Selective electrochemical determination of trace level copper using a salicylaldehyde azine/MWCNTs/Nafion modified pyrolytic graphite electrode by the anodic stripping voltammetric method

Article abstract of DOI:10.1039/c4ra12342e

A novel Cu²⁺ electrochemical sensor based on a salicylaldehyde azine/MWCNTs/Nafion-modified pyrolytic graphite electrode was prepared for anodic stripping analysis of Cu²⁺. Salicylaldehyde azine was synthesized and then used for the selective determination of the heavy metal pollutant Cu²⁺ due to its azine structure, which gave selective complexing ability toward Cu²⁺. The use of MWCNTs with their strong adsorption ability could greatly enhance the sensitivity. Nafion, a proton-exchange polymer, was used as the conductive matrix in which the salicylaldehyde azine and MWCNTs could be strongly fixed to the substrate electrode surface. The as-prepared electrochemical sensor showed remarkably enhanced selectivity and sensitivity towards Cu²⁺. The response current of the sensor was linear with Cu²⁺ concentration ranging from 5 to 300 nM under 15 min accumulation at open-circuit potential, with a very low detection limitation of about 1 nM. The hybrid functionalized electrode also exhibited good selectivity to avoid the interference of other heavy metal ions like Cd²⁺, Pb²⁺ and Hg²⁺ in the mixture solution together with Cu²⁺. Real application towards environmental sample analysis confirmed that the modified electrode could be applied for the selective determination of trace levels of Cu²⁺ in the Yellow River.

Full text of DOI:10.1039/c4ra12342e

RSC Advances
View Article Online
View Journal | View Issue
PAPER
Selective electrochemical determination of trace
level copper using a salicylaldehyde azine/
MWCNTs/Nafion modified pyrolytic graphite
electrode by the anodic stripping voltammetric
method†
Cite this: RSC Adv., 2015, 5, 3232
a
a
a
Yuan Liao,ab Qian Li, Ying Yue and Shijun Shao
*
A novel Cu2+ electrochemical sensor based on a salicylaldehyde azine/MWCNTs/Nafion-modified pyrolytic
graphite electrode was prepared for anodic stripping analysis of Cu2+. Salicylaldehyde azine was
synthesized and then used for the selective determination of the heavy metal pollutant Cu2+ due to its
azine structure, which gave selective complexing ability toward Cu2+. The use of MWCNTs with their
strong adsorption ability could greatly enhance the sensitivity. Nafion, a proton-exchange polymer, was
used as the conductive matrix in which the salicylaldehyde azine and MWCNTs could be strongly fixed to
the substrate electrode surface. The as-prepared electrochemical sensor showed remarkably enhanced
selectivity and sensitivity towards Cu2+. The response current of the sensor was linear with Cu2+
concentration ranging from 5 to 300 nM under 15 min accumulation at open-circuit potential, with a
very low detection limitation of about 1 nM. The hybrid functionalized electrode also exhibited good
selectivity to avoid the interference of other heavy metal ions like Cd2+, Pb2+ and Hg2+ in the mixture
solution together with Cu2+. Real application towards environmental sample analysis confirmed that the
modified electrode could be applied for the selective determination of trace levels of Cu2+ in the Yellow
River.
Received 14th October 2014
Accepted 3rd December 2014
DOI: 10.1039/c4ra12342e
www.rsc.org/advances
There are various techniques which have been used for the
determination of copper, such as uorescence,7 atomic
absorption spectroscopy,8,9 and inductively coupled plasma-
1. Introduction
The contamination of natural water by heavy metals is a serious
problem in the biosystem since heavy metals can cause many
disorders in the plant and animal kingdoms and tend to accu-
mulate through food chains.1,2 The copper ion (Cu2+) is an
essential heavy metal in the human body and plays an impor-
tant role in various physiological processes.3 Excess intake of
copper from polluted water and copper-rich food has frequently
occurred in recent years.4 Some serious diseases, such as
anemia, Menkes disease and Wilson’s disease, are associated
with an abnormal level of copper in the human body.5,6 Copper-
containing waste water indiscriminately pumped into rivers
during industrial production is still a serious global problem.
