Showing papers on "Supporting electrolyte published in 1996"

Preconcentration and Voltammetric Determination of Mercury(II) at a Chemically Modified Glassy Carbon Electrode.

Abstract: In this work, the organic compound 2-mercaptobenzimidazole was covalently bound on the surface of a glassy carbon rod, via silanization, yielding a material capable of selectively complexing Hg2+ ions. This material was applied as an electrode for voltammetric determination of mercury(II) following its nonelectrolytic preconcentration. After exchanging the medium, the voltammetric measurements were carried out by anodic stripping in the differential pulse mode (pulse amplitude, 50 mV; scan rate, 1.25 mV s-1) using 10-2 mol L-1 NaSCN solution as supporting electrolyte. An anodic stripping peak was obtained at 0.06 V (vs SCE) by scanning the potential from −0.3 to +0.3 V. After a 5 min preconcentration period in a pH 4.0 Hg2+ solution, this electrode shows increasing voltammetric response in the range 0.1−2.2 μg mL-1, with a relative standard deviation of 5% and a practical detection limit of 0.1 μg mL-1 (5.0 × 10-7 mol dm-3). Compared with the conventional stripping approach, this chemically modified glass...

Scanning Electrochemical Microscope-Induced Dissolution: Theory and Experiment for Silver Chloride Dissolution Kinetics in Aqueous Solution without Supporting Electrolyte

Abstract: The kinetics of silver chloride dissolution in aqueous solutions containing no supporting electrolyte have been investigated using the well-defined and high mass transport properties of the scanning electrochemical microscope (SECM). In this application a probe ultramicroelectrode (UME), positioned close to a silver chloride surface (pressed pellet or electrochemically grown film), is used to induce and monitor the dissolution process via the reduction of Ag+, from an initially saturated solution. Theory relating the current flow to rate laws in which dissolution is governed by either a first- or second-order dependence on the interfacial undersaturation has been developed numerically, using the alternating direction implicit finite difference method to solve the mass transport equation appropriate to the system of interest. It is shown that the two rate laws may readily be distinguished from steady-state approach (current−distance) measurements. Moreover, it is possible to measure rate constants (particu...

Voltammetric determination of silver at ultratrace levels using a carbon paste electrode with improved surface characteristics

Abstract: A differential pulse anodic stripping voltammetric method for the determination of silver is described. A new type of electrodeposition for preconcentrating the analyte, Ag+, was investigated, enhancing the electrolytic accumulation efficiency onto a carbon paste electrode by ion pair formation. A carbon paste electrode containing tricresyl phosphate as a pasting liquid was modified in situ with heptylsulfonic acid (sodium salt). The modifier gave rise to an additional accumulative effect towards the target ions based on ion pairing which resulted in an enhanced sensitivity of the electrode. Additional activation of the electrode surface at −1.0 V (vs. SCE) for 60 s improved the detection limit significantly. The detection limit was found to be 2.5 × 10−12 M Ag+ (accumulation time 15 min), and could be even lowered by increasing the period of preelectrolysis. The current response was linearly dependent on the concentration up to 2 × 10−5 M Ag under optimized conditions. The effects of paste composition, voltammetric parameters, composition of the supporting electrolyte as well as the influence of alkylsulfonic acids and of cathodic activation upon the determination of Ag were studied. Interferences from about 20 elements were investigated with particular attention to Cu, Hg, and Au. By masking with ethylenediaminetetraacetate (EDTA), Cu and Hg did not affect the response of Ag up to a 10000-fold and 500-fold molar excess in concentration, respectively. Au did not interfere with the determination of Ag up to a 100-fold molar excess if its absolute concentration was lower than 5 × 10−7 M. For higher concentration levels, [AuCl4]− could be separated by passing the analyte solution through an anion-exchanger column (Dowex-1) prior to stripping analysis. Due to the extremely low detection limit and high selectivity, the method could be applied to determine Ag at its ubiquitous level in tap water. With this method, the corrosion of silver cutlery in tap water could be monitored. The results agreed well with those obtained by using inductively coupled plasma mass spectrometry (ICP-MS).

