Showing papers on "Differential pulse voltammetry published in 1993"

Voltammetric determination of methyl parathion, ortho, meta and para nitrophenol with a carbon paste electrode modified with C18

Abstract: The determination of methyl-parathion (MPT), ortho (ONP), meta (MNP) and para nitrophenol (PNP) has been studied by differential pulse voltammetry with a carbon-paste electrode modified with 50% (w/w) of C18. A study of the influence of the pH in the preconcentration cell and the measurement cell was carried out for an electrode with 50% modifier and an accumulation time of 5 min. The voltammograms were recorded with a sweep rate of 40 mV s−1 and a pulse amplitude of 50 mV. With the optimum conditions of pH for both of the steps, various other variables were studied. The variables for each compound were optimized and the possibility of application to the determination of a mixture of the four compounds was investigated. The determination limits found for all the compounds are: 2 ng ml−1 for ONP, 5 ng ml−1 for MNP, 4.3 ng ml−1 for PNP and 7.9 ng ml−1 for MPT. The method was applied to samples of a small lake which gathers rain water and water filtered from land on which cereals are grown.

Voltammetric determination of gold using a carbon paste electrode modified with thiobenzanilide

Abstract: Gold(III) can be preconcentrated from acidic solution on a carbon paste electrode chemically modified with thiobenzanilide under open-circuit conditions. Using cathodic differential pulse voltammetry, 0.05–6 µg ml–1 of gold can be determined after preconcentration for 1 or 2 min. Except for mercury(II) and platinum group metals, common ions have little effect on the determination of gold(III). The preparation and regeneration of the modified electrode as well as the various methodical parameters for the preconcentration and measurement of gold(III) were investigated.

Determination of methoprotryne and terbutryn by adsorptive stripping voltammetry on the hanging mercury drop electrode

Abstract: Sensitive methods for the determination of the herbicides methoprotryne and terbutryn at nanomolar levels, by adsorptive stripping voltammetry at a hanging mercury drop electrode, are described. The electrocapillary curves, and cyclic voltammograms, demonstrate the adsorption of these compounds on the mercury electrode. A systematic study of the various experimental parameters that affect the stripping response was carried out by differential pulse voltammetry. The working medium chosen was 0.1 mol l–1 perchloric acid. By using an accumulation potential of –0.70 V and a 180 s accumulation time, the limits of detection were 5.2 × 10–10 and 2.4 × 10–9 mol l–1 for terbutryn and methoprotryne, respectively, and the relative standard deviations (n= 10) were 3.1% and 5.0% at concentration levels of 5.0 × 10–9 mol l–1 terbutryn and 1.0 × 10–8 mol l–1 methoprotryne, respectively. The degree of interference from some other herbicides on the differential pulse stripping signal for methoprotryne and terbutryn was evaluated. Finally, the methods were applied to the determination of terbutryn and methoprotryne in spiked irrigation and tap waters.

Determination of copper(I) ion with a chemically modified carbon paste electrode based on di(2-imino-cyclopentylidine mercaptomethyl) disulfide

Abstract: A copper-sensitive chemically modified electrode (CME) has been constructed by incorporating di(2-imino-cyclopentylidine mercaptomethyl) disulfide (didd) into the carbon paste composed of graphite powder and Nujol oil. Copper(I) ion was chemically deposited on the CME by immersing it in the Cu(I) solution. The resulting surfaces were characterized by cyclic and differential pulse voltammetry. The CME's surface could be regenerated by applying more positive potential than the stripping potential of the Cu(I) ion and then used for another deposition. After seven deposition/measurement/ regeneration cycles, the peak current of voltammograms of the analyte decreases slightly. The differential pulse technique was also applied to the above system. In this case, the detection limit for Cu(I) ion was 5 × 10−11 M for 30 minutes of deposition time. After reduction of Cu(II) ion to Cu(I) in the sample solution with hydroxylamine, satisfactory results were obtained for the determination of copper in certified standard urine reference material SRM's 2670 (trace elements in urine).

