L. Z. Pei1
Key Lab of Materials Science
and Processing of Anhui Province,
School of Materials Science and Engineering,
Anhui University of Technology,
Ma’anshan,
Anhui 243002, China
e-mail: lzpei@ahut.edu.cn, lzpei1977@163.com
Y. K. Xie
Key Lab of Materials Science
and Processing of Anhui Province,
School of Materials Science and Engineering,
Anhui University of Technology,
Ma’anshan,
Anhui 243002, China
Y. Q. Pei
Key Lab of Materials Science
and Processing of Anhui Province,
School of Materials Science and Engineering,
Anhui University of Technology,
Ma’anshan,
Anhui 243002, China
Z. Y. Cai1
Key Lab of Materials Science
and Processing of Anhui Province,
School of Materials Science and Engineering,
Anhui University of Technology,
Ma’anshan,
Anhui 243002, China
Determination of Cyanuric
Acid by Electrochemical Cyclic
Voltammetry Method Using
CuGeO3 Nanowires as Modified
Electrode Materials
A simple electrochemical method for the determination of cyanuric acid (CA) has been
developed based on a CuGeO3 nanowire modified glassy carbon electrode. The dense
CuGeO3 nanowire film can be formed on the surface of the glassy carbon electrode. The
roles of scan rate, CA concentration, and electrolytes with different pH values on the
electrochemical responses of CA have also been analyzed. The intensities of two anodic
peaks vary linearly with the increase of the scan rate from 25 to 200 mVs1. The intensity
of the electrochemical CV peak increases with the increase of the acidity of the electrolytes. The two anodic peak currents are linear with the CA concentration in the range of
0.005–2 mM. The linear correlation coefficient is 0.984 and 0.980 for the cyclic voltammogram peaks (cvp) cvp1 and cvp2, respectively. The detection limit is 4.3 lM and
2.1 lM for cvp1 and cvp2, respectively. The proposed electrochemical method is convenient and effective sensing of CA. [DOI: 10.1115/1.4026024]
C. G. Fan
Key Lab of Materials Science
and Processing of Anhui Province,
School of Materials Science and Engineering,
Anhui University of Technology,
Ma’anshan,
Anhui 243002, China
1
Introduction
Cyanuric acid (CA) belongs to the derivative compound of melamine. It is intentionally added into food ingredients to make the
products contain a higher protein content due to high nitrogen content of CA [1]. CA was also found as nonprotien nitrogen in pet
food. However, CA is thought to be harmful to humans, especially
the toxicity increases when the CA coexists with melamine forming a hydrogen-bonded biomolecule network which is the insoluble crystal in the kidneys of cats and other species [2,3]. In 2007,
numerous pet foods in the United States were recalled after dogs
and cats consuming the products suffered renal failure [4,5]. As an
additional adulterant, CA is also found in the pet foods. CA is not
approved by the U. S. FDA as a source of nonprotein nitrogen in
hog, chicken, fish or aquaculture feeds [6,7]. Therefore, CA should
not be present in foods at any level. Trace amounts of CA in foodstuff with high sensitivity have been an important research issue.
CA was found in the environment, such as a degradation product
of s-triazine pesticides. CA was also used as a microbicide and disinfectant in water treatment as a chlorine stabilizer [4]. A gas chromatography mass spectrometry (GC-MS) method was developed
for the relatively high CA concentrations which were found in
1
Corresponding author.
Manuscript received March 1, 2013; final manuscript received October 22, 2013;
published online November 28, 2013. Assoc. Editor: Jung-Chih Chiao.
adulterated pet foods and animal feeds [4,8]. The detection limit is
77.5 lM by the GC-MS method which is unsuitable for the concentration levels expected in the contaminated feeds. He et al. [9]
reported the detection of melamine, CA and melamine cyanurate
using surface-enhanced Raman spectroscopy (SERS) coupled with
gold nanosubstrates. The detection limit for CA, melamine, and
melamine cyanurate by SERS was estimated to be 0.26 lM. Ehling
et al. [10] reported the determination of the CA by highperformance liquid chromatography (HPLC) method. The method
allowed for the detection of CA at about 90 lg/g in wheat flour.