Thus, the monitoring of Cu2+ in environmental samples has
become essential.
optical emission spectroscopy.10 In comparison with other
methods, an electrochemical method has more attractive
features including simplicity, robustness and inexpensive-
ness.11 In the past, mercury based electrodes, chemically
modied electrodes based on gold coated diamond12–14 and
boron-doped diamond electrodes15 have been used for trace
heavy metals detection. Traditional methods also have some
disadvantages like toxicity, low chemical stability and inconve-
nience, and new electrode materials for trace heavy metals
detection are highly sought.16
Recently, the use of chemically modied electrodes (CME)
has been very common for the determination of several metallic
species, and the employment of this method could not only
enhance selectivity for the analyte but also improve detection
limits.17–19 The choice of modier could confer special charac-
teristics to the electrode surface. Electrodes modied with
synthesis receptors have been used for heavy metal detection,
where the receptors extracted particular metal ions by
complexation in the analysis.20–22 In the literature, various
receptors such as crown ethers,23 iminodiacetic acid,24 di-(2-
imino-cyclopentylidine mercaptomethyl) disulde,25 2,2-
aKey Laboratory of Chemistry of Northwestern Plant Resources of CAS and Key
Laboratory for Natural Medicine of Gansu Province, Lanzhou Institute of Chemical
Physics, Chinese Academy of Sciences, Lanzhou 730000, P. R. China. E-mail:
sjshao@licp.cas.cn; Fax: +86-931-8277088; Tel: +86-931-4968209
bUniversity of Chinese Academy of Sciences, Beijing 100039, P. R. China
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c4ra12342e
3232 | RSC Adv., 2015, 5, 3232–3238
This journal is © The Royal Society of Chemistry 2015

View Article Online
Paper
RSC Advances
biquinoline-Naon,26 and 1,2-bismethyl (2-aminocyclopentene- overnight. Aer completion of the reaction the obtained yellow
carbodithioate) ethane27 have been used for the determination precipitate was ltered and washed several times with cold
of metal ions by using CMEs. Though these receptors were ethanol with a yield of 85%. EI-MS: (M + H) 241.2. 1H NMR (400
known to exhibit higher selectivity, their exploitation in elec- Hz, DMSO-d6), d: 11.122 (s, 2H), 8.999 (s, 2H), 7.676–7.699 (m,
troanalysis areas was very limited owing to their non-conductive 2H), 7.372–7.414 (m, 2H), 6.943–6.982 (m, 4H).
properties.
Therefore, it is necessary to improve the matrix conductivity
when a receptor is employed in an electrochemical sensor.
Nanoscale materials, such as metal nanoparticles, carbon
materials, and mesoporous silica, exhibit unique chemical,
physical and electronic properties and thus have been applied
to fabricate novel modied electrodes for heavy metal ions
sensing.28–35
2.3 Preparation of the electrode
The modied electrodes were prepared by a casting method.
Prior to the surface coating, the pyrolytic graphite electrode
(PGE) was carefully polished with 1.0, 0.3, and 0.05 mm alumina
powders in series, and then treated with 50% nitric acid,
ethanol and water in an ultrasonic bath, respectively. The
original 5% w/w Naon solution was diluted to 0.5% w/w
solution with N,N-dimethylformamide (DMF). Then 1 mg of
MWCNTs and 1 mg of SA were added into the above solution
and sonicated for 20–30 min to form a homogeneous suspen-
sion. Finally, 5 mL SA/MWCNTs/Naon suspension was casted
on the pretreated PGE surface and dried under an infrared
lamp. For comparison, Naon/PGE, SA/Naon/PGE, MWCNTs/
Naon/PGE and SA/MWCNTs/Naon/PGE were prepared with
a similar method.
Herein we report a new method for the synthesis, the char-
acterization, and the metal recognition properties of salicy-
laldehyde
azine
(SA)
(2,20-(1E,10E)-hydrazine-1,2-
diylidenebis(methan-1-yl-1-ylidene) diphenol). In this work, a
receptor SA has been combined with MWCNTs as a novel
modier for selective determination of heavy metal copper
using differential pulse anodic stripping voltammetry (DPASV).
