Voltammetric resolution of dopamine in the presence of ascorbic acid and uric acid at poly (calmagite) film coated carbon paste electrode

Article abstract of DOI:10.1016/j.electacta.2010.06.091

The poly (calmagite) film was synthesized on the surface of carbon paste electrode by electrochemical method. The synthesized polymer film coated electrode exhibits excellent electrocatalytic activity towards the detection of dopamine at neutral pH. The scan rate effect was found to be adsorption controlled electrode process. The concentration effect of dopamine was studied. The redox peak potentials of dopamine were depend on pH. This polymer film coated electrode was very good at simultaneous study of dopamine in the presence of high concentrated ascorbic acid and uric acid. The incorporation study was done by varying the concentration of one species while other two are kept constant. The proposed method was applied to the detection of dopamine in injection samples.

Full text of DOI:10.1016/j.electacta.2010.06.091

Electrochimica Acta 55 (2010) 7166–7174
Contents lists available at ScienceDirect
Electrochimica Acta
journal homepage: www.elsevier.com/locate/electacta
Voltammetric resolution of dopamine in the presence of ascorbic acid and
uric acid at poly (calmagite) film coated carbon paste electrode
Umesh Chandra, B.E. Kumara Swamy∗, Ongera Gilbert, B.S. Sherigara
Department of P.G .Studies and Research in Industrial Chemistry, Kuvempu University, Jnana Sahyadri, Shankaraghatta 577451, Shimoga, Karnataka, India
a r t i c l e i n f o
a b s t r a c t
Article history:
The poly (calmagite) film was synthesized on the surface of carbon paste electrode by electrochemi-
cal method. The synthesized polymer film coated electrode exhibits excellent electrocatalytic activity
towards the detection of dopamine at neutral pH. The scan rate effect was found to be adsorption con-
trolled electrode process. The concentration effect of dopamine was studied. The redox peak potentials of
dopamine were depend on pH. This polymer film coated electrode was very good at simultaneous study
of dopamine in the presence of high concentrated ascorbic acid and uric acid. The incorporation study
was done by varying the concentration of one species while other two are kept constant. The proposed
method was applied to the detection of dopamine in injection samples.
Received 28 March 2010
Received in revised form 25 June 2010
Accepted 30 June 2010
Available online 7 July 2010
Keywords:
Poly (calmagite)
Carbon paste electrode
Dopamine
© 2010 Elsevier Ltd. All rights reserved.
Ascorbic acid
Uric acid
Cyclic voltammetry
Differential pulse voltammetry
1. Introduction
It is generally believed that direct redox reactions of these species
at bare electrode are irreversible and therefore requires high over
In recent days the electropolymer modified carbon paste elec-
trodes are showed very much excellent effort in acting as a sensor to
investigate the one of the neurotransmitters like dopamine [1–3].
Especially, the electropolymer film coated electrodes with dyes
have good stability, reproducibility, more active sites, homogene-
ity in electrochemical deposition [4,5]. The electropolymerisation
generally results in polymer film which is uniform and strongly
adherent to the electrode surface. In addition the polymer film
can be deposited onto the small area with high degree of geo-
metrical conformity and controllable thickness. Several redox dyes
are known to artificial electron donors [6]. Such dyes are able to
undergo electropolymerisation from aqueous solution producing
stable redox active layer [7,8].
Dopamine (DA) is a well-known biogenic amine acting as a neu-
rotransmitter in the brain. It has received considerable attention
because of its suspected role in a variety of neuropsychiatric disor-
ders such as Parkinson’s disease and Schizophrenia [9–12]. It has
been found that the dopamine possesses very strong electrochem-
ical activity by giving dopamine-o-quinone as oxidation product.
However the determination remains a challenge because of the
presence of large excess of ascorbic acid (AA) and uric acid (UA).
potential [13]. Moreover the direct redox reactions of these species
at bare electrodes take place at very similar potential and often suf-
fer from a fouling effect, which results in rather poor selectivity and
reproducibility. The ability to determine DA, UA and AA selectively
has been a major goal of electroanalytical research [14]. Develop-
ment of both sensitivity and selectivity are of equal importance in
voltammetric procedure.
