American Journal of Analytical Chemistry, 2012, 3, 656-663
http://dx.doi.org/10.4236/ajac.2012.39086 Published Online September 2012 (http://www.SciRP.org/journal/ajac)
Electrochemical Behavior of Chalcone at a Glassy Carbon
Electrode and Its Analytical Applications
Keerti M. Naik, Sharanappa T. Nandibewoor*
P. G. Department of Studies in Chemistry, Karnatak University, Dharwad, India
Received May 5, 2012; revised June 8, 2012; accepted June 18, 2012
ABSTRACT
A simple and rapid method was developed using cyclic, differential pulse and square wave voltammetric techniques for
the determination of trace-level chalcone at a glassy carbon electrode. Chalcone could produce two anodic peaks at
about 0.514 V and 1.478 V and a cathodic peak at about −0.689 V. The differential pulse voltammerty presents a good
linear response as compared to square wave voltammetry in the range of 0.2 - 10 μM with a detection limit of 0.18 μM.
The proposed method was used successfully for its quantitative determination in spiked human plasma and urine as real
samples.
Keywords: Chalcone; Voltammetry; Glassy Carbon Electrode; Electrochemical Determination; Oxidation
1. Introduction
Chalcone (1,3-Diphenyl-2-propen-1-one) (Scheme 1) is an
aromatic ketone that forms the central core for a variety
of important biological compounds, which are known col-
lectively as chalconoids. They show antibacterial, antifungal,
antitumor and anti-inflammatory properties [1]. Some cha-
lcones demonstrated the ability to block voltage-dependent
potassium channels [2]. They are also intermediates in the
biosynthesis of flavonoids, which are substances wide-
spread in plants and with an array of biological activities.
Chalcones are also intermediates in the Auwers synthesis
of flavones. Due to ineffective drugs, cancer is the second
most leading cause of death after heart attack. Therefore,
the researchers have accelerated their efforts for the gen-
eration of new anticancer drugs with high therapeutic in-
dex. In this connection, a clinically effective antitumor
derivative of chalcone (calicheamicin) has stimulated the
investigators to concentrate their studies on chalcones and
related compounds [3].
O H
H
Scheme 1. Chemical structure of chalcone.
Electrochemical methods have proved to be very sen-
sitive for the determination of organic molecules, includ-
ing drugs and related molecules in pharmaceutical dosage
forms and biological fluids [4-8]. The advance in experi-
mental electrochemical techniques in the field of analysis
of drugs is due to their simplicity, low cost and relatively
short analysis time when compared with the other tech-
niques. The use of carbon based electrodes, especially
glassy carbon electrode, for electroanalytical measure-
ments has increased in recent years because of their ap-
plicability to the determination of substances that un-
dergo oxidation reactions, a matter of great importance in
the field of clinical and pharmaceutical analysis. Redox
properties of drugs can give insights into its metabolic
fate or their in vivo redox processes or pharmaceutical
activity [9,10].
A review of the literature reveals that only the oxida-
tion of chalcone by trichloroisocyanuric acid in HOAc-
HClO4 medium [11] and the interaction of substituted
chalcone with DNA [12] have been reported. However,
no methods for determination of chalcone have been re-
ported so far. There is also no report on the electro-oxi-
dation of chalcone with any of the electrodes. In view of
the pharmaceutical importance of chalcone and the lack
of literature on its voltammetric determination, the elec-
tro oxidation of chalcone necessitates a method to be de-
veloped. The aim of the present study is to establish the
suitable experimental conditions, to investigate the oxid-
ation mechanism of chalcone and determine chalcone in
spiked human plasma and urine samples using cyclic, squ-
are wave and differential pulse voltammetric techniques.
*Corresponding author.
C
opyright © 2012 SciRes. AJAC

K. M. NAIK, S. T. NANDIBEWOOR 657
2. Experimental
2.1. Materials and Reagents
Pure chalcone in powdered form was obtained from Sigma
Aldrich and used without further purification. A stock solu-
tion of chalcone was prepared by direct dis-
solution in methanol, since it is insoluble in water. The
phosphate buffers from pH 3 - 11.2 were prepared in double
distilled water as described by Christian and Purdy [13].
All other reagents used were of analytical or reagent grade
and their solutions were prepared with double distilled
water.
