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Voltammetry
Kinds of Voltammetry Terms modified by Voltammetry Selected AbstractsDetermination of Diazepam, Temazepam and Oxazepam at the Lead Film Electrode by Adsorptive Cathodic Stripping VoltammetryELECTROANALYSIS, Issue 17-18 2010Katarzyna Tyszczuk Abstract The determination of psychoactive 1,4-benzodiazepine drugs is of relevant interest in clinical, biomedical areas. Therefore a highly sensitive and simple voltammetric method for the determination of temazepam, diazepam and oxazepam at an in situ plated lead film electrode was developed. The method was successfully applied to the determination of diazepam and temazepam in pharmaceutical formulations with minimum sample manipulation and oxazepam in human urine samples without any separation steps. The determinations of oxazepam in human urine samples were performed in a flow system. Therefore a previous extraction procedure was not necessary to separate the active compound before its determination. [source] Elimination Procedure as a Novel and Promising Mathematical Approach in Voltammetric MethodsELECTROANALYSIS, Issue 17-18 2010Nuria Serrano Abstract In the contribution, it has been demonstrated that Elimination Voltammetry with Linear Scan (EVLS) introduces an enhancement of the linear sweep and/or cyclic voltammetric results, and provides information about the type of the currents involved in the considered process. An extension of EVLS has been developed for any combination of scan rates (integers) for six elimination functions that are capable of conserving or eliminating of some voltammetric current components. Simple procedure to obtain the necessary coefficients from the chosen scan rates has been reported. In addition, the calculation and discussion of the relative error of elimination function (REEF) have been presented. The verification of the presented calculations has been done by studying different ratios of scan rates for reduction and oxidation processes of Cd(II) at a hanging mercury drop electrode (HMDE). [source] Study of Electrochemical Processes with Coupled Homogeneous Chemical Reaction in Differential Pulse Voltammetry at Spherical Electrodes and MicrohemispheresELECTROANALYSIS, Issue 16 2010Eduardo Laborda Abstract Homogeneous chemical reactions coupled to oxidation-reduction processes at electrode surfaces are very common in electrochemistry. In this paper we cope with the application of Differential Pulse Voltammetry at spherical electrodes and microhemispheres for the study of this kind of systems. Analytical expressions are deduced from which the influence of the different experimental variables is examined. Several diagnostic criteria for elucidation of the reaction mechanism from DPV peak parameters are given, as well as working curves for extraction of the kinetic rate constants of the chemical reaction. [source] As(III) Determination in the Presence of Pb(II) by Differential Alternative Pulses VoltammetryELECTROANALYSIS, Issue 15 2010Roumen Zlatev Abstract Differential Alternative Pulses Voltammetry (DAPV), introduced by the authors earlier, was applied with HMDE for direct As(III) determination in the presence of Pb(II) in natural water without sample pretreatment. Distinguishable peaks of As(III) and Pb(II) were registered in 1,M HCl supporting electrolyte at a concentration ratio as high as 1,:,6, while complete peak overlapping occurs applying DPP at any concentration ratio at the same experimental conditions. In-situ As(III) determinations in the presence of Pb(II) in contaminated ground waters in Mexico were performed, using especially designed disposable safe mercury drop electrodes. [source] Advances in the Study of Ion Transfer at Liquid Membranes with Two Polarized Interfaces by Square Wave VoltammetryELECTROANALYSIS, Issue 14 2010A. Molina Abstract A general analytical expression has been deduced for the I/E response of the square wave voltammetry corresponding to ion transfer processes in systems with two liquid/liquid polarized interfaces. This expression has been evaluated through the experimental study of a series of quaternary ammonium cations and metal chloro complex anions. We have found that systems with two liquid/liquid polarizable interfaces present the striking advantage that the difference between peak potentials of square wave voltammograms of cations