Chromatographic system based on zwitterionic hydrophilic interaction chromatography (ZIC-HILIC) columns was used for the detection of CA [11]. The method is applicable over the range of 0.5 to
50 lg/g. Wang et al. [12] previously described a liquid chromatography–mass spectrometry (LC-MS) method to simultaneously
determine CA and melamine and validated the method in pet foods
and biological matrices. The detection limits of the melamine and
CA were 0.0315 lM and 0.0304 lM, respectively. However, timeconsuming steps and expensive instruments limit the application of
the existing methods. Therefore, it is important to explore new,
convenient and effective methods for the detection of CA.
Compared to the present methods, much effort has been devoted
to the electrochemical sensors owing to their simplicity, low cost,
accurateness, high stability and sensitivity. Unfortunately, to date,
no literatures were reported using the electrochemical
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determination of CA at solid electrodes. In our past research, copper germanate (CuGeO3) nanowires attracted special interest
because CuGeO3 nanowires exhibited excellent electrochemical
properties for potential applications in nanoscale electrochemical
sensors [13–15]. In the paper, electrochemical method based on a
CuGeO3 nanowire modified glassy carbon electrode (GCE) has
been developed for the determination of CA by a cyclic voltammetry method. The electrochemical cyclic voltammogram (CV) peak
currents are linear with the CA concentration in the range of
0.005–2 mM with the linear correlation coefficient of 0.984 and
0.980 for cvp1 and cvp2, respectively. The detection limit is
4.3 lM and 2.1 lM for cvp1 and cvp2, respectively. The roles of
scan rate and electrolytes with different pH values on the electrochemical responses of CA have also been analyzed. The proposed
method will have great implication potential for the determination
of CA.
2
Experimental Methods
2.1 Preparation of the CuGeO3 Nanowire Modified GCE.
The CuGeO3 nanowires were obtained by the hydrothermal
deposition method which was described elsewhere [16]. The
hydrothermal deposition temperature and duration time were
250 C and 12 h, respectively. The CuGeO3 nanowire suspension
was prepared by dispersing 10 mg CuGeO3 nanowires in 10 ml
dimethylformamide (DMF) solvent with sufficient ultrasonication
for about 1 h. Then, the uniform CuGeO3 nanowire suspension
was obtained. Prior to modification, a GCE with the diameter of
3 mm was polished to a mirror using polish paper and alumina
pastes of 0.5 lm and cleaned thoroughly in an ultrasonic cleaner
with alcohol and water sequentially. A CuGeO3 nanowire modified GCE was prepared by coating 10 ll nanowire suspension on
the surface of bare GCE and allowed to be evaporated at room
temperature in air.
2.2 Characterization Methods. The surface morphology of
the CuGeO3 nanowire modified GCE was observed by scanning
electron microscopy (SEM) (JEOL JSM-6490LV SEM) with a
15-KV accelerating voltage. CA was purchased from Sinopharm
Chemical Reagent Co., Ltd. of China which was analytical grade.
Electrochemical (EC) measurement was performed in a model
CHI6046 electrochemical working station. The CuGeO3 nanowire
modified GCE served as the work electrode. Platinum plate and
saturated calomel electrode (SCE) served as the counter electrode
and reference electrode, respectively. All potentials in the study
were reported with respect to SCE. Cyclic voltammograms (CVs)
were recorded from 1.0 to 1.0 V at a potential scan rate of
Fig. 1 Surface morphology of the CuGeO3 nanowire modified
GCE
031003-2 / Vol. 4, AUGUST 2013
50 mVs1 in the mixed solution of 0.1 M KCl and CA with different concentrations.
3
Results and Discussion
3.1 Surface Morphology of the Modified GCE. The surface
morphology of the CuGeO3 nanowire modified GCE is shown in
Fig. 1. The diameter of the CuGeO3 nanowires is 50 nm to
200 nm. The CuGeO3 nanowires can form a dense film on the
surface of the GCE. Therefore, the glassy carbon substrate at
the CuGeO3 nanowire modified GCE might have no effect on the
electrochemical responses of the CA.
