Cetyltrimethyl ammonium bromide effect on highly electrocatalysis of methanol oxidation based on nickel particles electrodeposited into poly (m-toluidine) film on the carbon paste electrode

In this work, m-toluidine is electropolymerized at the surface of carbon paste electrode using consecutive cyclic voltammetry in 20 mM monomer aqueous solution in the presence of 6 mM cetyltrimethyl ammonium bromide (CTAB) as surfactant. Then transition metal of nickel is incorporated into the polymer by electrodepositing of Ni (II) from 1.5 M NiSO₄ acidic solution using chronoamperometry technique (−1.0 V versus Ag|AgCl|KCl (3 M) for 15 min). In alkaline medium (i.e. NaOH 0.1 M) a good redox behavior of Ni (III)/Ni (II) couple at the surface of Ni/poly (m-toluidine) modified carbon paste electrode (Ni/PMT/MCPE) in the absence and presence of CTAB (Ni/CTAB-PMT/MCPE) can be observed. Electrocatalytic oxidation of methanol has been studied on Ni/PMT/MCPE and Ni/CTAB-PMT/MCPE. The results show that CTAB significantly enhances the catalytic efficiency of nickel particles on the oxidation of methanol in aqueous alkaline media. Moreover, the effects of various parameters such as concentration of CTAB, concentration of methanol, electrodepositing time, film thickness and monomer concentration on the electrooxidation of methanol as well as long-term stability of the Ni/CTAB-PMT/MCPE have also been investigated. This polymeric modified electrode can oxidize the methanol with high current density (over 40 mA cm⁻²).     

Electrocatalytic oxidation of some amino acids on a cobalt hydroxide nanoparticles modified glassy carbon electrode

In this study we investigated the electrocatalytic oxidation of cysteine, cystine, N-acetyl cysteine, and methionine on cobalt hydroxide nanoparticles modified glassy carbon electrode in alkaline solution. Different electrochemical techniques such as cyclic voltammetry, chronoamperometry and steady-state polarization were used to track the oxidation process and its kinetics. From voltammetric studies we concluded that in the presence of amino acids the anodic peak current of Co(IV) species increased, followed by a decrease in the corresponding cathodic current peak. This indicates that amino acids were oxidized on the redox mediator which was immobilized on the electrode surface via an electrocatalytic mechanism. Using Laviron’s equation, the values of α_s and k_s for the immobilized redox species were determined as α_s,a = 0.63, α_s,c = 0.38 and k_s = 0.28 s⁻¹, respectively. The catalytic rate constants, the electron transfer coefficients and the diffusion coefficients involved in the electrocatalytic oxidation of amino acids were determined.     

Preparation of poly N,N-dimethylaniline/ferrocyanide film modified carbon paste electrode: Application to electrocatalytic oxidation of l-cysteine

Functionalized poly N,N-dimethylaniline film was prepared by adsorption of ferrocyanide onto the polymer forming at the surface of carbon paste electrode (CPE) in aqueous solution. The electrocatalytic ability of poly N,N-dimethylaniline/ferrocyanide film modified carbon paste electrode (PDMA/FMCPE) was demonstrated by oxidation of l-cysteine. Cyclic voltammetry and chronoamperometry techniques were used to investigate this ability. In the optimum pH (6.00), the electrocatalytic ability about 480 mV and the catalytic reaction rate constant, (k_h), can be seen 3.08 × 10³ M⁻¹ s⁻¹. The catalytic oxidation peak current determined by cyclic voltammetry method was linearly dependent on the l-cysteine concentration and the linearity range obtained was 8.00 × 10⁻⁵ –2.25 × 10⁻³ M. Detection limit of this method was determined as 6.17 × 10⁻⁵ M (2σ). At a fixed potential under hydrodynamic conditions (stirred solution), the calibration plot was linear over the l-cysteine concentration range 7.40 × 10⁻⁶ M–1.38 × 10⁻⁴ M. The detection limit of the method was 6.38 × 10⁻⁶ M (2σ).     

