VOLTAMMETRIC SENSOR BASED ON POLYELECTROLYTE COMPLEX AND AMINO ACID COMPLEX OF COPPER(II) FOR RECOGNITION AND DETERMINATION OF TYROSINE ENANTIOMERS
A voltammetric sensor based on a glass-carbon electrode modified by a composite of a polyelectrolyte complex of chitosan and succinyl chitosan with an amino acid complex of copper(II) [Cu(L-Phe)(Gly)] was developed for the recognition and determination of tyrosine enantiomers. According to cyclic voltammetry and electrochemical impedance spectroscopy, the effective surface area of the proposed composite sensor (A = 5.75 ± 0.13 mm<sup>2</sup>) and electron transfer resistance values (R<sub>et </sub>= 429.55 ± 4.02 Ohm) were calculated. The electrochemical and analytical characteristics of the developed sensor were studied when registering linear voltammograms of tyrosine enantiomers. The detection limit calculated by the 3s criterion for the D-enantiomer is 1.80·10<sup>-5</sup> M; for the L-enantiomer, the limit is 1.67·10<sup>-5</sup> M. The proposed sensor shows the greatest sensitivity to the D-enantiomer. The developed sensor was tested for the determination of L- and D-Tyr in model solutions of pure enantiomers in biological fluids. The relative standard deviation in the determination of Tyr enantiomers in all the cases did not exceed 5.16%, and the relative measurement error was 3.93%. Statistical evaluation of the results by the “added-found” method indicated the absence of a significant systematic error. The linear dependence of the potentials and currents of the oxidation peaks on the ratio of D- and L-Tyr in the mixture makes it possible to determine the enantiomers of Tyr in the mixture with good analytical characteristics. The data obtained indicate that this sensor can be successfully used for the analysis of a mixture of enantiomers and is an effective chiral platform for the recognition and determination of Tyr enantiomers in human plasma and urine samples.