Electroanalytical Parameters Research Articles

Anodized Edge-plane pyrolytic graphite for electroanalysis of pantoprazole in tablet dosage forms and human urine samples

Electroanalytical parameters of different graphitic carbon-based electrode materials were compared to select the best one for the pantoprazole electroanalysis. Such parameters include sensitivity, repeatability, residual background current, and signal-to background current ratio of the analytical response and such electrodes include conventional carbon-based electrodes such as glassy carbon (GC), carbon paste, edge-plane pyrolytic graphite (EPPG), and basal-plane pyrolytic graphite electrodes and film-coated modified GC electrodes with graphitic carbon-based materials such as carbon nanotube, nanographene, carbon black and graphite powder. The EPPG electrode, after applying a simple electrochemical anodization, showed more acceptable analytical performances compared with the other electrodes. Raman spectroscopy was employed to study the surface structural changes that occurred dring the anodic activation. Calibration plot with a good linearity was obtained in the concentration range of 0.2-25 and 0.02-8.5 µM, and the detection limit was estimated to be 0.055 and 0.0041µM using cyclic voltammetry and differential pulse voltammetry techniques, respectively. Finally, the electrochemically activated EPPG electrode was used successfully for the determination of pantoprazole in tablet dosage forms and human urine samples with satisfactory results.

USE OF EXPERIMENTAL PLANNING FOR OPTIMIZATION OF A PROCEDURE FOR SIMULTANEOUS VOLTAMMETRIC DETERMINATION OF METALS Zn, Cd, Pb AND Cu FREE IN COCONUT WATER

Optimization of the main parameters of SWASV using boron-doped diamond electrode was described for the simultaneous determination of Zn, Cd, Pb and Cu free in coconut water. The values of electroanalytical parameters studied were optimized with the factorial design and center composite design. The optimized parameters for the preconcentration of metals were -1.50 V for potential, and 240 s for deposition time. For SWV, the optimized value was 11.56 mV for step potential. In addition, frequency and pulse height were defined at 100 Hz and 55 mV, respectively. Furthermore, the concentration of the supporting electrolyte (acetate buffer, pH 4.7) was optimized in 0.206 mol L-1. The optimized procedure was applied in two samples of coconut water: natural and processed. The limits of detection (LOD) obtained for Zn, Cd, Pb and Cu were 7.2; 4.4; 3.3 and 1.5 µg L-1, respectively. The concentrations of Cd and Pb were not detected. On the other hand, the values found for the concentrations of Zn and Cu were: < LOD (29 µg L-1) and (6.8 ± 0.9) µg L-1 for the natural sample; and (85.8 ± 4.2) µg L-1 and (7.7 ± 0.6) µg L-1 for the processed sample, respectively.

Simultaneous Voltammetric/Amperometric Determination of Sulfide and Nitrite in Water at BDD Electrode.

This work reported new voltammetric/amperometric-based protocols using a commercial boron-doped diamond (BDD) electrode for simple and fast simultaneous detection of sulfide and nitrite from water. Square-wave voltammetry operated under the optimized working conditions of 0.01 V step potential, 0.5 V modulation amplitude and 10 Hz frequency allowed achieving the best electroanalytical parameters for the simultaneous detection of nitrite and sulfide. For practical in-field detection applications, the multiple-pulsed amperometry technique was operated under optimized conditions, i.e., −0.5 V/SCE for a duration of 0.3 s as conditioning step, +0.85 V/SCE for a duration of 3 s that assure the sulfide oxidation and +1.25 V/SCE for a duration of 0.3 s, where the nitrite oxidation occurred, which allowed the simultaneously detection of sulfide and nitrite without interference between them. Good accuracy was found for this protocol in comparison with standardized methods for each anion. Also, no interference effect was found for the cation and anion species, which are common in the water matrix.

Speciation of Trace Levels of Chromium with Bismuth Modified Pyrolyzed Photoresist Carbon Electrodes

AbstractPyrolyzed photoresist carbon electrodes modified with bismuth (Bi‐PPCEs) were prepared and used for the determination of trace levels of chromium. In order to lower the detection limit, the choice of the supporting electrolyte concentration and electroanalytical parameters were optimized. The adsorptive cathodic stripping voltammetric determination of Cr(VI) at Bi‐PPCE was selective even in the presence in Cr(III). A detection limit of 0.1 µg L−1 was obtained after 60 s preconcentration. After oxidation with UV light and oxygen, all chromium species were oxidized to Cr(VI) and the total inorganic Cr determination is possible. Finally, Bi‐PPCE was applied to trace Cr(VI) analysis in real samples such as waste water and tap water.

