Construction of an Optical Sensor for Cobalt Determination Based on Methyltrioctylammonium Chloride Immobilized on a Polymer Membrane

Abstract

An optical sensor has been designed for the determination of cobalt by spectrophotometry. The sensing membrane is made by immobilizing methyltrioctylammonium chloride on a triacetylcellulose membrane. In the presence of Co(II) and thiocyanate ions, the colorless membrane changes to blue. The response time of the optode was about 7 min. The sensor can readily be regenerated with 0.02 mol L^?1 sodium oxalate solution. This optode is stable and can be stored under water for more than a month without reagent leaching. The calibration curve was linear in the range of 8.5×10^?6–1.3×10^?4 mol L^?1 of Co(II) ion with a limit of detection 5.9×10^?6 mol L^?1. The relative standard deviations for seven replicate measurements of 3.4×10^?5 and 1×10^?4 mol L^?1 of Co(II) were 1.58 and 1.10%, respectively. The sensor was successfully applied to the determination of cobalt in food samples and vitamin B₁₂ ampoule.     

Determination of dopamine using the fluorescence quenching of 2, 3-diaminophenazine

A facile and sensitive fluorescent strategy for the determination of dopamine is reported using 2, 3-diaminophenazine. Dopamine caused autooxidation in the presence of oxygen with catalysis by Mn²⁺ and formed 2, 3-dihydro-1H-indole-5,6-dione. 2, 3-Diaminophenazine provided relatively strong fluorescence. 2, 3-Diaminophenazine in aqueous solution caused fluorescence quenching when the aminochrome condensed with 2, 3-diaminophenazine to allow the determination of dopamine. Under the optimized conditions, the linear dynamic range for dopamine was from 2.0 × 10^?6 mol · L^?1 to 6.1 × 10^?5 mol · L^?1 with a detection limit of 1.76 × 10^?6 mol · L^?1.     

Electrochemical Behavior of Uric Acid at a Meso‐2,3‐Dimercaptosuccinic Acid Self‐Assembled Gold Electrode

Abstract

The fabrication and electrochemical characteristics of a meso‐2,3‐dimercaptosuccinic acid (DMSA) self‐assembled monolayer modified gold electrode were investigated. The DMSA self‐assembled electrode can enhance the electrochemical stability of uric acid (UA) and the electrochemical reaction of UA on the DMSA electrode has been studied by cyclic voltammetry and electrochemical quartz crystal microbalance. Some electrochemical parameters, such as diffusion coefficient, standard rate constant, electron transfer coefficient, and protons transfer number have been determined for the electrochemical behavior on the DMSA self‐assembled monolayer electrode. The electrode reaction of UA is an irreversible process which is controlled by the diffusion of UA with two electrons and two protons transfer at the DMSA/Au electrode. In phosphate buffer (pH 5.0), the peak current is proportional to the concentration of UA in the range of 8.0×10^?5?1.0×10^?2 mol L^?1 and 8.0×10^?5?8.0×10^?3 mol L^?1 for the cyclic voltammetry and differential pulse voltammetry methods with the detection limits of 1×10^?6 and 8×10^?7 mol L^?1, respectively. This method can be applied to the determination of the UA concentration.     

A Chitosan-Graphene Electrochemical Sensor for the Determination of Copper(II)

Graphite oxide was prepared by oxidizing graphite powder, reduced to graphene using hydrazine hydrate, and the grapheme was mixed with chitosan to form a composite that was used to modify a glassy carbon electrode for the determination of copper(II). The electrochemical behavior of the modified electrode was studied by cyclic and square wave voltammetries. The morphology and structure of the composite were characterized by infrared spectroscopy, transmission electron microscopy, and scanning electron microscopy. In addition, the proportion of composite material, pH, and adsorption time was optimized. Under the optimized experimental conditions, the sensor showed a linear dynamic range from 1.0 × 10^?9 to 1.5 × 10^?8 mol · L^?1 for copper(II) with a limit of detection of 4.3 × 10^?10 mol · L^?1 at a signal-to-noise ratio of three. The sensor displayed excellent electrochemical response and high sensitivity.     