The selective complexing ability of SA and the electrical
conductivity of MWCNTs synergistically improved the electro-
chemical performance towards Cu2+ sensing. Naon,
a
2.4 Electrochemical measurements
sulfonated cation-exchange polymer, supplied good stability of
the functionalized hybrid electrode. It has been conrmed that
such a fabricated SA/MWCNTs/Naon hybrid modied PGE
could remarkably enhance the sensitivity and selectivity for
0.1 M PBS at pH 7.0 was used as the supporting electrolyte. The
SA/MWCNTs/Naon/PGE at open-circuit potential was
immersed into a buffer solution containing Cu2+ or other ions
for 15 min without applying any potential and stirring during
the accumulation period. As a comparison to the open-circuit
accumulation, electroaccumulation was performed by
applying a potential at ꢀ1.2 V for 15 min in a solution con-
taining Cu2+ or other ions. Subsequently, the electrode was
rinsed thoroughly with deionized water and transferred to the
fresh supporting electrolyte, which had been deoxygenated by
nitrogen bubbling for 30 min, while a potential of ꢀ0.6 V was
applied to the electrode for about 30 s to reduce Cu2+. Using
differential pulse anodic stripping voltammetry, quantitative
determinations of Cu2+ were performed at optimized condi-
tions: an amplitude of 0.05; a pulse width of 0.05 s; a sampling
width of 0.0167 s; a pulse period of 0.2 s; a quiet time of 2 s. Aer
each measurement, the modied electrode was regenerated by
applying 0.3 V for 200 s in fresh supporting electrolyte to remove
the previous residual copper from the electrode surface.
stripping measurements of Cu2+
.
2. Experimental
2.1 Apparatus and chemicals
The electrochemical measurements were carried out on a
CHI660C electrochemical workstation (CHI Instrument,
Shanghai, China). All measurements were performed in a
conventional three-electrode cell; an unmodied PGE (Tianjin
Aidahengsheng Technology Co., China) or modied PGE, a
saturated calomel electrode (SCE) and a platinum wire were
used as the working electrode, reference electrode, and counter
electrode, respectively. The morphology of the SA/MWCNTs/
Naon/PGE was determined with a JEOL 2010 TEM (JEOL,
Japan) equipped with a LaB6 lament at 200 kV. UV-vis spectra
were recorded on a Perkin Elmer Lambda 35 UV-vis Spectro-
photometer with a quartz cuvette (pathlength ¼ 1 cm).
All reagents were of analytical grade and used as received. 0.1
M phosphate buffer solution (PBS) at pH 7.0 was prepared from
NaH2PO4 and Na2HPO4 and the pH value was adjusted with 1 M
H2SO4 or NaOH solution. Naon was obtained from Aldrich.
Stock solutions of Cu2+, Cd2+, Pb2+ and Hg2+ were prepared from
their nitrate salts in deionised water. Multi-wall carbon nano-
tubes were synthesized according to the literature.36
3. Results and discussion
3.1 The selective binding properties of SA towards metal
ions
Based on the outstanding ability to selectively coordinate with
metal ions, bisazine-type receptors have been used as iono-
phore molecules for ion-selective electrodes and other applica-
tions.37–40 In this work, salicylaldehyde azine (SA) was
synthesized by an easy and effective method (ESI, Fig. S1†). The
metal ion binding properties of receptor SA have been rstly
2.2 Synthesis of SA
1.22 g salicylaldehyde was dissolved in 50 mL ethanol and 0.25 studied by using UV-vis spectroscopic techniques. SA itself
mL of hydrazine hydrate (99%) was added at room temperature. displayed two strong absorption bands at 290 and 350 nm in
The reaction mixture was stirred at room temperature CH3CN–H2O (1 : 1, v/v) mixture at neutral pH 7 buffered with
This journal is © The Royal Society of Chemistry 2015
RSC Adv., 2015, 5, 3232–3238 | 3233

View Article Online
RSC Advances
Paper
3.2 Characterization of SA/MWCNTs/Naon composite lm
Fig. 2 shows scanning electron microscope (SEM) images of
MWCNTs/Naon and SA/MWCNTs/Naon composite lms
coated on a PGE. It can be observed that the MWCNTs/Naon
composite lm was homogeneously casted on the electrode
surface (Fig. 2a). This surface morphology gave an large acces-
sible surface area. When SA was introduced into the MWCNTs/
Naon composite, the homogeneous distribution of MWCNTs
on the electrode surface was not affected (Fig. 2b). However, the
prole of the MWCNTs became rough and the conductivity
decreased because the SA and MWCNTs were miscible
throughout the matrix. This result was similar to a former
report.23 Furthermore, the MWCNTs formed a network on the
electrode and could be more effective for electron transfer,
increasing the sensitivity of the sensors.
