Di-tert-butylazodicarboxylate based PVC membrane sensor for Fe(III) ion measurement in pharmaceutical formulation

Preliminary solution study shows the selectivity of di-tert-butylazodicarboxylate (TBADC) toward Fe(III) ions. Due to this selectivity, it was applied as an ionophore for construction of a Fe(III) sensor. The proposed sensor exhibits a wide linear response range with a Nerstian slope of 19.4 ± 0.4 mV decade^− 1 and detection limit of 4.8 × 10^− 8 mol L^− 1. The sensor response is pH independent in the range of 2.3-3.4 and has a fast response time of < 10 s. It also shows very good selectivity to Fe(III) ion over many mono-,di- and trivalent transition and heavy metal ions. The life time of the electrode was at least 10 weeks. The application of the TBADC-based sensor to analysis of Fe(III) ion in a pharmaceutical formulation, and also to the monitoring of Fe(III) ion in mixtures of two, three and four different ions showed satisfactory results.     

Europium (III) PVC membrane sensor based on N-pyridine-2-carboxamido-8-aminoquinoline as a sensing material

Conductometric study in acetonitrile solution shows the selectivity of PCQ toward europium ion. Therefore, a new europium PVC membrane electrode was prepared based on N-pyridine-2-carboxamido-8-aminoquinoline (PCQ) as an ion carrier. The electrode has a wide concentration range from 1.0 × 10^− 2 and 1.0 × 10^− 6 mol L^− 1, Nernstian slope of 19.8 ± 0.3 mV per decade and a detection limit of 6.4 × 10^− 7 mol L^− 1. The potentiometric response is pH independent in the range of 2.4-7.4. The proposed sensor has a relatively fast response time less than 10 s and it can be used for at least 2 months without any considerable divergence in its potentials. The proposed electrode revealed good selectivity toward europium ion in comparison with variety of other metal ions. The practical utility of the electrodes has been demonstrated by their use as indicator electrodes in the potentiometric titration of Eu^3 + ions with EDTA and for determination of Eu^3 + ion concentration in mixtures of two and three different ions.     

Heptadentate Schiff-base based PVC membrane sensor for Fe(III) ion determination in water samples

Tests performed using heptadentate Schiff's base ((tris(3-(thiophenal)propyl)amine (TTA)) toward Fe(III) ions indicated that it could be used as an Fe(III) selective ionophore to be used in a plasticized polymeric membrane sensor. The resulting sensors were found to produce a linear response range of five orders of magnitude with a slope of 19.8 ± 0.3 mV decade^− 1 with a detection limit is 8.3 × 10^− 9 mol L^− 1. The sensor could be used in a pH window of 2.4-4.3 and the response time of the sensor was below 10 s, in addition to its very good Fe(III) selectivity over many mono-,di- and trivalent transition and heavy metal ions. The life time of the electrode was found to be at least 10 weeks.     

Amperometric biosensor based on direct electrochemistry of hemoglobin in poly-allylamine (PAA) film

Hemoglobin (Hb) was immobilized in poly-allylamine (PAA) film onto the gold electrode by layer by layer (LBL) method. The modified electrode exhibited a pair of well-defined peaks during cyclic voltammetry, which was attributed from the direct electron transfer of heme proteins. The immobilized Hb showed an excellent electrocatalytical response to the reduction of hydrogen peroxide. The sensor exhibited a fast response and high sensitivity. Through the use of optimized conditions, the linear range for H₂O₂ detection was from 2.5 × 10^− 6 M to 5 × 10^− 4 M with detection limit of 0.2 μM. The proposed biosensor showed long-lasting stability and excellent reproducibility.     

Modified carbon paste electrode for potentiometric determination of diquat dibromide pesticide in water and urine samples

A carbon paste electrode for diquat dibromide (Dq.2Br) was prepared and fully characterized in terms of composition, usable pH range, response time and temperature. The electrode was applied to the potentiometric determination of diquat ions in water and urine samples with average recoveries of 97.5-104.0% and relative standard deviations of 0.30-4.73%. The electrode is based on the ion pair, namely, diquat-phosphotungstate dissolved in 2-nitrophenyloctyl ether (2-NPOE) as pasting liquid with 1.0% Na-TPB as an additive. The modified electrode showed a near-Nernstian slope of 30.8 mV over the concentration range of 3.8 × 10^− 6to 1.0 × 10^− 3 M with the limit of detection 9.0 × 10^− 7 over the pH range 4.5-9.5. The electrode exhibits good selectivity for Dq cations with respect to a large number of inorganic cations, organic cations, sugars and amino acids. The proposed potentiometric method offers the advantages of simplicity, accuracy, automation feasibility and applicability to turbid and colored sample solutions.     

