American Journal of Anal yt ical Chemistry, 2011, 2, 284-288
doi:10.4236/ajac.2011.22035 Published Online May 2011 (
Copyright © 2011 SciRes. AJAC
Anodic Stripping Voltammetric Determination of Nitrite
Using Carbon Paste Electrode Modified with Chitosan
Ibrahim H. I. Habib
Microanalytical Chemistry Lab, Applied Organic Chemistry Department, National Research Centre, Cairo , Egypt
Received December 2, 2010; revised March 7, 2011; accepted May 14, 2011
A simple method for anodic stripping voltammetric determination of nitrite using carbon paste electrode
modified with biomolecular chitosan, is described. In this method, the electrode is activated electrochemi-
cally by scanning 5 replicates over the potential range from +500 to +1400 mV immersing in 0.5 M HCl so-
lution. Following this step, the nitrite sample containing 0.1 M KCl is pre-concentrated on the activated elec-
trode at +500 mV for 30 s. The deposited anions are then oxidized by different modes of sweep in the oxida-
tion direction. Chemical and electrical parameters affecting the voltammetric measurements are optimized.
The peak current is linear proportional to the 2
concentration within the range 0.41 - 4.1 µg/ml, with
detection limit 0.187 µg/m using differential pulse mode. The relative standard deviation is 0.285 % for 2.46
µg/ml (five replicates). No interference is observed due to oxygen dissolved in the sample so that nitrogen
purging is not needed in this case. The result obtained by the modified electrode is more accurate and selec-
tive than the unmodified electrode.
Keywords: Chitosan, Carbon Paste Electrode, Nitrite, Anodic Stripping Voltammetry
1. Introduction
Nitrite is one of the pollutants widely found in natural
waters, wastes from fertilizers or intentional additions of
nitrites for corrosion control or protection of meat prod-
ucts. Nitrite ions can interact with amines to form ni-
trosamines which are known as carcinogenic substances.
They also may react with hemoglobin and reduce the
oxygen carrying capacity of it [1,2]. Thus, its concentra-
tion in various types of samples has to be controlled by
sensitive methods.
The most commonly used method for nitrite determi-
nation ranging from trace to ultra trace levels is the elec-
trochemical techniques. This includes polarography [3-7],
amperimetry [8,9] and voltammetry [10-14]. The sensi-
tivity can be further enhanced if the surface of bare elec-
trodes is modified chemically with active thin film of-
fering significant advantageous for design and develop-
ment of electrochemical sensors. According to the litera-
ture survey, all electrodes modified by complexes of iron
[15,16], palladium [17], iridium [18], cobalt [19], copper
[20], mercury [21], cetyltrimethylammonium bromide
[10], phosphomolybdic [22,23] or silicotungestic acids
[24,25] have been used successfully for electrochemical
oxidation of nitrite. Boron-doped diamond electrode [26]
has also been applied for monitoring nitrite, but it needs
special instruments not ever available elsewhere.
Chitosan, on the other hand, is natural product extracted
from the shell of shrimps, crabs and insects [27]. Because
of its ability to bind strongly with many metals [28], chi-
tosan and its derivatives have been applied for electro-
chemical determination of silver [29,30], platinum [30],
palladium [30], gold [30,31], lead [32,33] and iron [34].
In the present work, carbon paste electrode modified
with natural chitosan represents the simplest and repro-
ducible analytical tool to determine nitrite in samples.
2. Experimental
2.1. Apparatus and Reagents
A Metrohm model 693 VA processor and 694 VA stand
equipped with a Ag/AgCl-3 M KCl and a platinum
counter electrode are employed. The modified carbon
paste electrode is used as the working electrode and pre-
pared as described below.
I. H. I. HABIB285
2.2. Preparation of the Modified Carbon Paste
The carbon paste is prepared by mixing 175 mg paraffin
oil (Fluka), 250 mg synthetic carbon powder 1 - 2 micron
(Aldrich) and 48 mg low-viscous Chitosan (Fluka) in
agate mortar. The electrode is consisted of stainless steel
tube with i.d. 2.5 mm and 30 mm deep, moving through
it an inner screwed stainless steel connector. The tube is
coated externally with Teflon. The tube is packed with
the modified carbon paste, compressed with inner screw
and smoothed on a wetted Whatman filter paper.
2.3. Procedure
The fresh surface electrode is first immersed in 0.5 M
HCl solution and electrically activated by direct current
sweep five replicates from +500 to +1400 mV with scan
rate 50 mV/s. The solution is then exchanged by 10 ml of
0.1 M KCl solution containing 0.41 - 4.1 µg of nitrite
and pre-concentrated for 30 s at +500 mV with stirring at
2000 rpm. After resting for 10 s, one of electrical modes
(direct current tast DC, differential pulse DP, square
wave SW or first-harmonic alternating current AC1) is
ramped from +500 to +1400 mV with scan rate 50 mV/s,
pulse amplitude 50 mV, pulse duration 20 ms, measure-
ment time 10 ms, frequency 30 Hz for SW and AC1. The
experiment is triplicated without electrode re- generation
and two standard solutions of nitrite are added sequen-
tially. Average of current peaks due to the sample and
standard solutions are taken. For new electrode, the ex-
periment is repeated with new activation of electrode as
described before.
