Determination of the Micellar Properties of Triton X-100 by Voltammetry Method

ABSTRACT

The diffusion coefficient of the micelle, the first CMC and the second CMC of Triton X-100 are determined by cyclic voltammetry without any probe. The first CMC and the second CMC of Triton X-100 are 3.1x lO^?1 and 1.3× 10^?1 respectively. The viscosity of the micelle solution, the micellar aggregation number and the micellar size increase but the diffusion coefficient decreases with Triton X-100 concentration increasing. The mechanism of the electrochemical reaction of Triton X-100 at platinum electrode is deduced by measurements of conductivity, pH and cyclic voltammetry.     

Determination of coumarins by voltammetric techniques in micellar and emulsified media

An electroanalytical study of the oxidation processes of umbelliferone and hymecromone at a glassy carbon electrode in micellar solution and emulsified medium by different voltammetric techniques is described. The non-ionic surfactant Triton X-405 in acetate-buffered medium at pH 4.8 was found to be the most suitable. Different ranges of linearity were obtained in the micellar solutions, depending on the technique used; the limits of determination for differential pulse voltammetry (DPV) at a stationary electrode were 2.9×10^?6 mol l^?1 and 3.3×10^?6 mol l^?1 for umbelliferone and hymecromone, respectively. In the emulsified medium formed with a mixture of toluene and ethyl acetate (3:2), the oxidation processes yielded similar results. With DPV, linear calibration plots were obtained in the ranges 1.0×10^?5–9.0×10^?7 mol l^?1 umbelliferone and 1.0×10^?5–2.0×10^?6 mol l^?1 hymecromone. The media used are predominantly aqueous so that special reference electrodes and solvent purification are not needed.     

An electroanalytical study of the anticancer drug dacarbazine

The electrochemical behaviour of dacarbazine [5-(3,3-dimethyl-1-triazenyl) imidazole-4-carboxamide; DTIC] was investigated by Tast and differential pulse polarography (d.p.p.) at the dropping mercury electrode, by cyclic and differential pulse voltammetry at the hanging mercury drop electrode and by anodic voltammetry at the glassy carbon electrode. Calibration graphs were obtained for 2×10^?8?2×10^?5 M DTIC by d.p.p., for 5×10^?9?1×10^?5 M by adsorptive stripping voltammetry ar a hanging mercury drop electrode, and for 1?10×10^?5 M by high-performance liquid chromatography with oxidative amperometric detection at a glassy carbon electrode. The methods are compared and applied to determine DTIC added to blood serum after a simple clean-up procedure.     

Construction of a modified carbon paste electrode based on TiO2 nanoparticles for the determination of gallic acid

A modified carbon paste electrode was prepared by incorporating the TiO₂ nanoparticles in the carbon paste matrix. The electrochemical behavior of gallic acid (GA) is investigated on the surface of the electrode using cyclic voltammetry and differential pulse voltammetry. The surface morphology of the prepared electrode was characterized using the scanning electron microscopy. The results indicate that the electrochemical response of GA is improved significantly at the modified electrode compared with the unmodified electrode. Furthermore, the capabilities of electron transfer on these two electrodes were also investigated by electrochemical impedance spectroscopy. Under the optimized condition, a linear dynamic range of 2.5?×?10^?6 to 1.5?×?10^?4?mol?L^?1 with detection limit of 9.4?×?10^?7?mol?L^?1 for GA is obtained in buffered solutions with pH 1.7. Finally, the proposed modified electrode was successfully used in real sample analysis.     