()
3
110 M
−
×
2.2. Instrumentation
Electrochemical measurements were carried out on a CHI
630 D electrochemical analyzer (CH Instruments Inc.,
USA). The voltammetric measurements were carried out
in a 10 ml single compartment three-electrode glass cell
with Ag/AgCl as a reference electrode, a platinum wire
as counter electrode and a 3 mm diameter glassy carbon
electrode (GCE) as the working electrode. All the poten-
tials are given against the Ag/AgCl (3 M KCl). The pH
measurements were performed with Elico LI120 pH me-
ter (Elico Ltd., India). All experiments were carried out
at an ambient temperature of 25˚C ± 0.1˚C.
The area of the electrode was calculated using 1.0 mM
K3Fe(CN)6 as a probe at different scan rates. For a reversi-
ble process, the Randles-Sevcik formula has been used [14].
()
53
pa
i2.6910=× 2 1212
0 0
nADCυ (1)
where ipa refers to the anodic peak current, n is the num-
ber of electrons transferred, A is the surface area of the
electrode, D0 is diffusion coefficient, υ is the scan rate
and C0 is the concentration of K3Fe(CN)6. For 1.0 mM
K3Fe(CN)6 in 0.1 M KCl electrolyte, n = 1. D0 = 7.6 ×
10−6 cm2·s−1 [14], then from the slope of the plot of ipa ver-
sus υ1/2, relation, the surface area of electrode was calcu-
lated. In our experiment, the slope obtained was 2.46 ×
10−6 and the surface area of glassy carbon electrode was
calculated to be 0.033 cm2.
2.3. Analytical Procedure
The GCE was carefully polished using 0.3 micron Al2O3
slurry on a polishing cloth before each experiment. After
polishing, the electrode was rinsed thoroughly with water.
After this mechanical treatment, the GCE was placed in
buffer solution and various voltammogramms were re-
corded until a steady state baseline voltammogram was
obtained.
The GCE was first activated in phosphate buffer (pH
3.0) by cyclic voltammetric sweeps between −2 to and
3.0 V until stable cyclic voltammograms were obtained.
Then electrodes were transferred into another 10 ml of
phosphate buffer (pH 3.0) containing proper amount of
chalcone. After accumulating for 10 s at open circuit under
stirring and following quiet for 10 s, potential scan was
initiated and cyclic voltammograms were recorded between
−2 and 3.0 V, with a scan rate of 50 m·Vs−1.
2.4. Plasma sample Preparation
Human blood samples were collected in dry and evacu-
ated tubes (which contained saline and sodium citrate so-
lution) from same healthy volunteer. The samples were
handled at room temperature and were centrifuged for 10
min at 1500 rpm for the separation of plasma within 1
hour of collection. The samples were then transferred to
polypropylene tubes and stored at 20˚C until analysis.
The plasma samples, 0.2 mL, were deproteinized with 2
mL of methanol, vortexed for 15 minutes centrifuged at
6000 RPM for 15 min, and supernatants were collected.
The supernatants were spiked with an appropriate volume
of chalcone. Appropriate volumes of this solution were
added to phosphate buffer pH 3.0 as supporting electro-
lyte and the voltammograms were then recorded.
3. Results and Discussion
3.1. Cyclic Voltammetric Behavior of Chalcone
In order to understand the electrochemical process occur-
ring at the glassy carbon electrode, cyclic voltammetry
was carried out. Chalcone was oxidized on glassy carbon
electrode between pH 3.0 and 11.2 of phosphate buffer,
producing two well-defined oxidation peaks and one re-
duction peak. The cyclic voltammograms of chalcone at
pH 3.0 in phosphate buffer was as shown in Figure 1.
The blank solution without chalcone was shown by curve
(b) and anodic peaks corresponding to chalcone oxida-
tion appeared at 0.514 V (peak A) and 1.478 V (peak B)
and a cathodic peak at −0.689 V (peak C) as shown in
Figure 1. Cyclic voltammogram obtained for 10 μM chal-
cone on glassy carbon electrode in pH 3.0 0.2 M buffer: (a)
chalcone and (b) blank run without chalcone at ν = 50 m·Vs−1:
accumulation time: 10 s (at open circuit).

K. M. NAIK, S. T. NANDIBEWOOR
658
curve (a). The peak current for the first wave was found
to increase with increase in concentration of chalcone.
The plot ip vs. concentration was linear in the range 0.2 to
10.0 μM and deviates from linearity above 10 μM. This is
due to the adsorption of chalcone or chalcone oxidation
product at higher concentration.
