Square wave

Because of the fact that real measurements are sometimes described in terms of the (formal) scan rate, the functional relationships between this parameter and the peak current in staircase (SCV) and square-wave voltammetry (SWV) were investigated theoretically. The real SCV peak current is proportional to the square-root of the formal scan rate, v, and inversely proportional to DE 0.0541 : 0541 . In SWV of a reversible electrode reaction the net peak current depends primarily on the frequency, while the influence of the formal scan rate is of minor importance:

A cathodically pretreated boron-doped diamond electrode was used for the simultaneous anodic determination of ascorbic acid (AA) and caffeine (CAF) by differential pulse voltammetry. Linear calibration curves (r ¼ 0.999) were obtained from 1.9 Â 10 À5 to 2.1 Â 10 À4 mol L À1 for AA and from 9.7 Â 10 À6 to 1.1 Â 10 À4 mol L À1 for CAF, with detection limits of 19 mmol L À1 and 7.0 mmol L À1 , respectively. This method was successfully applied for the determination of AA and CAF in pharmaceutical formulations, with results equal to those obtained using a HPLC reference method.

The cyclic voltammetric behavior of five common pesticides such as dicofol (DCF), cypermethrin (CYP), monocrotophos (MCP), chlorpyrifos (CPF) and phosalone (PAS) was investigated at a poly 3,4-ethylenedioxythiophene modified glassy carbon electrode (PEDOT/GCE). A method was developed for the detection and determination of these pesticides in trace level flowing stream, based on their redox behavior. The square wave stripping voltammetric principle was used to analyze the selected pesticides on PEDOT/GCE. Varying the accumulation potential and accumulation time, the best accumulation conditions were found out. Effects of initial scan potential, square wave pulse amplitude, step potential and frequency were examined for the optimization of stripping conditions. The peak current responses of analyte under optimum conditions were correlated over flow rate by using wall-jet PEDOT/GCE assembly. The calibration plots were linear over the pesticide's concentration range 0.10-72.60 g l −1 for DCF, 0.41-198.24 g l −1 for CYP, 0.22-220.95 g l −1 for MCP, 0.35-259.69 g l −1 for CPF and 1.07-141.46 g l −1 for PAS. The limit of detection was obtained between <0.09 and <1.0 g l −1 for five pesticides. It is low enough for trace pesticide determination in real samples. This method is applied for the determination of the five pesticides in soil samples. The recovery values obtained in spiked soil samples are 95.4 ± 5.4% for DCF, 93.7 ± 4.2% for CYP, 85.3 ± 8.4% for MCP, 94.6 ± 6.6% for CPF and 93.5 ± 4.9% for PAS.

This paper reports a novel architecture for multi-channel sine and square wave synthesizer. A phase accumulator is the core of multi-channel synthesizer. The phase accumulator’s output is multiplexed on the output channels and held by each channel latch. It is considered the MSB of the phase accumulator as the square wave synthesizer output. According to the proposed architecture, a 4-channel square wave
synthesizer is designed, simulated and implemented. Spartan-Xc3s400 from Xilinx-FPGA family is used to physically implementation. The system consumes 161 mW@40 MHz. The frequency resolution of the square wave synthesizer is 0.3 Hz in a range of 0-5 MHz. Finally, a novel architecture is proposed to produce sine from square wave and using designed 4-channel square wave synthesizer a 2-channel sine wave synthesizer is designed and simulate

The electrochemical oxidation of nicotine was studied in aqueous as well as micellar media at a pencil graphite electrode using cyclic, differential pulse and square-wave voltammetric techniques. The compound was oxidized irreversibly at low positive potentials in one (in acidic and neutral media) or two (in alkaline media) oxidation steps. The response was evaluated with respect to pH, scan rate, addition of surfactant and other variables. For analytical purposes, very resolved voltammetric peaks at +0.84 V (versus Ag/AgCl) were obtained in phosphate buffer at pH 7.0 containing 2 mM sodium dodecylsulfate using square-wave mode. The process could be used to determine nicotine concentrations in the range of 7.6-107.5 M with a detection limit of 2.0 M (0.33 mg L −1). The proposed method was applied to the determination of nicotine in different brands of commercial cigarettes.

A cathodically pretreated boron-doped diamond electrode was used for the simultaneous anodic determination of ascorbic acid (AA) and caffeine (CAF) by differential pulse voltammetry. Linear calibration curves (r ¼ 0.999) were obtained from 1.9 Â 10 À5 to 2.1 Â 10 À4 mol L À1 for AA and from 9.7 Â 10 À6 to 1.1 Â 10 À4 mol L À1 for CAF, with detection limits of 19 mmol L À1 and 7.0 mmol L À1 , respectively. This method was successfully applied for the determination of AA and CAF in pharmaceutical formulations, with results equal to those obtained using a HPLC reference method.

