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David D. Y. Chen - One of the best experts on this subject based on the ideXlab platform.
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Higher order equilibria and their effect on analyte Migration Behavior in capillary electrophoresis.
Analytical chemistry, 1998Co-Authors: Michael T. Bowser, David D. Y. ChenAbstract:This paper presents a quantitative investigation into the effect of analyte-additive interactions on analyte Migration Behavior in capillary electrophoresis (CE) when both 1:1 and 1:2 stoichiometries are present. Equations based on the individual capacity factors for each interaction are derived to account for the effect of both first- and second-order equilibria. The analyte Migration Behavior is described using these equations with a full account of how the microscopic equilibrium constants and microscopic mobilities are combined to give the macroscopic values. The binding isotherms of interactions with both 1:1 and 1:2 stoichiometries are compared with those of a 1:1 stoichiometry. 4,4'-Biphenol and 4-phenylphenol were chosen as analytes that undergo complexation with one and two hydroxypropyl-β-cyclodextrin (HP-β-CD) molecules; phenol was used as an analyte that interacts with only one HP-β-CD molecule. The process of calculating higher order equilibrium constants and complex mobilities from the binding isotherms is demonstrated. The effects of experimental conditions, such as the additive concentration range and the number of data points, on the error in the calculated constants and the ability of the equations to accurately describe the experimental data are discussed. A comparison of the linear transformations of the binding isotherm with respect to their ability to detect higher order equilibria is made, and the advantage of using the capacity factor in CE is illustrated.
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The effects of a mixture of charged and neutral additives on analyte Migration Behavior in capillary electrophoresis.
Electrophoresis, 1998Co-Authors: Andrea R. Kranack, Philip Britz-mckibbin, Michael T. Bowser, David D. Y. ChenAbstract:Multicomponent additives, such as derivatized cyclodextrins with various degrees of substitution, can be considered single-component additives as long as the fraction of each component remains constant. In this paper, equations are derived describing the effect of such additives on the Migration Behavior of analytes. These equations are used in the study of capillary electrophoresis (CE) systems with differentially charged cyclodextrins as additives. For weakly acidic analytes, the binding with highly negatively charged sulfobutyl ether beta-cyclodextrin (SBE-beta-CD) increases their negative electrophoretic mobility, while the binding with neutral hydroxypropyl-beta-cyclodextrin (HP-beta-CD) decreases their negative mobility. By obtaining the equilibrium constants and mobilities for each additive with each analyte (in this case, phenol, 2-naphthol and 1-naphthol), the Migration Behavior of these analytes in CE systems is quantitatively predicted at various concentrations of mixtures of the two additives. The properties of the contour lines in the binding isotherm surfaces of such CE systems are discussed.
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THE EFFECT OF COMPLEXATION ADDITIVES ON ANALYTE Migration Behavior IN CAPILLARY ELECTROCHROMATOGRAPHY
Electrophoresis, 1998Co-Authors: Michael T. Bowser, David D. Y. ChenAbstract:In capillary electrochromatography (CEC), analytes often have different mobilities in the mobile phase, and often are involved in multiple equilibria. In this paper, the Migration Behavior of an analyte in CEC is described by a general equation in which individual capacity factors are used to describe the tendency of the analyte to exist as the various analyte species present in a separation system, and the effects of both field and equilibrium are accounted for. The resolution of two analytes is shown to be related linearly to the ratio of their Migration rates. The effect of the electroosmotic flow (EOF) in CEC is more complicated than in CE because it is experienced only by a fraction of the analyte, whereas in CE, it is experienced by all analyte species. A procedure for calculating the electrophoretic mobility of the analyte based on the fraction of the analyte in the buffer is demonstrated. The effect of the EOF on resolution is also discussed.
