A Miniaturized Liquid Core Waveguide-Capillary Electrophoresis System with Flow Injection Sample Introduction and Fluorometric Detection Using Light-Emitting Diodes

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Abstract
A novel miniaturized capillary electrophoresis (CE) system is described where a Teflon AF-coated silica capillary serves both as the separation channel and as a transversely illuminated liquid core waveguide. This device uniquely uses flow injection (FI)-based split-flow sample introduction through a falling-drop interface. An H-channel structure fixed on a microscope glass slide utilizes a horizontal separation capillary with tubular sidearms on each end that serve as inlet and outlet flow-through electrode reservoirs. The inlet reservoir also functions as a falling-drop interface for coupling to the FI system. A blue LED is used as excitation source. A large-core optical fiber takes the emitted fluorescence to an inexpensive PMT with two layers of green plastic used for optical filtering. No focusing arrangement is needed. Continuous FI introduction of a series of 30-μL samples containing a mixture of of fluorescein isothiocyanate (FITC)-labeled amino acids allowed a throughput rate up to 144 samples/h, with ∼2% carryover and good precision (3.2% RSD). Baseline separation was achieved for FITC-labeled arginine, phenylalanine, glycine, and FITC in sodium tetraborate buffer (pH 9.5) with plate heights of 5.4−5.5 μm and plate numbers of 2.34 × 104−2.37 × 104 under electrical field strengths of 214 V/cm for injection and 500 V/cm for separation (14-cm capillary, 48-μm i.d.). Detection limits (S/N = 3) were 1.3 μM for arginine and 1.9 μM for phenylalanine and glycine.