共查询到20条相似文献,搜索用时 31 毫秒
1.
D. A. B. Young 《Colloid and polymer science》2000,278(5):464-468
The persuasive evidence for the role of colloid in the formation of Liesegang rings is nullified by the low diffusion constants
(less than 2 × 10−11 m2 s−1) of sol particles; however, those values were obtained for sols suspended in otherwise homogeneous solutions. The essential
randomness of Brownian motion in such situations is absent in Liesegang experiments, where the large excess of outer electrolyte
diffusing into the gel creates a bias in molecular bombardment resulting in sol particles moving a given distance in fewer
steps, hence in a shorter time. From Einstein's equation (D=x
2/2t) values for D of 2–4 × 10−10 m2 s−1 have been calculated for Liesegang experiments in the literature. It is suggested that such values could well pertain to
sol particles diffusing in the heterogeneous conditions existing in those experiments.
Received: 13 April 1999 Accepted: 16 November 1999 相似文献
2.
Jun Yue Bai Liang Wang Hong Jing Wang Peng Fei Huang Yu Qing Zhao Sheng Di Fan 《Mikrochimica acta》2006,156(3-4):321-326
The electrochemical behavior of epinephrine (EP) at a mercaptoacetic acid (MAA) self-assembled monolayer modified gold electrode
was studied. The MAA/Au electrode is demonstrated to promote the electrochemical response of epinephrine by cyclic voltammetry.
The possible reaction mechanism is also discussed. The diffusion coefficient D of EP is 6.85 × 10−6 cm2 s−1. In 0.1 mol L−1 phosphate buffer (pH 7.20), a sensitive oxidation peak was observed at 0.177 V, and the peak current is proportional to the
concentration of EP in the range of 1.0 × 10−5–2.0 × 10−4 mol L−1 and 1.0 × 10−7–1.0 × 10−6 mol L−1. The detection limit is 5 × 10−8 mol L−1. The modified electrode is highly stable and can be applied to the determination of EP in practical injection samples. The
method is simple, quick, sensitive and accurate. 相似文献
3.
The electrochemical behaviors of metol on an ionic liquid N-butylpyridinium hexafluorophosphate modified carbon paste electrode (IL-CPE) were studied in this paper. The results indicated
that a pair of well-defined quasi-reversible redox peaks of metol appeared with the decrease of overpotential and the increase
of redox peak current, which was the characteristics of electrocatalytic oxidation. The electrocatalytic mechanism was discussed
and the electrochemical parameters were calculated with results of the charge-transfer coefficient (α) as 0.45, the electrode reaction rate constant (k
s) as 4.02 × 10−3 s−1, and the diffusion coefficient (D) as 6.35 × 10−5 cm2/s. Under the optimal conditions, the anodic peak current was linear with the metol concentration in the range of 5.0 × 10−6 ∼ 1.0 × 10−3 mol/L (n = 11, γ = 0.994) and the detection limit was estimated as 2.33 × 10−6 mol/L (3σ). The proposed method was successfully applied to determination of metol content in synthetic samples and photographic solutions. 相似文献
4.
Krzysztof Miecznikowski James A. Cox Adam Lewera Pawel J. Kulesza 《Journal of Solid State Electrochemistry》2000,4(4):199-204
We describe a sol-gel approach by which iron hexacyanoferrate is immobilized in silica in a manner suited to investigation
by electrochemistry in the absence of a contacting liquid phase. Such physicochemical parameters as concentration of redox
sites (C
o) and apparent (effective) diffusion coefficient (D
app) are estimated by performing cyclic voltammetric and potential step experiments in two time regimes, which are characterized
by linear and spherical diffusional patterns, respectively. Values of D
app and C
o thereby obtained are 2.0 × 10−6 cm2 s−1 and 1.4 × 10−2 mol dm−3. The D
app value is larger than expected for a typical solid redox-conducting material. Analogous measurements done in iron(III) hexacyanoferrate(III)
solutions of comparable concentrations, 1.0 × 10−2 and 5.0 × 10−3 mol dm−3, yield D
app on the level of 5–6 × 10−6 cm2 s−1. Thus, the dynamics of charge propagation in this sol-gel material is almost as high as in the liquid phase. The residual
water in the silica, along with the pore structure, are important to the overall mechanism of charge transport, which apparently
is limited by physical diffusion rather than electron self-exchange. Under conditions of a solid state voltammetric experiment
which utilizes an ultramicroelectrode, encapsulated iron hexacyanoferrate redox centers seem to be in the dispersed colloidal
state rather than in a form of the rigid polymeric film.
