Electrocatalytic measurement of H2O2 concentration using bis(N-2-methylphenyl alicyldenaminato)copper(II) spiked in a carbon paste electrode

Article abstract of DOI:10.1016/S1872-2067(12)60753-0

The electrochemical behavior of a bis(N-2-methylphenyl-salicyldenaminato) copper(II) complex spiked in a carbon paste electrode (BMPSCu-CPE) and its electrocatalytic reduction of H₂O₂ were examined using cyclic voltammetry, chronoamp

Full text of DOI:10.1016/S1872-2067(12)60753-0

Chinese Journal of Catalysis 35 (2014) 247–254
ava i l a b l e a t w w w. s c i e n c ed i r e c t . c o m
j o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e /c h n j c
Article
Electrocatalytic measurement of H2O2 concentration using
bis(N‐2‐methylphenyl‐salicyldenaminato)copper(II) spiked in a
carbon paste electrode
Hossein Khoshro, Hamid R. Zare*, Rasoul Vafazadeh
Department of Chemistry, Yazd University, Yazd, 89195‐741, Iran
A R T I C L E I N F O
A B S T R A C T
Article history:
The electrochemical behavior of a bis(N‐2‐methylphenyl‐salicyldenaminato)copper(II)
complex spiked in a carbon paste electrode (BMPSCu‐CPE) and its electrocatalytic reduc‐
tion of H2O2 were examined using cyclic voltammetry, chronoamperometry, and differen‐
tial pulse voltammetry. Cyclic voltammetry was used to study the redox properties of
BMPSCu‐CPE at various potential scan rates. The apparent charge transfer rate constant
and the transfer coefficient for the electron transfer between BMPSCu and the carbon
paste electrode (CPE) were 1.9 ± 0.1 s–1 and 0.43, respectively. BMPSCu‐CPE had excel‐
lent electrocatalytic activity for H2O2 reduction in 0.1 mol/L phosphate buffer solution
(pH 5.0), and it decreased the overpotential by 300 mV as compared to CPE alone. The
diffusion coefficient and kinetic parameters such as the heterogeneous catalytic electron
transfer rate constant and electron transfer coefficient for the reduction of H2O2 at the
BMPSCu‐CPE surface were also determined using electrochemical methods. Differential
pulse voltammetry showed two linear dynamic ranges of 1.0–10.0 and 10.0–300.0
μmol/L and a detection limit of 0.63 μmol/L H2O2. The BMPSCu‐CPE has excellent repro‐
ducibility and long term stability, and it was successfully applied for the determination of
H2O2 in two pharmaceutical samples: an antiseptic solution and a hair dying cream.
© 2014, Dalian Institute of Chemical Physics, Chinese Academy of Sciences.
Received 29 August 2013
Accepted 4 November 2013
Published 20 February 2014
Keywords:
Electrochemical behavior
Bis(N‐2‐methylphenyl‐salicyldenaminato)copper(II)
complex
Hydrogen peroxides
Electrocatalytic reduction
Published by Elsevier B.V. All rights reserved.
1. Introduction
centration has been widely investigated using techniques such
as titrimetry [18], spectrometry [19], chemiluminescence
Much research has been conducted in recent years on how
to measure H2O2 concentration present in samples in the areas
of environmental control, clinical diagnosis, the food, chemical
and pharmaceutical industries, and the biological and medical
sciences [1–8]. H2O2 is also used as an oxidant in many liq‐
uid‐based fuel cells [2–8], and it is present in a variety of com‐
mercial products such as cosmetics and pharmaceutical prod‐
ucts [9,10]. Furthermore, H2O2 has emerged as an important
byproduct of enzymatic reactions in the field of biosensing
[11–17]. The accurate and reliable determination of H2O2 con‐
[20,21], chromatography [22–24], and electrochemical meth‐
ods [10,25,26]. The electrochemical methods have been found
appropriate for H2O2 determination because of their simplicity,
efficiency, high sensitivity, relatively low cost, and ease of op‐
eration [27–29]. However, the direct electrochemical detection
of H2O2 at many bare electrodes is not good enough for analyt‐
ical applications. This is due to slow electrode kinetics and high
overpotential required for its redox reactions. So, redox medi‐
ators have been used to decrease the overpotential and in‐
crease the electron transfer kinetics. Different electron transfer
* Corresponding author. Tel: +98‐351‐8122669; Fax: +98‐351‐8210991; E‐mail: hrzare@yazd.ac.ir
DOI: 10.1016/S1872‐2067(12)60753‐0 | http://www.sciencedirect.com/science/journal/18722067 | Chin. J. Catal., Vol. 35, No. 2, February 2014

Hossein Khoshro et al. / Chinese Journal of Catalysis 35 (2014) 247–254
mediators such as methylene green [30], platinum and iridium
The pharmaceutical samples of an antiseptic solution and a hair
dye cream were purchased from Fuadara Company (Iran).
