ISSN-1996-918X

Pak. J. Anal. Environ. Chem. Vol. 9, No. 1 (2008)
Short Communication

Voltammetric study of Arsenic (III) and Arsenic (V) in Ground
Water of Hajigonj and Kalkini in Bangladesh

Samir Chandra Paul, Mohammad Arifur Rahman, Nur-E-Alam Siddique
and A. M. Shafiqul Alam*

Department of Chemistry, University of Dhaka, Dhaka-1000, Bangladesh
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Abstract
The speciation of arsenic in groundwater samples using Square Wave Anodic Stripping
Voltammetry (SWASV), Differential Pulse Anodic Stripping Voltammetry (DPASV) and Normal
Pulse Anodic Stripping Voltammetry (NPASV) are described. Good resolution of the species,
arsenic (III) and arsenic (V) is achieved using SWASV. The reliability of the methods was
checked by analyzing the total arsenic content of the samples by Hydride Generation Atomic
Absorptioion Spectrophotometer and by analyzing prepared controlled laboratory standard
solution. Since this technique is comparatively cheaper than other available techniques it could be
a better analytical technique for arsenic speciation from water. In this study, the assessment of
inorganic arsenic species in ground water of Kalkini (Madaripur) and Hajigonj (Chandpur) is
reported. It shows that arsenic content in water in different locations is irregular. Most of the
locations contain higher level of As(III) than As(V). The highest concentration of arsenic is found
in Anayetnagor (554.46 ± 0.07 g/L) of Kalkini and Raichar (562 ± 0.50 g/L) of Hajigonj.
However, the level of total arsenic and As(III) of most of the villages of the study areas are more
than the WHO guideline value (50g/L). Therefore a proper monitoring process should be evolved
along with the development of methods to keep the water free from arsenic.

-------------------------------------------------------------------------------------------------------------------------------
Introduction

Arsenic is ubiquitous in the environment, being
naturally present in soil, air, water and food, and
concentrations may be increased by anthropogenic
contamination [1]. It is present in the environment in a
number of different inorganic and organic chemical
forms due to its participation in complex biological and
chemical process. Some of the most important arsenic
species from a toxicological perspective include the two
oxidation states As(III), As(V), monomethylarsenic acid
(MMA), dimethylarsinic acid (DMA), arsenobetaine
and arsenocholine [2].

In recent years, the presence of high levels of
arsenic in ground water, the main source of drinking
water in many countries around the world, has drawn
attention of the scientific communities. Moreover,
contamination of food chain by arsenic contaminated
water is another threat [3]. Numerous recent
investigations have demonstrated that arsenic
constitutes a serious health risk spot in Bangladesh

[2-6]. Bangladesh, a country in south Asia with a
population of about 150 million, is one of a number of
countries that has arsenic contamination in its
groundwater, which results from the underlying
mineralogy and geology of the area. Arsenic
contamination has been reported in groundwater in 41
out of 64 districts in Bangladesh [3]. About 61% of the
water analysed from tubewells has arsenic content
above 0.01 mg/L [4]. The average concentration of
arsenic in contaminated water is about 0.26 mg/L with a
maximum level of 0.83 mg/L. This is significantly
higher than the World Health Organization (WHO)
maximum permissible limit in drinking water which is
0.05 mg/L [7].

Moreover, Arsenic shows toxicity and

chemical property depending on its oxidation state and
physicochemical forms. Inorganic arsenic is known to
be more toxic than organic ones, and As3+ is reported at
least ten times more toxic than As5+ [8]. Thus it is
important to determine each of arsenic species rather *Corresponding Author E-mail: amsalam2004@yahoo.com

mailto:amsalam2004@yahoo.com

Pak. J. Anal. Environ. Chem. Vol. 9, No. 1 (2008)

than the total amount. Rasul et al., and Hussam et al.,
studied the As (III) and As (V) with the aid of anodic
stripping voltammetry (ASV) and other metals with
AASGF-Z (Zeeman Effect-Atomic Absorption
Spectrometer with Graphite Furnace) from groundwater
of Kustia, Bangladesh [9,10]. But there is no work has
been reported with study of the As(III), As(V) with
Square Wave Anodic Stripping Voltammetry
(SWASV), Differential Pulse Anodic Stripping
Voltammetry (DPASV) and Normal Pulse Anodic
Stripping Voltammetry (NPASV) at Hajigonj and
Kalkini of Bangladesh which are most endemic areas.
Therefore, speciation of arsenic rather than
quantification of total arsenic in drinking water present
in groundwater are necessary.