Preparation of Cu (II) imprinted polymer electrode and its application for potentiometric and voltammetric determination of Cu (II)

The Cu (II) imprinted polymer glassy carbon electrode (GCE/Cu-IP) was prepared by electropolymerization of pyrrole at GCE in the presence of methyl red as a dopant and then imprinting by Cu²⁺ ions. This electrode was applied for potentiometric and voltammetric detection of Cu²⁺ ion. The potentiometric response of the electrode was linear within the Cu²⁺ concentration range of 3.9 × 10^?6 to 5.0 × 10^?2 M with a near-Nernstian slope of 29.0 mV decade^?1 and a detection limit of 5.0 × 10^?7 M. The electrode was also used for preconcentration anodic stripping voltammetry and results exhibited that peak currents for the incorporated copper species were dependent on the metal ion concentration in the range of 1.0 × 10^?8 to 1.0 × 10^?3 M and detection limit was 6.5 × 10^?9 M. Also the selectivity of the prepared electrode was investigated. The imprinted polymer electrode was used for the successful assay of copper in two standard reference material samples.     

Determination of pesticides in vegetable samples using an acetylcholinesterase biosensor based on nanoparticles ZrO2/chitosan composite film

An amperometric pesticides inhibition biosensor has been developed and used for determination of pesticides in vegetable samples. To eliminate the interference of ascorbic acid, multilayer films of polyelectrolyte (chitosan/polystyrensulfonate) were coated on the glass carbon electrode. Then, acetylcholinesterase was immobilized on the electrode based on surface-treated nanoporous ZrO₂/chitosan composite film as immobilization matrix. As a modified substrate, acetylthiocholine was hydrolysed by acetylcholinesterase and produced thiocholine which can be oxidized at +700?mV vs. SCE. Pesticides inhibit the activity of enzyme with an effect of decreasing of oxidation current. The experimental conditions were optimized. The electrode has a linear response to acetylthiocholine within 9.90?×?10^?6 to 2.03?×?10^?3?M. The electrode provided a linear response over a concentration range of 6.6?×?10^?6 to 4.4?×?10^?4?M for phoxim with a detection limit of 1.3?×?10^?6?M, over a range of 1.0?×?10^?8 to 5.9?×?10^?7?M for malathion, and over a range of 8.6?×?10^?6 to 5.2?×?10^?4?M for dimethoate. This biosensor has been used to determine pesticides in a real vegetable sample.     

Single‐Piece Solid‐Contact Pb2+‐Selective Electrodes Based on Thiophene Oligomer

A single‐piece solid‐contact Pb²⁺‐selective electrode was prepared by adding a thiophene oligomer into the ion‐selective cocktail directly. The one‐step fabrication yielded an electrode with Nernstian response spanning a wide concentration range of 10^?3–10^?8 mol L^?1, and detection limit as low as 5.6×10^?9 mol L^?1. The electrode had a quick response time of approximately 10–15 s and showed excellent selectivity over the most common univalent and divalent cations. The practical application of the proposed electrode has been tested by determining Pb²⁺ in real water samples.     

Voltammetric Determination of Trace Antiepileptic Gabapentin with a Silver‐Nanoparticle Modified Multiwalled Carbon Nanotube Paste Electrode

For the first time, a novel carbon nanotube bed electrode impregnated with silver–nanoparticles (AgNPs) for the determination of trace amounts of gabapentin (GBP) is described. We synthesized the AgNPs via a new procedure. The voltammetric behavior of the electrode was investigated by cyclic voltammetry. There were linear relationships in the ranges from 3.1×10^?9 to 2.9×10^?2 M and from 1.0×10^?8 to 1.0×10^?2 GBP with square wave and differential pulse voltammetric peak currents, respectively. The detection limits were 5.6×10^?10 and 9.7×10^?9 M, respectively. The electrode showed excellent response over a period of 2 months and was successfully applied in human plasma and pharmaceutical capsular products.     

