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Abstract
Isotachophoresis (ITP) is a versatile electrophoretic technique that can be used for sample preconcentration, separation, purification, and mixing, and to control and accelerate chemical reactions. Although the basic technique is nearly a century old and widely used, there is a persistent need for an easily approachable, succinct, and rigorous review of ITP theory and analysis. This is important because the interest and adoption of the technique has grown over the last two decades, especially with its implementation in microfluidics and integration with on-chip chemical and biochemical assays. We here provide a review of ITP theory starting from physicochemical first-principles, including conservation of species, conservation of current, approximation of charge neutrality, pH equilibrium of weak electrolytes, and so-called regulating functions that govern transport dynamics, with a strong emphasis on steady and unsteady transport. We combine these generally applicable (to all types of ITP) theoretical discussions with applications of ITP in the field of microfluidic systems, particularly on-chip biochemical analyses. Our discussion includes principles that govern the ITP focusing of weak and strong electrolytes; ITP dynamics in peak and plateau modes; a review of simulation tools, experimental tools, and detection methods; applications of ITP for on-chip separations and trace analyte manipulation; and design considerations and challenges for microfluidic ITP systems. We conclude with remarks on possible future research directions. The intent of this review is to help make ITP analysis and design principles more accessible to the scientific and engineering communities and to provide a rigorous basis for the increased adoption of ITP in microfluidics.
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Affiliation(s)
- Ashwin Ramachandran
- Department of Aeronautics and Astronautics, Stanford University, Stanford, California 94305, United States
| | - Juan G Santiago
- Department of Mechanical Engineering, Stanford University, Stanford, California 94305, United States
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2
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Malý M, Boublík M, Pocrnić M, Ansorge M, Lorinčíková K, Svobodová J, Hruška V, Dubský P, Gaš B. Determination of thermodynamic acidity constants and limiting ionic mobilities of weak electrolytes by capillary electrophoresis using a new free software AnglerFish. Electrophoresis 2019; 41:493-501. [PMID: 31651992 DOI: 10.1002/elps.201900283] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2019] [Revised: 10/03/2019] [Accepted: 10/19/2019] [Indexed: 12/26/2022]
Abstract
Thermodynamic acidity constants (acid or acid-base dissociation constants, sometimes called also as ionization constants) and limiting ionic mobilities (both of them at defined temperature, usually 25°C) are the fundamental physicochemical characteristics of a weak electrolyte, that is, weak acid or weak base or ampholyte. We introduce a novel method for determining the data of a weak electrolyte by the nonlinear regression of effective electrophoretic mobility versus buffer composition dependence when measured in a set of BGEs with various pH. To correct the experimental data for zero ionic strength we use the extended Debye-Hückel model and Onsager-Fuoss law with no simplifications. Contrary to contemporary approaches, the nonlinear regression is performed on limiting mobility data calculated by PeakMaster's correction engine, not on the raw experimental mobility data. Therefore, there is no requirement to perform all measurements at a constant ionic strength of the set of BGEs. We devised the computer program AnglerFish that performs the necessary calculations in a user-friendly fashion. All thermodynamic pKa values and limiting electrophoretic mobilities for arbitrarily charged substances having any number of ionic forms are calculated by one fit. The user input consists of the buffer composition of the set of BGEs and experimentally measured effective mobilities of the inspected weak electrolyte.
