Novel n-octadecylcarboxamide CoPc: amperometric detections for bioanalytes using modified GCE

Article abstract of DOI:10.1007/s11696-021-01547-5

Here, we are reporting cobalt(II) phthalocyanine (CoPc) containing the active catalyst for the electrochemical investigations of bioanalytes. The synthesized tetra-n-octadecylcarboxamide cobalt(II) phthalocyanine was characterized by FT-IR, UV, TGA, mass and powder XRD analysis. In the present work, the synthesized complex was characterized by cyclic voltammetry and shows the redox behaviour corresponding to central metal (Co^+II/Co^+I) of the complex. Three biomolecules are well separated by their oxidation peaks in simultaneous detections of AA, DA and UA at 170, 350 and 550?mV with increasing high positive peak current. The low detection limit of AA, DA and UA was 40, 30 and 30?μmol by CV methods. The modified tetra substituted CoODAPc/GCE exhibits an excellent electrocatalytic activity, stability, high sensitivity, good linearity and selectivity without losing its catalytic activity and proves to be a versatile chemical sensor for commercial pharmaceutical samples, vitamin C tablets and dopamine injections. Graphic abstract: [Figure not available: see fulltext.]

Full text of DOI:10.1007/s11696-021-01547-5

Chemical Papers (2021) 75:2945–2956
https://doi.org/10.1007/s11696-021-01547-5
ORIGINAL PAPER
Novel n‑octadecylcarboxamide CoPc: amperometric detections
for bioanalytes using modiꢀed GCE
Mounesh1 · K. R. Venugopal Reddy · O. Nagaraja
1
2
Received: 14 July 2020 / Accepted: 29 January 2021 / Published online: 13 February 2021
Institute of Chemistry, Slovak Academy of Sciences 2021
©
Abstract
Here, we are reporting cobalt(II) phthalocyanine (CoPc) containing the active catalyst for the electrochemical investigations
of bioanalytes. The synthesized tetra-n-octadecylcarboxamide cobalt(II) phthalocyanine was characterized by FT-IR, UV,
TGA, mass and powder XRD analysis. In the present work, the synthesized complex was characterized by cyclic voltammetry
+
II
+I
and shows the redox behaviour corresponding to central metal (Co /Co ) of the complex. Three biomolecules are well
separated by their oxidation peaks in simultaneous detections of AA, DA and UA at 170, 350 and 550 mV with increasing
high positive peak current. The low detection limit of AA, DA and UA was 40, 30 and 30 µmol by CV methods. The modiꢀed
tetra substituted CoODAPc/GCE exhibits an excellent electrocatalytic activity, stability, high sensitivity, good linearity and
selectivity without losing its catalytic activity and proves to be a versatile chemical sensor for commercial pharmaceutical
samples, vitamin C tablets and dopamine injections.
