Electrocatalytic behavior of mixed-valent RuORu(CN) 6 4- SiMo12 O40 4- Hybrid film modified electrodes toward oxidation of neurotransmitters and iodate reduction

Article abstract of DOI:10.1149/1.2769326

Mixed-valent ruthenium oxide/hexacyanoruthenate/silicomolybdate (RuORu(CN) 6 4- SiMo12 O40 4-) hybrid film was grown on glassy carbon electrode by repetitive cyclic voltammetric scanning in H2 SO4 solution (pH 1.5) containing Ru3+, Ru(CN) 6 4- and SiMo12 O40 4- ions. Simultaneous cyclic voltammetry and electrochemical quartz crystal microbalance measurements demonstrate the steady growth of hybrid film. In pure supporting electrolyte, the modified electrode exhibits five obvious redox couples. The electrochemical responses of modified electrode resemble that of a surface immobilized redox couple. The hybrid film electrodes showed electrocatalytic activity toward oxidation of neurotransmitters, ascorbic acid and reduction of IO3-. The neurotransmitters oxidized on modified electrode at less positive potentials compared to bare electrode. The feasibility of using our modified electrodes for analytical application was also investigated.

Full text of DOI:10.1149/1.2769326

Journal of The Electrochemical Society, 154 ͑10͒ E153-E157 ͑2007͒
E153
0013-4651/2007/154͑10͒/E153/5/$20.00 © The Electrochemical Society
Electrocatalytic Behavior of Mixed-Valent
4−
RuO/Ru„CN…6 /SiMo12O440− Hybrid Film Modified Electrodes
Toward Oxidation of Neurotransmitters and Iodate
Reduction
,z
*
Shen-Ming Chen, Jun-Liang Song, and R. Thangamuthu
Department of Chemical Engineering and Biotechnology, National Taipei University of Technology, Taipei,
Taiwan 106
Mixed-valent ruthenium oxide/hexacyanoruthenate/silicomolybdate ͑RuO/Ru͑CN͒4−/SiMo12O440−͒ hybrid film was grown on
6
4−
glassy carbon electrode by repetitive cyclic voltammetric scanning in H2SO4 solution ͑pH 1.5͒ containing Ru3+, Ru͑CN͒ and
6
SiMo12O440− ions. Simultaneous cyclic voltammetry and electrochemical quartz crystal microbalance measurements demonstrate the
steady growth of hybrid film. In pure supporting electrolyte, the modified electrode exhibits five obvious redox couples. The
electrochemical responses of modified electrode resemble that of a surface immobilized redox couple. The hybrid film electrodes
showed electrocatalytic activity toward oxidation of neurotransmitters, ascorbic acid and reduction of IO−3. The neurotransmitters
oxidized on modified electrode at less positive potentials compared to bare electrode. The feasibility of using our modified
electrodes for analytical application was also investigated.
© 2007 The Electrochemical Society. ͓DOI: 10.1149/1.2769326͔ All rights reserved.
Manuscript submitted February 6, 2007; revised manuscript received June 14, 2007. Available electronically August 20, 2007.
Electrochemical analysis has become one of the most important
methods in industrial process control, environmental monitoring,
and different applications in medicine and biotechnology. The use of
bare electrodes for such analysis has numerous limitations such as
high overpotential, slow electron transfer reaction, low sensitivity
and lack of reproducibility, poor stability over a wide range of so-
lution composition, and so on. Therefore, for many applications, it is
necessary to modify the inexpensive electrode surfaces with redox
active thin films for analytical applications ͑e.g., electrochemical
sensors͒. During sensor operation, the redox active sites shuttle elec-
trons between the analytes and the electrode often with a significant
reduction in activation overpotential. Moreover, the chemically
modified electrodes are generally less prone to surface fouling com-
pared to bare electrodes.
A variety of compounds have been used for the modification of
electrode surfaces with different procedures.1-4 Among them, inor-
ganic materials are attractive due to excellent stability, good conduc-
tivity, and ease of preparation.5 Remarkable success in the early
work with inorganic coatings5,6 encouraged interest on these com-
pounds. Among the inorganic materials, metal hexacyanoferrates are
an important class of insoluble mixed-valence polynuclear com-
pounds extensively used to prepare chemically modified
electrodes.7-18 Because they can produce well characterized electro-
active films with properties in common not only with redox and
ion-exchange polymers but also with intercalation compounds.
