Simultaneous determination of acetaminophen,dopamine and ascorbic acid using a PbS nanoparticles Schiff base-modified carbon paste electrode

A highly sensitive method was investigated for the simultaneous determination of acetaminophen (AC), dopamine (DA), and ascorbic acid (AA) using a PbS nanoparticles Schiff base-modified carbon paste electrode (PSNSB/CPE). Differential pulse voltammetry peak currents of AC, DA and AA increased linearly with their concentrations within the ranges of 3.30 × 10⁻⁸–1.58 × 10⁻⁴ M, 5.0 × 10⁻⁸–1.2 × 10⁻⁴ M and 2.50 × 10⁻⁶–1.05 × 10⁻³ M, respectively, and the detection limits for AC, DA and AA were 5.36 × 10⁻⁹, 2.45 × 10⁻⁹ and 1.86 × 10⁻⁸ M, respectively. The peak potentials recorded in a phosphate buffer solution (PBS) of pH 4.6 were 0.672, 0.390, and 0.168 V (vs Ag/AgCl) for AC, DA and AA, respectively. The modified electrode was used for the determination of AC, DA, and AA simultaneously in real and synthetic samples.     

A simple fluorescence quenching method for berberine determination using water-soluble CdTe quantum dots as probes

A novel method for the determination of berberine has been developed based on quenching of the fluorescence of thioglycolic acid-capped CdTe quantum dots (TGA-CdTe QDs) by berberine in aqueous solutions. Under optimum conditions, the relative fluorescence intensity was linearly proportional to the concentration of berberine between 2.5 × 10^?8 and 8.0 × 10^?6 mol L^?1 with a detection limit of 6.0 × 10^?9 mol L^?1. The method has been applied to the determination of berberine in real samples, and satisfactory results were obtained. The mechanism of the proposed reaction was also discussed.     

Voltammetric sensor for buzepide methiodide determination based on TiO2 nanoparticle-modified carbon paste electrode

In this work, we have prepared nano-material modified carbon paste electrode (CPE) for the sensing of an antidepressant, buzepide methiodide (BZP) by incorporating TiO₂ nanoparticles in carbon paste matrix. Electrochemical studies indicated that the TiO₂ nanoparticles efficiently increased the electron transfer kinetics between drug and the electrode. Compared with the nonmodified CPE, the TiO₂-modified CPE greatly enhances the oxidation signal of BZP with negative shift in peak potential. Based on this, we have proposed a sensitive, rapid and convenient electrochemical method for the determination of BZP. Under the optimized conditions, the oxidation peak current of BZP is found to be proportional to its concentration in the range of 5 × 10⁻⁸ to 5 × 10⁻⁵ M with a detection limit of 8.2 × 10⁻⁹ M. Finally, this sensing method was successfully applied for the determination of BZP in human blood serum and urine samples with good recoveries.     

Sensitive electrochemical determination of calcium dobesilate on the carbon–iron nanoparticle modified glassy carbon electrode

A carbon–iron nanoparticle modified glassy carbon electrode (CIN-GCE) has been developed for the determination of calcium dobesilate (CD) in pharmaceutical formulations. The CINs were characterized by Transmission electron microscopy and X-ray diffraction. It was found that the CIN has strong electrocatalytic effect for CD and leads to a greatly improved anodic detection of CD including higher sensitivity and better reproducibility. A detection limit of 2.0 × 10⁻⁷ M (S/N = 3) was obtained. The proposed CIN-GCE was applied to detect CD in pharmaceutical formulations with satisfactory results. The proposed CIN electrochemical sensing platform holds great promise for simple, rapid and accurate detection of CD in pharmaceutical formulations.     

