Journal of Environmental Treatment Techniques  
2018, Volume 6, Issue 3, Pages: 60-65  
J. Environ. Treat. Tech.  
ISSN: 2309-1185  
Journal weblink: http://www.jett.dormaj.com  
Determination of Trace Amount of  
Cadmium by Modified Graphite Electrode  
in Aqueous Samples  
M. Bagheri*  
Department of Chemical Engineering, Jami Institute of Technology, Isfahan, Iran  
Received: 12/8/2018  
Accepted: 5/11/2018  
Published: 30/11/2018  
Abstract  
In this study the 2,3- Dihyroquinazolin-4(1H)-one was used successfully as an ionophore in construction of modified  
graphite electrode for Cd (II) cation measurement in aqueous samples, which was formed from a thin layer by Sol-Gel method.  
-
2
The electrode response to Cd (II) cation was reported with a Nernstian slope of -28.9 mV/decade, dynamic range of 1.0×10 -  
-9  
.8×10 M and pH range of 5.0-6.5. The electrode response time was 45 sec and its detection limit was recorded as 8.6×10  
-
8
1
2
+
M. The lifetime of electrode was about 40 days. The proposed electrode showed good selectivity for Cd compared to many  
metal cations. Finally, the desired electrode was satisfactorily used as an indicator electrode in potentiometric titration with  
2
+
EDTA. Also, it was used to determination of Cd in real samples and the results were compared with results of atomic  
absorption spectrophotometer.  
Keyword: Cadmium, Ion-selective electrode, Sol-Gel, Ionophore.  
Introduction1  
polymers [11-12]. Especially the mixture of Sol-Gel and  
1
Carbon has more stability in comparison with carbon and  
could be modified more adequately respect to organic  
compound electrode [13-14]. The modified electrode by  
Sol-Gel method could be used as indicator or reference  
electrode in Potentiometric and it can be used in the  
biosensor construction [15-17]. Isotonic Anhydride  
Compounds, which are part of the heterocyclic category,  
are used in the manufacture of many compounds as  
intermediates. Of these compounds, the two derivatives,  
namely quinazoline-4- (3-hydrogen) -1 and 3, 2-  
dihydroquinolin-4- (α-hydrogen) -1, are the most  
important ones. These compounds play a very important  
role in the synthesis of several batches of biological  
molecules, such as amino acids and peptides. In a recent  
study, the 2, 3- Dihyroquinazolin-4(1H)-one, one of the  
derivatives of the compounds above, was used as an  
ionophore in the construction of a graphite electrode [18-  
Cadmium can easily be dissolved and transported by  
water. As a result, the metal can easily enter the  
environment and the water cycle from various industries  
such as the rubber, painting, and battery industries.  
Permissive limit of cadmium content in drinking water is  
about 1.2 mg/Lit. Cadmium produces several  
complications such as anemia, bone, liver and kidney  
disease in the body [1-2]. Due to harmful cadmium  
poisoning effects, the ability of cadmium measurement in  
slight quantities is vital. Up To now, several methods have  
been used for measurement of Cd (II) cation such as:  
atomic absorption spectrometry (AAS) [3-4], inductively  
coupled plasma-optical emission spectroscopy (ICP-OES)  
[
5] and chromatography [6]. These methods usually are  
expensive and need to an expert operator for their usage,  
so there is a serious demand for law cost, fast, simple and  
also precise measurement methods. An approach with  
noted features is potentiometric with using ion selective  
electrode. Selective electrodes are designed based on a  
Carrier ligand [6-8].  
One of the methods used to modification and increase  
the electrode level is the sol-Gel method. The Sol-Gel  
method is based on the hydrolysis and concentrating of an  
alkoxide precursor and provides a new possibility for  
sensors modification, because the long range of organic,  
mineral and bio molecules could simply be duped with  
Sol-Gel texture [9-10]. For instant, this method could be  
used for modifying Carbone electrode since mineral silica  
polymers have profits like physical severity, law  
inflammation and chemical inactivity respect to organic  
2
0].  
2 Experimental  
2.1 Reagents  
Tetra ethoxy silane (TEOS), triton X-100,  
dimethylformamide (DMF), ethanol (C2H5OH), acetone  
((CH3)2CO), sodium hydroxide (NaOH), (2, 3-  
Dihyroquinazolin-4(1H)-one, acid: Chloridric (HCl)  
Nitrate Salt of various metals and Buffer: citric  
acid/sodium nitrate. All above materials were purchased  
from Aldrich.  
