American Journal of Anal yt ical Chemistry, 2011, 2, 470-474
doi:10.4236/ajac.2011.24056 Published Online August 2011 (
Copyright © 2011 SciRes. AJAC
Simultaneous Determination of Cadmium and Lead Using
PEDOT/PSS Modified Glassy Carbon Electrode
Sukeri Anandhakumar, Jayaraman Mathiyarasu*,
Kanala Lakshmi Narasimha Phani, Venkataraman Yegnaraman
Electrodics and Electrocatalysis Division, Central Electrochemical Research Institute, Karaikudi, India
Received December 30, 2010; revised March 4, 2011; accepted May 16, 2011
In this work, we report the simultaneous determination of cadmium and lead using glassy carbon electrodes
(GCE) modified by poly(3,4-ethylenedioxythiophene) (PEDOT) for linear sweep anodic stripping voltam-
metry (LSASV). The modification allows metal detection without involving oxygen removal, mechanical
stirring and introduction of alloying additions such as Hg, Bi, Sb, etc. during the pre-concentration step. In-
troduction of poly (4-styrenesulphonate) (PSS) as dopant in the PEDOT matrix improves reproducibility,
stability and sensitivity in the detection. Both cadmium and lead peaks were readily quantifiable over the
linear range of 2 - 10 g/ml and the detection limit being 1.47 g/ml and 1.15 g/ml respectively. The cali-
bration plot shows a linear response with correlation coefficient of 0.9911 and 0.9944 for cadmium and lead
respectively. Thus, the GC/PEDOT/PSS modified electrode suggested as a suitable matrix for rapid moni-
toring of these heavy metals at trace levels.
Keywords: Stripping Voltammetry, Cadmium, Lead, Conducting Polymer, PEDOT-PSS, Heavy Metals
1. Introduction
Contamination of water by trace levels of heavy metals
presents a major current environmental threat, resulting
in an ever-increasing demand for the detection and mon-
itoring of metal contaminants [1]. Electroanalytical tech-
niques provide efficient, versatile and highly sensitive
method of detecting a wide range of inorganic and or-
ganic substances at very low concentrations [2]. Anodic
stripping voltammetry (ASV) is one of the most efficient
techniques in this field, owing to an effective cathodic
pre-concentration step, in which the analyte metal ion is
reduced and deposited onto the electrode surface as a
thin layer, followed by a stripping step, the results of
which are readily quantifiable.
During the development of ASV over the past 50 years,
mercury film electrodes (MFE) and hanging mercury
drop electrode have been used due to their high sensitiv-
ity and remarkable reproducibility [3-5]. Due to its toxic-
ity, the traditional mercury drop electrode is being pro-
gressively replaced by modified glassy carbon electrode
and screen-printed electrodes [6,7] Wang et al. [8] found
that bismuth presents analogous analytical performance
when compared to mercury for stripping analysis. This
similarity can be explained taking into account the fact
that bismuth forms a “fused alloy” with metals [9].
Detection of trace heavy metals needs the removal of
dissolved oxygen, stirring and addition of any external
metals to improve the sensitivity of electrode surface.
During miniaturization of the electroanalytical devices,
the above condition needs to be avoided for the analyte
detection. We report for the first time the conducting
polymer modified electrode (GC/PEDOT/PSS) as a new
alternative electrode material for heavy metals detection
at micro- molar levels without involving the preparative
steps. Further, simultaneous detection of cadmium and
lead on a PEDOT/PSS modified glassy carbon electrodes
is achieved employing linear sweep anodic stripping
voltammetry in acetate buffer solution of pH 4.5.
The detection of cadmium and lead using conducting
polymer modified glassy carbon electrode has not been
reported in the literature to the best of our knowledge.
The electrodeposited conducting polymer matrices pos-
sess advantages such as: 1) thin, uniform and adherent
polymer films can be obtained; 2) polymer film can be
deposited electrochemically on a small surface area with
a high degree of geometrical conformity; and 3) deposi-
tion can be effected on selected areas, especially in the
case of microsensors. Among the numerous polymeric
materials developed and studied over the past few dec-
ades, polyanilines, polypyrroles and polythiophenes con-
stitute an important class. Among these, polythiophenes
have received a significant amount of attention as elec-
trode modifiers in a variety of applications such as organic
light-emitting devices, sensors, polymer batteries, electro-
chromic windows, etc. [10,11]. Our group has extensively
reported on the use of PEDOT modified electrodes for
sensing of biologically important analyte molecules in the
recent past [12,13].