and anions with similar standard ion transfer potential is much greater than in systems with a single polarizable one. [source] Electrode Modified with Cobalt Cyclohexylbutyrate for the Determination of Low Molecular Weight Thiol Group Bearing Compounds Using Catalytic Stripping VoltammetryELECTROANALYSIS, Issue 3 2010Petr Jakubec Abstract Glassy carbon electrode, modified with cobalt(II) cyclohexylbutyrate monohydrate immobilized in polystyrene matrix is usable for determination of thiol group bearing compounds both in oxidized and reduced forms using catalytic stripping voltammetry. The measurements are carried out in acetate buffer (pH,4.3) containing Tween 40. After the accumulation step at ,850,mV vs. Ag/AgCl a peak at ,170,mV is observed on linear sweep voltammogram, the height of which is proportional to the concentration of added thiol. Addition of carbon nanotubes into polystyrene film enhances the sensitivity of the modified electrode. The detection limit is 1×10,6,mol dm,3 for all studied thiols. The electrode can be regenerated by exposing it to the potential between 300,600,mV. [source] Stripping Voltammetry at Microdisk Electrode Arrays: TheoryELECTROANALYSIS, Issue 24 2009Abstract Anodic stripping voltammetry (ASV) is an extremely powerful tool for detection of metal ions in solution through a two step process of preconcentration of the metal at the electrode surface, followed by electrodissolution. The second phase produces an electroanalytical response proportional to the amount of material deposited in the first phase. This paper utilizes theory to explore the electrochemical signals produced when considering ASV at a microelectrode or ultramicroelectrode arrays. The theory outlined is applicable mostly to thin mercury film absorption and metal adsorption. [source] Fabrication of a Sensitive Cholesterol Biosensor Based on Cobalt-oxide Nanostructures Electrodeposited onto Glassy Carbon ElectrodeELECTROANALYSIS, Issue 24 2009Abdollah Salimi Abstract Electrodeposited cobalt oxide (CoOx) nanomaterials are not only used for immobilization of cholesterol oxidase (ChOx) but also as electron transfer mediator for oxidation of H2O2 generated in the enzymatic reaction. Voltammetry and flow injection analysis (FIA) were used for determination of cholesterol. FIA determination of cholesterol with biosensors yielded a calibration curve with the following characteristics: linear range up to 50,,M, sensitivity of 43.5,nA ,M,1 cm,2 and detection limit of 4.2,,M. The apparent Michaelis-Menten constant and the response time of the biosensor are 0.49,mM and 15,s, respectively. This biosensor also exhibits good stability, reproducibility and long life time. [source] The Electrochemical Behavior of Nitrazepam at a Screen-Printed Carbon Electrode and Its Determination in Beverages by Adsorptive Stripping VoltammetryELECTROANALYSIS, Issue 19 2009Natasha Abstract The cyclic voltammetric behavior of nitrazepam was investigated at screen-printed carbon electrodes over the range ,1.5,V to +1.5,V. Two reduction peaks were observable on the negative scan, at ,0.7,V, and ,1.2,V using pH,6 buffer. On the return scan a single oxidation peak was obtained at ,0.05,V. For quantitative analysis of beverages, we developed an anodic adsorptive stripping voltammetric method which required only dilution with buffer. The identification of nitrazepam and flunitrazepam could be achieved using cyclic voltammetry. [source] Renewable Ceramic (TiN) Ring Electrode in Stripping Voltammetry.ELECTROANALYSIS, Issue 16 2009Determination of Pb(II) Without Removal of Oxygen Abstract Characteristic features of the process of Pb(II) reduction and oxidation at a renewable ceramic ring electrode (RCRE) were studied by stripping voltammetry. The main constituents of the RCRE are: a specially constructed TiN ring electrode, a silver sheet used as silver counter/quasi-reference electrode and a silicon O-ring are fastened together in a polypropylene body. The renovation of this electrode is carried out through mechanical removal of solid contaminants and electrochemical activation in the electrolyte which fills the RCRE body. The optimal measurement conditions, composition of supporting electrolyte and procedures of the electrode activation were selected. The measurements were carried out from nondeaerated solutions. As shown on selected examples, RCRE