Pd Doped Ag@C Core-Shell Nanocomposite for Electrochemical Sensitive Determination of Bisphenol A

In this work, core–shell structured nanocomposites consisting of Pd doped Ag@C were synthesized by impregnation–reduction method. Then, sensing electrodes were fabricated by modifying Pd/Ag@C core-shell nanoparticles on screen-printed electrodes (SPE) for electrochemical determination of bisphenol A (BPA). The composition and morphology of nanocomposites were characterized by scanning electron microscopy, transmission electron microscopy, X ray diffraction and energy-dispersive X-ray spectroscopy. The electrochemical response characteristics of nanocomposites to BPA was investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The results indicated that, compared with Ag@C and Pd/C, Pd/Ag@C nanocomposite shows greater catalytic activity to the oxidation of BPA due to the synergistic effect of Pd and Ag. Among the four synthesized Pd/Ag@C-x (x=1-4) nanomaterials, the Pd/Ag@C-3 exhibits the best sensing performance toward the sensitive detection of BPA. The linear range for BPA determination was from 8.0×10-8 M to 1.5×10-5M with a detection limit of 1.0×10-8 M. A less than 9% oxidation peak current change was observed on the determination of BPA using Pd/Ag@C-3/SPE when added different interfering species into the BPA solution. The oxidation peak current attenuation of BPA on Pd/Ag@C-3/SPE within five weeks was found to be less than 3.6%.

Electrochemical evaluation of the antioxidant capacity of natural compounds on glassy carbon electrode modified with guanine-, polythionine-, and nitrogen-doped graphene

An electrochemical sensor based on guanine-, polythionine-, and nitrogen-doped graphene modified glassy carbon electrode (G/PTH/NG/GCE) was fabricated and applied for antioxidant capacity evaluation of natural compounds and complexes in electrochemical method since natural sources of active compounds exhibited various antioxidant activities. When the antioxidants existed in the system, the generated hydroxyl radicals were scavenged and the damage to guanine immobilized on the electrode was reduced less resulting in the oxidation peak current increased in square wave voltammetry. After the modifications of polythionine- and nitrogen-doped graphene, the oxidation peak current was improved. The effects of pH, incubation time, and concentrations of guanine and Fe2+ ions on the performances of the electrode were investigated and optimized. The G/PTH/NG/GCE showed good linearity, reproducibility, and storage stability for antioxidant capacity evaluation of ascorbic acid at the optimum conditions. The antioxidant capacities of three flavonoids and three plant extracts were measured using the G/PTH/NG/GCE and DPPH methods. Myricetin showed the highest antioxidant capacity in both electrochemical and DPPH methods. The proposed G/PTH/NG/GCE exhibited easy fabrication procedure, rapid detection time, and low cost for the detection of antioxidant activity for various kinds of samples.

Electrochemical antioxidant screening and evaluation based on guanine and chitosan immobilized MoS2 nanosheet modified glassy carbon electrode (guanine/CS/MoS2/GCE)

In this study, an electrochemical biosensor based on guanine and chitosan immobilized MoS2 nanosheet modified glassy carbon electrode (guanine/CS/MoS2/GCE) was developed and employed for antioxidant screening and antioxidant capacity evaluation. The oxidation peak current of guanine was improved and nearly tripled after modifications of chitosan and MoS2 nanosheet. The immobilized guanine could be damaged by hydroxyl radicals generated in Fenton solution. However, in the presence of antioxidants, the guanine was protected and the oxidation peak current of guanine increased. This process mimics the mechanism of antioxidant protection in human body. The factors affecting preparation of sensor and detection of antioxidant capacity were optimized. At the optimum conditions, the guanine/CS/MoS2/GCE showed wide linear range, low detection limit, satisfactory reproducibility and stability for detection. Ascorbic acid was used as a model antioxidant to evaluate the antioxidant capacity. A good linearity was observed with a correlation coefficient of 0.9959 in the concentrations between 0.5 and 4.0 mg L-1. The antioxidant capacities of three flavonoids were also tested and the rank of antioxidant capacities was ascorbic acid (51.84%), quercetin (45.82%), fisetin (34.39%) and catechin (16.99%). Due to the rapid measurement and low cost, this sensor could provide an available sensing platform for antioxidant screening and evaluation.

Sensitive Voltammetric Sensor for Tryptophan Detection by Using Polyvinylpyrrolidone Functionalized Graphene/GCE

In this paper, an electrochemical method for the measurement of tryptophan (Trp) was developed based on a glassy carbon electrode modified with polyvinylpyrrolidonefunctionalized graphene (PVP-GR)/glassy carbon electrode (GCE). In 0.1 M phosphate buffer solution (PBS, pH = 2.2), compared with bare GCE, PVP/GCE, and GR/GCE, the oxidation peak current of Trp increased dramatically at PVP-GR/GCE. The oxidation mechanism of Trp on the PVP-GR/GCE was discussed and the experimental conditions were optimized. Under the best experimental conditions, the oxidation peak current of Trp was proportional to its concentration in the range of 0.06 µM–10.0 µM and 10.0–100.0 µM, and the limit of detection (LOD) was 0.01 µM (S/N = 3). The target modified electrode with excellent repeatability, stability and selectivity, was successfully applied to detectTrp in drugs and biological samples.

