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ORIGINAL PAPER
Electrolyte type and concentration effectson poly(3-(2- aminoethyl thiophene) electro-coatedon glassy carbon electrode via impedimetric study
Murat Ates • Tolga Karazehir • Fatih Arican •
Nuri Eren
Received: 31 July 2012 / Accepted: 19 December 2012 / Published online: 9 January 2013
� Iran Polymer and Petrochemical Institute 2012
Abstract In this study, 3-(2-Aminoethyl thiophene)
(2AET) monomer was electropolymerized on glassy car-
bon electrode (GCE) using various electrolytes (lithium
perchlorate (LiClO4), sodium perchlorate (NaClO4), tetra-
butyl ammonium tetra fluoroborate (TBABF4) and tetra-
ethyl ammonium tetra fluoroborate (TEABF4) in
acetonitrile (CH3CN) as solvent. Poly(3-(2-aminoethyl
thiophene) (P(2AET))/GCE was characterized by cyclic
voltammetry (CV), Fourier transform infrared reflectance
spectrophotometry (FTIR-ATR), scanning electron
microscopy, energy dispersive X-ray analysis (EDX), and
electrochemical impedance spectroscopy (EIS) techniques.
The electrochemical impedance spectroscopic results were
given by Nyquist, Bode-magnitude, Bode-phase, capaci-
tance and admittance plots. The highest low frequency
capacitance (CLF) value obtained was 0.65 mF cm-2 in
0.1 M LiClO4/CH3CN for the initial monomer concentra-
tion of 1.5 mM. The highest double layer capacitance
(Cdl = ~0.63 mF cm-2) was obtained in 0.1 M LiClO4/
ACN for [2AET]0 = 0.5, 1.0 and 1.5 mM. The maximum
phase angles (h = 76.1o at 26.57 Hz) and conductivity
(Y00 = 3.5 mS) were obtained in TEABF4/ACN for
[2AET]0 = 0.5 and 1.0 mM, respectively. An equivalent
circuit model of R(Q(R(Q(R(CR))))) was simulated for
different electrolytes (LiClO4, NaClO4, TBABF4 and
TEABF4)/P(2AET)/GCE system. A good fitting was
obtained for the calculated experimental and theoretical
EIS measurement results. The electroactivity of P(2AET)/
GCE opens the possibility of using modified coated elec-
trodes for electrochemical micro-capacitor electrodes and
biosensor applications.
Keywords 3-(2-Aminoethyl thiophene) � Electrolyte �Scanning electron microscopy � Concentration �Circuit model
Introduction
Conjugated electroactive polymers have increasingly
become of significant interest worldwide due to their
inherently physical, mechanical and electronic properties
[1]. The modification by functionalization of the electro-
active monomer before polymerization [2–4], based on the
electronic properties of the neutral semiconducting form of
conjugated systems has had a great effect on the polymer
chemistry [5, 6]. The aspects of physical, mechanical and
electronic properties have been studied in charge storage
devices which were lightweight, formable, and redox stable
[7].
Conducting polymers were prepared either by chemical
or electrochemical polymerization. The electrochemical
synthesis offers several advantages, including rapidity,
simplicity, generation of the polymer in the doped state and
easy control of thickness of the film generated [8, 9].
Functional conjugated polymers show good electro-activity
due to their electro generation on the electrode surface
[10–14]. Due to their good processability and, outstanding
chemical and electrochemical stability, conducting poly-
mers have attracted more attentions and are expected to be
M. Ates (&) � T. Karazehir � F. Arican � N. Eren
Department of Chemistry, Faculty of Arts and Sciences,
Namik Kemal University, Degirmenalti Campus,
59030 Tekirdag, Turkey
e-mail: mates@nku.edu.tr
URL: http://mates-en.nku.edu.tr/
T. Karazehir
Department of Chemistry, Faculty of Arts and Sciences,
Istanbul Technical University, Maslak, Istanbul, Turkey
Iran Polymer and
Petrochemical Institute 123
Iran Polym J (2013) 22:199–208
DOI 10.1007/s13726-012-0117-z
used in many fields, such as sensors [15–18], supercapac-
itors [19–22] and solar cells [23, 24].