2. Experimental
2.1. Materials
All chemicals were of analytical grade and used without
further purification. 1000 g/ml stock solutions of
Pb(NO3)2 and CdCl2 were prepared by dissolving the
reagents in Milli-Q water (18.2 ) (Millipore). The mo-
nomer, 3,4-ethylenedioxythiophene (EDOT, Aldrich), poly
(4-styrenesulphonate) (PSS), tetrabutylammonium per-
chlorate (TBAPC, Fluka), acetonitrile (E-Merck), were
used as received. The acetate buffer solution (pH 4.5)
was prepared by adding CH3COONa (E-Merck) to a
CH3COOH (E-Merck) solution.
For voltammetric studies, a 3-mm diameter glassy
carbon disk (BAS Inc.) served as the working electrode
with a platinum wire and Ag/AgCl (3M NaCl) as auxil-
iary and reference electrodes respectively.
2.2. Instrumentation
Voltammetric experiments were carried out using a
PalmSens portable electrochemical analyzer (Palmsens
BV, The Netherlands) at ambient temperature (25 ± 1oC).
To record linear sweep voltammetry (LSV), the follow-
ing input parameters were used: Scan rate: 50 mV·s–1,
deposition potential: –1.1 V, deposition time: 120 s, equ-
ilibration time: 5 s.
2.3. Preparation of PEDOT/PSS – Modified
The GCE surface was polished first on a fine polishing
cloth using 1.0 and 0.06 μm alumina powder, and finally
sonicated in Milli-Q water for 5 minutes. Before elec-
tropolymerization, the polished electrode was pretreated
by cycling it between –0.9 to 1.5 V vs Ag wire at 50 mV
s-1 in acetonitrile containing TBAPC for 10 minutes.
PEDOT was electrodeposited on the GCE from a solu-
tion of 50 mM EDOT + 0.1 M TBAPC in acetonitrile by
cycling between –0.9 to 1.5 V vs Ag wire (pseudo-refer-
ence electrode). PEDOT film was allowed to grow on the
GC surface over three successive scans, as seen from the
increasing anodic and cathodic peak current density val-
ues. The electropolymerization of EDOT was highly
reproducible and the cyclic voltammograms obtained
during the electropolymerization process agreed closely
with that reported earlier [14].
To increase the anionic nature of GC/PEDOT film, the
electrode was cycled between –0.9 to 1.2 V vs Ag/AgCl
reference electrode at 50 mV·s–1 in 1% PSS solution.
This modified electrode is hereafter referred as GC/
3. Results and Discussion
Figure 1 shows the LSASV responses of 20 g/ml Cd2+
and Pb2+ at bare, PEDOT, PEDOT-PSS modified glassy
carbon electrodes. In Figure 1, a relatively small current
response is observed at the PEDOT modified GCE
(curve b), which shows difficulty for the metal ions to be
adsorbed onto the PEDOT surface. This may be reasoned
as the cationic nature of the PEDOT materials [15],
which does not favor adsorption of cationic metal species
on its surface. On the other hand, for the PEDOT-PSS
modified GCE electrode, the stripping peak current val-
ues for the two metal ions are larger than those obtained
from the bare and PEDOT modified GCE electrodes.
This can be explained that the PEDOT film doped with
PSS exerts negative charges on the surface. These
charges can favor accumulation of increasing amounts of
the positively charged metal ion on its surface. Hence,
the PEDOT film can be used as an excellent supporting
material for heavy metal ion sensor. Thus the peak cur-
rents of Cd2+ and Pb2+ at the GC/PEDOT/PSS are greatly
enhanced, which are attributed to PSS doping of the po-
lymer that exhibits a strong adsorptive power of the
heavy metal ions and hence an improved surface sensi-
tivity of the electrode is observed.
Since the preliminary experiments revealed the perti-
nence of the PEDOT-PSS electrode for trace heavy metal
detection by ASV, without involving oxygen removal,
alloying additions and stirring, further investigations
such as variable experimental conditions affecting the
stripping response of the PEDOT-PSS modified GCE are
also examined, including the film composition and depo-
sition parameters are carried out.
The anodic stripping response of GC/PEDOT/PSS to-
wards the presence of Cd2+ ion and Pb2+ ion were sepa-
rately investigated. The respective metal ion standard
additions were made to the acetate buffer solution (pH
4.5) and overlays of the voltammograms along with a
standard addition plot of metal ion concentration versus
peak current are shown in Figures 2 and 3 respectively.
The calibration plot is linear over the concentration range
Copyright © 2011 SciRes. AJAC
-1.2 -1.0 -0.8 -0.6 -0.4 -0.2
P o t e n t ia l/V vs Ag/AgCl
(a) Ba r e GC
Figure 1. LSASV of cadmium and lead (20 g/ml) in acetate
buffer (pH 4.5) solution. Deposition at –1.1 V for 120 s, scan
rate 100 mV·s–1. (a) Bare GC (b) GC/PEDOT (c) GC/PE-
of 4 to 20 g/ml with a correlation co-efficient of 0.9986
and a calculated limit of detection of 0.96 g/ml of lead.