It is shown that the reduction peak was observed in the
reverse scan, suggesting that the electrochemical reaction
was a quasi-reversible process [15]. Nevertheless, it was
found that the oxidation peak current of chalcone showed
a remarkable decrease during the successive cyclic volta-
mmetric sweeps. After every sweep, the peak current dec-
reased greatly and finally remained unchanged. This phe-
nomenon may be attributed to the consumption of adsor-
bed chalcone on the electrode surface or due to the fact
that the adsorption of oxidative product occurs at the elec-
trode surface. Therefore, the voltammograms correspond-
ing to the first cycle and peak A were generally recorded,
since peak A was more intense than B.
3.2. Influence of Accumulation Potential and
Time
It was important to fix the accumulation potential and time
when adsorption studies were undertaken. Both conditions
could affect the amount of adsorption of chalcone at the
electrode. Bearing this in mind, the effect of accumula-
tion potential and time on peak current response was stud-
ied by CV. The concentration of chalcone used was 10 μM.
When accumulation potential was varied from +0.4 to
−0.4 V, the peak current changed a little. Hence, accu-
mulation at open circuit was adopted. The peak current
increased very rapidly with increasing accumulation time,
which induced rapid adsorption of oxidative product on
the surface of the GCE. The peak current reached the
maximum at 10 s and their after being decreased which
indicates the saturation accumulation.
3.3. Influence of pH
The electrochemical oxidation of chalcone was studied with
different supporting electrolytes such as Britton-Robinson
buffer and phosphate buffer. Within the range of pH 3.0 -
11.2, the phosphate buffer gave the good results as com-
pared to other supporting electrolytes. Hence phosphate
buffers were taken as a supporting electrolyte. With in-
creasing the pH of the buffer solution, the peak potential
shifted to less positive values as shown in Figure 2.
The plot of Ep versus pH (Figure 3(a)) shows that the
peak potential is pH dependent. The variation of peak cur-
rent with pH is as shown in Figure 3(b). The peak cur-
rent decreased from pH 3 - 11.2. The voltammetric re-
sponse was markedly dependent on pH. From the experi-
mental results, (Figure 2) it is observed that highest peak
current and better shape of the voltammogram was ob-
served at pH 3.0, suggesting this pH is optimal pH value.
From the plot of current versus pH (Figure 3(b)) it is
evident that current goes on decreasing with increase in
pH. Hence pH variation is restricted to 11.2.
Figure 2. Influence of pH on the shape of the peaks in phos-
phate buffer solution at (a) pH 3.0; (b) pH 4.2; (c) pH 5.0;
(d) pH 6.0; (e) pH 7.0; (f) pH 8.0; (g) pH 9.2; (h) pH 10.4
and (i) pH 11.2. Other conditions are as in Figure 1.
Ep ( V )
pH
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
024681012
A
B
(a)
0
5
10
15
051015
Current x 1 0-4
A
pH
(b)
Figure 3. (a) Influence of pH on the peak potential of chal-
cone for peaks A and B. Other conditions are as in Figure 1;
(b) Variation of peak currents of peaks A and B with pH.
Other conditions are as in Figure 1.

K. M. NAIK, S. T. NANDIBEWOOR 659
3.4. Influence of Scan Rate
Useful information involving electrochemical mechanism
usually can be acquired from the relationship between peak
current and scan rate. Therefore, the electrochemical be-
havior of chalcone at different scan rates from 50 to 300
m·Vs−1 (Figure 4) was also studied. From this we observed
that increasing the scan rate, the peak potential of A is
shifted to more positive values. Simultaneously, the width
at half-height of peak A increases. It is suggested that this
corresponds to the oxidation of chalcone dimers formed
at the GCE surface. The formation of such kind of dimers
is well documented in the literature [16,17], but they can
only be observed when high scan rates are used probably
because they have short life time.
At the same time, the cathodic peak C is displaced to
more negative values whereas its current increases with
the scan rate. Nevertheless, the fact that peak current of
C is always smaller than the peak current of A suggests
that the oxidation product of chalcone is very unstable
and undergoes hydrolysis in the solution [18].
There is a good linear relationship between peak cur-
rent and scan rate. The equations are
,
() ()
41
p
I10 A4.6745Vs0.7531υ
−−
=−, r0.9821=
, r0.9828=
1
3,r0.9917==
6,r0.9842==
and
() ()
41
p
I10 A5.7583Vs0.8515υ
−−
=−
for peaks A and B, respectively as shown in Figure 5(a).