Among conducting polymers, poly(thiophenes) can be
used in many fields, such as solar cells [25], supercapacitors
[26], and field-effect transistors [27] due to its environ-
mental [28], thermal stability [29], and ease of structure
modification [30, 31]. Physicochemical properties of thio-
phene derivatives can be easily modified by substitution
of the macromolecular chain by different functional
groups [32, 33]. Polymerization of thiophene substituted in
b-position by an alkyl chain is not very difficult. However,
when the thiophene carries bulky substituents, the poly-
merization becomes frequently less easy or even impossible
[34, 35]. Thiophene-based functional conducting polymers
have problems of solubility and easy processability [36, 37].
This problem was overcome by the incorporation of sub-
stituents to the 3-position of the thiophene ring, which
produced not only processable conducting polymers, but
also allowed the complete chemical and physical charac-
terization of the prepared materials [38]. Introduction of
long alkyl side chains increases the solubility in organic
solvents, while hydrophilic substituents produce polythio-
phene soluble in water and/or polar solvents [39].
Electrochemical impedance spectroscopy (EIS) has been
considered as a technique that is suitable to study the
interfacial process [40] to supply important information,
such as double layer capacitance, charge transfer resis-
tance, diffusion impedance, and solution resistance
[41, 42]. EIS gives information on possible mechanisms in
electrochemical kinetics, but is unable to identify the nat-
ure of species formed or adsorbed at the electrode surface
during the reaction [43]. EIS results are analyzed by an
electrical equivalent circuit, which is a mathematical–the-
oretical model to interpret the experimental data [44, 45].
However, electrical or physical properties are not directly
obtained from an EIS experiment, and modeling impedance
data using an equivalent circuit is to assume that the
material behaves as a flat or even rough surface [46]. The
most used models for the interpretation of EIS data
for conducting polymers are based on insertion models
[47–49]. EIS is an outstanding electroanalytical measure-
ment technique when compared with other techniques,
such as cyclic voltammetry (CV), amperometry and po-
tentiometry since the potentials applied to the surfaces are
very small (typically 10–20 mV amplitude sinusoids) [50].
In this paper, electrolyte type and concentration effects
on poly(3-(2-aminoethyl thiophene)/GCE is given by
electrochemical impedance spectroscopy technique. In lit-
erature, there is limited amount of paper to investigate
three types of poly(thiophene)s having amino substituents
of poly(3-aminoethyl thiophene), poly(3-aminododecyl
thiophene) and poly[2,5-(3-octadecyl thiophene)-alt-2,5-
(3-aminoethyl thiophene)] [51]. Spin coated films of
hydrogen bromide salt of poly(aminoalkyl) substituents
were soaked in aqueous solution of PbBr2 by Noto et al.
[52]. As far as authors are aware, in literature, there is no
previous study on the electropolymerization of 3-(2-ami-
noethyl thiophene) on glassy carbon electrode in different
types and concentrations of electrolytes by EIS method.
Experımental
Materials
The monomer of 3-(2-aminoethylthiophene) (2AET) was
provided by Sigma-Aldrich, USA. All other reagents
included Acetonitrile (Aldrich, 99.93 %), and the sup-
porting electrolytes: lithium perchlorate (LiClO4, Fluka
Chemie GmbH, Bushs, Switzerland), sodium perchlorate
(Aldrich,[98.0 %), tetraethyl ammonium tetrafluoroborate
(Alfa Aesar, purity [98 %), tetrabutyl ammonium tetra-
fluoroborate (Alfa Aesar, purity[98 %) were used without
any treatment or further purification. Carbon fiber micro
electrodes (CFMEs, Sigri Carbon, Meitengen, Germany)
were prepared using a 3-cm long bundle of the electrodes
(average diameter *7 lm) attached to a copper wire with
a Teflon tape. Numbers of CFMEs in the bundle were about
10 which were counted under a digital microscope. One
centimeter of the CFME was dipped into the solution to
keep the electrode area (*0.022 cm2).
