Journal of New Materials for Electrochemical Systems 17, 205-208 (2014)

© J. New Mat. Electrochem. Systems

Short Communication

Determination of Lead (Pb2+) by Anodic Stripping Voltammetry Based on

[Ru(NH3)6]3+/Nafion Modified Electrodes

Shirley Tiong Palisoc*, Michelle Tiamzon Natividad†, Patricia Denise DeVera‡ and Benjamin Simone B. Tuason§

Materials Science Laboratory, Physics Department, De La Salle University, 2401 Taft Ave., Manila, Philippines

Received: October 10, 2014, Accepted: October 31, 2014, Available online: November 26, 2014

Abstract: Chemically modified [Ru(NH3)6]3+ doped Nafion® thin film was fabricated on indium tin oxide (ITO) coated glass electrodes
by using the drop-coating method to detect heavy metal ions of Pb(II) in de-ionized water analyte solution via anodic stripping voltamme-
try (ASV). This study also determined the effect of varying the concentration of the mediator ([Ru(NH3)6]3+) on the detection of the said
heavy metals. The redox mediator Ru(NH3)6] 3+ used in the study was effectively incorporated and immobilized within the Nafion modified
electrodes. Lead concentration in the electrolyte solution and the concentration of the redox mediator was varied to control the properties
of the fabricated electrodes which utilized for heavy metal detection through ASV. The conducting properties of ITO electrodes were en-
hanced with the deposition of Nafion® attaining minimal interference. The stripping current peaks increased with the concentration of the
heavy metal present in the solution as well as with the mediator concentration.

Keywords: Nafion, Drop Coating, Anodic Stripping Voltammetry, Heavy Metal, Electrochemistry

has limited anodic potential[11]. As an alternative to the mercury

electrodes, this study aimed to use chemically modified electrodes,
Trace elements of heavy metals (HMs) are beneficial important
which are conducting that have their surfaces enhanced. This was
at very low concentrations, but are toxic at high concentrations
to modify the electrochemical characteristics of the exposed
[1,2]. Lead is among the most widely distributed, naturally occur-
surface. Coating the electrode surface with a thin film using a pol-
ring, and potentially toxic elements. It has a very long half-life and
ymer such as Nafion® is one of the many common methods used in
mostly accumulates in the bones and the kidneys[3]. It is listed in
modifying electrodes [12].
the United States Environmental Protection Agency as one of the
primary contaminants of drinking water. With increasing industrial
use, environmental pollution and associated toxic exposure, con-
cern has increased about the huge disturbances it causes in the
ecological balance in nature [4]. In recent years, various heavy 5% w/v Nafion solution was obtained from Fuel Cell Earth
metal pollution incidents, such as the pollution of lead, cadmium, (Wakefield, Massachusetts, United States). Hexaamminerutheni-
chromium, and so on, result in serious ecological risk and human um(III) Chloride (98%) and ITO-coated rectangular glass slides
health. The major sources of heavy metal contamination include with surface resistivity 15-25 Ω sq.-1, PbCl2 powder was obtained
industry[5], traffic[6], domestic waste[7]. These sources of heavy from Aldrich (St Louis, Missouri, United States). All other chemi-
metals pollute the soil, water and the atmosphere. Thus, it is cals and reagents used in the research were reagent grade quality.
imperative to detect heavy metals existing in complex substances For the anodic stripping voltammetry, a standard three-electrode
in the environment [8]. setup was used with platinum coil as counter electrode, Calomel as
In previous studies, mercury has been used as a working elec- the reference electrode, and the fabricated electrodes as the work-
trode precursor because of its high reproducibility and sensitivity ing electrode.
to anodic stripping voltammetry[9,10]. However, it is toxic and

To whom correspondence should be addressed:

Email: *shirley.palisoc@dlsu.edu.ph, †michelle.natividad@dlsu.edu.ph,
‡patricia_devera@dlsu.edu.ph, §benjamin.tuason@dlsu.edu.ph All glasswares and other equipment were placed in the BANDE-

205
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Figure 1. Voltammogram and (B) calibration curve for Lead concentration with 5mg Ru(NH3)6]3+ electrodes

Figure 2. (A) Voltammogram and (B) calibration curve for Lead concentration with 10mg Ru(NH3)6]3+ electrodes

LIN SONOREX ultrasonic bath for about 5 minutes to clean the

materials from all unnecessary particulates that may affect the data. The heavy metal concentration varied at 100ppm, 200ppm, and
Using a diamond tip glass cutter, ITO coated glass substrates were 300ppm to obtain the calibration curves. A fresh electrode was
cut with dimensions 2.5 cm x 1.0 cm. used for every set of runs. During the stripping voltammetry proce-
The amounts of mediator to be dissolved were varied at 5mg, dure, the solution was stirred continuously by a metal stirrer apply-
10mg, and 15mg and were measured using the BOSCH SAE200 ing a potential of −1.40 V for 2 minutes. After the pre-
electronic balance. Solutions of 5% Nafion® with the said respec- concentration set-up, voltammograms were acquired through a
tive concentrations of hexammineruthenium chloride Ru(NH3)6Cl3 potential range of −1.4 and +0.2V. These showed the presence of
were then prepared. 6 mL of deionized water was then used to di- metal ions thorough the characteristic stripping current peak re-
lute the Ruthenium compound. 20 µL of each were mixed with 20 sponding to the heavy metal’s redox potential. After every meas-
µL of 5 wt% Nafion®. All these were measured through a Transfer- urement, the modified electrodes were stripped of impurities by
pette.®S micropipette. Each of the prepared solutions were diluted sustaining the potential at + 0.30V for 30 seconds.
with 1.0 mL methanol.

