American Journal of Anal yt ical Chemistry, 2011, 2, 284-288
doi:10.4236/ajac.2011.22035 Published Online May 2011 (http://www.SciRP.org/journal/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
Abstract
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 NO

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
Electrode
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
NH

 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
complexes
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.

I. H. I. HABIB 286
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
Intercepte
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

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
mode.
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
selectivity.
NO
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.
5. References
[1] P. F. Swann, “The Toxicology of Nitrate, Nitrite and
N-nitroso Compounds,” Journal of Agricultural and
Food Chemistry, Vol. 26, No. 1, January 1975, pp. 1761-
1970. doi:10.1002/jsfa.2740261119
[2] S. S. Mirvish, “Role of N-nitroso Compounds (NOC) and
N-Nitrosation in Etiology of Gastric, Esophageal, Naso-
pharyngeal and Bladder Cancer and Contribution to Can-
cer of Known Exposures to NOC,” Cancer Letters, Vol.
93, No. 1, June 1995, pp. 17-48.
doi:10.1016/0304-3835(95)03786-V
[3] P. Sharma and R. Sharma, “Sequential Trace Determina-
tion of Nitrate and Nitrite in Natural Waters by Differen-
tial Pulse Polarography,” International Journal of
Environmental Analytical Chemistry, Vol. 82, No. 1,
2002, pp. 7-11. doi:10.1080/03067310290024049
[4] H. Walter and J. J. Specchio, “Determination of Nitrite
and Nitrate by Differential Pulse Polarography with Si-
multaneous Nitrogen Purging,” Analytical Chemistry, Vol.
64, No. 11, 1992, pp. 1313-1322.
doi:10.1021/ac00035a021
[5] T. S. Sadallah and A. A. Banan, “Differential-Pulse
Polarographic Determination of Nitrite,” Analyst, Vol.
109, No. 12, 1984, pp. 1545-1547.
doi:10.1039/an9840901545
[6] Y. P. Cui, C. Z. Yang, W. Zeng, M. Oyama, W. H. Pu
and J. D. Zhang, “Electrochemical Determination of
Nitrite Using a Gold Nanoparticles-Modified Glassy
Carbon Electrode Prepared by the Seed-Mediated Growth
Technique,” Analytical Science, Vol. 23, No. 12, 2007,
pp. 1421-1425. doi:10.2116/analsci.23.1421
[7] Ü. T. Yilmaz and G. Somer, “Determination of Trace
Nitrite by Direct and Indirect Methods Using Differential
Pulse Polarography and Application,” Journal of Elec-
troanalytical Chemistry, Vol. 624, No. 1-2, 2008, pp.
59-63. doi:10.1016/j.jelechem.2008.07.025
[8] J. R. Caetano da Rocha, L. Angnes, M. Bertotti, K. Araki
and H. E. Toma, “Amperometric Detection of Nitrite and
Nitrate at Tetraruthenated Porphyrin-Modified Electrodes