The aim of our work was to fabricate stable electrode by elec-
tropolymerizing calmagite (the oxidation mechanism of calmagite
was shown in Scheme 1) on the surface of carbon paste electrode to
achieve the challenge of simultaneous determination of DA in the
presence of AA and UA in physiological pH. Although no examina-
tion of the detection of dopamine in the presence of both ascorbic
acid and uric acid in physiological pH at poly (calmagite) film
coated carbon paste electrode has been reported. This novel work
discussed about sensitivity, selectivity and reproducibility of neu-
rotransmitter atpoly(calmagite)film coatedcarbon paste electrode
at physiological pH.
2. Experimental
2.1. Reagents
∗
The graphite fine powder (Loba Chemie) and silicon oil (Hime-
dia) were used to prepare carbon paste electrode. 0.5 mM calmagite
Corresponding author. Tel.: +91 8282 256225l; fax: +91 8282 256255.
E-mail address: kumaraswamy21@yahoo.com (B.E. Kumara Swamy).
0013-4686/$ – see front matter © 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.electacta.2010.06.091

U. Chandra et al. / Electrochimica Acta 55 (2010) 7166–7174
7167
Scheme 1. Oxidation mechanism of calmagite.
in aqueous solution was used to synthesis electropolymer on the
surface of carbon paste electrode. DA was prepared 1 × 10−5 M
stock solution by dissolving in 0.1 M perchloric acid solution. UA
was prepared 1 × 10−4 M stock solution by dissolving in 0.1 M
sodium hydroxide solution and that of 1 × 10−4 M AA in double
distilled water. Phosphate buffer solution was prepared by mix-
ing the appropriate quantity of 0.2 M aqueous sodium dihydrogen
phosphate monohydrate and 0.2 M aqueous disodium hydrogen
phosphate. Chemicals mentioned above were all of analytical grade.
The water used in the preparation of solutions was double distilled
water.
in the 0.1 M HCl. A pair of redox broad peaks was obtained. On
increasing the scan rate the redox peak current also increased. The
anodic peak currents were linearly dependent of scan rate and the
correlation coefficient was found to be 0.999. The ratio of anodic
peak current to cathodic peak current was almost equal to unity.
The separation of peak potentials (ꢀEp) was 50 mV. With increas-
ing scan rate ꢀEp also increased. The above results suggest that the
electrode reaction was a quasi-reversible electron transfer process
[15].
3.3. SEM analysis of poly (calmagite) modified carbon paste
electrode
2.2. Apparatus
Fig. 3 explains the surface morphology of bare carbon paste
electrode and poly (calmagite) modified carbon paste electrode
using scanning electron microscopy. The surface of bare carbon
paste electrode was irregularly shaped micrometer sized flakes of
graphite. However, the poly (calmagite) film coated carbon paste
electrode has typical uniform arrangement of poly (calmagite)
molecules on the surface of carbon paste electrode. This confirms
the carbon paste electrode was coated by poly (calmagite) film.
The electrochemical experiments were carried out using a
model-201 electroanalyser (EA-201 chemilink system). All the
experiments were carried out in a conventional three electrochem-
ical cell. The electrode system contained a working electrode was
bare CPE and poly (calmagite) film modified CPE (3 mm in diam-
eter), a platinum wire as counter electrode and saturated calomel
electrode as reference electrode.
2.3. Preparation of poly (calmagite) modified carbon paste
electrode
3.4. Electrocatalytic response of DA at poly (calmagite) modified
carbon paste electrode
The carbon paste electrode was prepared by hand mixing 70%
graphite powder and 30% silicon oil in an agate mortar. The 0.5 mM
aqueous calmagite was placed in the electrochemical cell along
with 0.2 M phosphate buffer solution of pH 9.0. The CPE was
scanned 10 multiple cycles between the potential ranges from
−200 to 2000 mV at 100 mV s−1. After this process, the electrode
was immersed in 0.2 M phosphate buffer solution of pH 7.0 until
use.