In addition, there was a linear relation between log Ip and
log υ, corresponding to the following equation:
() ()
4
p
log I10A0.4881logVs+0.581υ
−−
and
() ()
41
p
log I10A0.516logVs+0.670υ
−− ,
for peaks A and B, respectively (Figure 5(b)). The slope
of 0.4881 and 0.516 is close to the theoretically expected
value of 0.5 for a diffusion controlled process [19].
Figure 4. Cyclic voltammograms of 10 μM chalcone on GCE
with different scan rates, (a) - (f) were 50, 100, 150, 200, 250
and 300 m·Vs–1, respectively. Other conditions are as in Fig-
ure 1.
υ (V/s)
Current × 10
–
4
A
A
B
0. 00
0. 50
1. 00
1. 50
2. 00
2. 50
3. 00
0.000.10 0.200.30 0.40
log υ (V/s)
(a)
-0. 2
-0. 1
0
0.1
0.2
0.3
0.4
0.5
-1.5 -1.3 -1.1-0.9 -0.7 -0.5 -0.3 -0.1
log Ip × 10
–4
A
A
B
(b)
0.0
0.4
0.8
1.2
1.6
2.0
-1.6 -1.2-0.8 -0.40.0
lo
g
υ
(
V/s
)
Ep (V)
A
B
()
()
1
p
EV0.5993logVs+1.2974 ν
−
=
()
()
1
pV0.2591 logVs+1.8196
ν
−
=
()
(c)
Figure 5. (a) Dependence of the oxidation peak current of
peaks A and B on the scan rate; (b) Dependence of the loga-
rithm of peak current on logarithm of scan rate for peaks A
and B; (c) Relationship between peak potential and loga-
rithm of scan rate for the peaks A and B.
The peak potential shifted to more positive values with
increasing the scan rates. The linear relationship between
peak potential and logarithm of scan rate can be expressed
as
and E,
for the peaks A and B, respectively (Figure 5(c)).
According to the quasi reversible electrode process, Ip
is defined by the following equation [20]:
() ()
1212 12
5
p
ao o
I2.6910nn ADC αν =×××××× (2)
where α (alpha) is the transfer coefficient, na the number

K. M. NAIK, S. T. NANDIBEWOOR
660
of electrons transferred, ν (nu) the scan rate, A is the elec-
trode area, Do is the diffusion coefficient and Co is the
concentration of electro active species (10 μM). Thus the
value of Do is taken from the slope of Ip versus ν1/2. In
this system, for peak A, the slope was 3.7 × 10−3. The αna
was calculated according to the following equation:
a
α =
pp 2
47.7
nmV
EE−
where Ep/2 is the potential where the current is at half the
peak value. Further, the number of electron (n) transferred
in the electro oxidation of chalcone was calculated to be
2.13 ≈ 2.0.
3.5. Mechanism
In the proposed method the chalcone undergoes oxidation
with two electrons and the possible mechanisms are as
shown in Scheme 2 for peaks A, B and C respectively
which are proposed based on the earlier literature [12].
Based on the kinetic data, the proposed mechanism of
oxidation of chalcone by trichloroisocynuric acid [TClCA]
in HOAc-HClO4 medium [11] is different. Hence the oxi-
dative pathways of electrochemical and chemical proc-
esses are different.
O
H
O H
H
O
e
-
e
-
.
+ H
.
+ H
.
H
.
+ H
.
H
2
(a)
C
H
2
C
H
C
H
2
C
H
O
C
H
2
C
H
C
H
2
C
H
O
O
-
-
.
.
+ 2 e
- O
(b)
C
H
C
H
C
H
C
H
O
OO
C
H2
C
H
C
H2
C
H
O
-
-
+ 2 e-+ 2 H+
-
-
.
.
(c)
Scheme 2. Proposed mechanisms of electrooxidation of chal-
cone for peaks (a), (b) and (c).
3.6. Calibration Curve
In order to develop a voltammetric method for determin-
ing the drug, we selected the differential pulse (DPV) and
square wave voltammetric (SWV) mode, because the peaks
are sharper and better defined at lower concentration of cha-
lcone, than those obtained by cyclic voltammetry, with
low background current, resulting in improved resolution.