3.2 Voltammetric Characteristics of CA at the Modified
GCE. CVs in 0.1 M KCl solution with and without CA at bare
GCE and CuGeO3 nanowire modified GCE are measured in the
potential ranging from 1.0 to þ1.0 V (Fig. 2). The potential scan
rate is 50 mVs1. No CV peaks are observed from the CV curves
at the nanowire modified GCE in 0.1 M KCl solution without CA.
Therefore, no electrochemical activity is shown at the CuGeO3
nanowire modified GCE in 0.1 M KCl solution without CA. It is
very interesting that two pairs of CV peaks are observed from the
electrochemical CV curve in 0.1 M KCl solution with 2 mM CA.
Two semi-irreversible electrochemical CV peaks are observed.
The anodic CV peaks (cvp1, cvp2) are located at 0.21 V and
0.01 V, respectively. And two cathodic CV peaks (cvp10 , cvp20 )
are located at 0.02 V and 0.52 V, respectively. These CV peaks
can only be shown from KCl solution with CA at the CuGeO3
nanowire modified GCE. Therefore, it is believed that the electrochemical CV peaks originate from the CA. CuGeO3 nanowires
have an essential role for the formation of the electrochemical CV
peaks. Two pairs of CV peaks are similar to those at the CuGeO3
nanowire modified GCE in KCl solution with 2 mM tartaric acid
and cysteine, respectively [13,15]. However, the potentials of the
CV peaks are different. Two anodic CV peaks (cvp1, cvp2),
located at 0.26 V and 0.04 V, and two cathodic peaks (cvp10 ,
cvp20 ), located at 0.15 V and 0.35 V, were obtained at the
CuGeO3 nanowire modified GCE for the analysis of cysteine,
respectively [13]. Two anodic CV peaks (cvp1, cvp2) were
located at 0.18 V and 0.02 V from the CV curve of 2 mM tartaric
acid. Two cathodic peaks (cvp10 , cvp20 ) were located at 0.05 V
and 0.33 V, respectively [15]. Thus, the CA and cysteine can
be distinguished via the potentials of the CV peaks by CV
method. The results show that CuGeO3 nanowires have different
electrochemical activity in KCl solution with CA. In order to
Fig. 2 CVs of the CuGeO3 nanowire modified GCE in 0.1 M KCl
solution in absence (a) and presence (b) of 2 mM CA, scan rate,
50 mVs21
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Fig. 3 CVs of the CuGeO3 nanowire modified GCE in 2 mM CA and different electrolytes. Scan rate, 50 mVs21. (a) KBr, (b)
NaOH, (c) H2SO4, and (d) CH3COONa-CH3COOH.
demonstrate whether the anodic and cathodic CV peaks are semireversible electrochemical reaction process, the experiments
with initial potential scan direction and different reversal potential
were conducted. The potentials and intensities of the electrochemical CV peaks maintain very similar when changing the initial
potential scan direction and reversing the potential scan at different positive potential. Therefore, the cvp1 and cvp2 are considered to be caused from the potential of cvp10 and cvp20 ,
respectively.
