Sensitive electrochemical detection of hydroquinone with carbon ionogel electrode based on BMIMPF6

An ionic liquid (IL) 1-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF₆) based carbon ionogel electrode (CIE) was fabricated for the sensitive voltammetric sensing of hydroquinone (HQ) in this paper. Due to the specific characteristics of the prepared working electrode, HQ exhibited an enhanced electrochemical response on CIE with a pair of well-defined redox peaks appeared in pH 2.5 phosphate buffer solution. The electrochemical behaviors of HQ on CIE were investigated by different electrochemical methods such as cyclic voltammetry and differential pulse voltammetry with the electrochemical parameters calculated. Under the optimal conditions the oxidation peak currents exhibited good linear relationship with the HQ concentration in the range from 0.13 to 100.0 μmol L⁻¹ with the detection limit of 0.07 μmol L⁻¹ (3σ). The CIE showed separated electrochemical response to HQ and catechol in the mixture solution. The proposed method was successfully applied to HQ detection in artificial wastewater with the recovery in the range from 98.9% to 102.0%.     

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.     

Electrochemical layer-by-layer modified imprinted sensor based on multi-walled carbon nanotubes and sol–gel materials for sensitive determination of thymidine

A novel electrochemical sol–gel imprinted sensor for sensitive and convenient determination of thymidine was developed. Thin film of molecularly imprinted sol–gel polymers with specific binding sites for thymidine was cast on carbon electrode by electrochemical deposition. Multi-walled carbon nanotubes (MWCNTs) were introduced for the enhancement of electronic transmission and sensitivity. The morphology and performance of the imprinted film was characterized by scanning electron microscopy (SEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), differential pulse voltammetry (DPV) and amperometric measurements (i–t) in detail. The results showed that the imprinted film exhibited high selectivity toward thymidine. The linear range is over the range from 2 to 22 μmol L⁻¹, and the linear regression equation for thymidine is I = 0.867C + 0.232 with the detection limit of 1.6 × 10⁻⁹ mol L⁻¹(S/N = 3). The imprinted sensor was successfully employed to detect thymidine in some zidovudine-tablet samples.     

Liquid membrane system for extraction and electrodeposition of silver(I)

The process of Ag⁺ ions extraction from nitric solutions by bulk liquid membranes containing di(2-ethylhexyl)phosphoric acid and tri-n-octylamine accompanied with silver(I) electrodeposition from perchloric acid solutions is studied at galvanostatic electrodialysis. The effects of the current density as well as of composition of the liquid membrane and aqueous solutions on the rate of the silver(I) transport are determined. More than 90% of silver ions was extracted from the feed solution containing 0.01 mol l⁻¹ AgNO₃ and about 40% of metal was electrodeposited during 1 h of electrodialysis. Sound adherent silver coatings have been deposited on platinum and copper cathodes.     

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.     

Exposure of Porphyromonas gingivalis to cortisol increases bacterial growth

Objective

Psychological stress is considered as a risk factor for periodontal diseases. The stress-related hormone, cortisol is one of the main molecules released during human stress response and is found in plasma and gingival crevicular fluid. This hormone has been suggested to modify composition of subgingival biofilms. The aim of this study was to investigate the effect of exposure to cortisol on Porphyromonas gingivalis (P. gingivalis) growth.

Materials and methods

P. gingivalis ATCC strain 33277 was cultured under strict anaerobic conditions at 37 °C in Brain Heart Infusion medium supplemented with hemin (5 μg ml⁻¹) and menadione (1 μg ml⁻¹). Bacterial cultures were incubated with or without hydrocortisone (0.04–10 μg ml⁻¹) at 37 °C for 12, 24 and 48 h and bacterial growth was evaluated by spectrophotometric method (OD_600 nm). Cortisol consumption has been followed by HPLC.

Results

Cortisol significantly increased P. gingivalis growth in the first 24 h peaking at 12 h but this increase was not related to the concentration used. During the time period, no consumption of cortisol was observed.

Conclusions

This study provides further support for the idea that stress-induced hormone; cortisol may influence the growth of P. gingivalis. This specific effect may be involved in the relationship between stress and periodontal diseases.     

