Bioactive Hydrogel Layers on Microdisk Electrode Arrays: Impedimetric Characterization and Equivalent Circuit Modeling

Microfabricated microdisk electrode arrays (MDEAs) of 50 μm (5184 disks), 100 μm (1296 disks) and 250 μm (207 disks) (d/r=4; A= 0.1 cm²) were coated with poly(hydroxyethylmethacrylate)‐based hydrogel membranes and studied by electrochemical impedance spectroscopy (EIS) in 1.0 mM ferrocene monocarboxylic acid (FcCO₂H). Equivalent circuit modeling showed an approximate three‐fold increase in solution resistance, R_sol, and an order of magnitude increase in charge transfer resistance, R_ct, resulting from a reduction in apparent diffusivity of FcCO₂H. Additionally, both resistive parameters decreased while the capacitance (Q) increased with decreasing microdisk diameter; consistent with an increase in effective electroactive area. The hydrogel layer did not compromise enhanced mass transport achieved by the MDEA and thus may be used to advantage in biosensors.     

Electrooxidation and Amperometric Detection of Ascorbic Acid at GC Electrode Modified by Electropolymerization of N,N‐Dimethylaniline

The polymer film of N,N‐dimethylaniline (DMA) is deposited on the electrochemically pretreated glassy carbon (GC) electrode by continuous electrooxidation of the monomer. This poly N,N‐dimethylaniline (PDMA) film‐coated electrode can be used as an amperometric sensor of ascorbic acid (AA). The polymer film (thickness (?): 0.3±0.02 μm) having positive charge in its backbone attracts the anionic species AA. Thus, the anodic peak potential (350 mV vs. Ag|AgCl|NaCl_(sat)) for the oxidation of AA at the bare electrode is largely shifted to the negative value (150 mV) at this electrode. The PDMA film‐coated electrode is stable in acidic, alkaline and neutral media and can sense AA at different pH's. The diffusion coefficients of AA in solution (D) and in film (D_s) were estimated by rotating disk electrode voltammetry: D=(5.5±0.1)×10^?6 cm² s^?1 and D_s=(6.3±0.2)×10^?8, (6.0±0.2)×10^?8 and (4.7±0.2)×10^?8 cm² s^?1 for 0.5, 1.5 and 3.0 mM AA, respectively. A permeability of AA through the PDMA film was found to decrease with increasing the concentration of AA in the solution. In the chronoamperometry, the current response for the oxidation of AA at different times elapsed after potential‐step application is linearly increased with the increase in AA concentration in a wide range of its concentration from 25 μM to 1.65 mM. In the hydrodynamic amperometry, a successive addition of 10 μM AA caused the successive increase in current response with equal amplitude and the sensitivity was calculated as 0.178 μA cm^?2 μM^?1. So, the fouling of the electrode surface caused by the oxidized product of AA is markedly eliminated at this PDMA film‐coated electrode. A flow injection analysis based on the present electrode was performed to estimate the concentration of vitamin C in fruit juice.     

Nanostructured Cobalt(II) Tetracarboxyphthalocyanine Complex Supported Within the MWCNT Frameworks: Electron Transport and Charge Storage Capabilities

The electrochemical redox properties of a surface‐confined thin solid film of nanostructured cobalt(II) tetracarboxyphthalocyanine integrated with multiwalled carbon nanotube (nanoCoTCPc/MWCNT) have been investigated. This novel nanoCoTCPc/MWCNT material was characterized using SEM, TEM, zeta analysis and electrochemical methods. The nanoCoTCPc/MWCNT nanohybrid material exhibited an extra‐ordinarily high conductivity (15 mS cm^?1), which is more than an order of magnitude greater than that of the MWCNT‐SO₃H (527 µS cm^?1) and three orders of a magnitude greater than the nanoCoTCPc (4.33 µS cm^?1). The heterogeneous electron transfer rate constant decreases as follows: nanoCoTCPc/MWCNT (k_app≈19.73×10^?3 cm s^?1)>MWCNT‐SO₃H (k_app≈11.63×10^?3 cm s^?1)>nanoCoTCPc (k_app≈1.09×10^?3 cm s^?1). The energy‐storage capability was typical of pseudocapacitive behaviour; at a current density of 10 µA cm^?2, the pseudocapacitance decreases as nanoCoTCPc/MWCNT (3.71×10^?4 F cm^?2)>nanoCoTCPc (2.57×10^?4 F cm^?2)>MWCNT‐SO₃H (2.28×10^?4 F cm^?2). The new nanoCoTCPc/MWCNT nanohybrid material promises to serve as a potential material for the fabrication of thin film electrocatalysts or energy‐storage devices.     