The BMPSCu (see Scheme 1) was synthesized in the labora‐
tory as reported in our previous work [47]. Briefly, the Schiff
base ligand was synthesized by the condensation reaction of
salicylaldehyde (10 mmol) and 2‐methylaniline (10 mmol).
Then it was treated in methanol (20 mL) at room temperature
for 30 min, and an orange powder was obtained with a yield of
72%. The powder was filtered off and recrystallized in diethyl
ether solution at room temperature [47]. To make BMPSCu, 2.5
mmol (0.499 g) of Cu(NO3)2·H2O was slowly added to 40.0 mL
of methanol solution containing 5.0 mmol of the Schiff base,
and the resulting solution was stirred for 1.0 h at room tem‐
perature. The brown precipitate obtained was collected by
filtering and washed with 10.0 mL of methanol. The Cu complex
was recrystallized from dichloromethane/acetone (1:1, v/v),
and brown plate‐like crystals were obtained with a yield of
40%. Anal. Calc. for C28H24CuN2O2: C 69.48, H 5.00, N 5.79;
Found: C 69.57, H 4.80, N 5.85%. IR (KBr, cm–1): υ(C=N) = 1607,
υ(C–O) = 1326. Electronic spectra in CHCl3: d–d, max (ε) 635
nm (148 mol–1 L cm–1).
[31–33], vanadium doped zirconia [34], iodine [35], and Prus‐
sian blue [36] cadmium sulfide nanoparticles [37] have been
used to improve the determination of H2O2.
Electrochemical reactions catalyzed by transition metal
complexes have received considerable attention in the past
several decades, and metal complexes are well recognized for
their excellent electrocatalytic properties [38,39]. The electro‐
chemical characteristics and electrocatalytic activity of Cu
complexes have been studied by several groups [40–42]. Wang
et al. [43] investigated the electrocatalytic activity of a new Cu
complex for the reduction of bromate, nitrite, and H2O2.
Marques et al. [44] studied the electrochemical reduction of O2
and H2O2 catalyzed by a Cu(II)‐2,4,6‐tris(2‐piridil)‐1,3,5‐tria‐
zine complex adsorbed on a graphite electrode. The overpoten‐
tial decrease of the H2O2 reduction at the carbon paste elec‐
trode (CPE) spiked with a bis(N‐2‐methylphenyl‐salicyldenam‐
inato)copper(II) complex (BMPSCu‐CPE) surface is comparable
to or more than those reported in the literature [43,44]. A CPE
spiked with different mediators has been widely used for the
electrocatalytic reaction of different analytes [45,46]. In this
study, we employed a BMPSCu‐CPE for the electrocatalytic
reduction of H2O2. Our findings indicated that this modified
electrode offered many advantages including good stability,
good repeatability, excellent reproducibility, high surface
charge transfer rate constant, low detection limit, and technical
simplicity in the electrocatalytic detection of H2O2. To evaluate
the utility of the modified electrode for analytical applications,
it was used for the voltammetric determination of H2O2 in two
pharmaceutical formulations.
2.2. Preparation of BMPSCu‐CPE
The carbon paste containing the modifier was prepared by
thoroughly hand‐mixing graphite powder (100.0 mg) and
BMPSCu (10.0 mg) in a mortar with a pestle. Paraffin oil was
added to the mixture, and they were mixed well to obtain a
uniform wetted carbon paste of the modifier, BMPSCu‐CP. To
fabricate a BMPSCu‐CP electrode (BMPSCu‐CPE), the paste was
inserted into the bottom of a glass tube (2 mm in diameter and
10 cm long). A copper wire was introduced into the opposite
side to establish electrical contact. The electrode surface was
smoothed using white paper. The modified electrode surface
can be easily and reproductively renewed by slightly polishing
it on a smooth paper. An unmodified CPE was prepared by
mixing graphite powder and paraffin to obtain a wetted paste.
