PVC Membrane electrode for trinitrobenzenesulfonate and its use for indirect determination of amino acids

A PVC membrane electrode of the conventional type was prepared which is selective for trinitrobenzenesulfonate (TNBS^–). It showed a rapid Nernstian response within the TNBS^– concentration range 1.0 × 10^–5 to 1.0 × 10^–2 M at 25 ± 0.1°C. The electrode was selective, precise (RSD < 0.87% for TNBS^– and < 1.32% for amino acids) and usable within the pH range 2.5–12. The standard electrode potentials,E°, were determined at different temperatures and used to calculate the isothermal temperature coefficient of the cell. Selectivity coefficients for numerous compounds are given. The electrode has been used for the direct determination of trinitrobenzenesulfonic acid in aqueous solutions either by the standard additions method or by potentiometric titration against cetyltrimethylammonium bromide (CTABr) at pH 7. The electrode has been also applied successfully for the indirect microdetermination of neutral, acidic and basic amino acids separately, and as binary or ternary mixtures of neutral amino-acids. Total amino acids were determined in urine samples.     

Potentiometric study using chemically modified silica gel with pyridinium as membrane for ClO 4 − ions

A potentiometric sensor for the perchlorate anion was developed by mixing chemically modified silicagel with pyridinium perchlorate, with an epoxy polymer and graphite. The electrode showed Nernstian response between 1.0 × 10^–2 and 1.0 × 10^–3 M perchlorate concentrations. The electrode showed high selectivity to this ion at solutions pH between 5.5 and 8.0. The presence of IO ₄ ^– , NO ₃ ^– ,Br^–, IO ₃ ^– , Cl^– and SO ₄ ^2– ions in the solutions, had only small interference in the electrode response in the range mentioned.     

Molarity and ionic strength of focused carrier ampholytes in isoelectric focusing

Focused 1% carrier ampholytes in the pH range 3.5–10 have a molarity of 9–1 0 mM, as determined by osmolarity measurements of fractions focused in free water. From electrophoretic and isoelectric focusing data of red blood cells, it has been demonstrated that the corresponding ionic strength is 0.5 mg-ions/1. Also theoretical considerations and conductivity measurements point to a value in the range of 0.5–1.0 mg-ions/1. The following equations for ionic strength (I) calculations have been derived:I = _amph + C_Hin the pH range 2.5–7 andI = _amph + C_OHin the pH range 7–11.     

魔芋多糖固定化肌红蛋白的直接电化学与电催化

用魔芋多糖(KGM)和N,N-二甲基甲酰胺(DMF)的加合物,将肌红蛋白(Mb)固定在玻碳电极(GCE)上,制备了稳定的Mb-KGM-DMF/GCE修饰电极,并研究了Mb在修饰电极上的直接电化学行为和电催化性能。该电极在pH=7.0的磷酸盐缓冲溶液(PBS)中,-0.38 V(E0′)处有一对氧化还原峰,峰电位差ΔEp=70 mV,该峰正是Mb中血红素辅基FeⅢ/FeⅡ电对的氧化还原特征峰。在0.2~9.0 V/s扫速的范围内,氧化还原峰峰电流大小和扫描速率成正比,呈现出表面控制行为。在pH为5.0~12.0的范围内,式电位和pH值呈线性关系,表明电子传递过程伴随着质子转移。同时,Mb-KGM-DMF/GCE修饰电极表现出良好的电催化性能,对氧、H2O2有显著的催化作用。在4.70~75.0μmol/L的范围内,其催化峰电流大小与H2O2的浓度有良好的线性关系,其线性回归方程i=0.127 0.093C,r=0.9989,表观米氏常数为80.8μmol/L。     

Estimation of Cr(VI) in water,tannery and plating wastes

Summary Estimation of Cr(VI) in Water, Tannery and Plating Wastes A zirconium tellurite membrane exhibits good selectivity for CrO₄ ^2– or CrO₇ ^2– ions at pH 3–6 and 8–11. Membrane electrode can be used to determine the activity of Cr(VI) ions in the concentration range 10^–1 to 7×10^–5 M at specified pH. The response time is 30 s and a large number of anions and cations do not interfere with the functioning of this assembly. It has been tried for the estimation of Cr(VI) in plating and tannery waste.     