A promethazine (PMZ) molecularly imprinted polymer (MIP) and a non-imprinted polymer (NIP) were synthesized by two different formulations of methacrylic acid-ethylene glycol dimethacrylate (MAA-EGDMA) and vinyl benzene-divinyl benzene (VB-DVB). Then, the MIPs were used to modify the carbon paste electrode (CP). The response difference between MIP-CP and NIP-CP electrodes, containing VB-DVB polymer, was higher than that for MIP-CP and NIP-CP modified with polymer of MAA-EGDMA, indicating the lower nonselective surface adsorption property of the VB-DVB based MIP. The MIP, incorporated in the carbon paste electrode, functioned as selectively recognition element and pre-concentrator agent for PMZ determination. The prepared electrode was used for PMZ measurement by the three steps procedure including analyte extraction in the electrode, electrode washing and electrochemical measurement of PMZ. It was shown that the electrode washing, after PMZ extraction, led to enhanced selectivity. Square wave voltammetry (SWV) for PMZ determination by proposed electrode was proved to be better than that of differential pulse voltammetry. Some parameters, effective on the electrode response, were optimized and then a calibration curve was plotted. Two dynamic linear range of 7 × 10 −9 to 4 × 10 −7 and 4 × 10 −7 to 7 × 10 −6 mol L −1 were obtained. The detection limit of the method was calculated equal to 3.2 × 10 −9 mol L −1 . This method was used successful for PMZ determination in blood serum sample.

A new rapid, convenient and sensitive electrochemical method based on a gold nanoparticles modified ITO (Au/ITO) electrode is described for the detection of dopamine and serotonin in the presence of a high concentration of ascorbic acid. The electrocatalytic response was evaluated by differential pulse voltammetry (DPV) and the modified electrode exhibited good electrocatalytic properties towards dopamine and serotonin oxidation with a peak potential of 70 mV and 240 mV lower than that at the bare ITO electrode, respectively. The selective sensing of dopamine is further improved by applying square wave voltammetry (SWV) which leads to the lowering of its detection limit. A similar effect on the detection limit of serotonin was observed on using SWV. Linear calibration curves are obtained in the range 1.0 × 10 −9 -5.0 × 10 −4 M and 1.0 × 10 −8 -2.5 × 10 −4 M with a detection limit of 0.5 nM and 3.0 nM for dopamine and serotonin, respectively. The Au/ITO electrode efficiently determines both the biomolecules simultaneously, even in the presence of a large excess of ascorbic acid. The adequacy of the developed method was evaluated by applying it to the determination of the content of dopamine in dopamine hydrochloride injections. The proposed procedure was also successfully applied to simultaneously detect dopamine and serotonin in human serum and urine.

An electrochemical method for the determination of the liposome-water partition coefficients of drugs was developed. Interactions of liposomes and b-blockers were studied using square wave voltammetry (SWV) at a water-DCE interface created at the tip of a micropipette. Five different b-blockers, propranolol, timolol, carteolol, nadolol and metoprolol were encapsulated in liposomes prepared using the extrusion method. The liposomes were made in three different sizes by varying the size of the pores in the polycarbonate membrane used in extrusion. The partition of five b-blockers between the cavity and the membrane of the liposome was determined.

A method to transmit one-directional wireless data with low power consumption has been investigated. This system, called the 'reflectenna', works on the principle of transmitting information by modulating an incident continuous wave carrier signal prior to re-transmission and consists of two orthogonally linear polarised, micromachined microstrip patch antennas and a single-pole-single-throw switch that modulates the carrier signal. This quasi-passive method to transmit data has been tested with a transceiver system that transmits a 10 GHz carrier signal and demodulates the received signal reflected back from the reflectenna. The carrier signal was modulated with a 2 kHz square wave and a link with a range up to 25 m was achieved.

This work reports the utility of inexpensive and disposable pencil-lead graphite as a substrate for bismuth-film electrodes (BFEs) for the simultaneous determination of Cd(II), Pb(II) and Zn(II) by square-wave anodic stripping voltammetry (SWASV). The BFE was generated in situ by depositing simultaneously the bismuth film and the metal cations by reduction at −1.4 V on the pencil graphite substrate. Then, the preconcentrated metals were oxidised by scanning the potential of the electrode from −1.4 to 0 V using a square-wave waveform. The stripping current arising from the oxidation of each metal was related to the concentration of each metal in the sample. The parameters for the simultaneous determination of the three metals were investigated with the view to apply this type of voltammetric sensor to real samples containing traces of these metals. Using the selected conditions, the limits of detection were 0.3 g l −1 for Cd and 0.4 g l −1 for Zn and Pb at a preconcentration time of 10 min and these values could be further decreased by the use of Nafion-covered pencil-lead BFEs. Finally, the pencil-lead BFEs were successfully applied to the determination of Pb and Zn in tap water with results in satisfactory statistical agreement with atomic absorption spectroscopy.

The electrochemical behavior of 1-hydroxypyrene at a thin-film mercury electrode was investigated to provide the basis for development of an inexpensive, sensitive, and reliable method for determination of polycyclic aromatic hydrocarbon (PAH) metabolites in biological matrices. Optimum experimental conditions for analytical applications were obtained in 0.01 M NaOH solution using an accumulation potential of −0.20 V, a scan rate of 200 mV s−1, a pulse height of 50 mV, and the square wave scan mode. The electrode response to 1-hydroxypyrene is linear up to 100 ppb. For an accumulation time of 10 min, the detection limit was 0.23 ppb (1.06 × 10−9 mol L−1). The method was applied to the determination of 1-hydroxypyrene in samples of human urine. Cyclic voltammetry and square wave voltammetry were used to characterize the interfacial and redox behavior.