Electrochemical Behavior of Nicotine at Unmodified Carbon Paste Electrode and Its Determination in a Set of Refilling Liquids for Electronic Cigarettes

AbstractIn this manuscript, a carbon paste electrode (CPE) from traditional components has been used to study the electrochemical oxidation of nicotine and its feasibility to be performed at unmodified and otherwise untreated carbon paste in an effort to propose a simple voltammetric method for the determination of nicotine in samples of refilling liquids for electronic cigarettes. As found out, irreversible oxidation of nicotine at CPE had occurred at −0.95 V vs. Ag/AgCl as a diffusion‐controlled process, when suitable pH for this redox transformation was either a neutral supporting medium (phosphate buffer, pH 7.5) or mild alkaline solution (of Britton‐Robinson buffer, pH 11). After having chosen the SWV mode and optimizing the key instrumental and electroanalytical parameters, the oxidation response of the substance of interest has been fairly proportional to concentration in the range of 50–500 µmol L−1 in phosphate buffer or even 50–1000 µmol L−1 in BrittonRobinson buffer. And if the reproducibility could substantially be improved by incorporating an effective conditioning step, the method could be applied for the determination of nicotine in real samples of refilling liquids for electronic cigarette with satisfactory results corresponding well to the values declared by manufacturer.

Effect of deglycosylation on the mediated electrocatalytic activity of recombinantly expressed Agaricus meleagris pyranose dehydrogenase wired by osmium redox polymer

The effect of deglycosylation of pyranose dehydrogenase (PDH) obtained from Agaricus meleagris (Am) and recombinantly expressed in Pichia pastoris on its electrocatalytic activity was investigated. Glycosylated (gAmPDH) and deglycosylated PDH (dgAmPDH) were immobilised on spectrographic graphite (G) simultaneously with an osmium redox polymer (Os-RP) using poly(ethylene glycol)(400) diglycidyl ether (PEGDGE) as cross-linking agent. The amperometric response to glucose, recorded at G/(Os-RP)-gAmPDH and G/(Os-RP)-dgAmPDH bioelectrodes, was optimised under flow injection conditions concerning the applied potential, enzyme loading, working pH and flow rate. The G/(Os-RP)-dgAmPDH bioelectrode is characterised by better kinetic and electroanalytical parameters compared with the G/(Os-RP)-gAmPDH bioelectrode: (i) a higher value of the maximum catalytic current density, jmax=(146.6±2.6)μAcm−2vs. jmax=(80.9±1.9)μAcm−2; (ii) a lower value of the apparent Michaelis–Menten constant, KMapp=2.4±0.1⁡mMvs. KMapp=7.5±0.3⁡mM; (iii) a higher slope of the linear domain, (43.6±1.1)μAcm−2mM−1vs. (9.74±0.16)μAcm−2mM−1. Additionally, the time dependent decay of the amperometric response to glucose shows a slightly better operational stability for the G/(Os-RP)-dgAmPDH bioelectrode than that for the G/(Os-RP)-gAmPDH. The enzyme deglycosylation induces significant changes in the order of substrate selectivity for gAmPDH and dgAmPDH.

Simultaneous/Selective Detection of Dopamine and Ascorbic Acid at Synthetic Zeolite-Modified/Graphite-Epoxy Composite Macro/Quasi-Microelectrodes

The present paper aims to miniaturize a graphite-epoxy and synthetic zeolite-modified graphite-epoxy composite macroelectrode as a quasi-microelectrode aiming in vitro and also, envisaging in vivo simultaneous electrochemical detection of dopamine (DA) and ascorbic acid (AA) neurotransmitters, or DA detection in the presence of AA. The electrochemical behavior and the response of the designed materials to the presence of dopamine and ascorbic acid without any protective membranes were studied by cyclic voltammetry and constant-potential amperometry techniques. The catalytic effect towards dopamine detection was proved for the synthetic zeolite-modified graphite-epoxy composite quasi-microelectrode, allowing increasing the sensitivity and selectivity for this analyte detection, besides a possible electrostatic attraction between dopamine cation and the negative surface of the synthetic zeolite and electrostatic repulsion with ascorbic acid anion. Also, the synthetic zeolite-modified graphite-epoxy composite quasi-microelectrode gave the best electroanalytical parameters for dopamine detection using constant-potential amperometry, the most useful technique for practical applications.

