Ionic liquids in electrokinetic chromatography

There is an interest in the application of ionic liquids as additives into the separation media to improve achiral and chiral separations in electrokinetic chromatography (EKC). This review will critically discuss the developments on the use of ionic liquids in the different modes of EKC during the last five years (2015-mid 2020). A healthy number of 48 research articles searched through Scopus were categorised into two: ionic liquids as sole pseudophase (micelles, microemulsions, ligand exchange pseudophase or molecular pseudophase) and ionic liquids with pseudophase (achiral or chiral). More than half of the papers dealt with chiral separations that were mostly facilitated by another additive or pseudophase. The role of ionic liquids for improvement of separations were analysed, and we provided some recommendations for further investigations. Finally, the use of ionic liquids in different on-line sample concentration or stacking methods (i.e., field enhancement and sweeping) was briefly discussed.

Capillary zone electrophoresis of proteins applying ionic liquids for dynamic coating and as background electrolyte component

The use of ionic liquids in capillary electrophoresis, either as coating material or as components of the background electrolyte needs systematic standardization to set up optimal conditions. Excellent separation of the proteins was achieved using 1-ethyl-3-methylimidazolium tetrafluoroborate ([emim][BF4 ]) or 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4 ]) ionic liquids using the properly made ionic-liquid-water binary mixtures for the experiments. The binary mixture has a distinctly stable and well perceptible low pH, which depends on the concentration of the ionic liquid, and on the preparation time of the mixture. Optimal conditions for the electrophoretic separation were obtained upon a multivariate analysis of the experimental parameters (applied voltage, migration time, concentration, and type of the ionic liquid). The standardized condition provides a low electroendosmotic flow toward the anode, which, however, did not hinder the proteins to migrate toward the cathode. The migration of cytochrome c, lysozyme, myoglobin, trypsin, and apo-transferrin at a pH around 2, far below the isoelectric points of the proteins, showed RSD values of the migration times less than 7.5% and less than 6.5% when using [emim][BF4 ] or [bmim][BF4 ], respectively, either in run-to-run or day-to-day experiments. The determination of the extent of the EOF is not possible with the commonly used EOF markers, due to interaction with the ionic-liquid constituents. The interaction of the ionic liquids with the proteins influences the migration order in zone electrophoresis. This method has been applied successfully for the analyses of real biological samples such as proteins from egg whites and human tears.

Simultaneous label-free screening of G-quadruplex active ligands from natural medicine via a microfluidic chip electrophoresis-based energy transfer multi-biosensor strategy

Rapid screening of active compounds plays a crucial role in the research and application of complex natural medicines. Herein, a new method of simultaneous label-free multi-drug screening based on a selective aptamer-carboxyfluorescein/graphene oxide energy transfer optical sensor combined with microfluidic chip electrophoretic separation is reported. In this study, seven traditional Chinese medicinal monomers were chosen as targets for the screening of G-quadruplex ligands. The screening results of the G-quadruplex active ligands, including daidzein, berberine hydrochloride, jatrorrhizine hydrochloride, and fangchinoline, and non-active ligands, including geniposide and oxymatrine, were consistent with those reported in literature. Moreover, one new potential G4DNA active drug, jujuboside A, was identified. Molecular simulation of the interaction between G4DNA and drugs was also carried out using HyperChem and AutoDock to verify the results of the experimental screening. It further demonstrated the reliability of our strategy. This novel separation and concentration based multi-sensing strategy provides a simple, rapid, and sensitive tool for simultaneous multi-drug screening, which is very meaningful for drug screening and bio-interaction analysis.

Recent trends in capillary electrophoresis for complex samples analysis: A review

CE has been a continuously evolving analytical methodology since its first introduction in the 1980s of the last century. The development of new CE separation procedures, the coupling of these systems to more sensitive and versatile detection systems, and the advances in miniaturization technology have allowed the application of CE to the resolution of new and complex analytical problems, overcoming the traditional disadvantages associated with this method. In the present work, different recent trends in CE and their application to the determination of high complexity samples (as biological fluids, individual cells, etc.) will be reviewed: capillary modification by different types of coatings, microfluidic CE, and online microextraction CE. The main advantages and disadvantages of the different proposed approaches will be discussed with examples of most recent applications.

Novel cationic coating agent for protein separation by capillary electrophoresis(†)

A novel positively charged surfactant N-dodecyl-N,N-dimethyl-(1,2-propandiol) ammonium chloride was used for the dynamic coating of the inner wall of a silica capillary. This paper covers the evaluation of dynamic coating and study of the influence of the analysis conditions for the magnitude and direction of electroosmotic flow as well as for the effective and selective separation of chosen proteins (ribonuclease A, cytochrome c, lysozyme, and myoglobin). The concentration of 0.1 mM of N-dodecyl-N,N-dimethyl-(1,2-propandiol) ammonium chloride enabled the reversal of the electro-osmotic flow, however, to separate basic as well as neutral proteins the higher concentration of the studied surfactant was necessary. The final conditions for the separation of studied proteins were set at 100 mM sodium acetate pH 5.5 with 10.0 mM of the studied surfactant. The results were also compared with those of two commercially available cationic surfactants, cetyltrimethylammonium bromide and dodecyltrimethylammonium bromide. Additionally, the developed method for protein separation was applied for the determination of lysozyme in a cheese sample. The limits of detection and quantification of lysozyme were 0.9 and 3.0 mg/L, respectively. The mean concentration of lysozyme found in the cheese sample was 167.3 ± 10.3 mg/kg.

Recent advances in the analysis of therapeutic proteins by capillary and microchip electrophoresis

The development of therapeutic proteins and peptides is an expensive and time-intensive process. Biologics, which have become a multi-billion dollar industry, are chemically complex products that require constant observation during each stage of development and production. Post-translational modifications along with chemical and physical degradation from oxidation, deamidation, and aggregation, lead to high levels of heterogeneity that affect drug quality and efficacy. The various separation modes of capillary electrophoresis (CE) are commonly utilized to perform quality control and assess protein heterogeneity. This review attempts to highlight the most recent developments and applications of CE separation techniques for the characterization of protein and peptide therapeutics by focusing on papers accepted for publication in the in the two-year period between January 2012 and December 2013. The separation principles and technological advances of CE, capillary gel electrophoresis, capillary isoelectric focusing, capillary electrochromatography and CE-mass spectrometry are discussed, along with exciting new applications of these techniques to relevant pharmaceutical issues. Also included is a small selection of papers on microchip electrophoresis to show the direction this field is moving with regards to the development of inexpensive and portable analysis systems for on-site, high-throughput analysis.

Recent advances of ionic liquids and polymeric ionic liquids in capillary electrophoresis and capillary electrochromatography

Ionic liquids (ILs) and polymeric ionic liquids (PILs) with unique and fascinating properties have drawn considerable interest for their use in separation science, especially in chromatographic techniques. In this article, significant contributions of ILs and PILs in the improvement of capillary electrophoresis and capillary electrochromatography are described, and a specific overview of the most relevant examples of their applications in the last five years is also given. Accordingly, some general conclusions and future perspectives in these areas are discussed.