Electrochemical behaviour of dexamethasone at the fullerene-C 60 -modified pyrolytic graphite electrode (PGE) has been investigated using Osteryoung square wave voltammetry (SWV). Compared to a bare PGE and fullerene-C 60 -modified glassy carbon electrode (GCE), the fullerene-C 60 -modified edge plane PGE exhibited an apparent shift of the peak potential to less negative potentials with a marked enhancement in the current response of dexamethasone. The peak potential was linearly dependent on pH with dE p /dpH as 59 mV/pH. Calibration plot having good linearity with a correlation coefficient 0.9983 is obtained in the concentration range of 0.05-100 M and the sensitivity of the method has been found to be 0.685 A M −1 . The detection limit is estimated to be 5.5 × 10 −8 M. The electrode showed good sensitivity, stability and reproducibility. The practical analytical utility of the method is illustrated by quantitative determination of dexamethasone in several commercially available pharmaceutical formulations and human blood plasma of patients being treated with dexamethasone. HPLC method was used to compare the results obtained for the quantitative estimation of dexamethasone in biological fluids.

An anodic stripping voltammetric method has been developed for determination of cadmium, lead, copper and zinc in acetic acid extract of glazed ceramic surfaces. An aliquot of 4% (v/v) acetic acid solution was kept in a ceramic ware for 24 h in the dark, then 10 mL of the extracted solution was placed in a voltammetric cell. The solution was purged with oxygen free nitrogen gas for 3 min before deposition of the metals was carried out by applying a constant potential of −1.20 V versus Ag/AgCl to the hanging mercury drop electrode (HMDE) for 45 s. A square wave waveform was scanned from −1.20 to 0.15 V and a voltammogram was recorded. A standard addition procedure was used for quantification. Detection limits of 0.25, 0.07, 2.7 and 0.5 g L −1 for cadmium, lead copper and zinc, respectively, were obtained. Relative standard deviations for 11 replicate determinations of 100 g L −1 each of all the metals were in the range of 2.8-3.6%. Percentage recoveries obtained by spiking 50 g L −1 of each metal to the sample solution were in the range of 105-113%. The method was successfully applied to ceramic wares producing in Lampang province of Thailand. It was found that the contents of cadmium, lead, copper and zinc released from the samples were in the range of <0.01-0.16, 0.02-0.45, <0.14 and 0.28-10.36 g dm −2 , respectively, which are lower than the regulated values of the Thai industrial standard. The proposed method is simpler, more convenient and more sensitive than the standard method based on FAAS.

A new modified electrode formed by carbon nanoparticle/chitosan film (CNP/CS) was used for electrocatalytic reduction of Niclosamide (NA). The electrochemical behavior of NA at the CNP/CS modified electrode was investigated in detail by the means of cyclic voltammetry. The reduction mechanism of NA, corresponds to the redox chemistry of nitro group, was thoroughly investigated. The effect of the experimental parameters e.g. potential and time of accumulation, pH of the buffered solutions and potential sweep rate on the response of the electrode was studied. The prepared electrode showed high stability and uniformity in the composite film, short response time, good reproducibility and an excellent catalytic activity toward the electro-reduction of NA leading to a significant improvement in response sensitivity. The square-wave adsorptive anodic stripping voltammetry (SWAASV) was used as an efficient method for the determination of NA. Under the optimal conditions, the modified electrode showed a wide linear response to the concentration of NA in the range of 0.01-2 lM with a detection limit of 7.7 nM. The prepared electrode was successfully applied for the determination of NA in pharmaceutical and clinical samples and satisfactory results are obtained.

The influence of the boron-doping levels in boron-doped diamond film electrodes on the electrochemical response of nitrofurantoin (NFT) and the development of an electroanalytical procedure for NFT determination were investigated. The investigations were carried out using the techniques of cyclic voltammetry and square wave voltammetry on diamond film electrodes with different boron-doping levels (i.e., 5000, 10,000 and 20,000 mg L −1 ). The level of boron-doping in the diamond film electrodes influenced the electrochemical reduction of NFT. The appropriate cyclic voltammetric response of NFT was obtained with Britton-Robinson buffer at pH 4 and for diamond films doped with 10,000 and 20,000 mg L −1 of boron. These two films were selected for the development of the electroanalytical procedure. The use of square wave voltammetry with the optimized parameters demonstrated a good linear relationship between the peak current and the NFT concentration for a wide range of concentration. The lower limit of detection for the electrodes doped with 10,000 and 20,000 mg L −1 of boron were 2.69 × 10 −8 mol L −1 (6.40 g L −1 ) and 8.15 × 10 −9 mol L −1 (1.94 g L −1 ), respectively, while the lower limits of quantification were 8.96 × 10 −8 mol L −1 (21.33 g L −1 ) and 2.72 × 10 −8 mol L −1 (6.47 g L −1 ), respectively. The applicability of the proposed procedure was tested using a commercial pharmaceutical formulation of NFT, and the results were compared with the procedure recommended by the British Pharmacopeia. The proposed procedure was sensitive, accurate and precise for analysis of NFT and did not require complex preparations or renovations of the electrode surface. This presents the advantage of eliminating mercury waste and minimizing the adsorptive problems related to the use of other electrodic solid surfaces.

This research investigated the forced cooling characterization of an impinging synthetic jet under combined wave excitation. The synthetic jet cooling used an air flowing in a vertical direction into the heated wall. The synthetic jet actuator used two oscilating membranes to push and pull the air from and to the cavity. The main purpose of this synthetic jet was to create vortices pair to come out from nozzle which will accelerate the heat transfer process occurring at the impinged wall. This heat transfer enhancement principles became the basis to simulate an alternative cooling system to substitute the conventional fan cooling in electronic devices application due to its advantage for having a small form factor and low noise. The investigation combined computational and experimental works. The model was simulated to examine the distribution of heat flow on the impinged walls using variation of turbulence model i.e. standard k-epsilon, realizable k-epsilon, standard k-omega and k-...