Instrumentation
Cyclic voltammetry (CV) was performed using PARSTAT
2273 (Princeton Applied Research, USA, software: pow-
ersuit and Faraday cage: BASI Cell Stand C3) in a three
electrode configuration, which employing glassy carbon
electrode (GCE) (area: 0.07 cm2) as the working electrode,
platinum wire as the counter electrode and Ag/AgCl as the
reference electrode.
Modified carbon fiber microelectrode (CFME) was
characterized by Fourier transform infrared-attenuated
transmittance reflectance (FTIR-ATR) spectroscopy
(Spectrum One B, Perkin Elmer, USA, with a universal
ATR attachment with a ZnSe crystal). Morphological
investigations were performed with scanning electron
microscopy (SEM) and energy dispersive X-ray analysis
(EDX) using a Carl Zeiss Leo 1430 VP, Germany.
Electrochemical impedance spectroscopy
EIS measurements were performed in 0.1 M four different
electrolytes (LiClO4, NaClO4, TEABF4 and TBABF4)/
acetonitrile (CH3CN). EIS measurements were done in
monomer-free electrolyte solution with perturbation
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amplitude of 10 mV over a frequency range between
0.01 Hz and 100 kHz with PARSTAT 2273 model
Potansiostat/galvanostat. Equivalent circuit model was
drawn the programme of ZSimpWin, version of 3.1.
Results and discussion
Electropolymerization of 3-(2-aminoethyl thiophene)
on GCE
Electropolymerization of 2AET at the glassy carbon elec-
trode has opened a field at the convergence between two
rich domains: electrochemistry of modified electrode
[53, 54] and conjugated systems [55]. Consequently, appli-
cation of modified electrodes in energy storage has been
enriched by the specific properties of intrinsically con-
ducting polymers. The cyclic voltammogram of 2AET thin
films electrochemically deposited on glassy carbon elec-
trode (GCE) recorded in 0.1 M four different electrolytes
(LiClO4, NaClO4, TEABF4 and TBABF4) as shown in
Fig. 1. The lowest oxidation potential of 2AET is *1.45 V
in 0.1 M LiClO4 (Fig. 1a) and TBABF4/CH3CN (Fig. 1c).
However, NaClO4 (Fig. 1b) and TBABF4 (Fig. 1d) have
higher oxidation potentials as *1.6 V and *1.75 V,
respectively. The highest total charges (Q = 4.22 mC)
during electro-growth process (8 cycle) was obtained in
TBABF4/CH3CN.
Effect of scan rate in monomer-free solution
A P(2AET)/GCE film was inserted into a monomer-free
electrolyte solution. Redox behavior of modified electrodes
was investigated via Randless-Sevcik equation as follows:
i ¼ 2:69� 105� �
� A� D1=2 � C0 � m1=2 ð1Þ
where, m (V s-1) is the scan rate, D (cm2 s-1) is the dif-
fusion coefficient of electro-active species, and C0 (mol/L)
is the concentration of electro-active species in solution.
Anodic and cathodic redox reaction of modified electrodes
formed in 0.1 M LiClO4, TEABF4 and TBABF4 solutions
showed both thin layer formation and diffusion controlled
process as evidenced by the linearity of the plots given in
Fig. 2. In NaClO4/CH3CN, the polymer only shows thin
layer formation due to regression fit values obtained from
current density versus scan rate graph (RAn = 0.99757 and
RCat = -0.99879) which were higher than the regression
fit values obtained from current density versus square root
of scan rate graph (RAn = 0.98788 and RCat = -0.98575)
FTIR-ATR
The FTIR-ATR spectrum of P(2AET)/CFME in 0.1 M
TBABF4/CH3CN was obtained by reflectance FTIR spec-
trophotometry (Fig. 3). The peak at 1052 cm-1 can be
attributed to dopant anion of BF4-. The peak at 2963 cm-1
is assigned to bond of C=C–H symmetric stretch in
Fig. 1 Cyclic voltammetry of
2AET on GCE in different
electrolytes of 0.1 M: a LiClO4/
CH3CN (Q = 2.93 mC),
b NaClO4/CH3CN
(Q = 2.16 mC), c TBABF4/
CH3CN (Q = 4.22 mC), and
d TEABF4/CH3CN
(Q = 2.23 mC)
([2AET]0 = 1 mM; 8 cycle;
scan rate: 25 mV s-1; potential
range: 0.0–2.0 V)
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benzene ring. The peak at 1495 cm-1 is indicated NH2
group of functional group of thiophene.
