Evaluation of a Separation-Based Fiber-Optic Sensor in a Micellar Electrokinetic Capillary Chromatography Mode of Operation
A fiber-optic sensor that integrates the separation-based selectivity of capillary electrophoresis with the sensitivity afforded by laser-induced fluorescence detection is evaluated. The evaluation involves measurements of neutral analytes that are separated via the micellar electrokinetic capillary chromatography (MECC) variation of capillary electrophoresis. This separation-based fiber-optic sensor (SBFOS) employs a single-reservoir, linear configuration that presents the challenges of overcoming gravity-driven hydrostatic flow and offsetting the effects of trapped gases. Hydrostatic flow resulting from nonlevel positioning of the separation capillary is reduced through the use of a restrictor capillary. MECC separations are performed in a frontal mode of operation using relatively short separation capillaries. Studies involve measuring the magnitude and reproducibility of retention time, efficiency, and signal over applied voltages spanning 2.0-4.0 kV for test mixtures composed of three fluorescentiy derivatized amines. The relative standard deviations in retention time and bandfront height are generally less than 10%, and efficiency is in the range of 103-104 theoretical plates for an 8-cm separation capillary. The optical configuration used with the SBFOS employs a single fiber optic to deliver excitation radiation and collect fluorescence from a small region at the sensor side of the separation capillary. Linear calibration curves are generated for single-component or multicomponent samples. A disadvantage of the frontal mode of operation is the eventual displacement of the running buffer in the capillary by the sample (reagent depletion). The effects of reagent displacement are investigated by varying the compositions of samples with respect to buffer and surfactant A preliminary separation of aflatoxins G1 and G2 illustrates the potential of the SBFOS for environmentally significant sensing.
Sepaniak, MJ; Tuan, VD; Tropina, V; Stokes, DL
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