The mechanism of electrochemical oxidation of (À)-epicatechin (EC) and (À)-epicatechin gallate (ECG) on a glassy carbon electrode was investigated over a wide range of conditions, using cyclic and square-wave voltammetry. Electrochemical behavior of gallic acid has been studied as well, in order to elucidate the influence of catechol and galloyl groups on the overall electrochemical response of ECG. The first oxidation peak of both catechins, ECG and EC, originates primarily from the oxidation of the catechol 3 0 ,4 0dihydroxyl groups. The oxidation of galloyl group in the molecule of ECG constitutes only a minor component of the response, and causes the shift of the ECG peak potential (ca. 20 mV) towards more positive values when compared with the peak potential of EC. The oxidation of the catechol group is a two electron two proton reaction. After successive scans, the oxidation products of EC and ECG adsorb at the electrode surface, forming a polymeric film that undergoes reversible oxidation at a lower potential than the catechol group.

A study on the preparation and characterisation of ex situ formed bismuth film microelectrodes (BiFMEs) is presented, focusing in particular on their stable and reliable stripping electroanalytical performance. The potentiostatic pre-plating of the bismuth film onto a single carbon fibre substrate microelectrode was investigated and optimised with the aim of achieving long-term electrochemical and mechanical film stability. Several important film preparation parameters, such as plating agent, potential and time, and composition of the plating solution were examined with respect to the current signals of 40 consecutive adsorptive cathodic stripping voltammetry (AdCSV) measurements of trace Co(II) as model analyte. A comparison, also presented, of the stripping performance between bismuth and mercury film microelectrodes revealed a distinct practical advantage of the BiFME. The resulting optimised BiFME exhibited, besides excellent long-term film functional stability, attractive stripping analytical performance. Employing AdCSV with square-wave voltammetric detection, highly linear behaviour was obtained in the examined concentration range, with limits of detection of 70 and 90 ng/l and excellent reproducibility with 2.4 and 2.9% relative standard deviation at the 1 g/l level (n = 10), for Co(II) and Ni(II), respectively, achieved using only 2 min preconcentration time in the presence of dissolved oxygen. In addition, the performance of the proposed ex situ prepared BiFME in both anodic stripping voltammetry (ASV) of Cd(II) and Pb(II) and in AdCSV of Co(II) and Ni(II) from the same test solution is demonstrated. The ex situ prepared BiFME represents a promising non-toxic, environmentally friendly microsensor for detection at microlocations and in microvolumes, in particular where in situ bismuth film electrode preparation is inappropriate, inconvenient or impossible.

The redox reaction of 5-fluorouracil (FU) at a hanging mercury drop electrode (HMDE) is studied by means of square-wave voltammetry (SWV). It is demonstrated that the redox reaction proceeds according to the scheme: L 2 − (aq) v L 2 − (ads) + Hg(l) v HgL(s)+ 2e − , which involves both chemisorption of FU on the electrode surface and creation of a sparingly soluble compound with the electrode material. The overall response exhibits properties of a surface process in which both the reactant and the product of the redox reaction are immobilized on the electrode surface. The square-wave voltammetric response of FU possesses features typical of surface confined processes such as 'split SW peaks' and a 'quasi-reversible maximum'. The proposed electrode mechanism is studied theoretically. The numerically calculated response under conditions of SWV is in qualitative agreement with the experimental data. Comparing the theoretical and the experimental data, the kinetic parameters of the redox reaction investigated are estimated. The standard rate constant appears to be within the interval 545 k s /s − 1 5 108, the adsorption constant is K =10 cm − 1 , and the transfer coefficient is h =0.549 0.01. The effect of the Cu(II) ions on the adsorptive SWV response of FU is discussed from an analytical point of view. It is demonstrated that SWV is a particularly appealing technique, which enables determination of FU at an ultra-trace concentration level. A linear calibration plot was established at 10 − 11 mol l − 1 concentration level with a correlation coefficient of R 2 = 0.992. The detection limit is 7.7× 10 − 12 mol l − 1 . The reproducibility of the results in terms of the relative standard deviation ranges from 0.9 to 3.2%.

Normally, the pancreatic digestive enzymes are created and carried into the duodenum in an inactive form. During pancreatitis attacks, these enzymes are inhibited from reaching the duodenum, become activated while still in the pancreas, and begin to autodigest and destroy the pancreas. In order to accurately detect lipase within seconds, a square wave technique was explored without immobilizing enzyme and any other biomolecules over the electrode surface. The cyclic voltammetric (CV) technique was used to coat a carbon electrode with a thin layer of polyaniline. This modified electrode proved to be highly sensitive and specific to detect lipase between 0 and 225 IU/L, which is well within the normal physiological range. The consistency and reliability of this technique proved to be a very formidable detector of lipase present in abnormal quantities due to pancreatitis and other pathological disorders. The interference test has been performed to detect the lipase in the presence of amylase 50, 100, and 150 IU/L to understand the interference phenomenon with lipase detection. There is no significant effect of the amylase concentration over lipase detection resulting from using a modified carbon electrode. The response time of the modified carbon electrode is approximately 5 s and the electrode has shown to be stable for 4 weeks at room temperature without special storage condition.