exhibits good performance in underpotential deposition stripping voltammetry (UPD-SV) applied for the determination of lead(II) in synthetic solutions with and without surfactants and in certified reference materials. The peak current is proportional to the concentration of lead(II) over the range 2×10,9,1×10,7,mol L,1, with a 3, detection limit of 1×10,9,mol L,1 with an accumulation time of 30,s. The obtained results showed good reproducibility, (RSD=2,5%; n=5) and reliability. [source] Square-Wave Voltammetry as a Tool for Investigation of Doxorubicin Interactions with DNA Isolated from Neuroblastoma CellsELECTROANALYSIS, Issue 3-5 2009Dalibor Huska Abstract We investigated ethidium bromide intercalation into DNA molecule as a model system to test square-wave voltammetry (SWV) as a suitable method for this purpose We found that 0.13,,g EtBr intercalates into 1,,g dsDNA in average. Further, SWV was utilized for investigation of doxorubicin-DNA interactions. Intercalated doxorubicin reduced observed dsDNA cytosine and adenine (CA) signal, but also provided new signal called DOXO at ,0.35,V. This phenomenon was observed at both single and double stranded DNA standards. We also employed adsorptive transfer stripping technique coupled with SWV for study of doxorubicin-DNA interactions. Doxorubicin intercalation into dsDNA molecule adsorbed onto working electrode was fast, because we observed considerable changes in CA and DOXO signals after 360,s. Finally, we detected doxorubicin-DNA adducts formed in doxorubicin treated neuroblastoma cells. [source] Cathodic Stripping Voltammetry of Uracil.ELECTROANALYSIS, Issue 1 2009Experimental, Theoretical Study Under Conditions of Square-Wave Voltammetry Abstract The electrode mechanism of uracil at a hanging mercury drop electrode (HMDE) is studied under cathodic stripping square-wave voltammetric mode owing to the cathodic dissolution of a sparingly soluble compound formed between the electrode material and uracil. The experimental results can be partly explained in the light of the recent theory for cathodic stripping processes of insoluble salts under conditions of square-wave voltammetry. It is established that the electrode reaction is complicated by attractive interactions between the deposited species of the insoluble compound. To elucidate the electrode mechanism completely a novel theoretical model is developed considering adsorption of the reacting analyte and lateral interactions between species of the insoluble compound. With the help of numerical simulations the effect of interactions is studied in detail, emphasizing the properties of the response that can be used as diagnostic criteria for recognition of the type of interaction forces. Theoretically predicted voltammetric properties agree well with the experimental results enabling clarification of the complex electrode mechanism of uracil at HMDE. [source] Simultaneous Quantitative Determination of Cadmium, Lead, and Copper on Carbon-Ink Screen-Printed Electrodes by Differential Pulse Anodic Stripping Voltammetry and Partial Least Squares RegressionELECTROANALYSIS, Issue 23 2008Michael Cauchi Abstract Water is a vital commodity for every living entity on the planet. However, water resources are threatened by various sources of contamination from pesticides, hydrocarbons and heavy metals. This has resulted in the development of concepts and technologies to create a basis for provision of safe and high quality drinking water. This paper focuses on the simultaneous quantitative determination of three common contaminants, the heavy metals cadmium, lead and copper. Multivariate calibration was applied to voltammograms acquired on in-house printed carbon-ink screen-printed electrodes by the highly sensitive electrochemical method of differential pulse anodic stripping voltammetry (DPASV). The statistically inspired modification of partial least squares (SIMPLS) algorithm was employed to effect the multivariate calibration. The application of data pretreatment techniques involving range-scaling, mean-centering, weighting of variables and the effects of peak realignment are also investigated. It was found that peak realignment in conjunction with weighting and SIMPLS led to the better overall root mean square error of prediction (RMSEP) value. This work represents significant progress in the development of multivariate