SEM
Morphology of P(2AET)/CFME was investigated via SEM
for sample obtained by cyclic voltammetry with a scan rate
of 25 mV s-1. It is not observed homogeneous thin film
due to deposition on some parts of fibers as shown in
Fig. 4.
Average values of EDX point and area analysis showed
the characteristic element analysis of Carbon (*35.12 %),
Nitrogen (*31.78 %), Fluorine (*32.8 %) and Sulfur
(*0.30 %) as shown in Table 1. EDX analysis proved us
the successfulness of electropolymerization process. And
also the existence of fluorine element into the polymer
structure gives us evidence of successfully performed
doped process.
Electrochemical impedance spectroscopy
EIS is a powerful technique to give information about the
surface configuration and capacitive behavior of modified
electrode. Among EIS plots, the more capacitive behavior
was obtained as directly proportional line with the angle of
90� from Nyquist plot, and the double layer capacitance
information was easily acquired [56]. The low frequency
capacitance values from impedance spectroscopy were
obtained from the slope of a plot of the imaginary com-
ponent (Z00) of the impedance at low frequencies versus
Fig. 2 Cyclic voltammetry of P(2AET)/GCE in monomer-free
solution in 0.1 M TBABF4/CH3CN at different initial monomer
concentrations: a [2AET]0 = 0.5 mM, b [2AET]0 = 1.0 mM, and
c [2AET]0 = 1.5 mM, 8 cycle, scan rate: 25–1000 mV s-1, potential
range: 0.0 to ?2.0 V. (Every graphics are in the same conditions on
the same line)
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inverse of the reciprocal frequency (f) (where f = 0.01 Hz)
using following equation [57]:
CLF ¼ �1 = 2p� f � Z 00 ð2Þ
The highest low frequency (10 mHz) capacitance (CLF)
value was obtained in 0.1 M LiClO4/CH3CN as CLF =
0.65, 0.64 and 0.66 mF cm-2 for the initial monomer
concentration ([2AET]0) of 0.5, 1.0 and 1.5 mM,
respectively. In 0.1 M NaClO4/CH3CN, CLF was obtained
as 0.45, 0.41 and 0.49 mF cm-2 for [2AET]0 = 0.5, 1.0
and 1.5 mM, respectively. In TEABF4/CH3CN, CLF was
calculated as 0.44 mF cm-2. And the lowest CLF values of
0.30, 0.37 and 0.35 mF cm-2 for [2AET]0 = 0.5, 1.0 and
1.5 mM in TBABF4/CH3CN, respectively (Fig. 5).
Bode-magnitude plot gives by extrapolating line to the
log Z axis at w = 1 (log x = 0) yielding the value of Cdl
from the following relationship [58]:
Zj j ¼ 1 =Cdl ð3Þ
Double layer capacitance of P(2AET)/GCE was taken
in four different electrolytes of LiClO4, NaClO4, TBABF4
and TEABF4. The highest Cdl was obtained as
*0.63 mF cm-2 in 0.1 M LiClO4/ACN for [2AET]0 =
0.5, 1.0 and 1.5 mM. The other Cdl values were obtained as
0.33, 0.32 and 0.31 mF cm-2 in 0.1 M NaClO4, TEABF4
and TBABF4, respectively (Fig. 6).
Bode-phase plot of P(2AET) was given by variation of
log (f) values. The maximum phase angles (h = 76.1� at
26.57 Hz) was obtained in 0.1 M TEABF4/ACN for
[2AET]0 = 0.5 mM. In addition, there was no so much
changes in the other electrolytes, such as in 0.1 M LiClO4/
ACN (h = 72� at 28.42 Hz) in NaClO4/ACN (h = 72.31�at 20.50 Hz) and in TBABF4/ACN (h = 73.2� at
37.22 Hz). The concentration of P(2AET) did not affect the
phase angle value through the variation of electrolyte types
as shown in Fig. 7.
