Microchip capillary electrophoresis with electrochemical detector for fast measurements of aromatic amino acids

A method based on microchip capillary electrophoresis with amperometric detection was developed for the rapid separation and direct detection of oxidizable aromatic amino acids (without prior derivatization). The working electrode was a thick-film carbon strip electrode positioned opposite the outlet of the separation channel. Factors influencing the separation and detection processes were examined and optimized. The five aromatic amino acids, tyrosine, 5-hydroxytryptophan, tryptophan, p-aminobenzoic acid, and m-aminobenzoic acid, can be well separated within 5 min using a separation voltage of 2000 V and a 25 mM phosphate buffer (pH 7.0) run buffer containing 50 mM sodium dodecylsulfate. Most favorable amperometric detection was obtained at +0.95 V. Linear calibration plots are observed for micromolar concentrations of the oxidizable amino acids. The new protocol offers good stability and for reproducibility, with relative S.D. of less than 5% for both migration times and peak currents (n=8). It should be useful for the analysis of aromatic amino acids, as desired for life sciences.