Fig. 1 Absorption spectra of SA (2.0 ꢁ 10ꢀ5 M) in CH3CN–H2O (1 : 1,
v/v) buffer solution upon addition of Cu2+ (0–20 equiv); inset: the
color change of the mixed solution of SA (2 ꢁ 10ꢀ5 M) upon addition of
1 equiv of Cu2+ in CH3CN–H2O (1 : 1, v/v) buffer solution.
3.3 Electrochemical behavior of Cu2+ at SA/MWCNTs/
Naon/PGE
The combination of accumulation and reduction prior to the
actual stripping detection process can enhance both the sensi-
tivity and the selectivity of the analysis of metal ions.41 For this
work, the structural features of SA facilitated the formation of a
SA$Cu2+ complex in the course of open-circuit accumulation.
The complex Cu2+ could be further reduced to Cu0, which was
deposited on the modied electrode under cathodic potentio-
static conditions for a dened time period. Finally, the depos-
ited Cu0 was stripped off the electrode and the stripping current
could be measured. A diagrammical illustration is depicted in
Scheme 1.
The typical cyclic voltammetric behaviour of SA/MWCNTs/
Naon/PGE in 0.1 M PBS is shown in Fig. 3. Compared with
the cyclic voltammogram of the electrode in pure PBS (dotted
line), a well-dened anodic voltammetric peak at ꢀ0.1 V,
attributed to the oxidation of metallic copper, can be obtained
aer the accumulation of Cu2+ (solid line).
HEPES–NaOH. In the presence of various cations such as Fe3+
,
Mn2+, Zn2+, Cd2+, Pb2+, Cu2+, Co2+, Ni2+, Ag+, Mg2+, Hg2+, Fe2+,
Na+, K+ and Ca2+ (all as their nitrate salts), only Cu2+ remarkably
changed the absorption spectrum of SA, whereas the other
cations tested induced negligible responses (ESI, Fig. S2†).
Upon addition of Cu2+ (0–20 equiv) to a solution of SA (2.0 ꢁ
10ꢀ5 M), as shown in Fig. 1, the absorption band of SA at 290 nm
gradually decreased along with a slight blue shi, and the
absorption band at 350 nm gradually disappeared while a new
red-shi absorption band centered at 405 nm appeared, which
was responsible for the mixed solution color change from
colorless to yellow-green (inset of Fig. 1). During the titration of
Cu2+ with the solution of SA, a clear isosbestic point at 380 nm
was observed, indicating the existence of a coordination equi-
librium between several structures. The ESI-MS analysis of the
interaction system of SA with Cu2+ exhibited one main peak at
m/z ¼ 304.00, assigned to the SA$Cu2+ complex (m/z calc. ¼
304.02).
To clarify the function of each component in the electrode
coating matrix, further investigation using differential pulse
anodic stripping voltammetry was carried out under the same
experimental conditions. Fig. 4 depicts the DPASV performance
of 5.0 mM Cu2+ in 0.1 M PBS (pH 7.0) for various modied PGEs.
No peaks were observed for the bare and Naon lm modied
electrodes aer accumulation at open-circuit potential for 15
min (Fig. 4a and b). A weak stripping peak was observed for SA/
Naon/PGE (Fig. 4c) due to the formation of the SA$Cu2+
complex on the modied electrode surface. Compared with SA/
Naon/PGE, a larger stripping peak at ꢀ0.17 V was observed for
MWCNTs/Naon/PGE (Fig. 4d), indicating that MWCNTs with a
large surface area could provide multiadsorbing sites and
increase the stripping currents. Further, the highest peak at
ꢀ0.15 V was found for SA/MWCNTs/Naon/PGE under the same
conditions (Fig. 4e), and the current response observed for SA/
MWCNTs/Naon/PGE was improved by nearly two times
compared to MWCNTs/Naon/PGE. The most probable reason
is that the MWCNTs can improve the accumulation capacity of
the modied electrode, and SA is capable of forming a strong
The above results indicate the highly selective metal ion
binding properties of SA, which can be used as a colorimetric
probe for the selective detection of Cu2+ in aqueous buffer
media. Based on the selective complexing ability of SA towards
Cu2+, SA-modied pyrolytic graphite electrodes were further
constructed for the electrochemical determination of Cu2+.