in a Continuous-Flow Assembly,” Analytica Chimica
Acta, Vol. 452, No. 1, January 2002, pp. 23-28.
doi:10.1016/S0003-2670(01)01440-4
[9] A. Salimi, A. Noorbakhash and F. S. Karonian, “Am-
perometric Detection of Nitrite, Iodate and Periodate on
Glassy Carbon Electrode Modified with Thionin and
Multi-Wall Carbon Nanotubes,” International Journal of
Electrochemcal Science, Vol. 1, No. 9 , 2006, pp. 435-446
[10] L. Guanghan, J. Hong and S. Dandan, “Determination of
Trace Nitrite by Anodic Stripping Voltammetry,” Food
Chemistry, Vol. 59, No. 4, 1997, pp. 583-587.
doi:10.1016/S0308-8146(96)00290-7
[11] J. Markus and M. Fedurco, “Vitamin B12 as Coordinating
Agent for the Voltammetric Determination of Nitrite in
Natural Waters,” Analytica Chimica Acta, Vol. 248, No.
1, July 1991, pp. 109-115.
doi:10.1016/S0003-2670(00)80875-2
[12] S. M. Silva and L. H. Mazo, “Differential Pulse Vol-
tammetric Determination of Nitrite with Gold Ultra-
microelectrode,” Electroanalysis, Vol. 10, No. 17, 1998,
pp. 1200-1203.
doi:10.1002/(SICI)1521-4109(199811)10:17<1200::AID-
ELAN1200>3.0.CO;2-5
[13] C. M. G. Van den Berg and H. Li, “Potentiometric and
Voltammetric Responses of Carbon Fibre Electrodes,”
Analytica Chimica Acta, Vol. 212, 1988, pp. 31-41.
doi:10.1016/S0003-2670(00)84126-4
[14] M. Badea, A. Amine, M. Benzine, A. Curulli, D.
Moscone, A. Lupu, G. Volpe and G. Palleschi, “Rapid
and Selective Electrochemical Determination of Nitrite in
Cured Meat in the Presence of Ascorbic Acid,” Micro-
chimica Acta, Vol. 147, No. 1-2, 2004, pp. 51-58.
doi:10.1007/s00604-004-0220-8
[15] J. E. Toth and F. C. Anson, “Electrocatalytic Reducetion
of Nitrite and Nitric Oxide to Ammonia with Iron-Subs-
tituted Polyoxotungstates,” Journal of the American
Chemical Society, Vol. 111, No. 7, March 1989, pp.
2444-2451. doi:10.1021/ja00189a012
[16] W. J. R. Santos, Ph. R. Lima, A. A. Tanaka, S. M. C. N.
Tanaka and L. T. Kubota, “Determination of Nitrite in
Food Samples by Anodic Voltammetry Using a Modified
Electrode,” Food Chemistry, Vol. 113, No. 4, 2009, pp.
1206-1211. doi:10.1016/j.foodchem.2008.08.009
[17] W. Sun, S. Zhang, H. Liu, L. Jin and J. Kong, “Electro-
catalytic Reduction of Nitrite at a Glassy Carbon Elec-
trode Surface Modified with Palladium (II)-Substituted
Keggin Type Heteropolytungstate,” Analytica Chimica
Acta, Vol. 388, No. 1-2, May 1999, pp. 103-110.
doi:10.1016/S0003-2670(99)00064-1
[18] W. Sun, F. Yang, H. Liu, L. Jin, J. Kong, S. Jin, G. Xie
and J. Deng, “Electrochemical and Electrocatalytic Prop-
erties of Iridium(IV)-Substituted Dawson Type Polyoxo-
tungstate,” Journal of Electroanalytical Chemistry, Vol.
451, No. 1-2, July 1998, pp. 49-57.
doi:10.1016/S0022-0728(97)00511-1