AuPt Nanoparticles Clusters on MWCNTs with Enhanced Electrocatalytic Activity for Methanol Oxidation

AuPt nanoparticles clusters (NPCs) were electrodeposited on multiwalled carbon nanotubes (MWCNTs). The as-prepared AuPt NPCs@MWCNTs nanocomposites exhibited considerably enhanced electrocatalytic activity than Pt NPs@MWCNTs for methanol oxidation in acid medium. In comparison with Pt NPs@MWCNTs, a remarkable resistance to CO poisoning and a higher If/Ib value (the ratio of the forward scan oxidation peak current (If) and reverse scan oxidation peak current (Ib)) was achieved by AuPt NPCs@MWCNTs electrocatalyst, which is attributable to the unique NPCs nanostructure with enlarged electrochemical active surface areas. These results demonstrated the potential of AuPt NPCs@MWCNTs, which can be considered as an efficient electrocatalyst for methanol oxidation in direct methanol fuel cells.

Deteksi Kurkumin dan Bisdemetoksikurkumin dengan Teknik Voltammetri Menggunakan Elektrode Boron-Doped Diamond

<p>Pada penelitian ini metode deteksi kurkumin dan bisdemetoksikurkumin dikembangkan dengan teknik voltammetri siklik menggunakan elektrode <em>boron-doped diamond</em>. Voltammogram siklik kurkumin dan bisdemetoksikurkumin dalam larutan elektrolit tetrabutilamonium heksafluorofosfat (TBAPF₆)-asetonitril masing-masing menunjukkan 2 puncak oksidasi, yaitu pada potensial +0,4 V dan +1,9 V vs. Ag/AgCl untuk kurkumin, serta +0,6 V dan +2,0 V vs. Ag/AgCl untuk bisdemetoksikurkumin. Hubungan linear diperoleh antara konsentrasi kurkumin maupun bisdemetoksikurkumin dengan arus puncak oksidasinya. Hubungan linear yang diperoleh adalah <em>I</em>(µA) = 8619,9C (M) + 0,7285 (<em>R²</em>=0,9995) dan <em>I</em>(µA) = 14658C (M) + 16,388 (<em>R²</em>=0,9299) berturut-turut untuk kurkumin puncak pertama dan kedua, serta <em>I</em>(µA) = 7953,2C (M) + 5,3977 (<em>R²</em>=0,9871) dan <em>I</em>(µA) = 5807,7 C (M) + 7,7616 (<em>R²</em>=0,9981) untuk bisdemetoksikurkumin puncak pertama dan kedua. Aplikasi metode yang dikembangkan terhadap sampel buatan yang mengandung campuran kurkumin dan bisdemetoksikurkumin menghasilkan 3 puncak oksidasi pada potensial +0,3 V, +1,2 V, dan +2,0 V vs Ag/AgCl mengindikasikan terjadinya tumpang tindih antara puncak kurkumin dan BDMC serta pergeseran puncak oksidasi. Nilai presisi pengukuran dengan metode yang dikembangkan ialah 15,86 dan 15,15% untuk kurkumin, serta 9,85 dan 31,47% untuk bisdemetoksikurkumin. Sementara nilai akurasi pengukuran ialah sebesar 96,69 dan 125,36% untuk kurkumin, serta 97,95 dan 127,54% untuk bisdemetoksikurkumin masing-masing berdasarkan puncak 1 dan 2. Hasil yang diperoleh menunjukkan performa analitik metode yang dikembangkan masih perlu ditingkatkan sebelum diaplikasikan untuk analisis kuantitatif.</p><p align="left"><strong>Detection of Curcumin and Bisdemetoxycurcumin by Voltammetric Technique using a Boron-Doped Diamond Electrode.</strong> This study develops a cyclic voltammetry method for simultaneous detection of curcuminoid by using boron-doped diamond electrode. Curcumin and bisdemethoxycurcumin (BDMC) in tetrabutylammonium hexafluorophosphate (TBAPF₆)-acetonitrile as electrolyte solution showed two oxidation peaks at +0.4 V and +1.9 V for curcumin, while those for BDMC appeared at +0.6 V and +2.0 V. Reduction peaks of both standards were not observed. In the optimum conditions, this method showed linear correlation between concentration of curcumin and BDMC with it’s oxidation peak current. The equations of <em>I</em>(µA) = 8619.9(C) (M) + 0.7285 (<em>R²</em>=0,9995) and <em>I</em>(µA) = 14658(C) (M) + 16.388 (<em>R²</em>=0.9299) were obtained for curcumin, <em>I</em>(µA) = 7953.2(C) (M) + 5.3977 (<em>R²</em>=0,9871) and <em>I</em>(µA) = 5807.7(C) (M) + 7.7616 (<em>R²</em>=0.9981) for BDMC. Meanwhile, the measurement of the artificial samples containing a mixture of curcumin and BDMC showed three oxidation peaks at +0.3 V, +1.2 V, and +2.0 V. This result indicated an overlapping between curcumin and BDMC peaks and peak shifting. Precision of the developed method was expressed as percent RSD, giving value of 15.86 and 15.15% for curcumin, and 9.85 and 31.47% for BDMC. The accuracy was 96.69 and 125.36% for curcumin, meanwhile for BDMC was 97.95 and 127.54% for peak 1 and 2. The result indicated that the method required further improvement before applied for quantitative analysis.</p>