Carbon Based Electrodes Modified with Horseradish Peroxidase Immobilized in Conducting Polymers for Acetaminophen Analysis

The development and optimization of new biosensors with horseradish peroxidase immobilized in carbon nanotubes-polyethyleneimine or polypyrrole nanocomposite film at the surface of two types of transducer is described. The amperometric detection of acetaminophen was carried out at −0.2 V versus Ag/AgCl using carbon based-screen printed electrodes (SPEs) and glassy carbon electrodes (GCEs) as transducers. The electroanalytical parameters of the biosensors are highly dependent on their configuration and on the dimensions of the carbon nanotubes. The best limit of detection obtained for acetaminophen was 1.36 ± 0.013 μM and the linear range 9.99–79.01 μM for the HRP-SWCNT/PEI in GCE configuration. The biosensors were successfully applied for the detection of acetaminophen in several drug formulations.

Determination of lead and cadmium in seawater using a vibrating silver amalgam microwire electrode

Silver amalgamated electrodes are a good substrate to determine lead (Pb) and cadmium (Cd) in seawater because they have properties similar to mercury but without the free mercury (Hg). Here a silver amalgamated microwire (SAM) electrode is optimised for the determination of Pb and Cd in coastal waters and uncontaminated ocean waters. The SAM was vibrated during the deposition step to increase the sensitivity, and electroanalytical parameters were optimised. The Hg coating required plating from a relatively concentrated (millimolar) solution, much greater (500×) than used for instance to coat glassy carbon electrodes. However, the coating on the ex situ amalgamated electrode was found to be stable and could be used for up to a week to determine trace levels of Pb in seawater of natural pH. The limit of detection square-wave ASV (50Hz) using the pre-plated SAM electrode was 8pM Pb using a 1-min plating time at pH 4.5. The limit of detection in pH 2 seawater was 4pM using a 5-min plating time, and it was 12pM using a 10-min plating time at natural pH in the presence of air, using a square-wave frequency of 700Hz. The vibrating SAM electrode was tested on the determination of Pb in reference seawater samples from the open Atlantic (at the 20pM level), Pacific, and used for a study of Pb in samples collected over 24h in Liverpool Bay (Irish Sea).

Differential Pulse Voltammetric Studies on Lamivudine: An Antiretroviral Drug

Lamivudine (also known as 3TC) is a dideoxynucleoside analogue, which undergoes intracellular phosphorylation in the putative active metabolite, lamivudine triphosphate. Lamivudine triphosphate prevents HIV replication by competitively inhibiting viral reverse transcriptase. Lamivudine has been extensively used in the treatment of HIV patients owing to its antiretroviral activity. For the determination of lamivudine in pharmaceuticals, an analytical methodology using voltammetry was developed. Lamivudine was reduced at a hanging mercury drop electrode (HMDE) at –1.16 V vs Ag/AgCl at pH 2.0. The influence of electroanalytical parameters such as scan rate (20 mV.s–1), amplitude (50 mV), nature of the support electrolyte (Clark-Lubs), and pH (2.0) on the voltammetric signal was optimized. Under these optimized conditions, the method had been validated using pharmaceutical formulations. The lamivudine peak current varied linearly with its concentration from 1.15 to 10.40 mg.L–1, detection and determination limits of 0.46 and 1.0 mg.L–1, respectively, and recovery of 95.15% with a relative standard deviation of 1.10%.

Silver-functionalized carbon nanofiber composite electrodes for ibuprofen detection

The aim of this study is to prepare and characterize two types of silver-functionalized carbon nanofiber (CNF) composite electrodes, i.e., silver-decorated CNF-epoxy and silver-modified natural zeolite-CNF-epoxy composite electrodes suitable for ibuprofen detection in aqueous solution. Ag carbon nanotube composite electrode exhibited the best electroanalytical parameters through applying preconcentration/differential-pulsed voltammetry scheme.