Corresponding author: M. Bagheri, Department of Chemical Engineering, Jami Institute of Technology, Isfahan, Iran.  
E-mail: miss.bagheri40@yahoo.com  
60  
Journal of Environmental Treatment Techniques  
2018, Volume 6, Issue 3, Pages: 60-65  
2
. 2. Apparatus  
reference electrode were used in Potentiometric method.  
All potentiometric measurements were carried out at  
5.0 ± 0.1 ºC with a pH/mV meter (ZagShimi, Iran). A  
All measurement was done in 25º C and the  
potensiometric cell was as: Hg/Hg Cl , KCl (satd.)│test  
2
2
2
digital pH meter (Jenway pH-meter, UK 3020) was used  
for pH measurements. UV/VIS Spectrophotometer (UV-  
solution│ graphite electrode. The measurements started  
by placing modified graphite and calomel electrodes in  
100 mL Beaker of dual distillated water. After that, to get  
2
100, JENUS, China ). Saturated calomel electrode (SCE)  
-
1
-10  
and graphite electrode, were purchased from Azar  
electrode, Iran. Digital-Scale by 0.0001 accuracy  
the 1×10 -1×10 M range of metal concentration,  
various volumes of standard Cd (II) nitrate solution was  
added with Hamilton micro liter syringe to the beaker. The  
magnet stirrer was used to make equal response and the  
solution potential was recorded after stirring in  
equilibrium condition. These steps were applied for  
different cations and modified graphite electrode potential  
was plotted versus calomel ones as a function of cations  
concentration. Fig. 2. (A and B). The experiments showed  
that the electrode response to Cd (II) cation was more than  
other cations considerably. According to the results of the  
experiments, the response of the modified electrode to  
(Shimadzu-AEL-200, Japan). Atomic absorption  
spectrometer (Shmadzu, AA-760, Japan) was used to  
determine metal ion under recommended conditions in the  
instrument manual.  
2
2
. 3 Procedures  
. 3. 1. Spectroscopic study  
The spectrophotometry was used for ligand-metal  
cation reaction to do this. Samples with constant  
concentration of ligand (I) Fig. 1 were prepared and  
different amounts of Metal cations were added to them and  
solution absorption spectra was recorded. In this way, at  
first the back ground correction was done with 2 mL of  
solvent DMF. Then 100 micro liter of 0.01 M solution of  
ligand in solvent DMF was added to quartz cell and its  
absorption spectrum was recorded. In the next steps,  
different volumes of 0.01 M Metal cations were added to  
the cell, so the photometric titration spectra of these  
cations were plotted. Among these various metal cations,  
the cadmium cation ligand complex had high selectivity  
and other cations didn’t have effective interaction with  
ligand.  
2
+
Cd was better than other reported metal cations  
significantly.  
2.3.5 Optimization of Sol-Gel composition  
It was optimized to increase sol in order to obtain the  
best response by the designed electrode, the proportions of  
the components used in the sol-gel should be optimized.  
Also, sol composition homogeneousness. In this way the  
2
amounts of ligand (I), DMF, (TEOS), H O, ethanol, HCl,  
and Triton X-100, also temperature and mixing times were  
changed to get optimal conditions. The results are shown  
in Table 1. According to the results, sol composition  
number 11 of Table 1. is the best one which is composed  
of 12 mg ligand, 1 mL DMF, 1.5 mL TEOS, 2 mL ethanol,  
R1  
H
2
1 mL H O, 0.5 mL HCl and 2 drops of triton X-100. This  
mixture was stirred for 24 hr, with temperature of 25º C.  
Its Nernstian slope and linear range were -29.03  
mV/decade and 1.0×10 -1.8×10 M, respectively which  
were the best ones.  
N
-
2
-8  
O
O
O
2
.3.6 The effect of pH on the electrode response  
N
One of the most important factors that can affect the  
response electrode is pH. To investigate the effect of pH  
on the electrode response, the 1.0×10 M Cd (II) nitrate  
solution was used and solution pH was adjusted by  
H
-
3
N
H
R
3
volumes of HNO and NaOH. The plot of electrode  
Fig. 1: The structure of ionophore 2,3- Dihyroquinazolin-4(1H)-  
one. (ligand (I))  
potential versus pH in range of 2.0-10 is shown in Fig. 3.  