Simultaneous determination of epinephrine and uric acid at a gold electrode modified by a 2-(2,3-dihydroxy phenyl)-1, 3-dithiane self-assembled monolayer

In the present paper, the use of a gold electrode modified by 2-(2,3-dihydroxy phenyl)-1,3-dithiane self-assembled monolayer (DPDSAM) for the determination of epinephrine (EP) and uric acid (UA) was described. Initially, cyclic voltammetry was used to investigate the redox properties of this modified electrode at various scan rates. The apparent charge transfer rate constant, k_s, and transfer coefficient, α, were calculated. Next, the mediated oxidation of EP at the modified electrode was described. At the optimum pH of 8.0, the oxidation of EP occurs at a potential about 155 mV less positive than that of an unmodified gold electrode. The values of electron transfer coefficients (α = 0.356), catalytic rate constant (k = 1.624 × 10⁴ M⁻¹ s⁻¹) and diffusion coefficient (D = 1.04 × 10⁻⁶ cm² s⁻¹) were calculated for EP, using electrochemical approaches. Based on differential pulse voltammetry, the oxidation of EP exhibited a dynamic range between 0.7 and 500.0 μM and a detection limit (3σ) of 0.51 μM. Furthermore, simultaneous determination of EP and UA at the modified electrode was described. Finally, this method was used for the determination of EP in EP ampoule.     

Electrocatalytic activity of thianthrene toward one-electron oxidation of guanosine and DNA in a non-aqueous medium

In this study, the electrochemical behavior of thianthrene (TH) and its application toward the electrocatalytic oxidation of guanosine (Gs) and DNA in a non-aqueous solution are investigated using different voltammetric techniques. Guanosine and DNA are adsorbed on the glassy carbon electrode (GCE) by applying a positive potential to the GCE. The rate constant of catalytic reaction between DNA and TH and also between Gs and TH were evaluated using chronoamperometry which gave rate constants of 2.41 × 10⁶ cm³ mol⁻¹ s⁻¹ and 2.68 (±0.19) × 10⁶ cm³ mol⁻¹ s⁻¹, respectively. Also the diffusion coefficient of TH was obtained using hydrodynamic voltammetry (3.17 × 10⁻⁵ cm² s⁻¹). Furthermore, using hydrodynamic voltammetry, a one-electron mechanism for oxidation of Gs is suggested.     

A differential pulse voltammetric method for simultaneous determination of ascorbic acid,dopamine, and uric acid using poly (3-(5-chloro-2-hydroxyphenylazo)-4,5-dihydroxynaphthalene-2,7-disulfonic acid) film modified glassy carbon electrode

A stable modified glassy carbon electrode based on the poly 3-(5-chloro-2-hydroxyphenylazo)-4,5-dihydroxynaphthalene-2,7-disulfonic acid (CDDA) film was prepared by electrochemical polymerization technique to investigate its electrochemical behavior by cyclic voltammetry. The properties of the electrodeposited films, during preparation under different conditions, and their stability were examined. The homogeneous rate constant, k_s, for the electron transfer between CDDA and glassy carbon electrode was calculated as 5.25(±0.20) × 10² cm s⁻¹. The modified electrode showed electrocatalytic activity toward ascorbic acid (AA), dopamine (DA), and uric acid (UA) oxidation in a buffer solution (pH 4.0) with a diminution of their overpotential of about 0.12, 0.35, and 0.50 V for AA, DA, and UA, respectively. An increase could also be observed in their peak currents. The modified glassy carbon electrode was applied to the electrocatalytic oxidation of DA, AA, and UA, which resolved the overlapping of the anodic peaks of DA, AA, and UA into three well-defined voltammetric peaks in differential pulse voltammetry (DPV). This modified electrode was quite effective not only for detecting DA, AA, and UA, but also for simultaneous determination of these species in a mixture. The separation of the oxidation peak potentials for ascorbic acid–dopamine and dopamine–uric acid were about 0.16 V and 0.17 V, respectively. The final DPV peaks potential of AA, DA and UA were 0.28, 0.44, and 0.61 V, respectively. The calibration curves for DA, AA, and UA were linear for a wide range of concentrations of each species including 5.0–240 μmol L⁻¹ AA, 5.0–280 μmol L⁻¹ DA, and 0.1–18.0 μmol L⁻¹ UA. Detection limits of 1.43 μmol L⁻¹ AA, 0.29 μmol L⁻¹ DA and 0.016 μmol L⁻¹ UA were observed at pH 4. Interference studies showed that the modified electrode exhibits excellent selectivity toward AA, DA, and UA.     