Similarly, polyoxometalates have been recognized as attractive
compounds for electrode surface modification due to their excellent
electrochemical and electrocatalytic properties.19,20 In the present
investigation, hybrid film of mixed-valent ruthenium oxide/
hexacyanoruthenate/silicomolybdate was grown on glassy carbon
electrode and its electrocatalytic behavior toward oxidation of some
biologically important compounds such as ascorbic acid, dopamine,
epinephrine, norepinephrine and reduction of iodate has been inves-
tigated.
trochemical experiments. Also, a continuous flow of nitrogen over
the aqueous solution was maintained during measurements.
The electrochemical experiments were carried out with a CH
Instruments ͑model CHI-400͒ using CHI-750 potentiostat. Cyclic
voltammograms were recorded in a three-electrode cell configura-
tion, in which a BAS glassy carbon electrode ͑area = 0.07 cm2͒ was
used as working electrodes. The auxiliary compartment contained a
platinum wire that was separated by a medium-sized glass frit. All
cell potentials were recorded using an Ag͉AgCl͉KCl ͑saturated so-
lution͒ electrode.
The working electrode for the electrochemical quartz crystal mi-
crobalance ͑EQCM͒ measurements was an AT-cut 8 MHz quartz
crystal coated with gold on both sides. The flow injection analysis
͑FIA͒ system mainly consisted of a peristaltic pump, an injection
valve and a flow cell. The peristaltic pump delivers the carrier
stream. The injection valve was equipped with an injection loop of
100 ␮L for the delivery of solutions containing the analyte.
Prior to film deposition, the glassy carbon electrode ͑GCE͒ was
polished with 0.05 ␮m alumina on Buehler felt pads and then ultra-
sonically cleaned for about 1 min in water. Finally, the electrode
was washed thoroughly with double distilled water and used.
The electrochemical deposition of mixed-valent ruthenium
oxide/ hexacyanoruthenate/silicomolybdate films was accomplished
by potentiodynamic cycling of the working electrode between
pre-set potential range in H2SO4 ͑pH 1.5͒ aqueous solution
4−
containing 1 ϫ 10−4
M , M Ru͑CN͒ , and 1
Ru3+ 1 ϫ 10−4
6
ϫ 10−4 M SiMo12O4− ions. After modification, the electrode was
rinsed with distilled 4w0 ater and used for further characterization.
Results and Discussion
Electrodeposition
brid film.— Figure 1 illustrates the electrodeposition of mixed-
valent ruthenium oxide/hexacyanoruthenate/silicomolybdate
of
RuO/Ru͑CN͒4Ϫ/SiMo12O440Ϫ
hy-
6
͓RuO/Ru͑CN͒4−/SiMo12O440−͔ hybrid film on glassy carbon elec-
6
trode from H2SO4 ͑pH 1.5͒ aqueous solution containing Ru3+
,
Experimental
4−
Ru͑CN͒ and SiMo12O440− ions during continuous potential cycling
6
between −0.2 and 1.1 V ͑vs Ag/AgCl͒. The increase in redox peak
currents with increasing number of potential scan is an indication of
hybrid film growth. As can be seen in the figure, five redox couples
with formal potentials about −0.05, 0.12, 0.25, 0.81, and 0.98 V
͑vs Ag͉AgCl͒ are observed. Based on the previous literature,6 in
All the chemicals used were of analytical grade and used without
further purification. The aqueous solutions were prepared using dou-
bly distilled deionized water and then deaerated by purging with
high purity nitrogen gas for about 20 min before performing elec-
which Kulesza has reported the formation of mixed-valent ruthe-
4−
nium͑III,IV͒ oxide/hexacyanoruthenate͑II,III͒, RuO/Ru͑CN͒
,
*
Electrochemical Society Active Member.