Voltammetric Study of the Facilitated Transfer of Lead(II) Ion by Macrocyclic Polythiaether 1,4,7,10,13,16-Hexathiacyclooctadecaneacross the Polarizable Nitrobenzene/Water Interface.

Abstract: Facilitated transfer of Pb2+ ion by macrocyclic polythiaethers across the polarizable nitrobenzene/water and 1, 2-dichloroethane/water interfaces has been studied by means of ion-transfer voltammetry. Well-defined voltammetric waves due to facilitated transfer of Pb2+ ion by 1, 4, 7, 10, 13, 16-hexathiacyclooctadecane (HTCO) were observed. The voltammetric waves at the nitrobenzene/water interface are shown to be due to the reversible transfer, assisted by the formation of 1:1(metal:ionophore) complex (PbHTCO2+). The half-wave potential of the facilitated transfer of Pb2+ ion was shifted to more positive potential with increasing concentration of acetate ion in water phase. This is explained by the formation of complexes of Pb2+ ion with acetate ion, using the theoretical equations of the half-wave potential of reversible facilitated ion-transfer across the oil/water interface. Also, the negative shift in the half-wave potential observed with increasing concentration of supporting electrolyte in oil phase can be attributed to the ionic association of PbHTCO2+ with the supporting electrolyte anion. The results suggest a new electrochemical method for the determination of Pb(II).

Surface characterization of glassy carbon electrodes anodized in 1-alkanols by their wettability and capacitance

Abstract: The surface conditions of glassy carbon (GC) electrodes anodized in n-CnH2n+1OH (2=2, 4, 6, 8 : electrodes 1-4), HO(CH2)nOH (n=2-5 : electrodes 5-8), and HO(CH2CH2O)2CH2CH2OR (R=H, Me : electrodes 9 and 10) were explored by measuring the wettability and capacitance as well as the voltammetric response to Fe(CN)3-6;wetting properties were evaluated by the contact angle formed by a drop of water; the ratio between the values of capacitance obtained before and after the anodic modification was used instead of the capacitance itself. The data have revealed that LiClO4 is recommended rather than conc. H2SO4 as a supporting electrolyte to fix 1-alkanol molecules more effectively to GC electrode surfaces in the anodic modification. The surface conditions of electrodes 1-10 have reflected the indentities of the modifer remarkably : electrodes 1-4 have surfaces with hydrophobicity and thickness correlated to the length of carbon chains of the modifiers; on the other hand, the surfaces of electrodes 5-10 are hydrophilic, which seemed to allow each of the modified electrodes, except for electrode 8, to have a double layer with a thickness similar to a bare GC electrode. The suppression in the electrode reaction of Fe(CN)3-6 was stronger at electrodes 6 and 8 than at electodes 5 and 7, which can be explained by the invocation of an"odd-even" effect.

Reversibly Adsorbed Monolayers on Microelectrodes: Effect of Potential on the Adsorption Thermodynamics

Abstract: Monolayers of 2-hydroxyanthraquinone (2OH-AQ) have been formed by reversible adsorption onto mercury microelectrodes. Cyclic voltammetry of these monolayers in contact with HClO4 as supporting electrolyte is nearly ideal and is consistent with reduction proceeding by a two-electron, two-proton transfer mechanism. Cyclic voltammetry reveals that the dependence of the surface coverage Γ on the bulk concentration of 2OH-AQ is accurately described by the Langmuir isotherm over the concentration range from 2 × 10-8 to 2 × 10-6 M. A limiting surface coverage Γs of (1.0 ± 0.08) × 10-10 mol cm-2 and an adsorption coefficient β of (6.3 ± 0.6) × 106 M-1 are observed. Since adsorption is reversible in this system, the effect of changing the potential at which the monolayer is formed on the surface coverage, or the adsorption thermodynamics, cannot be investigated by ex situ measurement of Γ in a blank electrolyte solution. To address this issue, microsecond time scale chronoamperometry has been used to time-resolve ...