Received: 8 April 1999 / Accepted: 13 August 1999 相似文献
5.
Liang Wang Jun Yue Bai Peng Fei Huang Hong Jing Wang Xiao Wei Wu Yu Qing Zhao 《Mikrochimica acta》2007,158(1-2):73-78
The electrochemical behaviors of uric acid (UA) at the penicillamine (Pen) self-assembled monolayers modified gold electrode
(Pen/Au) have been studied. The Pen/Au electrode is demonstrated to promote the electrochemical response of UA by cyclic voltammetry
(CV). The diffusion coefficient D of UA is 6.97 × 10−6 cm2 s−1. In differential pulse voltammetric (DPV) measurements, the Pen/Au electrode can separate the UA and ascorbic acid (AA) oxidation
potentials by about 120 mV and can be used for the selective determination of UA in the presence of AA. The detection limit
was 1 × 10−6 mol L−1. The modified electrode shows excellent sensitivity, good selectivity and antifouling properties. 相似文献
6.
A new modified electrode was prepared by electrodeposition of caffeic acid (CFA) at the surface of an activated glassy carbon
electrode. Cyclic voltammetry was used to investigate the redox properties of this electrode at various solution pH values
and at various scan rates. The pH dependence of the electrode response was found to be 58.5 mV/pH, which is very close to
the expected Nernstian value. The electrode was also employed to study electrocatalytic oxidation of reduced nicotinamide
adenine dinucleotide (NADH), using cyclic voltammetry, chronoamperometry and rotating disk voltammetry as diagnostic techniques.
It was found that the modified electrode exhibits potent and persistent electrocatalytic properties toward NADH oxidation
in phosphate buffer solution (pH 7.0) with a diminution of the overpotential of about 450 mV compared to the process at an
unmodified electrode. The electrocatalytic current increases linearly with NADH concentration in the range tested from 0.05
to 1.0 mM. The apparent charge transfer rate constant and transfer coefficient for electron transfer between the electrode
surface and immobilized CFA were calculated as 11.2 s−1 and 0.43, respectively. The heterogeneous rate constant for oxidation of NADH at the CFA-modified electrode surface was also
determined and found to be about 3 × 103 M−1 s−1. Finally, the diffusion coefficient of NADH was calculated as 3.24 × 10−6 cm2 s−1 for the experimental conditions, using chronoamperometric results.
Received: 6 January 1999 / Accepted: 11 May 1999 相似文献
7.
The electrocatalytic oxidation of quinine sulfate (QS) was investigated at a glassy carbon electrode, modified by a gel containing
multiwall carbon nanotubes (MWCNTs) and room-temperature ionic liquid of 1-Butyl-3-methylimidazolium hexafluorophate (BMIMPF6) in 0.10 M of phosphate buffer solution (PBS, pH 6.8). It was found that an irreversible anodic oxidation peak of QS with
E
pa as 0.99 V appeared at MWCNTs-RTIL/glassy carbon electrode (GCE). The electrode reaction process was a diffusion-controlled
one and the electrochemical oxidation involved two electrons transferring and two protons participation. Furthermore, the
charge-transfer coefficient (α), diffusion coefficient (D), and electrode reaction rate constant (k
f) of QS were found to be 0.87, 7.89 × 10−3 cm2⋅s−1 and 3.43 × 10−2 s−1, respectively. Under optimized conditions, linear calibration curves were obtained over the QS concentration range 3.0 × 10−6 to 1.0 × 10−4 M by square wave voltammetry, and the detection limit was found to be 0.44 μM based on the signal-to-noise ratio of 3. In
addition, the novel MWCNTs-RTIL/GCE was characterized by the electrochemical impedance spectroscopy and the proposed method
has been successfully applied in the electrochemical quantitative determination of quinine content in commercial injection
samples and the determination results could meet the requirement. 相似文献
8.