Magnetic and Electroanalytical Properties of Electrodeposited FePtP Films

FePtP films have been electrodeposited from a stable bath containing urea. By adjusting the current density and solution composition one can control the composition of the film. Effect of concentration of urea was studied. Vibration sample magnetometric studies indicate that urea has favourable impact on the magnetic properties of these films. Electroanalytical parameters like reduction potential and current for the FePtP deposition were studied using cyclic voltammeter. Reasons for variation in magnetic and electroanalytical properties are discussed.

Potentiometric sensors with membranes based on ionic liquid tetradecylammonium triethylammonio-closo-dodecaborate

Polymer compositions based on the ionic liquid tetradecylammonium triethylammonium-closododecaborate (TTCD) are proposed as the main components of membranes of potentiometric sensors (ion-selective electrodes) for determining ions [B12H11N(C2H5)3]−. Two types of polymer compositions are considered: conventional, polyvinyl chloride (PVC)-liquid ion-exchanger (solution of TTCD in o-nitrophenyl octyl ether) and another, PVC-TTCD (ionophore-plasticizer). The optimal composition of membranes for both types of electrodes are proposed, and their main electroanalytical parameters, such as selectivity, effect of pH, range of linear response, reproducibility, and stability of potential, were measured. A comparative analysis of the electroanalytical parameters of potentiometric sensors with membranes of two types is given. The detection limits for the electrodes of types I and II are 9 × 10−7 and 4 × 10−7 M. It is shown that [B12H11N(C2H5)3]− anions can be determined by potentiometric titration with indicator electrodes of different types.

Electroanalysis of Trace Inorganic Arsenic with Gold Nanoelectrode Ensembles

AbstractThe results of a study on the determination of trace levels of arsenic with nanoelectrode ensembles (NEEs) are reported. In order to lower the detection limit and to increase the number of performable analysis for each NEE, the right choice of the supporting electrolyte concentration and electroanalytical parameters were optimized. The electrochemical behavior of As(III) at NEEs was studied at first by cyclic voltammetry, while trace concentrations of As(III) were determined by anodic stripping square wave voltammetry. The method is characterized by a detection limit as low as 5 ng/L (65 pM) after 3 min preconcentration at −0.4 V. Finally, NEEs were applied to trace As analysis in real samples such as certified seawater samples.

Glassy carbon electrodes modified with hemin-carbon nanomaterial films for amperometric H2O2 and NO2− detection

In this work a new chemical sensor for the H2O2 and nitrite amperometric detection was assembled, using a glassy carbon (GC) bare electrode modified by two different nanocomposite materials. The nanocomposite films were prepared by casting a functionalised carbon nanofiber (CNF-COOH) and single-walled carbon nanotubes (SWCNT-OH, for comparison) on the glassy carbon electrode surface; then an iron(III) protoporphyrin IX (Fe(III)P) was adsorbed on these modified surfaces. A morphological investigation of the nanocomposite layers was also carried out, using the Scanning Electron Microscopy (SEM). The electrochemical characterization, performed optimising several electro-analytical parameters (such as different medium, pH, temperature, scan rate, and potential window), demonstrated that the direct electrochemistry of the Fe(III)P/Fe(II)P redox couple involves 1e−/1H+ process. A kinetic evaluation of the electron-transfer reaction mechanism was also carried out, demonstrating that the heterogeneous electron transfer rate constant resulted higher at CNF/hemin/GC biosensor than that evaluated at SWCNT/hemin/GC modified electrode. Finally, the electrocatalytic activity toward the H2O2 reduction was also demonstrated for both sensors but better results were observed working at CNF/hemin/GC modified electrode, especially in terms of an extended linearity (ranging from 50 to 1000μM), a lower detection limit (L.O.D.=3σ) of 2.0×10−6M, a higher sensitivity of 2.2×10−3AM−1cm−2, a fast response time (9s), a good reproducibility (RSD%<1, n=3) and operational stability. In addition, a nitrite electrocatalytic effect was also demonstrated only at CNF/hemin/GC modified electrode, showing an extended linearity (ranging from 5.0×10−3 to 2.5×10−1M), a lower detection limit (L.O.D.=3σ) of 3.18×10−4M, a higher sensitivity of 1.2×10−2AM−1cm−2, a fast response time of 10s, a good reproducibility (RSD% <1, n=3) and finally a good operational stability.