Effect of Ti defects on electrochemical properties of highly-ordered titania nanotube arrays

In this paper, highly-ordered TiO₂ nanotube (TNT) electrodes fabricated by anodization at 20 V in 0.1 M F⁻-based solution were annealed in O₂, N₂ and CO respectively. The surface properties of the TiO₂ electrodes after annealing treatment by different gases were studied by means of photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The electrochemical properties of the TNT electrodes were investigated by cyclic voltammetry, steady-state polarization and photocurrent response measurements. The results showed that Tiⁿ⁺ (n = 0-3) cations and oxygen vacancies existed in the TNT electrode after annealing in CO, leading to a very efficient electron transfer rate of 1.34 × 10^− 3 cm/s. Steady-state polarization measurement and photocurrent response demonstrated that the electrode potential of oxygen evolution reaction (OER) reduced by 20% and the photocurrent response increased by 50% for CO-annealed TNT electrode compared with O₂-annealed TNT electrode.     

Sensitive and selective imprinted electrochemical sensor for p-nitrophenol based on ZnO nanoparticles/carbon nanotubes doped chitosan film

A sensitive and selective molecularly imprinted electrochemical sensor for p-nitrophenol detection has been developed based on ZnO nanoparticles/multiwall carbon nanotubes (MWNTs)-chitosan (CTS) nanocomposite. This nanocomposite was dripped onto an indium tin oxide electrode and then imprinted sol-gel solution was electrodeposited onto the modified electrode to construct the proposed sensor. The morphologies and electrochemical behaviors of the imprinted sensor were characterized by scanning electron microscope, X-ray diffraction, electrochemical impedance spectroscopy, square wave voltammetry and cyclic voltammetry. The imprinted sensor displayed excellent selectivity towards the target molecule p-nitrophenol. Meanwhile, the introduced nanocomposite increased surface area and active sites for electron transfer, thus remarkably enhancing the sensitivity of the imprinted sensor. Under optimal conditions, the peak current was linear to p-nitrophenol concentration ranging from 1.0 × 10^− 8 to 2.0 × 10^− 4 mol·L^− 1 with a detection limits of 1.0 × 10^− 9 mol·L^− 1 (S/N = 3). This proposed sensor was applied to the detection of p-nitrophenol in various water samples successfully.     

Oxygen-sensing properties of ormosil hybrid materials doped with ruthenium(II) complexes via a sol-gel process

Organically modified silicate (ormosil) materials doped with [4,4′-dimethyl-2,2′-bipyridine-bis(2,2′-bipyridine)] ruthenium(II) dichloride ([Ru-mbpy]²⁺) and [4,4′-dimethylformate-2,2′-bipyridine-bis(2,2′-bipyridine)] ruthenium(II) dichloride ([Ru-dmfbpy]²⁺) were prepared by a sol-gel procedure for oxygen-sensing applications. The results indicated that the concentrations of the Ru(II) diimine complexes obviously influenced the linearity of Stern-Volmer plots (I₀ /I vs. O₂%). The best suitable concentrations of [Ru-mbpy]²⁺ and [Ru-dmfbpy]²⁺ in the sol for oxygen sensors were found to be 1.0 × 10^− 3 M and 2.5 × 10^− 3 M, respectively. The fluorescence quenching time and recovery time of oxygen sensor doped with [Ru-mbpy]²⁺ (1.0 × 10^− 3 M) were 18 s and 38 s and those doped with [Ru-dmfbpy]²⁺ (1.0 × 10^− 3 M) were 13 s and 32 s, respectively. The oxygen sensor based on Ru(II) complex modified by esterification demonstrated excellent linear calibration relationship and improved long-term stability.     

