Copper(II)-selective membrane electrode based on a recently synthesized naphthol-derivative Schiff’s base

A PVC membrane electrode for copper(II) ions based on a recently synthesized naphthol-derivative Schiff’s base as membrane carrier was prepared. The sensor exhibits a Nernstian response for Cu²⁺ ions over a wide concentration range (5.0 × 10^–6–5.0 × 10^–2 mol/L) with a detection limit of 3.1 × 10^–6 mol/L (0.2 μg/mL). It has a very short response time of about 5 s and can be used for ¶3 months without any divergence in potential. The proposed electrode revealed good selectivities over a wide variety of other cations including alkali, alkaline earth, transition and heavy metal ions and could be used in a pH range of 4.0–7.0. It was successfully applied to the direct determination and potentiometric titration of copper ion.     

Development of All‐solid‐state Antidiabetic Drug Metformin‐selective Microsensor and its Electrochemical Applications

In this study, all‐solid‐state type potentiometric PVC membrane selective microsensor was developed for Metformin (MET) which is an antidiabetic drug active substance. Metformin‐tetraphenylborate (MET‐TPB) ion‐pair was used as an ionophore in the structure of the sensor membrane. It was determined that the sensor membrane at the ratio of 69 % o‐nitrophenyl octyl ether, 27 % polyvinyl chloride and 4 % MET‐TPB performed the best potentiometric performance. In a wide concentration range (1×10^?5–1×10^?1 mol/L), the slope, detection limit, response time, pH range, and life‐time of the sensor were determined as 55.9±1.6 mV (R²=0.996), 3.35×10^?6 mol/L, 8–10 s, pH: 3–8, and ～10 weeks, respectively. The voltammetric performances of the sensor were also investigated. The prepared microsensor was successfully utilized for the determination of Metformin in a pharmaceutical drug sample by potentiometry and voltammetry. It was observed that the obtained results were in agreement with the results obtained by the UV spectroscopy method at 95 % confidence level.     

Analytical Study of New Creatininium and Tetramethyl-ammonium Cation Selective Membrane Electrodes

Abstract

Two new liquid membrane electrodes which respond to creatininium and tetramethylammonium cations are described. The creatininium cation electrode exhibits rapid and near Nernstian response to creatininium cation activity, at pH 3, in the 10^?3?10^?1 mol/L range. The useful concentration range extends to 10^?4 mol/L. The tetramethyl-ammonium cation electrode exhibits rapid and near Nernstian response to tetramethylammonium cation activity, at pH 2–11.5, in the 2x10^?5? 10^?1 mol/L range. Major interferences for the creatininium electrode are Na⁺, K⁺, NH⁺ ₄ and creatine. The pK_a of the creatininium cation was calculated. A method is described for the potentiometric precipitation titration of tetramethylammonium cation with sodium tetraphenylboron. Amounts of tetramethylammonium in the range 20–200 μol have been determined using Gran's plots, with an average error of about 0.6%.     

Carrier-facilitated liquid membrane extraction of penicillin G from aqueous streams

Kinetics and mechanism for the carrier-facilitated transport of penicillin G from aqueous solutions through a supported liquid membrane containing Amberlite LA-2 were investigated. The strip phase was either phosphate buffer or sodium carbonate solution. Experiments were performed as a function of the pH, the concentrations of penicillin G in the feed phase and of amine in the membrane phase. A transport model was proposed considering aqueous film diffusion, interfacial chemical reaction, and membrane diffusion. The calculated rates were found to agree with the measured ones (average standard error, 12%). Under the conditions investigated (feed pH 5.02–7.83, penicillin G concentration 10–500 mol/m³, amine concentration 50–1000 mol/m³), the present transport process was shown to be governed by combined interfacial chemical reaction and membrane diffusion.     

