Separation and determination of flavonoids using microemulsion EKC with electrochemical detection

The microemulsion electrokinetic capillary chromatography combined with reversed-electrode polarity stacking mode for enriching and quantifying lignanoids and ginsenosides in TCMs preparation Shengmai injection

An on-line large volume sample stacking with polarity switching (LVSS) method was proposed for simultaneously determining lignanoids and ginsenosides in MEEKC. The parameters including the pH value and concentration of buffer solution, SDS, organic modifier, oil phase, running voltage, and temperature as well as injection time, sample matrix, stacking voltage, and time influencing separation and stacking were systematically optimized. The method was verified by performing precision, accuracy, stability, and recovery. Its reliability was proved by separating and quantifying two lignanoids and three ginsenosides in Shengmai injectionSMI. The sensitivity of these compounds was improved by MEEKC-LVSS method for 6-11 times than conventional MEEKC. Thus, this developed on-line MEEKC-LVSS method was sensitive, practical, and reliable.

Surfactant-free microemulsion electrokinetic chromatography (SF-MEEKC) with UV and MS detection - a novel approach for the separation and ESI-MS detection of neutral compounds

Microemulsion electrokinetic chromatography (MEEKC) is a powerful tool to separate neutral species based on differences in their hydrophobic and hydrophilic properties. However, as a major drawback the conventionally used SDS based microemulsions are not compatible with electrospray ionization mass spectrometry (ESI-MS). In this work, a surfactant-free microemulsion (SFME) consisting of water, ethanol, and 1-octanol is used for surfactant-free microemulsion electrokinetic chromatography (SF-MEEKC). Ammonium acetate was added to the SFME enabling electrophoretic separations. The stability of SFMEs containing ammonium acetate was investigated using small-angle X-ray scattering and dynamic light scattering. A method for the separation of a model system of hydrophobic and hydrophilic neutral vitamins, namely the vitamins B₂ and D₃, and the cationic vitamin B₁ was developed using UV/VIS detection. The influence of the ammonium acetate concentration on the separation performance was studied in detail. The method was characterized concerning reproducibility of migration times and peak areas and concerning the linearity of the calibration data. Furthermore, SF-MEEKC was coupled to ESI-MS investigating the compatibility between SFMEs and the ESI process. The signal intensities of ESI-MS measurements of the model analytes were comparable for SFMEs and aqueous systems. Finally, the vitamin D₃ content of a drug treating vitamin D₃ deficiency was determined by SF-MEEKC coupled to ESI-MS using 25-hydroxycholecalciferol as an internal standard. Graphical abstract The concept of surfactant-free microemulsion electrokinetic chromatography coupled to electrospray ionization mass spectrometry.

Recent progress for capillary electrophoresis with electrochemical detection

Capillary electrophoresis (CE) is an attractive technique in separation science because of its high separation performance, short analysis time and low cost. Electrochemical detection (EC) is a powerful tool for CE because of its high sensitivity. In this review, developments of CE-EC from 2008 to August, 2011 are reviewed. We choose papers of innovative and novel results to demonstrate the newest and most important progress in CE-EC.

Recent advances in the methodology, optimisation and application of MEEKC

MEEKC is an electrodriven separation technique. Oil-in-water microemulsions (MEs) and to a lesser extent water-in-oil MEs have been used in MEEKC as BGEs to achieve separation of a diverse range of solutes. The more common (oil-in-water) MEs are composed of nanometre-sized droplets of oil suspended in an aqueous buffer. Interfacial tension between the oil and aqueous phase is reduced close to zero by the presence of a surfactant and a co-surfactant. MEEKC is capable of providing fast and efficient separations for a wide range of acidic, basic and neutral, water-soluble and -insoluble compounds. This review details the advances in MEEKC-based separations from the period 2006 to 2008. Areas covered include online sample concentration, chiral separation, suppressed electroosmosis MEEKC, MEEKC-MS, and the use of MEEKC in predicting migration behaviour and solute characteristics. A fundamental introduction to MEEKC, along with the presentation and discussion of recent applications is also included.

Microwave-assisted extraction followed by capillary electrophoresis-amperometric detection for the determination of antioxidant constituents in Folium Eriobotryae

A method based on capillary electrophoresis-amperometric detection has been developed for the determination of catechin, rutin, kaempferol, gentistic acid, and quercetin in Folium Eriobotryae with the aid of microwave-assisted solvent extraction. The effects of the acidity and the concentration of the running buffer, separation voltage, injection time, detection potential, and irradiation time were investigated to acquire the optimum analysis conditions. The detection electrode was a 300-mum-diameter carbon disc electrode at a detection potential of +0.90 V. The five analytes could be well separated within 12 min in a 40-cm length fused-silica capillary at a separation voltage of 12 kV in a 50-mM borate buffer (pH 9.0). The relation between peak current and analyte concentration was linear over about three orders of magnitude with detection limits (S/N=3) ranging from 2.1 to 4.5 microM for all the analytes.