Study of the sensitization of tetradecyl benzyl dimethyl ammonium chloride for the color development reaction between lysine and sodium 1,2-naphthoquinone-4-sulfonate and the determination of lysine in pharmaceutical and biological samples

A rapid, simple and sensitive method for the determination of lysine (Lys) using sodium 1,2-naphthoquinone-4-sulfonate (NQS) and tetradecyl benzyl dimethyl ammonium chloride (Zeph) is presented in this paper. The method is based on the russety product formed from Lys, NQS and Zeph in a buffer solution of pH 9.60, and the stoichiometric ratio of the product is 1:2:2. Beer's law is obeyed in a range of 0.09–18 μg ml−1 of Lys at the maximum absorption of 474 nm (ɛ474 is 8.1 × 105 l mol−1 cm−1). The equation of linear regression is A = 0.40427 + 0.06112C, with a linearly correlation coefficient of 0.9972. The limit of detection is 0.07 μg ml−1, R.S.D. 0.8%, and average recovery rate in a range of 98.9–100.1%. This paper further optimizes the determination of Lys compared with the previous methods, and the reaction mechanism is studied intensively. The proposed method has been successfully applied to the determination of Lys in pharmaceutical and biological samples. The common components as nutritional additives in pharmaceuticals and other compounds in biological samples nearly do not interfere with the proposed method.