Simultaneous electrokinetic and hydrodynamic injection with on-line sample concentration via micelle to solvent stacking in micellar electrokinetic chromatography

Simultaneous determination of five metal ions by on-line complexion combined with micelle to solvent stacking in capillary electrophoresis

A direct on-line complexion combined with micelle to solvent stacking method was proposed for simultaneous determination of metal ions by capillary electrophoresis coupled diode array detector. During the experiment, a plug of complexing agent was first injected to the inlet of capillary, followed by introducing the micelle-bound metal ions. Then the metal ions produced a micelle-to-solvent stacking effect and interacted with the complexing agent under a positive voltage. Continued application of voltage, the analytes were effectively focused and separated in the capillary zone electrophoresis. Repeatability was ranged from 1.89% to 1.94% for the migration time. The detection limits were 2.66-27.9 ng mL^-1 for Ni²⁺, Co²⁺, Cu²⁺, Hg²⁺ and Cd²⁺. Furthermore, the developed method showed a great potential for the determination of metal ions in the crayfish, beebread and Dendrobium officinale samples.

Capillary electrophoresis for the analysis of antidepressant drugs: A review

Depression is a common mental disorder that may lead to major mental health problems, and antidepressant drugs have been used as a treatment of choice to mitigate symptoms of major depressive disorders by ameliorating the chemical imbalances of neurotransmitters in brain. Since abusing antidepressant drugs such as selective serotonin reuptake inhibitors and tricyclic antidepressant drugs can cause severe adverse effects, continuous toxicological monitoring of the parent compounds as well as their metabolites using numerous analytical methods appears pertinent. Among them, capillary electrophoresis has been popularly utilized since the method has a lot of advantages viz. using small amounts of sample and solvents, ease of operation, and rapid analysis. This review paper brings a survey of more than 30 papers on capillary electrophoresis of antidepressant drugs published approximately from 1999 until 2018. It focuses on the reported capillary electrophoresis techniques and their applications and challenges for determining antidepressant drugs and their metabolites. It is organized according to the commonly used capillary zone electrophoresis method, followed by non-aqueous capillary electrophoresis and micellar electrokinetic chromatography, with details on breakthrough findings. Where available, information is given about the background electrolyte used, detector utilized, and sensitivity obtained.

Sweeping-micelle to solvent stacking for the on-line preconcentration and determination of organic acids in Angelica sinensis by capillary electrophoresis

A two-step on-line preconcentration technique has been applied to the analysis of organic acids in Angelica sinensis.

Unusual stacking with electrokinetic injection of cationic analytes from micellar solutions in capillary zone electrophoresis

Electrokinetic injection (EKI) in capillary zone electrophoresis (CZE) of charged analytes is by the electroosmotic flow (EOF) and electrophoretic mobility of analytes. In most forms of stacking with EKI, the sample ions were introduced via electrophoretic mobility and concentrated in a stacking boundary inside the capillary. In this work, we describe the unusual stacking of cationic analytes via EKI of sodium dodecyl sulfate (SDS) micelles into a fused silica capillary filled with acidic background solution (BGS) with 40-50 % acetonitrile. The analytes prepared with SDS micelles were injected because of their interaction with micelles or effective electrophoretic mobility. We observed two peaks from an analyte, and this suggested the concentration of analytes into two stacking zones. These two adjacent stacking zones were surprisingly maintained inside the capillary during EKI although the EOF was moving towards the inlet. The zones were identified as the SDS micelles (micelles zone) and organic solvent-rich stacking zone (solvent-rich zone) where the micelles zone was closer to the inlet end of capillary. The analytes concentrated in the solvent-rich zone through the mechanism of micelle to solvent stacking (MSS). The concentrated analytes in the micelles zone were from the concentrated analytes that electrophoretically migrated into the micelles zone from the solvent-rich zone during EKI. The analytes in the micelles zone were then re-stacked by MSS and formed the second sharp peak in CZE. This was prevented by reduction of acetonitrile concentration in the inlet BGS. A sensitivity enhancement factor of more than 100 was obtained for model cationic drugs (diphenhydramine and imipramine).

High-sensitivity analysis of anionic sulfonamides by capillary electrophoresis using a synergistic stacking approach

A synergistic stacking approach whereby field-enhanced sample injection and micelle-to-solvent stacking in capillary zone electrophoresis are combined has been developed and has been applied to the separation and quantification of anionic sulfonamides. Electrokinetic injection of the sample in a low conductivity alkaline diluent was performed for 90s at -15kV. Micelle-to-solvent stacking was then undertaken by hydrodynamic injection of micellar cetyltrimethylammonium bromide solution prior to the electrokinetic injection of sample that also contained 50% methanol. This combined stacking approach, when compared to a typical hydrostatic injection, provided improvements in peak height and corrected peak area in the range of 397-1024 and 758-1246, respectively. Limits of quantification in the range of 0.01-0.03μg/mL were obtained for sulfamerazine, sulfamethazine and sulfamethizole and were sufficient for the determination of these analytes in river water. The percentage recovery and accuracy values obtained for a fortified river water sample that had been subjected to sample preparation by evaporation and reconstitution with diluent were 74-135%. Intra-day and inter-day repeatabilities for migration time, peak height, and corrected peak area were in the range 0.5-5.0% (percentage relative standard deviation, n=8) and these relatively low values were attributed to the use of a stable capillary coating established by the successive multiple ionic-polymer layer technique.

Zero net-flow in capillary electrophoresis using acrylamide based hydrogel

Zero net-flow was observed when acrylamide based hydrogel was used in a vial at one end of a fused-silica capillary during electrophoresis with electroosmotic flow.

Recent advances in enhancing the sensitivity of electrophoresis and electrochromatography in capillaries and microchips (2010-2012)

CE has been alive for over two decades now, yet its sensitivity is still regarded as being inferior to that of more traditional methods of separation such as HPLC. As such, it is unsurprising that overcoming this issue still generates much scientific interest. This review continues to update this series of reviews, first published in Electrophoresis in 2007, with updates published in 2009 and 2011 and covers material published through to June 2012. It includes developments in the field of stacking, covering all methods from field amplified sample stacking and large volume sample stacking, through to isotachophoresis, dynamic pH junction and sweeping. Attention is also given to online or inline extraction methods that have been used for electrophoresis.

Recent methodological and instrumental development in MEKC

The review gives an update about the methodological and instrumental developments in micellar electrokinetic capillary chromatography as a type of CE analytical technique. Here, the last two years development of the technique are particularly presented. Recent approaches to improve sensitivity are discussed. Newly introduced concentration techniques and experimental methods for verification of the different mechanisms and processes of micellar electrokinetic chromatography analysis are highlighted. A theoretical model to explain changes in separation and electrophoretic mobility order of fully charged analytes are demonstrated. Modern approaches for improving compatibility of micellar electrokinetic capillary chromatography to mass spectrometry are also reported.