The electrode response was constant in pH range 4-7. By  
decreasing pH to lower than 5.0, the electrode potential  
increased which may was due to nitrogen atoms  
protonation in modifier. Also Cd (II) cation concentration  
decreased in pH higher than 6.5 due to Cd (II) complex  
formation with hydroxyl group then the electrode potential  
was decreased. According to the results, pH=6 was  
selected for next experiments.  
2
.3.2 Preparation of Sol-Gel  
Firstly different amounts of required reactants for cell  
preparation like ligand(I), DMF as a ligand solvent,  
TEOS, H O, ethanol, HCl and Triton X-100 were added  
2
to a poly ethylene vial. Then the reactants were mixed  
completely by magnetic stirrer in different temperatures  
diverse mixing times. With these conditions all needed  
processes for polymeric Sol-Gel network formation are  
accomplished.  
2
.3.7 Selectivity  
To calculation the selectivity coefficients, which are  
describe as the Cd (II) concentrations in the presence of  
other cations, the fixed interference method (FIM) was  
applied [22]. To do this, the electrode potential was read  
3
. 3 Electrode preparation  
In this section, at first to prepare the electrode,  
modified by sol-gel, the graphite electrode was washed  
twice with distilled water several times. Then the tip of the  
electrode was placed in a sol-gel mixture for 60 seconds.  
The modified electrode was ready to use after 24 hours.  
-
for solutions of 0.1 M of interfering cation and 0.01-2×10  
8
M of Cd (II). After potential record in each case, the plot  
of electrode potential versus the logarithm of main cation  
concentration was curved and main cation activity a , was  
A
obtained at intersection of plot’s extrapolated linear  
sections.  
3
.4 emf measurement  
The modified Graphite electrode was used as an  
indicator electrode and saturated calomel electrode as a  
61  
Journal of Environmental Treatment Techniques  
2018, Volume 6, Issue 3, Pages: 60-65  
3
3
2
2
1
1
50  
00  
50  
00  
50  
00  
3
3
50  
00  
(
B
(
A)  
Cd(II)  
K(I)  
Cd(II)  
Hg(II)  
Cr(III)  
Cu(II)  
Fe(III)  
Ni(II)  
Al(III)  
Na(I)  
Mg(II)  
Ca(II)  
Pb(II)  
Zn(II)  
250  
2
1
00  
50  
100  
0
1
2
3
4
5
6
7
8
9
10  
0
1
2
3
4
5
6
7
8
9 10  
pM  
pM  
-
1
-10  
Fig. 2: Potential response of sol gel electrode for various cations (1×10 -1×10 M).  
Table 1: The composition and characteristics of several typical membranes for sol-gel electrodes  
TEOS Ethanol HCl(0.1M) TX-100 DMF Ligand Stirrer Slope  
Linear  
range  
H
2
O
T
NO.  
(
mL)  
(mL) (mL)  
(mL) (Drops) (mL)  
(mg) (0C) Time(h) (mV/decade)  
(
-log C)  
1
2
3
4
5
6
7
8
9
0.5  
1.0  
1.3  
1.5  
1.7  
2.0  
1.5  
1.5  
1.5  
1.5  
2.0  
2.0  
2.0  
2.0  
2.0  
2.0  
1.0  
2.5  
2.0  
2.0  
2.0  
2.0  
2.0  
2.0  
1.0  
1.0  
1.0  
1.0  
1.0  
1.5  
1.0  
1.5  
1.0  
1.0  
1.0  
1.0  
1.0  
1.0  
0.5  
0.5  
0.5  
0.5  
0.5  
0.5  
0.5  
0.5  
1.0  
0.7  
0.5  
0.5  
0.5  
0.3  
4
3
2
2
2
2
2
2
2
1
2
2
2
2
0.5  
0.5  
1
5
50  
72  
72  
48  
48  
48  
24  
24  
24  
12  
12  
24  
24  
12  
24  
-27.94  
-28.25  
-28.2  
2.0-6.7  
10 50  
12 50  
12 40  
12 40  
12 40  
12 40  
12 30  
12 30  
12 30  
12 25  
2.0-7.1  
2.0-7.5  
2.0-7.0  
2.0-7.5  
2.0-7.3  
2.0-7.6  
2.0-7.6  
2.0-7.6  
2.0-7.0  
2.0-7.70  
2.0-6.50  
2.0-7.5  
2.0-7.6  
1
-28.35  
-28.63  
-28.43  
-27.74  
-29.20  
-28.11  
-31.05  
-29.03  
-27.93  
-27.30  
-30.85  
1
1
1
1
1
1
0
1
1
1* 1.5  
1
1
2
3
4
1.5  
1.5  
1.5  
05  
0.5  
1.2  
5
9
25  
25  
1
1
15 25  
62  
Journal of Environmental Treatment Techniques  