The mechanism of electrochemical oxidation of (À)-epicatechin (EC) and (À)-epicatechin gallate (ECG) on a glassy carbon electrode was investigated over a wide range of conditions, using cyclic and square-wave voltammetry. Electrochemical behavior of gallic acid has been studied as well, in order to elucidate the influence of catechol and galloyl groups on the overall electrochemical response of ECG. The first oxidation peak of both catechins, ECG and EC, originates primarily from the oxidation of the catechol 3 0 ,4 0dihydroxyl groups. The oxidation of galloyl group in the molecule of ECG constitutes only a minor component of the response, and causes the shift of the ECG peak potential (ca. 20 mV) towards more positive values when compared with the peak potential of EC. The oxidation of the catechol group is a two electron two proton reaction. After successive scans, the oxidation products of EC and ECG adsorb at the electrode surface, forming a polymeric film that undergoes reversible oxidation at a lower potential than the catechol group.

Eddy-current nondestructive evaluation is commonly carried out using single frequency time harmonic excitations, but a pulsed excitation offers a simple and effective alternative. The pulse signals have been calculated for a probe coil whose current rises and falls exponentially, approximating a square wave when the exponential time constant is small. Predictions of the induced electromotive force (EMF) across a coil above a half-space conductor and of the magnetic field on the coil axis have been compared with experiments. The comparison shows excellent agreement between theory and experiment.

Square-wave voltammetry was used for trace determination of azoxystrobin and dimoxystrobin in potatoes, grapes, and grape juice. Experimental conditions have been optimized to achieve simultaneous determination of these analytes using the hanging mercury drop electrode. Supporting electrolyte was HCl 0.1 mol L−1, and other optimized conditions were deposition potential (−300 mV), deposition time (30 s), amplitude (150 mV), frequency (150 Hz), and step height (2 mV). Azoxystrobin and dimoxystrobin redissolution peaks presented their maxima, respectively, at −928 mV and around −650 mV. Linear and homoscedastic analytical responses (r 2 > 0.99) have been observed. Limits of quantification as low as 119 µg L−1 (in grape juice) and 45 µg kg−1 (in potatoes and grapes) were found. A previous solid-phase extraction was necessary to eliminate interferences from potato and grape samples. For grape juice, no sample treatment was required. Satisfactory recoveries (from 72.3% to 96.7% for dimoxystrobin and from 81.7% to 102.3% for azoxystrobin) were found. Interferences from other strobilurins (piraclostrobin and picoxystrobin) were evaluated.

Novel biosensors based on laccase from Aspergillus oryzae and the ionic liquids (ILs) 1-n-butyl-3methylimidazolium hexafluorophosphate (BMIPF 6 ) and 1-n-butyl-3-methylimidazolium tetrafluoroborate (BMIBF 4 ) were constructed for determination of rosmarinic acid by square-wave voltammetry. The laccase catalyzes the oxidation of rosmarinic acid to the corresponding o-quinone, which is electrochemically reduced back to rosmarinic acid at +0.2 V vs. Ag/AgCl. The biosensor based on BMIPF 6 showed a better performance than that based on BMIBF 4 . The best performance was obtained with 50:20:15:15% (w/w/w/w) of the graphite powder:laccase:Nujol:BMIPF 6 composition in 0.1 mol L −1 acetate buffer solution (pH 5.0). The rosmarinic acid concentration was linear in the range of 9.99 × 10 −7 to 6.54 × 10 −5 mol L −1 (r = 0.9996) with a detection limit of 1.88 × 10 −7 mol L −1 . The recovery study for rosmarinic acid in plant extract samples gave values from 96.1 to 105.0% and the concentrations determined were in agreement with those obtained using capillary electrophoresis at the 95% confidence level. The BMIPF 6 -biosensor demonstrated long-term stability (300 days; 920 determinations) and reproducibility, with a relative standard deviation of 0.56%.

Redox behavior of three pesticides, namely isoproturon, carbendazim and methyl parathion was investigated electrochemically using hetropolyacid montmorillonite clay-modified glassy carbon electrode in the presence and absence of a surfactant, cetyl trimethyl ammonium bromide. A solution of 0.1 M H 2 SO 4 in 50% aqueous alcohol (pH 1.0) was found to be suitable medium for electroanalysis. Isoproturon exhibited one well-defined oxidation peak around 1.2 V along with one more oxidation and reduction peaks. Carbendazim showed only one well-defined anodic peak around 1.4 V. Methyl parathion exhibited one well-defined reduction peak around −0.26 V and the oxidation peak appeared around 0.510 V. In the second cycle, a new cathodic peak was found around 0.420 V. The presence of surfactant enhanced the peak current and hence stripping voltammetric determination procedures for all the three pesticides were developed. Square wave stripping mode was employed and the maximum current experimental conditions were arrived at. Calibration plot was made for all the three pesticides. The determination limit and standard deviations were arrived at. The applicability of the method was also verified in a soil sample and water analyte.

Square-wave adsorptive-stripping voltammetry technique has been used to develop a method for the determination of fenthion in olive oil. Due to the fact that fenthion does not give any electrochemical signal at mercury electrode, the method has been based on a previous oxidation of fenthion to its metabolite, fenthion-sulfoxide, by using KMnO 4. The metabolite gives rise to a peak due to an adsorptive-reductive process at −0.786 V. Fenthion is isolated from olive oil by carrying out a solid-liquid extraction procedure using silica cartridge, followed by a liquid-liquid partitioning with acetonitrile. The detection limit in olive oil is 78.8 ng g −1 and recoveries for four levels of fortification are ranged from 85% to 109%. On the other hand, it has been developed a method for the simultaneous determination of fenthion and its metabolite fenthion-sulfoxide, in river water. Pesticides are isolated from water by carrying out a liquid-liquid partitioning with trichloromethane. The detection limits are 0.41 ng g −1 and 0.44 ng g −1 , for fenthion and fenthion-sulfoxide, respectively. Recoveries for three levels of fortification are ranged from 96% to 103% for fenthion and 94% to 104% for fenthion-sulfoxide.