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Affiliation(s)
- Michal Malý
- Faculty of Science, Department of Physical and Macromolecular Chemistry, Charles University in Prague, Prague, Czech Republic
| | - Milan Boublík
- Faculty of Science, Department of Physical and Macromolecular Chemistry, Charles University in Prague, Prague, Czech Republic
| | - Marijana Pocrnić
- Department of Chemistry, Faculty of Science, University of Zagreb, Zagreb, Croatia
| | - Martin Ansorge
- Faculty of Science, Department of Physical and Macromolecular Chemistry, Charles University in Prague, Prague, Czech Republic
| | - Kateřina Lorinčíková
- Faculty of Science, Department of Physical and Macromolecular Chemistry, Charles University in Prague, Prague, Czech Republic
| | - Jana Svobodová
- Agilent Technologies Deutschland GmbH & Co. KG, Liquid Phase Separations Division, Waldbronn, Germany
| | - Vlastimil Hruška
- Agilent Technologies Deutschland GmbH & Co. KG, Liquid Phase Separations Division, Waldbronn, Germany
| | - Pavel Dubský
- Faculty of Science, Department of Physical and Macromolecular Chemistry, Charles University in Prague, Prague, Czech Republic
| | - Bohuslav Gaš
- Faculty of Science, Department of Physical and Macromolecular Chemistry, Charles University in Prague, Prague, Czech Republic
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3
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Moreno-Gordaliza E, van der Lee SJ, Demirkan A, van Duijn CM, Kuiper J, Lindenburg PW, Hankemeier T. A novel method for serum lipoprotein profiling using high performance capillary isotachophoresis. Anal Chim Acta 2016; 944:57-69. [DOI: 10.1016/j.aca.2016.09.038] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2016] [Revised: 09/29/2016] [Accepted: 09/30/2016] [Indexed: 01/22/2023]
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4
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Determination of thermodynamic values of acidic dissociation constants and complexation constants of profens and their utilization for optimization of separation conditions by Simul 5 Complex. J Chromatogr A 2014; 1364:276-88. [DOI: 10.1016/j.chroma.2014.08.070] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2014] [Revised: 08/20/2014] [Accepted: 08/21/2014] [Indexed: 11/23/2022]
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5
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Open source simulation tool for electrophoretic stacking, focusing, and separation. J Chromatogr A 2009; 1216:1008-18. [DOI: 10.1016/j.chroma.2008.12.022] [Citation(s) in RCA: 94] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2008] [Revised: 12/04/2008] [Accepted: 12/09/2008] [Indexed: 11/22/2022]
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6
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Mosher RA, Thormann W. High-resolution computer simulation of the dynamics of isoelectric focusing: In quest of more realistic input parameters for carrier ampholytes. Electrophoresis 2008; 29:1036-47. [DOI: 10.1002/elps.200700453] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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7
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Simó C, González R, Barbas C, Cifuentes A. Combining peptide modeling and capillary electrophoresis-mass spectrometry for characterization of enzymes cleavage patterns: recombinant versus natural bovine pepsin A. Anal Chem 2007; 77:7709-16. [PMID: 16316180 DOI: 10.1021/ac051067d] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Nowadays there is an increasing number of recombinant enzymes made available to industry. Before replacing the use of natural enzymes with their cognate recombinant counterparts, one important issue to address is their actual equivalence. For a given recombinant proteolytic enzyme, its equivalence can be investigated by comparing its cleavage specificity with that obtained from the natural enzyme. This is mostly done by analyzing the fragments (i.e., peptidic map) attained after enzymatic digestion of a given protein used as substrate. The peptidic maps obtained are typically characterized using separation techniques together with MS and MS/MS systems. However, these procedures are known to be difficult and labor-intensive. In this work, the combined use of a theoretical model that relates electrophoretic behavior of peptides to their sequence together with capillary electrophoresis-mass spectrometry (CE-MS) is proposed to characterize in a very fast and simple way the cleavage specificity of new recombinant enzymes. Namely, the effectiveness of this procedure is demonstrated by analyzing in few minutes the fragments obtained from a protein hydrolysated using recombinant and natural pepsin A. The usefulness of this strategy is further corroborated by CE-MS/MS. The proposed procedure is applicable in many other proteomic studies involving CE-MS of peptides.
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Affiliation(s)
- Carolina Simó
- Institute of Industrial Fermentations (CSIC), Juan de la Cierva 3, Madrid, Spain
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8
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Zusková I, Novotná A, Vceláková K, Gas B. Determination of limiting mobilities and dissociation constants of 21 amino acids by capillary zone electrophoresis at very low pH. J Chromatogr B Analyt Technol Biomed Life Sci 2006; 841:129-34. [PMID: 16567135 DOI: 10.1016/j.jchromb.2006.03.015] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2006] [Revised: 03/06/2006] [Accepted: 03/07/2006] [Indexed: 10/24/2022]
Abstract
The dependence of the effective electrophoretic mobility on pH of the background electrolyte was experimentally determined by capillary zone electrophoresis (CZE) for cationic forms of amino acids. The pH of the background electrolytes was in the highly acidic range, 1.6-2.6 pH units, to ensure a high degree of protonation of the amino acids. Poly(vinyl alcohol) was added to the background electrolytes to avoid possible adsorption of the analytes at the inner capillary wall. Non-linear regression of the experimental data was applied to obtain the parameters of the relevant regression functions--the actual mobilities and mixed dissociation constants corresponding to the actual ionic strength. The extended Onsager and Debye-Hückel law was used to calculate the limiting mobilities and thermodynamic dissociation constants. The comparison of the experimental electropherogram with the computer prediction by PeakMaster using the determined data is presented for the selected sample of amino acids.