Then it was fabricated as described above.
2. Experimental
2.1. Apparatus and chemicals
All the electrochemical experiments were carried out with
an EG&G PARSTAT 2273 equipped with a Power Suite soft‐
ware. A three‐electrode assembly in an electrochemical cell
containing a BMPSCu‐CPE as the working electrode, a Pt wire
as the counter electrode, and a Ag/AgCl/KCl (sat’d) as the ref‐
erence electrode was used for the experiments. All of the po‐
tentials were measured versus the Ag/AgCl/KCl (sat’d) elec‐
trode. The pH values were measured with a Metrohm model
691 pH/mV meter.
H2O2 (30%), graphite fine powder, and viscous paraffin
were obtained from Merck Company and used as received. All
the other chemicals, also purchased from Merck Company,
were of analytical reagent grades and were used without any
further purification. Doubly distilled water was used in the
experiments. The solutions were prepared just prior to use, and
all the experiments were carried out at the ambient tempera‐
ture of the laboratory (about 25 °C). All the test solutions were
deaerated by passing high purity N2 (99.999%) through them
for 30 min before the electrochemical experiments. A continu‐
ous flow of N2 was maintained in the sample solutions during
the experiments. The buffer solutions (0.1 mol/L) were made
up from H3PO4, and the pH was adjusted with 2.0 mol/L NaOH.
2.3. Pharmaceutical sample preparation
An antiseptic solution (0.5 mL, 0.882 mol/L) and a hair dye
cream (1.764 mol/L) were separately transferred to a flask and
diluted to volume of 100.0 mL with twice distilled water. 0.3
mL portion of each solution was diluted in a voltammetric cell
to 10.0 mL of a 0.1 mol/L phosphate buffer (pH 5.0), and the
differential pulse voltammograms were recorded.
CH3
O N
Cu
N O
H3C
Scheme 1. Structure of bis(N‐2‐methylphenyl‐salicyldenaminato)
copper(II) complex, BMPSCu.

Hossein Khoshro et al. / Chinese Journal of Catalysis 35 (2014) 247–254
scan rates. The redox couple which appeared in this figure was
(6)
(1)
attributed to the redox reaction of Cu(II)/Cu(I) of the BMPSCu
complex. The formal potential of this redox couple, obtained
from the equation E0'= Epa – α(Epa–Epc) [48] and using α = 0.43
(see below), was –10 mV and it was almost independent of the
potential scan rate in the range of 5–75 mV/s. The peak‐to‐
peak potential separation (∆Ep = Epa–Epa) at the potential scan
rate of 10 mV/s was 125 mV. However, at higher potential scan
rates, the separation between the peak potentials increased
with an increase in the scan rates. This result indicated that the
electrochemical process of the BMPSCu was quasi‐reversible,
and the rate of the redox process was controlled by charge
transfer kinetics. The plots of peak current versus potential
scan rates are shown in inset (a) of Fig. 2. The anodic and ca‐
thodic peak currents (Ip) were proportional to the potential
scan rate, suggesting that the redox process for BMPSCu‐CPE
was a surface‐confined process. The surface coverage of the
modified electrode was estimated by [49]:
12
0
-12
-0.4
-0.2
0.0
0.2
E (vs Ag/AgCl/KCl)/V
Fig. 1. Cyclic voltammograms of Cu‐CPE at various buffered pH at a
potential scan rate of 25 mV/s. Curves (1)–(6) correspond to pH of 2,
3, 4, 5, 6, and 7.
