAL SCI 2000. [DOI: 10.2116/analsci.16.837] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Affiliation(s)
- Zilin CHEN
- Department of Applied Chemistry, Graduate School of Engineering, Tokyo Metropolitan University
| | - Katsumi UCHIYAMA
- Department of Applied Chemistry, Graduate School of Engineering, Tokyo Metropolitan University
| | - Toshiyuki HOBO
- Department of Applied Chemistry, Graduate School of Engineering, Tokyo Metropolitan University
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47
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Chen Z, Lin JM, Uchiyama K, Hobo T. Determination of critical micelle concentrations of anionic surfactants based on ligand exchange micellar electrokinetic chromatography. Anal Chim Acta 2000. [DOI: 10.1016/s0003-2670(99)00565-6] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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48
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CHEN Z, UCHIYAMA K, HOBO T. Separation of hydroxy acid enantiomers by ligand exchange-micellar electrokinetic chromatography. BUNSEKI KAGAKU 2000. [DOI: 10.2116/bunsekikagaku.49.759] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Affiliation(s)
- Zilin CHEN
- Department of Applied Chemistry,Graduate School of Engineering,Tokyo Metropolitan University,1-1,Minamiosawa,Hachioji-shi,Tokyo 192-0397
| | - Katsumi UCHIYAMA
- Department of Applied Chemistry,Graduate School of Engineering,Tokyo Metropolitan University,1-1,Minamiosawa,Hachioji-shi,Tokyo 192-0397
| | - Toshiyuki HOBO
- Department of Applied Chemistry,Graduate School of Engineering,Tokyo Metropolitan University,1-1,Minamiosawa,Hachioji-shi,Tokyo 192-0397
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49
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Lin JM, Nakagawa M, Uchiyama K, Hobo T. Determination of critical micelle concentration of SDS in formamide by capillary electrophoresis. Chromatographia 1999. [DOI: 10.1007/bf02497314] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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50
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Chen Z, Lin JM, Uchiyama K, Hobo T. Simultaneous separation of sixteen positional and optical isomers of the tryptophan family by ligand-exchange micellar electrokinetic chromatography. Chromatographia 1999. [DOI: 10.1007/bf02467620] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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