Deformation and strain rate sensitivity of a Zr-Cu-Fe-Al metallic glass

The deformation behaviour of Zr₆₅Cu₂₀Fe₅Al₁₀ bulk metallic glass has been studied at room temperature under uniaxial compression conditions at the strain rate of 5 × 10⁻⁴ s⁻¹ and performing jump tests for the strain rates (SR) ranging between 5 × 10⁻⁶ s⁻¹ and 5 × 10⁻² s⁻¹. The alloy always shows the formation of shear bands and exhibits serrated flow. In the SR range of 5 × 10⁻⁶ to 5 × 10⁻³ s⁻¹ absence of strain rate sensitivity within the experimental error is observed. However, when the SR changes from 5 × 10⁻³ s⁻¹ to 5 × 10⁻² s⁻¹ the alloy exhibits a negative strain rate sensitivity of −0.0026. The number of shear bands on the side view appears to be correlated with the range of stress softening from the maximum stress to the stress at which the sample fails.     

Construction of new iodide selective electrodes based on bis(trans-cinnamaldehyde)1,3-propanediimine(L) zinc(II) chloride [ZnLCl2] and bis(trans-cinnamaldehyde) 1,3-propanediimine(L) cadmium(II) chloride [CdLCl2]

New plasticized PVC membranes iodide selective electrodes have been prepared by incorporating bis(trans-cinnamaldehyde)1,3-propanediimine zinc(II) chloride [ZnLCl2] and bis(trans-cinnamaldehyde) 1,3-propandiimine cadmium(II) chloride [CdLCl2] on the surface of graphite disk electrodes. At optimum value of variables the proposed electrodes have selective response to iodide with respect to a number of inorganic and organic anions with near-Nernstian slopes of − 60 ± 1.9 and − 58.5 ± 1.9 mV/decade of iodide concentration over the range 1.0 × 10^− 6-1.0 × 10^− 1 M with detection limits of 4.0 × 10^− 7 and 3.0 × 10^− 7 M for the electrodes based on [ZnLCl₂] and [CdLCl₂], respectively. The electrodes based on both ionophores have response times of about (6 s), with stable reproducible response during 2 months, while their responses is independent of pH over the range 2.5-10.5. The proposed electrodes successfully have been applied for evaluation of iodide ion content in real samples with complicated matrices including water and pharmaceutical samples.     

Lanthanide Recognition: Monitoring of Praseodymium(III) by a Novel Praseodymium(III) Microsensor Based on N′-(Pyridin-2-Ylmethylene)Benzohydrazide

In this work, for the first time, we introduce a highly selective and sensitive praseodymium(III) microsensor. Npsila-(pyridin-2-ylmethylene)benzohydrazide (PBH) was used as a membrane-active component to prepare a highly sensitive Pr(III)-selective polymeric membrane microelectrode. The electrode exhibits a Nernstian response toward Pr(III) ions over a very wide concentration range (1.0 times 10^-3 -1.0 times 10^-8 M), with a detection limit of 7.0 times 10^-9 M (~1 ng/ml). It has a very fast response time in the whole concentration range (~10 s). The proposed microelectrode can be used for at least six weeks without any considerable divergence in potentials. The proposed membrane sensor revealed very good selectivity toward Pr(III) ions over a wide variety of other metal ions including common alkali, alkaline earth and, specially, lanthanide ions. It could be used in the pH range of 3.0-8.5. The Pr(III) microelectrode was used as an indicator electrode for the titration of 20 ml of a 1.0 times 10^-6 M Pr(III) ions with a 1.0 times 10^-4 M EDTA.     

The impact of high-dose implantation into manganin on its thermo-resistance properties under high pressure

Using high-dose implantation into manganin of 253 MeV Kr ions (a surface dose of 2.5×10¹⁵ ion/cm²), as well as 250 keV Bi ions (a surface dose of 10¹⁷ ion/cm²) and 250 keV Kr ions (a surface dose of 10¹⁶ ion/cm²), the pressure and temperature sensitivities of manganin foil have been investigated. It was found that the pressure sensitivity of manganin increased (α=2.45×10⁻⁵ MPa⁻¹ before implantation and α_imp=4.60×10⁻⁵ MPa⁻¹ after complex implantation with 250 keV of Bi and Kr ions, the accuracy of estimation does not exceed 0.01×10⁻⁵ MPa⁻¹) and its temperature sensitivity remained appreciably reduced.     

