Determination of 2-(9-Anthryl)ethyl Chloroformate-Labeled Amino Acids by Capillary Electrophoresis and Liquid Chromatography with Absorbance or Fluorescence Detection

A new precolumn reagent for amino acid determination, 2-(9-anthryl)ethyl chloroformate (AEOC), was introduced to obtain higher sensitivity in two capillary separation techniques, liquid chromatography (LC) and electrophoresis (CE). The chromophore in the (9-fluorenyl)methyl chloroformate (FMOC) reagent was replaced by anthracene, which resulted in a reagent with very high molar absorptivity (epsilon 256 = 180,000 L mol-1 cm-1). This permits AEOC-tagged species to be detected at nanomolar levels with UV absorbance detection in standard 50-microns-i.d. fused silica capillaries. Weaker absorption bands match the UV argon laser lines of 351 and 368 nm, which allows for convenient laser-induced fluorescence (LIF) detection. In this mode, picomolar limits of detection are obtained. In addition to measuring the limits of detection, we examined micellar electrokinetic chromatography, free solution capillary electrophoresis, and packed capillary LC and compared these methods regarding the separation of amino acids.