Study of competitive binding of enantiomers to protein by affinity capillary electrochromatography

Affinity capillary electrochromatography (CEC) with zonal elution method was used to probe the competitive interactions of enantiomers with protein. In this approach, a known concentration of a competing agent is continuously applied to a CEC column with bovine serum albumin (BSA) physically adsorbed on SAX packing while injections of a small amount of analyte are made. The binding sites of solutes on the BSA molecule were determined by the changes in the retention factors of the solutes resulted from the addition of competitive agent. By using D- or L-tryptophan as competitive agents and D-, L-tryptophan and benzoin enantiomers as injected analytes showed that BSA molecule has a primary site to strongly bind L-tryptophan, but D-tryptophan dose not bind at this site; D- and L-tryptophan share a weak binding site on the BSA molecule. Benzoin enantiomers do not share any binding sites with either D- or L-tryptophan. Non-chiral compounds of trichloroacetic acid and n-hexanoic acid were applied as the competitive agents to study the binding of warfarin enantiomers to BSA, it was observed that trichloroacetic acid and n-hexanoic acid had a same binding site for warfarin enantiomers binding to BSA molecule. (C) 2002 Elsevier Science B.V. All rights reserved.

Retention modeling and optimization of pH value and solvent composition in HPLC using back-propagation neural networks and uniform design

A novel method for the optimization of pH value and composition of mobile phase in HPLC using artificial neural networks and uniform design is proposed. As the first step. seven initial experiments were arranged and run according to uniform design. Then the retention behavior of the solutes is modeled using back-propagation neural networks. A trial method is used to ensure the predicting capability of neural networks. Finally, the optimal separation conditions can be found according to a global resolution function. The effectiveness of this method is validated by optimization of separation conditions for both basic and acidic samples.

Photo-sensitized oxidation in natural water via .OH radicals

A method is presented for determining production and consumption rates of .OH radicals produced photochemically in natural surface waters. It is based on the determination of the kinetics by which the concentration of a specified trace compound decreases during irradiation. In samples from Lake Greifensee (Switzerland) low production rates for .OH limit its possible effects. In addition, fast consumptions by the natural dissolved organic solutes and by the bicarbonate protect organic micropollutants from oxidation by .OH. Neither direct nor indirect H2O2 photolysis was a significant source of .OH in the lakewater studied lacking iron, whereas nitrate photolysis could have been a source. Comparison with reaction kinetic formulations allows generalizations for other types of waters.

Successful establishment of MEKC with electrochemiluminescence detection based on one functionalized ionic liquid

Herein, one water-soluble functionalized ionic liquid, 1-butyl-3-methylimidazolium dodecyl sulfate ([BMIm(+)][C12H25SO4-]), was designed and its superiorities either used as supporting electrolytes or as additives for successful establishment of MEKC with electrochemiluminescence (ECL) detection (MEKC-ECL) method were investigated. Compared with the common supporting electrolytes such as phosphate solution, 1-butyl-3-methylimidazolium dodecyl sulfate solution used as running buffers led to greatly enhanced ECL intensities and column efficiencies for negative targets, a little increase for neutral-charge ones while maintained nearly unchanged for positive ones due to the electrostatic forces between the large cation BMIm(+) and the solutes and the hydrophobic interactions resulting from the large anion C12H25SO4.

A study of the dependence of ferrocene diffusion on chain length in polymer electrolytes

The diffusion rates of ferrocene have been estimated in five kinds of poly(ethylene glycol) solution, containing the electrolyte LiClO4, by using non-steady-state chronoamperometry. The D-app of ferrocene increases with increasing temperature, and the dependency of D-app on temperature obeys the Williams-Landel-Ferry equation. The D-app of ferrocene decreases with increasing polymer chain length. Both the chain length and temperature dependence conform to a simple free volume model. A relation between current and polymer chain length is suggested at room and high temperatures.

LIQUID-CHROMATOGRAPHY AMPEROMETRIC DETECTION OF CATECHOL, RESORCINOL, AND HYDROQUINONE WITH A COPPER-BASED CHEMICALLY MODIFIED ELECTRODE

A copper-based chemically modified electrode (CME) has been constructed and characterized for flow-through amperometric detection of catechol, resorcinol, and hydroquinone. Novel potential dependence of the detector response was first obtained for these analytes at the Cu CME, where negative peaks together with positive ones were observed in one definite chromatogram using amperometric detection. Its advantages in chromatographic applications were demonstrated. From these observations it is proposed that the detector response was governed by formation of copper complexes with the solutes. A dynamic linear range over two orders of magnitude was obtained, when operating the detector at +0.10 V vs. SCE, from which ng detection limits were achieved.

