Voltammetric determination of cysteine using carbon paste electrode modified with Co(II)-Y zeolite
Highlights
► Ion exchange of zeolites remains when a Co(II)-zeolite Y was incorporated in carbon paste electrode. ► Voltammetric response of the electrode depends on the electroactive Co(II) species in the zeolite structure. ► Co(II) shows a catalytic behavior in the voltammetric determination of Cysteine. ► The proposed electrode showed good results for real samples.
Introduction
Cysteine ([(R)-2-amino-3-mercaptopropanoic acid]), one of about 20 amino acids commonly found in natural proteins, is a sulfur-containing amino acid. Cysteine (CySH) is critical for the proper metabolism of a number of essential biochemicals such as: heparin, biotin, lipoid acid, coenzyme A and glutathione. It has been used as a prospective radiation protector and cancer indicator in a number of pathological conditions including Parkinson's and Alzheimer's diseases as well as autoimmune deficiency syndrome (AIDS) [1], [2]. Moreover, it has also been widely used in the food and pharmaceutical industries as an antioxidant and biomarker, respectively [3]. Low level of CySH causes certain diseases including slow growth in children, depigmentation of hair, edema, lethargy, liver damage, loss of muscle and fat, skin lesions, and weakness [4]. Therefore, the detection of CySH in body fluids has become more important from biological and pharmacological stand points. Several methods for its detection have been reported including flow injection [5], [6], high performance liquid chromatography (HPLC) [7], [8], colorimetry [9], [10], chemiluminescence [11], spectrofluorimetry [12] and electrochemistry [13], [14], [15], [16], [17], [18]. Compared with the other methods, electrochemical techniques offer several advantages such as simplicity, ease of preparation and method, high sensitivity and selectivity, and relatively low cost [19], [20].
Chemically modified electrodes (CMEs) have recently attracted much attention due to their significant advantages [21], [22], [23], [24], [25], [26]. So, various chemically modified electrodes have been developed for the oxidation and detection of CySH [27], [28]. As a subcategory of CMEs, zeolite-modified electrodes (ZMEs) have been greatly studied [29], [30], [31]. ZMEs have some advantages over other CMEs due to their ion-exchange capacity and the molecular (size, shape and charge) selectivity properties of zeolites [32]. Particularly, substantial efforts have been dedicated to the development of sensors and biosensors using ZMEs [33], [34], [35], [36], [37].
In this work, we constructed a novel modified carbon paste electrode by incorporation of Co(II)-exchanged zeolite Y (Co2+Y/ZMCPE). The Co(II)-Y was obtained by ion exchanging of the parent Na-Y zeolite in a Co(II) solution as nitrate salt. Our preliminary experiments showed that the obtained Co2+Y/ZMCPE electrode exhibits good voltammetric response towards CySH. Hence, the fabricated electrode was used for the determination of CySH. Finally, the analytical performance of the electrode was evaluated for the determination of CySH in the patient blood serum, urine, N-acetylcysteine (ACC) tablet and powdered poultry feed (PPF) samples.
Section snippets
Reagents
The Na-Y zeolite (Cat. No. 33444-8) and the spectroscopic grade mineral oil (Nujol) were obtained from Aldrich. All reagents were of analytical grade from Merck, Fluka, or Aldrich companies. Tablets of ACC and PPF as pharmaceutical samples were purchased respectively from Fluimucil Company of Swiss and Razak Company of Iran. Also, patient blood serum and urine as clinical samples were taken from local sources. Triple-distilled water was used throughout the experiments. Buffer solutions were
Effect of modifier
In preliminary experiments, effect of modification of the electrode on the voltammetric response was studied. The voltammetric behavior of the CPE and Co2+Y/ZMCPE in a 0.2 mol L−1 acetate–hydrochloric acid solution (pH 2.2) with a scan rate of 25 mV s−1 was studied and the corresponding voltammograms, which were recorded after several preliminary scans, are collected in Fig. 1. As the results show, no voltammetric response was observed for unmodified CPE (Fig. 1a) which is desirable. While, a well
Conclusions
In the present work a novel electrode based on Co(II) doped zeolite modified carbon paste was constructed. By forming of complex between Co(II) and CySH on the electrode surface, the oxidation–reduction peaks of Co(II) was increased in the presence of CySH. The electrode showed high stability in repetitive experiments due to the high affinity of zeolite Y for Co(II). The proposed electrode showed excellent analytical performance characteristics especially a very low detection limit with the
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