The 2 g/ml addition of Pb2+ ion gave a stripping peak
from the 4 g/ml addition and linear calibration plot
through to 20 g/ml. The corresponding calibration plot
for the additions was linear (R2 = 0.9972) and gave a
-1.0 -0.8 -0.6 -0.4
20 Cd
Po t e n ti a l/V vs A g/A g Cl
468 101214161820
25 B
R2 = 0.9986
Concentration (g/ml)
Figure 2. (A) Overlay of LSASVs at a GC/PEDOT/PSS
modified electrode in acetate buffer solution (pH 4.5) fol-
lowing the standard additions of Cd2+ over a 4 - 20 g/ml
concentration range. Deposition at –1.1 V for 120 s, scan
rate 50 mV·s–1. (B) Calibration plot of peak current versus
Cd2+ concentration.
-0.8 -0.7 -0.6 -0.5 -0.4 -0.3 -0.2
30 Pb
Potential/V vs Ag/AgCl
468 101214161820
35 B
R2 = 0.9972
Concentration (g/ml)
Figure 3. (A) Overlay of LSASVs at a GC/PEDOT/PSS
modified electrode in acetate buffer solution (pH 4.5) fol-
lowing the standard additions of Pb2+ over a 4 - 20 g/ml
concentration range. Deposition at –1.1 V for 120 s, scan
rate 50 mV·s–1. (B) Calibration plot of peak current versus
Pb2+ concentration.
limit of detection of 1.15 g/ml. Following the detection
of Cd and Pb on the modified electrode individually,
simultaneous detection of the two metal ion analytes was
attempted. Figure 4 illustrates a series of LSASV for the
PEDOT-PSS modified GCE for successive additions of
Cd2+ and Pb2+ in 2 g/ml steps in the concentration range
2-10 g/ml. The voltammogram exhibits well-developed
and separated stripping peaks. The characteristic peaks
of Cd2+ and Pb2+ were observed at –0.746 and –0.496 V
respectively, which agree with the individual metal ion
stripping characteristics (Figures 2 and 3) with a pre-
-concentration deposition time of 120 s (optimized for
this condition). The calibration plots for the Cd2+ and
Pb2+ are linear in the range of 2-10 g/ml with regression
co-efficient values of 0.9911 and 0.9944, respectively.
The relative standard deviations from 10 measurements
for 2 g/ml Cd2+ and Pb2+ by using the PEDOT-PSS
modified electrode are about 3.21% and 1.96% respec-
tively. Therefore, the detection limit of Cd2+ and Pb2+ are
about 1.47 g/ml and 1.15 g/ml, respectively.
Copyright © 2011 SciRes. AJAC
-1.0 -0.8-0.6 -0.4 -0.2
25 Pb
P ot entia l/V vs Ag /Ag Cl
24 BR2 = 0.9944 (Pb)
The authors thank the Department of Biotechnology,
New Delhi for financial assistance [BT/PR-10459/BCE/
R2 = 0.9911 (Cd)
Conc entration (g/ml)
Figure 4. (A) Overlay of LSASVs at a GC/PEDOT/PSS
modified electrode in acetate buffer solution (pH 4.5) fol-
lowing the standard additions of Cd2+ and P b2+ over a 2 - 10
g/ml concentration range. Deposition at –1.1 V for 120 s,
scan rate 50 mV·s–1. (B) Calibration plot of peak current
versus Cd2+ and Pb2+ concentration.
4. Conclusions
The use of GC/PEDOT/PSS modified glassy carbon elec-
trode for the simultaneous detection of cadmium and lead
has been presented. In this preliminary investigation, we
have achieved the detection of cadmium and lead simul-
taneously down to 1.47 g/ml and 1.15 g/ml respec-
tively, using conducting polymer modified glassy carbon
electrode in acetate buffer (pH 4.5) without the removal
of dissolved oxygen, stirring and any external metals like
Hg, Bi, Sb, etc. The merits of polymer-modified electrode
are: enhanced electroanalytical sensitivity, stability and
increased mass transport that facilitate estimation of
heavy metals at trace levels. Thus, the GC/PEDOT/PSS
modified electrode can be a suitable candidate for the
detection of heavy metals. Further optimization using this
polymer modified electrode to detect nanomolar/sub-
-nanomolar level of heavy metals and also the simultane-
ously detection of other heavy metals without involving
the pre-concentration step is in progress.
5. Acknowledgments
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