A cathodically pretreated boron-doped diamond electrode was used for the simultaneous anodic determination of ascorbic acid (AA) and caffeine (CAF) by differential pulse voltammetry. Linear calibration curves (r ¼ 0.999) were obtained from 1.9 Â 10 À5 to 2.1 Â 10 À4 mol L À1 for AA and from 9.7 Â 10 À6 to 1.1 Â 10 À4 mol L À1 for CAF, with detection limits of 19 mmol L À1 and 7.0 mmol L À1 , respectively. This method was successfully applied for the determination of AA and CAF in pharmaceutical formulations, with results equal to those obtained using a HPLC reference method.

Voltammetric investigation of two corticoid isomers-testosterone and epitestosterone has been carried out at bare and single-wall carbon nanotubes (SWNT)-modified edge plane pyrolytic graphite electrode (EPPGE). Square wave voltammetry (OSWV) has been used for the simultaneous determination of isomeric steroids. The reduction of the two isomers occurred in a pH dependent, 2e, 2H + process and well-defined voltammetric peaks were observed. Under the optimum experimental conditions, linear calibration curves are obtained within the concentration range 5-1000 nM for both the steroids with the limit of detection 2.8 × 10 −9 and 4.1 × 10 −9 M for testosterone and epitestosterone respectively. The developed protocol is successfully implemented for the analysis of both the compounds in the urine samples of normal subjects as well as in patients undergoing treatment with testosterone. The results obtained from the proposed voltammetric method were also compared with HPLC analysis and found to be similar.

A cathodically pretreated boron-doped diamond electrode was used for the simultaneous anodic determination of ascorbic acid (AA) and caffeine (CAF) by differential pulse voltammetry. Linear calibration curves (r ¼ 0.999) were obtained from 1.9 Â 10 À5 to 2.1 Â 10 À4 mol L À1 for AA and from 9.7 Â 10 À6 to 1.1 Â 10 À4 mol L À1 for CAF, with detection limits of 19 mmol L À1 and 7.0 mmol L À1 , respectively. This method was successfully applied for the determination of AA and CAF in pharmaceutical formulations, with results equal to those obtained using a HPLC reference method.

The voltammetric behavior of vardenafil was studied on glassy carbon electrode using cyclic, differential pulse (DPV) and Osteryoung square-wave (OSW) voltammetric techniques. Vardenafil exhibited irreversible anodic waves over the pH range 1.00-12.00 in different supporting electrolytes. The current-concentration plot was rectilinear over the range from 4 × 10 −7 to 2 × 10 −5 M with correlation coefficient of 0.999. The wave was characterized as being irreversible and diffusion-controlled. The developed procedure was successfully applied to the determination of vardenafil in tablets and in spiked human serum. Furthermore, results obtained by the proposed method have been compared with high-performance liquid chromatographic method.

An optimized digestion method coupled to electrochemical sensor for the determination of Cd, Cu, Pb and Hg in fish by square wave anodic stripping voltammetry a b s t r a c t An optimized digestion method coupled to electrochemical detection to monitor lead, copper, cadmium and mercury in fish tissues was developed. Square wave anodic stripping voltammetry (SWASV) coupled to disposable screen-printed electrodes (SPEs) was employed as fast and sensitive electroanalytical method for heavy metals detection. Different approaches in digestion protocols were assessed. The study was focused on Atlantic hake fillets because of their wide diffusion in the human nutrition. Best results were obtained by digesting fish tissue with hydrogen peroxide/hydrochloric acid mixture coupled to solid phase (SP) purification of the digested material. This combined treatment allowed quantitative extraction from fish tissue (muscle) of the target analytes, with fast execution times, high sensitivity and avoiding organic residues eventually affecting electrochemical measurements. Finally, the method has been validated with reference standard materials such as dogfish muscle (DORM-2) and mussel tissues (NIST 2977).

A preanodized nontronite-coated screen-printed electrode (NSPE∗) was developed for the sensitive detection of the pesticide amitrole by square-wave voltammetry (SWV) and flow injection analysis (FIA). The preanodization process was essential to improve the sensitivity because of the existence of higher iron oxidation state in the interlayer of nontronite clay. Factors influencing the SWV and FIA responses were evaluated in this

This article introduces the design and analysis of a single-phase single-stage transformer-less grid-tie buck-boost photovoltaic inverter topology for domestic purposes. Functionally, this new inverter can adjust to a wide range of photovoltaic dc variations, higher or lower dc voltages compared to utility line voltage, and in the meantime track the maximum amount of solar energy all in one single power stage. For switching of inverter power circuit, a combination of sinusoidal pulse width modulation (SPWM) and square wave signal under grid synchronization condition are used. Moreover, to control SPWM duty cycle and to regulate the inverter's instantaneous ac output voltage, a closed-loop SPWM control technique is used to stabilize the output as fast as possible. Besides, we also employed immittance conversion circuit topology in the inverter output terminal instead of conventional LC filter. The design and analysis of working principles of the inverter control circuit and grid synchronization methods are described in details. This paper mainly focuses on the analysis of working principles, computer simulation of the operation and design consideration of the inverter for grid-connected applications. The effectiveness of the proposed system is clarified through the following mathematical modeling and simulations.