6
z E-mail: smchen78@ms15.hinet.net
film on glassy carbon electrode during electro-oxidation of
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E154
Journal of The Electrochemical Society, 154 ͑10͒ E153-E157 ͑2007͒
Figure 1. Cyclic voltammograms recorded during electrodeposition of
RuO/Ru͑CN͒4−/SiMo12O440− hybrid film on glassy carbon electrode from
6
4−
6
H2SO4 solution ͑pH 1.5͒ containing 1 ϫ 10−4
M
Ru͑CN͒
ions, 1
ϫ 10−4 M Ru3+ ions and 1 ϫ 10−4 M SiMo12O440−. Scan rate = 100 mV s−1
.
1:1 ͑mM/mM͒ RuCl3:K4Ru͑CN͒ in 0.5 M KCl at pH 2, the
6
two redox couples corresponding to formal potentials of 0.81 and
0.98 V can be attributed to ͓Ru͑III͒-O/Ru͑II͒-CN͔/͓Ru͑III͒-O/
Ru͑III͒-CN͔, and ͓Ru͑III͒-O/Ru͑III͒-CN͔/͓Ru͑IV͒-O/Ru͑III͒-CN͔
redox transitions, respectively. The other two redox couples with
formal potentials about 0.12 and 0.25 V can be ascribed to the
redox transitions of SiMo12O440− anions viz., ͓H6SiMo12O40͔/
͓H8SiMo12O40͔ and ͓H8SiMo12O40͔/͓H10SiMo12O40͔. The redox
transition at about −0.05 V was contributed by both mixed-valance
ruthenium species and silicomolybdate, i.e., it resulted due to
overlap of ͓Ru͑III͒-O/Ru͑II͒-CN͔/͓Ru͑III͒-O/Ru͑III͒-CN͔, and
͓H4SiMo12O40͔/͓H6SiMo12O40͔ redox transitions.
Figure 2. ͑a͒ Cyclic voltammograms recorded during electrodeposition of
RuO/Ru͑CN͒4−/SiMo12O440− hybrid film on gold electrode from H2SO4 solu-
6
4−
tion of pH 1.5 containing 1 ϫ 10−4 M Ru͑CN͒ ions, 1 ϫ 10−4 M Ru3+
6
ions, and 1 ϫ 10−4 M SiMo12O440−. Scan rate = 20 mV s−1. ͑b͒ Concurrent
change
in
EQCM
frequency
during
electrodeposition
of
RuO/Ru͑CN͒4−/SiMo12O440− hybrid film.
6
about 236 ng/cm2 of RuO/Ru͑CN͒4−/SiMo12O440− hybrid film was
6
deposited in the first cycle, and a total of “about 1100 ng/cm2” after
the 11th cycle.
The electrodeposition process of RuO/Ru͑CN͒4−/SiMo12O440− hy-
6
The electrochemical properties of RuO/Ru͑CN͒4Ϫ/SiMo12O440Ϫ
brid film can be described as follows. When cycling the potential of
the electrode in the modification solution, a cationic Ru͑III,IV͒-oxo
polynuclear species and anionic CN-bridged Ru dimers21 are formed
initially. Later, along with SiMo12O440−, the anionic Ru dimer inter-
acted with cationic Ru͑III,IV͒-oxo species, which resulted in forma-
tion of mixed-valent ruthenium͑III,IV͒oxide/cyanoruthenate͑II,III͒/
6
hybrid film-modified electrode.— Figure 3 shows the cyclic voltam-
metric response of RuO/Ru͑CN͒4−/SiMo12O440− hybrid film-modified
6
electrode in pure supporting electrolyte at different scan rates. As
expected, the peak currents of all the redox couples increased with
scan rate and showed nearly linear dependence on scan rate. For
example, the anodic peak current ͑ipa͒ corresponds to peak at about
+0.24 V varies linearly with scan rate as shown in the inset. The
peak separation ͑⌬Ep͒ was small but nonzero in the entire scan rate
region studied. These behaviors resemble that of a thin-layer film
modified electrode. Therefore, it can be concluded that in the
silicomolybdate ͑RuO/Ru͑CN͒4−/SiMo12O440−͒ hybrid film.
