C.L. Ng

Retention of eleven priority phenols using micellar electrokinetic chromatography

The use of micellar electrokinetic chromatography (MECC) for the separation of eleven substituted phenols listed by the United States Environmental Protection Agency as priority pollutants was investigated. Solutions of potassium and sodium dodecyl sulphate in phosphate-borate buffer of pH 6.6, 7.0 and 7.5 were used as the electrophoretic media. Satisfactory separation of the eleven phenols was obtained using a 180-microns capillary at 10 kV and pH 6.6 with a solution containing both sodium and potassium dodecyl sulphate. Observations on the retention behaviour of the phenols in MECC were related to their physico-chemical properties.

Prevention of protein adsorption on surfaces by polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymers in capillary electrophoresis

Protein adsorption to untreated fused-silica capillaries in capillary electrophoresis was prevented by a chemical modification of the capillary surface. This was achieved through the coating of Pluronic polymers onto capillaries which were pre-derivatised with silylating agents. The polymers were made up of polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymers. The coatings prevent protein adsorption and provide high-efficiency separations. Two different types of silylating agents were used and the effects of the concentrations on the stability and efficiency of the columns were examined. The application of these columns for capillary electrophoretic separation of protein samples was demonstrated.

Systematic optimization of capillary electrophoretic separation of sulphonamides

The use of an optimization scheme for the separation of a group of sulphonamides is described. This scheme utilizes an interpretive optimization approach to predict the optimum conditions for the separation of a group of eight sulphonamides. By conducting nine preplanned experiments that span the maximum working range of the system, overall optimum conditions for separation can be obtained. To confirm the validity of the optimization procedure, additional experiments using the optimum conditions predicted by the scheme were performed. The results demonstrated that satisfactory separation could be achieved by using the optimum separation conditions predicted by the scheme.

Separation of Tamoxifen and Metabolites by Capillary Electro-Phoresis with Non-aqueous Buffer System

Abstract Tamoxifen and its metabolites were separated using a non-aqueous mobile phase consisting of ammonium acetate and a mixture of organic solvents, namely, methanol and acetonitrile. The effects of using other organic salts as the conducting medium and varying the composition of the mixture of acetonitrile and methanol on the separation were also investigated. Optimum separation was obtained by using 25 mM ammonium acetate in a 50:50 acetonitrile/ methanol mixture. High efficiency separations and short analysis times of less than 8 min were obtained. The reproducibility of migration time was better than 0.4%. The detection limits of tamoxifen and its metabolites were less than 40 pg.

Systematic optimization of micellar electrokinetic chromatographic separation of flavonoids

SummaryA simple and rapid systematic optimization scheme was described for the micellar electrokinetic chromatographic separation of a group of flavonoids. The scheme employed an interpretative optimization approach to predict the optimum conditions for the separation of a group of flavonoids by micellar electrokinetic chromatography. By performing a set of nine pre-planned experiments conducted over the maximum working range for the system, global optimum separation conditions could be determined. To validate the optimization procedure, additional experiments were performed using the optimum experimental conditions derived from the optimization scheme. The results showed that satisfactory separation of all the peaks could be obtained. In addition, the application of the method in micropreparative micellar electrokinetic chromatography of the flavonoids was demonstrated.

Determination of antihistamines in pharmaceuticals by capillary electrophoresis.

Capillary electrophoresis with on-column UV detection at 214 nm was used to separate a group of nine antihistamines. All these compounds were satisfactorily separated within ca. 6 min using a mixed carrier system containing sodium dodecyl sulphate with beta-cyclodextrin and tetrabutylammonium hydrogensulphate as modifiers. The application of the method to the determination of the amount of antihistamines present in commercial pharmaceutical samples was demonstrated. In addition, the migration behaviour of the antihistamines in the mixed carrier system was examined.

Separation of Dns-amino acids and vitamins by micellar electrokinetic chromatography

Abstract Fifteen Dns-amino acids were analysed by micellar electrokinetic chromatography (MEKC). All the amino acids were satisfactorily separated within ca . 26 min with 40 m M sodium dodecyl sulphate in phosphate—borate bufrer (pH 7.56). The migration behaviour of the amino acids at different pH values and SDS concentrations was examined. In addition, attempts were made to separate a mixture of amino acids and vitamins simultaneously in a single run by MEKC. Detection for this mixture was carried out with an on-column fluorescence detection system with the capability of performing multi-wavelength programming.

Determination of organolead and organoselenium compounds by micellar electrokinetic chromatography

The separation of selected organolead and organoselenium compounds by high-performance capillary electrophoresis was investigated. Satisfactory separation was achieved using β-cyclodextrin-modified micellar electrokinetic chromatography with on-column UV detection at 210 nm. This method was applied to the analysis of trialkyllead chlorides and organoselenium compounds in spiked distilled water and environmental samples. In addition, the effect of pH, sodium dodecyl sulphate and β-cyclodextrin concentrations on the migration behaviour of these compounds was examined.

Determination of sulphonamides in pharmaceuticals by capillary electrophoresis

Abstract A mixture of seven sulphonamides was separated using capillary electrophoresis with β-cyclodextrin as modifier. The separation was carried out with on-column UV detection at 210 nm. The effects of the pH of the electrophoretic media and β-cyclodextrin concentration on the selectivity and migration times of the sulphonamides were investigated. In addition, the migration behaviour of this group of compounds was examined. This technique was then applied to the determination of sulphonamides in pharmaceuticals.

Determination of components in propolis by capillary electrophoresis and photodiode array detection

The capillary electrophoretic separation of components in propolis, a commonly used natural medicine, was investigated. Optimum conditions for the separation were established. Photodiode-array detection permitted the rapid identification of the components in the samples analysed. The determination of these components, including caffeic acid, dimethylcaffeic acid, isoferulic acid and quercetin, was performed on a commercial propolis sample.