A voltammetric study of the binding of copper(II) to peptide fragments of prion

Binding of copper to three peptide fragments of prion (Cu²⁺ binding sites: 60–91, 92–96 and 180–193 amino acid residues) was investigated by anodic stripping voltammetry to determine the stoichiometries of Cu²⁺-prion peptide interactions. The method relies on the synthesis of N-terminally acetylated/C-terminally amidated peptide fragments of prion by solid-phase synthesis and direct monitoring of the oxidation current of copper in the absence and presence of each prion fragment. Titration curves of Cu²⁺ with Ac-PHGGGWGQ-NH₂, Ac-GGGTH-NH₂ and Ac-VNITKQHTVTTTT-NH₂ were obtained in concentrations ranging from 8.52 × 10^?7 to 5.08 × 10^?6, 3.95 × 10^?7 to 1.94 × 10^?6 and 7.82 × 10^?8 to 4.51 × 10^?7 M, respectively. The acquired data were used to calculate the stoichiometries (one peptide per Cu²⁺ ion for all the three studied systems) and apparent dissociation constants (K_d = 4.37 × 10^?8–3.50 × 10^?10 M) for the three complexes.     

Electrospun zirconia-embedded carbon nanofibre for high-sensitive determination of methyl parathion

Carbon nanofibers embedded with ultrafine zirconia nanoparticles (ZrO₂-CNFs) are fabricated via a new methodology. Polyvinylpyrrolidone (PVP) and polymethylmethacrylate (PMMA) binary polymers containing zirconium n-butoxide are first dissolved in dimethylformamide, and the resulting solution is electrospun and heat-treated. The tetragonal zirconia nanoparticles formed, with a size of 5 ± 2 nm in diameter, are uniformly distributed in the carbon nanofibres. Using Nafion as an additive, ZrO₂-CNFs are drop-cast onto the glassy carbon electrode (ZrO₂-CNF/GCE) and the modified electrode is then applied to detect methyl parathion (MP) using differential pulse voltammetry. Two linear relationships are found at the concentration ranges of 1 × 10^− 9–2 × 10^− 8 g/L and 2 × 10^− 8–2 × 10^− 7 g/L, with a detection limit of 3.4 × 10^− 10 g/L (S/N > 3). The electrospun-based ZrO₂-CNF is a very promising coating material for electrochemical sensing of organophosphorus compounds.     

Kinetic spectrophotometric method for trace determination of thiocyanate based on its inhibitory effect

A kinetic spectrophotometric method for the determination of thiocyanate, based on its inhibitory effect on silver(I) catalyzed substitution of cyanide ion, by phenylhydrazine in hexacyanoferrate(II) is described. Thiocyanate ions form strong complexes with silver(I) catalyst which is used as the basis for its determination at trace level. The progress of reaction was monitored, spectrophotometrically, at 488 nm (λ_max of [Fe(CN)₅PhNHNH₂]^3?, complex) under the optimum reaction conditions at: 2.5 × 10^?3 M [Fe(CN)₆]^4?, 1.0 × 10^?3 M [PhNHNH₂], 8.0 × 10^?7 M [Ag⁺], pH 2.8 ± 0.02, ionic strength (μ) 0.02 M (KNO₃) and temperature 30 ± 0.1 °C. A linear relationship obtained between absorbance (measured at 488 nm at different times) and inhibitor concentration, under specified conditions, has been used for the determination of [thiocyanate] in the range of 0.8–8.0 × 10^?8 M with a detection limit of 2 × 10^?9 M. The standard deviation and percentage error have been calculated and reported with each datum. A most plausible mechanistic scheme has been proposed for the reaction. The values of equilibrium constants for complex formation between catalyst–inhibitor (K_CI), catalyst–substrate (K_s) and Michaelis–Menten constant (K_m) have been computed from the kinetic data. The influence of possible interference by major cations and anions on the determination of thiocyanate and their limits has been investigated.     

Study on the performance of different types of three-dimensional chromatographic systems