3. Results and discussion
Ip = n2F2AΓν/4RT
(1)
3.1. Electrochemical behavior of BMPSCu‐CPE
where n represents the number of electrons involved in the
electrochemical reaction, A is the surface area (0.0962 cm2) of
BMPSCu‐CPE, Γ is the surface coverage (mol/cm2), and the
other symbols have their usual meanings. From the slope of the
anodic and cathodic peak currents versus potential scan rate
(Fig. 2, inset (a)), the surface coverage of the BMPSCu complex
on the CPE surface was 2.5 × 10–9 mol/cm2 for n = 1. Insets (b)
and (c) of Fig. 2 show the variations in the anodic and cathodic
peak potentials (Epa and Epc) as a function of the potential
sweep rate. When the potential scan rate was increased, the
anodic peak potential shifted to the positive direction, but the
cathodic peak potential shifted to the negative direction. Figure
2 inset (c) shows that the peak potential separation (n∆Ep)
The electrochemical behavior of BMPSCu‐CPE was studied
using a cyclic voltammetry method in a phosphate buffer solu‐
tion (0.1 mol/L, pH = 2.0–7.0) at the potential scan rate of 25
mV/s (Fig. 1). The results indicated that the stability of the
modified electrode was pH dependent, and there was higher
stability at pH 5.0 as compared to other pH values. Therefore,
the electrochemical behavior and electrocatalytic activity of the
modified electrode were studied in a phosphate buffer solution
(0.1 mol/L, pH 5.0).
Figure 2 shows the cyclic voltammograms of BMPSCu‐CPE
in the potential range of 0.15 to –0.25 V at different potential
60
25
(a)
0.3
(b)
Epa
Ipa
y = 209.35x + 1.1788
R2 = 0.9957
0
0.0
40
20
0
Epc
y = -234.47x -1.5177
R2 = 0.9994
Ipc
-25
0.00
-0.3
0.05
0.10
-1.75
0.00
log (V/s)
0.5
/(V/s)
(c)
y = 0.0971x + 0.1339
R2 = 0.9942
(10)
(1)
Epa
Epc
0.0
y = -0.125x - 0.169
R2 = 0.9963
-0.5
-0.7
0.0
log (V/s)
0.7
-20
0.0
0.4
E (vs Ag/AgCl/KCl)/V
0.8
Fig. 2. Cyclic voltammograms of BMPSCu‐CPE in phosphate buffer solution (0.1 mol/L, pH 5.0) at various potential scan rates. (1)–(10) corre‐
spond to 5, 10, 15, 20, 25, 30, 35, 40, 50, and 75 mV/s potential scan rates. Insets: (a) Variation of peak current (Ip) vs potential scan rates (v); (b)
Variation of peak potential (Ep) vs logv; (c) Magnification of the plots of (b) for fast potential scan rates.

Hossein Khoshro et al. / Chinese Journal of Catalysis 35 (2014) 247–254
value was larger than 200 mV, and that the anodic and cathodic
for BMPSCu‐CPE, while no redox response was observed at the
unmodified CPE. The cyclic voltammetric response of the elec‐
trocatalytic reduction of 1.0 mmol/L of H2O2 at BMPSCu‐CPE
appeared at a potential of –100 mV (Fig. 3(4)) while at the un‐
modified CPE, a peak potential with a weak current was ob‐
served at 400 mV (Fig. 3(2)). Therefore, a significant decrease
of 300 mV was achieved in the reduction of the overvoltage of
H2O2. Also, the comparison of the voltammograms of (3) and
(4) in Fig. 3 showed that upon the addition of H2O2, the cathodic
current increased markedly while the corresponding anodic
current disappeared. This result showed that BMPSCu‐CPE had
good electrocatalytic activity for the reduction of H2O2. The
possible electrocatalytic reduction process of H2O2 at the modi‐
fied electrode surface can be described by the EqC'i mechanism
[43,53].