2018, Volume 6, Issue 3, Pages: 60-65  
Selectivity coefficient was calculated through,  
Nikolsi-Eizenman equation:  
2.3.9 Response time and electrode lifetime  
In this study the response time was considered equal  
the IUPAC definition: response time is time at which the  
emf/time slope (ΔE/Δt) of response potential curve of  
solution becomes equal to a limiting value, after change of  
main ion concentration in the solution. To calculate  
response time, the average time of whole procedure, from  
aA  
pot  
A,B  
k
=
(1)  
(
Zꢀ⁄Zꢁ  
aB  
)
-
3
where Z  
A
, Z  
B
are respectively the charge of primary ion  
entering of electrode in 1.0×10 M Cd (II) solution until  
the response electrode became steady, was recorded. Then  
the plot of response potential electrode versus time was  
curved (Fig. 5.). The response time estimated about 35  
seconds at intersection of two extrapolated linear sections  
of this curve. A modified graphite electrode was used daily  
for 40 days, to analysis the electrode lifetime. The used  
electrode performance was not changed considerably after  
and interfering ion in the above equation, the results are  
listed in Table 2.  
4
3
3
3
3
2
2
00  
75  
50  
25  
00  
75  
50  
5
0 days.  
3
3
3
3
2
2
2
2
30  
20  
10  
00  
90  
80  
70  
60  
2
3
4
5
6
7
8
9
10 11  
pH  
Fig. 3: pH effect of the test solutions on the potential response of  
-
3
the cadmium sensor(1.0×10 M Cd (II)).  
Table 2: Selectivity coefficients of various interfering  
ions  
0
20  
40  
60  
80  
100  
120  
푝표푡  
퐶푢,퐵  
푝표푡  
퐾
퐶푢,퐵  
Mn+  
퐾
Mn+  
Na+  
2.5×10-4  
Hg2+  
8.1×10-3  
4.8×10-3  
3.3×10-3  
2.7×10-3  
1.2×10-3  
1.1×10-3  
Time(S)  
-
Fig. 5: Plot of optimum electrode response versus time ( 1.0×10  
K+  
3.7×10-4  
3.0×10-3  
6.1×10-4  
1.7×10-3  
1.9×10-3  
Pb2+  
Cu2+  
Cr3+  
Fe3+  
Al3+  
3
M Cd (II), pH=6 ).  
Ca2+  
Mg2+  
Ni2+  
Zn2+  
2
.3.10 Reversibility and Repeatability  
Required reversibility of modified electrode was  
surveyed in the reaching to final equilibrium ±1 mV  
potential. To do this, the noted electrode was immersed in  
-2  
-4  
two different solutions (1.0×10 and 1.0×10 M from Cd  
II)) frequently and its potential was recorded. This  
(
measurement was repeated 8 times again regarding  
electrode response time (Fig. 6.). Relative standard  
deviation (RSD %) for low and high Cd (II) concentration  
(
1
each 10 times measurement) RSD % was ±0.15 for  
.0×10 M and ±0.12 for 1.0×10 M concentration. The  
4
3
3
2
2
1
00  
50  
00  
50  
00  
50  
-
2
-
4
relative standard deviation showed that electrode behavior  
didn’t change when potentials were recorded from high to  
law or inverse. For the obtained results, response  
repeatability was supported in each concentration.  
2
.3.8 Calibration curve, linear range and detection limit  
To determine the curve slope, electrode potential of  
standard Cd (II) cation solution was recorded in different  
Cd (II) concentrations. The Nernstian slope of response  
-
2
-
potential curve in concentration range of 1.0×10 -1.8×10  
8
M was -28.9 mV/decade. Electrode detection limit was  
also estimated at intersection of two extrapolated linear  
sections in the lowest region of calibration curve about  
0
2
4
6
8
10  
pCd  
-9  
8
.6×10 M as it is shown in Fig. 4. Also characteristics of  
Fig. 4: Calibration curve of the cadmium electrode based on 2,  
- Dihyroquinazolin-4(1H)-one (1.0×10 -0.36×10 M Cd (II)  
and pH=6)  
-2  
-10  
modified electrode in this study were contrasted with other  
works that were listed in Table 3.  
