Simultaneous determination of chromium(VI) and chromium(III) of bioavailable fraction in bottom mud by flow injection-atomic absorption spectroscopy

A rapid and sensitive method for separation and determination of Cr(VI) and Cr(III) in bottom mud of lake by flow injection on-line preconcentrtion system and GFAAS was developed. The available Cr(VI) and Cr(III) were extracted by HOAc or EDTA + NH4 NO3 and adsorbed simultaneously by an anion and a cation resin microclummn and then eluted simultaneously by 2 mol/L NH4 NO3 + 0.05 mol/L ascorbate and 2 mol/L H2SO4, respectively. The elution was performed for 50 s after adsorption for 2 min, and the efficiencies of elution were 85.4% - 94.8% and 96.7% - 106% for Cr(VI) and Cr(M) respectively. The detection limits of the method were 0.9 mu g/L and 2.7 mu g/L with relative standard deviations of 3.5% and 6.4% for the determination of Cr(VI) and Cr(III) in sample, respectively.

Separation of acidic and basic compounds in capillary electrochromatography with polymethacrylate-based monolithic columns

Methacrylate-based monolithic columns with electroosmotic flow (EOF) or very weak EOF are prepared by in situ copolymerization in the presence of a porogen in fused-silica capillaries pretreated with a bifunctional reagent. Satisfactory separations of acidic and basic compounds on the column with EOF at either low or high pH are achieved, respectively. With sulfonic groups as dissociation functionalities, sufficient EOF mobility still remains as high as 1.74 x 10(-4) cm(2) s(-1) V-1 at low pH. Under this condition, seven acidic compounds are readily separated within 5.7 min. Moreover, at high pH, the peak shape of basic compounds is satisfactory without addition of any masking amines into running mobile phase since the secondary interaction between the basic compounds and the monolithic stationary phase are minimized at high pH. Reversed-phase mechanism for both acidic and basic compounds is observed under investigated separation conditions. In addition, possibilities of acidic and basic compound separations on a monolithic column with extremely low EOF are discussed. (C) 2004 Elsevier B.V. All rights reserved.

Short columns with molecularly imprinted monolithic stationary phases for rapid separation of diastereomers and enantiomers

Three molecularly imprinted monolithic columns with different length but almost identical column volume had been prepared. It was observed that the separation factors of diastereomers and enantiomers were almost unaffected by column length. However, the short column with dimension of 38 mm x 8 mm W. showed much lower resistance to flow rate so that it could be operated at much higher flow rates. By combining stepwise gradient elution with elevated flow rate, the diastereomers of cinchonine and cinchonidine and the enantiomers of Cbz-DL-Trp and Fmoc-DL-Trp were successfully separated within 3 min on the short column with dimension of 38 mm. x 8 mm i.d.. Based on the above results, a cinchonine imprinted monolithic disk with dimension of 10 mm x 16 mm W. was further developed. The SEM image and the pore size distribution profile showed that large flow-through pores are present on the prepared monolith, which allowed mobile phase to flow through the disk with very low resistance. Chromatographic performances on the monolithic disk were almost unchanged compared with the long columns. A rapid separation of cinchonine and cinchonidine was achieved in 2.5 min at the flow rate of 9.0 ml/min. Furthermore, it was observed that there was almost no effect of the flow rate on the dynamic binding capacity at high flow rates. In addition, the effect of the loading concentration of analytes on the dynamic binding capacity, namely adsorption isotherm, was also investigated. A non-linear adsorption isotherm of cinchonine was observed on the molecularly imprinted monolith with cinchonine as template, which might be a main reason to result in the peak tailing of template molecule. (C) 2004 Elsevier B.V. All rights reserved.