A HYDROGEN PEROXIDE SENSOR BASED ON PRUSSIAN BLUE AND DNA-MODIFIED ELECTRODE

The polyvinylpyrrolidone (PVP) protected Prussian blue (PB) nanoparticles were prepared for use as a sensor for the catalytic reduction of hydrogen peroxide. The nanoparticles were used to modify a gold electrode, which was applied to detect hydrogen peroxide. Impedance spectra and differential pulse voltammetry were applied to detect the performance of the novel electrode and its response to H₂O₂ and Ramos cell smash fluid. Under the optimized experimental conditions, hydrogen peroxide was detected in a linear range of 6.25 × 10^?7 to 1.0 × 10^?5 mol · L^?1, and the detection limit was 7.12 × 10^?8 mol · L^?1 according to 3σ rule. Under the same conditions, hydrogen peroxide was determined in Ramos cell smash fluid with a linear range from 400–80000 mol mL^?1, with a detection limit of 114 mL^?1 according to 3σ rule. The modified electrode with Prussian blue nanoparticles displayed high sensitivity, good reproducibility, and long-term stability to hydrogen peroxide.     

Determination of R‐Deprenyl using a Maltodextrin‐Based Enantioselective,Potentiometric Membrane Electrode

Abstract

The enantioselective, potentiometric membrane electrode (EPME) based on maltodextrin with dextrose equivalence (DE) 16.5–19.5 is proposed for the assay of R‐deprenyl. The linear concentration range for the proposed electrode is 10^?10?10^?3 mol L^?1. The slope of the electrode is 53.1 mV per decade of concentration. The detection limit is 3.6×10^?11 mol L^?1. The proposed electrode could be reliably employed for the assay of R‐deprenyl raw material and its pharmaceutical formulation, Lentogesic tablets.     

Electrochemical Behavior of Epinephrine at Two‐Component Self‐Assembled Monolayer of meso‐2,3‐Dimercaptosuccinic Acid and Penicillamine on Gold Electrode

Abstract

A mixed, self‐assembled monolayer (SAM) of meso‐2,3‐dimercaptosuccinic acid (DMSA) and penicillamine (PCA) was prepared on a gold electrode. The mixed SAM of DMSA and PCA, for which the volume ratio of DMSA:PCA was 2:1, showed an obvious electrochemical activity for the oxidation of epinephrine (EP). In the phosphate buffer (pH 7.7), a sensitive oxidation peak was observed at 0.213 V on the DMSA and PCA modified Au electrode. The peak current was proportional to the concentration of EP in the range between 5.0×10^?6 and 8.0×10^?4 mol L^?1. For the cyclic voltammetry (CV) and differential pulse voltammetry (DPV) methods, the detection limits were 3.9×10^?7 and 2.5×10^?7 mol L^?1, respectively. The reaction mechanism has been primarily discussed. The electrode reaction of EP was an irreversible process with two electrons and two protons transfer at the SAM gold electrode. The SAM gold electrode was applied to the determination of EP in epinephrine hydrochloride injection samples with satisfactory results.     

PVC MATRIX MEMBRANE SENSORS FOR POTENTIOMETRIC DETERMINATION OF ARECOLINE

The construction and electrochemical response characteristics of Poly (vinyl chloride) (PVC) membrane sensors for arecoline HBr (AR) are described. The sensing membranes incorporate ion association complexes of (AR) cation and sodium tetraphenyl borate (NaTPB) (sensor 1) or phosphomolybdic acid (PMA) (sensor 2) or phosphotungstic acid (PTA) (sensor 3) as electroactive materials. The sensors display a fast, stable and near-Nernstian response over a relative wide AR concentration range (1 × 10^?2 – 4 × 10^?5 M) and (1 × 10^?2 to 5 × 10^?6 M), with cationic slopes of 52.5, 50.5 and 51.5 mV per concentration decade for sensor 1, 2, and 3, respectively over a pH range of 3.0–6.0. The sensors show good discrimination of AR from several inorganic and organic compounds. The direct determination of 1.5–2360.0 μg/ml of AR show an average recovery of 99.0, 98.5 and 99.5% and a mean relative standard deviation of 1.7, 1.6 and 1.5% at 200.0 μg/ml for sensor 1, 2 and 3 respectively. The proposed sensors have been applied for direct determination of AR in human saliva. The results obtained for determination of AR in saliva using the proposed method comparable favorably with those obtained using HPLC method.     

