H.K. Lee

High-performance chiral separation of fourteen triazole fungicides by sulfated β-cyclodextrin-mediated capillary electrophoresis

In this paper, sulfated beta-cyclodextrin-mediated capillary electrophoresis (CE) is evaluated as a new approach for the chiral separation of triazole-type fungicides. The 14 fungicides investigated were bitertanol, cyproconazole, difenoconazole, diniconazole, flutriafol, hexaconazole, myclobutanil, paclobutrazol, penconazole, propiconazole, tebuconazole, tetraconazole, triadimefon and triadimenol. Under the optimal conditions, excellent enantioseparation was achieved for all the 14 fungicides, including those fungicides containing two chiral centers. To our knowledge, this is the only system to date that offers outstanding enantiodiscrimination towards all triazole-type fungicides. The impact of the molecular structures of the triazole compounds on their migration behavior was studied. Similar to other chemical systems involving host-guest complexation, the interaction between sulfated beta-cyclodextrin and the triazole compounds was found to be affected by a variety of factors, including electrostatic force, hydrogen bonding, steric effect and hydrophobicity. These factors, coupled with the countercurrent electroosmotic flow (EOF), were believed to be the major forces behind the exceptional chiral selectivity.

Micellar electrokinetic capillary chromatography of vitamin B6 with electrochemical detection

Abstract A system for interfacing electrochemical detection with micellar electrokinetic capillary chromatography is demonstrated. This system couples the separation column to a short length of the same column material together with a section of porous graphite tubing which forms an electrically conductive joint. The joint is immersed in a buffer reservoir together with the ground electrode of the high-power source (15 kV). The reservoir is electrically insulated from the electrochemical cell containing the carbon fibre detector. This configuration effectively separates the detector from the high separation potential applied. Amperometric detection with micellar solutions is demonstrated for a mixture of B 6 vitamers on a 50 μm I.D. column. A detection limit of ca. 4 fmol is obtained. The linear dynamic range of the calibration plot is slightly over two orders of magnitude (from ca. 1 to 200 ppm).

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.

Optimization of mobile phase composition for high-performance liquid chromatographic analysis of eleven priority substituted phenols.

The aim of the optimization scheme is to predict the best mobile phase composition consisting of mixtures of water with various proportions of three common organic modifiers, methanol, acetonitrile and tetrahydrofuran

Recent applications of high-performance liquid chromatography to the analysis of metal complexes

Interest in metal complexes in modern inorganic chemistry has resulted in increasing demands for the analysis of these compounds. This paper reviews the most recent applications of high-performance liquid chromatography (HPLC) to the analysis of metal complexes. The review centres on the use of the technique in metal complex syntheses, reactions, characterizations and complexations and retention behaviour of these compounds, as reported in the literature since 1994.

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.

Separation of polycyclic aromatic hydrocarbons by micellar electrokinetic chromatography with cyclodextrins as modifiers

Abstract The use of α-, β- and γ-cyclodextrins as modifiers to the electrophoretic medium containing sodium dodecyl sulphate and a phosphate-borate buffer in the micellar electrokinetic chromatography of polycyclic aromatic hydrocarbons (PAHS) was investigated. The results showed that the migration behaviour of PAHs could be related to their sizes and the cavity sizes of the cyclodextrins. With the addition of γ-cyclodextrin higher selectivity could be achieved, which consequently resulted in better separation of the seven PAHs investigated.

Microwave-assisted solvent elution technique for the extraction of organic pollutants in water

Solid phase extraction (SPE) with appropriate solid sorbents has been commonly used in the routine extraction of organic pollutants in water. The elution of analytes from the solid sorbents normally takes place by organic solvents under an applied vacuum. In this study, a microwave-assisted solvent elution technique was developed for the elution of analytes from C18 membrane disks during microwave irradiation from a microwave extraction system (MES). Several parameters, namely, elution solvent, elution temperature, duration of elution and the volume of solvent which may affect the elution efficiency of microwave-assisted solvent elution (MASE) technique towards organochlorine pesticides (OCPs), polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), phthalate esters (PAEs), organophosphorus pesticides (OPs), fungicides, herbicides and insecticides from the membrane disk were investigated. Good recoveries above 75% were obtained for most of the organic pollutants using the optimum SPE-MASE technique. The effect of sodium chloride and humic acid on the recoveries on the target analytes were also investigated.

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 biogenic amines by micellar electrokinetic chromatography

The separation by the micellar electrokinetic method of eight biogenic amines was investigated. Optimum separation of the amines: putrescine, histamine, tyramine, cadaverine, phenethylamine, tryptamine, spermidine and spermine was obtained. The method involved extraction and derivatization of the amines with fluoresceine isothiocyanate. The electrolyte system was borate modified with sodium dodecyl sulfate. Separation was achieved in less than 15 min. Detection limit obtained with a xenon lamp-based fluorescence detector was 10−8 M. The method developed was used for the analysis of biogenic amines in soy sauce.