Twenty underivatized essential amino acids were separated using capillary zone electrophoresis and consequently detected with contactless conductivity detection (CCD). A simple acidic background electrolyte (BGE) containing 2.3 M acetic acid and 0.1% w/w hydroxyethylcellulose (HEC) allowed the electrophoretic separation and sensitive detection of all 20 essential amino acids in their underivatized cationic form. The addition of HEC to the BGE suppressed both, electroosmotic flow and analyte adsorption on the capillary surface resulting in an excellent migration time reproducibility and a very good analyte peak symmetry. Additionally, the HEC addition significantly reduced the noise and long-term fluctuations of the CCD baseline. The optimized electrophoretic separation method together with the CCD was proved to be a powerful technique for determination of amino acid profiles in various natural samples, like beer, yeast, urine, saliva, and herb extracts.

Two constructions of the high-frequency contactless conductivity detector that are fitted to the specific demands of capillary zone electrophoresis are described. The axial arrangement of the electrodes of the conductivity cell with two cylindrical electrodes placed around the outer wall of the capillary column is used. We propose an equivalent electrical model of the axial contactless conductivity cell, which explains the features of its behavior including overshooting phenomena. We give the computer numerical solution of the model enabling simulation of real experimental runs. The role of many parameters can be evaluated in this way, such as the dimension of the separation channel, dimension of the electrodes, length of the gap between electrodes, influence of the shielding, etc. The conception of model allows its use for the optimization of the construction of the conductivity cell, either in the cylindrical format or in the microchip format. The ability of the high-frequency contactless conductivity detector is demonstrated on separation of inorganic ions.

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