MOVING BOUNDARY CAPILLARY ELECTROPHORESIS WITH CONCENTRATION GRADIENT DETECTION

A rugged and inexpensive Schlieren optics detection system consisting of a laser, focusing lens and light beam position sensor was combined with moving boundary electrophoresis performed in a 10 cm x 20-mu-m I.D. capillary. This system facilitated rapid analysis and universal detection of sample components. The laser beam, which is focused directly into the separation capillary, probes the refractive index gradients produced by the arrival of new boundaries. The frontal injection method used in this approach introduces samples into the capillaries without discrimination and provides higher sensitivities because of the lack of dilution during the separation process compared with the zone technique. A specially designed cartridge accommodates a short piece of the separation capillary and reservoirs for buffer and sample. The separation in this method is completed usually within 30 s. During this short separation time only a small dispersion associated with diffusion of analytes along the flow direction occurs, which ensures that high gradients are generated in the detection volume. The detection limits in this approach are sub-micromolar concentrations of analyte injected for low-molecular-weight compounds such as sucrose. This system has been applied to the separation of amino acids and carbohydrates.