Speciation of arsenic has been performed with

different hyphenated techniques, often the coupling of
ion chromatography or liquid-chromatography to
detection system like: direct UV detection, direct
coupling to atomic absorption spectrometry, AAS, on-
line hydride generation AAS (Hg-AAS), ICP atomic
emission spectrometry (ICP-AES), ICP mass
spectrometry [11-13]. These techniques are very
expensive. Several reports have appeared on
electrochemical stripping procedures for the
determinations of arsenic [9, 10, 14]. The
instrumentation required is relatively simple and
generally the cost is far less than that required for the
other techniques. Another advantage of electrochemical
techniques is their ability to distinguish between the
different oxidation states of arsenic. The anodic
stripping voltammetry is very sensitive [14] and
compared with expensive multielement analysis
techniques like ICP-MS, is an economical procedure for
trace determination of arsenic down to the g/l level.

In the present work, there are three different

electronalytical methods such as Square Wave Anodic
Stripping Voltammetry (SWASV), Differential Pulse
Anodic Stripping Voltammetry (DPASV) and Normal
Pulse Anodic Stripping Voltammetry (NPASV), were
used for the determination of arsenic with speciation to
satisfy the lack of proper analytical techniques and
implement such analytical methods that can provide
accurate and interference free measurements of arsenic
at the g/l levels of concentrations in water of Hajigonj
and Kalkini of Bangladesh.

Experimental
The study area

Tubewell water was collected from nine
villages of Hajigonj and nine villages of Kalkini.
Hajigonj Thana at Chandpur district is 53 kilometers
away from Comilla district and Kalkini Thana at

Madaripur district is 260 kilometer away from Dhaka
city.

Sampling

Tube well water was collected in polythene

containers which were washed before collecting
samples with 5% HNO3, distilled de-ionized water and
finally with the tube well water at the sampling sites for
several times. The information about the depth of the
tube well, year of installation and also red or green
marked were collected from the local inhabitants by
supplying the questions-answers sheets.

Sample preparation

The samples collected from different points

were filtered with a microfilter paper under vacuum and
preserved in acid (1ml conc. HCl per 100ml of water
sample). For the measurements of total arsenic, the
samples were mixed with concentrated HCl and Na2SO3
(s) (10ml sample + 10ml conc. HCl + 30-40 mg
Na2SO3(s)) in an acid clean Pyrex glass electrolysis cell
and heated at 70�80 0 C for 20-30 minutes without
stirring, then 15 minutes with stirring and also 15
minutes with purging nitrogen with stirring until all SO2
fumes cleared. The sample was then cooled to room
temperature and was thus made ready for the
measurements of the concentration of total arsenic [14].

Preparation of stock standard solutions

Standard 1000 mg/L stock solutions of As3+

and As5+ were prepared by dissolving As2O3 (Merck,
Germany, Analytical grade) and Na2HAsO4.7H2O
(Merck, Germany, Analytical grade) in deionized water
respectively. These solutions were made acidic by the
addition of 2-3 ml conc. HCl acid. Fresh standard
solutions of lower concentrations were made from the
stock solution at the beginning of the everyday
experiment.