calibration tools in conjunction with analytical techniques for water quality determination. It is the first time that multivariate calibration has been performed on DPASV voltammograms acquired on carbon-ink screen-printed electrodes. [source] The Influence of Electrode Porosity on Diffusional Cyclic VoltammetryELECTROANALYSIS, Issue 22 2008Denis Menshykau Abstract A simple generic model to predict the influence of electrode porosity on the cyclic voltammetric response of an electrode is presented. The conditions under which deviation from the behavior of a perfectly flat, planar electrode can be expected are predicted. The scope for misinterpretation when conventional flat electrode theory is applied to porous electrodes is highlighted, especially in respect to the extraction of electrode kinetic parameters and the influence of ,electrocatalysis'. [source] Electroanalytical Determination of Promethazine Hydrochloride in Pharmaceutical Formulations on Highly Boron-Doped Diamond Electrodes Using Square-Wave Adsorptive VoltammetryELECTROANALYSIS, Issue 18 2008Francisco, Wirley Abstract The electrochemical oxidation of promethazine hydrochloride was made on highly boron-doped diamond electrodes. Cyclic voltammetry experiments showed that the oxidation mechanisms involved the formation of an adsorbed product that is more readily oxidized, producing a new peak with lower potential values whose intensity can be increased by applying the accumulation potential for given times. The parameters were optimized and the highest current intensities were obtained by applying +0.78,V for 30 seconds. The square-wave adsorptive voltammetry results obtained in BR buffer showed two well-defined peaks, dependent on the pH and on the voltammetric parameters. The best responses were obtained at pH,4.0, frequency of 50,s,1, step of 2,mV, and amplitude of 50,mV. Under these conditions, linear responses were obtained for concentrations from 5.96×10,7 to 4.76×10,6,mol L,1, and calculated detection limits of 2.66×10,8,mol L,1 (8.51,,g L,1) for peak 1 and of 4.61×10,8,mol L,1 (14.77,,g L,1) for peak 2. The precision and accuracy were evaluated by repeatability and reproducibility experiments, which yielded values of less than 5.00% for both voltammetric peaks. The applicability of this procedure was tested on commercial formulations of promethazine hydrochloride by observing the stability, specificity, recovery and precision of the procedure in complex samples. All results obtained were compared to recommended procedure by British Pharmacopeia. The voltammetric results indicate that the proposed procedure is stable and sensitive, with good reproducibility even when the accumulation steps involve short times. It is therefore very suitable for the development of the electroanalytical procedure, providing adequate sensitivity and a reliable method. [source] Simultaneous Determination of Nickel and Cadmium by Adsorptive Stripping VoltammetryELECTROANALYSIS, Issue 12 2008B. Gholivand Abstract A sensitive and fast method for the simultaneous determination of trace amounts of nickel and cadmium in real samples has been described using differential pulse adsorptive stripping voltammetry (DPASV) by adsorptive accumulation of the N,N,-bis(salicylaldehydo)4-carboxyphenylenediamine (BSCPDA),complex on the hanging mercury drop electrode (HMDE). As supporting electrolyte 0.02,mol L,1 ammonia buffers containing ligand has been used. Optimal analytical conditions were found to be: BSCPDA concentration of 42,,M, pH,9.6 and adsorption potential at ,50,mV versus Ag/AgCl. With an accumulation time of 20,s, the peaks current are proportional to the concentration of nickel and cadmium over the 1,180, and 0.5,200,ng mL,1 with detection limits of 0.06 and 0.03,ng mL,1 respectively. The sensitivity of method for determination of nickel and cadmium were obtained 0.54 and 0.98,nA mL ng,1, respectively. The procedure was applied to simultaneous determination of nickel and cadmium in some real and synthetic artificial samples with satisfactory results. [source] Renewable Copper and Silver Amalgam Film Electrodes of Prolonged Application for the Determination of Elemental Sulfur Using Stripping VoltammetryELECTROANALYSIS, Issue 7 2008Robert Piech Abstract New, renewable copper (Hg(Cu)FE) and silver (Hg(Ag)FE) based amalgam film electrodes applied for the determination of