Capillary Electrophoresis

Abstract Over the past two decades, capillary electrophoresis (CE) has emerged as a family of powerful and versatile separation techniques. The electrically driven flow profiles generated in CE provide, routinely, separation efficiencies of 10 5 theoretical plates. Although theory predicts that the achievable separation efficiencies will be greatest for macromolecules with small diffusion coefficients, CE has also been successful in the analysis of small molecules, such as inorganic ions. Strategies to increase separation efficiencies on‐line have involved sample stacking and isotachophoretic techniques. The former promotes higher separation efficiencies based on differences in conductivity between the background electrolyte (BGE) and the sample buffer; the latter utilizes a discontinuous buffer system to create discrete solute zones. The instrumentation employed in CE is simple in design and is compatible with a variety of detection modes, including ultraviolet/visible (UV/VIS) absorbance, fluorescence, electrochemistry, mass spectrometry (MS), and chemiluminescence (CL). CE methodologies can be miniaturized on to a silicon wafer and integrated with sample preparation and chemical reactions. In addition to free‐solution capillary electrophoresis (FSCE) utilizing a BGE and potentially a variety of BGE additives, several alternative separation modes have been developed and implemented. These include micellar electrokinetic chromatography (MEKC), capillary isoelectric focusing (cIEF), size‐sieving capillary electrophoresis (SSCE), and capillary electrochromatography (CEC). Some of these separation modes have been adapted from the slab gel electrophoresis (SGE) format, or are reminiscent of separation mechanisms in liquid chromatography (LC). Currently, one of the greatest challenges in CE involves the maintenance of the capillary surface to provide reproducible electro‐osmotic flow (EOF) and significantly reduce capillary wall interactions. According to the mode of separation employed and the characteristics of the solutes to be analyzed, both covalent and noncovalent (dynamic) capillary wall modifications have been demonstrated.