Preparation and characterization of monolithic columns for capillary electrochromatography with weak electroosmotic flow

Monolithic columns of capillary electrochromatography (CEC) with weak electroosmotic flow (EOF) have been prepared by in situ polymerization of butyl methacrylate and ethylene dimethacrylate, without any charged groups in the reaction mixture. The reproducibility of such columns has been proved good no matter whether they are prepared in the same batch or in different batches. In the case of BMA-EDMA monoliths, besides the traditional ternary mixture - 1-propanol, 1,4-butanediol, and water, binary porogenic solvents with only alcohols have also been adopted. Compared with ternary porogenic solvents, the design with binary ones allows for fine control of the pore diameter and the formation of the specific surface of the monolithic polymers. The composition of porogenic reagents has also been shown to have an effect on EOF in the column systems. In addition, the Joule heat effect in such columns has been studied by varying the inner diameter of columns. Through the separation of acidic compounds, monolithic columns with low EOF have shown potential in the analysis of charged samples.

Separation of enantiomers by nanoliquid chromatography and capillary electrochromatography using a bonded cellulose trisphenylcarbamate stationary phase

A cellulose trisphenylcarbamate-bonded chiral stationary phase was applied to nano-liquid chromatography (nano-LC) and capillary electrochromatography (CEC) with nonaqueous and aqueous solutions as the mobile phases. Several chiral compounds were successfully resolved on the prepared phase by nano-LC. The applicability of nonaqueous CEC on a cellulose derivative stationary phase was investigated with the organic solvents methanol, hexane, 2-propanol, and tetrahydrofuran (THF) containing acetic acid, as well as triethylamine as the mobile phases. Enantiomers of warfarin and praziquantel were baseline-resolved with plate numbers of 82 300 and 38 800 plates/m, respectively, for the first eluting enantiomer. The influence of applied voltage, concentration of nonpolar solvent, apparent pH, and buffer concentration in the mobile phase on the electroosmotic flow (EOF) and the mobility of the enantiomers was evaluated. Enantioseparations of traps-stilbene oxide and praziquantel were also achieved in aqueous CEC with plate numbers of 111 100 and 107 400 plates/m, respectively, for the first eluting enantiomer. A comparison between nonaqueous CEC and aqueous CEC based on a cellulose trisphenylcarbamate stationary phase was discussed. Pressure-assisted CEC was examined for the chiral separation of praziquantel and faster analysis with high enantioselectivity was acquired with the proper pressurization of the inlet vial.

Separation of peptides on mixed mode of reversed-phase and ion-exchange capillary electrochromatography with a monolithic column

The mixed mode of reversed phase (RP) and strong canon-exchange (SCX) capillary electrochromatography (CEC) based on a monolithic capillary column has been developed. The capillary monolithic column was prepared by in situ copolymerization of 2-(sulfooxy)ethyl methacrylate (SEMA) and ethylene dimethacrylate (EDMA) in the presence of porogens. The sulfate group provided by the monomer SEMA on the monolithic bed is used for the generation of the electroosmotic flow (EOF) from the anode to the cathode, but at the same time serves as a SCX stationary phase. A mixed-mode (RP/SCX) mechanism for separation of peptides was observed in the monolithic column, comprising hydrophobic and electrostatic interaction as well as electrophoretic migration at a low pH value of mobile phase. A column efficiency of more than 280000 plates/m for the unretained compound has been obtained on the prepared monoliths. The relative standard deviations observed for to and retention factors of peptides were about 0.32% and less than 0.71% for ten consecutive runs, respectively. Effects of mobile phase compositions on the EOF of the monolithic column and on the separation of peptides were investigated. The selectivity on separation of peptides in the monolithic capillary column could be easily manipulated by varying the mobile phase composition.

Characteristics of electroosmotic flow and migration of neutral solutes under stepwise gradient elution of capillary electrochromatography

A theoretical study on the velocity of electroosmotic flow (EOF) and the retention times of neutral solutes under multiple-step gradient of capillary electrochromatography (CEC) was carried out, focusing on that with three kinds of mobile phases. Through the model computations, the detaining time of the second kind of mobile phase in the column was proved to play an important role in affecting EOF. The variation speed of EOF was shown to be determined by the differences among dead times in different steps. In addition, the prediction of the retention times of 13 aromatic compounds under gradient mode was performed with the deduced equations. A relative error below 3.3% between the calculated and experimental values was obtained, which demonstrated the rationality of the theoretical deduction. Our study could not only improve the comprehension of stepwise gradient elution, but also be of significance for the further optimization of separation conditions in the analysis of complex samples.