6
The formation and growth of RuO/Ru͑CN͒4−/SiMo12O440− hybrid
6
film was also confirmed by performing concurrent voltammetric and
microgravimetric experiments. Simultaneous cyclic voltammetry
and electrochemical quartz crystal microbalance ͑ECQM͒ measure-
ments permit continuous monitoring of surface mass changes with-
out disturbing experimental conditions. Figure 2a shows cyclic vol-
RuO/Ru͑CN͒4−/SiMo12O440− hybrid film modified electrode, the
6
charge transfer redox process was confined to the surface of modi-
fier.
tammograms recorded during RuO/Ru͑CN͒4−/SiMo12O440− hybrid
6
film formation on gold electrode in H2SO4 solution ͑pH 1.5͒ con-
Electrocatalytic behavior of RuO/Ru͑CN͒4Ϫ/SiMo12O440Ϫ
taining equimolar of Ru͑CN͒4−, Ru3+ and SiMo12O440−. Figure 2b
6
6
hybrid film-modified electrode.— Electrocatalytic
behavior
of
illustrates the change in EQCM frequency during the first 11 cycles
of the consecutive cyclic voltammetry between 0.9 and −0.2 V. The
increase in the voltammetric peak current in Fig. 2a and the decrease
in frequency ͑or increase in mass͒ in Fig. 2b are consistent with the
RuO/Ru͑CN͒4−/SiMo12O440− hybrid film-modified electrode was in-
6
vestigated toward oxidation of neurotransmitters and ascorbic acid,
as well as reduction of iodate using cyclic voltammetry.
Mediated oxidation of neurotransmitters and ascorbic
growth of RuO/Ru͑CN͒4−/SiMo12O440−. A major frequency change
6
acid.— Figure
4A
shows
cyclic
voltammograms
of
occurred at the potential range between 0.2 and −0.2 V due to for-
mation of molybdenum͑IV/VI͒ of silicomolybdate redox couple.
The calculation according to the Sauerbrey equation22 showed that
RuO/Ru͑CN͒4−/SiMo12O440− hybrid film-modified electrode in the
6
presence ͑curve b-d͒ and absence ͑curve a͒ of dopamine ͑DA͒.
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Journal of The Electrochemical Society, 154 ͑10͒ E153-E157 ͑2007͒
E155
Figure 3. Cyclic voltammograms of RuO/Ru͑CN͒4−/SiMo12O440− hybrid film
6
modified electrode in H2SO4 solution ͑pH 1.5͒ at different scan rates. Inner
to outer voltammograms correspond to scan rates of 10, 20, 30, 40, 50, 60,
70, 80, 90, and 100 mV s1, respectively. The inset shows plot of anodic peak
current at +0.24 V vs scan rate.
Curve a represents the electrochemical oxidation of DA on bare
Ј
GCE. It can be noticed that DA exhibited single oxidation and re-
duction peak on bare GCE. The higher oxidation current on modi-
fied electrode ͑at potential about 0.5 V͒ compared to bare GCE and
increase of oxidation peak currents with DA concentration indicate
that RuO/Ru͑CN͒4−/SiMo12O440− hybrid film mediate the DA oxida-
6
tion. It is worth mentioning that the electrocatalytic oxidation peak
of DA occurred at less positive potential ͑before the onset of oxida-
tion on bare GCE͒ on RuO/Ru͑CN͒4−/SiMo12O440− compared to that
6
on mixed ruthenium oxide/ruthenocyanide ͑mvRuO/RuCN͒ modi-
fied electrode.23
Figures 4B and 4C illustrate the electrocatalytic behavior of
RuO/Ru͑CN͒4−/SiMo12O440− hybrid film-coated electrode toward
6
epinephrine and norepinephrine, respectively. Both neurotransmit-
ters oxidized on modified electrode at less positive potentials com-
pared to bare GCE. It is obvious from the figures that for same
substrate concentration, the modified electrode yields higher oxida-
tion current than that on bare GCE. All these observations collec-
tively indicate that RuO/Ru͑CN͒4−/SiMo12O440− hybrid film-coated
6
electrode mediates the electro-oxidation of epinephrine and norepi-
nephrine. The electrocatalytic oxidation of neurotransmitters in-
volves participation of two electrons and same number of protons as
suggested in the literature.24-27
It can be observed from the voltammograms of neurotransmitters
that the amplification of electrocatalytic peak current is not dramatic
but clearly noticeable since the peak current value of modified elec-
trode in pure supporting electrolyte is almost negligible. The mod-
erate amplification and lower oxidation potential can be attributed to
better reversibility of the electrochemical reaction at the modified
surface.