Sayed Medhi Ghoreishi Mohsen Behpour Mohammad Hassan Motaghedi Fard 《Journal of Solid State Electrochemistry》2012,16(1):179-189
In this work, we investigate the electrochemical activity of dopamine (DA) and uric acid (UA) using both a bare and a modified
carbon paste electrode as the working electrode, with a platinum wire as the counter electrode and a silver/silver chloride
(Ag/AgCl) as the reference electrode. The modified carbon paste electrode consists of multi-walled carbon nanotubes (>95%)
treated with α-cyclodextrine, resulting in an electrode that exhibits a significant catalytic effect toward the electro-chemical
oxidation of DA in a 0.2-M Britton–Robinson buffer solution (pH 5.0). The peak current increases linearly with the DA concentration
within the molar concentration ranges of 2.0 × 10−6 to 5.0 × 10−5 M and 5.0 × 10−5 to 1.9 × 10−4 M. The detection limit (signal to noise >3) for DA was found to be 1.34 × 10−7 M, respectively. In this work, voltammetric methods such as cyclic voltammetry, chronoamperometry, chronocuolometry, differential
pulse and square wave voltammetry, and linear sweep and hydrodynamic voltammetry were used. Cyclic voltammetry was used to
investigate the redox properties of the modified electrode at various scan rates. The diffusion coefficient (D, cm2 s−1 = 3.05 × 10−5) and the kinetic parameters such as the electron transfer coefficient (α = 0.51) and the rate constant (k, cm3 mol−1 s−1 = 1.8 × 103) for DA were determined using electrochemical approaches. By using differential pulse voltammetry for simultaneous measurements,
we obtained two peaks for DA and UA in the same solution, with the peak separation approximately 136 mV. The average recovery
was measured at 102.45% for DA injection. 相似文献
9.
Functionalized polypyrrole films were prepared by incorporation of Fe(CN)6
3− as doping anion during the electropolymerization of pyrrole at a glassy carbon electrode from aqueous solution. The electrochemical
behavior of the Fe(CN)6
3−/Fe(CN)6
4− redox couple in polypyrrole was studied by cyclic voltammetry. An obvious surface redox reaction was observed and dependence
of this reaction on the solution pH was illustrated. The electrocatalytic ability of polypyrrole film with ferrocyanide incorporated
was demonstrated by oxidation of ascorbic acid at the optimized pH of 4 in a glycine buffer. The catalytic effect for mediated
oxidation of ascorbic acid was 300 mV and the bimolecular rate constant determined for surface coverage of 4.5 × 10−8 M cm−2 using rotating disk electrode voltammetry was 86 M−1 s−1. Furthermore, the catalytic oxidation current was linearly dependent on ascorbic acid concentration in the range 5 × 10−4–1.6 × 10−2 M with a correlation coefficient of 0.996. The plot of i
p versus v
1/2 confirms the diffusion nature of the peak current i
p.
Received: 12 April 1999 / Accepted: 25 May 1999 相似文献
10.
Sodium (3-dodecanoyloxy-2-hydroxy-propyl) succinate (SLGMS) is a conjugated anionic surfactant in which a glycerol residue
connects with a hydrophilic sodium succinate and dodecanoate. Aqueous micellar phase (Wm), hexagonal (H1), bicontinuous cubic (V1), and lamellar (Lα) phases are successively formed with increasing the surfactant concentration in a binary SLGMS-water system. The Krafft point
is below 0 °C. The effective cross sectional area per surfactant molecule, a
s, in the H1 phase is almost constant, 0.5 nm2, and the shape of cylindrical micelle is almost unchanged with surfactant concentration. The cmc value of SLGMS measured
by means of surface tension, electrical conductivity, and fluorescence probe methods is in the range of 4∼9 × 10−5 mol/l that is much lower than that of sodium dodecanoate, 2 × 10−2 mol/l, or SDS, 8 × 10−3 mol/l. Hence, it is considered that the polar glycerol part in the SLGMS acts as a hydrophobic part. The solubilization of
oil in the SLGMS solution is much higher than that in the SDS solution and this also suggests that the glycerol and succinic
units act as lipophilic moieties.
Received: 15 June 2000/Accepted: 27 July 2000 相似文献
11.