peak potentials were proportional to the logarithm of the po‐
tential scan rates higher than 400 mV/s. Under these condi‐
tions, the electron transfer coefficient (α) and the surface elec‐
tron transfer rate constant (ks) corresponding to electron
transfer between BMPSCu and the CPE can be determined from
the slopes of the plots in Fig. 2, inset (c), according to the Lavi‐
ron theory [50]. Based on the Laviron procedure, in the case of
nΔEp > 200 mV, it is possible to determine α from the slope of
Ep = f(logv). The graph Ep = f(logv) yielded two straight lines
with the slope 2.3RT/αanF for the anodic peak and –2.3RT/αcnF
for the cathodic peak. Figure 2 inset (c) shows that the slopes of
Epa and Epc versus logv were 0.097 and –0.125, respectively. So,
the estimated values for the kinetic parameters of αa (αa = 1–αc)
and αc (anodic and cathodic transfer coefficient) were 0.61 and
0.47. We accordingly used the value of 0.43 for αc (α) in subse‐
quent studies. Also, the following equation can be used to esti‐
mate the electron transfer rate constant (ks) between CPE and
BMPSCu:
BMPSCu(II)-CPE + e-
BMPSCu(I)-CPE
(Eq) (3)
2BMPSCu(I)-CPE + H2O2 + 2H+
2BMPSCu(II)-CPE + 2H2O
(C'i) (4)
logks = αlog(1–α) + (1–α)logα –
log(RT/nFv) – α(1–α)nF∆Ep/2.3RT
(2)
Figure 4 shows the cyclic voltammograms of BMPSCu‐CPE
In Eq. (2), v is the potential scan rate, and all the other sym‐
bols have their usual meanings. Based on ΔEp corresponding to
the different potential scan rates of 400–4000 mV/s, ks was
found to be 1.9 ± 0.1 s–1 for pH 5.0, which is in good agreement
with the value reported by Yu et al. [51], and is higher than
those reported by others [1,52].
0
250
(A)
40
20
0
(a)
(b)
-10
125
-20
0.0
3.2. Electrocatalytic reduction of H2O2 at BMPSCu‐CPE
0.1
1/2/V1/2 s1/2
0.2
0.000 0.015 0.030
/(V/s)
The potentials of the different electrodes for the electrocat‐
alytic reduction of H2O2 were obtained by the cyclic voltam‐
metric responses of an unmodified CPE and BMPSCu‐CPE in the
absence and presence of 1.0 mmol/L H2O2 solution. Figure 3
shows the cyclic voltammograms of the unmodified CPE and
BMPSCu‐CPE in 0.1 mol/L phosphate buffer (pH 5.0) solution
at the scan rate of 25 mV/s.
(1)
-20
(8)
-0.30
-0.05
0.20
E (vs Ag/AgCl/KCl)/V
As can be seen, there was a quasi‐reversible redox couple
1.0
0.7
0.4
(B)
(8)
(3)
(1)
0
(1)
(2)
-12
(4)
-0.034
-0.017
0.000
E (vs Ag/AgCl/KCl)/V
-24
-0.6
-0.3
0.0
0.3
Fig. 4. (A) Cyclic voltammograms of BMPSCu‐CPE in 0.1 mol/L phos‐
phate buffer solution (pH 5.0) containing 1.0 mmol/L H2O2 at different
potential scan rates. (1)–(8) correspond to 2, 4, 6, 8, 10, 15, 20, and 25
mV/s. Insets: (a) variation of the electrocatalytic peak current (Ip) vs
square root of potential scan rate (v1/2) and (b) variation of the poten‐
tial scan rate normalized current (Ipv–1/2) vs potential scan rate (v1/2).
(B) Tafel plots derived from the cyclic voltammograms recorded at (A).
E (vs Ag/AgCl/KCl)/V
Fig. 3. Cyclic voltammograms of an unmodified CPE in 0.1 mol/L
phosphate buffer solution (pH 5.0) at the potential scan rate of 25
mV/s in absence (1) and presence (2) of 1.0 mmol/L H2O2. (3) same
as (1) and (4) same as (2) for BMPSCu‐CPE.

Hossein Khoshro et al. / Chinese Journal of Catalysis 35 (2014) 247–254
in 0.1 mol/L phosphate buffer solution (pH 5.0) containing 1.0
3.3. Chronoamperometric studies
mmol/L of H2O2 at different potential scan rates. It can be noted
from Fig. 4 that with an increasing potential scan rate, the peak
potential for the electroreduction of H2O2 shifted to more nega‐
tive potentials, suggesting kinetic limitation in the reaction
between the redox active sites of the modified electrode and
H2O2. However, the catalytic peak current increased linearly
with the square root of the potential scan rate (Fig. 4, inset (a)),
suggesting that the reaction was diffusion limited at a sufficient
overpotential. Also, the plot of the scan rate normalized current
(Iv–1/2) versus the potential scan rate (Fig. 4, inset (b)) exhibit‐
ed a shape typical of a EqCi catalytic process. The number of
electrons participating in the reduction process of H2O2 at the
modified electrode surface (n) was found to be 1.8 (~ 2). This
calculation was done by using the slope of the straight line of Ip
versus v1/2 (Fig. 4, inset (a)). The following equation describes
the slope of the plot for a totally irreversible diffusion con‐
trolled process [54].