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Quantitative description of analyte Migration Behavior based on the dynamic complexation model in capillary electrophoresis
Canadian Journal of Chemistry, 1997Co-Authors: Xuejun Peng, Gwendolyn M. Bebault, David D. Y. Chen, Stephen L. SacksAbstract:A theory based on dynamic complexation is used to describe analyte Migration Behavior in capillary electrophoresis (CE). This theory is based on a one-phase system, instead of the commonly accepted two-phase system. The Migration Behavior of an analyte is described by three parameters (the electrophoretic mobility of the free analyte, the electrophoretic mobility of the analyte–additive complex, and the equilibrium constant (formation constant) that determines the fractions of the free analyte and the complex at a certain additive concentration). Varying the additive concentration shifts the equilibrium and changes the viscosity of the background electrolyte. Viscosity correction is crucial in interpreting the observed Migration Behavior of analytes. While electroosmotic flow in a capillary often varies from one capillary to another, the viscosity of a buffer is characteristic of the buffer composition and is constant for each buffer. The electrophoretic mobility of a certain species and the equilibrium c...
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Prediction of the Migration Behavior of analytes in capillary electrophoresis based on three fundamental parameters
Journal of Chromatography A, 1997Co-Authors: Philip Britz-mckibbin, David D. Y. ChenAbstract:Abstract The prediction of analyte Migration Behavior in capillary electrophoresis (CE) is essential for rapid method development. The dynamic complexation model, based on 1:1 interactions, was used to accurately predict the apparent electrophoretic mobilities and the Migration times of a group of deoxyribonucleotides (dNPs) at various concentrations of β-cyclodextrin (β-CD). The electrophoretic mobility of the analyte, the electrophoretic mobility of the analyte-additive complex and the equilibrium constant are the three fundamental parameters required to determine the mobility of an analyte. The apparent Migration time of the analyte can be predicted once the electroosmotic mobility and relative viscosity of the solution are known. Optimum separation conditions can be determined based on these parameters. Excellent agreement between observed analyte Migration Behavior and predicted values was demonstrated, with relative errors being often less than 1%. The theory was tested repeatedly under various conditions in order to assess its predictive capabilities and limitations. Analysis by molecular modeling, in conjunction with calculated electrophoretic parameters and equilibrium constants, provided deeper insight into the probable mechanisms of the separation process at the molecular level.
Ching-erh Lin - One of the best experts on this subject based on the ideXlab platform.
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Optimization of separation and Migration Behavior of chloropyridines in micellar electrokinetic chromatography.
Journal of chromatography. A, 2001Co-Authors: Ching-erh Lin, Chen-hsing Lin, Hung-wen Chen, Hui-chun Huang, Chia-chong Chen, Yu-chih LiuAbstract:The separation and Migration Behavior of pyridine and eight chloropyridines, including three monochloropyridines, four dichloropyridines, and 2,3,5-trichloropyridine were investigated by micellar electrokinetic chromatography using either sodium dodecyl sulfate (SDS) as an anionic surfactant or SDS-Brij 35 mixed micelles. Various parameters such as buffer pH, SDS concentration, Brij 35 concentration and methanol content that affect the separation were optimized. Complete separation of these chloropyridines was optimally achieved with a phosphate buffer containing SDS (30 mM) and methanol (10%, v/v) at pH 7.0. The resolution and selectivity of analytes could be considerably affected by the addition of methanol and/or Brij 35 to the background electrolyte. The Migration order of these chloropyridines depends primarily on their hydrophobicity. However, electrostatic interactions may also play a significant role in the determination of the Migration order of the positional isomers of chloropyridines.
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Optimization of separation and Migration Behavior of cephalosporins in capillary zone electrophoresis.
Journal of chromatography. A, 2000Co-Authors: Ching-erh Lin, Hung-wen Chen, Erick C. Lin, Kuo-shen Lin, Hui-chun HuangAbstract:Abstract The influences of buffer pH, buffer concentration and buffer electrolyte on the Migration Behavior and separation of 12 cephalosporin antibiotics in capillary zone electrophoresis using three different types of buffer electrolyte, including phosphate, citrate, and 2-( N -morpholino)ethanesulfonate (MES), were investigated. The results indicate that, although buffer pH is a crucial parameter, buffer concentration also plays an important role in the separation of cephalosporins, particularly when cefuroxime and cefazolin, cephalexin and cefaclor, or cefotaxime and cephapirin are present as analytes at the same time. The electrophoretic mobility of cephalosporins and electroosmotic mobility measured in citrate and MES buffers are remarkably different from those measured in phosphate buffer. With citrate buffer, optimum buffer concentration is confined to a small range (35–40 m M ), whereas buffer concentrations up to 300 m M can be used with MES buffer. Complete separations of 12 cephalosporins could be satisfactorily achieved with these three buffers under various optimum conditions. However, the separability of 12 cephalosporins with citrate or MES buffer is better than that with phosphate buffer. As a consequence of a greater electrophoretic mobility of cephalosporins than the electroosmotic mobility with citrate buffer at pH below about 5, some cephalosporins are not detectable. The cloudiness of the peak identification and of the magnitudes of the electrophoretic mobility of cefotaxime and cefuroxime reported previously are clarified. In addition, the p K a values of cephradine, cephalexin, cefaclor, and cephapirin attributed to the deprotonation of either an amino group or a pyridinium group are reported, and the Migration Behavior of these cephalosporins in the pH range studied is quantitatively described.