Heli Hossein Faramarzi F. Sattarahmady N. 《Journal of Solid State Electrochemistry》2010,14(12):2275-2283
The electrochemical behavior of sodium alendronate on copper microparticle- and copper nanoparticle-modified carbon paste
electrodes was investigated. In the voltammograms recorded using microparticles, a single anodic oxidation peak appeared,
while using nanoparticles, two anodic peaks appeared. The anodic currents were related to the electrocatalytic oxidation of
alendronate via the active species of Cu(III). The catalytic rate constant for the electrocatalytic oxidation process and
the diffusion coefficient of alendronate were obtained to be 1.57 × 103 cm3 mol−1 s−1 and 2.44 × 10−6 cm2 s−1, respectively. A sensitive and time-saving detection procedure was developed for the analysis of alendronate, and the corresponding
analytical parameters were reported. Alendronate was determined with a limit of detection of 11.26 μmol L−1 with a linear range of 50–6,330 μmol L−1. The proposed amperometric method was applied to the analysis of commercial pharmaceutical tablets, and the results were
in good agreement with the declared values. 相似文献
12.
Juliana Canto Duarte Rita de Cássia Silva Luz Flavio Santos Damos Adriano Bof de Oliveira Lauro Tatsuo Kubota 《Journal of Solid State Electrochemistry》2007,11(5):631-638
The electrocatalytical oxidation of hydrazine at low potential using tetracyanoquinodimethanide adsorbed on silica modified
with titanium oxide was investigated by cyclic voltammetry and amperometry. The modified electrode was prepared modifying
a carbon paste electrode employing lithium tetracyanoquinodimethanide adsorbed onto silica gel modified with titanium oxide.
This electrode showed an excellent catalytic activity and stability for hydrazine oxidation. With this modified electrode,
the oxidation potential of hydrazine was shifted toward less positive value, presenting a peak current much higher than those
observed on a bare GC electrode. The linear response range, sensitivity and detection limit were, respectively, 2 up to 100 μmol
l−1, 0.36 μA l μmol−1, and 0.60 μmol l−1. The repeatability of the modified electrode evaluated in term of relative standard deviation was 4.2% for 10 measurements
of 100 μmol l−1 hydrazine solution. The number of electrons involved in hydrazine oxidation (4), the heterogenous electron transfer rate
constant (1.08 × 103 mol−1 l s−1), and diffusion coefficient (5.9 × 10−6 cm2 s−1) were evaluated with a rotating disk electrode. 相似文献
13.
J. Aupiais 《Journal of solution chemistry》2011,40(9):1629-1644
The electrophoretic mobilities of a few halide isotopes in aqueous solution have been evaluated at 25 °C and infinite dilution
by analyzing a combination of data obtained by capillary electrophoresis (CE) and conductance data extracted from the literature.
The effect of the temperature on the electrophoretic mobility has been thoroughly re-investigated to give the following temperature
dependence for the chloride ion at 25 °C: 1.565%/ °C in 5×10−3 mol⋅L−1 sodium chromate + 3×10−3 mol⋅L−1 sodium borate buffer. The precise determination of the electrophoretic mobility of chloride and bromide ions, including the
evaluation of their associated uncertainties, has been performed from conductance data spanning over 75 years. The electrophoretic
mobilities are found to be −(79.124±0.020)×10−9 m2⋅V−1⋅s−1 for Cl− and −(80.99±0.04)×10−9 m2⋅V−1⋅s−1 for Br−. Thanks to the precise determination of the temperature contribution and the re-evaluation of conductance data, the following
values have been found for 35Cl−, 37Cl−, 79Br−, and 81Br− (in 10−9 m2⋅V−1⋅s−1): −(79.18±0.02), −(78.95±0.06), −(81.04±0.04), and −(80.94±0.04). 相似文献
14.