Vermiculite clay mineral as an effective carbon paste electrode modifier for the preconcentration and voltammetric determination of Hg(II) and Ag(I) ions

A vermiculite modified carbon paste electrode (VMCPE) was employed for the in situ preconcentration of traces of Hg(II) and Ag(I) via an ion-exchange route. Heavy metal ions were accumulated in Britton-Robinson (BR) buffer pH 7 for Hg(II) and pH 6 for Ag(I), and afterwards reduced at –0.7 V vs. Ag/AgCl in the separate measurement solution (BR buffer pH 5 + 0.05 mol/L NaNO₃) prior to the anodic stripping square-wave voltammetric (ASSWV) detection. For Hg(II) ions, at 15 min accumulation, a linear range from 1.0 × 10^–7 to 8.0 × 10^–6 mol/L was obtained, with a 5.7 × 10^–8 mol/L limit of detection. The VMCPE response was linear for Ag(I) ions in the concentration range from 2.0 × 10^–7 to 8.0 × 10^–6 mol/L, at 10 min accumulation with a corresponding limit of detection of 6.3 × 10^–8 mol/L. The relative standard deviation of the analytical procedure including accumulation from a 5 × 10^–7 mol/L solution of Hg (15 min) or Ag(I) (10 min), electrolysis, ASSWV detection, regeneration and activation of the VMCPE, was 4% (n = 6). The optimisation of the parameters for the application of the VMCPE in combination with ASSWV detection is presented and discussed.     

Transport of Tb3+in Dispersion Supported Liquid Membrane System with Carrier P507

The Tb³⁺ transport in dispersion supported liquid membrane (DSLM) consisting of polyvinylidene fluoride membrane (PVDF) as the liquid membrane support and dispersion solution including HCl solution as the stripping solution and 2‐ethyl hexyl phosphonic acid‐mono‐2‐ethyl hexyl ester (P507) dissolved in kerosene as the membrane solution, has been studied. The effects of pH value, initial concentration of Tb³⁺ and different ionic strength in the feed phase, volume ratio of membrane solution and stripping solution, concentration of HCl solution, concentration of carrier, different stripping agents in the dispersion phase on transport of Tb³⁺ has also been investigated, respectively. As a result, the optimum transport conditon of Tb³⁺ was that concentration of HCl solution was 4.0 mol/L, concentration of P507 was 0.10 mol/L, and volume ratio of membrane solution and stripping solution was 1.0 in the dispersion phase, and pH value was 5.2 in the feed phase. Ionic strength had no obvious effect on transport of Tb³⁺. Under the optimum condition studied, when initial concentration of Tb³⁺ was 1.0×10^?4 mol/L, the transport rate of Tb³⁺ was up to 95.2% during the transport time of 95 min. The kinetic equation was developed in terms of the law of mass diffusion and the theory of interface chemistry. The results were in good agreement with the literature data.     

Aqueous Systems Based on Metaphos in Low Concentration: The Relationship between Self-Assembly,Physico-Chemical,and Biological Properties

It has been shown for the first time that aqueous solutions of metaphos pesticide (1×10^–4–1×10^–17 mol/L) are disperse systems, the disperse phase undergoing rearrangement upon dilution. The relationship between nonmonotonic concentration dependences of the nanoassociate size, physico-chemical properties of the systems, and their action on higher plants and hydrocoles has been found.     

Development of Pr(III) Selective Electrode Using 1,6,7,12‐Tetramine‐2,5,8,11‐tetraoxo‐1(12),6(7)‐di(biphenyl)‐dodecane (TATODBDD) as a Neutral Carrier

A polyvinyl chloride (PVC) membrane based Pr(III) selective electrode was constructed using 1,6,7,12‐tetramine‐2,5,8,11‐tetraoxo‐1(12),6(7)‐di(biphenyl)dodecane (TATODBDD) as a neutral carrier. The sensor exhibits a Nernstian response for Pr(III) ions, a wide concentration range of 3.9×10^?7?1.0×10^?1 mol/L with a detection limit of 5.0×10^?8 mol/L and slope of 19.5 mV/decade. The developed sensor revealed relatively good selectivity and high sensitivity for Pr(III) ions over the other lanthanide ions. The potentiometric response of the sensor is independent in the pH range 2.9–9.5. The advantages of sensor are low resistance, very fast response time (<10 s) with good selectivity. This sensor can be used up to 6 weeks without any divergences in potential response.     