Molecularly imprinted monolithic stationary phases for liquid chromatographic separation of enantiomers and diastereomers

The method for preparation of molecularly imprinted monolithic stationary phase has been improved to achieve liquid chromatographic separation of enantiomers and diastereomers. By adopting low polar porogenic solvents of toluene and dodecanol and optimal polymerization conditions, the molecularly imprinted monolithic stationary phases with good flow-through properties and high resolution were prepared. Enantiomers of amino acid derivatives and diastereomers of cinchona alkaloids were completely resolved using the monolithic stationary phases. The influence of porogenic composition, monomer-template ratio and polymerization conditions on the chromatographic performance was investigated. Some chromatographic conditions such as the composition of the mobile phase and the temperature were characterized. Scanning electron microscopy showed that the molecularly imprinted monolithic stationary phase has a large through-pore structure to allow the mobile phase to flow through the column at very low backpressure. Accelerated separations of enantiomers and diastereomers were therefore achieved at elevated flow rates. Finally, the chiral recognition performance of the prepared stationary phase in aqueous media was investigated. Hydrophobic interaction, and ionic and/or hydrogen bonding interactions were proposed to be responsible for the recognition mechanism. (C) 2002 Elsevier Science B.V. All rights reserved.

Separation of peptides by pressurized capillary electrochromatography

A pressurized electrochromatography (pCEC) instrument with gradient capability was used in this work for separation of peptides. Three separation modes, namely, pCEC, high-performance liquid chromatography and capillary electrophoresis can be carried out with the instrument. In pCEC mode, the mobile phase is driven by both electroosmotic flow and pressurized flow, facilitating fine-tuning in selectivity of neutral and charged species. A continuous gradient elution can be carried out conveniently on this instrument, which demonstrates that it is more powerful than isocratic pCEC for separation of complicated samples. The effects of applied voltage, supplementary pressure and ion-pairing agents on separation of peptides in gradient pCEC were investigated. The effects of flow-rate of the pump and the volume of the mixer on resolution were also evaluated. (C) 2002 Elsevier Science B.V. All rights reserved.

Separation and detection of chlorpromazine hydrochloride and promethazine hydrochloride using electrochemiluminescence followed by capillary electrophoresis

Phenothiazine drugs, chlorpromazine hydrochloride (CPZ) and promethazine hydrochloride (PMZ), were determined with Ru(bpy)(3)(2+) electrochemiluminescene by the capillary electrophoresis (CE-ECL). It was found that both CPZ and PMZ could produce an intermediate that acted as coreactants to react with Ru(bpy)(3)(2+) to produce excited states which were capable of emitting light. This CE-ECL detection method had high sensitivity, good selectivity and reproducibility for CPZ and PMZ determination.

Microchip Micellar Electrokinetic Chromatography Based on One Functionalized Ionic Liquid and Its Excellent Performance on Proteins Separation

Herein, one water-soluble functionalized ionic liquid (IL), 1-butyl-3-methylimidazolium dodecanesulfonate (BAS), was designed, investigated and successfully applied to microchip micellar electrokinetic chromatography (MEKC) construction. It possessed the properties of both IL and surfactant. A fairly stable pH value similar to 7.4, which was fit to pH values of general biological buffers, was nicely placed at the optimum concentration of 20 mM BAS solution. While applying BAS solution as running buffer in poly(dimethylsiloxane) (PDMS) microfluidic systems, significantly enhanced electroosmotic flow (8-fold) and resolutions between analytes were obtained than that using other supporting electrolytes or surfactants.