Fig. 4 demonstrates the cyclic voltammogram of DA (1 × 10−5 M)
at bare carbon paste electrode and poly (calmagite) modified car-
bon paste electrode at sweep rate of 50 mV s−1. It is easily oxidizable
catecholamine, showed poor sensitivity and reproducibility at bare
carbon paste electrode (dotted line). The cyclic voltammogram of
DA in phosphate buffer solution of pH 7.0 as supporting electrolyte
at sweep rate of 50 mV s−1, showed its anodic (Epa) and cathodic
peak potentials (Epc) at 229 and 130 mV respectively. The peak
3. Results and discussion
3.1. Electrochemical polymerization of calmagite on carbon paste
electrode
Calmagite is a redox indicator which is undergoing electropoly-
merisation between the ranges of −200 and 2000 mV on the surface
of carbon paste electrode at the sweep rate of 100 mV s−1 for 10
cycles. Fig. 1 shows the growth of polymer film of 0.5 mM aqueous
calmagite solution on the surface of carbon paste electrode in 0.2 M
phosphate buffer solution of pH 9.0 as supporting electrolyte. Dur-
ing the process of multiple cycles the voltammogram has gradually
descended with increase of cyclic time increasing. This indicates
that the poly (calmagite) film was formed and deposited on the
surface of carbon paste electrode [15].
3.2. Electrochemical characterization of poly (calmagite) film
coated CPE
Fig. 1. Cyclic voltammogram of preparation of poly (calmagite) film coated CPE.
Fig. 2 exhibits the typical voltammogram of the poly (calmagite)
film coated CPE in the range of −200–600 mV at various sweep rates
0.5 mM aqueous calmagite in 0.2 M phosphate buffer solution of pH 9.0 at 10 cycles
with sweep rate of 100 mV s−1
.

7168
U. Chandra et al. / Electrochimica Acta 55 (2010) 7166–7174
Scheme 2. Electrocatalytic oxidation of DA at the surface of poly (calmagite) film coated CPE.
potentials difference (ꢀEp) was found to be 99 mV. The anodic and
cathodic peak current ratio (Ipa/Ipc) was about 1.5. However, in the
same condition, our polymer coated electrode (solid line) exhibited
excellent sensitivity for DA. Both anodic and cathodic peak cur-
rent signals were got 19-fold increments when comparing the bare
Fig. 2. (a) Cyclic voltammogram of poly (calmagite) film coated CPE in 0.1 M HCl at
different scan rate (a–f; 25, 50, 75, 100, 125 and 150 mV s−1). (b) Graph of anodic
peak current vs scan rate.
Fig. 3. SEM image of (a) bare carbon paste electrode and (b) poly (calmagite) film
coated CPE.

U. Chandra et al. / Electrochimica Acta 55 (2010) 7166–7174
7169
Fig. 4. Cyclic voltammogram of 1 × 10−5 M DA in 0.2 M phosphate buffer solution
of pH 7.0 at bare CPE (dotted line) and poly (calmagite) film coated CPE (solid line).
electrode. The Epa and Epc were located at 238 and 181 mV. The
ꢀEp was found to be 57 mV. The Ipa/Ipc was 1.07. This high elec-
trocatalytic activity of poly (calmagite) modified CPE because of
−
formation of high concentration of negative charged –SO3 group
and electron rich oxygen atom on the electrode surface at neutral
pH. These electron rich groups result in that the poly (calmagite)
modified electrode shows a well affinity towards the DA positive
ions by exchanging the electrons and enhanced the oxidation of DA.
This process was represented in Scheme 2.
Scheme 2 shows the oxidation mechanism of DA at poly (cal-
magite) film coated carbon paste electrode surface. The calmagite
was scanned in positive direction in sufficient potential window
at carbon paste electrode in phosphate buffer solution at pH 9.0,
the electrode gains the electrode gains the 2 electron from the
calmagite and gives the respective oxidation product. Depending
on applied the multiple scan, the oxidation product of calmagit−e
forms a uniform layer which was rich in negatively charged –SO3
ions. The negatively charged ions drag the cation containing DA
towards itself by means of electrostatic attraction. This poly (cal-
magite) layer already lost its 2 electron, hence it eager to take the 2
electrons from the DA by oxidizing it to dopa-o-quinone and could
get back to its original calmagite structure in forward scan. The elec-
trochemical behavior of DA shows reversible nature, hence while
in reverse scan DA takes back its 2 electron and it retains its original
structure [15,16].