3
63  
Journal of Environmental Treatment Techniques  
2018, Volume 6, Issue 3, Pages: 60-65  
3
Analytical Application  
The modified graphite electrode with ligand (I) was  
3
3
2
2
75  
25  
75  
25  
used to determine cadmium extent of 4 actual samples  
including soil, pipeline water, well water and river water.  
To preparation of soil sample, 20 mg of soil was mixed  
with 20 mL distillated water in a beaker. Then 12 mL of  
concentrated nitric acid and 3 mL of peroxide hydrogen  
were added dropwise to the mixture. Next, the beaker was  
heated to reduce volume mixture by half. After cooling  
and filtering the mixture, it was diluted to volume of 25  
mL. At the end of the process of preparing soil sample, the  
pH was adjusted to 6 using a phosphate buffer [38]. After  
samples preparation (except for soil sample), the noted  
electrode was used to measure their Cd contents by  
method of standard addition. The obtained results with this  
electrode were compared by flame atomic absorption  
spectrophotometry (Table 3). According to Table 3, there  
is not meaningful difference between the results of two  
methods.  
0
200 400 600 800 1000 1200 1400  
Time(S)  
Fig. 6: Dynamic response time of the cadmium electrode for  
step changes in the concentration of Cd(II) (1.0×10 and  
-2  
-4  
.0×10 M and pH=6).  
1
Table 3: Determination of cadmium ion in different samples using sol-gel electrode and AAS method  
Found: A (M) and B (W/W%)  
Sample  
Real sample  
Cd2+ added (M)  
RR(%)  
Proposed electrode  
1.5(±0.27) ×10-6  
(AAS)  
1.9×10-6  
a
-6  
A:pipeline water  
A:Well water:  
A:River water:  
B: Soil  
N.D.  
N.D.  
N.D.  
1.0×10  
1.0×10  
1.0×10  
103.0  
109.0  
107.0  
94.7  
a
-6  
-6  
-6  
1.15×10  
1.8 (±0.12) ×10  
1.8 (±0.20) ×10  
a
-6  
-6  
-6  
1.6×10  
-
3
-3  
-3  
1.55×10  
1.55×10 (w/w%)  
-
1.47 (±0.18) ×10  
a
Relative recovery  
Not detected  
b
Also the stability of this modified electrode for the  
has remarkable selectivity for Cd (II) cation in the  
presence of wide range of alkali metals, alkaline earth  
metals and heavy cation metals. This electrode was used  
successfully in actual samples measurements.  
actual sample (pipeline water) was evaluated. For this  
purpose, the measured solution with concentration  
-
6
of1.0×10 and the electrode were kept at room  
temperature for 10 days. After which the electrode  
response did not change significantly (0.62%). After 40  
days of holding the electrode at ambient temperature, the  
electrode response was changed to less than 8.12% of the  
percentage of the electrode's initial response. Therefore,  
these results indicate that proposed electrode has the  
potential to be used to measure cadmium ion (II) over a  
relatively long period of time (Table 4.).  
References  
[
[
[
1] D. Pan, l. Zhang, J. Zhuang, W. Lu, R. Zhu, W. Qin,  
New application of tin–bismuth alloy for  
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Letters, 2012, 68, 472–474.  
2] A. M. Cheraghali, F. Kobarfard, N. Faeizy, Heavy  
metals contamination of table salt consumed in iran,  
Iranian Journal of Pharmaceutical Research, 2010, 9,  
Table 4: Inter-day precisions for real samples analysis  
1
29–132.  
(
for pipeline water)  
3] M. Payehghadr, S. Esmaeilpour, M. K. Rofouei, L.  
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Table Salt after Solid Phase Preconcentration Using  
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Derivative of Pyridine , Journal of Chemistry,2012,  
2013, 1-6.  
Real  
amount (µM)  
Measured  
value (µM)  
Day  
Change %  
1
1.6  
1.6  
1.6  
1.6  
1.6  
1.6  
1.6  
1.6  
1.59  
1.58  
1.55  
1.51  
1.47  
1.43  
-
1
2
3
4
4
5
0
0
0
0
5
0
0.62  
1.25  
3.12  
5.6  
8.12  
10.62  
[4] M. Tuzen M. Soylak, Multi-element coprecipitation  
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4
Conclusion  
The preparation Sol-Gel method of modified graphite  
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65