A new ionic strength adjustor for nitrate analysis in waters,soils and plants using ion-selective electrode

A new ionic strength adjustor, ISA (ISA-Pb) composed of 0.02M Pb(CH₃COO)₂–0.01M PbO–0.02M CH₃COOK–0.01M NH₂SO₃H, was tested for the rapid nitrate analysis of waters, soil and plant extracts by means of ion-selective electrode (ISE). It was found that nitrate can be determined accurately and precisely within the concentration range of 5 × 10^–2 M to 2 × 10^–6 M. The proposed ISA-Pb, with a pH of 6.8, controlled the interferences of Cl^–, HCO ₃ ^– , NO ₂ ^– , and organic anions effectively, and gave results comparable to those obtained by the commonly used ISA with Ag₂SO₄ (ISA-Ag) and to well established chemical methods as well. ISA-Pb is much cheaper than ISA-Ag, and can therefore economically replace the latter when ISE is used for nitrate determination.Part of the senior author's doctorate thesis     

Spectroelectrochemical study of the corrosion of a copper electrode in deaerated 1.0 M HCl solutions containing Fe(III): Effect of the corrosion inhibitor benzotriazole

The corrosion rate of a copper electrode in deaerated 1.0 M HCl by Fe(III) ions, in the absence and presence of benzotriazole (BTAH), has been evaluated through weight-loss experiments using a rotating disk electrode (RDE). The corrosion process is controlled by transport of the Fe(III) ions to the electrode surface both in the absence and presence of BTAH. The inhibiting action is initiated at BTAH concentrations around 10 mM and the Langmuir adsorption isotherm is obeyed in the BTAH concentration range from 10 to 45 mM with an apparent equilibrium adsorption constant of 10 M⁻¹. Above this concentration, the Langmuir plot is not obeyed due to the formation of a multilayer. The surface films formed during the corrosion process have been investigated by “in situ” and “ex situ” fluorescence and Raman spectroscopy and characterized as being composed of the polymeric [Cu(I)BTA] complex and [Cu(I)CIBTAH]₄, the former as an inner layer response for the corrosion inhibition process.     

Preconcentration and voltammetric determination of the herbicide metamitron with a silica-modified carbon paste electrode

A carbon paste electrode incorporating silica (Si-MCPE) was fabricated to accumulate Metamitron at the electrode surface. Several electroanalytical techniques were used to explore its reductive behaviour. The results indicate that the system is irreversible and fundamentally controlled by adsorption. The adsorptive stripping response has been evaluated with respect to accumulation time, deposition potential, scan rate, pH and other variables, using differential pulse voltammetry (DPV) and square wave voltammetry (SWV) as redissolution techniques. In both cases a voltammetric peak is obtained, at –0.542 V (DPV) and –0.421 V (SWV) in Britton-Robinson buffer (pH 1.9). The detection limits were 3.66 × 10^–1 M and 4.22 × 10^–9 M for AdS-DPV and AdS-SWV, respectively. Under optimum conditions the Metamitron reduction peak gave two linear regions in the range from 4.0 × 10^–9 M to 8.0 × 10^–8 M by means of AdS-DPV, with a coefficient of variation of 2.19% (n = 10) for 1 × 10^–8 M herbicide solution. A method was developed for determination of Metamitron in soils, with a recovery of 98.8% and a coefficient of variation of 5.26% (0.01 g/g of soil).     

Flow injection analysis of gallic acid with inhibited electrochemiluminescence detection

A flow injection (FI)–electrochemiluminescent (ECL) method has been developed for the determination of gallic acid, based on an inhibition effect on the Ru(bpy)₃²⁺/tri-n-propylamine (TPrA) ECL system in pH 8.0 phosphate buffer solution. The method is simple and convenient with a determination limit of 9.0×10^–9 mol/L and a dynamic concentration range of 2×10^–8–2×10^–5 mol/L. The relative standard deviation (RSD) was 1.0% for 1.0×10^–6 mol/L gallic acid (n=11). It was successfully applied to the determination of gallic acid in Chinese proprietary medicine—Jianming Yanhou Pian. The inhibition mechanism proposed for the quenching effect of the gallic acid on the Ru(bpy)₃²⁺/TPrA ECL system was the interaction of electrogenerated Ru(bpy)₃^2+* and o-benzoquinone derivative at the electrode surface. The ECL emission spectra and UV-visible absorption spectra were applied to confirm the mechanism.     