Electrodeposited indigotetrasulfonate film onto glutaraldehyde-cross-linked poly-l-lysine modified glassy carbon electrode for detection of dissolved oxygen

The nano composited film of indigotetrasulfonate (ITS) electrodeposited onto poly-l-lysine (PLL)–glutaraldehyde (GA) (ITS/PLL–GA) was modified on glassy carbon electrode (GCE) by multiple scan cyclic voltammetry. Composited of the proposed film was characterized by atomic force microscopy (AFM), scanning electron microscopy (SEM), electrochemical quartz crystal microbalance (EQCM), electrochemical impedance spectroscopy (EIS), and UV–vis spectrum for the absorption at λ_max at 566 nm. For the electrocatalytic reduction of dissolved oxygen, ITS/PLL–GA film modified electrodes was determined in 0.1 M acetate buffer solution (pH 5.6) by cyclic voltammetry and rotating disk electrode voltammetry. This dissolved oxygen electrochemical sensor exhibited a linear response range (from 0 to 178.4 μM, R² = 0.9949), lowest detection limit (2.2 μM), lowest overpotential at −0.09 V, high sensitivity (906 μA mM⁻¹) and relative standard deviation (RSD) for determining dissolved oxygen (n = 3) was 4.2%. In addition, the ITS/PLL–GA/GCE was advantageous in terms of its simple preparation, specificity, stability and the ability of regeneration.     

Electrochemical impedimetry of electrodeposited poly(propylene imine) dendrimer monolayer

Voltammetric and electrochemical impedance spectroscopic (EIS) studies of generation one poly(propylene imine) (G1 PPI) dendrimer as an electroactive and catalytic nanomaterials both in solution and as an electrode modifier based on a simple one step electrodeposition method is presented. The G1 PPI exhibited a reversible one electron redox behaviour at E^0′ ca 210 mV in phosphate buffer pH 7.2 with diffusion coefficient and Warburg coefficient of 7.5 × 10⁻¹⁰ cm² s⁻¹ and 8.87 × 10⁻⁴ Ω s^−1/2 respectively. Cyclic voltammetric electrodeposition of a monolayer of G1 PPI on glassy carbon electrode was carried out between −100 mV and 1100 mV for 10 cycles. The nanoelectrode was electroactive in PBS at E^0′ ca 220 mV. Kinetic profiles such as time constant (4.64 × 10⁻⁵ s rad⁻¹), exchange current (1.55 × 10⁻⁴ A) and heterogeneous rate constant (4.52 × 10⁻³ cm s⁻¹) obtained from EIS showed that the dendrimer layer catalysed the redox reaction of Fe^2+/3+ in [Fe(CN)₆]^3−/4− redox probe.     

Electrocatalytic oxidation of dopamine at aluminum electrode modified with nickel pentacyanonitrosylferrate films,synthesized by electroless procedure

The electrocatalytic oxidation of dopamine (DA) at a home-made aluminum electrode modified with nickel pentacyanonitrosylferrate (NiPCNF) film, has been studied by electrochemical approaches. The immobilization of NiPCNF film was performed by a simple dip-coating procedure. The cyclic voltammogram of the resulting modified Al electrode prepared under optimum conditions, shows a well-behaved redox couple due to the [Ni^IIFe^III/II(CN)₅NO]^0/?1 system. The NiPCNF films, formed on the Al electrode show excellent electrocatalytic activity toward the oxidation of DA. The effect of the solution pH on the voltammetric response of DA was examined using phosphate buffer solution of different pHs. Under optimum conditions a linear calibration graph was obtained over the DA concentration range 2–33 mM. The kinetics of the catalytic reaction were investigated by cyclic voltammetry and rotating disk electrode voltammetry. The results were explained using the theory of electrocatalytic reactions at chemically modified electrodes. The rate constant for the catalytic reaction k, the diffusion coefficient of DA in the solution D, the electron diffusion coefficient in the film D_e and transfer coefficient α, were found to be 3.1×10² M^?1 s^?1, 3.4×10^?6 cm² s^?1, 2.2×10^?11 cm² s^?1 and 0.67, respectively. The interference of ascorbic acid was investigated and greatly reduced using a thin film of Nafion^® on the surface-modified electrode. Further examination of the modified electrode shows that the modifying layers (NiPCNF) on the aluminum substrate show reproducible behavior and a high level of stability during electrochemical experiments, making it interesting for analytical applications.     