Analytical procedure for quantification of As3+ and
As5+

At first the gold electrode was made shiny

yellow, almost scratch free surface by polishing with
fine alumina powder (0.3µm) on wet polishing cloth.
Then the electrode was cleaned with deionised water
and then 1M HCl and also stored in 6M HCl. For
measurements of As3+, the stair bar was put into the cell
and the cell was filled with 10 ml sample and 10 ml 6M
HCl [9]. The solution was purged for 10 minutes with
nitrogen. All the electrodes were inserted and tapped off
to remove any bubbles from them. A computerized
electrochemical system, model HQ-2040 by Advanced

Pak. J. Anal. Environ. Chem. Vol. 9, No. 1 (2008)

E(mV) vs. Ag/AgCl (sat. KCl)

-200 -100 0 100 200 300 400 500 600

C
u

rr
e

n
t,
i

(µ
A

)
-5

NPASV

SWASV

DPASV

Background current

Analytics, USA was used for the analysis. The
deposition potential (Initial potential), accumulation or
deposition time (Initial delay), quit time delay is -
150mV, 120sec. and 30 sec. respectively. The run
replication (number of addition) is 3. In these analytical
measurement procedures two standard additions were
performed and corresponding currents were measured
after subtraction of background current. The signal
current was then plotted against concentration. The
concentration of arsenic was calculated from the slop of
the regression line drawn through the points using
software sigma plot based on MS-Excel. Total arsenic
was determined by same procedure after treatment of
sample with NaHSO3 as described in sample preparation
method. As5+ was evaluated with subtraction of As3+
from total arsenic [14].

Results and Discussion

Pulse voltammetric techniques, introduced by
Barker and Jenkin [15], are aimed at lowering the
detection limits of voltammetric measurements. By
substantially increasing the ratio between the faradaic
and nonfaradaic currents, such techniques permit
convenient quantification down to the 10-8M
concentration level. Because of their greatly improved
performance, modern pulse techniques have largely
supplemented classical polarography in the analytical
laboratory. Among the voltammetric techniques Normal
Pulse Voltametry (NPV), Differential Pulse Anodic
Stripping Voltammetry (DPASV), Square Wave
Voltametry (SWV) was checked to evaluate the
sensitivity for the trace arsenic analysis and speciation
from groundwater.

Analytical comparison between SWV, DPV and NPV

The SWAS, DPAS and NPAS voltammograms

of arsenic (As3+) for a 50 ppb standard solution at solid
gold electrode (Au- button) are demonstrated in
Figure1. Out of three ASV techniques in use, NPASV is
considered to be least sensitive and selective method
due to its highest signal to background ratio. In NPV,
the non- faradaic current could not be avoided
completely because the current is sampled once at the
end of pulse amplitude. This charging current increases
the signal current and for this reason NPV shows high
signal current with respect to SWV and DPV where the
current is sampled twice, just before the pulse
application and late pulse life. Although in NPV, small
amount of charging current is present it is also good
sensitive method for As3+ analysis. Out of these
techniques used for arsenic analysis, the SWASV
technique is most sensitive and selective
electroanalytical method because of its ability to
enhance the analytical signal by removing non-faradaic

current. So less time is required for arsenic analysis and
ultra trace analysis can be easily performed with this
method. However, among these methods DPASV shows
moderate signal for arsenic but it is also a sensitive
method for arsenic analysis.

Figure 1: Comparison between three different electroanalytical
methods for As3+(same concentration) at solid gold electrode.

Speciation of arsenic in ground water

It is reported that shallow aquifer layer is

contaminated with arsenic in almost all of the districts
of Bangladesh (DPHE-BGS, 2000). In this study,
arsenic level is determined in Hajigonj (Chandpur) and
Kalkini (Madaripur) two contaminated areas of
Bangladesh.

The different species of arsenic (As3+and As5+)

content of ground water samples from different
locations of the study area was measured with three
different electroanlytical methods (SWASV, DPASV
and NPASV) and the data thus obtained are represented
in the Table 2 and Table 3. From the results, it is clear
that the distribution of arsenic is not regular rather
scattered due to the spatial variation. This is because of
the variation in the depth of tube wells, amount of water
withdrawn and also the geological phenomenon. In
Hajigonj, the level of As3+ ranges from 48.19 to 285.28
g/L. Among all the water samples collected from the
nine different villages of Hajigonj, the highest arsenic
(III) concentration was found in Raichar (285.28 g/L)
and the lowest was in Toraghor (48.19g/L). The value
of As5+ is also the lowest in Satbaria (40.05g/L) and
the highest in Raichar (276.95g/L). However, all of the

Pak. J. Anal. Environ. Chem. Vol. 9, No. 1 (2008)

water samples contain total arsenic above the WHO
guide line value (50 g/L).