Direct Electrochemistry of Hemoglobin Entrapped in Composite Electrodeposited Chitosan‐Multiwall Carbon Nanotubes and Nanogold Particles Membrane and Its Electrocatalytic Application

Hemoglobin was entrapped in composite electrodeposited chitosan‐multiwall carbon nanotubes (MCNTs) film by assembling gold nanoparticles and hemoglobin step by step. In phosphate buffer solution (pH 7), a pair of well‐defined and quasireversible redox peaks appeared with formal potential at ?0.289 V and peak separation of 100 mV. The redox peaks respected for the direct electrochemistry of hemoglobin at the surface of chitosan‐MCNTs‐gold nanoparticles modified electrode. The parameters of experiments have also been optimized. The composite electrode showed excellent electrocatalysis to peroxide hydrogen and oxygen, the peak current was linearly proportional to H₂O₂ concentration in the range from 1×10^?6 mol/L to 4.7×10^?4 mol/L with a detection limit of 5.0×10^?7 mol/L, and this biosensor exhibited high stability, good reproducibility and better selectivity. The biosensor showed a Michaelis–Menten kinetic response as H₂O₂ concentration is larger than 5.0×10^?4 mol/L, the apparent Michaelis–Menten constant for hydrogen peroxide was calculated to be 1.61 μmol/L.     

Adsorptive Voltammetric Measurement of Trace Level of Iron(III) with 4–(2–Pyridylazo) Resorcin

Abstract

The polarographic behavior of the complex of iron–4– (2–pyridylazo) resorcin(PAR) was studied. In HAc– NaAc– EDTA buffer solution, the complex can be adsorped on a hanging mercury drop electrode giving a sensitive adsorptive complex reduction peak with a peak potential at -0.36V(vs. SCE). Optimum experimental conditions were found by the use of 0.08mol/L HAc, 0.06mol/L NaAc, 5.0 × 10^?3mol/L EDTA and 1.0 × 10^?5mol/L PAR. With preconcentration for 60s, the derivative peak height of the complex compound is linearly proportional to the concentration for Fe in the range from 1.0 × 10^?9mol/L to 1.0 × 10^?7mol/L. For a 2–min pre–concentration time, the detection limit found was 2.0 × 10^?10mol/L. This method has high sensitivity and selectivity. It has been applied to the determination of trace iron in food and water samples without any pre–separation step.     

Separation of Trivalent Samarium through Facilitated Stripping Dispersion Hollow Fiber Liquid Membrane Using p204 as Mobile Carrier

The separation of Sm(III) through stripping dispersion hollow fiber liquid membrane system (SDHFLM) containing feed phase adding acetate buffer solution and dispersion solution with HCl solution as the stripping solution and membrane solution of di(2‐ethylhexyl) phosphoric acid (p204) dissolved in kerosene, has been studied. A set of factors were studied, including pH value, initial concentration of Sm(III) and different ionic strength of feed phase, volume ratio of membrane solution and stripping solution (O/W), HCl concentration, carrier concentration, different stripping agents of dispersion phase on Sm(III) separation. Experimental results indicate that the optimum separation conditions of Sm(III) were obtained as that HCl concentration was 4.00 mol/L, p204 concentration was 0.150 mol/L, and volume ratio of membrane solution and stripping solution (O/W) was 1.00 in the dispersion phase, and pH value was 4.60 in the feed phase. Ionic strength had no obvious effect on separation of Sm(III). When initial Sm(III) concentration was 1.00×10^?4 mol/L, the separation rate of Sm(III) was up to 93.5% in 85 min. The kinetic equation was developed in terms of the law of mass diffusion and the theory of interface chemistry. The modeled results were in good agreement with the experiment data.     

A Neutral Carrier Membrane Calcium-Sensitive Electrode with Wide Working pH Range

Abstract

A poly(vinyl chloride) (PVC) membrane calcium-sensitive electrode based on a new type of synthetic carrier 1,7-di[2-(1-phenylazo)naphtyl]-1,4,7-trioxaheptan is introduced. This electrode exhibited Nernstian response over the concentration range 1.0×10^?1 - 3.0×10^?8 mol/L Ca²⁺ with a slope of 28.8 mV/pCa in calcium ion buffer solutions. The detection limit for calcium ion was 1.0X10^?8 mol/L. The response time varied from 10 to 30 seconds. The working pH range for the electrode was 3.5 - 12.3 when the concentration of Ca²⁺ was 10^?3 mol/L. The lifetime of the electrode was proved to exceed 8 months. It was applied successfully in the determination of calcium ion in river water, mineral water and cosmetic. A method for the determination of total calcium in urine was developed.     