Fig. 5. (a) Variation of scan rate for DA at poly (calmagite) film coated CPE (a–h;
50–400 mV s−1). (b) Graph of Ipa vs scan rate of DA.
The both anodic and cathodic peak potentials were shifted to less
positive side with increasing in the pH values. The anodic peak
potential of DA shifted from 331 to 249 mV with respect the pH
from 2 to 9. The potential diagram was constructed by plotting the
graph of calculated E0 vs pH of the solution (Fig. 6b). The graph
has good linearity with a slope of 52 mV/pH this behavior is nearly
obeyed the Nernst Equation for equal number of electron and pro-
ton transfer reaction [17,18]. From the graph of Ipa vs pH, it can be
seen that the current was maximum at pH 3.5. This is because the
pKa value of R-SO3H (R: Aryl or Alkyl moiety) is between 3 and 4
[15,16]. Thus, in this pH, the poly−(calmagite) film dissociates favor-
ably into negative charged –SO3 group hence high current signal.
But we are interested in investigate the electro-oxidation of DA at
neutral condition, hence we selected pH 7.0 (Fig. 7).
3.5. The effect of scan rate
The effect of scan rate for DA was studied by CV at poly
(calmagite) modified CPE. Poly (calmagite) modified CPE showed
increase in the redox peak current with increase in scan rate
(50–400 mV s−1) (Fig. 5a). The graph of current (Ipa) vs square root
of scan rate (ꢁ) was plotted. The graph obtained was good linear-
ity between the scan rate and Ipa (Fig. 5b). In the range from 50 to
400 mV s−1 the anodic peak currents were proportional to the scan
rate (ꢁ). The correlation coefficient was 0.999, which indicate the
electrode reaction was adsorption controlled.
3.7. Electrocatalytic oxidation of AA and UA at poly (calmagite)
modified CPE
Fig. 8a reveals the oxidation of AA at bare carbon paste elec-
trode and poly (calmagite) modified CPE in 0.2 M phosphate buffer
solution of pH 7.0 at sweep rate of 50 mV s−1. From Fig. 8a it can
be notice that the oxidation peak of AA (1 × 10−4 M) at bare carbon
paste electrode was broad and poor in sensitivity (dotted line). The
anodic potential was found around at 160 mV. However, at poly
(calmagite) modified CPE the oxidation peak for AA was shifted
towards negative direction with high current enhancement (solid
line). The anodic peak potential was located at 110 mV. This shift-
3.6. Effect of pH
The electrochemical response of DA at poly (calmagite) modified
CPE was generally pH dependent. The voltammograms of DA were
recorded at 0.2 M phosphate buffer solution of different pH by cyclic
voltammetric method. Fig. 6a demonstrates the pH dependence of
DA at poly (calmagite) modified CPE at sweep rate of 50 mV s−1
.

7170
U. Chandra et al. / Electrochimica Acta 55 (2010) 7166–7174
Fig. 7. (a) Cyclic voltammogram for different concentration of DA (a) 1 × 10−5
DA, (b) 1.5 × 10−5 M DA, (c) 2 × 10−5 M DA, (d) 2.5 × 10−5 M DA and (e) 3 × 10−5
M
M
Fig. 6. (a) Cyclic voltammogram of 1 × 10−5 M DA for different pH (from 3.6 to 9 pH)
DA at poly (calmagite) film coated CPE with scan rate 50 mV s−1. (b) Graph of Ipa vs
concentration of DA.
at poly (calmagite) film coated CPE. (b) Graph of Epa vs different pH.
ing of peak potential and enhancing the current signal confirms the
electrocatalytic activity of poly (calmagite) modified CPE towards
AA. Further the scan rate effect was done by varying the scan rate
from 50 to 400 mV s−1. The graph of anodic peak current vs scan rate
shows linear relationship and correlation coefficient was found to
be 0.9988 (Fig. 8b). The concentration of AA was varied from the
0.5 × 10−4 to 5 × 10−4 M. The graph of anodic peak current vs con-
centration of AA was shown very good linearity (data not shown).
