On-line preconcentration methods for capillary electrophoresis

The limits of detection (LOD) for capillary electrophoresis (CE) are constr ained by the dimensions of the capillary. For example, the small volume of the capillary limits the total volume of sample that can be injected into t he capillary. In addition, the reduced pathlength hinders common optical de tection methods such as UV detection. Many different techniques have been d eveloped to improve the LOD for CE. In general these techniques are designe d to compress analyte bands within the capillary, thereby increasing the vo lume of sample that can be injected without loss of CE efficiency. This on- line sample preconcentration, generally referred to as stacking, is based o n either the manipulation of differences in the electrophoretic mobility of analytes at the boundary of two buffers with differing resistivities or th e partitioning of analytes into a stationary or pseudostationary phase. Thi s article will discuss a number of different techniques, including field-am plified sample stacking, large-volume sample stacking, pH-mediated sample s tacking, on-column isotachophoresis, chromatographic preconcentration, samp le stacking for micellar electrokinetic chromatography, and sweeping.