Electrochemical Oxidation of Methionine Mediated by a Fullerene‐C60 Modified Gold Electrode

The usefulness of a C₆₀‐fullerene modified gold (Au) electrode in mediating the oxidation of methionine in the presence of potassium ions electrolyte has been demonstrated. During cyclic voltammetry, an oxidation peak of methionine appearing at +1.0 V vs. Ag/AgCl was observed. The oxidation current of methionine is enhanced by about 2 times using a C₆₀ modified gold electrode. The current enhancement is significantly dependent on pH, temperature and C₆₀ dosage. Calibration plot reveals linearity of up to 0.1 mM with a current sensitivity of close to 50 mA L mol^?1 and detection limit of 8.2×10^?6 M. The variation of scan rate study shows that the system undergoes diffusion‐controlled process. Diffusion coefficient and rate constant of methionine were determined using hydrodynamic method (rotating disk electrode) with values of 1.11×10^?5 cm² s^?1 and 0.0026 cm s^?1 respectively for unmodified electrode while the values of diffusion coefficient and rate constant of methionine using C₆₀ modified Au electrode are 5.7×10^?6 cm² s^?1 and 0.0021 cm s^?1 respectively.     

Application of a 1‐benzyl‐4‐ferrocenyl‐1H‐[1,2,3]‐triazole/carbon nanotube modified glassy carbon electrode for voltammetric determination of hydrazine in water samples

The electrochemical behaviour of hydrazine at a 1‐benzyl‐4‐ferrocenyl‐1H‐[1,2,3]‐triazole‐triazole/carbon nanotube modified glassy carbon electrode has been studied. The modified electrode shows an excellent electrocatalytic activity for the oxidation of hydrazine and accelerates electron transfer rate. The electrocatalytic current increases linearly with hydrazine concentration in the range 0.5–700.0 μm and the detection limit for hydrazine was 33.0 ± 2.0 nm . The diffusion coefficient (D = 2.5 ± 0.1 × 10^?5 cm² s^?1) and kinetic parameters such as the electron transfer coefficient, (α = 0.52) and the heterogeneous rate constant (k′ = 5.5 ± 0.1 × 10^?3 cm s^?1) for hydrazine were determined using electrochemical approaches. Finally, the method was employed for the determination of hydrazine in water samples. Copyright © 2013 John Wiley & Sons, Ltd.     

Detection of Dexamethasone Sodium Phosphate in Blood Plasma: Application of Hematite in Electrochemical Sensors

We studied sensor application of a graphene oxide and hematite (α‐Fe₂O₃/GO) composite electrode well‐characterized by the SEM and XRD. Through differential pulse voltammetry (DPV), oxidation of dexamethasone sodium phosphate (DSP) was studied at the surface of a glassy carbon electrode (GCE) modified with graphene oxide nanosheets (GO) and the α‐Fe₂O₃/GO composite. The values of the transfer coefficient (α) and the diffusion coefficient (D) of DSP were 0.5961 and 4.71×10^?5 cm² s^?1 respectively. In the linear range of 0.1–50 μM, the detection limit (DL) was 0.076 μM. In the second step, a GCE was modified with α‐Fe₂O₃/GO composite and the DSP measurement step was repeated to analyzed and compare the effects of hematite nanoparticles present on graphene oxide surfaces. According to the results, α and D were 0.52 and 2.406×10^?4 cm² s^?1 respectively and the DL was 0.046 μM in the linear range of 0.1–10.0 μM. The sensor is simple, inexpensive and uses blood serum.     