*
Mounesh
mounesh.m.nayak@gmail.com
1
Department of Studies and Research in Chemistry,
Vijayanagara Sri Krishnadevaraya University,
Ballari-583105, Karnataka, India
2
Department of Studies and Research in Chemistry Kuvempu
University, Jnanasahyadri, Shankaragatta-577451, Karnataka,
India
Vol.:(0
1
123456789)
3

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Chemical Papers (2021) 75:2945–2956
Graphic abstract
Ascorbic Acid
OH
O
H
H
OH
III
O
2
Co Pc+
OH
H
O
H
O
OH
O
O
Cyclic Voltametry
O
O
H
HCH
O
H
NH2
H
CH
H
HC
H
CH
III
HC
H
2Co Pc+
H
CH
HC
H
H
CH
O
H
HC
H
H
CH
Surface Drop Dry Method
HC
H
Dopamine
H
CH
HC
H
O
H
CH
C
NH
H
HC
H
CH
C
H H
C
H
O
NH2
HC CH
H
CH
C
H
CHHH
C
H
H
HC
H
HC
C
H
H
H
HC
H
C
C
H
C
H
H
CH
C
CH
N
CH
HH
N
C
C
N
H
H
C
CH
H
H
H
C
CH
N
CH
C
H
HC
H
H
C
C
C
C
CH
H
H
C
+2H+
C
H
O
C
C
+
+
H
H
C
H
HC
H
C
H
C
H
C
N
Co
N
C
O
H
H
C
H
C
H
H
CH
C
N
C
CH
C
H
C
CH
C
H
N
C
C
N
HC NH
H
H
H
C
H
H
O
H
CH
C
H
C
H
C
H
H
H
C
C
H
C
H
CH
C
CH
H
CH
H
H
H
H
H
C
H
HC
H
C
H
CH
C
O
CH
H
CH
Dopamine (Oxn)
H
C
HC
CH
H
CH
H H
NH
H
H
HC
CH
H
H
O
HC
CH
H
DPV
H
H
N
HC
H
CH
H
III
HC
H
CH
2Co Pc+
NH
H
HC
H
CH
O
H
HC
H
HCH
H
N
H
N
H
O
UricAcid
Modified Octadecylcarboxamide
CoPc/GCE
H
N
O
O
II
2
Co PC+
NH2
N
H
NH
UricAcid (Oxn)
O
Amperometry
Keywords Sensors · Ascorbic acid · DCC · GCE · DA · UA · CoPc
Introduction
the determination of these biological molecules in rou-
tine analysis. Several methods and catalytic materials have
been used for the detection and sensing of these biomol-
ecules (Colín-Orozco1 et al. 2012; Weihua et al. 2014;
Ensaꢀ Ali et al. 2009). The literature survey reveals that
phthalocyanine was also used for the investigation and
sensing of AA, DA and UA molecules (Mounesh et al.
2019a, b). Metallophthalocyanines (MPCs), with the pla-
nar 18 π-electron conjugated systems, are a well-known
class of N4-macrocyclic metal compounds (Mounesh et al.
2020; Mounesh et al. 2020; Mounesh et al. 2020; Mounesh
et al. 2020; Mounesh et al. 2021). In spite of their versa-
tile electrochemical applications, a very less attention was
paid towards the synthesis of octadecylamine derivatives
containing macrocyclic moiety.
DA (3,4dihydroxyphenylethylamine) and other catecho-
lamine play an important role in central nervous system,
cardiovascular, renal and hormonal systems as well as
in drug addiction and Parkinson disease (Salimi et al.
2
006). Abnormal release of DA may relate to many dis-
eases, such as Parkinson’s disease, Huntington’s disease,
tardive dyskinesia and Alzheimer’s diseases. AA also
known as vitamin C exists widely in food, plant and ani-
mal tissues. Excess AA intake will lead to urinary stone,
diarrhoea and stomach convulsion. UA is the purine and
its metabolism product in the human body. The UA leads
to several diseases (e.g. gout, allergic, rashes, prickly heat,
hyperuricaemia and LeschNyhan syndrome). Therefore,
it is essential to develop simple and rapid methods for
The present study was related to the synthesis of novel
tetra-n-octadecylcarboxamide cobalt(II) phthalocyanine
1
3

Chemical Papers (2021) 75:2945–2956
2947
(
CoODAPc) containing macrocyclic moiety and explored
Synthesis of tetra‑n‑octadecylcarboxamide
the electrochemical investigations for analytes like AA,
DA and UA. The CoTcPc complex substituted with octa-
decylamine (ODA) was expected to enhance the solubility
of CoPc in organic solvents and tendency towards sensing
of biomolecules in PBS (pH = 7) electrolyte. The modi-
cobalt(II) phthalocyanine (CoODAPc) complex
Tetra-carboxy cobalt(II) phthalocyanine (CoTcPc) (1 g,
0.0013 mol), K CO (0.92 g, 0.0066 mol) and N,N´ dicy-
2
3
clohexylcarbodiimide as catalyst was dissolved in dimethyl-
formamide (DMF, 20 mL) with constant stirring for 20 min
and the solution of octadecylamine (1.8 g, 0.0066 mol) was
added slowly with stirring (Scheme S1). The reaction mix-
ture was stirred for 48 h at room temperature. The reaction
mixture was poured into ice cold water to yield dark green
precipitate and further puriꢀed with hot water followed by
hexane and dried over P O in vacuum desiccator (Mounesh
ꢀ
ed CoTODAPc/GCE was used for micro-molar solution
in simultaneous and individual detection of AA, DA and
UA and interferences studies and real samples analysis
using cyclic voltammetry (CV), diꢁerential pulse voltam-
metry (DPV) and chrono-amperometry (CA) techniques.