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Affiliation(s)
- Iva Zusková
- Department of Physical and Macromolecular Chemistry, Faculty of Science, Charles University, Prague, Czech Republic.
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9
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Lisková A, Krivánková L. Determination of dissociation constants of compounds with potential cognition enhancing activity by capillary zone electrophoresis. Electrophoresis 2005; 26:4429-39. [PMID: 16273587 DOI: 10.1002/elps.200500433] [Citation(s) in RCA: 16] [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
Accurate determination of pK(a) values is important for proper characterization of newly synthesized molecules. In this work we have used CZE for determination of pK(a) values of new compounds prepared from intermediates, 2, 3 and 4-(2-chloro-acetylamino)-phenoxyacetic acids, by substituting chloride for 2-oxo-pyrrolidine, 2-oxo-piperidine or 2-oxo-azepane. These substances are expected to have a cognition enhancing activity and free radicals scavenging effect. Measurements were performed in a polyacrylamide-coated fused-silica capillary of 0.075 mm ID using direct UV detection at 254 nm. Three electrolyte systems were used for measurements to eliminate effects of potential interactions between tested compounds and components of the BGE. In the pH range 2.7-5.4, chloride, formate, acetate and phosphate were used as BGE co-ions, and sodium, beta-alanine and epsilon-aminocaproate as counterions. Mobility standards were measured simultaneously with the tested compounds for calculations of correct electrophoretic mobilities. Several approaches for the calculation of the pK(a) values were used. The values of pK(a) were determined by standard point-to-point calculation using Henderson-Hasselbach equation. Mobility and pH data were also evaluated by using nonlinear regression. Three parameter sigmoidal function fitted the experimental data with correlation coefficients higher than 0.99. Results from CZE measurements were compared with spectrophotometric measurements performed in sodium formate buffer solutions and evaluated at wavelength where the highest absorbance difference for varying pH was recorded. The experimental pK(a) values were compared with corresponding values calculated by the SPARC online calculator. Results of all three used methods were in good correlation.
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Affiliation(s)
- Anna Lisková
- Institute of Chemical Drugs, University of Veterinary and Pharmaceutical Sciences Brno, Brno, Czech Republic
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10
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Marák J, Nagyová I, Kaniansky D. Computer-assisted choice of discrete spacers for anionic isotachophoresis separations. J Chromatogr A 2003; 1018:233-49. [PMID: 14620574 DOI: 10.1016/j.chroma.2003.08.030] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
In isotachophoresis (ITP), the sample constituents migrate, depending on their concentrations in the loaded sample, either in fully developed zones or in the boundary layers between the zones of constituents of the corresponding effective mobilities. The latter (spike) migration mode is analytically beneficial in selective detections of trace analytes, especially, when appropriately chosen discrete spacers minimize detection interferences due to matrix constituents. To facilitate a search for suitable mixtures of discrete spacers, a two-step calculation procedure was developed in this work. Using a pool of discrete spacers consisting of 42 anionic and zwitterionic constituents, this procedure was shown effective in the anionic ITP separations performed at pH = 6.5-10.0. Besides the predictions of the migration orders, it was helpful in identifying the spacing constituents that could cause resolution problems due to an uncertainty with which pH of the leading electrolyte solution is known. The ionic mobility and pKa data, taken for the spacing constituents from the literature and the ones obtained from the ITP experiments carried out in this work, were used in the calculations performed in a context with the choice of spacers. Although the data obtained from the ITP experiments provided better results, small uncertainties with which they were acquired (attributable to fluctuations in the experimental conditions) set practical limits in the calculation based choice of multi-component mixtures of the spacing constituents.