Fig. 2 SEM images of the electrode surfaces prepared with different
modifiers: (a) Nafion/MWCNTs/PGE and (b) SA/MWCNTs/Nafion/PGE. complex with Cu2+. The combination of MWCNTs with SA on
3234 | RSC Adv., 2015, 5, 3232–3238
This journal is © The Royal Society of Chemistry 2015

View Article Online
Paper
RSC Advances
Scheme 1 Schematic illustration of Cu2+ detection using a SA/MWCNTs/Nafion modifier.
for subsequent measurements. Furthermore, the effect of
accumulation time on peak current is illustrated in Fig. 5b. The
peak current increased rapidly with increasing accumulation
time from 5 min to 15 min. Further increasing the accumula-
tion time, there was a gradual increase in the current response.
A similar process was observed in the inuence of reduction
time on peak current (Fig. 5c). The current response increased
sharply with increasing the reduction time from 30 s to 120 s,
and then increased slightly from 120 s to 300 s. Based on the
sensitivity and short analysis time, 15 min accumulation time
Fig. 3 Cyclic voltammograms of the SA/MWCNTs/Nafion/PGE in 0.1
M pH 7.0 PBS with (solid line) and without (dotted line) open-circuit 15
min accumulation. Accumulation solution: PBS containing 5.0 mM
Cu2+. Scan rate: 100 mV sꢀ1. Reduction potential ꢀ0.6 V for 120 s.
Naon/PGE could synergistically enhance the accumulation of
Cu2+ from the sample solution to the modied electrode surface
and result in the signicant increase of the stripping peak
current.
3.4 Optimization of experimental parameters
Fig. 5a shows the effect of the pH of the supporting electrolyte
on the Cu2+ differential pulse anodic stripping peak current at
SA/MWCNTs/Naon/PGE. The peak current increased notably
with the pH from 6.0 to 7.0, and then decreased from 7.0 to 8.0,
which is due to SA instability at low pH values and the precip-
Fig. 4 Differential pulse anodic stripping voltammetry of 5.0 mM Cu2+
in 0.1 M PBS pH 7.0: (a) bare PGE electrode; (b) Nafion/PGE; (c) SA/
Nafion/PGE; (d) MWCNTs/Nafion/PGE; (e) SA/MWCNTs/Nafion/PGE.
Amplitude of 0.05 V; pulse width of 0.05 s; pulse period of 0.2 s; quiet
itation of Cu2+ at high pH values. Therefore, pH 7.0 was selected time of 2 s.
This journal is © The Royal Society of Chemistry 2015
RSC Adv., 2015, 5, 3232–3238 | 3235

View Article Online
RSC Advances
Paper
Fig. 5 Differential pulse anodic stripping voltammetry of 5.0 mM Cu2+ in 0.1 M PBS pH 7.0: (a) effect of pH; (b) effect of accumulation time; (c)
effect of reduction time; (d) effect of reduction potential. Amplitude of 0.05 V; pulse width of 0.05 s; pulse period of 0.2 s; quiet time of 2 s.
3.5 Determination of Cu2+ at SA/MWCNTs/Naon/PGE
Fig. 6 shows the DPASV of varying concentrations of Cu2+ in 0.1
M PBS for SA/MWCNTs/Naon/PGE with an open-circuit accu-
mulation of 15 min. The stripping peak current increased
linearly with Cu2+ concentration ranging from 5.0 nM to 300
nM. The correlation coefficient was found to be 0.997 and the
calculated limit of detection for 15 min of open-circuit accu-
mulation was 1.0 nM. The performance characteristics of the
proposed electrode for Cu2+ electroanalysis was comparable or
superior to some reported chemically modied electrodes, as
summarized in Table 1. The relative standard deviation of 10
determinations for 40 nM is 0.91%, indicating good reproduc-
ibility of the modied electrode. The current response for SA/
MWCNTs/Naon/PGE had no signicant change aer its prep-
aration for three weeks under ambient conditions, showing
Fig. 6 Differential pulse anodic stripping voltammetry of 5.0–300 nM
high stability of SA/MWCNTs/Naon/PGE.