The voltammograms of AA, DA and UA which are in
the micro-molar solutions level concentrations and most
suitable for biological ꢂuids, food, plant and animal tissue
in neutral PBS electrolyte solutions and for Vitamin ‘C’,
dopamine hydrochloride injection and human urine real
samples analysis.
2
5
et al. 2020).
−
1
Yield: 87%. Mol. Wt.: 1753. IR (KBr, cm ): 3322
(–CONH), 2928–2846 (Ar–CH), 1625 (C=N), 1513 (C=C),
−
1
1452 (C–C), 1303, 1227, 1149, 1092, 893, 837, 629 cm
are attributed to the various skeletal vibration of PC ring
Fig. S1).
(
Materials and methods
Preparation of modiꢀed electrode
Instrumentations
The bare glassy carbon electrode was polished to mirror sur-
face by gentle polishing sequentially with 0.3 and 0.05 μm
alumina slurry on a Buehler polishing pad. Then, electrode
was sonicated two times each in doubly distilled water and
alcohols separately for 5 min to remove alumina particles
trapped on the surface. The GCE rinsed with excess water,
dried and kept in a desiccator. The green ink of CoTODAPc
(5 mg CoTODAPc was suspended in 0.5 mL dry DMF sol-
vent) was prepared ink was drop cast on the glassy carbon
electrode and dried in room temperature.
Ultraviolet–visible (UV–Vis) absorption spectra were
recorded on Shimadzu UV-2550 spectrophotometer and
infrared spectra on Perkin-Elmer spectrum 100 FT-IR
spectrometer. X-ray powder diffraction patterns were
recorded using a Cu Kα radiation (λ = 1.5405 Å, nickel
ꢀ
lter), on a Bruker D8 Discover equipped with a Lynx
Eye detector. The data were obtained in the range of 2θ,
–100°. The X-ray diꢁraction (XRD) analysis was carried
5
out using Eva (evaluation curve ꢀtting) software. Thermal
gravimetric analysis (TGA) was recorded on a Shimadzu
DTG-TG 60H with a gas ꢂow of 120 ml/min and operated
under nitrogen atmosphere. A mass spectrometry study of
the ꢀnal compound was conꢀrmed by ESIMS MALDI-
Micromass QTOF2 equipment. All the electrochemical
measurements were carried out on a CHI620E electro-
chemical workstation USA with a conventional three-
electrode system (glassy carbon electrode, platinum wire
electrode and Ag/AgCl electrode).
Results and discussion
The synthesis of CoTODAPc complex was shown in Scheme
S1. The amine group of n-octadecylamine is reacted with
carboxylic group of CoTCPc to yield amide bridged tetra-
n-octadecylcarboxamide cobalt(II) phthalocyanine (CoTO-
DAPc). The elemental analysis data fairly agreed with the
theoretical values indicating the synthesized complex is
pure in nature. The CoTODAPc complex is blue coloured in
nature and readily soluble in concentrated sulphuric acid and
DMSO. The synthesized complex has been characterized by
various spectroscopic as well as electrochemical techniques.