Electrochemistry of magnolol and interaction with DNA

The electrochemical behaviors of magnolol have been studied at glassy carbon electrode using cyclic voltammetry, linear sweep voltammetry and chronocoulometry. Moreover, its interaction with DNA was investigated in solution by electrochemical methods and ultraviolet–visible spectroscopy. The experiment results indicated that the electrochemical oxidation of magnolol was an irreversible process with one proton and one electron transfer. The electron transfer coefficient (α) was calculated to be 0.441 ± 0.001. At the scan rate from 100 mV/s to 450 mV/s, the electrode process was controlled by the adsorption step and at the range of 600–950 mV/s the electrochemical oxidation was diffusion controlled process. The corresponding electrochemical rate constant (k_s) was 0.0760 ± 0.0001 s⁻¹. Through chronocoulometry experiment, the diffusion coefficient (D) and the surface concentration (Γ) were obtained as (3.76 ± 0.01) × 10⁻⁷ cm²/s and (2.98 ± 0.01) × 10⁻¹⁰ mol/cm². In addition, the interaction of magnolol and DNA was ascribed to be electrostatic interaction and the calculated association constant (β) and Hill coefficient (m) were 1.14 × 10⁵ M⁻¹ and 0.973. At last a sensitive and convenient electrochemical method was proposed for the determination of magnolol.     

Determination of trace vanadium(V) by adsorptive anodic stripping voltammetry on an acetylene black paste electrode in the presence of alizarin violet

A sensitive and simplified voltammetric method is developed for the determination of trace amounts of vanadium(V) by adsorptive anodic stripping voltammetry using an acetylene black (AB) paste electrode. The method is based on the preconcentration of the V(V)–alizarin violet (AV) complex at open circuit while stirring the solution for 90 s in 0.15 mol dm⁻³ hexamethylenetetraamine–hydrochloric acid buffer (pH 4.4), the adsorbed complex is then oxidized, producing a response with a peak potential of 564 mV when scanning linearly from 0 to 1000 mV. For voltammetric determination of V(V), the parameters influencing the peak current have been optimized. Under the selected conditions, the peak current and concentration of V(V) accorded with linear relationship in the range of 8.0 × 10⁻¹⁰ mol dm⁻³–1.0 × 10⁻⁷ mol dm⁻³ (c_AV = 2.0 × 10⁻⁶ mol dm⁻³) and 1.0 × 10⁻⁷ mol dm⁻³–8.0 × 10⁻⁶ mol dm⁻³ (c_AV = 2.0 × 10⁻⁵ mol dm⁻³), the detection limit (three times signal to noise) was estimated to be 6.0 × 10⁻¹⁰ mol dm⁻³ for 90 s accumulation. The relative standard deviation (RSD) is 1.9% and 2.3% for V(V) concentrations of 1.0 × 10⁻⁷ mol dm⁻³ and 1.0 × 10⁻⁸ mol dm⁻³ respectively. Finally, this proposed method was successfully applied to the determination of V(V) in natural water samples.     