The diffusion coefficient of H2O2 in solution can be estimat‐
ed by a chronoamperometric experiment. For an electroactive
material with a diffusion coefficient D, the current response
under diffusion control is described by Cottrell’s equation [56]:
I = nFAD1/2Cbπ–1/2 –1/2
t
(8)
In this equation, I is the current controlled by the diffusion
of H2O2 from the bulk solution to the electrode/solution inter‐
face. Figure 5(a) shows the experimental plots of I versus t–1/2
with the best fits for the different concentrations of H2O2. The
plots were derived from the chronoamperogram data at BMP‐
SCu‐CPE and different H2O2 concentrations at a potential step
of –220 mV. As can be seen in Fig. 5(a), the plots of I versus t–1/2
were straight lines. The slopes of the resulting straight lines
were then plotted versus the H2O2 concentration (Fig. 5(b)).
The slope in Fig. 5(b) of 7.01 × 10–6 cm2/s was calculated for
the diffusion coefficient, D, of H2O2 under the working condi‐
tions. Although this value is in good agreement with the values
reported by others [57], it is higher than that reported by Yu et
al. [48] and Kumar et al. [58].
Slope = 3.01 × 105n [(1 – α)nα]1/2ACD1/2
(5)
where (1 – α)nα = 0.40 (as obtained below from the Tafel plot),
A, D, and C are the electrode area (cm2), diffusion coefficient
(cm2/s), and substrate concentration (mol/cm3), respectively.
For the case of low potential scan rates (v) and a large catalytic
rate constant (k'), Andrieux and Saveant [55] showed that Ip is
proportional to v1/2for a heterogeneous reaction, in accordance
with Eq. (6):
3.4. Differential pulse voltammetric (DVP) determination of
H2O2 at BMPSCu‐CPE
Figure 6(a) shows the DPV data obtained for the reduction
of different concentrations of H2O2 at the BMPSCu‐CPE surface.
The dependence of the electrocatalytic peak current, corrected
for any residual current of the modified electrode in the sup‐
Ip = 0.496nFADCbv1/2(nF/RT)1/2
(6)
where D and Cb are the diffusion coefficient (cm2/s) and the
bulk concentration (mol/cm3) of H2O2, respectively, and the
other symbols have their own usual meanings. Low values of k'
resulted in coefficient values lower than 0.496. For low poten‐
tial scan rates (6–25 mV/s), this constant was found to be 0.23
for BMPSCu‐CPE with a net surface area (A) of 0.0962 cm2, and
D = 7.01 × 10–6 cm2/s (obtained by chronoamperometry as
below) in the presence 1.0 mmol/L of H2O2. Using the approach
of Andrieux and Saveant [55] and using the data of Fig. 2 in
their paper [52], a value of k' = (7.4±2.9) × 10–4 cm/s was cal‐
culated.
In order to obtain information on the rate determining step,
the Tafel plots were drawn using the data from the rising part
of the cyclic voltammograms (known as the Tafel region) rec‐
orded at different potential scan rates (Fig. 4(B)). This part of
the voltammogram was affected by the electron transfer kinet‐
ics between H2O2 and BMPSCu‐CPE. These data can be used to
evaluate the kinetic parameters of H2O2 electrocatalytic reduc‐
tion at the modified electrode surface. Referring to Eq. (7) [56],
the charge transfer coefficient (α) of the electrode process can
be evaluated from the slope of the cathodic Tafel plot if the rate
25.0
(a)
(4)
y = 35.009x + 10.125
R2 = 0.9924
y = 29.186x + 6.6811
R2 = 0.9973
12.5
y = 24.912x + 5.9331
R2 = 0.999
(1)
y = 19.637x + 4.3763
R2 = 0.9994
0.0
0.00
0.15
0.30
t
1/2/s1/2
40
(b)
20
0
y = 27.741x + 14.096
R2 = 0.9958
determining step of the electrode process includes
one‐electron transfer, nα = 1.
a
Cathodic Tafel slope = −αnαF/2.3RT
(7)
0.4
0.8
Based on the above results and from the slopes of the Tafel
plots in Fig. 4(B), the cathodic charge transfer coefficient, αave
[H2O2] (mmol/L)
,
Fig. 5. (a) Plot of I vs t1/2 from chronoamperogram data recorded at
the BMPSCu‐CPE surface in 0.1 mol/L phosphate buffer solution (pH
5.0) at a potential step of −220 mV for different concentrations of
H2O2. Numbers of (1)−(4) correspond to 0.2, 0.4, 0.6, and 0.8 mmol/L.