Figure
4.
͑Color
online͒
Cyclic
voltammograms
of
a
RuO/Ru͑CN͒4−/SiMo12O440− hybrid film coated electrode in a pH 1.5 aqueous
6
solution containing different concentrations of: dopamine ͑A͒: ͑a͒ 0; ͑b͒ 2
ϫ 10−4; ͑c͒ 4 ϫ 10−4; ͑d͒ 6 ϫ 10−4 M, epinephrine ͑B͒: ͑a͒ 0; ͑b͒ 2
ϫ 10−4; ͑c͒ 4 ϫ 10−4; ͑d͒ 6 ϫ 10−4 M, and norepinephrine ͑C͒: ͑a͒ 0; ͑b͒
1 ϫ 10−4; ͑c͒ 2 ϫ 10−4; ͑d͒ 3 ϫ 10−4; ͑e͒ 4 ϫ 10−4 M. a in A, B and C
Ј
represents oxidation of 6 ϫ 10−4
M
dopamine, epinephrine and
norepinephrine, respectively, on bare GCE. Scan rate
= 100 mV s−1
4
ϫ 10−4
M
.
Besides neurotransmitters, the electrocatalytic activity of
RuO/Ru͑CN͒4−/SiMo12O440− hybrid film was also tested toward oxi-
6
dation of ascorbic acid ͑AA͒ and the results are presented in Fig. 5.
AA oxidation occurs at modified electrode approximately 200 mV
less positive potential compared to bare GCE. Thus, the overpoten-
tial of AA oxidation is reduced due to electrode modification. Also,
the catalytic current increases with increasing substrate concentra-
tion. These observations suggest that RuO/Ru͑CN͒4−/SiMo12O440−
6
hybrid film catalyzes the AA oxidation.
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E156
Journal of The Electrochemical Society, 154 ͑10͒ E153-E157 ͑2007͒
Figure 5. Cyclic voltammograms of a RuO/Ru͑CN͒4−/SiMo12O440− hybrid
Figure 6. Cyclic voltammograms of RuO/Ru͑CN͒4−/SiMo12O4− hybrid film
6
6
coated electrode in a pH 1.5 aqueous solution containing diff4e0rent concen-
film coated electrode in a pH 1.5 aqueous solution containing different con-
centrations of ascorbic acid: ͑a͒ 0; ͑b͒ 2 ϫ 10−4; ͑c͒ 4 ϫ 10−4; ͑d͒ 6
trations of KIO3: ͑a͒ 0; ͑b͒ 1 ϫ 10−4; ͑c͒ 2 ϫ 10−4; ͑d͒ 3 ϫ 10−4 M. a
Ј
ϫ 10−4 M. a represents 6 ϫ 10−4 M ascorbic acid oxidation on bare glassy
Ј
represents 3 ϫ 10−4 M KIO3 reduction on bare glassy carbon. Scan rate
carbon. Scan rate = 100 mV s−1
.
= 100 mV s−1
.
The cyclic voltammetric results of neurotransmitters and AA
demonstrate that RuO/Ru͑CN͒4−/SiMo12O440− hybrid film-modified
6
shows typical FIA response for subsequent injections of KIO3
standard solutions. Linear calibration plot is obtained in the
electrode can be used conveniently to determine these biologically
important compounds separately. However, the present modified
electrode may have some limitations for selective determination due
to possible overlapping of oxidation potentials of neurotransmitters
and AA. Another aspect, which is important in the context of bio-
logical application of modified electrode, is the linear range. The
range of 0.1 − 0.3 mM KIO3 ͑r2 = 0.9995͒, with the slope of
4−
14.19 ␮A/mM. The lowest detection limit for RuO/Ru͑CN͒
/
6
SiMo12O440− hybrid film-coated electrode was calculated to be
50 ␮M.