Sensitive amperometric pyridoxine sensor based on self‐assembled Prussian blue nanoparticle‐modified poly(o‐phenylenediamine)/glassy carbon electrode

Prussian blue nanoparticles (PBNPs) were prepared by a self‐assembly process on a glassy carbon electrode (GCE) modified with poly(o‐phenylenediamine) (PoPD) film. The stepwise fabrication process of PBNP‐modified PoPD/GCE was characterized using scanning electron microscopy and electrochemical impedance spectroscopy. The prepared PBNPs showed an average size of 70 nm and a homogeneous distribution on the surface of the modified electrode. The PBNPs/PoPD/GCE showed electrocatalytic activity towards the oxidation of pyridoxine (PN) and was used as an amperometric sensor. The modified electrode exhibited a linear response for PN oxidation over the concentration range 3–38.5 μM with a detection limit of ca 6.10 × 10^?7 M (S/N = 3) and sensitivity of 2.79936 × 10³ mA M^?1 cm^?2 using an amperometric method. The mechanism and kinetics of the catalytic oxidation reaction of PN were investigated using cyclic voltammetry and chronoamperometry. The values of α, k_cat and D were estimated as 0.36, 1.089 × 10² M^?1 s^?1 and 8.9 × 10^?5 cm² s^?1, respectively. This sensor also exhibited good anti‐interference and selectivity. Copyright © 2016 John Wiley & Sons, Ltd.     

Investigation into Charge Transport Dynamics of [Os(bpy)2(picolinate)]Cl Nafion Films

This work examines the charge transport properties of redox films of the immobilized enzyme mediator [Os(bpy)₂(picolinate)]Cl ([Os(bpy)₂Pic]⁺). Chronoamperometry was used to calculate D_CT values (typically of the order of 1.5×10^?8 cm² s^?1) and the effect of %loading of redox material was determined for three electrolytes over a range of concentrations. The data obtained implies that charge transfer within the film occurs via a redox site diffusion mechanism. The concentration of redox sites was determined using an approximate film thickness of 7 μm, as determined from profilometry studies. Experiments were also performed using immobilized carbon nanotubes within the redox film in order to examine the impact of the increased surface area and conductivity. The presence of the carbon nanotubes had the effect of doubling the surface coverage values and enhancing D_CT^1/2 C_M values from 1.9×10^?9 to 16.1×10^?9 mol cm^?1 s^?1.     

Electrocatalytic Oxidation of Sulfite on a Cobalt Pentacyanonitrosylferrate Film Modified Glassy Carbon Electrode

The electrocatalytic oxidation of sulfite has been studied on the cobalt pentacyanonitrosylferrate modified glassy carbon electrode (CoPCNF). The CoPCNF films on the glassy carbon electrodes show an excellent electrocatalytic activity toward the oxidation of sulfite in 0.5 M KNO₃. The kinetics of the catalytic reaction was investigated by using cyclic voltammetry, rotating disk electrode (RDE) voltammetry and chronoamperometry. The average value of the rate constant, K, for the catalytic reaction and the diffusion coefficient, D, were evaluated by different approaches for sulfite and found to be 2.9×10² M^?1s^?1 and 4.6×10^?6 cm²s^?1, respectively. At a fixed potential under hydrodynamic conditions (stirred solutions), the oxidation current is proportional to the sulfite concentration and the calibration plot was linear over the concentration range 5×10^?6–1×10^?4 M. The detection limit of the method is 3×10^?6 M., low enough for the trace sulfite determination.     

