Abstract: Capillary electrophoresis (CE) has wide applications in many fields because of its extraordinary advantages, such as high efficiency of separation, high speed, and high throughput. However, the detection sensitivity is relatively low due to short detection window and short optical length. To improve the detection sensitivity, a number of on-line sample focusing and stacking modes have been developed, such as field-amplified sample stacking, pH gradient preconcentration, micellar electrokinetic capillary chromatography (MEKC), isotachophoresis (ITP). These on-line focusing techniques have been of intensive interest because of the ease of operation and simultaneous focusing during capillary electrophoresis separation. Here, we review the principle, advanced techniques and latest applications of on-line capillary electrophoresis focusing.

Key words: on-line focusing, preconcentration, review, stacking, capillary electrophoresis （CE）