Simultaneous determination of adenine and guanine utilizing PbO2-carbon nanotubes-ionic liquid composite film modified glassy carbon electrode

A novel and reliable electrochemical sensor based on PbO₂-carbon nanotubes-room temperature ionic liquid (i.e., 1-butyl-3-methylimidazolium hexafluorophosphate, BMIMPF6) composite film modified glassy carbon electrode (GCE) (PbO₂–MWNT–RTIL/GCE) was proposed for simultaneous and individual determination of guanine and adenine. The guanine and adenine oxidation responses were monitored by differential pulse voltammetric (DPV) measurement. Compared with the bare electrode, the PbO₂–MWNT–RTIL/GCE not only significantly enhanced the oxidation peak currents of guanine and adenine, but also lowered their oxidation overpotentials, suggesting that the synergistic effect of PbO₂, MWNT and RTIL could dramatically improve the determining sensitivity of guanine and adenine. The PbO₂–MWNT–RTIL/GCE showed good stability, high accumulation efficiency and enhanced electrocatalytic ability for the detection of guanine and adenine. Besides, the modified electrode also exhibited good behaviors in the simultaneous detection of adenine and guanine with the peak separation of 0.29 V in 0.1 M pH 7.0 phosphate buffer solution (PBS). Under the optimal conditions, the detection limit for individual determination of guanine and adenine was 6.0 × 10⁻⁹ M and 3.0 × 10⁻⁸ M (S/N = 3), respectively. The proposed method for the measurements of guanine and adenine in herring sperm DNA was successfully applied with satisfactory results.     

Sorption of water, ethanol or ethanol/water solutions by light-cured dental dimethacrylate resins

Objectives

This work is concerned with the study of the sorption and desorption process of water, ethanol or ethanol/water solution 50% (v/v) or 75% (v/v) by the dental resins prepared by light curing of Bis-GMA, Bis-EMA, UDMA, TEGDMA or D₃MA.

Methods

A thin resin disc is placed in a bath of time to obtain the sorption curve m_t = f(t). Then the liquid is desorbed until a constant mass for the disc is reached and the desorption curve is recorded. These experimental curves help in the determination of the sorbed/desorbed liquid amount at equilibrium, the percentage of the extracted mass of unreacted monomer known as “solubility”, and the sorption/desorption diffusion coefficient which expresses correspondingly the rate of the liquid sorption/desorption.

Results

The highest liquid uptake by dental resins was 13.3 wt% ethanol for Bis-GMA-resin, 12.0 wt% ethanol for UDMA-resin, 10.10 wt% ethanol/water solution for TEGDMA-resin, 7.34 wt% ethanol for D₃MA-resin and 6.61 wt% ethanol for Bis-EMA-resin. The diffusion coefficient for all resins was higher in water than in ethanol/water solution or ethanol. Bis-GMA-resin showed the highest diffusion coefficient (11.01 × 10⁻⁸ cm² s⁻¹) followed by Bis-EMA-resin (7.43 × 10⁻⁸ cm² s⁻¹), UDMA-resin (6.88 × 10⁻⁸ cm² s⁻¹), D₃MA-resin (6.22 × 10⁻⁸ cm² s⁻¹) and finally by TEGDMA-resin (1.52 × 10⁻⁸ cm² s⁻¹).

Significance

All studied dental resins, except TEGDMA-resin, absorbed higher amount of pure ethanol than water or ethanol water solution. TEGDMA-resin absorbed higher amount of ethanol/water solution (50/50 or 75/25 (v/v)) than water or ethanol. For all studied dental resins the diffusion coefficient was higher in water than in ethanol/water solution or ethanol.     

Application of surfactant modified zeolite membrane electrode towards potentiometric determination of perchlorate

