Abstract
Electrooxidation of glutathione (GSH) was studied at the surface of 2,7-bis (ferrocenyl ethyl) fluoren-9-one modified carbon paste electrode (2,7-BFEFMCPE). Cyclic voltammetry (CV), double potential-step chronoamperometry, and differential pulse voltammetry (DPV) were used to investigate the suitability of this ferrocene derivative as a mediator for the electrocatalytic oxidation of GSH in aqueous solutions with various pH. Results showed that pH 7.00 is the most suitable pH for this purpose. At the optimum pH, the oxidation of GSH at the surface of this modified electrode occurs at a potential of about 0.410 V versus Ag|AgCl|KClsat. The kinetic parameters such as electron transfer coefficient, α = 0.61, and rate constant for the chemical reaction between GSH and redox site in 2,7-BFEFMCPE, kh = 1.73 × 103 cm3 mol−1 s−1, were also determined using electrochemical approaches. Also, the apparent diffusion coefficient, Dapp, for GSH was found to be 5.0 × 10−5 cm2 s−1 in aqueous buffered solution. The electrocatalytic oxidation peak current of GSH showed a linear dependence on the glutathione concentration, and linear calibration curves were obtained in the ranges of 5.2 × 10−5 M to 4.1 × 10−3 M and 9.2 × 10−7 M to 1.1 × 10−5 M with cyclic voltammetry and differential pulse voltammetry methods, respectively. The detection limits (3σ) were determined as 1.4 × 10−5 M and 5.1 × 10−7 M for the CV and DPV methods, respectively. This method was also examined as a selective, simple, and precise new method for voltammetric determination of GSH in real sample such as hemolysed erythrocyte.
Highlights
Purity is the most important indicator of a good quality of pharmaceutical substances
Since specific impurities in glutathione are dipeptides and amino acids, they, like glutathione itself, can react with dancil chloride to form dancil derivatives which can be further determined during chromatographic separation by RP high-performance liquid chromatography (HPLC) method
As a result of RP-HPLC chromatography of glutathione derivatized by dancyl chloride it was established that this reaction allows detecting impurities in glutathione (Figure 1)
Summary
Purity is the most important indicator of a good quality of pharmaceutical substances. The purity determination of any pharmaceutical substance is reduced to the determination of impurities. Impurities can be residues of intermediate products of synthesis or can be accumulated during the storage as a result of impact of various physical (heat, light, oxygen, moisture) or chemical (heavy metals, pH) factors on the main active component. Impurities can have a man-made character, i. E., be acquired during an active ingredient production process; such impurities most often include residual solvents. E. able to have a negative impact on the body or to have a different nature of pharmacological activity which is often opposite to the original substance.
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