Batch and Flow‐Injection Determination of Catecholamines Using Ion Selective Electrodes

Abstract

New epinephrine (EP), dopamine (DA), and L‐Dopa (LD) ion selective PVC membrane electrodes based on ion‐pairs of catecholamines with tetraphenylborate (TPhB) are prepared. In the present work, plastic membrane selective electrodes have been constructed. They are based on the incorporation of EP‐TPhB, DA‐TPhB, or LD‐TPhB ion exchangers in poly(vinylchloride) (PVC) membranes plasticized with di(2‐ethylhexyl)sebacate (DES). The electrodes show a near – Nernstian response in the concentration ranges: 1.0×10^?4—1.0×10^?2 mol/L (epinephrine), 5.0×10^?5–1.0×10^?2 mol/L (dopamine), and 5.0×10^?4–1.0×10^?2 mol/L (L‐Dopa). The electrodes selective for epinephrine and L‐Dopa are used as detectors in the flow injection system. The proposed methods allow determination of catecholamines in pharmaceutical preparations.     

Characterization and application of lornoxicam,europium(III), and lysozyme fluorescence

A novel and sensitive spectrofluorimetric method was developed for the determination of lornoxicam. The method was based on the fluorescence enhancement of europium(III) by formation of a ternary complex with lornoxicam in the presence of lysozyme as the co-ligand. The fluorescence signal for the lornoxicam-europium (III)-lysozyme system was monitored at an excitation wavelength of 620 nm and an emission wavelength of 390 nm. The parameters affecting the fluorescence intensity were optimized systematically and under these conditions the signal was directly proportional to the concentration of lornoxicam from 9.0 × 10^?5 to 1.0 × 10^?2 µg · mL^?1. The detection limit was 2.7 × 10^?5 µg · mL^?1. The relative standard deviation for thirteen replicate measurements of 1.0 × 10^?3 µg · mL^?1 lornoxicam was 1.8%. This method was employed for the determination of lornoxicam in pharmaceutical formulations and biological fluids. The mechanism of fluorescence for the lornoxicam-europium(III)-lysozyme system was discussed.     

PVC Membrane Sensor for Potentiometric Determination of Atropine in Some Pharmaceutical Formulations

Abstract

The construction and general performance of a novel potentiometric membrane sensor for determination of atropine has been developed. It is based on the formation of the ion association complex of the atropinium cation with phosphotungstate counter anion as electroactive material dispersed in a PVC matrix, β‐Cyclodextrin and o‐nitrophenyl octyl ether serve as a plasticizer. The sensor shows a fast, stable, near Nernstian response for 1×10^?2 M to 1×10^?6 M atropine at 25°C over the pH range of 3–8 with a cationic slope of 51±0.5 mV/decade. The lower detection limit is 8×10^?7 M and the response time is 20–45 sec. Selectivity coefficients of atropine, relative to a number of interfering substances, were investigated. There are negligible interferences caused by most of the studied cations, anions, and pharmaceutical excipients. The direct determination of atropine shows an average recovery of 98.6% and a mean relative standard deviation (RSD) of 1.6% at 100 µg/mL. The results obtained by determination of atropine in some formulations (atropine injection and eye drops) are favorably comparable with those obtained by the British Pharmacopoeia method. The developed membrane electrode has been used as end point indicator electrode for some potentiometric titrations.     

PVC Membrane Sensor for Potentiometric Determination of Fluoxetine in Some Pharmaceutical Formulations

Abstract

The construction and general performance of a novel potentiometric membrane sensor for determination of fluoxetine has been developed. It is based on the formation of the ion association complex of fluoxetine with picrolonic acid as electroactive material, dispersed in a PVC matrix and o‐nitrophenyl octyl ether as a plasticizer. The sensor shows a fast, stable, and near Nernstian response for 1×10^?2 M to 8×10^?6 M fluoxetine at 25°C over the pH range of 1–5 with a cationic slope of 51±0.5 mV/decade. The lower detection limit is 6×10^?6 M and the response time 20–35 sec. Selectivity coefficients for fluoxetine, related to number of interfering substances, were investigated. There are negligible interferences from the studied cations, anions, and pharmaceutical excipients. The determination of fluoxetine in aqueous solution shows an average recovery of 98.6% and a mean relative standard deviation (RSD) of 1.5% at 100 µg/mL. The direct determination of fluoxetine in some formulations gave results that compare favorably with those obtained by a spectrophotometric method. The developed membrane electrode has been used as an end point indicator electrode, e.g., potentiometric titration of fluoxetine with sodium tetraphenylborate as a titrant has been monitored.     

