Simultaneous Resolution and Electrochemical Quantification of Tyrosine and Tryptophan at a Poly (Diphenylamine) Modified Electrode

Polydiphenylamine modified pencil graphite was fabricated for the simultaneous electrochemical determination of tyrosine and tryptophan. Both tyrosine and tryptophan underwent an irreversible electroxidation at the modified electrode surface in phosphate buffer pH 9. These amino acids generally exhibit proximities in their oxidation overpotential, overlapping oxidation signals and interferences from other co-existing biomolecules. These points have been addressed using the developed electrode. The sensor has been characterized morphologically and electrochemically. The kinetic parameters such as charge transfer coefficient and the heterogeneous rate constant at the modified electrode surface were estimated using cyclic voltammetry. Differential pulse voltammetry was employed to quantify both tyrosine and tryptophan simultaneously with good sensitivity and high selectivity. A wide linearity of 20 M-1 mM and 20 M-1.4 mM was obtained using the sensor for tyrosine and tryptophan respectively. Practical utility of the developed sensor was tested in real human serum samples and obtained satisfactory recovery percentage.