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A thiocyanate ion selective electrode was prepared. The electrode showed a good selectivity and sensitivity, wide dynamic range, low detection limit, fast response time and applicable for analytical samples.

In this paper electropolymerization of a thin film of para‐phenylenediamine (PPD) is studied at glassy carbon electrode (GCE) in sulfuric acid media by cyclic voltammetry. The results showed that this polymer was conducting and had a reproducible redox couple in the potential region from 0.0 to 0.4 V in phosphate buffer solution. This modified GCE (p‐PPD‐GCE) was applied for simultaneous determination of ascorbic acid (AA), dopamine (DA) and uric acid (UA) using differential pulse voltammetry (DPV). The p‐PPD‐GCE in 0.1 M phosphate buffer solution (pH 5.0) separated the DPV signals of AA, DA and UA with sufficient potential differences between AA–DA and DA–UA and also enhanced their oxidation peak currents. The oxidation currents were increased from 2.0 to 2000.0 µM for AA, 10.0 to 1250.0 µM for DA and 50.0 to 1600.0 µM for UA. The detection limits were evaluated as 0.4, 1.0 and 2.5 µM for AA, DA and UA, respectively (S/N=3).

A PVC membrane electrode based on copper(II) bis(N-2-bromophenylsalicyldenaminato) as ionophor was prepared. The ion selective electrode was tested by inorganic anions and showed a good selectivity for iodide ion. This sensor exhibited Nernstian behavior with a slope of −57.8mV per decade at 25°C. The proposed electrode showed a linear range from 1.0×10−5to 1.0×10−1mol/L with a detection limit of 5.0×10−6mol/L. The electrode response was independent of pH in the range of 3.0–10.0. The proposed sensor was applied to determine the iodide in water and antiseptic samples.

Abstract: Simultaneous kinetic-potentiometric determination of binary mixture of permanganate (MnO4−) and dichromate (Cr2O72−) by H-point standard addition method (HPSAM), partial least squares (PLS) and principal component regression (PCR) is described. In this work, the difference between the rate of the oxidation reaction of Fe(II) to Fe(III) in the presence of MnO4− and Cr2O72− formed the basis of the method. The rate of the consumed fluoride ion for making the complex was detected by a fluoride ion selective electrode (FISE). The results show that the simultaneous determination of MnO4− and Cr2O72− could be conducted in their concentration ranges of 0.5–10.0 and 0.1–20.0 μg ml−1, respectively. The total relative standard error (RSE) for applying the PLS and PCR methods to 9 synthetic samples was 5.30 and 3.17, respectively in the concentration range of MnO4−, and 3.30 and 2.04, respectively, in the concentration range of Cr2O72−. In order for the selectivity of the method to be assessed, we evaluated the effects of certain foreign ions upon the reaction rate. The proposed methods (HPSAM, PLS and PCR) were evaluated using a set of synthetic sample mixtures and then applied to the simultaneous determination of MnO4− and Cr2O72− in different water samples.

A carbon-paste electrode (CPE) was chemically modified with TiO2nanoparticles and quinizarine (QZ). This was used as an electrochemical sensor for the determination of minor amounts of hydroxylamine (HX). The modified electrode showed very efficient electrocatalytic activity for the anodic oxidation of hydroxylamine, owing to a substantial decrease in anodic overpotentials. Under optimal conditions, the linear range span of HX concentration was 1.0 μM to 400.0 μM and the detection limit was 0.173 μM at a signal-to-noise ratio of 3, using differential pulse voltammetry (DPV). The diffusion coefficient and kinetic parameters (e.g., electron transfer coefficient for HX) were also determined using electrochemical approaches. The sensor demonstrated good stability and reproducibility. To evaluate the applicability of the proposed method to real samples, the modified CPE was applied to the determination of HX in water samples.

Abstract: A sensitive and selective electrochemical method for the determination of L-cysteine was developed using a modified carbon paste electrode (MCPE) with quinizarine. Cyclic voltammetry was used to investigate the redox properties of this modified electrode at various solution pH values and at various scan rates. The apparent charge transfer rate constant, ks and transfer coefficient for electron transfer between quinizarine and carbon paste electrode (CPE) were calculated as 2.76 s−1 and 0.6, respectively. This modified carbon paste electrode shows excellent electrocatalytic activity toward the oxidation of L-cysteine in a phosphate buffer solution (pH 7.0). The linear range of 1.0 × 10−6 to 1.0 × 10−3 M and a detection limit (3s) of 2.2 × 10−7 M were observed in pH 7.0 phosphate buffer solutions. In differential pulse voltammetry, the quinizarine modified carbon paste electrode (QMCPE) could separate the oxidation peak potentials of L-cysteine and tryptophan present in the same solution, though at the unmodified CPE the peak potentials were indistinguishable. This work introduces a simple and easy approach to selective detection of L-cysteine in the presence of tryptophan. Also, the modified electrode was employed for the determination of L-cysteine in the real samples such as serum of blood and acetylcysteine tablet.

A new sulfate-selective electrode based on the complex N,N′-bis(2-amino-1-oxo-phenelenyl)phenylenediamine copper(II) (CuL) as the membrane carrier was developed. The electrode exhibited a good Nernstian slope of -29.5 ±0.5 mV/decade and a linear range of 1.0 × 10−7- 1.0 × 10−1M for sulfate. The limit of detection was 1.0 × 10−8M. It has a fast response time of 10 s and can be used for more than three months. The selective coefficients were determined by the fixed interference method (FIM). The electrode could be used in the pH range 3.5-8.0. It was employed as an indicator electrode for direct determination of sulfate in pharmacy and cement samples.

The construction, performance characteristics and applications of a polymeric membrane electrode for Cuii ion are reported. The electrode was prepared by incorporating C-p-nitrophenyl-N-phenylnitrone as the charge carrier into a plasticized polyvinyl chloride membrane. The influence of membrane composition, pH and concentration of the solution were investigated. The electrode exhibits a potentiometric response for Cu2ion over the concentration range 1 × 10−6–1 × 10−1M with a detection limit of 5 × 10−7M Cu2. It shows a relatively fast response time of about 15 s and can be used for about two months without any considerable divergence in potential. The electrode can be used at a pH of between 4.0–8.0. The selectivity of proposed electrode for Cu2in the presence of several metal ions. It was used as an indicator electrode in the potentiometric titration of Cu2with EDTA.