elemental sulfur using differential pulse cathodic stripping voltammetry are presented. With surface areas adjustable from 1 to 12,mm2, both electrodes are characterized by very good surface reproducibility (,2%) and long-term stability (a few thousand measurement cycles). The mechanical refreshing of the amalgam film takes about 1,2 seconds. The effects of various factors such as instrumental parameters and the supporting electrolyte composition were optimized. Interferences from sulfides are easily removed by the addition of acid, and bubbling with argon, for Hg(Ag)FE. In the case of Hg(Cu)FE, sulfides did not interfere. The calibration graph is linear within the studied range from 16,ng L,1 to 4.8,,g L,1 for Hg(Cu)FE, and up to 6.4,,g L,1 for Hg(Ag)FE (tacc=15,s). The correlation coefficients for the two electrodes were at least 0.997. The detection limits for a low concentration of S(0) and tacc=60,s are as low as 14,ng L,1 for Hg(Cu)FE and 4,ng L,1 for Hg(Ag)FE. The proposed method was successfully applied and validated by studying the recovery of S(0) from spiked river water. [source] Electrochemical Detection of Arsenic(III) in the Presence of Dissolved Organic Matter (DOM) by Adsorptive Square-Wave Cathodic Stripping Voltammetry (Ad-SWCSV)ELECTROANALYSIS, Issue 4 2008Tsanangurayi Tongesayi Abstract This study has demonstrated that As(III) can be electrochemically detected and quantified in the presence of fulvic acid (FA) and dissolved organic matter (DOM). This eliminates the need to remove DOM prior to measurement of As(III) in environmental samples. Apart from reducing analysis time and the cost of the analysis, this could be potentially useful for the development of electrochemical methods for the detection and measurement of As(III) onsite. Both synthetic samples in which FA was added and a real sample with 22.16,mg/L total organic carbon (TOC) were analyzed. [source] Stripping Voltammetry of Cerium(IIl) with a Chemically Modified Carbon Paste Electrode Containing Functionalized Nanoporous Silica GelELECTROANALYSIS, Issue 2 2008Mehran Javanbakht Abstract This research introduces the design of an adsorptive stripping voltammetric method for the cerium(III) determination at a carbon paste electrode, chemically modified with dipyridyl-functionalized nanoporous silica gel (DPNSG-CPE). The electroanalytical procedure comprised two steps: the Ce(III) chemical accumulation at ,200,mV followed by the electrochemical detection of the Ce(III)/dipyridyl complex, using anodic stripping voltammetry. The factors, influencing the adsorptive stripping performance, were optimized including the modifier quantity in the paste, the electrolyte concentrations, the solution pH and the accumulation potential or time. The resulting electrode demonstrated a linear response over a wide range of Ce(III) concentration (1.0,28,ng mL,1). The precision for seven determinations of 4 and 10,ng mL,1 Ce(III) was 3.2% and 2.5% (relative standard deviation), respectively. The prepared electrode was used for the cerium determination in real samples and very good recovery results were obtained. [source] L -Cysteine Voltammetry at a Carbon Paste Electrode Bulk-Modified with Ferrocenedicarboxylic AcidELECTROANALYSIS, Issue 17 2007Jahan-Bakhsh Raoof Abstract The electrochemical behavior of L -cysteine studied at the surface of ferrocenedicarboxylic acid modified carbon paste electrode (FDCMCPE) in aqueous media using cyclic voltammetry, differential pulse voltammetry and double potential step chronoamperometry. It has been found that under optimum condition (pH,8.00) in cyclic voltammetry, the oxidation of L -cysteine occurs at a potential about 200,mV less positive than that of an unmodified carbon paste electrode. The kinetic parameters such as electron transfer coefficient, ,, and catalytic reaction rate constant, kh were also determined using electrochemical approaches. The electrocatalytic oxidation peak current of L -cysteine showed a linear dependent on the L -cysteine concentration and linear analytical curves were obtained in the ranges of 3.0×10,5 M,2.2×10,3 M and 1.5×10,5 M,3.2×10,3 M of L -cysteine concentration with cyclic voltammetry (CV) and differential pulse voltammetry (DPV) methods respectively. The detection limits (3,) were determined as 2.6×10,5 M and 1.4×10,6 M by CV and DPV methods. [source] Determination of Diclofenac