Capillary electrophoresis: Recent advancements and applications of micellar electrokinetic capillary chromatography

Abstract

The article discusses capillary electrophoresis (CE) as an advanced technique used for the separation and detection of various pharmaceutical drugs. CE involves the application of high voltages across buffer-filled capillaries to produce separation based on various separation theories, including capillary zone electrophoresis (CZE), micellar electrokinetic capillary chromatography (MEKC), capillary gel electrophoresis, and capillary isoelectric focusing. While traditional CZE is not suitable for the separation of neutral substances, MEKC was developed by Shigeru Terabe in the early 1990s to expand the use of CE to neutral analytes that cannot be separated using straightforward free solution CE. MEKC employs an ionic micellar solution that interacts with the analytes through partitioning processes like a chromatographic technique. To create a pseudostationary phase, a surfactant such as sodium dodecyl sulfate (SDS) is added to the buffer solution at a concentration higher than its critical micellar concentration. The anionic SDS micelles are electrostatically drawn towards the anode, while the electro-osmotic flow carries the bulk solution toward the negative electrode due to the negative charge on the inside surface of the silica capillaries. When a neutral analyte is introduced into the micellar solution, a portion is integrated into the micelle, while the remaining fraction of the analyte migrates with the electroosmotic velocity. Separation depends on the individual partitioning equilibrium of the various analytes between the micellar and the aqueous phase. The bigger percentage of analyte dispersed inside the micelle, the slower it will travel. This article provides an in-depth understanding of the separation principle and the mechanism involved in MEKC, highlighting its usefulness in separating neutral analytes that cannot be separated using traditional CZE.