According to the obtained results, it was possible to ap-
ply these techniques to the quantitative analysis of chal-
cone. The phosphate buffer solution of pH 3.0 was selected
as the supporting electrolyte for the quantification of cha-
lcone as it gave maximum peak current at pH 3.0. The
peak at about 0.275 V in DPV and 0.26 V in SWV was
considered for the analysis. Differential pulse voltammo-
grams and square wave voltammograms obtained with in-
creasing amount of chalcone showed that the peak cur-
rent increased linearly with increasing concentration, as
shown in Figures 6(a) and (b) .
(a)
(b)
Figure 6. (a) Differential-pulse voltammograms of GCE in
chalcone solution at different concentraions: a: 0.2, b: 1, c:
2, d: 4, e: 6, f: 8 and g: 10 μM. Inset plot of the peak current
against concentration of chalcone; (b) Square wave voltam-
mograms of GCE in chalcone solution at different concen-
trations: a: 0.2, b: 1, c: 2, d: 4, e: 6, f: 8 and g: 10 μM. Inset
plot of the peak current against concentration of chalcone.

K. M. NAIK, S. T. NANDIBEWOOR 661
Using the optimum conditions described above, linear
calibration curves were obtained for chalcone in the range
of 0.2 to 10.0 μM. The linear equation was
() (
p
IμA72100C0.8606 r0.9832=+ =
)
, C is inμM
)
5
Cisin 10M
and
() (
5
p
I10 A78200C1.7644r0.9726,=+ =
for DPV and SWV respectively. The DPV presents a good
linear response as compared to SWV in view of a less int-
ercept of linear plot of Ip versus concentrations. Deviation
from linearity was observed for more concentrated solu-
tions, due to the adsorption of oxidation product on the
electrode surface. It was also observed that the peak po-
tential (Ep) and half peak potential (Ep/2) were shifted tow-
ards more positive value suggesting that product under-
goes adsorption at the surface of GCE. Related statistical
data of the calibration curves were obtained from five dif-
ferent calibration curves. The limit of detection (LOD) and
quantification (LOQ) were 0.18 μM and 0.6 μM, respec-
tively. The LOD and LOQ were calculated using the fol-
lowing equations:
LOD3, LOQ10
s
msm==
where s is the standard deviation of the peak currents of
the blank (five runs) and m is the slope of the calibration
curve.
3.7. Stability and Reproducibility
In order to study the stability and reproducibility of the
electrode, a 10 μM chalcone solution were measured within
the same electrode (renewed every time) for every several
hours within day, the RSD of the peak current was 2.88%
(number of measurements = 5). As to the between day re-
producibility, it was similar to that of within a day if the
temperature was kept almost unchanged which could be
attributed to the excellent stability and reproducibility of
GCE.
3.8. Effect of Surfactant
Surfactants even in trace quantities can exert a strong ef-
fect on the electrode process. Adsorption of such substances
at the electrode may inhibit the electrolytic process, bring
about the irregularity in the voltammograms, and shift in
the wave to more negative potentials [21,22].
Surface-active substances have the common tendency
of accumulation at interfaces. The lack of affinity between
the hydrophobic portion of the surfactant and water leads
to a repulsion of these substances from the water phase
as a consequence of reduction of the microscopic chal-
cone water interface. Experimental results showed that
the addition of cationic surfactant, cetyltrimethylammo-
nium bromide, as anionic surfactant, sodiumdodecyl sul-
fate and the non-ionic surfactant, Triton X-100 have no
much influence on the peak current and peak potential.
3.9. Effect of Interferents
For the analytical applications of the proposed method, the
effect of potential interferents that are likely to be in bio-
logical samples were evaluated under the optimum experi-
mental conditions. Differential-pulse voltammetric experi-
ments were carried out for 1.0 μM chalcone in the pres-
ence of 1.0 mM of each of the interferents. The experimen-
tal results (Table 1) showed that thousand-fold excess of
glucose, starch, sucrose, dextrose, gum acacia, citric acid,
tartaric acid and oxalic acid did not interfere with the volt-
ammetric signal of chalcone. Therefore, the proposed meth-
od can be used as a selective method.