One-step construction of an electrode modified with electrodeposited Au/SiO2 nanoparticles, and its application to the determination of NADH and ethanol

A new electrode was developed by one-step potentiostatic electrodeposition (at ?2.0 V for 20 s) of Au/SiO₂ nanoparticles on a glassy carbon electrode. The resulting electrode (nano-Au/SiO₂/GCE) was characterized by scanning electronic microscopy, X-ray photoelectron spectroscopy and electrochemical techniques. The electrochemical behavior of dihydronicotinamide adenine dinucleotide (NADH) at the nano-Au/SiO₂/GCE were thoroughly investigated. Compared to the unmodified electrode, the overpotential decreased by about 300 mV, and the current response significantly increased. These changes indicated that the modified electrode showed excellent catalytic activity in the oxidation of NADH. A linear relationship was obtained in the NADH concentration range from 1.0?×?10^?6 to 1.0?×?10^?4 mol?L^?1. In addition, amperometric sensing of ethanol at the nano-Au/SiO₂/GCE in combination with alcohol dehydrogenase and nicotinamide adenine dinucleotide was successfully demonstrated. A wide linear response was also found for ethanol in the range from 5.0?×?10^?5 to 1.0?×?10^?3 mol?L^?1 and 1.0?×?10^?3 to 1.0?×?10^?2 mol?L^?1, respectively. The method was successfully applied to determine ethanol in beer and biological samples.     

Preconcentration of tranquilizers by adsorption/extraction at a wax-impregnated graphite electrode

The tranquilizers promethiazine, diethazine, trifluoperazine, fluphenazine and clozapin adsorb at the surface and extract into the wax-impregnated graphite electrode (WIGE) as shown by chronocoulometry. Extraction/adsorption at the electrode serves as a preconcentration step which improves the limit of detection for the drugs by differential pulse voltammetry. A 15-min preconcentration gave a linear range of 10^?4–5 × 10^?8 M with a detection limit of 5 × 10^?9 M for clozapin in pH 7 phosphate buffer. The determination of tranquilizers in urine and plasma required no preliminary treatment; the detection limits were 5 × 10^?8 M in urine and 10^?7 in plasma. Plasma measurements were made at a WIGE covered with a Spectrapor membrane to prevent electrode fouling by protein adsorption.     

Simultaneous Determination of Pb and Cd Traces in Water Samples by Anodic Stripping Voltammetry Using a Modified GC Electrode

The determination of Pb and Cd with a Nafion‐modified glassy carbon electrode and Cu‐DPABA complex (Cu‐DPABA–NA/GCE; DPABA is methyl 3,5‐bis{bis‐[(pyridin‐2‐yl)methyl]amino}methyl‐benzoate) as an alternative electrode for anodic stripping voltammetry was described. Pb and Cd were accumulated in acetate buffer pH 4 at a potential of ?1.4 V (vs. Ag/AgCl electrode) for 120 s followed by a DPASV scan from ?1.2 to ?0.2 V. Under optimum conditions the calibration curves were linear in the range of 4.8×10^?9–5.0×10^?5 and 5.0×10^?9–5×10^?5 mol L^?1 for Pb and Cd, respectively. Detection limits were 1.8×10^?9 and 1.2×10^?9 mol L^?1 for Pb and Cd, respectively. Different parameters and conditions, such as membrane ingredients, accumulation time, potential and pH value were optimized. A study of interfering substances was also performed. A significant increase in current was achieved at the modified electrode in comparison with the bare glassy carbon electrode. The validation of the proposed method was made by Pb and Cd determination in the certified reference material Groundwater CRM 610 (BCR, Community Bureau of Reference, Brussels, Belgium). The electrode was successfully applied for determination of Pb and Cd in river water with a high content of organic contaminants without any pretreatment.     

Determination of uranium(VI) in sea water by cathodic stripping voltammetry of complexes with catechol