Fig. 9a the UA (0.5 × 10−4 M) shows its anodic peak at 304 mV
at bare CPE at 50 mV s−1 sweep rate in 0.2 M phosphate buffer
solution of pH 7.0. The obtained voltammogram at bare CPE was
less sensible. However, the voltammogram obtained at poly (cal-
magite) modified CPE for UA in the same condition was with high
current signal comparing to bare CPE. The anodic peak potential
was located at 330 mV. This result of enhancement in current sig-
nal showed very good sensor activity of poly (calmagite) modified
CPE for UA. The scan rate study was done by varying the scan rate
from 50 to 400 mV s−1. The anodic peak current was increased with
increase in the scan rate. The graph of anodic peak current vs scan
rate results in linear relationship and correlation coefficient was
found to be 0.9992 (Fig. 9b). The concentration of UA was varied
from the 0.1 × 10−4 to 3 × 10−4 M. The graph of anodic peak cur-
rent vs concentration of UA was results very good linearity (data
not shown).
calculated Epa/2, n and k0 for AA and UA were tabulated in
Tables 1 and 2. In each case the number of electrons (n) was nearly
equal to 2 for electrocatalytic oxidations. This shows that both AA
and UA follows 2 electron change at the surface of poly (calmagite)
film coated carbon paste electrode and this oxidation mechanism
was shown in Scheme 3.
3.8. Simultaneous determination of DA, AA and UA
AA and UA were present along with DA in mammalian brain
and the concentrations of these were much higher than that of
DA. Since, the oxidation potential of both AA and UA was nearly
same as that of DA result in an overlapped voltammetric response
at bare CPE. Fig. 10a showed the cyclic voltammetric response
Table 1
Electrochemical parameters of AA at different scan rates.
Scan rate (mV s−1
)
Epa (mV)
Epa/2 (mV)
n
k0/s−1
50
100
150
200
250
300
350
400
110
125
137
150
163
170
175
189
7.5
65
1.8
0.0479
0.0864
0.1500
0.2347
0.3262
0.3660
0.4019
0.4728
1.76
1.92
1.88
1.71
1.74
1.83
1.77
110
135
152
155
165
181
The obtained experimental results from Figs. 8b and 9b were
used to calculated the number of electron (n) and the heteroge-
neous rate constant (k0) as in the literature [19]. The experimentally

U. Chandra et al. / Electrochimica Acta 55 (2010) 7166–7174
7171
Scheme 3. Mechanism of electrocatalytic oxidation of AA and UA at poly (calmagite) film coated carbon paste electrode.
Fig. 8. (a) Cyclic voltammogram of 1 × 10−4 M AA at bare CPE (dotted line) and poly
(calmagite) film coated CPE (solid line) with scan rate of 50 mV s−1. (b) Graph of
anodic peak current vs scan rate.
Fig. 9. (a) Cyclic voltammogram of 0.5 × 10−4 M UA at bare CPE (dotted line) and
poly (calmagite) film coated CPE (solid line) with scan rate of 50 mV s−1. (b) Graph
of anodic peak current vs scan rate.

7172
U. Chandra et al. / Electrochimica Acta 55 (2010) 7166–7174
Table 2
Electrochemical parameters of UA at different scan rates.
Scan rate (mV s−1
)
Epa (mV)
Epa/2 (mV)
n
k0/s−1
50
100
150
200
250
300
350
400
330
350
375
382
390
412
430
451
210
299
335
360
380
395
415
435
1.91
1.88
1.75
1.72
1.76
1.83
1.77
1.89
0.0478
0.105
0.139
0.194
0.2472
0.2827
0.3352
0.3381
of DA (1 × 10−5 M) in the presence of UA (0.5 × 10−4 M) and AA
(1 × 10−4 M) in phosphate buffer solution of pH 7.0 at both bare CPE
and poly (calmagite) modified CPE. The voltammogram obtained
for mixture of sample at bare CPE was broad, less sensible and over-
lapped wave at the potential of 220 mV (dotted line). However, our
poly (calmagite) modified CPE faced this challenge and achieved the
separation. The resulted voltammogram at poly (calmagite) modi-
fied CPE had three well defined peaks for DA, AA and UA at different
potentials. The oxidation peak potentials of DA, AA and UA were at
235, 80 and 380 mV respectively. The peak to peak separation of
DA–AA was 155 mV and that of DA–UA was 145 mV. This results
were large sufficient to identify DA in the presence of AA and UA at
poly (calmagite) modified CPE.
