Question

why the peak of capillary electrophoresis are narrow compared with GC or HPLC ?

Answer 1

Capillary electrophoresis (CE) is an important separation technique for the analysis in liquid phase. Capillary electrophoresis is a liquid separation technique using a high- voltage electric field as the driving force and a capillary tube as the separation channel to achieve separation based on different velocities of movement and distribution coefficients of the components in the sample.

Principle:-

Capillary electrophoresis is an analytical technique that separates ions based on their electrophoretic mobility with the use of an applied voltage.Neutral species are not affected, only ions move with the electric field. If two ions are the same size, the one with greater charge will move the fastest.The capillary is made of negatively charged fused silica inner wall which forms an electrical double layer with cations in the running buffer.The migration order is thus(i) positively-charged,(ii) neutral, (iii) negatively-charged molecules.A molecule's electrophoretic mobility depends on its charge and how much it is attracted or repelled by the voltage as well as the frictional drag force that resists movement.Friction is proportional to the radius of the molecule.

When a negative voltage is applied to the end of the capillary, it pulls the cations from the double layer, which also pulls the solution around it due to frictional forces.This type of flow is plug-shaped that is in this type of flow of fluid the velocity of the fluid is assumed to be constant across any cross-section of the pipe perpendicular to the axis of the pipe and it leads to less band-broadening or narrow bands than the parabolic-shaped flow plugs of HPLC.

Capillary Electrophoresis has a flat flow, compared to the pumped parabolic flow of the HPLC and the flat flow results in narrower peaks and better resolution. CE has a greater peak capacity than high-performance liquid chromatography (HPLC)and Gas Chromatography (GC) meaning the separations are more efficient and more peaks can be detected.