The maximum achievable performance of possible types of three-dimensional chromatographic systems (LC × LC × LC) has been investigated. The Pareto-optimization approach was applied to establish a trade-off between three main objectives (total peak capacity, analysis time and dilution of the sample) and Pareto-front values were obtained. The performances of ^xLC × ^xLC × ^xLC (three-dimensional separation in space), ^tLC × ^tLC × ^tLC (three-dimensional separation in time) and the hybrid ^xLC × ^xLC × ^tLC system were compared mutually and with two-dimensional chromatographic systems. It was found that ^xLC × ^xLC × ^xLC performs best in terms of maximum achievable peak capacity in shortest analysis time. Based on current thin-layer-chromatography performance it should be possible to obtain a peak capacity of 50,000 within 20 min. If contemporary column-packing standards can be upheld the achievable limit is approximately 50% higher. However, in an ^xLC × ^xLC × ^xLC chromatographic system analytes remain in the separation domain after the analysis, which complicates the detection. Use of an ^xLC × ^xLC × ^tLC system with elution in the last dimension alleviates the detection problem. The maximum achievable peak capacity in the same analysis time is lower for ^xLC × ^xLC × ^tLC than for ^xLC × ^xLC × ^xLC. Using the same (reasonable) length of the separation domain (e.g. a cube 200 × 200 × 200 mm) for both systems, it is possible to achieve peak capacities of 78,000 for ^xLC × ^xLC × ^tLC operated in the gradient mode, which is twice higher than for an ^xLC × ^xLC × ^xLC system. A three-dimensional (three-column) time-based ^tLC × ^tLC × ^tLC system does not greatly improve the performance of ^tLC × ^tLC in terms of (maximum) peak capacity and (minimum) analysis time. Dilution factors in ^tLC × ^tLC × ^tLC are very high. Decreasing the dilution has a detrimental influence on the peak capacity. The trade-off between these objectives is of crucial importance. The influence of several parameters (length of the separation domain, particle size, etc.) on the performance of chromatographic systems was investigated, optimal ranges were found.     

Hydrogen sensing properties of a Pd/SiO2/AlGaN-based MOS diode

Hydrogen sensing properties of a Pd/AlGaN-based Schottky diode are improved by the deposition of SiO₂ at the metal/semiconductor (MS) interface. The wide Schottky barrier height variation of the MOS diode could be attributed to the large electric field across the SiO₂ layer. This leads to the presence of more hydrogen dipoles caused by the polarization effect. The sensing response of the MOS diode at room temperature (1.3 × 10⁵) is comparable to that of the MS one at 150 °C (2.04 × 10⁵). Thus, the MOS-type sensing device shows the benefit of low-temperature operation. Kinetic analyses confirm that the short response times of the MOS diode are attributed to high reaction rate at the Pd/SiO₂ interface.     

Synthesis and physical characterization of electrically conducting polymers of polynuclear aromatic sulfonyl compounds

Potentially useful conducting polymers of sulfonyl substituted phenanthrene derivatives and non-conducting linear polymers, such as, polystyrene and poly(N-vinylcarbazole) have been synthesized and characterized using IR, thermogravimetric and dielectric measurements. The phenanthrene-based benzene, naphthalene and biphenyl copolysulfones have also been prepared and characterized through these techniques. These pendant and backbone polymer sulfones have exceptionally high thermal stability and electrical conductivity, such that dc conductivity in the range 2.80 × 10^?16 to 2.82 × 10^?7 Ω^?1 cm^?1 and ac conductivity in the range 1.69 × 10^?7 to 2.10 × 10^?6 Ω^?1 cm^?1.     

Strontium(II) selective PVC membrane electrode based acetophenone semicarbazone (ACS) as an ionophore

A new PVC membrane based strontium(II) ion-selective electrode has been constructed using acetophenone semicarbazone as a neutral carrier. The sensor exhibits a Nerstian response for strontium(II) ion over a wide concentration range 1.0 × 10⁻²–1.0 × 10⁻⁷ M with the slope of 29.4 mV/per decade. The limit of detection was 2.7 × 10⁻⁸ M. It was relatively fast response time (<10 s for concentration ⩾1.0 × 10⁻³ and <15 s for concentration of ⩾1.0 × 10⁻⁶ M) and can be used for 8 months without any considerable divergence in potentials. The proposed sensor revealed relatively good selectivity and high sensitivity for strontium(II) over a mono, di, trivalent cation and can be used in a pH range of 2.5–10.5. It was also successfully used as an indicator electrode in potentiometer titration and in the analysis of concentration in various real samples.     