A NEW ELECTROCHEMICAL SENSOR BASED ON MODIFIED CARBON NANOTUBE-GRAPHITE MIXTURE PASTE ELECTRODE FOR VOLTAMMETRIC DETERMINATION OF RESORCINOL

Objective: A new carbon nanotube (CNT)-graphite mixture paste electrode modified by Sodium dodecyl sulfate (SDS) surfactant (SDSMCNTGMPE) was prepared and applied for sensitive electrochemical determination of resorcinol (RS).Method: Cyclic voltammetry, variable pressure scanning electron microscopy, and differential voltammetry were employed for the surface analysis of the bare CNT-graphite mixture paste electrode and SDSMCNTGMPE. Comparison between the unmodified electrode and modified electrode, the modified electrode oxidation peak current significantly improved. The effects of the pH, scan rate, and concentration of RS on the peak current were investigated.Results: Results indicated that the peak current of RS is highest in 0.2 M pH 7.0 phosphate buffer solutions and that the electrode reaction corresponds to a rate controlled process. Under optimized experimental conditions, the oxidation peak current of RS was linear over a concentration range of 2×10−6 to 1.0×10−3 M with a detection limit of 5.8×10−6 M and quantification limit of 19×10−6 M.Conclusion: The prepared sensor also shows other features such as good stability, reproducibility and repeatability. The proposed sensor exhibits good application toward the detection of RS in commercial RS lotion samples.

In situ detection of intermediates from the interaction of dissolved sulfide and manganese oxides with a platinum electrode in aqueous systems

Environmental contextDissolved sulfide results in soil acidification and subsequent contaminant leaching via oxidation processes, usually involving manganese oxides. In this work, redox processes were monitored in situ by cyclic voltammetry and HS– concentrations were semi-quantitatively determined. The method provides qualitative and semi-quantitative assessment for dissolved sulfide and its oxidation intermediates in aqueous systems. AbstractDissolved sulfide can be oxidised by manganese oxides in supergene environments, while the intermediates including S0, S2O32– and SO32– are easily oxidised by oxygen in air, resulting in some experimental errors in conventional analyses. In this work, the electrochemical behaviours of HS–, S2O32– and SO32– on a platinum electrode were studied by cyclic voltammetry and constant potential electrolysis, and in situ detection of the intermediates was conducted in aqueous systems of HS– and manganese oxides. The results showed that HS– was first oxidised to S0, and then transformed to SO42–. The peak current for the oxidation of HS– to S0 had a positive linear correlation with the used starting HS– concentration. S2O32– and SO32– were directly electrochemically oxidised to SO42–. The oxidation current peak potentials at 0, 0.45 and 0.7V were respectively observed for HS–, S2O32– and SO32– at pH 12.0. Cyclic voltammetry was conducted to monitor the redox processes of HS– and manganese oxides. The oxidation peak current of HS– to S0 decreased, and that of S2O32– to SO42– was observed to increase as the reaction proceeded. The rate of the decrease of the oxidation peak current of HS– indicated that the oxidation activity followed the order of birnessite>todorokite>manganite.

A Novel Electrochemical Method for Protionamide Determination Based on Its Interaction with Alizarin Red S

The interaction of protionamide with alizarin red S (ARS) and its analytical application were carefully investigated in this contribution. The interaction conditions were carefully studied and optimized by cyclic voltammetry. Under the optimum conditions, the cyclic voltammetry curve of ARS showed an oxidation peak with the peak potential of 0.57 V. After the addition of protionamide to the ARS solution, the peak potential was negatively moved, and meanwhile the oxidation peak current decreased apparently to the concentration of protionamide and then a new method for the protionamide determination was established. The linear equation between the decreasing current (Δip) and protionamide concentration was got as Δip (μA) = 0.01514C(mg/L) −0.01553 (n=9; r=0.991)with the linear range of 10.0~50.0 mg/L, and the detection limit (3σ) was got as 8.25 μg/mL. The effects of coexisting substances on the determination were carefully investigated and the protionamide artificial and tablet samples were detected with satisfactory results.

The effect of acidity, hydrogen bond catalysis and auxiliary electrode reaction on the oxidation peak current for dopamine, uric acid and tryptophan

Dopamine was oxidized at the 316L-PAIUCPE, while oxygen dissolved in the solution was reduced at the cathode (Pt). The H+released in the anode reaction compensated for H+consumed in the cathode reaction. The effect of the acidity on the degree of anode–cathode reaction was explored in detail.