Pitzer and Pitzer–Simonson–Clegg modeling approaches: Ternary HCl + ethanol + water electrolyte system

We report in this work, for the first time, the results obtained from both Pitzer, Pitzer–Simonson–Clegg (PSC) and an extended PSC ion-interaction approaches for modeling the non-ideal behavior of HCl electrolyte in the mixed ethanol + water solvent systems. In this context, a review of literature shows that the use of an exact and complete form of PSC ion-interaction approach for modeling electrolyte in mixed solvent systems was only limited to the works of two research groups. In this work, the modeling purposes were achieved based on the experimental potentiometric data of a galvanic cell containing a pH glass membrane and Ag/AgCl electrodes. The measurements were achieved over the HCl electrolyte molality ranging from 0.02 up to about 5 mol kg⁻¹ in mixed ethanol (x%) + water (100 − x%) solvent with different solvent mass fractions percent (x% = 10%, 20%, 30%, 40% and 50%), at 298.15 ± 0.05 K.     

Ionic liquid–polymer gel electrolytes from hydrophilic and hydrophobic ionic liquids1

Ionic liquid–polymer gels were prepared by incorporating hydrophilic EMIBF₄ and EMI(triflate) (EMI⁺=1-ethyl-3-methylimidazolium) and hydrophobic BMIPF₆ (BMI⁺=1-(1-butyl)-3-methylimidazolium) room-temperature ionic liquids into a poly(vinylidene fluoride)–hexafluoropropylene copolymer (PVdF(HFP)) matrix. Gel electrolytes prepared with ionic liquid:PVdF(HFP) mass ratios of 2:1 exhibited ionic conductivities of >10^?3 S cm^?1 at room temperature and >10^?2 S cm^?1 at 100°C. The BMIPF₆-PVdF(HFP) gel was incorporated into electrochemical cells, employing graphite intercalation electrodes for both the anode and cathode, to construct single and bipolar cells displaying open-circuit voltages of 3.77 and 7.86 V, respectively. New inexpensive preparative routes for the hydrophilic ionic liquids were developed that utilize the metathesis reaction of EMICl with the appropriate ammonium salt in acetone or acetonitrile to produce high purity products.     

Low overpotential reduction of dinitrogen to ammonia in aqueous media

The molecular nitrogen fixation to ammonia is one of the most important processes in chemistry. In this connection, our aim was to realize an electrochemical reaction under extremely mild conditions in an aqueous media for the first time. The reduction of dinitrogen was achieved on a polypyrrole electrode in aqueous 0.1 M Li₂SO₄/0.03 M H⁺ solution at 60 bar N₂-pressure. The reaction product was only ammonia and the ammonia formation efficiency depends strongly on the applied pressure, temperature, electrode potential, supporting electrolyte, film thickness of polymer electrode, as well as on the amount of proton source added to the electrolyte medium. The maximum yield of NH₃ was 53 μM obtained at −0.165 V_NHE after 5 h of electrolysis.     

Light cola drink is less erosive than the regular one: An in situ/ex vivo study

Objective

This in situ/ex vivo study assessed the erosive potential of a light cola drink when compared to a regular one.

Methods

During 2 experimental 14-days crossover phases, eight volunteers wore palatal devices with 2 human enamel blocks. The groups under study were: group light, erosive challenge with light cola drink and group regular, erosive challenge with regular cola drink. During 14 days, erosive challenges were performed extraorally 3X/day. In each challenge, the device was immersed in 150 ml of light cola (group light) or regular cola (group regular) for 5 min. Erosion was analysed by surface profilometry (μm) and surface microhardness change (%SMH). The data were statistically analyzed using paired t test (p < 0.05).

Results

Group light (0.6 ± 0.2 μm) showed significantly lesser wear than group regular (3.1 ± 1.0 μm). There was no significant difference between the groups for the %SMH (group light −63.9 ± 13.9 and group regular −78.5 ± 12.7).

Conclusions

The data suggest that the light cola drink is less erosive than the regular one.     

