Simultaneous voltametric determination of L-tryptophan and L- tyrosine with the screen printed electrode modified by Fe3O4/GOX-COOH

L-tryptophan (Trp) and L-tyrosine (Tyr) are two main amino acids owing to their crucial roles in biological systems. They are precursors of hormones and neurotransmitters such as thyroxin and dopamine, as well as other physiologically important biomolecules [1]. Electrochemical methods have found many applications in the determination of the amino acids such as tyrosine and tryptophan owing to their electro-active aromatic groups [2]. In the many studies the chemically modified electrodes used to improve the anodic oxidation of amino acids. Other investigations have also indicates the importance of the carboxyl group in the surface adsorption of the related molecules. Moreover, the aromatic amino acids were quickly adsorbed onto the surface of the graphene oxide nano-composite with the strong π-π interactions [3]. Here, the Fe3O4–graphene oxide carboxylic acid (Fe3O4/GO-COOH) nanocomposite was prepared. The composite (1-5 mg) was dispersed in 10 mL doubly distilled water and ultrasonicated for 2 h until a homogenous dispersion obtained. Subsequently a mixture of Fe3O4/GO-COOH and chitosan (%1 w/w) was electrodeposited onto the surface of a screen printed carbon electrode (SPCE) in a constant potential (-2 V vs. Ag/AgCl) for 80 s. The electrochemical behavior of the modified electrode exhibits an electrocatalytic activity towards the oxidation of the Trp and Tyr. The experimental conditions, including the ratio of Fe3O4/GO-COOH and chitosan, the electrodeposion time and potential and also the pH value were studied by differential pulse voltammetry (DPV). The peak potentials of tryptophan and tyrosine are closed at the pH values greater than 2. Therefore, their simultaneous determination by the SPCE/(Fe3O4/GO-COOH/Chitosan electrode in pH 2 is possible. Under the optimized conditions, the oxidation peak current was linear over a concentration range of 0.50 to 40.0 ppm for Try and 0.20 to 50.0 ppm for Tyr with a detection 13th Annual Electrochemistry Seminar of Iran Materials and Energy Research Center (MERC), 22- 23 Nov, 2017 30 limit of 0.20 and 0.15 ppm for Try and Tyr respectively. The modified electrode was successfully applied for the simultaneous determination of Trp and Tyr in some food samples.