Ion-selective electrodes for the determination of closoborate anions

Ion-selective electrodes are proposed on the basis of tetradecylammonium salts for determining [B12H12]2−, [B10H10]2−, and [B10Cl10]2−closoborate anions. Their basic electroanalytical parameters, selectivity, linear response range, detection limit, potential stability, and the pH effect on electrode indications are estimated. The closoborate anions can be arranged in the following series by the selectivity of their determination: [B10Cl10]2− ≫ [B12H12]2− > [B10H10]2−.

Ion-selective electrode for the determination of dimethylbenzylammonium ions

A sensor is proposed for the direct potentiometric determination of dimethylbenzylammonium in acid and neutral aqueous solutions. The sensor membrane is made of a polymeric composition on the basis of polyvinylchloride containing an ion associate and a solvent as a plasticizer. Salts of the tetraphenylborate anion and its derivatives served as ionophores. Basic electroanalytical parameters of the developed potentiometric sensors are studied and the pH range of their possible application is determined. The developed sensor is used as a reference electrode in the potentiometric titration of dimethylbenzylammonium with tetraphenylborate anions.

Electroanalytical parameters of carbon nanotubes are inferior with respect to well defined surfaces of glassy carbon and EPPG

This paper reports on the electroanalytical parameters of single – (SWCNT), double – (DWCNT) and multi-walled carbon nanotubes (MWCNT) compared with the standard, well defined surfaces of glassy carbon (GC) and edge-plane pyrolytic graphite (EPPG) electrodes. Such parameters include repeatability, sensitivity and linearity of the analytical response, and selectivity of the materials using differential pulse voltammetry in two important biological compounds; uric acid and guanine. In terms of repeatability, all CNTs demonstrate extremely poor RSD values; only those for GC and EPPG are deemed analytically acceptable. The final parameter, selectivity, demonstrated that in both uric acid and guanine, some CNTs showed the lowest peak width; however they had an exceptionally high RSD compared with GC. One might wonder whether it is worth using CNTs at all when glassy carbon can give considerably more consistent results. This is an especially pressing issue for the real world, such as in industrial applications of electrochemical sensors, where the reliability is absolutely crucial.

Electrochemical Determination of Diclofenac Sodium in Aqueous Solution on Cu‐Doped Zeolite‐Expanded Graphite‐Epoxy Electrode

AbstractThe electrochemical oxidation and determination of diclofenac sodium (DCF) at Cu‐doped zeolite‐modified expanded graphite‐epoxy composite (CuZEGE) electrode was evaluated for a new alternative of quantitative determination of sodium diclofenac in aqueous solutions. Cyclic voltammetry was used to characterize the electrochemical behaviour of the electrode in the presence of diclofenac sodium in a 0.1 M NaOH supporting electrolyte. This modified electrode exhibited electrocatalytic effect towards sodium diclofenac oxidation, allowing its determination in aqueous solution. The linear dependence of the current versus diclofenac concentration was obtained using cyclic voltammetry, chronoamperometry, differential‐pulsed voltammetry. The limit of detection for DCF reached by direct analysis on CuZEGE is from 2×10−5 to 3×10−7 M in relation with used technique and the potential value. Substantial enhancement of the electroanalytical parameters, e.g. the limit of detection of 5×10−8 M. for the determination of DCF at CuZEGE electrode was reached by applying a chemical preconcentration step prior to voltammetric quantification.

Determination of Zidovudine in Pharmaceuticals by Differential Pulse Voltammetry

The zidovudine (AZT) has been extensively used in the treatment of HIV patients due to its antiretroviral activity. The quality control of this substance in drugs is of outstanding importance to public health because of its undesirable effects and short therapeutic interval. For the determination of AZT in pharmaceuticals, an alternative analytical methodology using voltammetry was developed. The reduction of AZT at a hanging mercury drop electrode (HMDE) is at −0.96 V at pH 8.0. The influence of electroanalytical parameters, such as scan rate (20 mV/s), amplitude (50 mV), nature of the support electrolyte (phosphate buffer), and pH (8.0) on the voltammetric signal, was optimized. Under these optimized conditions, the AZT peak current varied linearly with its concentration from 0.25 to 1.25 mg/L (1 to 5 μM). Detection and determination limits of 0.0025 and 0.025 mg/L, respectively, and recovery of 99.88% with a relative standard deviation of 0.95% were obtained. The results obtained using this methodology in analyzing drugs containing AZT were compared favorably with those obtained by technique liquid chromatography as recommended by The United States Pharmacopoeia.