Fig. 11. (a) Differential pulse voltammogram of (a) 9.0 × 10−6 M, (b) 9.2 × 10−6 M, (c)
9.4 × 10−6 M, (d) 9.6 × 10−6 M, (e) 9.8 × 10−6 M, (f) 1.0 × 10−5 M, (g) 1.5 × 10−5 M, (h)
2 × 10−5 M, (i) 2.5 × 10−5 M, (j) 3.0 × 10−5 M and (k) 3.5 × 10−5 M DA in 0.2 M phos-
phate buffer solution of pH 7.0 in the presence of 1.0 × 10−4 M AA and 0.5 × 10−4
M
UA at poly (calmagite) film coated CPE. (b) Differential pulse voltammogram of (a)
0 M, (b) 2 × 10−4 M, (c) 4 × 10−4 M, (d) 6 × 10−4 M, (e) 8 × 10−4 M and (f) 10 × 10−4
M
AA in 0.2 M phosphate buffer solution of pH 7.0 in the presence of 1 × 10−5 M DA and
0.5 × 10−4 M UA at poly (calmagite) film coated CPE. (c) Differential pulse voltammo-
gram of (a) 0 M, (b) 0.2 × 10−4 M, (c) 0.4 × 10−4 M, (d) 0.6 × 10−4 M, (e) 0.8 × 10−4
M
and (f) 1 × 10−4 M UA in 0.2 M phosphate buffer solution of pH 7.0 in the presence
of 1 × 10−5 M DA and 1 × 10−4 M AA at poly (calmagite) film coated CPE.
Fig. 10. (a) Cyclic voltammogram for simultaneous determination of 1 × 10−5 M DA,
1 × 10−4 M AA and 0.5 × 10−4 M UA at bare CPE (dashed line) and poly (calmagite)
film coated CPE (solid line) with the scan rate of 50 mV s−1. (b) Differential pulse
voltammogram for simultaneous detection of 1 × 10−5 M DA, 1 × 10−4 M AA and
5 × 10−5 M UA at poly (calmagite) film coated CPE (solid line) and at bare CPE (dotted
line) with the scan rate of 50 mV s−1
.

U. Chandra et al. / Electrochimica Acta 55 (2010) 7166–7174
7173
Table 3
Comparison of different modified electrodes for DA determination.
Electrode
Detection limit (mol/L)
Method
Reference
Metallothioneins self-assembled gold electrode
Ionic liquid modified carbon paste electrode
Poly (caffeic acid)/GCE
6.0 × 10−6
7.0 × 10−7
2.0 × 10−7
1.0 × 10−6
6.0 × 10−7
1.0 × 10−8
CV
CV
CV
DPV
DPV
DPV
[25]
[26]
[27]
[28]
[29]
This work
␣-CD/CNT/PGE
Poly (p-toluene sulfonic acid) modified glassy carbon electrode
Poly (calmagite) film coated carbon paste electrode
Table 4
DPV was used for the determination of DA, AA and UA at poly
(calmagite) modified CPE because to get higher current sensitiv-
ity and better resolution. The simultaneous study was carried out
in the potential range from −200 to 600 mV (Fig. 10b). The DPV
showed the simultaneous determination of DA, AA and UA with
well separated three anodic peaks corresponding to their oxidation
could be possible at poly (calmagite) modified CPE. The 1 × 10−5 M
DA showed its Epa at 211 mV, 1 × 10−4 M AA was at −21 mV and
0.5 × 10−4 M UA was at 385 mV. The peak separation between DA
and AA was 232 mV and for DA and UA the peak separation was
174 mV which were greater when comparing to peak separation
occurred by CV.
Detection of DA in injection samples (n = 5).