The fabrication and electrochemical characteristics of a penicillamine (PCA) self-assembled monolayer modified gold electrode
were investigated. The electrode can enhance the electrochemical response of uric acid (UA), and the electrochemical reaction
of UA on the PCA electrode has been studied by cyclic voltammetry and differential pulse voltammetry. Some electrochemical
parameters, such as diffusion coefficient, standard rate constant, electron transfer coefficient and proton transfer number
have been determined for the electrochemical behavior on the PCA self-assembled monolayer electrode. The electrode reaction
of UA is an irreversible process, which is controlled by the diffusion of UA with two electrons and two protons transfer at
the PCA/Au electrode. In phosphate buffer (pH 5.0), the peak current is proportional to the concentration of UA in the range
of 6.0 × 10−5–7.0 × 10−4 mol L−1 and 2.0 × 10−5–7.0 × 10−4 mol L−1 for the cyclic voltammetry and differential pulse voltammetry methods with the detection limits of 5.0 × 10−6 and 3.0 × 10−6 mol L−1, respectively. The method can be applied to determine UA concentration in real samples. 相似文献
15.
Mohammad Ali Kamyabi Z. Asgari H. Hosseini Monfared 《Journal of Solid State Electrochemistry》2010,14(9):1547-1553
A carbon past electrode modified with [Mn(H2O)(N3)(NO3)(pyterpy)],
( \textpyterpy = 4¢- ( 4 - \textpyridyl ) - 2,2¢:\text6¢,\text2¢¢- \textterpyridine ) \left( {{\text{pyterpy}} = 4\prime - \left( {4 - {\text{pyridyl}}} \right) - 2,2\prime:{\text{6}}\prime,{\text{2}}\prime\prime - {\text{terpyridine}}} \right) complex have been applied to the electrocatalytic oxidation of nitrite which reduced the overpotential by about 120 mV with
obviously increasing the current response. Relative standard deviations for nitrite determination was less than 2.0%, and
nitrite can be determined in the ranges of 5.00 × 10−6 to 1.55 × 10−2 mol L−1, with a detection limit of 8 × 10−7 mol L−1. The treatment of the voltammetric data showed that it is a pure diffusion-controlled reaction, which involves one electron
in the rate-determining step. The rate constant k′, transfer coefficient α for the catalytic reaction, and diffusion coefficient of nitrite in the solution, D, were found to be 1.4 × 10−2, 0.56× 10−6, and 7.99 × 10−6 cm2 s−1, respectively. The mechanism for the interaction of nitrite with the Mn(II) complex modified carbon past electrode is proposed.
This work provides a simple and easy approach to detection of nitrite ion. The modified electrode indicated reproducible behavior,
anti-fouling properties, and stability during electrochemical experiments, making it particularly suitable for the analytical
purposes. 相似文献
16.
Wolfgang Preis Michael Holzinger Werner Sitte 《Monatshefte für Chemie / Chemical Monthly》2001,132(4):499-508
Summary. The van der Pauw method has been applied to conductivity relaxation experiments on YBa2Cu3O6+δ at 600°C in order to determine the chemical diffusion coefficient as a function of the oxygen partial pressure in the surrounding
atmosphere (100 > p
O
2/bar > 10−3). It is shown that the van der Pauw technique is suitable for monitoring the conductivity relaxation when the oxygen diffusion is perpendicular to the direct
current flowing through the sample in accordance with the van der Pauw geometry using thin tablets as samples. The oxygen partial pressure is changed stepwise (generally Δlogp
O
2 ≤ 0.5) by employing appropriate gas mixtures as well as an electrochemical oxygen pump device. An evaluation formula is given
for the determination of the chemical diffusion coefficient neglecting slow surface processes. In addition, the electronic
conductivity of YBa2Cu3O6+δ has been measured at 600°C as a function of oxygen partial pressure of the ambient atmosphere (100 > p
O
2/bar > 10−5) by means of the van der Pauw method applying the same experimental set-up. Typical values of the chemical diffusion coefficient are in the range of 10−6 cm2·s−1; the results of the conductivity measurements are interpreted in terms of an appropriate defect model.
Received May 30, 2000. Accepted June 8, 2000 相似文献
17.