The highest conductivity value (Y00 = 3.5 mS) was
observed in TEABF4/ACN. However, the lowest conduc-
tivity (Y00 = 2.7 mS) was obtained in LiClO4/ACN as
shown in Fig. 8a. In NaClO4/ACN, (Y00 = 2.6 mS) for
[2AET]0 = 0.5 and 1.0 mM, (Y00 = 1.6 mS) for [2AET]0 =
1.5 mM were obtained as given in Fig. 8b. In TBABF4/ACN,
(Y00 = 3.1 mS) for [2AET]0 = 1.0 mM, (Y00 = 2.9 mS) for
[2AET]0 = 0.5 mM, (Y00 = 2.7 mS) for [2AET]0 = 1.5 mM
were obtained from admittance plot (Fig. 8c). In TEABF4/
ACN (Y00 = 3.5 mS) for [2AET]0 = 0.5 mM was obtained as
shown in Fig. 8d.
As a result, the variation of electrolyte is more sig-
nificant than the variation of monomer. The highest
capacitance value from low frequency capacitance
Fig. 3 FTIR-ATR spectrum of 2AET/GC at [2AET]0 = 1 mM; 8
cycle; scan rate: 25 mV s-1; potential range: 0.0 to ?2.0 V; 0.1 M
TBABF4/CH3CN (Q = 60.14 mC); 30 cycle
Fig. 4 SEM analysis of a point
analysis of P(2AET) on a single
CFME at [2AET]0 = 1.0 M
potential range: 0.0 to ?2.0 V,
scan rate: 25 mV s-1, 0.1 M
TBABF4/CH3CN, 30 cycle, and
Q = 58.15 mC; b area analysis
of P(2AET) on a single CFME
at [2AET]0 = 1.0 mM,
potential range: 0.0 to ?2.0 V,
scan rate: 25 mV s-1, 0.1 M
TBABF4/CH3CN, 30 cycle, and
Q = 58.15 mC
Table 1 EDX analysis of P(2AET)/CFME
Elements/K series P(2AET)/CFME
Point analysis Area analysis
Carbon 33.51 36.74
Nitrogen 31.91 31.65
Fluorine 34.16 31.44
Sulfur 0.42 0.17
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(CLF = 0.66 mF cm-2) for [2AET]0 = 1.5 mM and double
layer capacitance (Cdl = *0.63 mF cm-2) for all electrolytes
were obtained in the electrolyte of LiClO4. The concentration
effect does not significantly influence the Cdl value.
Equivalent circuit model
The impedance spectra were analyzed in detail with
impedance plane: Nyquist (Fig. 9a), Bode-magnitude,
Fig. 5 Nyquist plots of
P(2AET)/GCE, a LiClO4/ACN,
b NaClO4/ACN,
c TBABF4/ACN, and
d TEABF4/ACN at different
initial monomer concentrations:
[2AET]0 = 0.5 mM,
[2AET]0 = 1.0 mM and
[2AET]0 = 1.5 mM
Fig. 6 Bode-magnitude plots of
P(2AET)/GCE at:
a LiClO4/ACN;
b NaClO4/ACN;
c TBABF4/ACN;d TEABF4/
ACN and different initial
monomer concentrations:
[2AET]0 = 0.5 mM;
[2AET]0 = 1.0 mM;
[2AET]0 = 1.5 mM
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Bode-phase (Fig. 9b) and admittance plots (Fig. 9c). The
results of this analysis were fitted to ZSimpwin pro-
gramme. As criteria for a good fit, the Chi-squared (v2, i.e.
the sum of the square of the differences between theoretical
and experimental points) and the relative errors were
chosen in the estimated parameters. The value of v2 was in
the range of 10-3–10-4. The equivalent circuit model of
R(Q(R(Q(R(CR))))) was given inset of Fig. 9a. R3 is in
parallel with an interfacial double layer capacitance (Cdl).