Synthesis and electrochemical characterizations of nano size Ce doped LiMn2O4 cathode materials for rechargeable lithium batteries

LiCe_xMn_2−xO₄ (x = 0.00–0.10) cathode materials for rechargeable lithium-ion batteries were synthesized by simple sol–gel technique using aqueous solutions of metal nitrates and succinic acid as the chelating agent. The gel precursors of metal succinates were dried in vacuum oven for 10 h at 120 °C. After drying, the gel precursors were ground and heated at 900 °C. The structural characterization was carried out by X-ray powder diffraction and X-ray photoelectron spectroscopy to identify the valence state of Mn and Ce in the synthesized materials. The sample exhibited a well defined spinel structure and the lattice parameter linearly increased with increasing the cerium contents in LiCe_xMn_2−xO₄. Surface morphology and particle size of the synthesized materials were determined by scanning electron microscopy and transmittance electron microscopy respectively. Electrochemical properties were characterized for assembled Li/LiCe_xMn_2−xO₄ coin type cells using galvanostatic charge/discharge studies at 0.5C rate and cyclic voltammetry in the potential range between 2.75 and 4.5 V at a scan rate of 0.1 mV s⁻¹. Among them cerium doped spinel LiCe_0.05Mn_1.90O₄ has improved structural stability, high reversible capacity and excellent electrochemical performance of rechargeable lithium batteries.     

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).     

Oxygen reduction reaction selectivity of RuxSey in formic acid solutions

Carbon-supported and non-supported cluster-like Ru_xSe_y were synthesized in aqueous media. The structure and morphology were analyzed by XRD and TEM, respectively. Particles dispersed uniformly on the support with an averaged size of 2.1 nm were obtained. The oxygen reduction reaction (ORR) in presence of HCOOH was investigated by means of rotating disk electrode at 25 °C on Ru_xSe_y nanoclusters. The kinetics of HCOOH oxidation for non-supported and carbon-supported Ru_xSe_y catalysts was analyzed. A reaction order of 1/1.4 and 1/1.6 was determined for Ru_xSe_y and Ru_xSe_y/C, respectively. This reaction order indicates that the reaction mechanism is similar to Pt/C. The chalcogenide catalyst showed a high tolerance and selectivity towards the ORR in electrolytes containing up to 0.1 M HCOOH. At the highest formic acid concentration (5 M) the potential, at e.g. current density of 0.2 mA cm⁻², shifts to negative for non-supported and carbon-supported Ru_xSe_y by 0.24 V and 0.28 V, respectively. The results reported in this work are the basis for overcoming the negative impact of fuel cross-over in microfluidic formic acid fuel cells that currently use Pt as cathode catalyst.     

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.     

Selective electrochemical sensing of calcium dobesilate based on an ordered mesoporous carbon-modified pyrolytic graphite electrode

Cyclic voltammetric investigation of calcium dobesilate (CD) in aqueous acid media was carried out by using an ordered mesoporous carbon-modified pyrolytic graphite electrode (OMC/PGE). A pair of well-defined redox peaks of CD was observed at the OMC/PGE, showing its good elelctrochemial response towards CD. The anodic current is linear with CD concentration in the range of 1.0 × 10⁻⁷–1.3 × 10⁻³ mol L⁻¹, with a detection limit of 4.0 × 10⁻⁸ mol L⁻¹. Meanwhile, the proposed electrode can avoid some interference coexisting with CD, such as uric acid, serotonin, and ascorbic acid. The proposed method can be potentially applied for selective electrochemical sensing of CD in physiological condition.     

Electroanalytical determination of sildenafil in Viagra tablets using screen-printed and conventional carbon paste electrodes

This work compares the electroactivity of a conventional carbon-paste electrodes and screen-printed carbon electrodes. Potentiometric sensors responsive to sildenafil citrate (SILC) drug (the active component of Viagra) are described, characterized, compared and used for drug assessment. The proposed carbon paste electrode is fully characterized in terms of plasticizer type, response time, life span, soaking time, titrant, pH and temperature. The electrodes exhibited linear response with a Nernstian slope of 58.20 ± 1 and 58.82 ± 0.5 mV decade⁻¹ for SILC in the concentration range from 1.0 × 10⁻⁷ to 1.0 × 10⁻² and 5.30 × 10⁻⁷ to 1.0 × 10⁻² mol L⁻¹ with good reproducibility for CPE and SPE, respectively. Both CPE and SPE could be used in the pH range 3.0–5.0 and the isothermal coefficient is found to be 0.98 and 0.85 mV/°C, respectively. The limit of detection was found to be 9.0 × 10⁻⁸ and 3.5 × 10⁻⁷ mol L⁻¹ for CPE and SPE, respectively. They were applied to potentiometric determination of SILC in pure state and pharmaceutical preparation under batch conditions. The CPE and SPE sensors display good selectivity for SILC drug over large number of inorganic cations, sugars and amino acids commonly used in drug formulations. The CPE and SPE show high selectivity for the drug under investigation. The results obtained using the fabricated CPE is compared with those obtained by SPE for spiked pharmaceutical samples.     

