Liquid chromatographic determination of the total available free and intrachain lysine in various foods

A method for the quantitative determination of the total available lysine in various foods is developed. The method is based on the reaction of the amino groups on the lysine molecule with fluorodinitrobenzene and is capable of furnishing simultaneous determination of the available intrachain lysine (known as N-ε-[2,4-dinitrophenyl]-L-lysine) or the available free and/or N-terminal lysine (known as N,N′-di-[2,4-dinitrophenyl]-L-lysine). Optimum conditions for separation and quantitation are studied. The results show the proposed method to be both accurate and precise and suitable for food samples containing hydrolyzed proteins.