I. H. I. HABIB 288
[19] M. Thamae and T. Nyokog, “Cobalt (II) Porphyrazine
Catalysed Reduction of Nitrite,” Journal of Electroana-
lytical Chemistry, Vol. 470, No. 2, July 1999, pp. 126-
135. doi:10.1016/S0022-0728(99)00224-7
[20] C. S. Fung and K. Y. Wong, “Electrocatalytic Reduction
of Nitrite by Copper Complexes of 1, 10-Phenanthroline
and 2,2′:6′,2″-Terpyridine,” Journal of Electroanalytical
Chemistry, Vol. 401, No. 1-2, January 1996, pp. 263-268.
doi:10.1016/0022-0728(95)04414-0
[21] L. Ruhlmann and G. Genet, “Wells–Dawson-derived
Tetrameric Complexes {K28H8[P2W15Ti3O60.5]4} Electro-
chemical Behaviour and Electrocatalytic Reducetion of
Nitrite and of Nitric Oxide,” Journal of Electroanalytical
Chemistry, Vol. 568, July 2004, pp. 315-321.
doi:10.1016/j.jelechem.2004.02.020
[22] S. Liu, Z. Shi and S. Dong, “Preparation of a Composite
Film Electrode Containing 12-Tungstosilicic Acid and Its
Electrocatalytic Reduction for Nitrite,” Electroanalysis,
Vol. 10, No. 13, 1998, pp. 891-896.
[23] S. Dong, X. Xi and M. Tian, “Study of the Electrocata-
lytic Reduction of Nitrite with Silicotungstic Heter-
opolyanion,” Journal of Electroanalytical Chemistry, Vol.
385, No. 2, 1995, pp. 227-233.
doi:10.1016/0022-0728(94)03770-4
[24] L. Cheng and S. Dong, “Electrochemical Behavior and
Electrocatalytic Properties of Ultrathin Films Containing
Silicotungstic Heteropolyanion SiW12O404–,” Journal of
the Electrochemical Society, Vol. 147, No. 2, 2000, pp.
606-612. doi:10.1149/1.1393241
[25] X. Wang, E. Wang and C. Hu, “Hybrid Inorganic- Or-
ganic Material Containing 12-Molybdophosphate
Bulk-Modified Carbon Paste Electrode,” Chemistry Let-
ters, Vol. 30, No. 10, 2001, pp. 1030-1031.
doi:10.1246/cl.2001.1030
[26] N. Spataru, T. N. Rao, D. A. Tryk and A. Fujishima,
“Determination of Nitrite and Nitrogen Oxides by Anodic
Voltammetry at Conductive Diamond Electrodes,” Jour-
nal of Electrochemical Society, Vol. 148, No. 3, 2001, pp.
E112-E117.
[27] A. J. Varma, S. V. Deshpande and J. F. Kennedy; “Metal
Complexation by Chitosan and its Derivatives: A Re-
view,” Carbohydrate Polymers, Vol. 55, No. 1, January
2004, pp. 77-93. doi:10.1016/j.carbpol.2003.08.005
[28] E. Guibal; “Interactions of Metal Ions with Chitosan-
Based Sorbents: A Review,” Separation and Purification
Technology, Vol. 38, No. 1, July 2004, pp. 43-74.
[29] Q. H. Yang, X. Z. Ye and Z. C. Hong, “LihuaJianyan,
Huaxue-Fence,” Analytical Abstracts, Vol. 36, No. 161,
2000.
[30] X. Z. Ye, Q. H. Yang; Y. Wang and N. Q. Li, “Electro-
chemical Behaviour of Gold, Silver, Platinum and Palla-
dium on the Glassy Carbon Electrode Modified by Chi-
tosan and its Application,” Talanta, Vol. 47, No. 5, De-
cember 1998, pp. 1099-1106.
doi:10.1016/S0039-9140(98)00189-1
[31] Q. H. Yang, X. Z. Ye and H. Wang, “Fenxi-Shi-yanshi,”
Analytical Abstracts, Vol. 17, 1998, p. 5.
[32] R. A. Y. Hassan, I. H. I. Habib and H. N. A. Hassan,
“Voltammetric Determination of Lead (II) in Medical
Lotion and Biological Samples Using Chitosan-Carbon
Paste Electrode,” International Journal of Electrochem-
cal Science, Vol. 3, No. 8, 2008, pp. 935-945.
[33] J. R. Xu and B. Liu, “Preconcentration and Deter-
mination of Lead Ions at a Chitosan-Modified Glassy
Carbon Electrode,” Analyst, Vol. 119, No. 7, 1994, pp.
1599-1601. doi:10.1039/an9941901599
[34] G. H. Lu, X. Yao, X. G. Wu and T. Zhan, “Determination
of the Total Iron by Chitosan-Modified Glassy Carbon
Electrode,” Microchemical Journal, Vol. 69, No. 1, May
2001, pp. 81-87. doi:10.1016/S0026-265X(01)00066-2
[35] J. A. Cox and P. J. Kulesza, “Oxidation and Determina-
tion of Nitrite at Modified Electrodes,” Journal of Elec-
troanalytical Chemistry, Vol. 175, No. 1-2, September
1984, pp. 105-118. doi:10.1016/S0022-0728(84)80349-6
[36] R. B. Almeida, S. S. S. Borges and M. G. Gomes, “De-
termination of Nitrite in Aqueous Solutions Using the
Linear Sweep Voltammetry Technique,” Analytical Let-
ters, Vol. 32, No. 6, 1999, pp. 1203-1210.
doi:10.1080/00032719908542889
[37] J. C. Miller and J. N. Miller, “Statistics for Analytical
Chemistry,” 2nd Edition, 1988, Ellis Horwood Ltd.,
Chichester, p. 115.