Direct Observation of Chloride Transfer across the Water/Organic Interface and the Transfer of Long-Chain Dicarboxylates

Abstract: We have extended the negative side of the potential window by using the organic reference electrode Ag/AgTPB and a low supporting electrolyte concentration in the aqueous phase. We have observed directly, for the first time, the voltammetric wave of chloride transferring across the water(W)/1,2-dichloroethane (1,2-DCE) and the water/nitrobenzene (NB) interfaces. The standard potentials (and the standard Gibbs free energies of transfer) have been evaluated by consideration of half-wave potentials, the variations of the activity coefficients in both phases, and ion-pair formation. Our best estimate for the free energy of Cl- transfer to water-saturated 1,2-DCE is 45−46 kJ/mol, and for NB 38 ± 2 kJ/mol. The Gibbs free energies of transfer of a homologous series of long-chain dicarboxylates have also been obtained for the first time. They show a similar dependence on carbon number as monocarboxylates. The transfers of the singly and doubly ionized dicarboxylic acids can also be observed simultaneously when th...

Electrochemical copolymerization of thiophene and aniline

Abstract: In this study homopolymer, copolymer, and composites of aniline and thiophene were synthesized in nitrogen atmosphere by using TEATFB (Tetraethyl ammonium tetrafluoroborate) and Lithium perchlorate as supporting electrolytes. In order to analyze their structure and characteristics, IR spectrums of the samples were taken and thermogravimetric analysis (TGA) was applied. Also, the samples were photographed under scanning electron microscope (SEM) for microstructure analysis and their electrochemical properties were observed and conductivities were obtained by four probe method. Homopolymerization and copolymerization reactions were carried out in two different solvents viz. acetonitrile and benzonitrile in order to see the solvent effect on polymerization. However, changing the solvent was found to have no significant effect on the resulting properties. It was concluded that changing the supporting electrolyte caused a structural difference in the resulting homopolymer. It also affects the properties considerably. During the bilayer preparation changing the coating turn led to variations in the properties of the samples. When polythiophene (PT) was coated with polyaniline (PA), the resulting system was a composite. However, in coating PA with PT the system was identified to be a copolymer. © 1996 John Wiley & Sons, Inc.

The Polarographic Determination of Tenoxicam in the Pharmaceutical Preparations

Abstract: In this study, the polarographic behaviour and the optimum polarographic conditions for the determination of TNX using DC (direct current), DP (differential pulse), SCAP (superimposed constant amplitude pulse) and SIAP (superimposed increasing amplitude pulse) polarographic techniques are described based on the reduction of enol group of the molecule on the dropping mercury electrode. The experiments were conducted in the aqueous supporting electrolyte solution containing 0.2 M KCl and 0.2 M buffer solution. Single waves were obtained at various pH values. The limiting currents were decreased and E1/2 values were linearly shifted to more negative potentials with an increase in the pH. The system was irreversible at both the acidic and the basic media and it was adsorptional in the acidic medium and diffusional at pH 10.8. The variation in the limiting current was found to be 0.86 μA/°C. Good relations were obtained for DC, DP, SCAP and SIAP polarographic techniques at pH 10.8. The determination o...

Electrosynthesis of poly(3-methylthiophene) films with high strength and stabile conductive properties

Abstract: The electrochemical polymerization of 3-methylthiophene was significantly facilitated by the presence of freshly distilled boron fluoride-ethyl ether as supporting electrolyte and stainless steel as electrode during the polymerization. The lower oxidation potential of the monomer led to high overall stereoregularity and stacking order of poly(3-methylthiophene) chains. A current density of 1 mA/cm 2 and a monomer concentration of 35-70 mmol/L turned out to be optimal electrosynthesis conditions. Poly(3-methylthiophene) films had high tensile strength (73 MPa) and flexibility. The high stereoregularity of poly(3-methylthiophene) resulted in high conductivity with improved environmental stability.

Voltammetric Studies of Counterion Transport in Solutions of Chondroitin Sulfate

Abstract: The transport of hydrogen counterions was studied in solutions of a linear polyelectrolyte, chondroitin sulfate, CS, by voltammetric measurements at a platinum disk microelectrode. The use of microelectrodes enables voltammetry of the counterion in solutions with little or no supporting electrolyte over a wide range of polyelectrolyte concentrations. The voltammetric interactions of counterions with polyions diminish transport-limited current for reduction of electroactive counterions, as shown by comparing results for a polymeric strong acid, poly(styrenesulfonic acid), and simple strong acids. The experimental results agree reasonably well with Manning's theory, which describes the effect of ionic interactions on the transport of simple ions in the presence of polyelectrolytes. The data agree equally well with a much simpler semiempirical theory. The experimentally determined limiting value (no supporting electrolyte) of the transport ratio, D/Do, is 0.53, where D and Do are the diffusion coefficients o...