3. Results and Discussion
Preliminary experiments are carried out to optimize the
sensor composition. The height of peak current obtained
for nitrite is used to compare the performance of the dif-
ferent chemical and physical parameters. Each parameter
is analyzed triplicate with the same sensor and the cor-
responding average value of peak height is plotted. The
working electrode containing 40% (w/w) water-immis-
cible organic binders (pasting liquids), viz. paraffin or
silicon oils, with/without 4% chitosan are prepared and
examined under identical conditions, i.e. immersing in
0.5 M HCl prior accumulation and differential pulse
stripping voltammetric measurements of nitrite in 0.1 M
KCl solution. It is obvious from Figure 1, the 40% par-
affin oil with 4% chitosan accumulates afforded highest
stripping peak at potential of about +900 mV. Thus, the
modifier enhances the sensitivity of the electrode twice
more than using paraffinic bare CPE. This enhancement
Figure 1. Differential pulse DP cathodic stripping voltam-
mograms for determining nitrite in absence and presence of
chitosan with scan rate 60 mV/s, pulse amplitude 50 mV in
0.3 M KCl.
could be explained by the fact that the – NH2 group is
converted into 3
making it easy to increase the
electrostatic attraction of negatively charged nitrite ions
on its surface in a similar manner for determining nega-
tively charged palladium, platinum30 and lead32 chloride
The sensitivity and linear responses towards the nitrite
concentrations can also be enhanced by increasing the
proportion of chitosan up to 10% (w/w) chitosan. Be-
yond this proportion a depression in the sensitivity is
observed as shown in Figure 2.
On the other hand, the influence of HCl and KCl, sep-
arately or in mixture solutions, revealed that in acidic
solutions (pH < 3.3) nitrite is escaped as NO gas and lost
Figure 2. Effect of chitosan (%, w/w) on the stripping cur-
rent at different concentrations of nitrite (0.41 - 2.46 µg/mol
NO2) using DP mode with scan rate 60 mV/s, pulse ampli-
tude 50 mV in 0.3 M KCl.
Copyright © 2011 SciRes. AJAC
more when nitrogen gas is bubbled giving up weak peak
current. In a neutral medium, pH > 3.3, nitrite anion is
predominated promoting to strong peak current. Thus, in
order to avoid NO gas formation, two separating solu-
tions on two sequential steps are achieved, 0.5 M HCl
solution for the protonation of chitosan followed by 0.1
M KCl solution for applying as a neutral supporting
electrolyte medium. The latter effect is as depicted in
Figure 3 where the concentration of 0.1 M KCl gives the
highest peak current and best linear relation.
The variation of scan rate from 10 to 120 mV/s re-
vealed that the diffusion current is related linearly with
square root of scan rate, but the oxidation reaction pro-
ceeded irreversibly as the peak potential shifted linearly
to more positive potential with increasing the scan rate.
No reduction peak is observed on the reverse scan within
the studied potential range indicating that the overall
process is chemically irreversible in agreement with the
previous reports for nitrite oxidation at different types of
electrodes [35,36].
Modulating the direct current tast ramp DCT with
various wave forms by using superimposed differential
pulse DP, square-wave SW or first harmonic a.c. modu-
lation AC also studied to explore which one of modes
will enhance the sensitivity.
As shown in Figures 4 and 5, variation of current with
concentration of nitrite ions showed a linear behavior
between 0.41 and 4.1 µg/mol of nitrite with correlation
coefficients 0.994, 0.999, 0.998 and 0.998 for different
modes of sweep DC, DP, SW and AC1, respectively.
The detection limit based on “three standard deviations
of the blank 3sB method [37] is found to be in turn, 0.281,
0.187, 0.207 and 0.241 µg/ml nitrite. The analytical pa-
rameters for nitrite determination are reported in Table 1.
Figure 3. Effect of KCl on the stripping current at different
concentrations of nitrite (0.41 - 2.46 µg/ml NO2) using 10%
chitosan carbon paste electrode and DP mode with scan rate
60 mV/s and pulse amplitude 50 mV.
Figure 4. Different modes of sweeps, DCT, DP, SW and
AC1, at different concentrations of nitrite (0.41 - 2.46 ug/ml
NO2) using 10% chitosan carbon paste electrode with scan
rate 60 mV/s, pulse amplitude 50 mV in 0.1 M KCl.
Figure 5. Regression lines for determining nitrite using
different modes of sweep.
Table 1. Analytical parameters for nitrite determination at
chitosan modified CP electrode.
ModeR Slope,
nA/µg LOD µg Repeatability
RSD, %
AC10.998204.78– 74.76 0.241 0.668
DP 0.999208.35– 66.17 0.187 0.285
DC 0.994360.86– 173.00 0.281 1.018
SW 0.998404.86– 169.084 0.206 0.437
An extremely attractive feature of the chitosan modi-
fied carbon paste electrode is its highly stable response
toward nitrite oxidation. Repeatability “RSD” using dif-
ferent mode is found to be 1.018%, 0.285%, 0.437% and
0.668%, respectively, for five successive determination
of 2.46 µg/ml nitrite. For the same modified chitosan
Copyright © 2011 SciRes. AJAC
I. H. I. HABIB287
electrode, reproducibility, without and with successive
cut off/polishing five times, is found to be 0.285% and
0.347%, respectively, for 2.46 µg/ml nitrite and using DP
It is concluded that the new and simple carbon paste
electrode modified with chitosan has been shown to offer
comparable performance to the more expensive glassy
carbon or diamond electrodes for the practical use to
analysis 2ions at trace concentrations in real samples
by anodic striping voltammetry with high sensitivity and
4. Acknowledgements
Thanks are due to Volkswagen Stiftung, Kastanienallee
35, 30519 Hannover, Germany, for the financial support
of purchasing the Metrohm model 693 VA processor and
694 VA stand.
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