Thermodynamics of the xanthoconite-proustite and pyrostilpnite-pyrargyrite phase transition as determined by abrasive stripping voltammetry

Abstract: The electrochemical reduction of xanthoconite, proustite, pyrostilpnite, and pyrargyrite was studied by abrasive stripping voltammetry, a technique which is based upon a preliminary mechanical transfer of trace amounts of the mineral onto the surface of a paraffin impregnated graphite electrode. Because the electrochemical reduction proceeds near to reversibility and is very similar for each pair of minerals, the peak potentials in differential pulse voltammetry can be used to calculate the standard enthalpy of phase transformation of xanthoconite to proustite and of pyrostilpnite to pyrargyrite: ΔT H (xanth → proust) O = 35.46 ± 14.15 kJ/mol and ΔT H (pyrostilp → pyrarg) O = 38.85 ± 6.60 kJ/mol. These values are not accessible otherwise until now.

Synthesis, characterization and crystal structure of 2-dicyanomethylene-1,3-bis(ferrocenylmethyl)-1,3-diazolidine

Abstract: By reaction of N,N′-ethylenebis(ferrocenylmethylamine)1 with tetracyanoethylene in dichloromethane the yellow compound 2-dicyanomethylene-1,3-bis(ferrocenylmethyl)-1,3-diazolidine 2 can be isolated. The single-crystal structure of 2 has been determined. It crystallizes in the non-centrosymmetric trigonal space group P3221, a= 12.255(2), c= 13.831(7)A, Z= 3. Refinement of the atomic parameters by least-squares techniques gave a final R factor of 0.038 (R′= 0.034) for 1782 observed reflections having I > 2.5δ(I). Anomalous values of the bond distances and the vinyl carbon chemical shift in the 13C NMR spectrum of 2 are explained on the basis of a polarization due to a combination of the electron-donating behaviour of the nitrogen atoms with the electron-acceptor character of the cyano groups in the dicyanovinyl diamine fragment. The non-linear optical properties were investigated. A second harmonic generation signal for 2 was detected by powder techniques with a low efficiency. Electrochemical experiments in dimethyl sulfoxide revealed a two-electron diffusion-controlled oxidation process according to two consecutive one-electron steps involving the two ferrocenyl fragments the potentials of which are separated by 43 mV. A comproportionation constant Kc of 5.3 was found by differential pulse voltammetry, indicating that the mixed-valence species [FeIIIFeII]+ is basically not stabilized.

Voltammetric determination of aluminium in haemodialysis concentrates using the adsorption of the Al(III)-1,2-dihydroxyantraquinone-3-sulphonic acid complex in presence of calcium

Abstract: This paper describes a method for the quantitative determination of aluminium in haemodialysis concentrates, based on the adsorption on a static mercury drop electrode of the Al-1,2 dihydroxyantraquinone-3-sulphonic acid complex. The signal was notably increased in presence of calcium. The electrolysis was carried out at -0.900 V. After 60 sec the aluminium contents were measured by differential pulse voltammetry. In these conditions aluminium can be determined in the range 0.65–38 ng/ml with a detection limit (3[sgrave]) of 0.20 ng/ml. The relative standard deviation was in all instances less than 2.1%.

Voltammetric and Potentiometric Determination of Gold in Gold-Plated Electrotechnical Components

Abstract: Differential pulse voltammetry was used to determine gold in gold-plated electrotechnical components. Samples were dissolved to form tetrachlorourate, which was determined on a carbon paste electrode containing tricresyl phosphate as pasting liquid. A characteristic cathodic peak for tetrachlorourate, whose selective accumulation is based on extraction, is obtained during cathodic scan from +0.8 to -0.5 V vs Ag/AgCl electrode. The accompanying Fe(III) and Cu(II) ions from the matrix are masked by adding EDTA. Gold can be determined in the presence of their thousand-fold excess in the concentration range 1 . 10 -5 - 1 . 10 -7 mol l -1 . The results were confirmed by potentiometric titration with a solution of 1-(ethoxycarbonyl)pentadecyltrimethylammonium bromide (Septonex) by using a coated-wire indicator electrode with a softened plastic membrane.

Determination of manganese using the method of electrochemical enrichment

Abstract: Manganese was determined by differential pulse voltammetry in pre-enriched solution. The metal was first deposited on the surface of a hanging mercury drop electrode by electrolysis, and after a short oxidation interval, the reformed manganese(II) ions were determined by differential pulse cathodic polarization scan. The detection limit (with 120 seconds deposition) was 2 μg L−1. The only interfering element was cobalt (when present at tenfold concentration excess). Compared with conventional stripping voltammetry the described method has a lower detection limit value, and the analysis is performed during a shorter time interval. The proposed method was applied for the determination of manganese in natural waters.