Adsorptive cathodic stripping voltammetric determination of hexavalent chromium

Abstract: A sensitive and selective voltammetric method of analysis is developed for determination of trace amounts of Cr(VI) ions in neutral nitrate phosphate media. This method is based on controlled adsorptive preconcentration of chromium species at Hanging Mercury Drop Electrode (HMDE). The adsorptive stripping response was evaluated with respect to preconcentration time and potential and dependence on composition of supporting electrolyte. As low as 5x10−9 mol L−1 (0.25 μg/L) and 1x109 mol L−1 (0.52 μg/L) Cr(VI) can be detected using Cathodic Linear Sweep Stripping Voltammetry (CLSSV) and Differential Pulse Cathodic Stripping Voltammetry (DPCSV), respectively. The precision of the method is satisfactory with a relative deviation of 1.24% with ten experiments at the 0.52 μg 1−1 Cr(VI) level. The effect of various cations, anions and surface active substances (SAS) in synthetic aqueous samples has been investigated.

Anodic oxidation of dimethyl sulfoxide based electrolyte solutions: An in situ FTIR study

Abstract: Anodic oxidation of dimethyl sulfoxide (DMSO) based electrolyte solutions, containing LiClO4, LiBF4 and KPF6, on platinum (Pt), glassy carbon (GC) andn-TiO2 (anatase), electrodes was studied usingin situ Fourier transform infrared spectroscopy (FTIR). All solutions contained small amounts of H2O. Regardless of the supporting electrolyte all systems were unstable at potentials above 1.0 V vs SCE. The major oxidation product is dimethyl sulfone, formation of which is initiated by the trace water breakdown. In contrast to acetonitrile based solutions there is no evidence of electrolyte involvement in the breakdown process. Photoanodic decomposition of dimethyl sulfoxide based solutions proceeds in the same way as the anodic oxidation in the dark. In the presence of nucleophilic agent (iodides) the prevailing redox process is iodide oxidation. Small amounts of, probably, methylsulfinyliodide are also formed. The irreversible consumption of charge mediator significantly restricts the possible practical use of DMSO in photoelectrochemical devices.

Electrosynthesis and co-ordination chemistry of polymer films coated on electrode surfaces from pyrrole polypyridyls

Abstract: New functionalized polypyrrole films containing transition-metal complexes of the type [Mn(bipy)3]2+(bipy = 2,2′-bipyridine) and [MIL(diene)]+(M = Rh or Ir, L = 2,2′-bipyridine or 1,10-phenanthroline, diene = cycloocta-1,5-diene or norborna-2,5-diene) have been synthesized and characterized by electrochemical techniques and UV/VIS spectroscopy. The strategy is based on the complexation of Mn2+ cations and [{MI(diene)Cl}2] precursor complexes in polymer films, coated on platinum and carbon electrodes by oxidative electropolymerization of pyrrole-substituted 2,2′-bipyridine and 1,10-phenanthroline monomers in acidic MeCN electrolyte. The redox behaviour of poly[MIL(diene)+] is strongly dependent on the size of the cation of the supporting electrolyte. This appears to be a consequence of its permeation through the film to maintain electroneutrality in the polymer.

Method and apparatus for forming electrolytic water and apparatus for washing semiconductor substrate using electrolytic water-forming apparatus

Abstract: In forming an electrolytic water, pure water or ultra-pure water is added to at least one solid supporting electrolyte selected from the group consisting of oxalic acid, ammonium oxalate, ammonium formate, ammonium bicarbonate, and ammonium tartrate to prepare a solution saturated with the supporting electrolyte. The solution containing the supporting electrolyte is subjected to hydrolysis to obtain an anodic water and a cathodic water.