catalytic current of RuO/Ru͑CN͒4−/SiMo12O440− hybrid film elec-
6
trode increases linearly up to 6 ϫ 10−4 M for neurotransmitters as
well as AA. It is worth mentioning that in biological fluids
concentration of AA is higher ͑10−4 M͒ compared to that of neu-
rotransmitters ͑10−8–10−6 M͒.28,29 The concentration range of
Stability of RuO/Ru͑CN͒4Ϫ/SiMo12O440Ϫ hybrid film-modified
6
electrodes.— An important requirement of modifier layer deposited
on electrode surfaces, especially in terms of analytical applications,
is its stability when in contact with the supporting electrolyte or
RuO/Ru͑CN͒4−/SiMo12O440− hybrid film electrode for AA falls
sample. The stability of the RuO/Ru͑CN͒4−/SiMo12O440− hybrid film-
6
6
within its concentration in the biological system but for neurotrans-
mitters the range is higher.
modified electrode was evaluated in pure supporting electrolyte by
scanning the electrode potentiodynamically. The results indicated
that Ru–O/Ru͑CN͒4−/SiMo12O440− hybrid film-modified electrode
Mediated reduction of Iodate.— Figure 6 shows cyclic voltammo-
6
grams of RuO/Ru͑CN͒4−/SiMo12O440− hybrid film-modified electrode
was relatively stable as the peak current of the modified electrode
remains nearly unchanged ͑not shown͒ for a reasonable period of
time. The FIA results presented in the previous section also indicate
6
in H2SO4 solution ͑pH 1.5͒ containing different concentration of
KIO . It can be inferred from curve a that iodate is electrochemi-
Ј
3
that the stability of RuO/Ru͑CN͒4−/SiMo12O440− hybrid film-
cally inactive on bare GCE. In the case of modified electrode, only
cathodic waves corresponding to the reduction of the molybdic an-
ion from zero to two electron, two electron to four electrons and
four electron to six-electron reduction products have the catalytic
activity toward IO−3 reduction. A similar type of observation was
found for BrO−3.30,31 The catalytic process of IO−3 reduction at the
modified electrode can be expressed as follows
6
modified electrode is satisfactory.
Conclusion
Mixed-valent films of ruthenium oxide/hexacyanoruthenate/
silicomolybdate ͑RuO/Ru͑CN͒4−/SiMo12O440−
͒
were prepared
6
by cycling the working electrode continuously between −0.2 and
1.1 V ͑vs Ag/AgCl͒ in the modification solution. From the EQCM
study, it was found that a total of “about 1100 ng/cm2” of
SiMon− + 2e − + 2H+ → H2SiMon−
H2SiMon− + IO3− + 4H+ → SiMon− + I− + 3H2O
͓1͔
͓2͔
RuO/Ru͑CN͒4−/SiMo12O440− deposit formed on the gold electrode
6
after 11 cyclic voltammetric scans. The RuO/Ru͑CN͒4−/SiMo12O440−
RuO/Ru͑CN͒4Ϫ/SiMo12O440Ϫ hybrid film-modified electrodes in
6
6
film modified electrode exhibited four chemically reversible redox
couples in pH 1.5 aqueous solution. Further electrochemical charac-
terization suggested that the redox process of the modified electrode
analytical applications-flow injection analysis of KIO3 reduc-
tion.— The sensor output for a series of 22 consecutive measure-
ments, in which KIO3 concentration was kept constant at 0.1 mM is
shown in Fig. 7A. The current generated at the electrodes is given as
a function of time. Each KIO3 concentration level was measured 22
times to assess the variability of the measurements. FIA responses
increased rapidly just after injection of the sample and returned to
base line within about 5 s, as shown in Fig. 7A. A relative standard
deviation of 2.3% was obtained for these measurements. Fig. 7B
was confined to the surface. The RuO/Ru͑CN͒4−/SiMo12O440− modi-
6
fied electrode catalyzes the electrocatalytic oxidation of neurotrans-
mitters, ascorbic acid and reduction of iodate. The overpotential of
neurotransmitters was reduced considerably compared to bare elec-
trode. Finally, analytical application of our modified electrodes was
tested successfully by applying for the estimation of IO−3 in FIA.
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Journal of The Electrochemical Society, 154 ͑10͒ E153-E157 ͑2007͒
Acknowledgment
E157
This work was financially supported by the National Science
Council of Taiwan ͑ROC͒.
National Taipei University of Technology assisted in meeting the publi-
cation costs of this article.
References
1. R. W. Murray, in Electroanalytical Chemistry, A. J. Bard, Editor, Vol. 13, p. 191,
Dekker, New York ͑1983͒.