As shown in Fig 1 to 3, the peak stripping current of Pb2+ in-

In this step, a Transferpette.®S micropipette was used to drop
creased linearly as the heavy metal concentration was increased
coat the ITO coated substrates with the respective concentrations of
from 100 ppm to 300 ppm. The linearity of the calibration curves
the prepared casting solution for the fabrication of Nafion® elec-
obtained yielded correlation values(r) close to 1. Results were ob-
trodes. The coated substrates were air dried at and ambient temper-
tained from getting the averages of three trials on each electrodes.
ature 26oC ± 1oC for 24 hours.
The electrode utilized was fabricated using the 5mg Ru(NH3)6]3+
mediator casting solution. Stripping peaks were obtained at the
potentials -0.45 V to -0.34 V signifying that the heavy metal detect-
 207

Figure 3. (A) Voltammogram and (B) calibration curve for Lead concentration with 15mg Ru(NH3)6]3+ electrodes

ed was lead (Pb2+).

From the calibration curves, the lead (Pb2+) concentrations (
γ = m / stdev(I)
[Pb2+]) at which the resulting peak currents are zero are 1.25ppm, - where m is the slope of the calibration curve and stdev(I) is the
300ppm, and -400ppm, for the three electrodes respectively. This corresponding standard deviation of the current measurement for
means that the given values are the minimum concentrations at each concentration.[13] Summarized in the table below are the
which the electrode will not have any peak current. However, these analytical sensitivity of each measurement from each set of elec-
concentrations can be accounted for by the noise from the empirical trode.
data. This implies that the signal from samples containing no Pb2+
ions would not be zero(attributed to noise in the order of 10-9 to
10-7 Ampere) as given in the calibration curve. Thus, when [Pb2+] =
This study was able to fabricate chemically modified electrodes
0, the resulting peak currents are I1 = -5x10-6, I2 = 6x10-4, and I3 =
and detect Lead ions in deionized water solution using anodic strip-
8x10-4.
ping voltammetry. The drop coating method was used to success-
From these graphs, pertinent information can be derived such as
fully produce redox-active thin films of Nafion. The redox media-
the sensitivity of the sensor which is defined as the instrument’s
tor Ru(NH3)6]3+ used in the study was effectively incorporated
ability to distinguish minute variances in concentration and respond
within the Nafion modified electrodes. As seen from the results,
to small changes in analyte concentration. Calibration sensitivity is
parameters such as the Lead concentration in the analyte solution
defined to be equal to the slope of the calibration curve and among
and the concentration of the redox mediator was varied to control
the three sets of electrodes, the 5mg Ru[(NH6)]3+ electrodes’ yield-
the properties of the fabricated electrodes to undergo heavy metal
ed the steepest calibration curve. The larger slope for the calibra-
detection through ASV. The stripping current peaks increased with
tion curve implies a larger change in signal per unit change in ana-
the concentration of the lead ions present in the solution as well as
lyte concentration, thus higher sensitivity.
with the concentration of the mediator, [Ru(NH3)6]3+. The calibra-
Analytical sensitivity (γ), on the other hand can be computed for
tion curves provided can be used as basis for determining Lead
each concentration to incorporate precision in the sensitivity defini-
concentration in contaminated water with unknown contamination
tion and compare the sensors with equal calibration curve slopes.
levels. It was seen that the 5mg Ru[(NH6)]3+ electrode yielded the
That is,
highest calibration sensitivity and analytical sensitivity suggesting
that the first electrode is the most sensitive among the three that
were fabricated.

Table 1. Analytical Sensitivity values for each concentration of

Pb2+ computed for the three electrodes
The authors wish to give acknowledgement to De La Salle Uni-
Analytical Sensitivity (γ) versity for providing financial and administrative support.
Electrode 100ppm 200ppm 300ppm

5mg Ru[(NH6)]3+ 0.04330 0.12372 * [1] M. OmPrakash, G. Ashish, K. Yogesh, and P. Rajayashree, Int.
10mg Ru[(NH6)] 3+
0.00996 0.00840 0.00888 J. ChemTech., Res., 3, 1596 (2011).
[2] G. Aragay, and A. Merkoçi, Electrochim. Acta, 84, 49 (2012).
15mg Ru[(NH6)]3+ 0.01138 0.03381 0.04142
[3] M. Rainio, T. Eeva, T. Lilley, J. Stauffer, S. Ruuskanen, Comp.
*peak current values that were averaged were equal
208

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