in Urine Samples by Molecularly-Imprinted Solid-Phase Extraction and Adsorptive Differential Pulse VoltammetryELECTROANALYSIS, Issue 15 2007Laura Fernández-Llano Abstract A molecularly imprinted polymer for diclofenac (DCF) was prepared by thermal polymerization over silica beads using 2-(dimethylamino)ethyl-methacrylate as functional monomer. After silica elimination by HF treatment, the polymer was applied to the selective solid-phase extraction of the drug from urine followed by its quantification by adsorptive differential pulse voltammetry. Results indicate that the drug could be selectively extracted from the sample and quantified at clinically relevant concentrations (,g/mL). [source] A Versatile System for Arbitrary Function Large-Amplitude Fourier Transformed VoltammetryELECTROANALYSIS, Issue 13 2007Lishi Wang Abstract A novel low-cost instrument for arbitrary function large-amplitude Fourier transformed voltammetry was developed. Description of both hardware and software was given in detail in this paper. A micro-control-unit (MCU) in combination with a field programmable gate array (FPGA) was designed to act as the controller of the instrument. Profiting from the built-in USB2.0 standard interface of the MCU, vast amount of data to/from the high resolution digital-to-analog converter (DAC)/analog-to-digital converter (ADC) then could be exchanged with computer in real-time, instead of being temporarily stored at the capacity limited memory of the instrument which always restricted the length of sampling time and the size of the collected data set. In the [Fe(CN)6]4+/3+ system, by superimposing a sinusoidal waveform with an amplitude of 120,mV onto a triangular potential and then applying to a macro electrode through the instrument, voltammograms up to the eighth harmonic could be well resolved by FT-IFT method. Excellent agreement was attained with Bond's similar experiment [Anal. Chem. 76 (2004) 3619] in respect of the shape and relative peak height of each harmonic. With the simply structured instrument, stable performance, flexible and versatile function was achieved. Arbitrary forms of AC perturbation which may not necessarily be sinusoidal or square-wave or other regular formed periodic signal could be synthesized and superimposed onto a DC potential as the excitation signal with this instrument. Some more useful electrode process information was expected to unveil by utilizing the FT-IFT algorithm to dissect the response signal. [source] Voltammetry as an Alternative Tool for Trace Metal Detection in Peloid Marine SedimentsELECTROANALYSIS, Issue 13 2007Irena Ciglene Abstract Here was demonstrated for the first time a possible application of abrasive stripping voltammetry in the direct measurement of trace metals in anoxic, sulfidic marine sediments (peloid mud) from a small and shallow (0.2,1,m) marine lagoon in Central Dalmatia, Croatia. Trace amounts of sample compounds are transferred to the graphite electrode surface and electrochemical reduction or oxidation processes are followed by the cyclic voltammetry in seawater or 0.55,M NaCl as electrolyte. After a preelectrolysis at potentials ranging from ,1.0 to ,1.5,V (vs. SCE) a well-defined anodic stripping peak corresponding to the oxidation of metal deposits generated at deposition potentials is obtained around ,0.74,V (vs. SCE). The same samples were studied by anodic stripping voltammetry at the Hg electrode and inductively coupled plasma-mass spectrometer (ICP-MS). ICP-MS showed higher concentrations of trace metals such as Al, Fe, Mo, Mn. A relatively high concentration of reduced sulfur species (RSS) (10,3 M) is determined electrochemically in porewater of the peloid mud, indicating that the magnitude of metal enrichment in the sediments is probably controlled by precipitation with sulfide. [source] DNA Determination in the Presence of Copper in Diluted Alkaline Electrolyte by Adsorptive Stripping Voltammetry at the Mercury Film ElectrodeELECTROANALYSIS, Issue 11 2007Augusto, Mardini Farias, Percio Abstract A stripping method for the determination of single-stranded DNA in presence of copper at the submicromolar concentration levels is described. The method is based on controlled adsorptive accumulation of adenine (from acid-treated DNA) at thin-film mercury electrode followed by linear scan voltammetry measurement of the surface species. Optimum