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Migration Behavior and separation of s-triazines in micellar electrokinetic capillary chromatography using a cationic surfactant
Journal of Chromatography A, 1999Co-Authors: Ching-erh Lin, Chung-chuan Hsueh, Ta-zen Wang, Tai-chia Chiu, Yung-chih ChenAbstract:Abstract The Migration Behavior and separation of various s-triazines, including five chloro-, three methoxy- and five alkylthio-s-triazines, were investigated in micellar electrokinetic chromatography (MEKC) using a cationic surfactant. In this study, tetradecyltrimethyl ammonium bromide (TTAB) was selected as a cationic surfactant. The results indicate that the selectivity of neutral species of s-triazines in each class is not significantly influenced by buffer pH and micelle concentration, but the overall selectivity is considerably affected by these two separation parameters when charged solutes are present, particularly, at buffer pH below 5.0. Complete separation of thirteen s-triazines was optimally achieved within 6 min on addition of TTAB (15 mM) to a phosphate buffer (70 mM) at pH 4.75 or 3.8. Based on a model that describes the relationship of the effective electrophoretic mobility of a neutral solute and micelle concentration in MEKC, the Migration Behavior of chloro-s-triazines at pH 6.0 is predicted and the binding constants of s-triazines to TTAB micelles are evaluated. The correlation between the binding constants and Pow (the partition coefficient of a solute between 1-octanol and water) reveals that the Migration order of s-triazines in each class is primarily determined by the hydrophobicity of the solutes.
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Migration Behavior and separation of aromatic triazole and thiazole compounds by capillary zone electrophoresis
Journal of Chromatography A, 1996Co-Authors: Ching-erh Lin, Chia-chong ChenAbstract:Abstract The separation by capillary zone electrophoresis (CZE) of aromatic triazole and thiazole compounds, including benzotriazole (BTA), 5-tolyltriazole (5-TTA), dimethylbenzotriazole (DBTA), and 2-mercaptobenzothiazole (MBT), is described. These compounds, widely used as inhibitors of copper corrosion, were effectively separated using a fused-silica capillary with phytic acid (10 mM) as background electrolyte at pH above 8, except for pH of about 9.24 at which BTA and MBT migrate together. The Migration Behavior of these four analytes was investigated and their pKa values were determined by CZE. This method was successfully applied to the analysis of a commercial product.
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Migration Behavior of dichlorophenols for replicate separations without replenishment of buffer electrolyte in micellar electrokinetic capillary chromatography
Journal of Chromatography A, 1996Co-Authors: Ching-erh Lin, Wei-chen LinAbstract:The Migration Behavior of dichlorophenols in replicate separations, without replenishment of buffer electrolyte between runs, in micellar electrokinetic capillary chromatography (MECC) was investigated. The results indicated that the pH of the buffer electrolyte drifts as a result of electrolysis of the buffer solution during electrophoresis and that the pH drift, being independent of the micelle concentration, is responsible for the variation in electrophoretic mobilities of analytes in MECC when the buffer is not replenished. The influences of the buffer pH and micelle concentration on the Migration Behavior of analytes were demonstrated to be correlated at small micelle concentrations. The variation of electrophoretic mobility of an analyte as a function of buffer pH at a given micelle concentration is quantitatively described. 2,6-Dichlorophenol is selected for illustration. The variation of electrophoretic mobility agrees satisfactorily between predicted and observed data.
Michael T. Bowser - One of the best experts on this subject based on the ideXlab platform.