Precursors
Octadecylamine (ODA) was procured from Sigma Aldrich.
N,N′ dicyclohexylcarbodiimide, N,N′ dimethylformamide,
potassium carbonate anhydrous were procured from spec-
trochem Pvt, Ltd. Dopamine was purchased from Hi-Media
Laboratories Pvt, Ltd. (INDIA), ascorbic acid and uric acid
were procured from SDFCL Ltd Co, (INDIA), and used
without further puriꢀcations.
UV–Vis spectrum
The best indications for phthalocyanine systems are given by
their UV–Vis spectra in solution. Two principle π–π* transi-
tions are seen for PCs: a lower energy Q-band region (visible
blue and red region) at around 650–700 nm, π–π* transition
1
3

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Chemical Papers (2021) 75:2945–2956
from highest occupied molecular orbital (HOMO) to low-
est unoccupied molecular orbital (LUMO) of the complexes
and a higher energy B band region at around 300–400 nm,
deeper π–π* transition from the highest occupied MO’s
(
Fig. 1 inset a and b curve) to the LUMO (Mounesh et al.
2
020). The B bands within the UV range of 320–400 nm
were due to the transitions from the deeper π levels to the
LUMO (Fig. 1 inset a curve) a shoulder peak at 600–650 nm
was observed in the Q-band region may be due to vibronic
ꢀ
ne structure as well as presence of dimer and oligomeric
complex species in solution. Hence, the absorption spectrum
of this novel complex can be tuned for spectral shifts by
varying the substituent attached to the CoTODAPc (Fig. 1
inset a curve) and CoTCPc (Fig. 1 inset b curve).
Fig. 2 TGA of a CoTCPc b CoTODAPc
FT‑IR spectra
4
00–570 °C (21% weight loss of Pc ring) Pc complex and
IR spectral data clearly indicate the formation of com-
pound by the appearance of new absorption bands at
570–800 °C (29% weight loss of CoO). The degradation
temperature was found to vary as a function of temperature.
Figure 2b shows that the thermal stability of the CoTODAPc
complex was higher than that of pure Pcs where the degra-
dation temperature is signiꢀcantly shifted to higher values
(Fig. 2a) (Mounesh et al. 2019a, b; Jilani et al. 2020).
−
1
3
317–3322 cm (–CONH), (–COOH) and (–NH2) Fig.
−1
S1a and b, 2840–2928 (Ar–CH), 1625–1628 cm for C=N,
−
1
−1
−1
1
1
513–523 cm for C=C, 1450 452 cm for C–C, 1313,
227, 1086, 887, 837, 741, 636 are attributed to the various
skeletal vibration signals of CoTCPc and CoTODAPc ring
and substituted ligand for octadecylamine as shown in Fig.
S1.
X‑ray diꢁraction analysis
X-ray powder diꢁraction (XRD) was employed to elucidate
the crystal nature and size of the substituted CoPc. The pat-
terns are qualitative and are similar to that of CoTODAPc;
however, the pattern was more dispersive in intensity than
the corresponding metal phthalocyanine. The XRD pattern
was used to explain qualitatively the degree of crystallinity
(Sawada et al. 2005; Mounesh et al. 2021). The XRD pat-
tern indicates that the obtained CoTODAPc is amorphous
in nature. The 8, 9, 15, 17, 18, 19, 21, 23, 26, 30 peaks that
were observed at room temperature disappeared and four
other lines emerged (Fig. 3). This peak corresponds to long
Thermal properties
The thermal stability of the bare CoTCPc and CoTODAPc
was studied using TGA. Figure 2a, b illustrates typical
TGA thermograms of weight loss as a function of tempera-
ture range from 100 to 800 °C. The sample (50 mg) was
heated from room temperature to 800 °C at rate of 5 °C/min
in nitrogen. The TGA curve (above) is labelled in terms of
the identity of the complex. The temperature ranges from
1
00 to 400 °C (50% weight loss of substituted ligand),
Fig. 1 UV–visible spectra of a CoTODAPc and b CoTCPc
Fig. 3 X-ray diꢁractograms of CoTODAPc
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3

Chemical Papers (2021) 75:2945–2956
2949
aliphatic chains that are located randomly within the colum-
nar mesosphere with an average spacing of 4.6 Å. A less
broad peak was found around 3.4 Å, which was the stacking
distance of phthalocyanine core within the columns. These
results are similar to the data of the CoODAPc obtained
(Sleven et al. 2001; Jilani et al. 2019). The observed patterns
are very much similar to parent phthalocyanines except the
broadening of the peaks. The broadening may be due to the
presence of substituent and which seems to play an impor-
tant role in the stacking of the substituted phthalocyanine
derivative.