Potentiometric electrodes based on the incorporation of surfactant-modified zeolite Y (SMZ) particles into poly vinyl chloride (PVC) membranes were described. The electrode characteristics were evaluated regarding the response towards perchlorate ions. PVC membranes plasticized with dioctyl phthalate and without lipophilic additives (co-exchanger) are used throughout this study. The influence of membrane composition on the electrode response was studied. The electrode exhibited a Nernstian response towards perchlorate in the concentration range of 7.9 × 10⁻⁶–8.0 × 10⁻² M with a slope of 59.7 ± 0.9 mV per decade of perchlorate concentration with a working pH range of 1.7–9.5 with a fast response time of ≤10 s. The lower and upper detection limits were 4.07 × 10⁻⁷ and 0.13 M, respectively. The electrode response to perchlorate remains constant in the temperature range of 20–40 °C and in the presence of 2.5 × 10⁻⁶–1 × 10⁻² M NaNO₃. The selectivity coefficients for perchlorate anion as test species with respect to other anions were determined. The proposed modified zeolite-PVC electrode can be used for at least 30 days without any considerable divergence in potential. It was applied as indicator electrode in water samples with satisfactory results. The results of this study and our previous work show HDTMA plays different roles according to the zeolite type and matrix, as HDTMA-zeolite Y in a carbon paste matrix showed a good Nernstian behavior towards phosphate anion.     

Highly temperature dependent mass-transport parameters for ORR in Nafion® 211

Nafion® 211 differs from previous versions of Nafion in that the membrane is cast from a dispersion rather than being melt-extruded. As such, the water sorption properties are different, as is the rate of increase in water content with temperature. Kinetic and mass-transport parameters for dispersion-cast Nafion® 211 were determined using solid-state electrochemistry in the temperature range 30–70 °C, 100% relative humidity, and 30 psi oxygen pressure. Exchange current densities, Tafel slopes, and transfer coefficients for ORR in Nafion® 211, are similar to those observed in Nafion® 117; mass-transport parameters are not. At 30 °C and 100% RH oxygen solubility and the diffusion coefficient is determined to be 1.16 × 10⁻⁵ mol cm⁻³ and 1.13 × 10⁻⁶ cm² s⁻¹, respectively. Oxygen permeability at 30 °C (1.28 × 10⁻¹¹ mol cm⁻¹ s⁻¹) is lower than in Nafion® 117 (5.31 × 10⁻¹¹ mol cm⁻¹ s⁻¹) by factor of 4, while at T > 60 °C the permeability of Nafion® 211 increases significantly to values higher than Nafion® 117, and is correlated with the increase in water content and hydration number (λ) with temperature.     

Electrocatalytic oxidation of hydrazine using glassy carbon electrode modified with carbon nanotube and terpyridine manganese(II) complex

Here, we report a simple and extremely effective method to modify a glassy carbon (GC) electrode with carbon nanotubes (CNTs) and [Mn(CH₃COO)(CH₃OH)₂(pyterpy)]ClO₄, (pyterpy = 4′-(4-pyridyl)-2,2′:6′,2′′-terpyridine) complex. The kinetics of the reaction between, the terpyridine manganese(II) complex, mediator and hydrazine has been characterized using cyclic voltammetry and rotating disk electrode voltammetry. The catalytic currents were proportional to the concentration of hydrazine giving rise to calibration curves characterized by two linear segments. The linear segment over the concentration range of 1.00 × 10⁻³–1.05 mM could be used with analytical purposes to determination of hydrazine with a detection limit of 0.50 μM and a sensitivity of 0.038 μA/μM. The heterogeneous rate constant, k′ for the oxidation of hydrazine at the surface of the modified electrode was determined by rotating disk electrode voltammetry using the Koutecky–Levich plot. The transfer coefficient (α) for electrocatalytic oxidation of hydrazine and the diffusion coefficient of this substance under the experimental conditions were also investigated. The resulting modified electrode retains its initial response for at least one month if stored dry in air.     

Selective determination of dopamine in the presence of ascorbic acid at a multi-wall carbon nanotube-poly(3,5-dihydroxy benzoic acid) film modified electrode

A sensitive and selective method for determination of dopamine (DA) using multi-wall carbon nanotube (MWCNT)-poly(3,5-dihydroxy benzoic acid) [poly(DBA)] modified electrode is developed. The modified electrode shows excellent electrocatalytic activity toward the oxidation of dopamine in phosphate buffer solutions at pH 7.4. Using cyclic voltammetry, the linear range of 1 × 10⁻⁷–7.0 × 10⁻⁵ M in the interference of 500 μM ascorbic acid (AA) and the detection limit of 1.0 × 10⁻⁸ M were estimated for the measurement of DA in pH 7.4 phosphate buffer solutions. The value of DA current retained 98.36% of the initial response current after the modified electrode exposed to the air for one week. The interference studies showed that the modified electrode excludes effectively large excess of AA. The kinetic characteristics of the transfer of DA demonstrated that the electron propagation between DA and electrode was accelerated at MWCNT-poly(DBA) modified electrode. The work provided a valid and simple approach to selectively detect dopamine in the presence of AA in physiological environment.     