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Affiliation(s)
- Jozef Marák
- Department of Analytical Chemistry, Faculty of Natural Sciences, Comenius University, Mlynská Dolina CH-2, SK-842 15 Bratislava, Slovak Republic
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11
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Fujiya NM, Tavares MFM. Analysis of underivatized amino acids in protein hydrolysates for cosmetic application by capillary electrophoresis. J Sep Sci 2003. [DOI: 10.1002/jssc.200390077] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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12
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Abstract
This article gives a review of the recent developments in capillary electrophoresis (CE) of peptides. New approaches to the theoretical description of electromigration behavior of peptides are described, and methodological aspects of CE separations of peptides such as selection of separation conditions, sample treatment, suppression of peptide adsorption to the capillary wall and specificities of CE separation modes are discussed. Progress in application of high performance detection schemes, namely laser-induced fluorescence and mass spectrometry, in peptide separations by CE is presented. Applications of different CE techniques, zone electrophoresis, isotachophoresis, isoelectric focusing, affinity electrophoresis, electrokinetic chromatography and electrochromatography to peptide analysis, preparation and physicochemical characterization are demonstrated.
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Affiliation(s)
- V Kasicka
- Institute for Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Prague.
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13
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Kaniansky D, Mar�k J, La??tinec J, Reijenga JC, Onuska FI. Capillary zone electrophoresis with on-line isotachophoretic sample pretreatment: Sample clean-up aspects. ACTA ACUST UNITED AC 1999. [DOI: 10.1002/(sici)1520-667x(1999)11:2<141::aid-mcs7>3.0.co;2-2] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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14
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15
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Abstract
Capillary isotachophoresis is a powerful electromigration separation method with a pronounced capability to concentrate trace components in diluted samples. At present, capillary isotachophoresis is utilized predominantly as the first step in on-line combination with capillary zone electrophoresis. This article is a continuation of previous reviews and summarizes the results published during 1993-1996.
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Affiliation(s)
- P Gebauer
- Institute of Analytical Chemistry, Academy of Sciences of the Czech Republic, Brno
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16
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Cifuentes A, Poppe H. Behavior of peptides in capillary electrophoresis: effect of peptide charge, mass and structure. Electrophoresis 1997; 18:2362-76. [PMID: 9456051 DOI: 10.1002/elps.1150181227] [Citation(s) in RCA: 78] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
In the last decade the large potential of capillary electrophoresis as a technique for separation and characterization of peptides has been demonstrated extensively. In this field, a large number of chemical structures has to be taken into consideration, for which very often no data or even standards are available. As a result, there has been a strong desire to relate electrophoretic behavior to molecular properties and structure of the compounds. The activities in that direction, in the area of capillary zone electrophoresis, are critically reviewed. Special attention is paid to peptide charge, mass, hydrophobicity and structure, and their influence on the selectivity of the separation. Also, some complexation phenomena are discussed.
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Affiliation(s)
- A Cifuentes
- Institute of Organic Chemistry (CSIC), Madrid, Spain
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17
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Xu X, Kok W, Poppe H. Noise and baseline disturbances in indirect UV detection in capillary electrophoresis. J Chromatogr A 1997. [DOI: 10.1016/s0021-9673(97)00616-x] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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18
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Acid-base behaviour of tripeptides in solvents used in liquid chromatography. Correlation between pK values and solvatochromic parameters of acetonitrile-water mixtures. Anal Chim Acta 1997. [DOI: 10.1016/s0003-2670(97)00163-3] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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19
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Barbosa J, Hernández-Cassou S, Sanz-Nebot V, Toro I. Variation of acidity constants of peptides in acetonitrile-water mixtures with solvent composition: effect of preferential solvation. THE JOURNAL OF PEPTIDE RESEARCH : OFFICIAL JOURNAL OF THE AMERICAN PEPTIDE SOCIETY 1997; 50:14-24. [PMID: 9273883 DOI: 10.1111/j.1399-3011.1997.tb00615.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The dissociation constant values of a series of peptides in 5.54, 10, 16.30, 25.03 and 50% (w/w) acetonitrile-water mixed solvents at 298.15 K were determined according to the criteria endorsed by IUPAC. A pronounced change in the acid-base pK values of carboxylic, phenol and thiol groups was observed as the solvent was enriched in acetonitrile. By contrast, pK values of protonated amino-terminal groups were influenced slightly as the solvent was enriched in acetonitrile, although continually increasing pK values were observed. The variation of the pK values obtained, over the whole composition ranged studies, was explained by taking into account the preferential solvation of electrolytes in acetonitrile-water mixtures. To obtain pK values in all possible binary solvent acetonitrile-water mixtures, relationships between pK values and different bulk properties were examined and the Linear Solvation Energy Relationships methodology was applied. The pKa values were then correlated with the Kamlet-Taft, phi, alpha and beta solvatochromic parameters of acetonitrile-water mixtures. The equations obtained allowed calculation of the pK values of peptides in acetonitrile-water mixtures up to 50% (w/w) and thus permitted the acid-base behavior of these substances in the widely used acetonitrile-water media to be known.