Cu2+ in 0.1 M PBS pH 7.0 for SA/MWCNTs/Nafion/PGE. Amplitude of
0.05 V; pulse width of 0.05 s; pulse period of 0.2 s; quiet time of 2 s.
3.6 Interference
The stripping analysis of Cu2+ can be affected by interferences
and 120 s reduction time were chosen in subsequent experi-
ments. Finally, the effect of reduction potential was investigated
in the presence of other heavy metal ions such as Cd2+, Pb2+ and
Hg2+, which generate large errors in stripping analysis, espe-
in the potential range of ꢀ0.8 V to ꢀ0.4 V, as depicted in Fig. 5d.
cially in the presence of higher concentrations (>0.1 mM).41 In
The peak current increased with the reduction potential from
this work, Cd2+, Pb2+ and Hg2+ were selected to evaluate the anti-
ꢀ0.8 V to ꢀ0.6 V, and decreased from ꢀ0.6 V to ꢀ0.4 V, which
interference of the modied electrode. Fig. 7 shows the differ-
ential pulse stripping voltammograms obtained for the SA/
might be attributed to substantial hydrogen evolution at the
modied PGE surface. Hence, a potential of ꢀ0.6 V was chosen
MWCNTs/Naon/PGE using electroaccumulation and open-
for further experiments.
circuit accumulation for Cu2+ in the presence of a 10-fold
excess of Cd2+, Pb2+, Hg2+, respectively. Four peaks were
3236 | RSC Adv., 2015, 5, 3232–3238
This journal is © The Royal Society of Chemistry 2015

View Article Online
Paper
RSC Advances
Table 1 Comparison of various modified electrodes for the detection of Cu2+
Modier
Method
Linear range (M)
Limit of detection (M)
Reference
2-Aminothiazole
Natural zeolite
PCHA
Mercury lm
Calix[4]arene
Salicylidine-functionalized polysiloxane
BHAB
SA/MWCNTs/Naon
DPASV
DPASV
DPASV
DPASV
7.5 ꢁ 10ꢀ8–2.5 ꢁ 10ꢀ6
5.0 ꢁ 10ꢀ8–5.0 ꢁ 10ꢀ6
1.0 ꢁ 10ꢀ8–1.0 ꢁ 10ꢀ6
1.0 ꢁ 10ꢀ5–5.0 ꢁ 10ꢀ9
5.0 ꢁ 10ꢀ8–1.6 ꢁ 10ꢀ6
2.3 ꢁ 10ꢀ7–1.0 ꢁ 10ꢀ3
5.0 ꢁ 10ꢀ8–1.0 ꢁ 10ꢀ2
5.0 ꢁ 10ꢀ9–3.0 ꢁ 10ꢀ7
3.1 ꢁ 10ꢀ8
1.5 ꢁ 10ꢀ8
5.0 ꢁ 10ꢀ10
1.0 ꢁ 10ꢀ9
1.1 ꢁ 10ꢀ8
2.7 ꢁ 10ꢀ8
3.0 ꢁ 10ꢀ8
1.0 ꢁ 10ꢀ9
42
43
44
45
46
47
48
DPASV
Potentiometry
Potentiometry
DPASV
This work
observed for the SA/MWCNTs/Naon/PGE using open-circuit
accumulation was less than at the same electrode by electro-
deposition, which might be due to less Cu2+ adsorption on the
electrode surface during the open-circuit accumulation.
3.7 Application to real sample analysis
In order to test its accuracy in practical analysis, SA/MWCNTs/
Naon/PGE was used for the determination of Cu2+ in the
Yellow River. Yellow River samples were ltered through a
standard 0.45 mm lter and analyzed using the standard addi-
tion method. The results are shown in Table 2. Thus the SA/
MWCNTs/Naon/PGE has a great potential for real sample
analysis with a high accuracy and good reliability.
Fig. 7 Differential pulse anodic stripping voltammetry obtained for SA/
MWCNTs/Nafion/PGE in 0.1 M PBS pH 7.0 containing 0.5 mM Cu2+
+
5.0 mM Pb2+ + 5.0 mM Hg2+ + 5.0 mM Cd2+. Solid line: open-circuit 15
min accumulation. Dotted line: electroaccumulation at ꢀ1.2 V for 15
min. Amplitude of 0.05 V; pulse width of 0.05 s; pulse period of 0.2 s;
quiet time of 2 s.
4. Conclusion
In this work, a novel chemically modied pyrolytic graphite
electrode for selective determination of Cu2+ has been devel-
oped. Due to the combination of the selective complexing ability
of SA with Cu2+ and the good conductivity of MWCNTs, SA/
MWCNTs/Naon/PGE has shown a remarkably enhanced
sensitivity and selectivity for Cu2+ determination in the pres-
ence of other metal ions. The as-fabricated electrochemical
sensor was successfully applied in determining Cu2+ in real
water samples with satisfactory results. In addition, the present
results suggest that such a designing scheme could provide an
excellent platform for electroanalysis and has potential for the
fabrication of chemical sensors for heavy metals.