Cvp1-cvp10 obtained from the CVs of ascorbic acid at the
CuGeO3 nanowire modified GCE was assigned to the oxidation
and reduction process between ascorbic acid and dehydroascorbic
acid [14]. Similarly, cvp1-cvp10 obtained from CuGeO3 nanowire
modified GCE in CA solution is also considered to be the electrochemical oxidation and reduction process between cyanuric acid
and dehydrocyanuric acid. The adsorption and desorption process
of cysteine have also been analyzed by impedance spectroscopy
indicating the adsorption and desorption process of cysteine and
cystine at gold electrode, respectively [17]. The electrochemical
responses of tartaric acid and ascorbic acid at the CuGeO3 nanowire modified GCE also showed adsorption and desorption behavior [14,15]. Therefore, cvp2-cvp20 obtained from the CVs of CA
is considered to contribute to the adsorption and desorption pro-
3.3 Effect of the Electrolytes. The electrochemical responses
of the CA at the CuGeO3 nanowire modified GCE under various
electrolytes with different pH values are shown in Fig. 3. NaOH
(pH ¼ 12), KBr (pH ¼ 7), CH3COOH-CH3COONa (pH ¼ 5) and
H2SO4 (pH ¼ 2) with the concentration of 0.1 M are used as the
electrolytes so as to show the role of different electrolytes on the
electrochemical responses of CA at the nanowire modified electrode. In 0.1 mM KBr solution with 2 mM CA, the electrochemical responses of the CA (Fig. 3(a)) are similar to those in KCl
solution. But the peak potential of cvp1 shifts to more positive
direction. The potential of cvp1 is þ0.29 V. In addition, the slight
difference on the intensities of the anodic CV peaks is also
observed. No electrochemical CV peaks are observed from the
CV curve of the CA in alkaline solution (Fig. 3(b)). Therefore, it
is shown that the CuGeO3 nanowire modified GCE has no electrochemical activity in alkaline solution with CA. However, a broad
and strong anodic peak occurs instead of cvp1 and cvp2 obtained
from neutral solution when the electrochemical measurement was
carried out in acidic solution (Figs. 3(c) and 3(d)). The peak
Journal of Nanotechnology in Engineering and Medicine
AUGUST 2013, Vol. 4 / 031003-3
cess of cyanuric acid and dehydrocyanuric acid at the nanowire
modified GCE.
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Fig. 4 CVs of the CuGeO3 nanowire modified GCE in 0.1 M KCl
and 2 mM CA solution using different scan rates. The inset in
the bottom-left part is the calibration plots of the intensities of
anodic peaks against the scan rate.
Fig. 5 CVs of the CA with different concentrations at the
CuGeO3 nanowire modified GCE. KCl, 0.1 M, scan rate,
50 mVs21. The inset in the bottom-left part is the calibration
plots of the intensities of anodic peaks against the CA
concentrations.
Table 1 Analytical data of the CA
CV peaks
Regression equation
Correlation coefficient (R)
Linear range (mM)
Detection limit (lM)b
cvp1
cvp2
Ip ¼ 15.132þ17.684C
Ip ¼ 25.658þ36.042C
0.984
0.980
0.005–2
0.005–2
4.3
2.1
a
a
Where Ip and C represent the peak current (lA) and the concentration of the CA (mM).
The detection limit of the CA was analyzed using a signal-to-noise ratio of 3 (S/N ¼ 3).
b
potential of the strong anodic peak located between the potential
of cvp1 and cvp2 which originates from the hydrogen ions and
varies in different acidic solution. The intensity of the electrochemical CV peak increases obviously with the increase of the
acidity of the electrolytes. It is considered that the hydrogen ions
may participate in the electrochemical reaction of the CA which is
similar to those of other biological molecules at the CuGeO3
nanowire modified GCE [14,15].
by an adsorption process [18,19]. The role of the scan rate on the
electrochemical behavior of the CA is similar to that of tartaric
acid and ascorbic acid at the CuGeO3 nanowire modified GCE
[14,15]. Scan rate may promote the electrochemical reaction
between cyanuric acid and dehydrocyanuric acid.
3.5 Effect of the CA Concentration. By measuring different
CV curves of the CA with different concentrations in KCl solution
3.4 Effect of the Scan Rate. The role of the scan rate on the
electrochemical responses of the CA at the CuGeO3 nanowire
modified GCE has been analyzed using the scan rate from 25 to
200 mVs1. The CV curves of 2 mM CA in 0.1 M KCl solution at
the CuGeO3 nanowire modified GCE are shown in Fig. 4. The
potentials of the anodic and cathodic peaks for the CA are very
similar. However, the intensities of the CV peaks increase obviously with the increase of the scan rate from 25 to 200 mVs1.
