Fluorescence Detection in Capillary Zone Electrophoresis Using a Charge-Coupled Device with Time-Delayed Integration

A fluorescence detection system for capillary zone electrophoresis is described in which a charged-coupled device (CCD) views a 2-cm section of an axially illuminated capillary column. The CCD is operated in two readout modes: a snapshot mode that acquires a series of Images in wavelength and capillary position, and a time-delayed integration mode that allows long exposure times of the moving analyte zones. By use of the latter mode, the ability to differentiate a species based on both its fluorescence emission and migration rate is demonstrated for fluoresceln and sulforhodamine 101. The detection limit for fluorescein isothiocyanate (FITC) is 1.2 × 10^-20 mol; detection limits for FITC-amino acids are in the (2-8) × 10^-20 mol range.