Table 2 Recovery study of Cu2+ in Yellow River
Added (Cu2+ nM)
Found (nM)
Recovery (%)
40
60
80
41.7 ꢂ 1.7
59.3 ꢂ 2.1
81.0 ꢂ 1.4
104
98.8
101
observed at potentials of ꢀ0.82, ꢀ0.61, ꢀ0.16 and 0.72 V by
using 15 min electroaccumulation in the mixture solution,
which were assigned to the stripping peaks of Cd2+, Pb2+, Cu2+
and Hg2+, respectively. This showed that the interfering metal
ions were electrodeposited together with the target ion at the
modied electrode during the electroaccumulation procedure,
which resulted in poor selectivity. This phenomenon was
Acknowledgements
This work was supported by the National Natural Science
Foundation of China (20972170 and 21275150) and the Funds
for Distinguished Young Scientists of Gansu (1210RJDA013).
similar to
a
former report.41 Compared to the electro-
accumulation, only one stripping peak of Cu2+ was obtained at
ꢀ0.16 V by using 15 min open-circuit accumulation. This might
be attributed to SA with an outstanding ability to selectively
coordinate with Cu2+. These results showed that the modied
electrode exhibited high selectivity and sensitivity for Cu2+ over
other interfering or competing metal ions using the open-
circuit accumulation procedure. The current peak of Cu2+
References
1 C. Tu, Y. Shao, N. Gan, D. Xu and Z. J. Guo, Inorg. Chem.,
2004, 43, 4761–4766.
2 E. L. S. Wong, E. Chow and J. J. Gooding, Electrochem.
Commun., 2007, 9, 845–849.
3 Y. J. Zheng, Q. Huo, P. Kele, F. M. Andreopoulos, S. M. Pham
and R. M. Leblanc, Org. Lett., 2001, 21, 3277–3280.
This journal is © The Royal Society of Chemistry 2015
RSC Adv., 2015, 5, 3232–3238 | 3237

View Article Online
RSC Advances
Paper
4 S. A. Reddy, K. J. Reddy, S. L. Narayan and A. V. Reddy, Food 28 P. K. Sahoo, B. Panigrahy, S. Sahoo, A. K. Satpati, D. Li and
Chem., 2008, 109, 654–659. D. Bahadur, Biosens. Bioelectron., 2013, 43, 293–296.
5 C. Vulpe, B. Levinson, S. Whitney, S. Packman and 29 R. Z. Ouyang, S. A. Bragg, J. Q. Chambers and Z. L. Xue, Anal.
J. Gitschier, Nat. Genet., 1993, 1, 7–13. Chim. Acta, 2012, 722, 1–7.
6 L. Zeng, E. W. Miller, A. Pralle, E. Y. Isacoff and C. J. Chang, J. 30 W. Chemnasiry and F. E. Hernandez, Sens. Actuators, B, 2012,
Am. Chem. Soc., 2006, 128, 10–11. 173, 322–328.
7 M. T. Fernandez-Arguelles, W. J. Jin, J. M. Costa-Fernandez, 31 A. Mohadesi, Z. Motallebi and A. Salmanipour, Analyst, 2010,
R. Pereiro and A. Sanz-Medel, Anal. Chim. Acta, 2005, 549,
135, 1686–1690.
20–25.
32 J. Chang, G. Zhou, E. R. Christensen, R. Heideman and
J. Chen, Anal. Bioanal. Chem., 2014, 1–19.
33 A. Ahami, F. Soltani-Felehgari, T. Madrakian, H. Ghaedi
and M. Rezaeivala, Anal. Chim. Acta, 2013, 771, 21–30.
34 D. P. Wang, Y. Tang and W. D. Zhang, Microchim. Acta, 2013,
180, 1303–1308.
8 M. Yuce, H. Nazir and G. Donmez, Bioelectrochemistry, 2010,
79, 66–70.
9 B. Rezaei, E. Sadeghi and S. Meghdadi, J. Hazard. Mater.,
2009, 168, 787–792.
¨
¨
¨
10 M. Bingol, G. Yentur, B. Erand and A. B. Oktem, Czech J. Food
Sci., 2010, 28, 213–216.
11 C. A. Sahin and I. Tokgoz, Anal. Chim. Acta, 2010, 667, 83–87.
35 M. Sadhukhan and S. Barman, J. Mater. Chem. A, 2013, 1,
2752–2756.