Disperse systems based on chloracetophos in the low concentration range: self-organization,physicochemical properties and influence on representatives of higher plants and hydrobionts

A set of physicochemical methods was used to establish that aqueous solutions of chloracetophos fungicide and bactericide (1) in the range of calculated concentrations from 1?10^–18 to 1?10^–4 mol L^–1 are disperse systems in which a dispersed phase hundreds of nanometers in size is formed above and below a threshold concentration of 1?10^–9 mol L^–1. Upon dilution disperse systems 1 are capable of non-monotonic changing the physicochemical properties and changing the toxicity profile (inhibition–stimulation) when influencing the growth and development of unicellular algae Chlorella vulgaris. The formation of domains and nanoassociates is accompanied by the appearance in the UV spectrum of an absorption band at 210–300 nm with a maximum at ~220 nm (A₂₂₀). The interrelated concentration dependences of A₂₂₀, the size of the dispersed phase, and electrical conductivity indicates that the observed spectral features of systems 1 are caused by the properties of the domains and nanoassociates.     

Kinetics of the <Emphasis Type="Italic">n</Emphasis>-Decanol Oxyethylation Reaction with Allowance for Association

The kinetics of n-decanol oxyethylation in the temperature range of 60–150°C at a pressure of 1.4MPa is investigated under conditions of base catalysis and an excess of alcohol in the initial step of the reaction (initial concentration of ethylene oxide in the reaction mixture, approximately 1 mol/L; that of the catalyst, 10^?1 to 10^?3 mol/L). The experimental results are satisfactorily described by a kinetic equation that allows for the association of alcohol molecules and is first order with respect to the concentration of alcohol associates. Based on kinetic studies and thermogravimetry, it is concluded that the structural rearrangement of liquid decanol occurs at a temperature of around 87.5°C.     

Electrochemical Polymerization of Azure Blue H and Its Electro-catalytic Activity toward NADH Oxidation

Poly (azure blue II) (PABII) thin film modified electrode was successfully assembled on the surface of a glassy carbon electrode by means of electrochemical polymerization, which was carried out with cyclic voltammetric sweeping in the potential range of ‐ 0.6 to + 1.3 V (vs. SCE) in Britton‐Robinson buffer solution (pH = 9.8) containing 1.25 ± 10–⁴ mol/L azure blue II. The effect of pH on the polymerization process of azure blue II and the electrochemical characteristics of the polymer‐modified electrodes were studied in detail. The experimental results indicated that the electropolymerization of azure blue II could take place in basic or neutral media. The cyclic voltammograms of poly (azure blue II) thin film modified electrode showed the presence of two couples of redox peaks. The film modified electrode exhibited potent and persistent electrocatalysis for oxidation of dihydronicotiamide adenine dinucleotide (NADH) in phosphate buffer media with a diminution of the overpotential of about 410 mV and an increase in peak current. The presence of some divalent cations in an electrolyte can greatly enhance the electrocatalytic current for oxidation of NADH. The electrocatalytic current increased linearly with NADH concentration from 1.0 ± 10–⁵ to 8.0 ± 10–³ mol/L in the presence of 4.0 ± 10–² mol/L Mg²⁺ cation. The detection limit (3s_b1/S) was 5.0 ± 10–⁶ mol/L, and the relative standard deviation of determination results was 4.2% for six successive determinations of 5.0 ± 10–⁴ mol/L NADH in the presence of Mg²⁺ cation.     

Metallophthalocyanine Based Carbon Paste Electrodes for the Determination of 2′,3′‐Dideoxyinosine

Novel electrochemical sensors based on carbon paste impregnated with metallopthalocyanine (MPc, M=Co, Fe) complexes, have been constructed for the assay of anti‐HIV drug 2′,3′‐dideoxyinosine (didanosine, DDI). Both modified electrodes showed electrocatalytic activity towards the oxidation of dideoxyinosine in phosphate buffer pH 7.4 with a working concentration range of 10^?6–10^?4 mol/L and a detection limit of 10^?7 mol/L magnitude order. The sensor proved to be highly reliable for the assay of the purity of DDI ‐ raw material as well as for the uniformity content test of Videx tablets.     