experimental conditions were found to be the use of a 5.0×10,3,M NaOH solution, an accumulation potential of ,0.40,V and a scan rate of 200,mV s,1. The response of adenine,copper is linear over the concentration range 50,250,ppb. For an accumulation time of 15,minutes, the detection limit was found to be 4,ppb. The more convenient relation to measuring the ssDNA in presence of metals and nitrogenated bases were also investigated. The utility of the method is demonstrated by the presence of adenosine-triphosphate (ATP) and amino acids. [source] Determination of Trace Amounts of Copper in Tap Water Samples with a Calix[4]arene Modified Carbon Paste Electrode by Differential Pulse Anodic Stripping VoltammetryELECTROANALYSIS, Issue 10 2007Çelik Canpolat Abstract A calix[4]arene modified carbon paste electrode was used for trace determination of copper. The study of the preconcentration of copper as well as the other heavy metal ions at the modified electrode, with subsequent measurement by differential pulse anodic stripping voltammetry (DPASV), indicates the efficient open-circuit accumulation of the analytes onto the electrode. Many parameters such as the composition of the paste, pH, preconcentration time and stirring rate influence the response of the measurement. The procedure was optimized for copper determination. For a 10-minute preconcentration time at pH,6.5,7.5, the detection limit (LOD) was 1.1,,g L,1. The optimized method was successfully applied to the determination of copper in tap water sample by means of standard addition procedure. The copper content of the sample was comparable with the result obtained with AAS method. [source] Simultaneous Determination of Quinoline and Pyridine Compounds in Gasoline and Diesel by Differential Pulse VoltammetryELECTROANALYSIS, Issue 6 2007Leonardo Abstract The presence of trace basic organonitrogen compounds such as quinoline and pyridine in derivative petroleum fuels plays an important role in maintaining the engines of vehicles. However, these substances can contaminate the environment and so must be controlled because most of them are potentially carcinogenic and mutagenic. For these reasons, a reliable and sensitive method was developed for the determination of basic nitrogen compounds in fuel samples such as gasoline and diesel. This method utilizes preconcentration on an ion,exchange resin (Amberlyte IR,120,H) followed by differential pulse voltammetry (DPV) on a glassy carbon electrode. The electrochemical behavior of quinoline and pyridine as studied by cyclic voltammetry (CV) suggests that their reduction occurs via a reversible electron transfer followed by an irreversible chemical reaction. Very well resolved diffusion-controlled voltammetric peaks were obtained in dimethylformamide (DMF) with tetrabutylammonium tetrafluoroborate (TBAF4 0.1,mol L,1) for quinoline (,1.95,V) and pyridine (,2.52,V) vs. Ag|AgCl|KClsat reference electrode. The proposed DPV method displayed a good linear response from 0.10 to 300,mg L,1 and a limit of detection (LOD) of 5.05 and 0.25,,g L,1 for quinoline and pyridine, respectively. Using the method of standard additions, the simultaneous determination of quinoline and pyridine in gasoline samples yielded 25.0±0.3 and 33.0±0.7,mg L,1 and in diesel samples yielded 80.3±0.2 and 131±0.4,mg L,1, respectively. Spike recoveries were 94.4±0.3% and 101±0.5% for quinoline and pyridine, respectively, in the fuel determinations. This proposed method was also compared with UV-vis spectrophotometric measurements. Results obtained for the two methods agreed well based on F and t student's tests. [source] Enhanced Resolution of Copper and Bismuth by Addition of Gallium in Anodic Stripping Voltammetry with the Bismuth Film ElectrodeELECTROANALYSIS, Issue 24 2006Chad Prior Abstract This paper presents the enhanced analysis of copper on a bismuth electrode upon addition of gallium(III). The presence of gallium alleviates the problems of overlapping stripping signals usually observed between copper and bismuth when using the Bismuth Film Electrode. In addition, it has been found that the presence of gallium improves the reproducibility of the bismuth stripping signal. Simultaneous deposition of copper and bismuth at ,1500,mV for 2,minutes in a supporting electrolyte composed of 0.1,M pH,4.75 acetate buffer with 250,,g L,1 gallium yields