The response to the square-wave voltammetric waveform with large amplitude and large effective potential scan rate is examined in detail both theoretically and experimentally. Characteristics of the voltammograms include peak current, peak width at half-height and the modified semilog-plot (similar to the polarographic semilog-plot). These were examined for varying square-wave amplitude and period. The other interesting characteristic of the voltammogram is the area encompassed by the bell-shaped voltammogram and the base line. This area is demonstrated theoretically to be proportional to the square-wave amplitude for any electrode geometry. The relation between the area and the square-wave amplitude was examined experimentally for various values of the period.

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The influence of the boron-doping levels in boron-doped diamond film electrodes on the electrochemical response of nitrofurantoin (NFT) and the development of an electroanalytical procedure for NFT determination were investigated. The investigations were carried out using the techniques of cyclic voltammetry and square wave voltammetry on diamond film electrodes with different boron-doping levels (i.e., 5000, 10,000 and 20,000 mg L(-1)). The level of boron-doping in the diamond film electrodes influenced the electrochemical reduction of NFT. The appropriate cyclic voltammetric response of NFT was obtained with Britton-Robinson buffer at pH 4 and for diamond films doped with 10,000 and 20,000 mg L(-1) of boron. These two films were selected for the development of the electroanalytical procedure. The use of square wave voltammetry with the optimized parameters demonstrated a good linear relationship between the peak current and the NFT concentration for a wide range of concentration. The lower limit of detection for the electrodes doped with 10,000 and 20,000 mg L(-1) of boron were 2.69 x 10(-8) mol L(-1) (6.40 microg L(-1)) and 8.15 x 10(-9) mol L(-1) (1.94 microg L(-1)), respectively, while the lower limits of quantification were 8.96 x 10(-8) mol L(-1) (21.33 microg L(-1)) and 2.72 x 10(-8) mol L(-1) (6.47 microg L(-1)), respectively. The applicability of the proposed procedure was tested using a commercial pharmaceutical formulation of NFT, and the results were compared with the procedure recommended by the British Pharmacopeia. The proposed procedure was sensitive, accurate and precise for analysis of NFT and did not require complex preparations or renovations of the electrode surface. This presents the advantage of eliminating mercury waste and minimizing the adsorptive problems related to the use of other electrodic solid surfaces.

The electrochemical behaviour of dysprosium(III) was investigated in the LiF-CaF 2 eutectic mixture on molybdenum, nickel and copper electrodes in the 840-930°C temperature range using cyclic voltammetry, square wave voltammetry and chronopotentiometry. On Mo electrode, the study showed that Dy(III) ions were reduced into Dy metal in a one-step diffusion-controlled process exchanging three electrons: DyðIIIÞ þ 3e À $ Dy: The diffusion coefficients verify the Arrhenius law, allowing the activation energy to be calculated. The study of the electrochemical reduction of Dy(III) ions on reactive electrodes (Ni, Cu) first by cyclic voltammetry showed that the reduction potential of Dy(III)/Dy on reactive electrodes was observed at more positive values than those on inert electrode and then open-circuit chronopotentiometry put into evidence the formation of intermetallic compounds at more anodic potentials than pure dysprosium. Preparation of alloys layers was finally carried out by intentiostatic electrolyses at underpotential compared to the pure metal deposition; SEM observations of the layer allowed the most stable compounds prepared by this way to be identified.

Carbon nanotubes (CNTs) have attracted extensively interest of scientists and engineers due to their outstanding physical properties such as low density, high aspect ratio, Young's modulus, electrical and thermal conductivities. When single-wall carbon nanotubes (SWCNTs) or multiwall carbon nanotubes (MWCNTs) are introduced into ceramics, metals and polymers as matrices, ultra-high strength and/or multifunctional composites can be developed as expected. Recently, CNT composite refractories have been the subject of intense research activities. In this chapter, MWCNTs (hereafter named as CNTs) were introduced into refractories to improve their mechanical properties and thermal conductivity, such as Al 2 O 3 -C refractories for slide gates and carbon blocks for blast furnaces in iron and steel making industry.

A novel approach of using a gold disc microelectrode to analyze sweat samples for copper ions by anodic square wave stripping voltammetry (SW stripping voltammetry) is described. Sweat was collected from the lower back of four subjects after physical exercise and the sample volume required for the determinations was 100 L. Under the optimized conditions, the calibration plot was linear over the range 1-100 mol L −1 Cu(II) with a limit of detection of 0.25 mol L −1 . The precision was evaluated by carrying out five replicate measurements in a 1 mol L −1 Cu(II) solution and the standard deviation was found to be 1.5%. Measurements were performed by inserting the microelectrode into sweat drops and Cu(II) concentrations in the analyzed samples ranged from 0.9 to 28 mol L −1 . Values obtained by the proposed voltammetric method agreed well with those found using graphite furnace atomic absorption spectroscopy (GFAAS).

The proteins streptavidin and avidin were electrochemically detected in solution by adsorptive transfer stripping square wave voltammetry (AdTS SWV) at a carbon paste electrode (CPE). AdTS SWV was used to quantify biotinylated oligonucleotides, DNA hybridizations, and avidin in extracts of transgenic avidin maize. The detection limits of denatured and native streptavidin were 6 pM and 120 nM, respectively. The results demonstrated that streptavidin/avidin AdTS SWV is a sensitive and specific method for quantifying DNA and proteins in biological samples such as foods and tissue extracts, including genetically modified crops (avidin maize) and other plants in neighboring fields.