Study on the Electrochemical Behavior of Dopamine and Uric Acid at a 2‐Amino‐5‐mercapto‐[1,3,4] Triazole Self‐Assembled Monolayers Electrode

Selected from a series of structurally related heteroaromatic thiols, a newly synthesized reagent 2‐amino‐5‐mercapto‐[1,3,4] triazole (MATZ) was used to fabricate self‐assembled monolayers (SAMs) on gold electrode for the first time. The MATZ/Au SAMs was characterized by electrochemical methods and scanning electronic microscopy (SEM). In 0.04 mol/L Britton–Robinson buffer solution (pH 5), the electrochemical behavior of dopamine showed a quasireversible process at the MATZ/Au SAMs with an electrode kinetic constant 0.1049 cm/s. However, the electrochemical reaction of uric acid at the SAMs electrode showed an irreversible oxidation process, the charge‐transfer kinetics of uric acid was promoted by the SAMs. By Osteryoung square‐wave voltammetry (OSWV), the simultaneous determination of dopamine and uric acid can be accomplished with an oxidation peak separation of 0.24 V, the peak current of dopamine and uric acid were linearly to its concentration in the range of 2.5×10^?6–5.0×10^?4 mol/L for dopamine and 1×10^?6–1×10^?4 mol/L for uric acid with a detection limit of 8.0×10^?7 mol/L for dopamine and 7.0×10^?7 mol/L for uric acid. The MATZ/Au SAMs electrode was used to detect the content of uric acid in real urine and serum sample with satisfactory results.     

Determination of Trace Copper by Adsorptive Voltammetry Using a Multiwalled Carbon Nanotube Modified Carbon Paste Electrode

A new method for the determination of trace copper was described. A multiwalled carbon nanotube modified carbon paste electrode was prepared and the adsorptive voltammetric behavior of copper‐alizarin red S (ARS) complex at the modified electrode was investigated. By use of the second‐order derivative linear sweep voltammetry, it was found that in 0.04 mol/L acetate buffer solution (pH 4.2) containing 4×10^?6 mol/L ARS, when accumulation potential is 0 mV, accumulation time is 60 s and scan rate is 100 mV/s, the complex can be adsorbed on the surface of the electrode, yielding one sensitive reduction peak at ?172 mV (vs. SCE). The peak current of the complex is proportional to the concentration of Cu(II) in the range of 2.0×10^?11–4.0×10^?7 mol L^?1 with a detection limit (S/N=3) of 8.0×10^?12 mol/L (4 min accumulation). The proposed method was successfully applied to the determination of copper in biological samples with satisfactory results, the recoveries were found to be 96%–102%.     

A new molecularly imprinted polymer for selective extraction and pre‐concentration of guaifenesin in different samples: Adsorption studies and kinetic modeling

This paper describes the synthesis of a molecularly imprinted polymer by chemical oxidation of pyrrole as the functional monomer, and at the presence of guaifenesin as the template. The prepared polymer was used as adsorbent in molecularly imprinted solid‐phase extraction followed by spectrophotometric determination. Different parameters in the solid‐phase extraction including sample pH, adsorbent weight, washing solution, and elution solvent were studied to determine optimum conditions for isolation and enrichment of guaifenesin. The results showed guaifenesin was quantitatively adsorbed on the molecularly imprinted polymer at pH 6.0 and completely eluted with an ethanol–water solution (50% v/v). An enrichment factor of four with satisfactory recoveries (87.0–95.0%) was obtained. The solid‐phase extraction columns could be used for up to six consecutive elution‐loading cycles without significant decreases in the analyte recoveries. The method had a dynamic range of 3.0 × 10^?6–1.5 × 10^?4 mol/L with a limit of detection and limit of quantification of 1.4×10^?6 and 4.5×10^?6 mol/L, respectively. The proposed procedure was used for the extraction and determination of guaifenesin in different pharmaceutical formulations, with satisfying results being achieved.     

A PVC-based cryptand C2B22 membrane potentiometric sensor for zinc(II)

A PVC membrane electrode for zinc ions based on cryptand C2_B22 as membrane carrier was prepared. The electrode exhibits a linear stable response over a wide concentration range (5.0 × 10^–2– 5.0 × 10^–5 mol/L) with a slope of 24 mV/ decade and a limit of detection of 3.98 × 10^–5 mol/L (2.6 μg/g). It has a fast response time of about 30 s and can be used for at least 4 months without any divergence in potential. The proposed sensor revealed good selectivities for Zn²⁺ over a wide variety of other metal ions and could be used in a pH range of 4–7. It was used as an indicator electrode in potentiometric titration of zinc ion. Received: 26 February 1998 / Revised: 25 May 1998 / Accepted: 28 May 1998