well resolved copper and bismuth signals when analyzed with square-wave anodic stripping voltammetry. Simultaneous analysis of copper and lead yielded linear calibration plots in the range 10 to 100,,g L,1 with regression coefficients of 0.997 and 0.994 respectively. The theoretical detection limit for copper was calculated to be 4.98,,g L,1 utilizing a 2,minutes deposition time. The relative standard deviation for a copper concentration of 50,,g L,1 was 1.6% (n=10). [source] Determination of Rutin in Green Tea Infusions Using Square-Wave Voltammetry with a Rigid Carbon-Polyurethane Composite ElectrodeELECTROANALYSIS, Issue 10 2006Andréa Abstract This paper presents a comparative study on the electrochemical behavior of the flavonoid rutin on a rigid carbon-polyurethane composite electrode and on a glassy carbon electrode. The electrochemical oxidation reaction of rutin was found to be quasireversible and affected by adsorption on the electrode surface. A square-wave voltammetric method was developed for determination of rutin in green tea infusion samples using the RCPE electrode and data treatment by a deconvolution procedure. The detection limit achieved in buffered solutions was 7.1×10,9,mol L,1 using the RCPE and 1.7×10,8,mol L,1 using the GC electrode the average reproducibility for five determinations being 3.5%. [source] Highly Sensitive and Selective Measurement of Bismuth in Seawater and Drug with 1,2-Phenylenedioxydiacetic Acid by Cathodic Adsorptive Stripping VoltammetryELECTROANALYSIS, Issue 7 2006B. Gholivand Abstract A new method is presented for determination of bismuth based on cathodic adsorptive stripping of complex bismuth with 1,2-phenylenedioxydiacetic acid (PDA) at a hanging mercury drop electrode (HMDE). The effect of various parameters such as pH, concentration of ligand, accumulation potential and accumulation time on the selectivity and sensitivity were studied. The optimum conditions for determination of bismuth include nitric acid concentration 0.01,M, 8.0×10,4,M PDA and accumulation time 120,s, accumulation potential of ,200,mV. The limits of detection are 0.25 and 0.05,nM, and responses are linear 1,1000 and 0.1,400,nM at tacc of 60 and 120,s, respectively. Many common anions and cations do not interfere in the determination of bismuth. The method was applied to the determination of bismuth in some real samples such as sea , and spring water and drug. [source] Fourier Transformed Large Amplitude Square-Wave Voltammetry as an Alternative to Impedance Spectroscopy: Evaluation of Resistance, Capacitance and Electrode Kinetic Effects via an Heuristic ApproachELECTROANALYSIS, Issue 15-16 2005Abstract A detailed simulation of Fourier transformed large amplitude square-wave voltammetry is presented in the frequency domain for the process Red,Ox+e,. The simulation takes into account the influence of the electrode kinetics (Butler,Volmer model), uncompensated resistance (Ru) and double layer capacitance (Cdl). Of particular significance is the prediction that the even harmonic responses are only detected in the presence of quasi-reversibility or uncompensated resistance, and also are essentially devoid of charging current. In contrast, the DC and odd harmonic AC components exhibit much larger faradaic currents and also contain charging current. Conveniently, detailed analysis of the simulated DC and AC harmonic components reveals the presence of readily recognised patterns of behaviour with unique levels of sensitivity to electrode kinetics, Ru and Cdl, that facilitate quantitative analysis of these terms. These electrochemical parameters are generally calculated by small amplitude impedance spectroscopy and utilisation of linear analysis of equivalent circuits. Experimental studies on the one electron oxidation of ferrocene in dichloromethane (0.1,M Bu4NPF6) and the one electron reduction of [Fe(CN)6]3, in aqueous 0.5,M KCl electrolyte analysed via heuristic forms of data analysis based on recognition of patterns of behaviour, are presented as examples of a reversible process with significant uncompensated resistance and a quasi-reversible process with minimal ohmic drop, respectively. Results demonstrate the advantages of a more intuitively implemented form of data analysis than presently available with conventional forms of impedance spectroscopy. [source] | ||||||||||||||||||||||||||||||||||