Ozone reduction at Nafion modified Au electrode and the measurement of ozone concentration in highly resistive solutions

The mass transport and charge transfer kinetics of ozone reduction at Nafion coated Au electrodes were studied in 0.5 mol/L H2SO4 and highly resistive solutions such as distilled water and tap water. The diffusion coefficient and partition coefficient of ozone in Nafion coating are 1.78×10-6 cm2·s-1 and 2.75 at 25℃ (based on dry state thickness), respectively. The heterogeneous rate constants and Tafel slopes for ozone reduction at bare Au are 4.1×10-6 cm·s-1, 1.0×10-6 cm·s-1 and 181 mV, 207 mV in 0.5 mol/L H2SO4 and distilled water respectively and the corresponding values for Nafion coated Au are 5.5×10-6 cm·s-1, 1.1×10-6 cm·s-1 and 182 mV, 168 mV respectively. The Au microelectrode with 3 μm Nafion coating shows good linearity over the range 0-10 mmol/L ozone in distilled water with sensitivity 61 μA·ppm-1 ·cm-2, detection limit 10 ppb and 95% response time below 5 s at 25℃. The temperature coefficient in range of 11-30℃ is 1.3%.     

Enhancing a Novel Robust Multicomposite Materials Platform for Glucose Biosensors

An effective, stable enzymatic glucose biosensor was fabricated on a glassy carbon electrode (GCE) surface using simple multicomposite materials (MCM): a solution of prepared poly(diallyldimethylammonium chloride)‐capped gold nanoparticles‐nickel ferrite particles‐carbon nanotubes‐chitosan (PDDA‐AuNPs‐NiFe₂O₄‐CNTs‐CHIT), electropolymerization of poly(o‐phenylenediamine) (PoPD) and immobilization of glucose oxidase (GOx). Biocompatibility and synergy of the MCM enhanced the immobilization and the reaction of GOx and as well as the electron transfer from an oxidation reaction of hydrogen peroxide in the system. The NiFe₂O₄ was synthesized by co‐precipitation and calcined at 700 °C. Characterization was carried out by field emission scanning electron microscopy (FE‐SEM), energy‐dispersive X‐ray spectroscopy (EDX), Fourier transform infrared spectroscopy (FTIR) and X‐ray diffraction (XRD) which presented both tetrahedral and octahedral metal stretching with a cubic NiFe₂O₄ crystal phase. The GOx/PoPD/MCM/GCE yielded a 0.77 s^?1 charge transfer rate constant (K_s), a 2.28×10^?6 cm² s^?1 diffusion coefficient value (D), a 0.21 mm² electroactive surface area (A_e) and a 1.93×10^?8 mol cm^?2 surface concentration ( ) as determined by cyclic voltammetry. The modified electrode showed a durable operation time (n=97, more than 50 % I), repeatability (%RSD=0.38, n=10), reproducibility (%RSD=1.60, n=10), high sensitivity (853.07 μA mM^?1 cm^?2), selectivity without effects of electroactive species (aspirin, uric acid, caffeine, cholesterol, ascorbic acid and dopamine) and two linear ranges from 0.5 to 10 μM (R²=0.998) and 10 to 15,000 μM (R²=0.991) with a low detection limit (0.35 μM, S/N=3). Its Michaelis‐Menten constant (K_m) was calculated as 93.51 μM with 46.30 μA maximum current (I_max). This proposed simple method was successfully applied for glucose determination in human blood samples.     

A laser flash photolysis/IR diode laser absorption study of the reaction of chlorine atoms with selected alkanes