Calculations of the exchange current density for hydrogen electrode reactions: A short review and a new equation

After reviewing relevant equations for the calculation of exchange current density, a new equation is derived for hydrogen electrode reactions to correct for the influences of the hydrogen concentration change in the vicinity to the electrode surface. This equation is able to describe the polarization curve shape in the small polarization region as well as to calculate the exchange current (density). The abilities of this equation are demonstrated by the data obtained with a Pt rotating disk electrode in 0.1 mol l⁻¹ KOH solution. The exchange current density at 298 K under 1 atmosphere hydrogen pressure is found to be 0.103 mA cm⁻² with an apparent activation energy of 33.5 kJ mol⁻¹. At a constant temperature, the exchange current is found to be proportional to the square root of the hydrogen partial pressure in the solution.     

Development of a carbon nanotubes paste electrode modified with crosslinked chitosan for cadmium(II) and mercury(II) determination

A functionalized carbon nanotubes paste electrode modified with cross-linked chitosan for the determination of trace amounts of cadmium(II) and mercury(II) by linear anodic stripping voltammetry is described. Under optimal experimental conditions, the peak current was linear in the Cd(II) concentration range from 5.9 × 10⁻⁸ to 1.5 × 10⁻⁶ mol L⁻¹ with a detection limit of 9.8 × 10⁻⁹ mol L⁻¹ and, for Hg(II) from 6.7 × 10⁻⁹ to 8.3 × 10⁻⁸ mol L⁻¹with a detection limit of 2.4 × 10⁻⁹ mol L⁻¹. The proposed method was successfully applied for the determination of Hg(II) in natural and industrial wastewater samples, and Cd(II) in sediments, human urine, natural, and industrial wastewater samples.     

Temperature-dependent polymerization shrinkage stress kinetics of resin-composites

Objectives

To determine temperature dependence of shrinkage stress kinetics for a set of resin composites formulated with dimethacrylate monomer matrices.

Methods

Six representative resin composites with a range of resin matrices were selected. Two of them were considered as low shrinking resin composites: Kalore and Venus Diamond. The shrinkage stress kinetics at 23 °C and 37 °C were measured continuously using a Bioman instrument for 60 min. Stress levels between materials were compared at two intervals: 2 min and 60 min. Specimen temperatures were controlled by a newly designed heating device. Stress measurements were monitored for 1 h, after irradiation for 40 s at 550 mW/cm² (energy density = 22 J/cm²). Three specimens (n = 3) were used at each temperature per material.

Results

Shrinkage stress at 23 °C ranged from 2.93 MPa to 4.71 MPa and from 3.57 MPa to 5.42 MPa for 2 min and 60 min after photo-activation, respectively. The lowest stress-rates were recorded for Kalore and Venus Diamond (0.34 MPa s⁻¹), whereas the highest was recorded for Filtek Supreme XTE (0.63 MPa s⁻¹). At 37 °C, shrinkage stress ranged from 3.27 MPa to 5.35 MPa and from 3.36 MPa to 5.49 MPa for 2 min and 60 min after photo-activation, respectively. Kalore had the lowest stress-rate (0.44 MPa s⁻¹), whereas Filtek Supreme XTE had the highest (0.85 MPa s⁻¹). Materials exhibited a higher stress at 37 °C than 23 °C except for Kalore and Venus Diamond. Positive correlations were found between shrinkage stress and stress-rate at 23 °C and 37 °C (r = 0.70 and 0.92, respectively).

Significance

Resin-composites polymerized at elevated temperature (37 °C) completed stress build up more rapidly than specimens held at 23 °C. Two composites exhibited atypical reduced stress magnitudes at the higher temperature.