2. Molecular Design of Electrode Surfaces R. W. Murray, Editor, Techniques in
Chemistry Series, Vol. XXII, Wiley, New York ͑1992͒.
3. N. Oyama and F. C. Anson, Anal. Chem., 52, 1192 ͑1980͒.
4. H. R. Zare, F. Memarzadeh, M. M. Ardakani, M. Namazian, and S. M. Golabi,
Electrochim. Acta, 50, 3495 ͑2005͒.
5. J. A. Cox and P. J. Kulesza, Anal. Chem., 56, 1021 ͑1984͒.
6. P. J. Kulesza, J. Electroanal. Chem. Interfacial Electrochem., 220, 259 ͑1987͒.
7. W. Hou and E. Wang, J. Electroanal. Chem. Interfacial Electrochem., 316, 155
͑1991͒.
8. C. H. Luangdilok, D. J. Arent, A. B. Bocarsly, and R. Wood, Langmuir, 8, 650
͑1992͒.
9. J. Joseph, H. Gomathi, and G. P. Rao, J. Electroanal. Chem., 431, 231 ͑1997͒.
10. J. Zhou and E. Wang, Electroanalysis, 6, 29 ͑1994͒.
11. S. M. Chen, Electrochim. Acta, 43, 3359 ͑1998͒.
12. B. D. Humphrey, S. Sinka, and A. B. Bocarsly, J. Phys. Chem., 91, 586 ͑1987͒.
13. S. M. Chen, J. Electroanal. Chem., 521, 29 ͑2002͒.
14. C. W. Liu and S. J. Dong, Electroanalysis, 9, 839 ͑1997͒.
15. S. Q. Liu and H. Y. Chen, J. Electroanal. Chem., 528, 190 ͑2002͒.
16. M. H. Pournaghi-Azar and H. Dastango, J. Electroanal. Chem., 523, 26 ͑2002͒.
17. P. Wang, X. Jing, W. Zhang, and G. Zhu, J. Solid State Electrochem., 5, 369
͑2001͒.
18. X. Cui, L. Hong, and X. Lin, J. Electroanal. Chem., 526, 115 ͑2002͒.
19. M. Sadakane and E. Steckhan, Chem. Rev. (Washington, D.C.), 98, 219 ͑1998͒, and
references therein.
20. T. R. I. Cataldi and G. E. De Benedetto, J. Electroanal. Chem., 458, 149 ͑1998͒.
21. F. C. Crean and K. Schug, Inorg. Chem., 23, 853 ͑1984͒.
22. G. Sauerbrey, Z. Phys., 155, 206 ͑1959͒.
23. S. M. Chen and S. H. Hsueh, J. Electroanal. Chem., 566, 291 ͑2004͒.
24. P. Hernandez, I. Sanchez, F. Paton, and L. Hernandez, Talanta, 46, 985 ͑1998͒.
25. X. L. Wen, Y. H. Jia, and Z.-L. Liu, Talanta, 50, 1027 ͑1999͒.
26. J. Wang and A. Walcarius, J. Electroanal. Chem., 407, 183 ͑1996͒.
27. S. M. Chen and K. T. Peng, J. Electroanal. Chem., 547, 179 ͑2003͒.
28. M. Ghita and D. W. M. Arrigan, Electrochim. Acta, 49, 4743 ͑2004͒.
29. R. A. de Toledo, M. C. Santos, E. T. G. Cavalheiro, and L. H. Mazo, Anal. Bioanal.
Chem., 381, 1161 ͑2005͒.
Figure 7. FIA responses for 100 ␮L injection of ͑A͒ 1 ϫ 10−4 M KIO3
stock solution; ͑B͒ sequential injection of different concentration KIO3: ͑a͒
1 ϫ 10−4; ͑b͒ 2 ϫ 10−4; ͑c͒ 3 ϫ 10−4 M. Electrode potential was held at
−0.2 V.
30. L. Wang, D. Xiao, E. Wang, and L. Xu, J. Colloid Interface Sci., 285, 435 ͑2005͒.
31. X. L. Wang, E. B. Wang, Y. Lan, and C.-W. Hu, Electroanalysis, 14, 15 ͑2002͒.
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