A high‐resolution IR diode laser in conjunction with a Herriot multiple reflection flow‐cell has been used to directly determine the rate coefficients for simple alkanes with Cl atoms at room temperature (298 K). The following results were obtained: k(Cl + n‐butane) = (1.91 ± 0.10) × 10^?10 cm³ molecule^?1 s^?1, k(Cl + n‐pentane) = (2.46 ± 0.12) × 10^?10 cm³ molecule^?1 s^?1, k(Cl + iso‐pentane) = (1.94 ± 0.10) × 10^?10 cm³ molecule^?1 s^?1, k(Cl + neopentane) = (1.01 ± 0.05) × 10^?10 cm³ molecule^?1 s^?1, k(Cl + n‐hexane) = (3.44 ± 0.17) × 10^?10 cm³ molecule^?1 s^?1 where the error limits are ±1σ. These values have been used in conjunction with our own previous measurements on Cl + ethane and literature values on Cl + propane and Cl + iso‐butane to generate a structure activity relationship (SAR) for Cl atom abstraction reactions based on direct measurements. The resulting best fit parameters are k_p = (2.61 ± 0.12) × 10^?11 cm³ molecule^?1 s^?1, k_s = (8.40 ± 0.60) × 10^?11 cm³ molecule^?1 s^?1, k_t = (5.90 ± 0.30) × 10^?11 cm³ molecule^?1 s^?1, with f( ? CH₂^? ) = f (? CH₂^? ) = f (?C?) = f = 0.85 ± 0.06. Tests were carried out to investigate the potential interference from production of excited state HCl(v = 1) in the Cl + alkane reactions. There is some evidence for HCl(v = 1) production in the reaction of Cl with shape n‐hexane. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 34: 86–94, 2002     

Kinetics of hydroxyl radical reactions with formaldehyde and 1,3,5-trioxane between 290 and 600 K

Absolute rate constants are measured for the reactions: OH + CH₂O, over the temperature range 296–576 K and for OH + 1,3,5-trioxane over the range 292–597 K. The technique employed is laser photolysis of H₂O₂ or HNO₃ to produce OH, and laser-induced fluorescence to directly monitor the relative OH concentration. The results fit the following Arrhenius equations: k (CH₂O) = (1.66 ± 0.20) × 10^?11 exp[?(170 ± 80)/RT] cm³ s^?1 and k(1,3,5-trioxane) = (1.36 ± 0.20) × 10^?11 exp[?(460 ± 100)/RT] cm³ s^?1. The transition-state theory is employed to model the OH + CH₂O reaction and extrapolate into the combustion regime. The calculated result covering 300 to 2500 K can be represented by the equation: k(CH₂O) = 1.2 × 10^?18 T^2.46 exp(970/RT) cm³ s^?1. An estimate of 91 ± 2 kcal/mol is obtained for the first C? H bond in 1,3,5-trioxane by using a correlation of C? H bond strength with measured activation energies.     

Electrochemical Behaviors of Adenosine‐5′‐triphosphate on Molecular Wire Modified Carbon Paste Electrode and Its Sensitive Detection

A new electrochemical method was proposed for the determination of adenosine‐5′‐triphosphate (ATP) based on the electrooxidation at a molecular wire (MW) modified carbon paste electrode (CPE), which was fabricated with diphenylacetylene (DPA) as the binder. A single well‐defined irreversible oxidation peak of ATP appeared on MW‐CPE with adsorption‐controlled process and enhanced electrochemical response in a pH 3.0 Britton‐Robinson buffer solution, which was due to the presence of high conductive DPA in the electrode. The electrochemical parameters of ATP were calculated with the electron transfer coefficient (α) as 0.54, the electron transfer number (n) as 1.9, the apparent heterogeneous electron transfer rate constant (k_s) as 2.67 × 10^?5 s^?1 and the surface coverage (Γ_T) as 4.15 × 10^?10 mol cm^?2. Under the selected conditions the oxidation peak current was proportional to ATP concentration in the range from 1.0 × 10^?7 mol L^?1 to 2.0 × 10^?3 mol L^?1 with the detection limit as 1.28 × 10^?8 mol L^?1 (3σ) by sensitive differential pulse voltammetry. The proposed method showed good selectivity without the interferences of coexisting substances and was successful applied to the ATP injection samples detection.     