3.10. Detection of Chalcone in Spiked Human
Plasma Samples
The developed differential-pulse voltammetric method for
the chalcone determination was applied to spiked human
plasma samples. The recoveries from human plasma were
measured by spiking drug free plasma with known amounts
of chalcone. The plasma samples were prepared as de-
scribed in experimental section. A quantitative analysis can
be carried out by adding the standard solution of chalcone
into the detect system of plasma sample. The calibration
graph was used for the determination of spiked chalcone
in plasma samples. The results of four plasma samples
obtained are listed in Table 2. The recovery determined
was in the range from 98.0% to 103.0% and the RSD was
2.05%.
Table 1. Influence of potential interferents on the voltam-
metric response of 1.0 μM chalcone.
Interferent Concentration (mM) Signal change (%)
Glucose 1.0 −1.6
Starch 1.0 −1.2
Sucrose 1.0 −1.6
Dextrose 1.0 −1.6
Citric acid 1.0 −1.2
Tartaric acid 1.0 −1.6
Oxalic acid 1.0 −1.2
Gum acacia 1.0 −1.6
Table 2. Determination of chalcone in spiked human plasma
samples.
Human
plasma Spiked (μM) Detection(a) (μM) Recovery (%)SD ± RSD (%)
Sample 1 0.3 0.3046 98.17 0.0011 ± 3.83
Sample 2 0.7 0.7003 99.59 0.0079 ± 1.13
Sample 3 3.0 2.8981 103.19 0.0092 ± 3.17
Sample 4 7.0 6.941 100.04 0.0057 ± 0.82
(a)Mean average of five determinations.

K. M. NAIK, S. T. NANDIBEWOOR
662
Table 3. Determination of chalcone in urine samples.
Urine Spiked (μM) Detected(a) (μM) Recovery (%) SD ± RSD (%)
Sample 1 0.3 0.2946 101.22 0.0014 ± 4.89
Sample 2 0.7 0.6773 103.03 0.0180 ± 2.65
Sample 3 3.0 3.001 99.75 0.0144 ± 0.47
Sample 4 7.0 7.123 98.98 0.0757 ± 1.07
(a)Mean average of five determinations.
3.11. Detection of Chalcone in Urine Samples
The applicability of the DPV to the determination of chal-
cone in spiked urine was investigated. The recoveries from
urine were measured by spiking drug free urine with known
amounts of chalcone. The urine samples were diluted 100
times with the phosphate buffer solution before analysis
without further pretreatments. A quantitative determina-
tion can be carried out by adding the standard solution of
chalcone into the detect system of urine sample. The cali-
bration graph was used for the determination of spiked
chalcone in urine samples. The detection results of four
urine samples obtained are listed in Table 3. The recov-
ery determined was in the range from 98.0% to 103.0%
and the R.S.D. was 2.77%. Thus, satisfactory recoveries
of the analyte from the real samples and a good agree-
ment between the concentration ranges studied and the
real ranges encountered in the urine samples when treated
with the drug make the developed method applicable in
clinical analysis.
4. Conclusion
A glassy carbon electrode was used first time for the oxi-
dation of chalcone in phosphate buffer solution. When the
potential was made to move, chalcone produced two an-
odic and one cathodic peak at about 0.513 V, 1.478 V
and −0.689 V in pH 3.0 phosphate buffer, respectively. A
suitable mechanism was proposed. The peak at about 0.51
V was suitable for analysis and the peak current was lin-
ear to chalcone concentrations over a certain range under
the selected conditions. This method can be used for volt-
ammetric determination of selected analyte as low as 0.18
μM with good reproducibility. The proposed method of-
fered the advantages of accuracy and time saving as well
as simplicity of reagents and apparatus. In addition, the
results obtained in the analysis of chalcone in spiked
human plasma and urine samples demonstrated the ap-
plicability of the method for real sample analysis.
5. Acknowledgements
One of the authors, Keerti M. Naik, acknowledges Dr. B.
E. Kumara Swamy, Department of Industrial Chemistry,
Kuvempu University, Shankaraghatta, India for useful dis-
cussions.
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Abbreviations
CV: Cyclic voltammetry; DPV: Differential pulse volt-
ammetry; SWV: Square wave voltammetry; n: Number
of electrons transferred; Ipa: Anodic peak current; D0: Dif-
fusion coefficient; A0: Surface area of the electrode; υ:
Scan rate; C0: Concentration; T: Absolute temperature; R:
Gas constant; F: Faradays constant; Ep: Peak potential; α:
Transfer coefficient; LOD: Limit of detection; LOQ: Limit
of quantification; RSD: Relative standard deviation.