Capillary electrochromatography (CEC) is an important modern separation technique that combines the high separation efficiency of capillary electrophoresis (CE) with the selective retention mechanism of high-performance liquid chromatography (HPLC). It is particularly useful for the separation and analysis of complex mixtures containing charged, neutral, polar, and non-polar compounds. In CEC, a narrow-bore capillary is packed or coated with a stationary phase, while an electric field is applied across the capillary to drive the mobile phase by electroosmotic flow. The technique therefore combines chromatographic partitioning with electrophoretic and electroosmotic transport. The basic principle of CEC is based on electroosmotic flow and chromatographic interactions. The inner wall of a fused-silica capillary generally contains silanol groups. At a suitable pH, these groups become negatively charged. When an electrolyte solution is introduced into the capillary, positive ions from the solution accumulate near the negatively charged wall, forming an electrical double layer. Application of a high electric field causes the mobile phase to move toward the cathode by electroosmotic flow. Unlike conventional pressure-driven HPLC flow, electroosmotic flow has an approximately flat velocity profile across the capillary. This greatly reduces band broadening and contributes to the high efficiency of CEC. The stationary phase is another essential aspect of capillary electrochromatography. In packed-column CEC, the capillary is filled with small particles, commonly silica-based particles modified with groups such as C18. These particles provide a large surface area for chromatographic interactions. Monolithic stationary phases can also be prepared directly inside the capillary. In open-tubular CEC, the stationary phase is chemically bonded to the inner wall of the capillary. The choice of stationary phase determines the nature of interactions between analytes and the stationary phase and consequently controls selectivity and retention. The movement of an analyte in CEC depends on both its electrophoretic mobility and its chromatographic retention. Charged compounds are influenced by their electrophoretic mobility, which depends on their charge, size, and the properties of the surrounding electrolyte. At the same time, analytes interact with the stationary phase through mechanisms such as hydrophobic interactions, adsorption, partitioning, ion exchange, or other specific interactions. Neutral compounds do not possess electrophoretic mobility under ordinary conditions, but they can still be separated because their movement is governed by electroosmotic flow and their different degrees of interaction with the stationary phase. This ability to separate both charged and neutral compounds is one of the major advantages of CEC. Electroosmotic flow is strongly affected by experimental conditions. Important parameters include the pH and ionic strength of the buffer, the nature of the electrolyte, the applied voltage, temperature, and surface properties of the capillary. Increasing the magnitude of the applied voltage generally increases electroosmotic velocity and reduces analysis time, although excessive voltage can cause significant Joule heating. Buffer pH affects the ionization of surface silanol groups and therefore influences electroosmotic flow. Ionic strength affects the thickness of the electrical double layer and the magnitude of electroosmotic flow. Optimization of these parameters is essential for obtaining reproducible and efficient separations. The applied electric field is a particularly important operational parameter. CEC commonly uses high voltages to generate electroosmotic flow. The resulting flow can be much more efficient than conventional pressure-driven flow because of its relatively flat velocity profile. However, high electric fields