Miniaturized movable contactless conductivity detection cell for capillary electrophoresis

A miniaturized capacitively coupled contactless conductivity detector (mini-C4D) cell has been designed which is small enough to allow it to slide along the effective capillary length inside the capillary cassette of an Agilent capiillary electrophoresis system (CE) (or other CE brand of similar construction), including the possibility of positioning it close to the point of optical detection (4 cm), or even putting two such detector cells in one cassette. The cell was tested and the performance characteristics (noise, sensitivity, and peak width) were compared with those obtained with the previously used large C4D cell. No significant differences were observed. The mini-C4D was used in simultaneous separations of common cations and anions where its advantage over a larger C4D cell is the ability to vary the point of detection with the mini-C4D cell continuously at any point along the capillary length, so that the optimum apparent selectivity can be chosen. Other applications include providing a convenient second point of detection in addition to photometric detection, such as to measure accurately the linear velocity of a zone, or to allow placement of two mini-C4D cells in one capillary cassette simultaneously.