(b) Plot of the slopes of the straight lines vs H2O2 concentration.
was evaluated as 0.60±0.03. The exchange current density, j0, is
accessible from the intercept of the Tafel plots [56]. The j0 of
H2O2 at the BMPSCu‐CPE surface was found to be 33.1±4.1
μA/cm2.

Hossein Khoshro et al. / Chinese Journal of Catalysis 35 (2014) 247–254
15
10
5
6
(a)
(b)
(17)
5
y = 0.142x + 4.108
R2 = 0.9961
4
0
6
12
[H2O2] (mol/L)
(c)
10.5
7.0
(1)
y = 0.018x + 5.31
R2 = 0.9969
0
-0.30
-0.07
0.16
0
160
[H2O2] (mol/L)
320
E (vs Ag/AgCl/KCl)/V
Fig. 6. (a) Differential pulse voltammograms of BMPSCu‐CPE in 0.1 mol/L phosphate buffer solution (pH 5.0) containing different concentrations of
H2O2. (1)–(17) correspond to 1.0–300.0 µmol/L H2O2. (b) and (c) show the plots of the electrocatalytic peak current as a function of H2O2 concen‐
tration for two concentration ranges of 1.0–10.0 and 10.0–300.0 µmol/L H2O2, respectively.
porting electrolyte, on the H2O2 concentration is shown in Fig.
6(b) and (c). They show clearly that the plot of the peak current
versus H2O2 concentration is made up of two linear segments
with different slopes of 0.142 and 0.018 μA μmol–1 L, corre‐
sponding to two different ranges of 1.0–10.0 and 10.0–300.0
μmol/L. A comparison of the sensitivities of the two linear
segments indicated a decrease of sensitivity in the second line‐
ar range of the calibration plot.
It is well known that when an analyte concentration in‐
creases in a solution, the thickness of the diffusion layer and
mass transfer limitation are reduced [56]. Therefore, it is logi‐
cal to conclude that under these conditions, the electron trans‐
fer kinetics between the analyte and the electrodeposited mod‐
ifier at the electrode surface is mainly responsible for the cur‐
rent limitation. In other words, the decrease of the sensitivity of
the calibration plot in the higher concentration range of H2O2
(Fig. 6(c)) was likely due to the electron transfer kinetic limita‐
tion between H2O2 and BMPSCu(I)‐CPE already shown in Eq.
(4). In Table 1, some of the analytical parameters obtained for
H2O2 determination at the modified electrode surface are com‐
pared with those previously reported by others [43,44,51,
58–60]. As can be seen, the linear range and the detection limit
has been improved in comparison with those previously re‐
ported for other modified electrodes.
3.5. Interference study
The selectivity and applicability of BMPSCu‐CPE for the de‐
termination of H2O2 in the presence of the usual interfering
species was evaluated by the investigation of the effect of some
common species that accompany H2O2 in real samples. This
study was done for a phosphate buffer solution (0.1 mol/L, pH
5.0) containing 100.0 μmol/L of H2O2. The tolerance limit was
defined as the molar ratio of the interference species to H2O2
that caused a relative error of 5% for H2O2 determination. The
results presented in Table 2 indicated that the nitrite ion and
L‐cysteine have serious interfering effects on H2O2 determina‐
tion.
3.6. Determination of H2O2 in real samples
To confirm the usefulness of BMPSCu‐CPE, the applicability
and reliability of this modified electrode were tested for the
determination of H2O2 in two pharmaceutical samples of an
antiseptic solution and a hair dye cream. The pharmaceutical
samples were prepared as described in Section 2.3. The meas‐
urements were performed using the calibration curve shown in
Fig. 6(b). Table 3 presents the nominal values on the label for
these products, and the values obtained using the differential
Table 1
Comparison of some parameters of the electrocatalytic detection of H2O2 at different modified electrode surfaces.