Determination of tantalum with hexafluorotantalate(V)-selective coated graphite electrode

A hexafluorotantalate(V)-selective coated-graphite electrode was prepared by coating a graphite rod with brilliant green-hexafluorotantalate(V) extract in 1-chloronaphthalene in a PVC matrix. Potential measurements were made against an HF-resistant plastic sleeve (Ag/AgCl) external reference electrode. The concentrations of sulfuric and hydrofluoric acids, for the optimum response of the electrode to hexafluorotantalate(V), were found to be 1M each in the test solutions. The electrode responded to hexafluorotantalate(V) in the linear range 5.0 × 10^–6-5.0 × 10^–3 M, with a slope of -58 mV per decade and detection limit of 8.0 × 10^–7 M within 5–15s. The relative standard deviation for six determinations of 1.0 × 10^–4 M tantalum(V) was 2%. The life-time of the electrode was 60 days. The effects of forty diverse ions on the electrode response to the hexafluorotantalate(V) were studied and the electrode was found to be highly selective to hexafluorotantalate(V). Niobium, the element that commonly occurs with tantalum ores, showed a very low level of interference. The newly developed coated-graphite electrode has been applied to the determination of tantalum in tantalite-columbite ores and several synthetic matrices by direct, sample addition, standard addition, and Gran's plot potentiometric techniques with reasonable precision (2–4%) and accuracy.     

A novel nitrate-selective electrode based on precipitated nitron nitrate

Summary A nitrate-selective electrode based on precipitated nitron nitrate in an epoxy resin matrix has been prepared. The lower detection limit is 10^–5 M, the optimum pH range is 2.0–8.5, and the response time is 1 min. The electrode is selective in presence of CH₃COO^–, SO₄ ^2–, C₂O₄ ^2–, PO₄ ^3–, NO₂ ^–, Cl^– and Br^–, but I^– interferes. Results for nitrate in soil samples were in agreement with values obtained spectrophotometrically.

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Eine neue nitrat-spezifische Elektrode auf der Basis gefällten Nitronnitrats

Zusammenfassung Eine nitrat-spezifische Elektrode auf der Basis gefällten Nitronnitrats in einer Epoxyharz-Matrix wurde hergestellt. Die untere Nachweisgrenze ist 10^–5 M, das pH-Optimum liegt zwischen 2,0 und 8,5, die Reaktionszeit beträgt 1 Minute. Die Elektrode ist selektiv in Gegenwart von Acetat, Sulfat, Oxalat, Phosphat, Nitrit, Chlorid und Bromid; aber Jodid stört. Ergebnisse der Nitratbestimmung in Bodenproben stimmen mit spektrophotometrischen Resultaten überein.

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Presented at the 8th International Microchemical Symposium, Graz, August 25–30, 1980.     

A polynuclear mixed-valent ruthenium oxide/cyanoruthenate composite that yields thin coatings on a glassy carbon electrode with high catalytic activity toward methanol oxidation

Polynuclear ruthenium oxide/cyanoruthenate films on carbon substrates were grown by cycling the potential between 0.5 and 1.0 V (vs SCE) for 5–90 min in fresh 2 mM RuCl₃·3 H₂O, 2 mM K₄Ru(CN)₆·3 H₂O, 0.5 M KCl solution at pH 2. During the positive scans, the cationic Ru(III,IV)-oxo polynuclear species interacted with the simultaneously formed anionic CN-bridged Ru dimers to yield sparingly soluble deposits on the electrode surfaces. Different thicknesses, typically corresponding to 2–50×10⁻¹⁰ mol cm⁻², could be obtained by varying the cycling times. The absorption spectra of the coatings obtained at SnO₂-covered glass electrodes were different from those known for RuO₂ films and exhibited two absorption bands at about 400 and 700 nm. IR spectroscopic measurements confirmed the presence of a CN group in the deposit, as well as showing significant aquation of the entire coating. Ru, O, N and K (from KCl) were detected by means of Auger electron spectroscopy. The surface electrochemistry and stability of the film were significantly enhanced in K⁺-containing supporting electrolytes. The system provides a durable catalytic surface which allows the voltammetric oxidation of methanol; in 0.5 M H₂SO₄+0.5 M K₂SO₄ electrolyte the resulting anodic peak is at 1.01 V (vs. SCE). Electrooxidation was not possible at bare carbon electrodes, at least before the onset of the electrolyte decomposition.     