The inset in bottom-left part of Fig. 4 indicates the relationship
between the scan rate and current of the anodic CV peaks. The linear relation is shown from the anodic current and scan rate in the
range of 25–200 mVs1. The result demonstrates that the kinetic
of the overall electrochemical reaction process may be controlled
Table 2 Electrochemical determination of CA using CuGeO3
nanowire modified GCE in milk
Sample
(milk)
1
2
3
Amount
added (lM)
Amount found (lM)
(average of five times)
Recovery
(%)
5
20
40
4.87 6 0.13
19.78 6 0.22
41.15 6 0.32
97.4
98.9
102.9
031003-4 / Vol. 4, AUGUST 2013
Fig. 6 CVs of the CuGeO3 nanowire modified GCE in 0.1 M KCl
solution with 2 mM CA recycling for the 1st and 20th time. Scan
rate, 50 mVs21.
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using the CuGeO3 nanowire modified GCE, the linear range and
detection limit are obtained. Figure 5 shows the CVs of the CA in
the concentration range of 0.005–2 mM. The calibration plots of
the intensities of anodic peaks and CA concentration are shown in
the inset in the bottom-left part of Fig. 5. Increasing the CA concentration, the intensities of the CVs of the CA at the CuGeO3
nanowire modified GCE increase obviously. The linear range,
detection limit and correlation coefficient for detecting CA using
the CuGeO3 nanowire modified GCE are obtained in the concentration range of 0.005–2 mM. The data are shown in Table 1. The
linear range is 0.005–2 mM with the correlation coefficient of
0.984 and 0.980 for cvp1 and cvp2, respectively. The detection
limit is 4.3 lM and 2.1 lM for cvp1 and cvp2, respectively, at a
signal-to-noise ratio of 3. Compared with the detection of the CA
by other methods, the CuGeO3 nanowire modified GCE exhibits a
low detection limit and wide linear range [4,6–9].
As a practical use, the CuGeO3 nanowire modified GCE has
been used to detect CA in milk samples. The CA concentration in
the milk samples is 5, 20, and 40 lM, respectively. The measured
values were calculated from five separate measurements. The
recoveries of CA were determined by standard addition and the
corresponding results are listed in Table 2. Good results suggest
that the CuGeO3 nanowire modified GCE is very reliable and sensitive for the determination of CA.
graduate Supervisor Innovation Fund Project by Anhui University
of Technology (D201101).
References
This work was supported by the Natural Science Foundation of
the Education Bureau of Anhui Province of China (KJ2012Z038,
KJ2011A042), Natural Science Foundation of Anhui Province of
China (1308085ME72), Innovative Research Foundation of Postgraduate of Anhui University of Technology (2012021) and Post-
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Journal of Nanotechnology in Engineering and Medicine
AUGUST 2013, Vol. 4 / 031003-5
3.6 Stability and Reproducibility of the Modified GCE.
The stability and reproducibility of the CuGeO3 nanowire GCE
have been analyzed in a continuous operation mode. Figure 6
shows the CVs of 2 mM CA with the repeat detection for the 1st
and 20th time in 0.1 M KCl solution using same CuGeO3 nanowire modified GCE. The relative standard deviation (RSD) is
4.71% and 2.73% for cvp1 and cvp2, respectively. The CuGeO3
nanowires can attach firmly to the GCE showing the stability.
Therefore, the stability and reproducibility of the CuGeO3 nanowire modified GCE are good. The CuGeO3 nanowire modified
GCE can be used at least for two weeks with only a slightly
decline in the electrochemical signal.
4
Conclusion
In summary, the electrochemical detection performance for
cyanuric acid using CuGeO3 nanowire modified GCE has been
analyzed by cyclic voltammetry method. Two pairs of semiirreversible electrochemical CV peaks with anodic CV peaks
(cvp1, cvp2) at 0.21 V and 0.01 V, and cathodic peaks (cvp10 ,
cvp20 ) at 0.02 V and 0.52 V, are observed, respectively. The intensity of the CV peaks increases linearly with the increase of the
CA concentration and scan rate. The linear range is 0.005–2 mM
and detection limit is 4.3 lM and 2.1 lM for cvp1 and cvp2,
respectively. The CuGeO3 nanowires are showed to have potential
application potential for the detection of CA.
Acknowledgment
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