Modifier
Method
pH
Linear range (µmol/L) Detection limit (µmol/L)
Ref.
[Cu2(Dpq)2(Ac)2(H2O)2] (ClO4)2·H2O
[Cu(II)(TPT)]2+
CV
CV
2.0
5.3
2000–20000
—
—
—
[43]
[44]
Gallium hexacyanoferrate
poly(p‐aminobenzene sulfonic acid)
MnO2
PNMA (SDS)/Co
Bis(N‐2‐methylphenyl‐salicyldenaminato)copper(II)
Amperometry
Amperometry
Amperometry
DPV
6.8
7.0
7.4
13.0
5.0
4.9–400.0
50–550
100–690
1.0
10
2.0
3.0
0.63
[51]
[58]
[59]
[60]
5–48
DPV
1.0–10.0, 10.0–300.0
this work

Hossein Khoshro et al. / Chinese Journal of Catalysis 35 (2014) 247–254
SCu) modified carbon paste electrode (BMPSCu‐CPE) was pre‐
Table 2
pared and tested for its electrocatalytic reduction of H2O2. The
kinetic parameters of the electron transfer rate constant, ks,
and the transfer coefficient, α, corresponding to the redox reac‐
tion of BMPSCu were obtained. The electrocatalytic reduction
of H2O2 was significantly improved at the BMPSCu‐CPE surface
in comparison to a bare CPE. The heterogeneous catalytic elec‐
tron transfer rate constant, k', and α were also determined for
the reduction of H2O2 at the modified electrode surface using
cyclic voltammetry. Differential pulse voltammetric measure‐
ments exhibited two linear ranges of 1.0–10.0 and 10.0–300.0
μmol/L and a detection limit of 0.63 μmol/L for H2O2. The
modified electrode was successfully applied to determine H2O2
in two pharmaceutical samples. A low detection limit, excellent
catalytic activity, good repeatability for H2O2 determination,
simplicity of preparation, good reproducibility, and low cost of
the modified electrode are the important advantages of BMP‐
SCu‐CPE.
Interference studies of some species on the determination of 100.0
μmol/L of H2O2 (in 0.1 mol/L phosphate buffer solution, pH 5.0) at the
BMPSCu‐CPE surface using differential pulse voltammetry.
Interference species
Ascorbic acid
Uric acid
Dopamine
Glucose
Molar ratio (Interference/H2O2)
10:1
20:1
20:1
20:1
1:2
100:1
100:1
5:1
L‐Cysteine
NaCl
Na2SO4
Na2NO2
Table 3
Determination of hydrogen peroxide in two pharmaceutical samples of
antiseptic solution and a hair dye cream using BMPSCu‐CPE (DPV
method) and the titration method.
Labeled value Our method Titration method
Sample
(mol/L)
0.882
(mol/L)
0.864 ± 0.022
(n = 3)
1.717 ± 0.085
(n = 3)
(mol/L)
0.860 ± 0.04
(n = 3)
1.730 ± 0.07
(n = 3)
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4. Conclusions
A bis(N‐2methylphenyl‐salicyldenaminato)copper(II) (BMP‐

Hossein Khoshro et al. / Chinese Journal of Catalysis 35 (2014) 247–254
Graphical Abstract
Chin. J. Catal., 2014, 35: 247–254 doi: 10.1016/S1872‐2067(12)6753‐0
Electrocatalytic measurement of H2O2 concentration using
bis(N‐2‐methylphenyl‐salicyldenaminato)copper(II) spiked in a
carbon paste electrode
10
-2
BMPSCu-CPE in
absence of H2O2
Unmodified CPE in
absence of H2O2
Hossein Khoshro, Hamid R. Zare*, Rasoul Vafazadeh
Yazd University, Iran
Unmodified CPE in presence
of 1.0 mmol/L H2O2
-14
-26
BMPSCu-CPE in presence of
1.0 mmol/L H2O2
-0.6
-0.3
0
0.3
A Cu(II) complex (BMPSCu) used for the electrocatalytic reduction of
H2O2 gave excellent activity. It successfully detected H2O2 in two phar‐
maceutical samples.
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