AN EXPERIMENTAL-STUDY ON MEMBRANE DISTILLATION CRYSTALLIZATION FOR TREATING WASTE-WATER IN TAURINE PRODUCTION

The solution of non-volatile solutes can be concentrated to saturation by membrane distillation. If the solute is easy to crystalize, the membrane distillation-crystallization phenomenon will appear during the membrane distillation of saturated solutions. It is possible that crystalline products are separated from concentrated solutions by a membrane process. In this work the PVDF capillary membrane, which was improved on hydrophobicity by using LiCl instead of a water-soluble polymer as an additive, has been used for treating the waste water of taurine. The crystalline product has been obtained from the waste water by the membrane distillation-crystallization technique. The results have shown good prospects for a membrane distillation application for treatment of industrial waste water.

LIQUID-CHROMATOGRAPHY AMPEROMETRIC DETECTION OF CARBOXYLIC-ACIDS AND PHENOLIC-ACIDS WITH A COPPER-BASED CHEMICALLY-MODIFIED ELECTRODE

A copper-based chemically-modified electrode has been constructed and characterized by various experimental parameters in flow-through amperometric detection of carboxylic acids and phenolic acids. Novel hydrodynamic voltamperograms were first obtained in flow-through amperometric detection with the Cu-based CME and subsequently negative and positive peaks were observed in a single chromatogram. This unique and flexible potential dependence could be of great benefit in chromatographic speciation and quantification. These observations suggest that the detector response was governed by the complexation reaction of copper ions with the solutes.

Capillary electrochromatography using a strong cation-exchange column with a dynamically modified cationic surfactant

A novel mode of capillary electrochromatography (CEC), called dynamically modified strong cation-exchange CEC (DMSCX-CEC), is described in this paper. A column packed with a strong cation-exchange (SCX) packing material was dynamically modified with a long-chain quaternary ammonium salt, cetyltrimethylammonium bromide (CTAB), which was added to the mobile phase. CTAB ions were adsorbed onto the surface of the SCX packing material, and the resulting hydrophobic layer on this packing was used as the stationary phase. Using the dynamically modified SCX column, neutral solutes were separated with the CEC mode. The highest number of theoretical plates obtained was about 190 000/m, and the relative standard deviations (RSD's) for migration times and capacity factors of alkylbenzenes were less than 1.0% and 2.0% for five consecutive runs, respectively. The effects of CTAB and methanol concentrations and the pH value of the mobile phase on the electroosmotic flow and the separation mechanism were investigated. Excellent simultaneous separation of the basic and neutral solutes in DMSCX-CEC with a high-pH mobile phase was obtained, A mixture containing the acidic, basic, and neutral compounds was well separated in this mode with a low-pH mobile phase; however, peak tailing for basic compounds was observed in this mobile phase.

Capillary electrochromatography with a silica column with a dynamically modified cationic surfactant

A novel mode of capillary electrochromatography (CEC), called dynamically modified silica-capillary electrochromatography, is described in this paper. The column packed with bare silica was dynamically modified with long chain quaternary ammonium salt, cetyltrimethylammonium bromide (CTAB), which was added into the mobile phase. CTAB ions were adsorbed onto the surface of bare silica, and the resulted hydrophobic layer on the silica gel was used as the stationary phase; Using the dynamically modified silica column, neutral solutes were separated by CEC. The highest number of theoretical plates obtained was about 71 500/m and the relative standard deviations for t(0) and capacity factor of toluene were 4.7% and 4.9% for 20 consecutive runs, respectively. The separation mechanism of neutral solutes and the influence of mobile phase composition on the separation was investigated. The separation of nitrogen-containing solutes was carried out with this mode and the peak tailing of basic solute was effectively eliminated because the adsorption of basic solute on silica was blocked by the preferred adsorption of CTAB. (C) 1999 Elsevier Science B.V. All rights reserved.

Separation of neutral compounds by high speed capillary electrochromatography

With using short capillary column packed with porous and non-porous ODS stationary phases, high speed separation of 6 neutral aromatic compounds within 36 s by capillary electrochromatography (CEC) has been performed. Good reproducibility of the migration times for those solutes in high speed CEC was observed with RSD less than 1%. Both the linear velocity of EOF and the current linearly increases with the applied voltage, which means that the thermal effect by Joule heating was small. However, the capacity factor of solutes was found to decrease with the increase of the applied voltage, which was caused by the fact that about several seconds needed for the increase of voltage from 0 to applied value on a commercial CE instrument made larger contributions to the migration times of the early eluted compounds than those of lately eluted ones during high speed CEC, and voltage effect would increase with the higher applied voltage used. The linear relationship between the logarithm of capacity factor and the number of carbon for homologous compounds was observed, and positive value of slope means that the hydrophobicity of solutes is one of the main contribution factors to retention in high speed CEC packed with ODS stationary phases.