The level of As3+ ranges from 26.91 to 286.0

g/L in Kalkini. Among the nine water samples
collected from the nine different villages of Kalkini, the
highest arsenic(III) concentration was found in

Anayetnagor (286.0g/L) and the lowest was in
Charluxmi (26.91g/L). The lowest value of As5+ is in
Shadipur (26.10g/L) and the highest in Anayetnagor
(268.46g/L). Most of the water samples contain total
arsenic above the WHO guide line value (50 g/L).

Table 1. Concentration of As3+and As5+ in ground water of the study area, Hajigonj (Chandpur)

Sample no. Sampling location
Depth of

tube wells

Methods Conc. of As3+
Conc. of total As

(As3++ As5+)
Conc.of As5+

(feet) (g/LSD) (g/LSD) (g/L)

SWASV 80.73.0.05 120.78.0.09 40.50

DPASV 72.530.12 119.900.16 47.37 1 Satbaria 90

NPASV 74.580.70 116.540.30 41.96

SWASV 72.710.07 118.670.70 45.96

DPASV 76.560.09 123.090.17 46.53 2 Khalpara 100

NPASV 78.750.06 115.430.18 36.68

SWASV 197.090.21 320.870.01 123.78

DPASV 198.94.0.08 307.270.06 108.33 3 Bolakhal 140

NPASV 190.060.09 312.120.13 122.06

SWASV 80.240.30 129.450.07 49.21

DPASV 70.800.70 115.560.06 44.76 4 Bakila 100

NPASV 72.760.16 121.490.18 48.73

SWASV 285.280.90 562.230.50 276.95

DPASV 288.330.60 594.530.13 306.20 5 Raichar 120

NPASV 203.430.23 437.600.23 243.17

SWASV 276.570.04 380.890.60 104.32

DPASV 296.340.30 389.600.30 93.26 6 Uchaa gram 140

NPASV 280.980.50 381.260.04 100.28

SWASV 83.560.40 140.430.40 56.87

DPASV 85.900.30 145.870.30 59.97 7 Dherra 100

NPASV 84.370.13 143.590.60 59.22

SWASV 48.190.70 94.540.30 46.35

DPASV 46.470.15 91.010.19 44.54 8 Toraghor 70

NPASV 41.580.50 82.920.50 41.34

SWASV 120.270.20 209.760.50 89.49

DPASV 121.680.40 209.00.40 87.32 9
Shendra

110

NPASV 110.100.14 187.230.16 77.13

No. of analysis (n=3)

Pak. J. Anal. Environ. Chem. Vol. 9, No. 1 (2008)

Table 2. Concentration of As3+and As5+ in ground water of the study area, Kalkini (Madaripur)

No. of analysis (n=3)

The variation of arsenic concentration with
depth of the different tube wells is presented in Table 1
and Table 2. It was found that the concentration of total
arsenic was increased with the increase of depth within
this range of 70 to 160 ft. This indicates high percentage
of water was withdrawn from these aquifers. Moreover,
it is interesting that the concentration of As (III) and As
(V) varied with the depth of the tube well. This may be
due to the change of geology with the variation of
depth of soil. Hussam et al., 2003 found the

concentration of As (III) and As (V) was present as
AsO3

3- (0.712 mg/l) and AsO4
3- (0.973 mg/l) in

groundwater at Kustia respectively [10].

From the Table 1 and Table 2, it is noticed that

most of the locations of Kalkini and Hajigonj contain
higher level of As(III) than As(V). This observation
implies that more inorganic arsenic in ground water
present in reduced form.

Sample
no.