Evolution of microstructure and crack pattern in NiO thin films under 200 MeV Au ion irradiation

NiO thin films grown on Si (100) substrate by electron beam evaporation method and sintered at 700 °C were irradiated with 200 MeV Au¹⁵⁺ ions. The fcc structure of the sintered films was retained up to the highest fluence (1×10¹³ ions cm^?2) of irradiation. However the microstructure of the pristine film underwent a considerable modification with increasing ion fluence. 200 MeV Au ion irradiation led to compressive stress generation in NiO medium. The diameter of the stressed region created by 200 MeV Au ions along the ion path was estimated from the variation of stress with ion fluence and found to be ～11.6 nm. The film surface started cracking when irradiated at and above the fluence of 3×10¹² ions cm^?2. Ratio of the fractal dimension of the cracked surface obtained at 200 MeV and 120 MeV (Mallick et al., 2010a) Au ions was compared with the ratio of the radii of ion tracks calculated based on Coulomb explosion and thermal spike models. This comparison indicated applicability of thermal spike model for crack formation.     

Flow injection potentiometric sensor for determination of phenylpropanolamine hydrochloride

A new polymeric membrane electrode has been constructed for the determination of phenylpropanolamine hydrochloride. The electrode was prepared by solubilizing the phenylpropanolamine-phosphomolybdate ion associate into a polyvinyl chloride matrix plasticized by dibutylphthalate as a solvent mediator. The electrode showed near-Nernstian response over the concentration range of 1 × 10^?5–1 × 10^?2 M with low detection limit of 6.3 × 10^?6 M. The electrode displays a good selectivity for phenylpropanolamine with respect to a number of common inorganic and organic species. The electrode was successfully applied to the potentiometric determination of phenylpropanolamine ion in its pure state and its pharmaceutical preparation in batch and flow injection conditions.     

Electrochemical biosensor based on hairpin DNA probe using 2-nitroacridone as electrochemical indicator for detection of DNA species related to Chronic Myelogenous Leukemia

In this article, a new kind of hairpin DNA Electrochemical biosensor using nitroacridone as electrochemical indicator was first designed, and used to detect BCR/ABL fusion gene in Chronic Myelogenous Leukemia (CML). The results indicated that in pH 7.0 Tris–HCl buffer solution, the oxidation peak current was linear with the concentration of complementary strand in the range of 6.2 × 10⁻⁸–3.1 × 10⁻⁷ mol/l with a detection limit of 5.3 × 10⁻⁹ mol/l. This new hairpin DNA electrochemical biosensor demonstrates its excellent specificity for single-base mismatch and complementary (dsDNA) after hybridization, and this probe has been used for assay of PCR product of a real sample with satisfactory result.     

Modelling of mass transfer in facilitated supported liquid membrane transport of copper(II) using MOC-55 TD in Iberfluid

The transport of copper(II) through a supported liquid membrane using MOC-55 TD (oxime derivative), dissolved in Iberfluid, as a carrier has been studied. A physico-chemical model is derived to describe the transport mechanism which consists of: diffusion process through the feed aqueous diffusion layer, fast interfacial chemical reaction and diffusion through the membrane. The experimental data can be explained by mathematical equations describing the rate of transport. The mass transfer coefficient was calculated from the described model as 2.8×10⁻³ cm s⁻¹, the thickness of the aqueous boundary layer as 2.6×10⁻³ cm⁻¹ and the membrane diffusion coefficient of the copper-containing species as 1.2×10⁻⁸ cm² s⁻¹.     

Zirconium(IV) phosphosulphosalicylate-based ion selective membrane electrode for potentiometric determination of Pb(II) ions

Zirconium(IV) phosphosulphosalicylate, a cation exchanger was synthesized by mixing zirconium oxychloride to a mixture of 5-sulphosalicylic acid and phosphoric acid. The material showed good efficiency for the preparation of an ion-selective membrane electrode. The membrane was characterized affinity for Pb(II) ions. Due to its Pb(II) selective nature, the ion-exchanger was used as an electroactive by XRD and SEM analysis. The electrode responds to Pb(II) ions in a linear range from 1 × 10⁻⁵ to 1 × 10⁻¹ M with a slope of 43.8 mV per decade change in concentration with detection limit of 4.78 × 10⁻⁶ M. The life span of electrode was found to be 90 days. The proposed electrode showed satisfactory performance over a pH range of 4.0–6.5, with a fast response time of 15 s. The sensor has been applied to the determination of Pb(II) ions in water samples of different origins. It has also been used as indicator electrode in potentiometric titration of Pb(II) ion with EDTA.     