Characterization of a Novel Tellurite Selective Electrode

Tellurium was determined by introducing a solid membrane for the selective determination of tellurite ion. An electrode composed of a compressed disk containing a mixture of HgTeO₃and Hg₂Cl₂was found to give a typical Nernstian response of 29 mV/concentration decade for the concentration range 10⁻⁵to 10⁻¹M). The connection was made by Hg metal instead of aqueous inner filling. The optimum pH was 3.5–10.5. The selectivity of the electrode toward several inorganic and organic anions was estimated. The electrode was applied to the determination of tellurium in binary mixtures with a mean recovery of 98.99% and relative standard deviation range of 0.19–0.51%.     

Solvent Extraction Separation of Th(IV) and U(VI) with PC-88A

Liquid-liquid extraction of Th(IV) and U(VI) has been investigated by commercial extractant PC-88A in toluene. The optimum conditions for extraction of these metals have been established by studying the various parameters like acid concentration/pH, reagent concentration, diluents and shaking time. The extraction of Th(IV) was found to be quantitative with 0.1–1.0M HNO₃ acid and in the pH range 1.0–4.0 while U(VI) was completely extracted in the pH range 1.0–3.5 with 2.5·10^–2M and 2.·10^–2M PC-88A in toluene, respectively. The probable extracted species have been ascertained by log D-log C plot as ThR₄·4HR and UO₂R₂·2HR, respectively. The method permits separation of Th(IV) and U(VI) from associated metals with a recovery of 99.0%.     

A new tetrafluoroborate liquid membrane electrode for selective determination of boron

Summary The construction and performance characteristics of a new liquid membrane electrode selective for BF^– ₄ ion are described. The electrode incorporates nitron-tetrafluoroborate ion-pair complex in nitrobenzene as a liquid membrane. The electrode shows a rapid Nernstian response for BF ₄ ^– ion over the concentration range of 10^–1 to 10^–5 M and the potential is almost independent of the pH over the range of 3–9. The selectivity coefficient values obtained for 21 different anions and cations show no significant interference. The electrode is satisfactorily used for the determination of 0.5–500 g/ml of boron after conversion to BF ₄ ^– . The average recovery is 98.8% and the mean standard deviation being 2.1%.

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Neue Tetrafluoborat-Flüssigmembranelektrode zur selektiven Bestimmung von Bor

Zusammenfassung Der Aufbau und die Charakteristiken einer für BF ₄ ^– selektiven Elektrode werden beschrieben. Die Elektrode enthält den Nitron-Tetrafluoborat-Ionenpaar-komplex in Nitrobenzol als flüssige Membran. Nernstsches Verhalten ergibt sich über einen Konzentrationsbereich von 10^–1 bis 10^–5 M BF ₄ ^– . Das Potential ist fast pH-unabhängig im Bereich von 3 bis 9. Aus den Selektivitätskoeffizienten von 21 verschiedenen Anionen und Kationen ergeben sich keine signifikanten Störungen. Die beschriebene Elektrode kann mit guten Ergebnissen zur Bestimmung von 0,5 bis 500g/ml Bor nach Umsetzung zu BF ₄ ^– ₄ eingesetzt werden. Die durchschnittliche Wiederfindungsrate beträgt 98,8%, die mittlere Standardabweichung 2,1%.

     

Glucose biosensor based on glucose oxidase immobilized in sol–gel chitosan/silica hybrid composite film on Prussian blue modified glass carbon electrode

An improved amperometric glucose biosensor based on glucose oxidase immobilized in sol–gel chitosan/silica hybrid composite film, which was prepared from chitosan (CS) and methyltrimethoxysilane (MTOS), on the surface of Prussian blue (PB)-modified glass carbon electrode was developed. The film was characterized by FT-IR. Effects of some experimental variables such as ratio of CS to silica, buffer pH, temperature, and applied potential on the current response of the biosensor were investigated. The biosensor fabricated under optimal conditions had a linear response to glucose over the range 5.0×10^–5 to 2.6×10^–2 M with a correlation coefficient of 0.9948 and a detection limit of 8.0×10^–6 M based on S/N =3. The biosensor had a fast response time of less than 10 s, a high sensitivity of 420 nA mM^–1, a long-term stability of over 60 days, and a good selectivity. The apparent Michaelis–Menten constant K_m was found to be 3.2×10^–3 M. The activation energy for enzymatic reaction was calculated to be 21.9 kJ mol^–1. This method has been used to determine the glucose concentration in real human blood samples.     

