Rejection of capillary wall background light in an on-column confocal fluorescence detector

Minimization of the background arising from the capillary wall is of extreme importance in laser induced fluorescence on-column detection for capillary electrophoresis. A sensitive confocal fluorescence detection scheme is described. The intense capillary wall background light was effectively rejected by an adjustable precision slit in a confocal configuration. Rhodamine 640 was used as a standard fluorophore. Detection linearity was demonstrated over four orders of magnitude of concentration and the concentration detection limit was 3.38 x 10(-11) M.