Mass spectrum
The ESI–MS mass spectrum of compound CoTODAPc is
depicted in scheme S1 and conꢀrmed the proposed structure.
The molecular ion peaks at m/z=1753; Mass: m/z=Found
Fig. 4 Cyclic voltammograms plot of CoTODAPc/GCE in PBS
(
pH=7) electrolyte solution at peaks; bare GCE (red curve), a modi-
(
M+Z) 1754 (Fig. S2).
ꢀ
ed GCE, b 15 µM of AA, c 10 µM for DA and d 10 µM for UA; At
−1
scan rate=50 mV s
Electrochemical investigation
of biomolecules
currents increase correspondingly. The scan rate of cyclic
voltammetry exhibits a profound eꢁect on the oxidation
peak current of AA predicts the cathodic peak potential
(170 mV) and increasing scan rates with increasing positive
current (Fig. S3A), AA is displayed the linear responses,
linear equation; Y=0.2035 (AA)+4.0414 with a correlation
Simultaneous detections electrocatalytic oxidation
for AA, DA and UA
Cyclic voltammogram for the oxidation of tetra CoTODAPc/
GCE in PBS (pH = 7) electrolyte solution was utilized to
assess the electrochemical sensing studies of AA, DA
and UA by modiꢀed GC electrode. The bare GCE Fig. 4
2
coeꢃcient of R =0.998 (inset Fig. S3A). The AA inpres-
ence DA is detecting the diꢁerent cathodic peak potential,
with increasing high positive peak current responded (Fig.
S3B), and linear regression curve of peak current vs. various
scan rate of AA and DA; Y=0.178 (AA)+5.293, Y=0.20
(
inset red curve) and CoTODAPc/GCE exhibit a peak at
cathodic peak potential 120 mV and positive current Fig. 4
inset a curve. The 15 µM of AA is detecting the cathodic
peak potential (130 mV) as shown in Fig. 4 inset b curve
2
(DA)+6.178 with correlation coeꢃcient of R =0.999 and
0.999 (inset Fig. S3B). When the scan rate increases in the
range of 10–100 mV/s, simultaneous determinations of AA,
DA and UA exhibit positive shifts in the three diꢁerent oxi-
dation peaks (Fig. S3C), suggesting that the adsorption of
DA, UA and AA does not occur on CoTODAPc/GCE in PBS
(pH7) solution. The redox peak currents do not increase as
the scan rate increases, while a linear relationship is estab-
lished between the positive peak current and the square root
of scan rate. The linear equations are expressed as follows:
(
Zucolotto et al. 2006), and 10 µM DA shows a cathodic
peak at potential 350 mV (Fig. 4 inset c curve) with applied
−1
scan rate of 50 mV s . Further, AA and DA keep at constant
at same electrolyte solution in presence of UA (10 µM) is
detecting cathodic peak potential 520 mV (Fig. 4 inset d
curve), (Tsierkezos et al. 2016). DA is detecting the cathodic
peak potential at 350 mV and three species were detection by
three diꢁerent peak potential as shown in Fig. 4 (Thiagarajan
et al. 2007). Here, the CoTODAPc/GC electrode is highly
electro-catalytically active towards three diꢁerent poten-
tial peaks, sensitivity and selectivity, as shown in Table S1
1
/2
−1
2
AA: Ipa (µA) = 0.161 ʋ (mV s ) + 6.662, R = 0.999;
1
/2
−1
2
DA: Ipa (µA) = 0.163 ʋ (mV s ) + 8.488, R = 0.999;
1
/2
−1
2
UA: Ipa (µA) = 0.2272 ʋ (mV s ) + 12.754, R = 0.999
(inset Fig. S3C); the above results indicate that the modi-
ꢀed CoODAPc/GC electrode shows a highly electrocatalytic
activity.