A. Tsuchida K. Taguchi E. Takyo H. Yoshimi S. Kiriyama T. Okubo M. Ishikawa 《Colloid and polymer science》2000,278(9):872-877
Rate coefficients (k) in the colloidal crystallization of monodispersed silica spheres in the presence of sodium chloride are studied in microgravity
achieved by parabolic flights of an aircraft. Time-resolved reflection spectroscopy is made with a continuous circulating-type
stopped-flow cell system. The k values decrease as the salt concentration increases both at 0 and 1 G and those in microgravity are smaller than those in
normal gravity by 16% (maximum), especially in water and in the presence of a small amount of the salt lower than 2 × 10−6 mol/l. The rates in flight at 1 G are larger by 15% (maximum) compared with those at 1 G on the ground. The k values obtained at 0 G, 1 G in flight and 1 G on the ground agree excellently with each other for the suspensions with 3 × 10−6 and 4 × 10−6 mol/l sodium chloride. Disappearance of the downward diffusion of spheres and no convection of the suspensions are important
for retardation in microgravity.
Received: 20 January 2000 Accepted: 9 March 2000 相似文献
18.
Y. Hatano R. Hitaka M. Sugisaki M. Hayashi 《Journal of Radioanalytical and Nuclear Chemistry》1999,239(3):445-448
The diffusion behavior of hydrogen in the oxide films of zircaloy-4 specimens containing different size of Zr(Fe,Cr)2 precipitates was examined. In the case of the specimen containing fine precipitates, hydrogen diffused uniformly through
the zirconium oxide phase. The diffusion coefficient was 2·10−21 m2·s−1 at room temperature and 6·10−19 m2·s−1 at 673 K. The transport rate of hydrogen in the oxide film of the specimen containing coarse precipitates was significantly
higher than that of the specimen containing fine ones at both room temperature and 673 K. 相似文献
19.
Razika Brahimi Mohamed Trari Aïssa Bouguelia Yassine Bessekhouad 《Journal of Solid State Electrochemistry》2010,14(7):1333-1338
The delafossite CuAlO2 single crystal, prepared by the flux method, is a low mobility p-type semiconductor with a hole mobility of 1.2 × 10−5 cm−2 V−1 s−1. The chronoamperometry showed an electrochemical O2− insertion with a diffusion coefficient D
303K of 3.3 × 10−18 cm2 s−1. The thermal variation of D in the range 293–353 K gave an enthalpy of diffusion (ΔH) of 44.7 kJ mol−1. CuAlO2 is photoactive, and the Mott–Schottky plot indicates a flat band potential of +0.42 V vs saturated calomel electrode and
a holes density (N
A) of 1016 cm−3. The photocurrent spectra have been analyzed by using the Gartner model from which the absorption coefficients and diffusion
lengths were determined. An optical transition at 1.66 eV, indirectly allowed, has been obtained. The spectral photoresponse
provides a high absorption at 480 nm. The low quantum yield (η) is attributed to a small depletion length (440 nm) and a hole diffusion width (271 nm) compared to a very large penetration
depth (12 μm). 相似文献
20.
Ai-Lin Liu Jia-Dong Wang Wei Chen Xing-Hua Xia Yuan-Zhong Chen Xin-Hua Lin 《Journal of Solid State Electrochemistry》2012,16(4):1343-1351
A simple, rapid, sensitive, and accurate method for simultaneous electrochemical determination of procaine and its metabolite
(p-aminobenzoic acid, PABA) for pharmaceutical quality control and pharmacokinetic research was developed using a graphite paste
electrode. The differential pulse voltammetric results revealed that procaine and p-aminobenzoic acid, respectively, showed well-defined anodic oxidation peaks on a carbon paste electrode with a current peak
separation of 155 mV at a scan rate of 100 mV s−1. This well separation of the current peaks for these two compounds in voltammetry enables us to simultaneously determine
them. Good linearity (r > 0.998) between oxidation peak current and concentration was obtained in the range of 5.0 × 10−7–5.0 × 10−5 M for procaine and 5.0 × 10−7–2.0 × 10−5 M for PABA in pH 4.50 acetate buffer solution. The detection limit for both analytes is 5 × 10−8 M (S/N = 3:1). The present voltammetric method has been successfully used to determine trace p-aminobenzoic acid in procaine hydrochloride injection and procaine in plasma with a linear relationship of current to its
concentration ranging from 1.0 × 10−6 to 5.0 × 10−5 M (correlation coefficient of 0.9981) with a low detection limit of 5.0 × 10−7 M (S/N = 3:1). This validated method is promising to the study of pharmacokinetics in Sprague–Dawley rat and rabbit plasma after
an intravenous administration of procaine hydrochloride injection. 相似文献