Sample
Content (mg/mL)
Found (mg/mL)
RSD (%)
Recovery (%)
1
2
3
4.0
4.0
4.0
3.97
4.02
4.02
2.4
2.1
2.5
99.25
100.5
100.5
3.9. Interference study
The simultaneous determination of DA, AA and UA in the
mixture was carried out at poly (calmagite) modified CPE when
concentration of one species changed, whereas the others remained
kept constant. From Fig. 11a, it can be seen that the peak current of
DA was proportional to its concentration, which was increased from
0 to 3 × 10−5 M when keeping the concentration of UA 0.5 × 10−4 M
and AA 1 × 10−4 M. There were no change in the peak current and
peak potential occurred for AA and UA. Similarly in Fig. 11b and c
self explains the concentration effect of AA from 0 to 1 × 10−3 M
and UA from 0 to 1 × 10−4 M respectively. These results show that
the DA, AA and UA were exist independently in their mixtures of
samples.
Fig. 12. Calibration plot of DA concentration.
To study the effect of concentration of DA, differential
pulse voltammetric technique was used [20–22]. The con-
centration of DA was varied from 9 × 10−6 to 35 × 10−6 M.
Fig. 12 shows that the graph of anodic peak current vs
concentration of DA shows two linear relationships ranges
9 × 10−6–1 × 10−5 and 1 × 10−5–3.5 × 10−5 M with the linear
regression equations as Ipa (␮A) = 40.02 C ␮M/L − 3.6 × 10−4 and
Ipa (␮A) = 1.99 C ␮M/L + 2.05 × 10−5, respectively. The correlation
coefficient for the first linearity was 0.99997 and for the second it
was found to be 0.99966. The decrease of sensitivity (slope) in the
second linear range is likely to be due to kinetic limitation [23]. The
detection limit for DA in the lower range region was found to be
1 × 10−8 M and quantification limit was 3.3 × 10−8 M. The detection
limit and quantification limit was calculated by using the formulas,
LOD = 3S/M and LOQ = 10S/M [24]. Where S is the standard devia-
tion and M is the slope obtained from the three calibration plots.
The detection limit of various electroanalytic methods proposed
for determination of DA is compared with our analytical data in
Table 3. From the data shown, a lower limit of detection (LOD) can
be achieved using the proposed method [25–29].
were acceptable, showing that the proposed methods could be effi-
ciently used for the determination of DA in injections with recovery
in the range 99.25–100.5% (Fig. 12).
4. Conclusion
In conclusion the synthesized poly (calmagite) modified CPE
can detect DA electrochemically in mixture of solution, at physi-
ological pH, containing large excess of AA and UA both by cyclic
voltammetry and differential pulse voltammetry techniques. The
detection limit of DA was 1 × 10−8 M. The modified electrode
showed excellent sensitivity, selectivity and anti-fouling proper-
ties. The proposed methods can be applied to the detection of DA
in injection. We believe that this approach can readily be applied
to the development of electrochemical sensors for dopamine and
related neurotransmitters.
Acknowledgements
The authors are very thankful to the Department of Science and
Technology Government of India, New Delhi for the funding given
through project no DST/TSG/ME/2007/44.
3.10. Analytical application
The modified electrode was applied to the determination of
dopamine hydrochloride injection. The DA injection sample pur-
chased from sterile specialities India Private Ltd with a specified
content of DA of 40.0 mg/mL. The sample was used after suitable
dilution. 0.2 M phosphate buffer was used for diluting the injection
samples. The results were shown in Table 4. The recovery and RSD
References
[1] O. Gilbert, U. Chandra, B.E. Kumara Swamy, M. Panduranga Char, C. Nagaraj,
B.S. Sherigara, Int. J. Electrochem. Sci. 3 (2008) 1186.
[2] M. Pandurangachar, B.E. Kumara Swamy, U. Chandra, O. Gilbert, B.S. Sherigara,
Int. J. Electrochem. Sci. 4 (2009) 672.

7174
U. Chandra et al. / Electrochimica Acta 55 (2010) 7166–7174
[3] O. Gilbert, B.E. Kumara Swamy, U. Chandra, B.S. Sherigara, Int. J. Electrochem.
Sci. 4 (2009) 582.
[16] H. Yao, Y. Sun, X. Lin, Y. Tang, A. Liu, G. Li, W. Li, S. Zhang, Anal. Sci. 23 (2007)
677.