(
Zucolotto et al. 2006; Tsierkezos et al. 2016; Thiagarajan
et al. 2007; Yanga et al. 2014).
Eꢁects of Scan rates for AA, DA and UA
DPV studies
Fig. S3 shows the inꢂuence of diꢁerent scan rate on CV
response of AA, DA and UA at CoTODAPc/GCE. With the
increase in scan rate from 10 to 100 mV/s, the anodic peak
The excellent electrocatalytic activity of CoTODAPc/GCE
provides a substantial basis for simultaneous determination
1
3

2950
Chemical Papers (2021) 75:2945–2956
of AA, DA and UA in PBS (pH 7) electrolyte solution. In
these measurements, the concentration of the target biomol-
ecule was only changed, while concentrations of the other
two biomolecules were kept constant. Fig. S4C shows three
peaks located at 170, 350 and 550 mV corresponding to the
oxidation of AA, DA and UA that are well separated on the
CoTODAPc. The peak currents of AA oxidation increase
linearly in the range of 2–20 µM with the detection limit
performance towards the simultaneous determination of AA,
DA and UA.
The outstanding performance of the CoTODAPc/GC
electrode was detecting the various concentrations of mix-
tures (AA, DA and UA) with detecting the three diꢁerent
positive potential (170, 350, 550 mV) as shown in Fig. 5A.
The calibration curves of the peak currents were linear in
the concentration ranges of 2–20 µM for AA, DA and UA.
The linear equations of AA, DA and UA (Fig. 5B) were Ip,
AA=2.04(AA)+2.30, Ip, DA=2.5217(DA)+2.1553 and
Ip, UA=3.00(UA)+2.646 with the correlation coeꢃcients
of 0.99854, 0.999 and 0.9939, respectively. These results
demonstrate that the simultaneous determination of these
biomolecules on CoTODAPc can be achieved with excellent
sensitivity, good linear range and selectivity. Thus, CoTO-
DAPc with unique structure and electrocatalytic properties
represents a promising candidate for the construction of
highly sensitive and selective biosensors, Table S1.
−
7
of 6×10 M in the presence of DA and UA. In addition,
the successive addition of the AA into the electrochemical
system (AA detecting the excellent cathodic peak potential
(
170 mV) as shown Fig. S4A) does not generate dramatic
eꢁects on the peak potentials of the DA and UA. The linear
equation of AA is Ip, Y=1.630(AA)+7.228, with the cor-
relation coeꢃcient of 0.999 (inset Fig. S4A). Similarly, in
Fig. S4B and C, the oxidation peak currents of DA and UA
increased linearly with the increase in their corresponding
concentrations by keeping the concentrations of another
biomolecule constant. Three species are detected with well-
deꢀned potential (170, 350 and 550 mV), having detection
Amperometric determination of individual
and interference studies
−7
limits of 6, 5 and 1.67×10 M at S/N=3, respectively. The
linear equations of DA and UA are Ip, Y=2.20(DA)+14.484
(
inset Fig. S4B) and Ip, Y = 2.208(UA)-0.177 (inset Fig.