Polarographic (d.c.) measurements showed that complex ions of uranium(VI) with catechol adsorb on the dropping mercury electrode. This effect is used to determine uranium(VI) directly in sea water. Optimal conditions include pH 6.8, 2 × 10^?3 M catechol, and a collection potential between ?0.1 and ?0.4 V (vs. Ag/AgCl) at a hanging mercury drop electrode. The cathodic scan is made with the linear-scan or differential-pulse mode (d.p.c.s.v.). The detection limit with the d.p.c.s.v, mode is 3 × 10^?10 M after a collection period of 2.5 min. Between pH 6 and 8, the peak height increases with pH and with catechol concentration up to 5 × 10^?3 M. There is linear relationship between the collection time and the measured peak height until the drop surface becomes saturated. With a collection period of 3 min, the reduction current increases linearly with the metal concentration up to about 5 × 10^?3 M U(VI). The maximum adsorption capacity of the mercury drop is 4.4 × 10^?10 mol cm²; each complex ion then occupies 0.38 nm², equivalent to the size of about one catechol molecule. Interference by high concentrations of Fe(III) is overcome by selectively adsorbing U(VI) at a collection potential near the reduction potential of Fe(III). Organic surfactants reduce the peak height for uranium by up to 75% at unnaturally high concentrations only (4 mg l^?1 Triton X-100). Competition by high concentrations of Cu(II) for space on the surface of the drop is eliminated by addition of EDTA.     

New Copper(II) Ion-Selective Membrane Electrode Based on Erythromycin Ethyl Succinate as a Neutral Ionophore

Abstract

The potentiometric response characteristics of a new copper(II) ion-selective PVC membrane electrode based on erythromycin ethyl succinate (EES) as ionophore were investigated. The electrode exhibited a Nernstian response to Cu²⁺ ions over the activity range of 1.5 × 10^?2 to 2.0 × 10^?6 mol L^?1 with a limit of detection of 6.3 × 10^?7 mol L^?1. Stable potentials were obtained in the pH range of 5.5–6.5. The potentiometric selectivity coefficients were calculated by using fixed interference method and revealed no important interferences except for Ag⁺. This electrode was successfully applied as an indicator electrode in determination of copper ions in real water samples.     

Electrochemical determination of tryptophan based on silicon dioxide nanopartilces modified carbon paste electrode

Silicon dioxide nanoparticles modified carbon paste electrode was fabricated and used for electrochemical investigation of tryptophan. Compared with the unmodified electrode, the peak current significantly increased. Experimental conditions for tryptophan determination were optimized. Linear relationship between the peak current and tryptophan concentration was obtained in the range of 1.0 × 10^?7?5.0 × 10^?6 mol L^?1 and 5.0 × 10^?6?5.0 × 10^?5 mol L^?1 with an estimated detection limit of 3.6 × 10^?8 mol L^?1 (S/N = 3). Tryptophan in pharmaceutical and human serum samples were successfully determined by the proposed method.     

Immobilization of Horseradish Peroxidase on a Biocompatible Titania Layer–Modified Gold Electrode for the Detection of Hydrogen Peroxide

Abstract

A procedure for fabricating an enzyme electrode has been described based on the effective immobilization of horseradish peroxidase to an ultrathin titania layer–modified self‐assembled gold electrode. The resulting electrode exhibits excellent electrocatalytical activity to hydrogen peroxide in the presence of hydroquinone as a mediator. The analytical conditions were studied in detail by using an amperometric method. Under the optimized conditions, a detection limit of 7.1×10^?7 mol l^?1 and a linear response to hydrogen peroxide that ranged from 1×10^?6 mol l^?1 to 7.6×10^?4 mol l^?1 were obtained. The reproducibility and stability were examined with satisfactory results.     

Neutral lipid enzyme electrode based on ion-sensitive field effect transistors

An enzyme electrode for neutral lipid determination based on hydrogen ion-sensitive field effect transistors (pH-FET's) is described. The electrode is composed of two pH-FET's with an immobilized lipase membrane on one pH-FET, and a platinum wire. Triglycerides are solubilized with 10% (v/v) Triton X-100. The electrode is used to determine triglycerides over wide concentration ranges with response times of ca. 2 min. Relations between signal and the logarithm of the concentration are linear over the ranges 100–400 mM triacetin, 3–50 mM tributylin and 0.6–3 mM triolein. In the case of triolein, the detection limit is 9 μg ml^?1 (signal/noise = 3:1). The effect of Triton X-100 on the electrode response is discussed.     

