A novel on-line method is presented for the extraction and preconcentration of amino acids using a sol-gel coated column coupled to a conventional UV/vis detector. Extraction, stacking and focusing techniques are used in the preconcentration procedures. Sol-gel coatings are created by using N-Octadecyldimethyl[3(trimethoxysilyl)proply] ammonium chloride (C.sub.18-TMS) in the coating sol solutions. The resulting sol-gel coating carries a positive charge. For extraction, the pH of the samples is properly adjusted to impart a net negative charge to amino acids. A long plug of the sample is then passed through the sol-gel coated capillary to facilitate extraction via electrostatic interaction between the positively charged sol-gel coating and the negatively charged amino acid molecules. The focusing of the extracted amino acids is accomplished through desorption of the extracted amino acid molecules carried out by local pH change. The described procedure provides 150,000-fold enrichment effect for alanine.