Electrolyte resistance (Rs) is in parallel connection with R1,
R2, Q1 and Q2. The constant phase element (Q) behavior of
interfaces has been ascribed to a fractal nature (especially
Fig. 7 Bode-phase plots of
P(2AET)/GCE at:
a LiClO4/ACN;
b NaClO4/ACN;
c TBABF4/ACN;
d TEABF4/ACN and different
initial monomer concentrations:
[2AET]0 = 0.5 mM;
[2AET]0 = 1.0 mM;
[2AET]0 = 1.5 mM
Fig. 8 Admittance plots of
P(2AET)/GCE at:
a LiClO4/ACN;
b NaClO4/ACN;
c TBABF4/ACN;
d TEABF4/ACN and different
initial monomer concentrations:
[2AET]0 = 0.5 mM;
[2AET]0 = 1.0 mM;
[2AET]0 = 1.5 mM
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geometry of the roughness) of the interface [59, 60]. The
admittance representation of the CPE (Q) is given by the
following equation:
YCPE ¼ Y0 jxð Þn¼ Y0x
00 � cos 1=2npð Þ þ j Y0xn � sin 1=2npð Þ ð4Þ
where Y0 and n (0 B n B 1) are frequency independent
parameters. The condition n = 0 represents an ideal
resistor, n = 0.5 A Warburg impedance, and n = -1 an
inductor. Cdl is the interfacial double layer capacitance
(high frequency surface capacitance). The Warburg
impedance is usually associated with an electrochemical
process dominated by diffusion control [61, 62]. The
highest resistance of solution and constant phase elements
(Q1 = 6.85 lS 9 s–n and Q2 = 8.95 lS 9 s–n) was
obtained for NaClO4 electrolyte as Rs = 174.4 X as shown
Fig. 9 a Nyquist plot for P(2AET)/GCE obtained from ZSimpWin
programme. Inset equivalent circuit model of R(Q(R(Q(R(CR))))),
b bode magnitude and phase plot of P(2AET)/GCE, c admittance plot
of P(2AET)/GCE (electrochemically polymerization in 0.1 M
LiClO4/ACN at [2AET]0 = 1.5 mM)
Table 2 Impedance parameter
values extracted from
ZSimpWin programme to fit the
equivalent circuit model of
R(Q(R(Q(R(CR))))) at 0.1 M
solution of four different
electrolytes (LiClO4, NaClO4,
TBABF4 and TEABF4) in
solvent of ACN for P(2AET)
coated GCE
R(Q(R(Q(R(CR))))) Electrolytes
Circuit components LiClO4 NaClO4 TBABF4 TEABF4
Rs/X 110.2 174.4 147.8 90.9
Q1/Yo (lS 9 s–n) 5.23 6.05 3.24 4.08
n 0.54 0.71 0.65 0.52
R1/X 38.64 5.86 9 105 1.23 9 102 26.68
Q2/Yo (lS 9 s–n) 4.36 8.95 1.52 2.72
n 0.88 0.84 0.92 0.91
R2/X 8.25 9 105 1.07 9 106 168.9 186.5
Cdl/F 4.33 9 10-6 1.03 9 10-6 2.63 9 10-6 3.43 9 10-7
R3/X 1.09 9 106 3.46 9 106 1.58 9 106 2.68 9 106
v2 9.27 9 10-4 5.98 9 10-3 6.90 9 10-3 4.67 9 10-4
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in Table 2. The highest (Cdl = 4.33 9 10-6 F) was
obtained in the LiClO4 electrolyte. Circuit model results
are consistent with experimental results.
Conclusion
3-(2-Aminoethylthiophene) (2AET) monomer was electro-
coated on GCE in four different electrolytes of LiClO4,
NaClO4, TBABF4 and TEABF4/ACN by CV. The char-
acterizations of modified CFMEs were performed by
FTIR-ATR, SEM-EDX, and EIS methods. The highest low
frequency capacitance (CLF = 0.66 mF cm-2) for [2AET]0 =
1.5 mM, and double layer capacitance (~0.63 mF cm-2)
for [2AET]0 = 0.5, 1.0, 1.5 mM were obtained in the
electrolyte of LiClO4. Equivalent circuit model of
R(Q(R(Q(R(CR))))) was obtained a good agreement to fit
the experimental and theoretical data.
Acknowledgments Financial support for this work by the Research
Foundation of Namik Kemal University (Turkey) project number:
NKU.BAP.00.10.AR.11.01) is gratefully acknowledged.
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