Pretreated Platinum Electrode Research Articles

Polyaniline Supported Atomic Gold Electrode Toward Glucose Oxidation

Gold is reported to have unique catalytic properties for oxidization of alcohols in alkaline media, and the catalytic ability is dependent on size of the gold, which enhancement in the catalytic activity is observed following reduction of the size [1]. As size of the gold reduced to atomic level, the property would vary depending on the number of atoms in a gold cluster [1, 2]. For instance, the alcohol oxidation catalytic activity is promoted when there is an even number of gold atoms in a cluster and demoted when the gold cluster contains odd number of atoms [1, 3]. Simulation results indicate that the HOMO-LUMO gap switches between conductor and semi-conductor when the atom number changes [2]. Deposition of atomic level gold clusters is realized by a cyclic atomic gold deposition process utilizing polyaniline (PANI) as the supporting substrate [1, 3]. In this study, PANI decorated with different numbers of gold atoms is prepared, and effect of the gold atom number in glucose oxidation is evaluated for application in glucose electrochemical sensor.Figure 1 shows the fabrication process of the PANI/Au electrode. The PANI was prepared by electropolymerization on a pretreated platinum electrode. The electrolyte was composed of 0.1 M aniline monomer in 2 M HBF4. Color of the surface of the Pt electrode changed from silver to blue after the polymerization process. Thereafter, KAuCl4 was used as source of the gold in the cyclic atomic gold deposition process. Figure 2 shows sequence of the cyclic atomic deposition process for gold. In one cycle of the deposition, one and only one gold ion was attracted to an amine group in the PANI, and the attracted gold ion was reduced to form a gold atom. After preparation of the PANI/Au N (N indicates the number of the deposition cycle conducted) electrode, glucose oxidase (GOD) was immobilized as an enzyme on the electrode surface by a comprehensive crosslinking method.Figure 3 shows cyclic voltammogram (CV) results of glucose oxidation on the PANI/Au2 electrode when the glucose concentration in a phosphate buffer solution (PBS) was varied from 0 to 20 mM. Anodic current generated from oxidation of the glucose was confirmed when the concentration was higher than 5 mM. In order to reveal effects of the gold atom number on oxidation of glucose, PANI/Au N electrodes with the N changed from 1 to 3 were prepared. In the CV scans, a scan rate of 50 mV/s and 10.0 mM glucose were used. Figure 4 shows the CV results when using the PANI/Au N electrode as the working electrode. Anodic current caused by oxidation of glucose was observed in all the three electrodes. The current response increased when the deposition cycle was increased from 1 to 2, and the PANI/Au3 produced current responses between those of the PANI/Au1 and PANI/Au2. This implies that the glucose oxidation is lowered when an odd number of gold atoms is deposited. [1] Alex P. Jonke, Mira Josowicz and Jiří Janata, J. Electrochem. Soc. 159 2012 40-43. [2] E. M. Fernandez, J. M. Soler, I. L. Garzon, L. C. Balbas, Phys. Rev. B 70 2004 165403. [3] J. Janata, T. Nakamoto, IEEJ Transaction 11 2016 261-267. Figure 1

Lab-on-valve (LOV) system coupled to irreversible biamperometric detection for the on-line monitoring of catechol

The analytical performance of lab-on-valve (LOV) system using irreversible biamperometry for the determination of catechol was evaluated. By integrating miniaturized electrochemical flow cell (EFC) designed and processed which is furnished with two identical polarized platinum electrodes, into the LOV unit, the lab-on-valve system combines sampling with analysis, realizing automated on-line analysis for catechol in a closed system. The biamperometric detection system was established to record the relationship between oxidation current and time by coupling the irreversible oxidation of catechol at one pretreated platinum electrode with the irreversible reduction of platinum oxide at the other pretreated platinum electrode. Factors influencing the analytical performance were optimized, including the potential difference (Δ E), buffer solution and pH, and flow variables in the LOV. A linear calibration curve was obtained within the range of 1.0 × 10 −6–5.0 × 10 −4 mol L −1 of catechol with the detection limit (3 σ) of 5.09 × 10 −7 mol L −1. The relative standard deviation (R.S.D.) was 2.39% for 11 successive determinations of 1 × 10 −5 mol L −1 catechol and the sample throughput was 35 h −1. Moreover, this proposed method was applied to the analysis of catechol in beer sample, which was testified by high-performance liquid chromatography (HPLC).