Sampling location
Depth of

tube wells

Methods
Concentration of

As3+

Concentration of
total As

(As3++ As5+)

Concentration
of As5+

(feet) (g/LSD) (g/LSD) (g/L)

SWASV 166.290.21 306.510.05 140.22

DPASV 161.170.03 299.590.09 138.42 1 Charbivagdi 120

NPASV 166.640.08 287.260.13 120.62

SWASV 51.970.12 98.200.12 46.23

DPASV 41.550.30 89.670.50 48.12 2 Dharichar 90

NPASV 42.750.40 72.810.80 30.06

SWASV 32.530.08 47.590.07 15.06

DPASV 32.400.10 51.840.14 19.44 3 Charluxmi 70

NPASV 26.910.14 42.420.30 15.51

SWASV 75.960.16 102.060.80 26.10

DPASV 95.160.06 126.770.17 31.61 4 Shadipur 80

NPASV 82.160.09 102.520.07 20.36

SWASV 46.300.70 76.270.15 29.97

DPASV 35.520.12 69.560.19 34.04 5
Kashimpur

NPASV 30.600.15 64.020.10 33.42

SWASV 110.710.05 197.310.07 86.60

DPASV 110.110.07 190.610.40 80.50 6 Shikar mangol 120

NPASV 89.960.40 156.220.08 89.96

SWASV 53.800.50 76.240.09 22.44

DPASV 47.520.09 67.760.40 20.24 7 Khishnanagor 70

NPASV 39.680.08 51.720.05 12.04

SWASV 126.180.4 186.200.20 60.02

DPASV 97.440.07 160.510.70 63.07 8 Alipur 120

NPASV 86.460.23 138.900.04 52.44

9 Anayet nagor 160 SWASV 286.00.14 554.460.07 268.46

DPASV 275.450.16 539.400.20 263.95

NPASV 268.210.02 542.400.09 274.19

Pak. J. Anal. Environ. Chem. Vol. 9, No. 1 (2008)

Table 3. Concentration of arsenic in water sample of manikgonj considered as controlled area (SWASV method).

Sample

no.
Locations Concentration of As3+

Concentration of total As
(As3++ As5+)

Concentration of As5+

(g/LSD) (g/LSD) (g/L)

1 Nabagram 14.43  0.05 24.12  0.02 9.69

2 Khilinda 9.02  0.6 16.45  0.13 7.43

3 Jagir 10.98  0.82 19.76  0.09 8.78

4 Macshimul 8.12  0.7 19.67  0.41 11.55

No. of Analysis (n=3)

Table 4. Validation of results with HG-AAS with developed anodic stripping voltammetry

Methods Variation with HG-AAS

HG-AAS
SWASV DPASV NPASV SWASV DPASV NPASV

Controlled
Lab. Standard

(g/l) (%)

125.0  1.20 119.900.16 116.54  0.30 120.78  .0.09 4.08 6.78 4.22 8.25

95.4  1.50 98.200.12 89.67  0.50 72.81  0.80 2.93 6.02 23.68 9.50

120.5  2.20 118.670.70 123.09  0.17 115.43  0.18 1.51 2.14 4.20 8.35

No. of analysis (n=3)

Comparison of the endemic areas with the controlled
area

The water samples of Manikgonj which was
considered as a controlled area (Free from arsenic
contamination) were also analysed with SWASV
method as presented in Table 3. The average value of
As content in this area was found 20 g/L. On the other
hand, the average As contents in different locations of
the study areas are about 10 times higher than the
average content of the controlled area.

Validation of the results by HG-AAS

To validate the results obtained from the

electroanalytical method, Few water samples were
analysed by HG-AAS. It was observed that the results
obtained by the electroanalytical methods were closed
to results obtained by the HG-AAS method. This
indicates that the results obtained by the developed
electroanalytical methods were effective to analyse
arsenic from the groundwater where the variation of
results between HG-AAS and electroanalytical method
was about 1.5-9.5%.

Conclusion

From the study of the three electroanlytical

methods (SWASV, DPASV and NPASV), the SWASV
technique is most selective and suitable electroanalytical
method. This method could be a better analytical
technique for arsenic speciation from water. Moreover
this technique is comparatively cheaper than other
available methods. The results obtained in this study
have been compared with the value of unaffected area
(Manikgonj).The observations show that arsenic content
of the study area in ground water about 10 times higher
than the average content of the controlled area. The total
arsenic content and arsenic (III) in water is higher than
the WHO guide line value (50gL-1). So, arsenic
contamination in ground water of the study areas is in
alarming proportions. Therefore, a proper monitoring
process should be evolved along with development of
methods to keep the water free from arsenic.

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