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Affiliation(s)
- J Barbosa
- Department of Analytical Chemistry, University of Barcelona, Spain.
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20
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Martens JH, Reijenga JC, ten Thije Boonkkamp JH, Mattheij RM, Everaerts FM. Transient modelling of capillary electrophoresis. J Chromatogr A 1997. [DOI: 10.1016/s0021-9673(97)00121-0] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
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21
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Reijenga JC, Verheggen TP, Martens JH, Everaerts FM. Buffer capacity, ionic strength and heat dissipation in capillary electrophoresis. J Chromatogr A 1996. [DOI: 10.1016/0021-9673(96)00273-7] [Citation(s) in RCA: 50] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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22
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23
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Cifuentes A, Poppe H. Effect of pH and ionic strength of running buffer on peptide behavior in capillary electrophoresis: theoretical calculation and experimental evaluation. Electrophoresis 1995; 16:516-24. [PMID: 7588520 DOI: 10.1002/elps.1150160185] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
The effect of pH and ionic strength of running buffer on peptide behavior in capillary electrophoresis (CE) is studied. A system for predictions of peptide migration in CE (SPPMCE) developed in our laboratory has been tested in a wide range of pH and buffer concentrations. The SPPMCE consists of a computer program for calculating peptide pKa values, an equation which relates peptide structures to their electrophoretic mobilities and a coupled computer program for the prediction of electropherograms. More than 25 different buffers have been employed, covering a pH range of 2-11 and a concentration range of 5-100 mM. Results from experiments are compared with the theoretical predictions. Good agreement is observed, which confirms the utility of the SPPMCE and allows fast and easy optimization of peptide separations in CE, with nothing more than the amino acid sequence of the linear peptide as the input.
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Affiliation(s)
- A Cifuentes
- Laboratory of Analytical Chemistry, University of Amsterdam, The Netherlands
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24
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Cifuentes A, Poppe H. Simulation and optimization of peptide separation by capillary electrophoresis. J Chromatogr A 1994; 680:321-40. [PMID: 7952009 DOI: 10.1016/0021-9673(94)80083-9] [Citation(s) in RCA: 72] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
The different mobility equations that have appeared in the literature for predicting peptide mobility were compared. A modified equation that relates the mobility of individual proteolytic species of a peptide to its composition has been obtained: mu = 1758 log(1 + 0.297q)/M0.411, where mu is the electrophoretic mobility in 10(-9) m2/s.V, q is the integral value of the charge of the species and M its molecular mass. Also, a rough estimation of the set of pKa values for a peptide was developed. The usefulness of this equation together with a computer program for predicting separations of compounds by capillary zone electrophoresis is demonstrated, employing real electropherograms of peptides from the literature or from experiments.
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Affiliation(s)
- A Cifuentes
- Laboratory for Analytical Chemistry, University of Amsterdam, Netherlands
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25
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Kobayashi M, Kitaoka Y, Tanaka Y, Kawamoto K. Electrophoretic behaviour and infrared spectra of dihydroxyboryl compounds in aqueous di- and tricarboxylic acids: Paper electrophoresis as a tool for determining the chemical states of a substance in solution. J Chromatogr A 1994. [DOI: 10.1016/0021-9673(94)80483-4] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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26
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27
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Reijenga J, Kenndler E. Computational simulation of migration and dispersion in free capillary zone electrophoresis. J Chromatogr A 1994. [DOI: 10.1016/0021-9673(94)85083-6] [Citation(s) in RCA: 85] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
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