Improvement of the electrocatalytic activity of platinum in oxidation of aromatic compounds

The electrochemical oxidation of aromatic compounds (ACs) at pre-treated platinum electrodes was studied by cyclic voltammetry (CV). An understanding of the mechanism of the different electrochemical processes is possible only if taking into account the state of the Pt electrode surface, which is strongly affected by oxide formation and reduction. Long-time treatment by CV yields increased Pt oxide coverage and leads to very important electrocatalytic properties towards many organic electro-oxidation reactions. Three aromatic compounds were studied: phenol, hydroquinone and p-benzoquinone. The results show that the increase of the charge Q which characterizes the surface quality of the pre-treated Pt electrodes entails an increase in active sites with respect to the discharge of water to form PtOH species which typically starts at ca. 0.12 V. Once such species are formed they react with both free and adsorbed molecules. It results in the multiplication of the oxidation current by factors of 46 and 21 for phenol and p-benzoquinone, respectively, when Q increases from 0.3 to 4 mC. In the case of hydroquinone this factor is only about 3 for the same increase of Q. The oxidation of hydroquinone is not catalyzed by the PtOH species because it takes place at potential lower than 0.12 V. The results show that phenol is quantitatively oxidized by CV on a pre-treated platinum electrode to produce by the intermediary of catechol, hydroquinone, p-benzoquinone, oxalic and maleic acids, whose degradation leads to carbon dioxide.

Determination of chlorogenic acid by flow injection irreversible biamperometry

A flow injection irreversible biamperometric method for the determination of chlorogenic acid is described. The proposed method is based on the electrochemical oxidation of chlorogenic acid at pretreated platinum electrode and the reduction of permanganate at another electrode to form an irreversible biamperometric detection system. Under the external potential difference (Δ E) of 0 V, in the 0.05 mol/L sulfuric acid, chlorogenic acid can be determined over the range 0.8–120 mg/L with a sample measurement frequency of 80 samples/h. The detection limit is 0.18 mg/L. The proposed method exhibits the satisfactory reproducibility with a relative standard derivation (R.S.D.) of 2.21% for 19 successive determinations of 40 mg/L.

Flow-injection biamperometry of pyrogallol compounds

A biamperometric method for the direct determination of pyrogallol compounds has been designed for flow-injection analysis. The method is based on the electrocatalytic oxidation of pyrogallol compounds at one pretreated platinum electrode and the reduction of platinum oxide at the other pretreated platinum electrode to form a biamperometric detection system with the applied potential difference of 10 mV. Three important compounds, pyrogallol, gallic acid and tannic acid, have been detected by the method. The linear relationships between currents and the concentrations of pyrogallol, gallic acid and tannic acid are obtained over the range 1.0×10 −6–1.0×10 −4, 1.0×10 −6–1.0×10 −4 and 1.0×10 −6–2.0×10 −4 mol l −1 with the detection limit of 6.0×10 −7, 6.0×10 −7 and 8.0×10 −7 mol l −1 (S/N=2), respectively. The R.S.D. observed for 30 successive determinations of 5.0×10 −5 mol l −1 pyrogallol, gallic acid and tannic acid are 1.9, 2.5 and 2.0%, respectively. Most ions and organic compounds tested are found not to cause significant interference in the determinations. The method is simple, selective and efficient (180 h −1), performing well as a routine assay, and has been validated by the determination of pyrogallol compounds in tea and Chinese gall.

Determination of [formula omitted]-Cysteine in Amino Acid Mixture and Human Urine by Flow-Injection Analysis with a Biamperometric Detector

Based on the electrocatalytic oxidation of cysteine at pretreated platinum electrode and the flow-injection biamperometry for irreversible couple, a novel electrochemical detector is proposed for the selective determination of cysteine in amino acid mixtures and human urine samples. A thin-layer flowthrough cell was used to achieve large electrode surface area to volume ratio. Two identical pretreated platinum electrodes were mounted in the cell with an applied potential difference of 10 mV. By coupling two independent and irreversible electrode processes, namely, the oxidation of cysteine and the reduction of platinum oxide, the biamperometric detection scheme has been established. The resulting current is linear to cysteine over the range 4 × 10−7–4 × 10−5 M with the detection limit 1 × 10−7 M (15 pmol). The selectivity of the detector is tested by 55 foreign species including 26 ions, 11 amino acids, 6 vitamins, and 12 other compounds possibly found in urine. The detector performs well as a routine assay, showing high efficiency (180 samples/h) and good reproductivity shown by a RSD of 0.6% for eight repeated determinations of 2 × 10−6 M cysteine. The urine samples are detected directly without the need of pretreatment or adding other reagents.