Growth, spectroscopic properties and laser performance of Nd-doped potassium ytterbium tungstate laser crystal

The 5 at.% Nd³⁺-doped potassium ytterbium tungstate (Nd³⁺:KYb(WO₄)₂, hereafter Nd:KYbW) laser crystal with the dimension up to 28 mm × 15 mm × 12 mm was grown by the top seeded solution growth (TSSG) method. The infrared spectrum of crystal sample was measured, and the vibrational peaks were assigned. According to the absorption and emission spectra of crystal sample, the absorption and emission cross-sections are 16.03 × 10⁻²⁰ cm² at 808 nm and 10.72 × 10⁻²⁰ cm² at 1067 nm, respectively. The fluorescence life of ⁴F_3/2 energy level is 196.33 μs, and the fluorescence branching ratio for the ⁴F_3/2-⁴I_11/2 transition at 1067 nm is 55.74%. The energy transfer between Nd³⁺ and Yb³⁺ ions was observed from the fluorescence spectra pumped by 808 and 980 nm LD sources and the Stark levels of Yb³⁺ in Nd:KYbW crystal were determined. Highly efficient laser output up to 305 mW of Nd:KYbW crystal at 1067 nm has been achieved under pumping by a CW 808 nm laser diode at room temperature. The optical-optical conversion efficiency is 33.9% and the slope efficiency is 46.8%.     

The effect of MgO and SiO2 codoping on the properties of Nd:YAG transparent ceramic

Nd:YAG transparent ceramics were fabricated by a reactive sintering method under vacuum using SiO₂, MgO and compound additives (SiO₂ and MgO) as sintering aids. The effects of SiO₂ and MgO on the microstructure and sintering process of Nd:YAG ceramics were studied. High quality Nd:YAG ceramics with compound sintering aids obtained by vacuum sintering at 1780 °C are composed of grains of the size ∼10 μm, and their transmittance is 82% at 400 nm. It was found the absorption coefficient of 1.0 mol% Nd:YAG ceramic was 8.6 cm⁻¹ at 808 nm and its absorption cross section was calculated to be 6.26 × 10⁻²⁰ cm².     

Formation and characterization of thin films from phthalocyanine complexes: An electrosynthesis study using the atomic-force microscope

(μ-Cyano)(phthalocyaninato)metal(III) [PcMCN]_n species with a central transition metal ion, such as Fe(III) and Co(III), were used to prepare molecular films on a highly oriented pyrolytic graphite electrode substrate by using the cyclic voltammetry technique. In order to investigate the influence of the ligand on the film properties, 1,8-dihydroxyanthraquinone and 2,6-dihydroxyanthraquinone as bivalent ligands were employed. The structure of the molecular materials was analyzed by infrared spectroscopy. The in situ film formation, texture, composition and conductivity of each film were further investigated using atomic force microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy and the four-probe technique, respectively. The [PcMCN]_n complexes provided conductive films with an electrical conductivity of 1 × 10^− 6 Ω^− 1 cm^− 1 at 298 K.     

Direct electrochemical behavior of cytochrome c on sodium dodecyl sulfate modified electrode and its application to nitric oxide biosensor

Polyacrylamide (PAM), sodium dodecyl sulfate (SDS) and cytochrome c (Cyt c) were immobilized on the surface of a glass carbon electrode (GCE), respectively, to form a Cyt c /SDS/PAM/GCE. The modified electrode was characterized with the electrochemical impedance. The direct electrochemical behaviors of Cyt c on SDS/PAM/GCE were obtained by using cyclic voltammetry. A pair of well-defined and reversible redox peaks could be observed in a 0.10 M pH 7.0 phosphate buffer solution. The anodic and cathodic peak potentials of Cyt c were at 0.051 V and − 0.003 V (vs. Ag/AgCl), respectively. The Cyt c on SDS/PAM/GCE exhibited well electrocatalytic activity to reduction of nitric oxide. The relative electrochemical parameters were obtained. The resulted electrode displayed a rapid amperometric response to the reduction of nitric oxide. The catalytic current is linear to the nitric oxide concentration in the range of 8.0 × 10^− 7 M to 9.5 × 10^− 5 M and the detection limit was 1.0 × 10^− 7 M (Signal/Noise = 3). The proposed biosensor could be used to detect quantitatively nitric oxide.     