Studies on the voltammetric behavior of a bismuthiol I‐containing carbon paste electrode: Determination of traces of bismuth

Abstract: The voltammetric behavior of a bismuthiol I-containing carbon paste electrode was studied. Bismuthiol 1 is electroactive, when mixed with carbon paste as an electrode modifier, and is oxidized at 0.3 V and re-reduced at −0.6 V (vs. SCE). Nevertheless, it can be used as a modifier of carbon paste electrodes for the preconcentration and subsequent voltammetric measurement of bismuth, if suitable measurement conditions for the analysis are met. Bismuth(III) can be preconcentrated from acidic solutions onto this electrode under open circuit conditions. Linearity between current response and concentration can be achieved for 0.005 to 4 μg/ml bismuth using cathodic differential pulse voltammetry after preconcentration for 0.5 or 2 minutes. The interferences as well as various parameters for the preconcentration and measurement of bismuth(III) were investigated.

Electroanalytical methods for transition metal analysis in heavy metal fluoride melts

Abstract: Ab in situ, non-destructive method for the analysis of heavy metal fluoride melts by electrochemical means has been developed. The technique involves differential pulse voltammetry at a rotating carbon disc electrode. The electrode is swept cathodically in the melt at 600°C at a fixed rate to a potential beyond the deposition potentials of the analytic ions and then swept in the reverse direction. During the cathodization process, various transition metal ions including copper, iron, nickel and cobalt are reduced from the melt onto the electrode. Previous studies have shown that the main ZBLAN melt cations are all more stable against reduction than these problematic contaminating ions. In the anodic sweep the ions reduced onto the surface of the electrode are oxidized off and the resultant current is monitored. Spiking the melt with known amounts of the contaminant allows the construction of a calibration curve. Typical analytical sensitivity is found to be at least 100 ppb in each of copper, iron, nickel and cobalt. The technique shows separate peaks for copper, iron and nickel. Cobalt lies close to nickel such that quantitative separation is not possible. Differential pulse anodic stripping voltammetry has also been used in this work. This technique was found to produce peak currents that were too large to be easily measurable using our equipment. This suggests that analytical sensitivity of 10 ppb or less may be possible.

Voltammetric Determination of Cu(II) Ion at a Chemically Modified Carbon-Paste Electrode Containing 1-(2-pyridylazo)-2-naphthol

Abstract: Cu(II) ion-responsive chemically modifed electrodes (CMEs) were constructed by incorporating 1-(2-pyridylazo)-2-naphthol (PAN) into a conventional carbon-paste mixture of graphite powder and Nujol oil. Cu(II) ion was chemically deposited on the surface of the PAN-chemically modified electrode in the absence of an applied potential by immersion of the electrode in a buffer solution (pH 3.2) containing Cu(II) ion, and then reduced at a constant potential in 0.1 M KNO. And a well-defined voltammetric peak could be obtained by scanning the potential to the positive direction. The electrode surface could be regenerated with exposure to acid solution and reused for the determination of Cu(II) ion. In 5 deposition / measurement / regeneration cycles, the response could be reproduced with 6.1 relative standard deviation. In case of using the differential pulse voltammetry, the calibration curve for Cu(II) was linear over the range of 2.0 10 ∼ 1.0 10 M. And the detection limit was 6.0 10 M. Studies of the effect of diverse ions showed that Co, Ni, Zn, Pb, Mg and Ag ions added 10 times more than Cu(II) ion did not influence on the determination of Cu(II) ion, except EDTA and oxalate ions.

A study of the differential-pulse voltammetric behavior of organic and inorganic selenium-compounds and its analytical applications

Abstract: N-(1-methylpropyl)-2-phenylselenenyl-2-phenyl-butyramide(I), N-(1-methylpropyl)-2-phenylselenenyl-2-phenylacetamide(II), N-(isopropyl)-2-phenylselenenyl-2-phenylacetamide(III) and diphenyldiselenide(IV) undergo homolytic fission of their Se-C bonds (and in the latter case the Se-Se bond) followed by formation of adsorbable Ph-Se-Hg at the stationary mercury drop electrode. Ph-Se-Hg can then be cathodically stripped with LODs of 9 . 10(-9) mol/l, 3.6 . 10(-8) mol/l, 1.4 . 10(-8) mol/l and 10(-8) mol/l, respectively. Selenium(IV) can be determined by formation of adsorbable HgSe with an LOD of 5 . 10(-10) mol/l. Differential pulse voltammetry with adsorptive preconcentration of the reducible species cannot discriminate between the studied organoselenium compounds (I)-(IV) or between the organoselenium compounds and Se(IV), due to the similarity of electrode processes.