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Higher order equilibria and their effect on analyte Migration Behavior in capillary electrophoresis.
Analytical chemistry, 1998Co-Authors: Michael T. Bowser, David D. Y. ChenAbstract:This paper presents a quantitative investigation into the effect of analyte-additive interactions on analyte Migration Behavior in capillary electrophoresis (CE) when both 1:1 and 1:2 stoichiometries are present. Equations based on the individual capacity factors for each interaction are derived to account for the effect of both first- and second-order equilibria. The analyte Migration Behavior is described using these equations with a full account of how the microscopic equilibrium constants and microscopic mobilities are combined to give the macroscopic values. The binding isotherms of interactions with both 1:1 and 1:2 stoichiometries are compared with those of a 1:1 stoichiometry. 4,4'-Biphenol and 4-phenylphenol were chosen as analytes that undergo complexation with one and two hydroxypropyl-β-cyclodextrin (HP-β-CD) molecules; phenol was used as an analyte that interacts with only one HP-β-CD molecule. The process of calculating higher order equilibrium constants and complex mobilities from the binding isotherms is demonstrated. The effects of experimental conditions, such as the additive concentration range and the number of data points, on the error in the calculated constants and the ability of the equations to accurately describe the experimental data are discussed. A comparison of the linear transformations of the binding isotherm with respect to their ability to detect higher order equilibria is made, and the advantage of using the capacity factor in CE is illustrated.
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The effects of a mixture of charged and neutral additives on analyte Migration Behavior in capillary electrophoresis.
Electrophoresis, 1998Co-Authors: Andrea R. Kranack, Philip Britz-mckibbin, Michael T. Bowser, David D. Y. ChenAbstract:Multicomponent additives, such as derivatized cyclodextrins with various degrees of substitution, can be considered single-component additives as long as the fraction of each component remains constant. In this paper, equations are derived describing the effect of such additives on the Migration Behavior of analytes. These equations are used in the study of capillary electrophoresis (CE) systems with differentially charged cyclodextrins as additives. For weakly acidic analytes, the binding with highly negatively charged sulfobutyl ether beta-cyclodextrin (SBE-beta-CD) increases their negative electrophoretic mobility, while the binding with neutral hydroxypropyl-beta-cyclodextrin (HP-beta-CD) decreases their negative mobility. By obtaining the equilibrium constants and mobilities for each additive with each analyte (in this case, phenol, 2-naphthol and 1-naphthol), the Migration Behavior of these analytes in CE systems is quantitatively predicted at various concentrations of mixtures of the two additives. The properties of the contour lines in the binding isotherm surfaces of such CE systems are discussed.
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THE EFFECT OF COMPLEXATION ADDITIVES ON ANALYTE Migration Behavior IN CAPILLARY ELECTROCHROMATOGRAPHY
Electrophoresis, 1998Co-Authors: Michael T. Bowser, David D. Y. ChenAbstract:In capillary electrochromatography (CEC), analytes often have different mobilities in the mobile phase, and often are involved in multiple equilibria. In this paper, the Migration Behavior of an analyte in CEC is described by a general equation in which individual capacity factors are used to describe the tendency of the analyte to exist as the various analyte species present in a separation system, and the effects of both field and equilibrium are accounted for. The resolution of two analytes is shown to be related linearly to the ratio of their Migration rates. The effect of the electroosmotic flow (EOF) in CEC is more complicated than in CE because it is experienced only by a fraction of the analyte, whereas in CE, it is experienced by all analyte species. A procedure for calculating the electrophoretic mobility of the analyte based on the fraction of the analyte in the buffer is demonstrated. The effect of the EOF on resolution is also discussed.
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Quantitative description of analyte Migration Behavior based on dynamic complexation in capillary electrophoresis with one or more additives.
