Abstract
The amperometric determination of cysteine, using an electrode based on ternary silver-copper sulfide, is presented. Electrochemical characterizations (using cyclic voltammetry) of three electrode materials revealed that the electrode based on the material that consists of jalpaite (Ag3CuS2), doped with a small amount of metallic silver, has the best electrocatalytical performance for cysteine oxidation. For the amperometric determination, 0.142 V at pH 5 and 0.04 V at pH 7 vs. Ag/AgCl, related to the electrocatalytical oxidation of thiol group, were chosen. Electrochemical impedance spectroscopy together with Fourier transform infrared spectroscopy (FTIR) revealed that oxidation takes place on the electrode surface with fouling effect, which does not affect a wide linear working range between 1 μM and 100 μM. Sensitivities, at pH 5 and pH 7, are calculated to be 0.11 μA μM−1 and 0.10 μA μM−1, respectively. The detection limits were determined to be 0.036 μM and 0.024 μM for pH 5 and pH 7, respectively. In the presence of uric acid, folic acid, ascorbic acid, and glucose no interference was noticed. This electrode showed remarkable stability and excellent reproducibility. The electrode was exploited for the determination of cysteine in a dietary supplement with the excellent recoveries.
Highlights
Cysteine has an important role in biochemical processes, as well as in environmental systems [1,2].Cysteine, as non-essential amino acid, can be found in protein food, various cosmetics, and pharmaceutical products [3]
Cysteine is involved in the formation of reactive sulfur species (RSS) and in appearance of a specific type of oxidative stress, which is associated with the oxidation of the pair cysteine/cystine, called disulfide stress [7]
Many techniques have been developed for the determination of cysteine, such as high-performance liquid chromatography (HPLC) [8,9,10,11], spectrophotometry [12,13], or gas chromatography/mass spectrometry [14], the most exploited and reported techniques are electrochemical due to a favorable
Summary
Cysteine has an important role in biochemical processes, as well as in environmental systems [1,2].Cysteine, as non-essential amino acid, can be found in protein food, various cosmetics, and pharmaceutical products [3]. Cysteine has an important role in biochemical processes, as well as in environmental systems [1,2]. Determination and quantification of cysteine or its derivates in biological fluids (urine, blood, etc.) is very important, since cysteine plays a role in several diseases such as depigmentation of hair, growth disorder in children, liver damage, as well as in some pathological conditions such as Alzheimer’s or Parkinson’s disease [4,5,6]. It was shown that cysteine is a major extracellular antioxidant and that it plays an important role in various physiological antioxidant systems. Up to now the determination of cysteine has attracted considerable attention. Many techniques have been developed for the determination of cysteine, such as high-performance liquid chromatography (HPLC) [8,9,10,11], spectrophotometry [12,13], or gas chromatography/mass spectrometry [14], the most exploited and reported techniques are electrochemical due to a favorable
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