Capillary electrophoresis method for the determination of amino acids in pharmaceutical samples based on precolumn derivatization using 1,2-naphthoquinone-4-sulfonate

Abstract

A new method for the determination of amino acids by capillary electrophoresis based on derivatization with 1,2-naphthoquinone-4-sulfonate is developed. The separation of amino acid derivatives can be performed in a fused-silica capillary with a 40mM aqueous sodium tetraborate solution-isopropanol background electrolyte solution (3:1, v/v) under an applied potential of 30 kV. Glutamic and aspartic acids and cysteine can be separated faster in a 20mM sodium tetraborate solution at 15 kV. Amino acid derivatives are spectrophotometrically detected at 480 nm. The precapillary derivatization is developed for 5 min at 65°C and pH 10. The linear range for lysine is up to 1.25 × 10-3 M, the repeatability is 3.0%, and the detection limit is 0.67 pmol when injecting 22.5 nl. The method is applied to the determination of amino acids in pharmaceutical samples. Good agreement is found between the method proposed and the standard method.