Direct Voltammetry of Copper,Zinc‐Superoxide Dismutase Immobilized onto Electrodeposited Nickel Oxide Nanoparticles: Fabrication of Amperometric Superoxide Biosensor

Direct electron transfer of immobilized copper, zinc‐superoxide dismutase (SOD) onto electrodeposited nickel‐oxide (NiOx) nanoparticle modified glassy carbon (GC) electrode displays a well defined redox process with formal potential of ?0.03 V in pH 7.4. Cyclic voltammetry was used for deposition of (NiOx) nanoparticles and immobilization of SOD onto GC electrode. The surface coverage (Γ) and heterogeneous electron transfer rate constant (k_s) of immobilized SOD are 1.75×10^?11 mol cm^?2 and 7.5±0.5 s^?1, respectively. The biosensor shows a fast amperometric response (3 s) toward superoxide at a wide concentration range from 10 µM to 0.25 mM with sensitivity of 13.40 nA µM^?1 cm^?2 and 12.40 nA µM^?1 cm^?2, detection limit of 2.66 and 3.1 µM based on anodically and cathodically detection. This biosensor exhibits excellent stability, reproducibility and long life time.     

Electroless Deposition of Thionin onto Glassy Carbon Electrode Modified with Single Wall and Multiwall Carbon Nanotubes: Improvement of the Electrochemical Reversibility and Stability

A simple procedure was developed to prepare a glassy carbon electrode modified with carbon nanotubes (CNTs) and thionin. Abrasive immobilization of CNTs on a GC electrode was achieved by gently rubbing the electrode surface on a filter paper supporting carbon nanotubes, then immersing the GC/CNTs‐modified electrode into a thionin solution (electroless deposition) for a short period of time (5–50 s for MWCNTs and 5–120 s for SWCNTs ). Cyclic voltammograms of the resulting modified electrode show stable and a well defined redox couple with surface confined characteristic at wide pH range 2–12. The electrochemical reversibility and stability of modified electrode prepared with incorporation of thionin into CNTs film was compared with usual methods for attachment of thionin to electrode surfaces such as electropolymerization and adsorption on the surface of preanodized electrodes. The formal potential of redox couple (E°′) shifts linearly toward the negative direction with increasing solution pH. The surface coverage of thionin immobilized on CNTs glassy carbon electrode was approximately 1.95×10^?10 mol cm^?2 and 3.2×10^?10 mol cm^?2 for MWCNTs and SWCNTs, respectively. The transfer coefficient (α) was calculated to be 0.3 and 0.35 and heterogeneous electron transfer rate constants (K_s) were 65 s^?1 and 55 s^?1 for MWCNTs/thionin and SWCNTs/thionin‐modified GC electrodes, respectively. The results clearly show a great facilitation of the electron transfer between thionin and CNTs adsorbed on the electrode surface. Excellent electrochemical reversibility of redox couple, high stability, technically simple and possibility of preparation at short period of time are of great advantages of this procedure for modification of electrodes.     

A Three‐Photon Active Organic Fluorophore for Deep Tissue Ratiometric Imaging of Intracellular Divalent Zinc

Deep tissue bioimaging with three‐photon (3P) excitation using near‐infrared (NIR) light in the second IR window (1.0–1.4 μm) could provide high resolution images with an improved signal‐to‐noise ratio. Herein, we report a photostable and nontoxic 3P excitable donor‐π‐acceptor system (GMP) having 3P cross‐section (σ₃) of 1.78×10^?80 cm⁶ s² photon^?2 and action cross‐section (σ₃η₃) of 2.31×10^?81 cm⁶ s² photon^?2, which provides ratiometric fluorescence response with divalent zinc ions in aqueous conditions. The probe signals the Zn²⁺ binding at 530 and 600 nm, respectively, upon 1150 nm excitation with enhanced σ₃ of 1.85×10^?80 cm⁶ s² photon^?2 and σ₃η₃ of 3.33×10^?81 cm⁶ s² photon^?2. The application of this probe is demonstrated for ratiometric 3P imaging of Zn²⁺ in vitro using HuH‐7 cell lines. Furthermore, the Zn²⁺ concentration in rat hippocampal slices was imaged at 1150 nm excitation after incubation with GMP, illustrating its potential as a 3P ratiometric probe for deep tissue Zn²⁺ ion imaging.     