A gold nanoparticle-modified PVC/TTF-TCNQ composite amperometric biosensor for glucose determination

A comparison of the analytical performances of several enzyme biosensor designs, based on the use of different tailored gold nanoparticle-modified composite PVC/TTF-TCNQ electrodes, is discussed. The analytical characteristics of glucose calibration plots and kinetic parameters of the enzyme reaction were compared for the biosensors tested: Au_coll + GOx, GOx + Au_coll, Mixed GOx + Au_coll and PVC/TTF-TCNQ-Au_coll. The presence of this nanomaterial enhances the analytical performance with respect to the precursor biosensor without Au. The proposed biosensor can be applied in batch (response linear up to 2.0 mM, sensitivity of 45 ± 0.5 mA M⁻¹ with a limit of detection, s/n = 3, of 6.2 × 10⁻⁶ M) and in FIA systems (linear range between 0.1 and 8 mM, sensitivity of 3.67 ± 0.3 mA M⁻¹ with a limit of detection, s/n = 3, of 1.9 × 10⁻⁵ M).     

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.     

Electrodeposition of Au from [EMIm][TFSA] room-temperature ionic liquid: An electrochemical and Surface-Enhanced Raman Spectroscopy study

In this paper we report in situ Surface-Enhanced Raman Scattering (SERS) experiments carried out during the electrochemical deposition of gold from Au(I) cyanocomplexes in the room-temperature ionic liquid (RTIL) 1-ethyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl) amide ([EMIm][TFSA]). The obtained SERS spectra indicated the co-adsorption of CN⁻ and both anions and cations of the RTIL in the range from −1.8 to +0.3 V vs. an Au quasi-reference electrode (QRE). The surface CN⁻ peak exhibits a Stark tuning of ca. 28 cm⁻¹ V⁻¹. The oxidation of CN⁻ to OCN⁻ was observed at potentials more anodic than 0.3 V. The study was complemented by cyclic voltammetry, pinpointing RTIL reactivity at an Au electrode as well as CN⁻ adsorption effects and Au(I) reduction. SEM observations allowed to identify the conditions for the achievement of continuous Au films as well as the morphological peculiarities of Au electrodeposited from [EMIm][TFSA]. XPS measurements proved that no RTIL is incorporated into the Au film, under the investigated conditions.     

Does strontium play a role in the cariostatic activity of glass ionomer?: Strontium diffusion and antibacterial activity

Objectives

The aim of this work was to evaluate the activity of strontium ions on the main pathogens of the oral flora. The leaching of strontium from resin modified glass ionomer cements (RMGIC) was evaluated together with its uptake by superficial dental enamel.

Methods

The antibacterial activity was measured by the growth inhibition method following exposure of supra- and sub-gingival bacteria to a range of strontium concentrations (0.19 mol l⁻¹, 0.37 mol l⁻¹, 0.74 mol l⁻¹ and 1.11 mol l⁻¹). Strontium concentrations were analyzed chemically and migration at 5 μm and 15 μm depths was quantified by microprobe following Fuji Ortho LC application on the vestibular enamel of extracted teeth.

Results

Strontium was found in appreciable amounts (0.8 wt.%) in superficial enamel, but in insignificant concentrations deeper in. At the same time, 8% fluoroapatite was formed in the enamel. Under our experimental conditions, strontium had no significant antibacterial activity; only one log reduction of activity was observed at the highest concentrations tested.

Conclusions

RMGIC releases strontium ions which are rapidly exchanged for calcium ions in the superficial enamel. No significant antibacterial activity was observed for strontium ions alone at the concentrations considered. However synergistic effects with fluoride could promote antibacterial activity.