Square-wave Waveform Research Articles

The Design of Signal Generator of Electrical Fast Transients Burst

With the improvement of output frequency of electric fast transients (EFT) burst generator, amplitude attenuation of pulse train appeared in the high frequency. Therefore, the method of pulse width programmed digitally ,and realized by Field Programmable Gate Array (FPGA) device was put forward to overcome burst amplitude attenuation. The technology of direct digital frequency synthesis was used to adjust the output signal frequency changes. The linear array memory with one bit was adopted to store square-wave waveform, the output signal duty cycle is digital adjustable, which is achieved by changing the waveform data in the linear array memory. Brust generator is designed by using VHDL languages in the QUARTUS II 6.0 simulation platform. The simulation and experiment results show that when the frequency of the output signal reaches 1 MHz, frequency resolution arrives at 6Hz, error of pulse width is less than 10 ns.

Assessment of Lead and Cadmium in Canned Foods by Square-Wave Anodic Stripping Voltammetry

This work reports the simultaneous determination of lead and cadmium in canned foods samples using square-wave anodic striping voltammetry (SWASV) on a bismuth film electrode (BiFE). The metal ions and bismuth were simultaneously deposited by reduction at −1 V on a rotating carbon-paste disk electrode. Then, the preconcentrated metals were oxidized by scanning the potential of the electrode from −1 to −0.4 V using a square-wave waveform. The electrode displayed excellent linear behavior in the examined concentration range, from 5 to 150 µg/L of cadmium and lead (r2 = 0.999 for both). Using the optimized conditions, the limits of detection were 0.27 µg/L for cadmium and 0.35 µg/L for lead. The reproducibility of the proposed sensor, evaluated in terms of relative standard deviation (RSD), were 5.8% and 3.7% of Cd and Pb, respectively for five measurements. Finally, the system based on BiFEs combined with rotating disk electrode was applied to determination of lead and cadmium in canned food samples. The results obtained were validated by inductively coupled plasma optical emission spectroscopy (ICP-OES).

On-line Preconcentration and Determination of Trace Heavy Metals by Sequential Injection-Anodic Stripping Voltammetry Using Bismuth Film Screen-printed Carbon Electrode

An automated on-line preconcentration method was developed for simultaneous determination of Pb(II), Cd(II) and Zn(II) by square-wave anodic stripping voltammetry (SWASV) using bismuth film screen-printed carbon electrode (Bi-SPCE). The preconcentration of metal ions was performed with a mini-column of a chelating resin, which was installed on a switching valve in the automated system consisted of a syringe pump, an 8-port selection valve and a switching valve. The laboratory-assembled automated on-line pretreatment system (Auto-Pret ASV system) was controlled by the Visual Basic program written by the authors. The metal ions collected on the resin were eluted with 1 M hydrochloric acid, subsequently transported into the flow cell for on-line deposition of analytes on Bi-SPCE at -1.4 V vs. Ag/AgCl; then the flow of the solution was stopped and the voltammogram was recorded from -1.2 to 0.2 V vs. Ag/AgCl by scanning a potential in the square-wave waveform. Experimental conditions, such as pH of sample, a sample flow rate, an eluent volume and its flow rate were optimized. Under the optimum conditions, the analytical characteristics were studied. In addition, the proposed method was applied to the analysis of water samples.

Three validated stripping voltammetric procedures for determination of the anti-prostate cancer drug flutamide in tablets and human serum at a mercury electrode

Flutamide is a nonsteriodal anti-androgen drug, which is commonly used in the treatment of advanced prostate cancer. Based on the reduction of the nitro organic moiety of the drug molecule in acetate buffer of pH 5 at the hanging mercury drop electrode, three adsorptive cathodic stripping voltammetric procedures were optimized for determination of flutamide in bulk, tablets, and human serum applying linear-sweep, differential-pulse, and square-wave waveforms. The achieved limits of detection of the bulk drug were 1.9 × 10–7, 8.7 × 10–8, and 9.7 × 10–9 mol L–1 by using the optimized differential-pulse, linear-sweep, and square-wave adsorptive stripping voltammetric procedures, respectively. Repeatability of the results was studied for 1 × 10–6 mol L–1 of the drug and the recoveries obtained were 98.51 ± 1.56% (LSV), 98.89 ± 0.87% (DPV), and 99.21 ± 1.03% (SWV). The proposed procedures were successfully applied to the determination of the drug in pharmaceutical formulation (Eulexin® tablets) and human serum. The detection limits of the drug in bulk, pharmaceutical formulation, and human serum achieved by means of the proposed procedures showed that the square-wave mode was more reliable for determination of the drug especially in its low concentration levels.Key words: flutamide, linear-sweep, differential-pulse, square-wave, cathodic adsorptive stripping voltammetry, determination, Eulexin® tablets, human serum.

A study of pencil-lead bismuth-film electrodes for the determination of trace metals by anodic stripping voltammetry

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 μg l −1 for Cd and 0.4 μg 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.

A study of bismuth-film electrodes for the detection of trace metals by anodic stripping voltammetry and their application to the determination of Pb and Zn in tapwater and human hair

This work reports the simultaneous determination of Cd(II), Pb(II) and Zn(II) at the low μg l −1 concentration levels by square wave anodic stripping voltammetry (SWASV) on a bismuth-film electrode (BFE) plated in situ. The metal ions and bismuth were simultaneously deposited by reduction at −1.4 V on a rotating glassy carbon disk electrode. 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 low concentrations of metals. Using the selected conditions, the limits of detection were 0.2 μg l −1 for Cd and for Pb and 0.7 μg l −1 for Zn at a preconcentration time of 10 min. Finally, BFE's were successfully applied to the determination of Pb and Zn in tapwater and human hair and the results were in satisfactory statistical agreement with atomic absorption spectroscopy (AAS).

Modified Square-Wave Cathodic Stripping Voltammetry for Determination of Se(IV) at Trace and Ultratrace Levels

A method for the improvement of the signal-to-noise ratio in square-wave (SW) voltammetry is proposed. It is based on the modification of a square-wave waveform. This method is applied to cathodic stripping voltammetric (CSV) determination of selenium(IV) in nitric acid solutions. Hanging mercury drop electrode (HMDE) was used in the presence of Cu(II) ions. The optimal conditions were chosen: square-wave waveform mode, pH, time and potential of electrodeposition. Kinetic processes of copper selenide reduction with the use of SWCSV, applying different square-wave waveforms, are studied. Quasi-reversible processes are observed. The standard reaction rate constants are evaluated for different square-wave waveforms. It is shown that the determination of Se(IV) by this modified SWCSV technique is possible with an excellent sensitivity (the detection limit 8×10−12 mol L−1 only for 5 min of electrodeposition) and good reproducibility (Sr<8%) in a wide range of concentration (1×10−11−1×10−6 mol L−1) of Se(IV). The presence of Mo(VI), Pb(II), Ni(II), Zn(II), Cr(VI) metal ions with molar excess around 1000 do not prevent the detection of Se(IV) signals.

Pulsed voltammetric stripping at the thin-film mercury electrode

A computer-controlled data acquisition system was used to generate comparative data for thin-film anodic stripping voltammetry with staircase, differential pulse and squarewave waveforms. Each waveform was tested for its sensitivity and speed of analysis. The square-wave form is the most sensitive, whether square wave or differential pulse measurements are used. This waveform offers the advantages of fast analysis time and discrimination against charging currents.