Rate coefficients for the reactions of OH with n‐propanol and iso‐propanol between 237 and 376 K

The rate coefficients for the reaction OH + CH₃CH₂CH₂OH → products (k₁) and OH + CH₃CH(OH)CH₃ → products (k₂) were measured by the pulsed‐laser photolysis–laser‐induced fluorescence technique between 237 and 376 K. Arrhenius expressions for k₁ and k₂ are as follows: k₁ = (6.2 ± 0.8) × 10^?12 exp[?(10 ± 30)/T] cm³ molecule^?1 s^?1, with k₁(298 K) = (5.90 ± 0.56) × 10^?12 cm³ molecule^?1 s^?1, and k₂ = (3.2 ± 0.3) × 10^?12 exp[(150 ± 20)/T] cm³ molecule^?1 s^?1, with k₂(298) = (5.22 ± 0.46) × 10^?12 cm³ molecule^?1 s^?1. The quoted uncertainties are at the 95% confidence level and include estimated systematic errors. The results are compared with those from previous measurements and rate coefficient expressions for atmospheric modeling are recommended. The absorption cross sections for n‐propanol and iso‐propanol at 184.9 nm were measured to be (8.89 ± 0.44) × 10^?19 and (1.90 ± 0.10) × 10^?18 cm² molecule^?1, respectively. The atmospheric implications of the degradation of n‐propanol and iso‐propanol are discussed. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 42: 10–24, 2010     

Electrochemical Oxidative Detection of Guanosine‐5′‐triphosphate Based on a New Ionic Liquid Modified Carbon Paste Electrode

An ionic liquid (IL) 1‐(3‐chloro‐2‐hydroxy‐propyl)‐3‐methylimidazolium trifluoroacetate was used as the modifier for the preparation of the modified carbon paste electrode (CPE). The IL‐CPE showed excellent electrocatalytic activity towards the oxidation of guanosine‐5′‐triphosphate (5′‐GTP) in a pH 5.0 Britton‐Robinson buffer solution. Due to the presence of high conductive IL on the electrode surface, the electrooxidation of 5′‐GTP was greatly promoted with a single well‐defined irreversible oxidation peak appeared. The electrode reaction was an adsorption‐controlled process and the electrochemical parameters of 5′‐GTP on IL‐CPE were calculated with the electron transfer coefficient (α) as 0.44, the electron transfer number (n) as 1.99, the apparent heterogeneous electron transfer rate constant (k_s) as 2.21 × 10^?9 s^?1 and the surface coverage (Γ_T) as 1.53 × 10^?10 mol cm^?2. Under the selected conditions a linear calibration curve between the oxidation peak currents and 5′‐GTP concentration was obtained in the range from 2.0 to 1000.0 μmol L^?1 with the detection limit as 0.049 μmol L^?1 (3σ) by differential pulse voltammetry. The proposed method showed good selectivity to the 5‘‐GTP detection without the interferences of coexisting substances and the practical application was checked by measurements of the artificial samples.     

Photocurrent kinetics during electron emission from metal into electrolyte solution: Part III. H3O+ solutions

The photocurrent kinetics in acid solutions have been investigated. The diffusion coefficients of atoms H?((7±2)×10^?5cm²s^?1) and D?((4±1)×10^?5cm²s^?1) and OH^? and OD^? radicals ((1±0.3)×10^?5cm²s^?1) are found. The rate constants of capture of solvated electrons by H₃O⁺ and D₃O⁺ ions are identical and equal to (8±1)×10⁹M^?1s^?1. From the shape of the kinetic curves it follows that electrochemical desorption of atomic hydrogen occurs from the adsorbed state. The rate constant of this process has been measured. It is shown that the rate constant of electrochemical desorption depends only slightly on the potential.