Determination of tyrosine by stripping voltammetry on electrodes modified with EuHCF

This paper presents the results of the development of a method for the determination of tyrosine by stripping voltammetry in dietary supplements and medicines. The possibility of using a europium hexacyanoferrate film on a glassy carbon electrode as a modifier that enhances the analytical signal of tyrosine is shown. Some important quantitative characteristics of the EuHCF film have been determined, such as the area of the electroactive coating of the electrode surface and the film thickness. These values were 5.31∙10-10mol/cm2 and 0.841 nm, respectively. The modification was shown to be effective in enhancing the analytical signal of tyrosine. Optimal conditions for the formation of an electrochemical signal of tyrosine under conditions of voltammetry with a linear potential sweep were selected. For this purpose, studies were conducted with variations in the parameters of medium acidity, scanning rate, time and the magnitude of the analyte accumulation potential. The best results were achieved with the following parameters: pH = 6.80, W = 100 mV/s, E accumulation = -1.5 V, t accumulation < 90 s. The dependence of the peak current on concentration obeys the equation I = 0,428C - 0,113 (R2 = 0,998). A possible mechanism of europium hexacyanoferrate film formation and a possible mechanism of tyrosine oxidation are proposed. It has been established that the diffusion stage is the limiting stage of the tyrosine oxidation process. An algorithm for the quantitative determination of tyrosine by stripping voltammetry (SV) on an electrode modified with EuHCF is proposed. The use of the modification reduced the detection limit to 7 10-6 M and expanded the boundaries of the determination interval, where a linear dependence of the current on the concentration was observed. The range of detectable concentrations of the substance is: 9∙10-6 1∙10-4 mol/l, while the unmodified GCE covers the range of 2∙10-5∙1∙10-4 mol/l. The proposed method for voltammetric determination of tyrosine was tested on the TYROSINE product from MISTER PROT, which contains 100% L-tyrosine according to the manufacturer, which was confirmed during the research. The relative error of determination was less than 0.25%. Contribution of the authors: the authors contributed equally to this article. The authors declare no conflicts of interests.

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