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Spectrophotometric Determination Of Some Amino Acids Using 7,7',8,8'-Tetracyanoquinodimethane Reagent

Theia�?�?�?¢�?�?�?�?�?�?�?�?a N.Al-Sabha, Najwa M.Al-Karemy

A sensitive and selective spectrophotometric method is described for the determination of some amino acids namely; glycine, glutamine, valine, and lysine. The method is based on the interaction of these amino acids as electron donors with 7,7,8,8-tetracyanoquinodimethane (TCNQ) as a π-acceptor in acetonitrile at 70°C (80°C in the case of valine), to give highly yellowish-green colored charge transfer complexes which are exhibit maximum absorption at 841nm. Beer’s law is obeyed over the concentration range 0.1-4, 0.1-8, 0.3-3 and 0.1-3.5 μg/ml with molar absorptivity of 2.2058×104, 3.9184×104, 2.6999×104 and 4.2056×104 L.mol-1.cm-1for glycine, glutamine, valine, and lysine respectively. The different experimental parameters affecting the development and stability of the color were carefully studied and optimized. A proposal of the reaction pathway has been postulated.