Anode-supported planar SOFC with high performance and redox stability

Solid oxide fuel cells with full ceramic anodes have recently attracted increasing attention, because the conventional Ni/YSZ cermet anodes may fail during practical operation due to their weak mechanical stability in the case of re-oxidation of the nickel. However, until now the reported fuel cells based on ceramic anodes have been fabricated only as small pellet-sized cells and electrochemical performance has been barely satisfactory, making it difficult to evaluate these attempts with respect to commercial feasibility. Herein, we report single cells based on Y-substituted SrTiO₃ anode substrates. These planar cells have outer dimensions of 50 × 50 mm², which has not been reached for a ceramic anode-supported cell before. They show power densities of 0.7–1.0 W cm^? 2 at 0.7 V and 800 °C, which are sufficient for technical applications. The cells survived 200 anode-gas changes between fuel and air (redox cycles), providing a new direction for the development and commercialisation of anode-supported solid oxide fuel cells.     

The determination of cysteine at Bi-powder carbon paste electrodes by cathodic stripping voltammetry

The determination of cysteine by means of square wave cathodic stripping voltammetry (SWCSV) is reported here for the first time at Bi-modified carbon paste electrodes (CPEs). The modified electrodes are 17% w/w metallic Bi powder mixed with CP (Bi-CPEs) and the technique is based on the enhancement of Bi surface oxidation in the presence of cysteine at a carefully chosen accumulation potential and the subsequent reduction-stripping of the product (proposed to be bismuth(III) cysteinate) by potential scanning to more negative values. The wide concentration range of 1 × 10⁻⁶–5 × 10⁻⁵ M for cysteine can be assessed by SWCSV using Bi-CPEs and, by appropriate choice of accumulation times, two linear response concentration regimes could be identified: 1 × 10⁻⁶–1 × 10⁻⁵ M (accumulation for 600 s) and 1 × 10⁻⁵–5 × 10⁻⁵ M (accumulation for 100 s), with estimated detection limits of 3 × 10⁻⁷ and 2 × 10⁻⁶ M, respectively.     

Direct observation for photophysical and photochemical processes of folic acid in DMSO solution

Using the fast optical technique of laser flash photolysis by a kinetic absorption detector, the photophysical and photochemical processes of folic acid have been observed. By comparison of transient absorptions from photolysis between folic acid and its components, pteroic acid, pterin and 6-carboxypterin, it has been demonstrated that electron-transfer reactions from 4-aminobenzoyl group to the triplet pterin moiety occur through intra- and inter-molecular processes of folic acid. The intermolecular electron-transfer reaction is suggested to be mediated by two tautomers of triplet states of folic acid, lactim and lactam, in different rate constants, 1.4 × 10⁹ and 1.6 × 10⁸ M⁻¹ s⁻¹, respectively.     

Microstructural modifications in swift ion irradiated PET

Polyethylene terephthalte (PET) was irradiated with carbon (70 MeV) and copper (120 MeV) ions to analyze the induced modifications with respect to optical, structural and thermal properties. In the present investigation, the fluence for carbon irradiation was varied from 1×10¹¹ to 1×10¹⁴ ions cm⁻², while that for copper beam was kept in the range of 1×10¹¹ to 1×10¹³ ions cm⁻². UV–vis, FTIR, XRD and DSC techniques were utilized to study the induced changes. The analysis of UV–vis absorption studies reveals that there is decrease of optical energy gap up to 10% on carbon ion irradiation (at 1×10¹⁴ ions cm⁻²), whereas the copper beam (at 1×10¹³ ions cm⁻²) leads to a decrease of 49%. FTIR analysis indicated the formation of alkyne end groups along with the overall degradation of polymer with copper ion irradiation. X-ray diffraction analysis revealed that the semi-crystalline PET losses its crystallinity on swift ion irradiation. It was found that the carbon beam (1×10¹⁴ ions cm⁻²) decreased the crystallite size by 16% whereas this decrease is of 12% in case of the copper ion irradiated PET at 1×10¹³ ions cm⁻². The loss in crystallinity on irradiation has been supported by DSC thermograms.