Electrochemical determination of hydrogen peroxide using a novel prussian blue–polythiophene–graphene oxide membrane-modified glassy carbon electrode

A polythiophene–graphene oxide compound membrane and Prussian blue were deposited sequentially on the surface of a glassy carbon electrode by cyclic voltammetry. Due to its excellent electrocatalysis and its analogy with peroxidase enzymes, Prussian blue has been widely used in amperometric biosensors. The polythiophene–graphene oxide compound membrane exhibited good electroconductibility and a large specific surface area. The fabricated Prussian blue/polythiophene/graphene oxide/glassy carbon electrode was characterized by transmission electron microscopy, scanning electron microscopy, and cyclic voltammetry. Under the optimal experimental conditions, the detection of hydrogen peroxide was studied by its amperometric current–time curve. Due to the presence of polythiophene–graphene oxide compound membrane and Prussian blue, the hydrogen peroxide sensor shows a linear calibration range of 1.0?×?10^?6–1.0?×?10^?4?mol?L^?1, detection limits of 3.2?×?10^?7?mol?L^?1 at a signal-to-noise ratio of 3, and recoveries from 95.0 to 105.0%. The results show that the modified glassy carbon electrode has potential practical application for the determination of hydrogen peroxide based on its sensitivity and long-term stability.     

Electrochemical determination of hydrogen peroxide on a gold nanoparticle–nitrogen-doped graphene glassy carbon electrode

A novel nonenzymatic sensor based on gold nanoparticle–nitrogen-doped graphene was synthesized by electrochemical sequential deposition on the surface of a glassy carbon electrode. Nitrogen-doped graphene was synthesized by a hydrothermal method using graphene oxide and carbamide as the raw materials mixed in specific proportions. The gold nanoparticles were used in the electrochemical sensor to provide unique electronic and electrochemical properties. Under the optimized conditions, hydrogen peroxide was determined by differential pulse voltammetry with a linear relationship for concentrations from 1.0?×?10^?7 to 1.0?×?10^?5?mol?L^?1. The detection limit was 4.9?×?10^?8?mol?·?L^?1 (according to the 3σ rule) and the recoveries were 95.0–98.0%. This sensor is simple, reproducible, and demonstrates that nitrogen-doped graphene oxide has potential applications for electrochemical sensors.     

A GREEN METHOD FOR THE DETERMINATION OF CHROMIUM(VI) AND IRON(III) IN WATER BY SEQUENTIAL INJECTION ANALYSIS AND SPECTROPHOTOMETRIC DETECTION

In this article, an organic-reagent-free method was described for the determination of Cr(VI) and Fe(III) by double-system double-wavelength sequential injection technique with a single sample injection. In this approach, the determination of Cr(VI) was based on the detection of a blue unstable intermediate compound resulting from the reaction of Cr(VI) with hydrogen peroxide, and the determination of Fe(III) was based on the color reaction of Fe(III) with thiocyanate in acidic medium. Sequential injection analysis (SIA) parameters, including spacer solution volume, aspiration order, aspiration volumes, flow rate, acid medium, solution acidity, and reagent concentrations, were optimized. The linear range for the determination was 3.0–60.0 μg mL^?1 for Cr(VI) and 1.0–40.0 μg mL^?1 for Fe(III), respectively. The limit of detection (LOD) was 0.6 μg mL^?1 for Cr(VI) and 0.2 μg mL^?1 for Fe(III), and the limit of quantitation (LOQ) was 2.0 μg mL^?1 for Cr(VI) and 0.67 μg mL^?1 for Fe(III). The total volume of the reagent consumed in each determination was only 0.11 mL. The proposed method was applied to the simultaneous determination of Cr(VI) and Fe(III) in electroplating wastewater and environmental waters. The results were in good agreement with those obtained by atomic absorption spectrometry. The recoveries were in the range of 97.5–101.1%.     

Resonance Rayleigh Scattering of K2Zn3[Fe(CN)6]2 Nanoparticles and its Application for the Determination of Vitamin C

Abstract

In Britton-Robinson buffer medium, (pH 4.43), potassium ferricyanide (K₃[Fe(CN)₆]) could react with vitamin C (VC) to produce potassium ferrocyanide (K₄[Fe(CN)₆]), which further reacted with Zn²⁺ to form potassium zinc hexacyanoferate K₂Zn₃[Fe(CN)₆]₂ nanoparticles. The shapes and diameters of the K₂Zn₃[Fe(CN)₆]₂ nanoparticles have been observed with transmission electron microscopy, which showed the shapes of these nanoparticles was cubic and their average sizes were about 50 nm in the presence of 2.0 × 10^?5 mol L^?1 VC. The characteristics of resonance Rayleigh scattering (RRS) spectra of this reaction have been studied. The optimum reaction condition for the determination of VC has been investigated. It was found that the RRS intensity of the system at the RRS peak of 363.4 nm was proportional to the VC concentration in the range of 4.0?80.0 µmol L^?1, and the detection limit (3σ) for VC was 0.075 µmol L^?1. A novel and simple RRS method for the determination of VC based on the formation of K₂Zn₃[Fe(CN)₆]₂ nanoparticles has been established.     