Electrochemical determination of iron in YBa2(Cu1–xFex)3O7 superconducting compounds

Abstract: The electrochemical determination of iron in doped YBaCuO superconducting compounds has been investigated by differential pulse polarography (SMDE) and by differential pulse voltammetry using a glassy carbon electrode A well-defined peak for iron was observed at –015 V (vs Ag-AgCl) reference electrode in sodium citrate/EDTANa2H2 pH 6 The electrochemical results have been validated by spectroscopic procedures, including atomic absorption and energy dispersion X-ray spectroscopy The differential pulse polarography using the standard addition method for peak validation has been found to be most appropriate

FIA Immunoassays with Electrochemical and Optical Detection

Abstract: Different approaches have been made for developing novel immuno FIA (FIIA) systems for herbicide detection: antigens have been labeled with ferrocene and enzymes, anti-herbicide antibodies were labeled with fluorophores (Europium chelates)

Electrochemical oxidation of methylenedioxy amphetamines

Abstract: Surnrnary-Four amphetamine derivatives bearing a methylenedioxy group at positions 3 and 4 of the benzene ring and differing in their substitution at C(6) were studied by differential pulse voltammetry in aqueous media. These experiments showed a single oxidation peak for the C(6)-H, -Br and -CI compounds, while the C(6)-N02 analogue was not oxidized. The oxidation peak is interpreted as due to the removal of one eleetron from the aromatic eleetrophore with formation of a radical cation stabilized by the dioxole ring. The linear relationship between the peak current and the concentration of the derivatives is appropriate for development of a quantitative method for their determination. pK' values were determined using both eleetrochemical and spectrophotometric methods.

Carbon Film Electrodes from the Pyrolysis of Two Aromatic Anhydrides

Abstract: Two new carbon film electrodes have been prepared from the low pressure pyrolysis of aromatic anhydrides onto quartz substrates. The anhydrides employed are safer and more volatile than those previously used for preparing carbon film electrodes. The voltammetric response of the film electrodes both in millimolar dopamine and in background electrolyte was studied. The differential pulse voltammetry response with a mixture of dopamine, homovanillic acid and ascorbic acid was studied. Also, the application of the electrode as an optically transparent carbon electrode was examined. The film electrodes had lower background current than glassy carbon, but the reversibility with dopamine was not ideal. These two new films appear to have utility similar to previously studied films, with the advantage of rapid and safe production.

Electrochemical analysis of some drug substances in complex matrices

Abstract: This thesis describes the development of several analytical methods, based on electrochemical techniques, for the determination of various drug substances in formulations, biological fluids and environmental samples. The work included a study of the voltammetric behaviour of both sumatriptan succinate and salbutamol sulphate at a glassy carbon electrode. Based on these studies, simple, rapid and sensitive voltammetric methods were developed for the determination of these drugs in tablet dosage forms without any interferences from the excipients. Using differential pulse voltammetry, the dissolution profile of salbutamol tablets was also investigated. The principal criteria for designing electrochemical flow detectors, and the great advantages of carbon fibre electrodes, have been utilized in the development of a versatile electrochemical detector for HPLC that is based on a carbon fibre (14 pm diameter) placed in a polyethylene tube connected directly to the end of the chromatographic column. The analysis of salbutamol in human plasma was then developed based on extracting the drug from the plasma into an organic solvent and separation of the drug on a reversed-phase Cjg column, followed by detection using the carbon fibre flow electrode. Several advantages of the carbon-fiber flow electrodes over conventional electrodes have also been demonstrated. The cell was then used for monitoring of terbutaline concentrations in human plasma in the range of 1-35 ngml'l using columnswitching LC. The method involved direct injection of the plasma sample into a Ci 8 extraction column for sample clean-up. This method was also applied for the simultaneous determination of both salbutamol and terbutaline at overdose levels in human plasma. A method was then developed to determine the suspected carcinogen gentian violet in human urine and in poultry feed. Liquid chromatography with electrochemical detection was also applied in environmental studies for the analysis of malachite green in drinking water and river water.