12 A. Economou and P. R. Fielden, Analyst, 2003, 128, 205–212. 36 L. Chen, H. Liu, K. Yang, J. Wang and X. Wang, Mater. Chem.
13 O. A. Farghaly and M. A. Ghandour, Environ. Res., 2005, 97,
229–235.
14 Y. Song and G. M. Swain, Anal. Chim. Acta, 2007, 593, 7–12.
15 O. El Tall, N. Jaffrezic-Renault, M. Sigaud and O. Vittori,
Electroanalysis, 2007, 19, 1152–1159.
16 I. Svancara, C. Prior, S. B. Hocever and J. Wang,
Electroanalysis, 2010, 22, 1405–1420.
17 M. R. Ganjali, N. Motakef-Kazami, F. Faridbod, S. Khoee and
P. Norouzi, J. Hazard. Mater., 2010, 173, 415–419.
Phys., 2008, 112, 407–411.
37 M. Suresh, A. K. Mandal, S. Saha, E. Suresh, A. Mandoli,
R. D. Liddo, P. P. Parnigotto and A. Das, Org. Lett., 2010,
12, 5406–5409.
38 Y. Y. Fu, H. X. Li and W. P. Hu, Eur. J. Org. Chem., 2007, 15,
2459–2463.
39 A. Caballero, R. Martinez, V. Lloveras, I. Ratera, J. Vidal-
Gancedo, K. Wurst, A. Tarraga, P. Molina and J. Veciana, J.
Am. Chem. Soc., 2005, 127, 15666–15667.
18 B. C. Janegitz, L. H. Marcolino-Junior, S. P. Campana-Filho, 40 R. Martinez, A. Espinosa, A. Tarraga and P. Molina, Org. Lett.,
R. C. Faria and O. Fatibello-Filho, Sens. Actuators, B, 2009,
142, 260–266.
19 P. R. Oliveira, A. A. Tanaka, N. R. Stradiotto and
M. F. Bergamini, Curr. Anal. Chem., 2012, 8, 520–527.
20 D. W. M. Arrigan, Analyst, 1994, 119, 1953–1966.
2005, 7, 5869–5872.
41 D. W. Pan, Y. Wang, Z. P. Chen, T. T. Lou and W. Qin, Anal.
Chem., 2009, 81, 5088–5094.
42 R. M. Takeuchi, A. L. Santos, P. M. Padilha and
N. R. Stradiotto, Talanta, 2007, 71, 771–777.
21 K. Kalcher, J. M. Kaumann, J. Wang, I. Svancara, K. Vytras, 43 S. K. Alpat, U. Yuksel and H. Akcay, Electrochem. Commun.,
C. Neuhold and Z. Yang, Electroanalysis, 1995, 7, 5–22. 2005, 7, 130–134.
22 P. Ugo and L. M. Moretto, Electroanalysis, 1995, 7, 1105– 44 H. Alemu and B. S. Chandravanshi, Anal. Chim. Acta, 1998,
1113. 368, 165–173.
23 S. Anandhakumar and J. Mathiyarasu, Microchim. Acta, 2013, 45 B. S. Sherigara, Y. Shivaraj, R. J. Mascarenhas and
180, 1065–1071. A. K. Satpati, Electrochim. Acta, 2007, 52, 3137–3142.
24 R. Agraz, M. T. Sevilla and L. Hernandez, Anal. Chim. Acta, 46 E. C. Canpolat, E. Sar, N. Y. Coskun and H. Cankurtaran,
1993, 283, 650–656. Electroanalysis, 2007, 19, 1109–1115.
25 M. S. Won, J. H. Park and Y. B. Shim, Electroanalysis, 1993, 5, 47 H. M. Abu-Shawish, S. M. Saadeh and A. R. Hussien, Talanta,
421–426.
2008, 76, 941–948.
26 Z. Gao, A. Ivaska and P. Li, Anal. Sci., 1992, 8, 337–343.
27 A. Safavi, M. Pakniat and N. Maleki, Anal. Chim. Acta, 1996,
335, 275–282.
48 M. B. Gholivand, M. Rahimi-Nasrabadi, M. R. Ganjali and
M. Salavati-Niasari, Talanta, 2007, 73, 553–560.
3238 | RSC Adv., 2015, 5, 3232–3238
This journal is © The Royal Society of Chemistry 2015