A novel nanostructured composite formed by interaction of copper octa(3-aminopropyl)octasilsesquioxane with azide ligands: Preparation, characterization and a voltammetric application

This study presents the preparation, characterization and application of copper octa(3-aminopropyl)octasilsesquioxane following its subsequent reaction with azide ions (ASCA). The precursor (AC) and the novel compound (ASCA) were characterized by Fourier transform infrared spectra (FTIR), nuclear magnetic resonance (NMR), electron paramagnetic resonance (EPR), scanning electronic microscopy (SEM), X-ray diffraction (XRD), Thermogravimetric analyses and voltammetric technique. The cyclic voltammogram of the modified graphite paste electrode with ASCA (GPE-ASCA), showed one redox couple with formal potential () = 0.30 V and an irreversible process at 1.1 V (vs. Ag/AgCl; NaCl 1.0 M; v=20 mV s−1). The material is very sensitive to nitrite concentrations. The modified graphite paste electrode (GPE-ASCA) gives a linear range from 1.0 × 10⁻⁴ to 4.0 × 10⁻³ mol L⁻¹ for the determination of nitrite, with a detection limit of 2.1 × 10⁻⁴ mol L⁻¹ and the amperometric sensitivity of 8.04 mA/mol L⁻¹.     

Fabrication of Neisseria gonorrhoeae biosensor based on chitosan-MWCNT platform

We report results of studies relating to preparation and characterization of DNA electrodes based on the chitosan-MWCNT/ITO nanobiocomposite platform for electrochemical detection of gonorrhoea, the most common bacterial sexually transmitted disease. (STD). This biosensing electrode has been characterized using FT-IR, SEM, cyclic voltammetry and differential pulse voltammetry, etc. The sensing characteristics have been investigated in phosphate buffer saline using methylene blue as the hybridization indicator. This DNA biosensor has a response time of 60 s and is found to be stable for about 4 months when stored at 4 °C. The results of DPV studies reveal that this bioelectrode can detect complementary DNA concentration in a wide range of 1 × 10^− 6 M to 1 × 10^− 17 M with a detection limit of 1 × 10^− 16 M.     

Pd-modified TiO2 electrode for electrochemical oxidation of hydrazine, formaldehyde and glucose

The electrocatalysis of the oxidation of hydrazine, formaldehyde and glucose on a nanoporous Pd-modified TiO₂ electrode, prepared by the hydrothermal process, was investigated in 0.1 M NaOH solutions. The electrocatalytic activity of the Pd-modified TiO₂ electrode for the electrochemical oxidation of hydrazine, formaldehyde and glucose is characterized by the low onset potentials of −0.80, −0.70 and −0.85 V (vs Ag,AgCl), respectively. Compared to the oxidation of formaldehyde and glucose, the hydrazine oxidation on the Pd-modified TiO₂ presents the highest anodic oxidation current densities, showing that the Pd-modified TiO₂ electrode is more electro-active for the hydrazine oxidation than for the oxidation of formaldehyde and glucose. Chronoamperograms at different concentrations of hydrazine and formaldehyde showed that the Pd-modified TiO₂ electrode is a promising electrochemical sensor for the detection of hydrazine with a sensitivity of 0.554 mA cm⁻² mM⁻¹ and a detection limit of 0.023 mM, and for the detection of formaldehyde with a sensitivity of 0.20667 mA cm⁻² mM⁻¹ and a detection limit of 0.015 mM. However, it was found from the chronoamperometric responses at various glucose concentrations that a linear plot of the anodic oxidation current density versus glucose concentration developed only in the range of 7-35 mM glucose while an obvious deviation from the linear relationship was observed at both low and large glucose concentrations. Results show that the prepared Pd-modified TiO₂ electrode could be applied to the direct liquid (hydrazine, formaldehyde, and glucose) fuel cells as an effective anodic catalyst, in addition to be a promising electrochemical sensor for the detection of hydrazine and formaldehyde.     

Voltammetric determination of 4-nitrophenol using a modified carbon paste electrode based on a new synthetic crown ether/silver nanoparticles

A novel modified carbon-paste electrode (CPE) with a new synthetic ligand: 6,7,9,10,17,18,19, 20,21, 22-decahydrodibenzo[h,r][1,4,7,11,15]trioxadiazacyclonanodecine-16,23dione(DTD)/Ag nanoparticles (AgNP) was employed for 4-nitrophenol measurement in natural water. Various parameters such as pH, modifier, accumulation time and scan rate were optimized. The proposed electrode showed a good response towards 4-nitrophenol determination. Under the optimized conditions the reduction peak current, showed a good linear relationship with the nitrophenol concentration in the range comprised between 1 × 10^− 6 mol L^− 1 and 1 × 10^− 4 mol L^− 1. The developed electrode was successfully applied for the determination of 4-nitrophenol in water samples.