Soil column chromatography for correlation between capacity factors and soil organic partition coefficients for eight pesticides

A soil column chromatographic method was developed to measure the capacity factors (k') of pesticides, in which soil acted as a stationary phase and methanol-water mixture as an eluent. The k' values of eight pesticides, including three insecticides (methiocarb, azinphos-methyl, fenthion), four fungicides (triadimenol, fuberidazole, tebuconazole, pencycuron), and one herbicide (atrazine), were found to be well fitted to a retention equation, ln k'=ln k(w)'-S-phi. Due to similar interactions of solutes with soil and solvent in both sorption determination and retention experiment, log k' has a good linear correlation with log K-oc for the eight pesticides from different classes, in contrast with poor correlation between log k' from C-18 column and log K-oc. So the method provides a tool for rapid estimation of K-oc from experimental k'. (C) 1999 Elsevier Science Ltd. All rights reserved.

Capillary electrochromatography with monolithic poly(styrene-co-divinylbenzene-co-methacrylic acid) as the stationary phase

A new kind of monolithic capillary electrochromatography column with poly(styrene-co-divinylbenzene-co-methacrylic acid) as the stationary phase has been developed. The stationary phase was found to be porous by scanning electron microscopy and the composition of the continuous bed was proved by IR spectroscopy to be the ternary polymer of styrene, divinylbenzene, and methacrylic acid. The effects of operating parameters, such as voltage, electrolyte, and organic modifier concentration in the mobile phase on electroosmotic flow were studied systematically, The retention mechanism of neutral solutes on such a column proved to be similar to that of reversed-phase high performance liquid chromatography. In addition, fast analyses of phenols, chlorobenzenes, anilines, isomeric compounds of phenylenediamine and alkylbenzenes within 4.5 min were achieved.

Chiral separation of enantiomers of amino acid derivatives by high-performance liquid chromatography on a norvancomycin-bonded chiral stationary phase

A novel norvancomycin-bonded chiral stationary phase (NVC-CSP) was synthesized by using the chiral selector of norvancomycin. The chiral separation of enantiomers of several dansyl-amino acids by high-performance liquid chromatography (HPLC) in the reversed-phase mode is described. The effects of some parameters, such as organic modifier concentration, column temperature, pH and flow rate of the mobile phase, on the retention and enantioselectivity were investigated. The study showed that ionic, as well as hydrophobic interactions were engaged between the analyte and macrocycle in this chromatographic system. Increasing pH of buffers usually improved the chiral resolution for dansyl-alpha-amino-n-butyric acid (Dns-But), dansyl-methionine (Dns-Met) and dansyl-threonine (Dns-Thr), but not for dansyl-glutamic acid (Dns-Glu) which contains two carboxylic groups in its molecular structure. The natural logarithms of selectivity factors (In alpha) of all the investigated compounds depended linearly on the reciprocal of temperature (1/T), most processes of enantioseparation were controlled enthalpically. Interestingly, the process of enantioseparation for dansyl-threonine was enthalpy-controlled at pH of 3.5, while at pH of 7.0, it was entropy-controlled according to thermodynamic parameters Delta(R,S)DeltaHdegrees and Delta(R,S)DeltaSdegrees afforded by Van't Hoff plots. In order to get baseline separation for all the solutes researched, norvancomycin was also used as a chiral mobile phase additive. In combination with the NVC-CSP remarkable increases in enanselectivity were observed for all the compounds, as the result of a "synergistic" effect. (C) 2003 Elsevier B.V. All rights reserved.

An empirical equation for the calculation of retention time with extrapolation of temperature in gas chromatography

An empirical equation is proposed to accurately correlate isothermal data over a wide range of temperature With the equation ln k = A* + B*/T-lambda the retention times of different solutes tested on OV-101, SE-54 and PEG 20M capillary columns have been achieved even when lambda is assigned a constant value of 1.7 Comparison with ln k = A + B/T and in k = c + d/T+ h/T-2, shows that the proposed equation is of higher accuracy and is applicable to extrapolation calculation, especially from data at high temperature to those at low temperature. Parameters A* and B* as well as A and B are also discussed. The linear correlation of A* and B* is weaker than that of A and B.