Linear scan stripping voltammetry of copper(II) at the chemically modified carbon paste electrode

A new chemically modified electrode (CME), -benzoinoxime (CUPRON) modified carbon paste electrode, for determining copper(II) is reported because of its excellent selectivity and sensitivity. The electrode is made by mixing a quantity of CUPRON (25%, w/w) with graphite powder (50%, w/w) and paraffin oil (25%, w/w). The CME preferentially deposits copper from the pH 8.5 NH₃-NH₄Cl buffer solution containing copper(II) under an open circuit and most of metal ions do not interfere with the measurements. The detection limit (S/N of three) for determining Cu(II) is 3 × 10^–10 g/ml after 10 min accumulation in fast linear scan stripping voltammetric measurement. Linear calibration curves are obtained for Cu(II) concentration ranged from 1 × 10^–8 M to 1 × 10^–6 M. The response can be maintained with relative standard deviation of 6.0% in a 5 × 10^–6 M Cu(II) solution after eight accumulation/measurement/ regeneration cycles at the same electrode surface. The effect resulted from carbon paste preparation, reduction potential, electrode renewal, electrolyte and solution pH, preconcentration time, concentration dependence, possible interference and other variables has been evaluated. As for application, the CME demonstrates its high sensitivity and copper-selectivity in complex composition samples, such as anodic mud and polluted water.     

Electrochemical sensor of nitrite based on an inorganic film modified glassy carbon electrode

The electrocatalysis of nitrite in solutions at an inorganic film modified glassy carbon electrode was studied. The modifier was an electrodeposited thin inorganic film of the copper-heptacyanonitrosylferrate (CuHNF). Cyclic voltammetry of the modified electrode in a nitrite solution revealed that both oxidation and reduction of nitrite were catalyzed and the electrocatalytic currents were controlled by the diffusion of nitrite. Voltammetric and amperometric responses were investigated. When applied as an amperometric sensor in a flow injection system, the modified electrode permitted detection at — 0.55 V, over 500 mV lower than at the naked electrode surface. A linear response range extending from 1 × 10^–6 to 1 × 10^–3 M nitrite was obtained, with a detection limit of 3 × 10^–7 M. The relative standard deviation for 50 repetitive injections with a 5 × 10^–5 M nitrite solution was less than 4%. The procedure was applied to the determination of nitrite in saliva and nitrate.     

Primary amine drug sensitive electrodes based on macrocyclic polyethers with 2,2′-dinaphthyl subunits

Dinaphthyl macrocyclic polyethers were synthesized and used as neutral carriers for preparing primary amine drug sensitive PVC membrane electrodes. Contrary to the ion-associate based electrodes, which show an excellent potentiometric response to quaternary ammonium ions and the like, but a very poor response to primary amines, the macrocyclic polyether-based electrodes showed potentiometric response characteristics with primary amines preferred. Dinaphthyl macrocyclic polyether-based electrodes are superior to those based on common macrocyclic polyethers for their potentiometric selectivity coefficients much lower than those of the latter. The main characteristics of a dinaphthyl-20-crown-6-based benzyl amine sensitive electrode are as follows: linear response range, 4.2 × 10^–5 – 1.0 ×10^–1 M; slope, 51.3 mV/decade; and detection limit, 4.6 × 10^–6 M. A mexiletine sensitive electrode was prepared using dinaphthyl-23-crown-7 with following performance features: linear response range, 2.0 × 10^–5 – 1.0 ×10^–1 M; slope, 52.1mV/decade; and detection limit, 5.0 × 10^–6 M.     

Fabrication of an ion-selective electrode for determination of propylhexedrine

Electrodes of both conventional and micro-sizes were based on the use of propylhexedrine-reineckate as the ion-exchanger in a plastic membrane. The electrodes exhibited Nernstian response towards propylhexedrine (PX) over the concentration range 10^–6–10^–2 M and had life spans of up to 2 days continuous work. The working pH range was 2.3–8. Investigation of diverseions reveals good selectivity for propylhexedrine over several inorganic cations, amines, aminoacids, sugars and some pharmaceutical compounds. The electrode was applied for determination of the drug in urine with 99.1% recovery and 0.15–0.31% relative standard deviation.