Adsorption voltammetry of the vanadium-2-(5′-bromo-2′-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) system

The behaviour of the vanadium(V) complex with 5-Br-PADAP at a mercury electrode was investigated in HOAcNaOAc. The adsorption phenomena were observed by linear-sweep voltammetry. The mechanism of the electrode reaction was found to be the irreversible reduction of the V(V) in the complex adsorbed on the surface of the electrode to the V(IV) complex with 5-Br-PADAP. In 0.02 mol l^?1 HOAc-0.012 mol l^?1 NaOAc (pH 4.5) and 1 × 10^?6 mol l^?1 5-Br-PADAP, the detection limits of linear-sweep adsorption voltammetry and 1.5th-order derivative adsorption voltammetry are 5 × 10^?10 and 2.5 × 10^?11 mol l^?1 , respectively. The method was applied to samples of ore (Geological Deposit).     

The electrochemistry of uric acid at a gold electrode modified with L-cysteine, and its application to sensing uric urine

The electrochemistry of uric acid at a gold electrode modified with a self-assembled film of L-cysteine was studied by cyclic voltammetry and differential pulse voltammetry. Compared to the bare gold electrode, uric acid showed better electrochemical response in that the anodic peak current is stronger and the peak potential is negatively shifted by about 100 mV. The effects of experimental conditions on the oxidation of uric acid were tested and a calibration plot was established. The differential pulse response to uric acid is linear in the concentration range from 1.0?×?10^?6 to ~?1.0?×?10^?4 mol?L^?1 (r?=?0.9995) and from 1.0?×?10^?4 to ~?5.0?×?10^?4 mol?L^?1 (r?=?0.9990), the detection limit being 1.0?×?10^?7 mol?L^?1 (at S/N?=?3). The high sensitivity and good selectivity of the electrode was demonstrated by its practical application to the determination of uric acid in urine samples.

Electrocatalytic oxidation of methanol by ZSM-5 nanozeolite-modified carbon paste electrode in alkaline medium

Development of a novel modified electrode for electrocatalytic oxidation of methanol in order to decrease overvoltage is importance. In this paper, carbon paste electrode (CPE) was modified by ZSM-5 nanozeolite. The average diameter of used nanozeolite was 97 nm. Ni²⁺ ions were incorporated to the nanozeolite by immersion of the modified electrode in a 0.1 M nickel chloride solution. Then, electrochemical studies of this electrode were performed by using cyclic voltammetry(CV) in alkaline medium. This modified electrode was used as an anode for the electrocatalytic oxidation of methanol in 0.1 M of NaOH solution. The obtained data demonstrated that ZSM-5 nanozeolite at the surface of CPE improves catalytic efficiency of the dispersed nickel ions toward methanol oxidation. The values of electron transfer coefficient, charge-transfer rate constant, and the electrode surface coverage are obtained 0.61, 0.2342 s^?1, and 4.33 × 10^?8 mol cm^?2, respectively. Also, the mean value of catalytic rate constant between the methanol and redox sites of electrode and diffusion coefficient were found to be 2.54 × 10⁴ cm³ mol^?1 s^?1 and 1.85 × 10^?8 cm² s^?1, respectively. Obtained results from both CV and chronoamperometric techniques indicated that the electrode reaction is a diffusion-controlled process.     

多臂碳纳米管/Nafion复合材料修饰玻碳电极测定痕量的铅离子

A composite material of nitric acid oxidized multiwalled carbon nanotube （MWNT） and Nation was prepared. Such composite was modified on a glassy carbon electrode to determine trace of lead by differential pulsed voltammetry. In pH=6.47 NaNO3 solution, Pb^2＋ ions were accumulated on the modified electrode at -0.4 V. Compared with a bare and a Nation film coated electrode, the composite coated GC electrode can reduce the accumulating potential and eliminate the toxic character of mercury. The calibration plots were linear at low concentration of 5.0× 10^-9-2.0× 10^-8 mol/L and high concentration of 2.5× 10^-8-5.0× 10^-6 mol/L. The performances characteristics indicate that the electrode can be used to determine trace Pb^2＋ ions.