Mass transfer kinetics of neodymium(III) extraction by calix[4]arene carboxylic acid using a constant interfacial area cell with laminar flow

BACKGROUND: Thermodynamics and kinetics data are both important to explain the extraction property. In order to develop a novel separation technology superior to current extraction systems, many promising extractants have been developed including calixarene carboxylic acids. The extraction thermodynamics behavior of calix[4]arene carboxylic acids has been reported extensively. In this study, the mass transfer kinetics of neodymium(III) and the interfacial behavior of calix[4]arene carboxylic acid were investigated.

Extraction kinetics of cerium(IV) from sulfuric acid medium by the primary amine N1923 using a constant interfacial area cell with laminar flow

BACKGROUND: Thermodynamic studies on Ce(IV) extraction with primary amine N1923 demonstrate that primary amine N1923 is an excellent extractant for separation of Ce(IV) from Re(III). In order to clarify the mechanism of extraction and to optimize the parameters in practical extraction systems used in the rare earth industry, the extraction kinetics was investigated using a constant interfacial area cell with laminar flow in the present work.RESULTS: The data indicate that the rate constant (k(ao).) becomes constant when stirring speed exceeds 250 rpm. The apparent forward extraction rate is calculated to be 10(-1.70). The activation energy (E.) was calculated to be 20.5 kJ/mol from the slope of log kao against 1000/T. The minimum bulk concentration of the extractant necessary to saturate the interface (C-min) is lower than 10(-5) mol L-1.CONCLUSION: Studies of interfacial tension and the effects of stirring rate and specific interfacial area on the extraction rate show that the extraction rate is kinetically controlled, and a mass transfer model has been proposed. The rate equation has been obtained as: -d[Ce(IV)]/dt = 10(-1.70)[Ce(IV)] [(RNH3)(2)SO4](1.376). The rate-controlling step has been evaluated from analysis of the experimental results.

Extraction kinetics of Sc(III), Y(III), La(III) and Gd(III) from chloride medium by Cyanex 302 in heptane using the constant interfacial cell with laminar flow

The extraction kinetics of Sc, Y, La and Gd(III) from the hydrochloric acid medium using Cyanex 302 (hereafter HL) in heptane solution have been measured by the constant interfacial cell with laminar flow. Reaction regions are explored at liquid-liquid interface. Extraction regimes are deduced to be diffusion-controlled for Sc(Ill) and mixed controlled for Y, La and Gd(Ill). Extraction mechanisms are discussed according to the dimeric model of Cyanex 302 in non-polar solution. From the temperature dependence of rate measurement, the values of E-a, Delta H-+/-, Delta S-+/- and Delta G(300)(+/-) are calculated and it is found that the absolute values of these parameters keep crescent trend for Sc, Y, La and Gd(III). At the same time, it is found that it can easily achieve the mutual separation among the Sc, Y and La(III) with kinetics extraction methods.

Hole nucleation and growth induced by crystallization and microphase separation of thin semicrystalline diblock copolymer films

We have investigated the hole nucleation and growth induced by crystallization of thin crystalline-coil diblock copolymer films. Semicrystalline rodlike assemblies from neutral/selective binary solvent are used as seeds to nucleate crystallization at temperatures above the glass transition temperature (T-g) but below melting point (T-m). The crystallization of nanorods drives neighboring copolymer chains to diffuse into the growing nanorods. Depletion of copolymer chains yields hole nucleation and growth at the edge of the nanorods. Simultaneously, the polymer chains unassociated into the nanorods were oriented by induction from the free surface and the substrate, leading to limitation of the hole depth to the lamellar spacing, similar to20 nm. The holes, as well as the nanorods, grow as t(alpha), where t is the annealing time and a crossover in the exponent a. is found. The orientation and stretching of the copolymer chains by the surface and interface are believed to accelerate the crystallization, and in turn, the latter accelerates the growth rate of the holes. At T > T-m, the grains melt and the copolymer chains relax and flow into the first layer of the film.