A comparison of edge plane pyrolytic graphite substrate is made with other substrates like indium tin oxide, glassy carbon, gold and basal plane pyrolytic graphite as a substrate for fullerene modification for the determination of nandrolone by Osteryoung square wave voltammetry (OSWV) in phosphate buffer media. Comparative study of voltammetric response of nandrolone at untreated, purified and super-purified fullerene modified edge plane pyrolytic graphite electrode (EPPGE) is also carried out to determine the role of embedded metallic impurities of fullerene on determination of nandrolone. It is observed that EPPGE serves as best substrate among the studied for casting fullerene. The removal of embedded metals from fullerene shifts the peak potential of nandrolone to more positive potentials and peak current decreases. A linear calibration curve is obtained in the concentration range of 0.01-50 nM with a detection limit and sensitivity of 1.5 × 10 −11 M and 1.838 A nM −1 , respectively. The developed method was satisfactorily applied to the determination of nandrolone in several commercially available medicinal samples.

An electrochemical hybridization biosensor based on peptide nucleic acid (PNA) probe is presented. PNA were attached covalently onto a quinone-based electroactive polymer. Changes in flexibility of the PNA probe strand upon hybridization generates electrochemical changes at the polymer–solution interface. A reagentless and direct electrochemical detection was obtained by detection of the electrochemical changes using square wave voltammetry (SWV). An increase in the peak current of quinone was observed upon hybridization of probe on the target, whereas no change is observed with non-complementary sequence. In addition, the biosensor is highly selective to effectively discriminate a single mismatch on the target sequence. The sensitivity is also presented and discussed.

This paper proposes a simple and non-expensive electroanalytical methodology for classification of edible vegetable oils with respect to type (canola, sunflower, corn and soybean) and conservation state (expired and non-expired shelf life). The proposed methodology employs an alcoholic extraction procedure followed by square wave voltammetry (SWV). Two chemometric methods were compared for classification of the resulting voltammograms, namely Soft Independent Modelling of Class Analogy (SIMCA) and Linear Discriminant Analysis (LDA) with variable selection by the Successive Projections Algorithm (SPA). The results were evaluated in terms of errors in a set of samples not included in the modelling process. The best results were obtained with the SPA-LDA method, which correctly classified all samples in terms of type and conservation state.

The redox reaction of 5-fluorouracil (FU) at a hanging mercury drop electrode (HMDE) is studied by means of square-wave voltammetry (SWV). It is demonstrated that the redox reaction proceeds according to the scheme: L 2 − (aq) v L 2 − (ads) + Hg(l) v HgL(s)+ 2e − , which involves both chemisorption of FU on the electrode surface and creation of a sparingly soluble compound with the electrode material. The overall response exhibits properties of a surface process in which both the reactant and the product of the redox reaction are immobilized on the electrode surface. The square-wave voltammetric response of FU possesses features typical of surface confined processes such as 'split SW peaks' and a 'quasi-reversible maximum'. The proposed electrode mechanism is studied theoretically. The numerically calculated response under conditions of SWV is in qualitative agreement with the experimental data. Comparing the theoretical and the experimental data, the kinetic parameters of the redox reaction investigated are estimated. The standard rate constant appears to be within the interval 545 k s /s − 1 5 108, the adsorption constant is K =10 cm − 1 , and the transfer coefficient is h =0.549 0.01. The effect of the Cu(II) ions on the adsorptive SWV response of FU is discussed from an analytical point of view. It is demonstrated that SWV is a particularly appealing technique, which enables determination of FU at an ultra-trace concentration level. A linear calibration plot was established at 10 − 11 mol l − 1 concentration level with a correlation coefficient of R 2 = 0.992. The detection limit is 7.7× 10 − 12 mol l − 1. The reproducibility of the results in terms of the relative standard deviation ranges from 0.9 to 3.2%.

The electrochemical properties of valacyclovir, an antiviral drug, were investigated in pH range 1.8-12.0 by cyclic, differential pulse and squarewave voltammetry. The drug was irreversibly oxidized at a glassy carbon electrode in one or two oxidation steps, which are pH-dependent. For analytical purposes, a very resolved diffusion controlled voltammetric peak was obtained in Britton-Robinson buffer at pH 10.0 using differential pulse and square-wave modes. Limits of detection were 1.04 × 10 −7 and 4.60 × 10 −8 M for differential pulse and square-wave voltammetry, respectively. The applicability to direct assays of tablets, spiked human serum and simulated gastric fluid, was described.

Molecularly Imprinted poly[tetra(o-aminophenyl)porphyrin] is presented as an electrosynthesized coating for the development of selective microsensors. A carbon fiber microelectrode has been modified with this covering by cyclic voltammetry in the potential range from À0.15 to 1.0 V (scan rate 50 mV s À1) obtaining a microsensor able to recognize the template molecule. To carry out this study dopamine was chosen as model to work with, since this molecule presents electroactivity as it can be oxidized on carbon electrodes. The MIP sensor presented a linear response to the dopamine concentration in the range from 10 À6 to 10 À4 M with good repeatability (RSD 6.22%). The selectivity shown by the microsensor was found to be excellent as it was able to differentiate between different catecholamines. A method has been developed for the determination of dopamine in brain tissue samples using the MIP microsensor.