Flow-injection biamperometry for direct determination of hydroxylamine at two pretreated platinum electrodes

Flow-injection biamperometry is used for the direct determination of hydroxylamine based on coupling two independent and irreversible electrode processes, the oxidation of hydroxylamine and the reduction of platinum oxide. In operation a potential difference of 0 V is imposed between two platinum wire electrodes pretreated by an anodization step, and the resulting current is measured. Hydroxylamine can be determined in the range of 6×10 −7 to 4×10 −5 mol l −1 with the detection limit of 1×10 −7 mol l −1. Nitrogen-containing compounds such as nitrate, nitrite and ammonia that often accompany hydroxylamine in the process of nitrogen cycle do not cause significant interference. The stability of the detector is shown by a relative standard deviation (R.S.D.) of 1.4% for 50 replicate determinations of 1×10 −5 mol l −1 hydroxylamine.

Electrochemical cell system for voltammetry of high purity solvents

A two-compartment cell system was designed to carry out high purity electrochemical experiments. Features of this cell include a monolithic quartz body, quartz isolation frit, pretreated platinum electrode, hydrogen reference electrode, snap-on cell tops, purified “type I” water, high purity supply gases, fluoropolymer tubing, and gas-tight cell integrity. An advantage of this design is the allowance for internal pre-electrolysis of the test solution. The system was quality tested by obtaining cyclic voltammograms of 0.5 molar sulfuric acid solution. To demonstrate its utility for high purity work, novel cyclic voltammograms of type I water were obtained with a platinum microelectrode in the absence of electrolyte. The water voltammograms exhibited three electroactive features: reduction potential limit near E=−0.2 V versus r.h.e. (H2), oxidation potential limit near E=+1.6 V (O2), and one surface reduction peak at E=+0.4 V. Thus, the voltammetric “potential window” for water was determined to be 1.8 V.

Passivation d'electrodes de platine et d'or lors de l'oxydation electrochimique indirecte du xylene

The electrosorption of xylenes and their oxidation products on electrochemical pretreated platinum electrode from aqueous solution containing Ce 3+ is studied. The oxide layer of platinum electrode electrocatalyses the oxidation of Ce 3+ and decreases the adsorption of xylenes and their oxidation products. The adsorbability of xylenes decreases in the order: p-xylene > o-xylene > m-xylene. The adsorbability of p-xylene and its oxidation products decreases in the order: p-xylene > p-tolualdehyde > p-methylbenzylalcohol. The adsorption of xylenes and their oxidation products on electrochemical pretreated gold electrode is lower.

The electrochemical activity determination of trypsin-like enzymes I - trypsin

Since 1970, a number of chromogenic substrates have been synthesized for the assay of the activities of enzymes intervening along the blood clotting process. The related studies have in all cases been restricted to homogeneous media. The aim of this work is to establish the conditions for the determination of enzymatic activities in the presence of solid dispersions. The principle of this analytical technique is based on the electrochemical detection of electroactive species, which can be directly related to the extent of an enzyme-catalyzed hydrolysis. For that purpose, a new substrate, benzoyl D,L arginyl p-aminodiphenylamide hydrochloride ( D,L BAPADA) has been synthesized and the method has been tested with trypsin as the enzyme. The substrate proved to be specific toward this enzyme. The amine released during the hydrolysis, the p-aminodiphenylamine (pADA), is electroactive in the anodic potential range, where neither the reduction of oxygen, nor the background discharge interfere. The amount of amine is periodically detected by its oxidation peak produced with an adequate potentiodynamic signal. The effects of several parameters which may affect the response signal have been checked by comparison with the calibration curve of the amine traced in the conditions met for the assay. Although the oxidation peak of the amine is qualitatively affected, the amperometric procedure nevertheless allows to use the calibration curve in order to convert the currents in terms of concentrations. By the use of a pretreated platinum electrode, first-order kinetics were obtained for the trypsin-substrate system. The magnitude of the kinetic constants fairly well compares with the spectrophotometric experiments carried out with substrates of the same kind.

Zero-current bipotentiometric indication using two differently pretreated electrodes

A new potentiometric technique of zero-current bipotentiometry using differently pretreated platinum electrodes is described, and its application to various redox titrations discussed. The potential across the electrodes appears to be generated by differences in kinetics of the reactions occurring on the two dissimilar electrode surfaces.