Electrophoresis, 1997Co-Authors: Xuejun Peng, Gwendolyn M. Bebault, Philip Britz-mckibbin, Michael T. Bowser, Jamie R. Morris, David D. Y. ChenAbstract:A comprehensive theory is proposed to describe the Migration Behavior of analytes in capillary electrophoresis (CE) when one or more additives are present in the buffer solution. This theory amalgamates and extends the previous work done by others. The capacity factor (k') in this theory is defined as the product of the equilibrium constant and the additive concentration, thus, k' changes linearly with additive concentration. The net electrophoretic mobility of an analyte is a function of k', therefore, it can be changed by varying the additive concentration. Three parameters are needed to predict the mobility of an analyte in a one-additive CE system: the mobility of the free analyte, the mobility of the complex, and the equilibrium constant for the analyte-additive interaction (which determines the fraction of the free analyte at different additive concentrations). When additives are used, the change in viscosity obscures this relationship, therefore, a viscosity correction factor is required to convert all mobilities to an ideal state where the viscosity remains constant. The Migration Behavior of an analyte in a solution with multiple additives can be predicted and controlled, once the equilibrium constants of the interactions between the analyte and each of the additives are obtained separately. beta-Cyclodextrin and hydroxypropyl-beta-cyclodextrin are used as additives and the Migration Behavior of phenol, p-nitrophenol, and benzoic acid are studied as a model system to verify this theory. When the necessary viscosity correction factor is included, the net electrophoretic mobilities of the analytes obtained from experimental results agree with the values predicted by the theory based on dynamic complexation. Although only experiments with one and two additives were carried out to verify the theory, the equations apply to situations when more than two additives are used. The relationship between the theories of electrophoresis and chromatography is clarified.
A.k.m. Akther Hossain - One of the best experts on this subject based on the ideXlab platform.
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Characterization of local soils and study the Migration Behavior of radionuclide from disposal site of LILW.
Journal of environmental radioactivity, 2011Co-Authors: M. Anwar Hossain, M. Shamsuzzaman, Sanjukta Ghose, A.k.m. Akther HossainAbstract:Abstract Migration Behavior of radionuclide is one of the most important factors to be considered for the long-term safety assessment of a radioactive waste disposal facility in a wet geological formation. In the present study, laboratory based column experiments have been carried out to assess the radionuclide Migration Behavior of 137 Cs and 60 Co and to evaluate the retardation factor through a clay soil layers using gamma spectrometry. Investigation was performed for a range of particle sizes and fixed column lengths to determine an appropriate value of Migration rate of 137 Cs and 60 Co. The distribution pattern of particle size in soil samples were measured by sieved method. Two different particle sizes (≤90 μm and mixed size) were used in the column experiments. The Migration rate in the clay type soil layer of particle size ≤90 μm was found by the order of 60 Co > 137 Cs. The maximum Migration length of 60 Co in the soil layer was found to be 0–25 cm, however in the case of 137 Cs it was found at a maximum length of 0–10 cm. The distribution coefficient of 60 Co was found nearly same as that of 137 Cs. The retardation factor was found to be 1.79 and 1.94 for 60 Co and 137 Cs, respectively. The experimental breakthrough from this study indicates that the amount of radioactive cesium and cobalt released depends upon the composition of the soils.
Ryan D Dorland - One of the best experts on this subject based on the ideXlab platform.
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aggregation and vertical Migration Behavior of euphausia superba
Deep-sea Research Part Ii-topical Studies in Oceanography, 2004Co-Authors: Meng Zhou, Ryan D DorlandAbstract:Aggregation and vertical Migration Behavior of Euphausia superba were studied in Marguerite Bay and its vicinity west of the Antarctic Peninsula using a vessel-mounted, Acoustic Doppler Current Profiler, and a Multiple Opening and Closing Nets and Environmental Sensing System, during the 2001 and 2002 fall US Southern Ocean GLOBEC project cruises. The kinematics of aggregation Behavior of E. superba associated with diel Migration is studied using observations of their abundance and swimming velocities: during the day, E. superba reduce their swimming at a depth of 250 m; and at night, they swim randomly at their cruising speed in the upper part of an aggregation near the surface, and coherently as schooling in the lower part of an aggregation. The causes for the aggregation Behavior and vertical Migration of krill are explored by examining the relationship with ice coverage and presence of predators. The motion of euphausiids is further analyzed in terms of kinetic energy and force balance, leading to new considerations of mathematical theories and models of aggregation Behavior. The results show a diel variation of the energy demand for maintaining their locomotion. The horizontal scale of an aggregation is studied in conjunction with horizontal gradients of currents. Results indicate that the swimming capability of euphausiids determines the maintenance of an aggregation in the mesoscale circulation field.