Determination of propyl gallate in edible oil by high-performance liquid chromatography with chemiluminescence detection

A novel and convenient method based on high-performance liquid chromatography coupled with chemiluminescence (HPLC) for the determination of propyl gallate in edible oil is reported. The detection was based on the inhibition of chemiluminescence between luminol and hydrogen peroxide in alkaline solution. The analysis was performed using a C₁₈ column with isocratic 60:40 methanol/water. Under the optimum conditions, the concentration of propyl gallate was linear from 9?×?10^?6?mol?L^?1 to 1?×?10^?4?mol?L^?1 with a detection limit of 2?×?10^?7?mol?L^?1. The method is simple, sensitive, and inexpensive and was used for the determination of propyl gallate in edible oil.     

SENSITIVE L-CYSTEINE AMPEROMETRIC SENSOR BASED ON A GLASSY CARBON ELECTRODE MODIFIED BY MnO2 NANOPARTICLES

A sensitive amperometric sensor for the determination of L-cysteine was fabricated by electrodeposition of modified MnO₂ nanoparticles on a glassy carbon electrode. The morphology of the nanoparticles was characterized by scanning electron microscopy. Cyclic voltammetry was applied to investigate the mechanism of film formation and the electrochemical properties of the MnO₂ nanoparticle-modified electrode. The results of electrochemical experiments showed that the modified electrode had a favorable catalytic ability for the electrochemical oxidation of L-cysteine. Under optimized conditions, the MnO₂ nanoparticle-modified electrode exhibited a linear dependence on the concentration of L-cysteine from 1.0 × 10^?6 to 6.4 × 10^?4 M, and a detection limit of 8.0 × 10^?7 M (signal/noise = 3). The modified electrode was highly resistant towards typical inorganic salts and some biomolecules. In addition, the sensor was applied for the determination of L-cysteine in human serum with high accuracy, demonstrating its potential for practical applications.     

CERIUM(IV)-BASED CHEMILUMINESCENCE OF FELODIPINE SENSITIZED BY RHODAMINE 6G

A simple, rapid, and sensitive flow injection chemiluminescence (FI-CL) method was proposed for the determination of felodipine. The method was based on the CL-emitting reaction between the studied drug and cerium(IV) in a nitric acid medium and measurement of the CL intensity produced by rhodamine 6G used as a sensitizer. Under the optimum conditions, the proposed procedure had a linear range between 5.0 × 10^?9 and 7.0 × 10^?6 g mL^?1, with a detection limit of 2.0 × 10^?9 g mL^?1. The relative standard deviation was 2.3% for 1.0 × 10^?7 g mL^?1 felodipine solution (n = 11). It was applied to the determination of felodipine in pharmaceutical preparations and biological fluids with satisfactory results. The possible mechanism of the chemiluminescence reaction was also discussed briefly.     

Low-cost potentiometric sensor based on a molecularly imprinted polymer for the rapid determination of matrine in herbal medicines

Abstract

A low-cost potentiometric sensor based on a molecularly imprinted polymer was developed for the determination of matrine in herbal medicine samples. The imprinted material was synthesized by the use of matrine as template, methacrylic acid (MAA) as the monomer, ethylene glycol dimethyl acrylate (EGDMA) as the cross linker, 2,2′-azo-bisisobutyronitrile (AIBN) as the initiator, and toluene and dodecanol as the porogenic agent. The electrode sensing membrane was fabricated by incorporating the ground imprinted particles into the polyvinyl chloride substrate that was subsequently incorporated into a laboratory constructed ion-selective electrode. The prepared imprinted sensor exhibited a rapid Nernst response across the concentration range from 1?×?10^?5 to 1?×?10^?1 M with a detection limit equal to 9.3?×?10^?6 M. The analytical capabilities support the direct determination of matrine in herbal medicine. The analytical results were verified by a standard ultraviolet absorption spectrophotometry protocol. The proposed sensor manifested a series of advantages, including high selectivity and sensitivity, enhanced stability and low cost, that provides a wide number of potential applications for herbal analysis.