[4] Y. Ohnuki, T. Ohsaka, H. Matsuda, N. Oyama, J. Electroanal. Chem. 158 (1983)
55.
[5] A. Volkov, G. Tourillon, P.C. Lacaze, J.E. Dubois, J. Electroanal. Chem. 115 (1980)
279.
[17] B.D. Jones, J.D. Ingle Jr., Talanta 55 (2001) 699.
[18] M.C. Shen, H.C. Gheng, V.S. Vasantha, J. Electoanal. Chem. 588 (2006) 235.
[19] S.C. Avendan, G.A. Angeles, M.T.R. Silva, G.R. Pina, M.R. Romo, M.P. Pardave, J.
Electroanal. Chem. 609 (2007) 17.
[6] C.X. Cai, K.H. Xue, Microchem. J. 58 (1998) 197.
[7] A.A. Karyakin, O.A. Bobrova, E.E. Karyakina, J. Electroanal. Chem. 399 (1995)
179.
[20] S. Corona-Avendano, M.T. Ramirez-Silva, M. Palomar-Pardave, L. Hernandez-
Martinez, M. Romero-Romo, G. Alarcon-Angeles, J. Appl. Electrochem. 40
(2010) 463.
[8] A.A. Karyakin, E.E. Strakhova, E.E. Karyakina, S.D. Varfolomeyev, A.K. Yat-
simirsky, Bioelectrochem. Bioenerg. 32 (1993) 35.
[9] S. Sharath Shankar, B.E. Kumara Swamy, U. Chandra, J.G. Manjunatha, B.S. Sheri-
gara, Int. J. Electrochem. Sci. 4 (2009) 592.
[10] O. Gilbert, B.E. Kumara Swamy, U. Chandra, B.S. Sherigara, J. Electroanal. Chem.
636 (2009) 80.
[11] U. Chandra, B.E. Kumara Swamy, O. Gilbert, M. Pandurangachar, B.S. Sherigara,
Int. J. Electrochem. Sci. 4 (2009) 1479.
[12] Rekha, B.E. Kumara Swamy, R. Deepa, V. Krishna, O. Gilbert, U. Chandra, B.S.
Sherigara, Int. J. Electrochem. Sci. 4 (2009) 832.
[21] S. Corona-Avendano, G. Alarcon-Ángeles, M.T. Ramirez-Silva, M. Romero-
Roma, A. Cuan, M. Palomar-Pardavea, J. Electrochem. Soc. 156 (2009) J375.
[22] G. Alarcon-Angeles, S. Corona-Avendano, M. Palomar-Pardave, A. Rojas-
Hernandez, M. Romero-Romo, M. Teresa Ramirez-Silva, Electrochim. Acta 53
(2008) 3013.
[23] M. Mazloum-Ardakani, H. Rajabi, H. Beitollahi, B.B. Fatemah Mirjalili, A. Akbari,
N. Taghavinia, Int. J. Electrochem. Sci. 5 (2010) 147.
[24] R.N. Hegde, B.E. Kumara Swamy, N.P. Shetty, S.T. Nandibewoor, J. Electroanal.
Chem. 635 (2009) 51.
[25] Q. Wang, N. Li, W. Wnag, Anal. Sci. 18 (2002) 635.
[26] W. Sun, M. Yang, K. Jiao, Anal. Bioanal. Chem. 389 (2007) 1283.
[27] N.B. Li, W. Ren, H.Q. Luo, Electroanalysis 19 (2007) 1496.
[28] G.Y. Wang, X.J. Liu, G.A. Luo, Z.H. Wang Chin, J. Chem. 23 (2005) 297.
[29] P.F. Huang, L. Wang, J.Y. Bai, H.J. Wang, Y.Q. Zhao, S.D. Fan, Microchim. Acta 157
(2007) 41.
[13] R.N. Adams, Anal. Chem. 48 (1976) 1126A.
[14] R. Raghavendra Naik, B.E. Kumara Swamy, U. Chandra, E. Niranjana, B.S. Sheri-
gara, H. Jayadevappa, Int. J. Electrochem. Sci. 4 (2009) 855.
[15] Y. Hong, S. Yuanyuan, L. Xinhua, T. Yuhai, H. Liying, Electrochim. Acta 52 (2007)
6165.