Real-Time Imaging through Optical Fiber Array-Assisted Laser-Induced Fluorescence of Capillary Electrophoretic Enantiomer Separations

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Abstract
An advanced detection system based on laser-induced fluorescence imaging for capillary electrophoresis (CE) is presented. An optical fiber array was constructed for collection and transportation of the emitted fluorescent light to the charge-coupled device (CCD) camera. The fiber array makes the setup compact compared with a setup where the capillary is imaged through a camera objective. The imaging detector captures the sample zones in motion during the migration through the capillary. This allows unique studies on dynamic events otherwise unrevealed. During the study, unexplained nonlinear migration behavior was revealed. Enantiomer separations of dansylated amino acids using cyclodextrins, imaged between 1.5 and 12 cm of a 28-cm-long 50-μm i.d. capillary, were used for evaluation of the system. Comparing the optical fiber array with a camera lens system, the signal-to-noise-ratio (S/N) was 10 times higher. This is due to a combination of both higher signal and lower noise levels. To improve the S/N ratio further, a computer program for signal processing was designed. Using dichlorofluorescein, a concentration limit of detection (CLOD) of 350 pM was achieved and improved 10 times to 35 pM with computer postprocessing using 79 images. This is equal to 400 zeptomole for a 3-mm-long sample zone in a 50-μm i.d. capillary.