The CoTODAPc/GCE-based sensor was probed further
using amperometric Fig. 6. Initially, only PBS (pH 7) was
present in the cell. Stirring was initiated, the electrode
was poised at selected working potential (0.300 V for AA,
0.500 V for DA and 0.500 V for UA, respectively) and
aliquots (50 mL) of AA, DA or UA stock solution (with
stock concentrations of 20 µM for AA, DA and UA) were
added at 50 s intervals. Figure 6a shows the amperometric
responses of CoTODAPc/GCE to the successive addition
of AA, DA or UA into the PBS buꢁer. The CoTODAPc/
S4C) with the correlation coeꢃcients of 0.999 and 0.999,
respectively. These experimental results indicated that the
simultaneous determination of the above three species
was feasible in mixture using DPV method. In addition,
all the parameters were listed for the three biomolecules
in Table S1 (Wei et al. 2013; Yang et al. 2014; Yan et al.
2
013; Chen et al. 2015; Zhao et al. 2016). Based on the
presented results, we can conclude that the electrochemical
sensor based on the CoTODAPc/GCE shows an attractive
Fig. 5 Diꢁerential pulse voltammograms plot of CoTODAPc/GCE
in PBS (pH=7) electrolyte solution at peaks; a three mixtures deter-
minations of diꢁerent concentrations (2–20 µM) for AA, DA, UA/µM
and b linear plot of cathodic peak current (Ipc) vs. diꢁerent concen-
trations of AA, DA, UA/µM
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Chemical Papers (2021) 75:2945–2956
2951
Fig. 6 Individual amperometric responses of CoTODAPc/GCE
in PBS (pH=7) electrolyte solution at peaks; a diꢁerent amounts
of (5–50 µL) for 20 µM AA, DA UA and b linear plot of cathodic
peak current (Ipc) vs. diꢁerent amounts of AA (black curve), DA (red
curve), UA (green curve)
GCE electrode was found to exhibit linear response to addi-
tions of AA, or DA, or UA up to some concentration, after
which the noise generated by stirring precluded the accu-
rate measurement of the current. Inset Fig. 6b describes
response of AA with addition of diꢁerent amounts of 5–50
µL. The linear equation of Ipa with diꢁerent amounts of
AA (the inset in Fig. 6b black curve) was described as Ipa
DA and UA in presence of diꢁerent interfering compounds
in PBS is shown in Fig. S5. An increase in amperometric
current response was observed for the successful addition of
10 µM AA, DA and UA to the electrolyte containing inter-
fering compounds. It was also observed that even after the
addition of high concentration (10 µM) of the interference
compounds like Glucose, l-Cysteine, Tyrosine, H O and
2
2
(
(
µA) = 0.9346(AA)—4.7141, with correlation coeꢃcient
Glycine, did not have any signiꢀcant response and also the
interfering ions did not inꢂuence the AA, DA and UA detec-
tion. The addition of diꢁerent interfering biochemical’s in
phosphate buꢁer solution did not inꢂuence the amperometric
response for AA, DA and UA indicating the selective and
superiority of the electrode (Saithip et al. 2014).
2
R ) of 0.999. The response range is 5 to 50 µM/L with a
−
7
detection limit of 6×10 M at a signal-to-noise ratio (S/N)
of 3 Table S1. Figure 6b depicts the amperometric response
of DA at a ꢀxed potential of 0.500 V. The linear equation
(
(
the inset in Fig. 6b red line curve) was presented as Ipa
2
µA) = 1.738 (DA)—6.91, (R = 0.999), with a sensitivity
−
1
of 1.738µA µM . The response range is 5 to 50 µM with a
Individual detections
−
7
detection limit of 5×10 µM (S/N=3). In Fig. 6b (green
line curve), the linear range could be observed between the
current response and concentration of UA from 5 to 50 µM
Detection of AA
with a linear regression equation (the inset in Fig. 6B) Ip
The electrocatalytic activity of CoTODAPc modiꢀed GCE
towards AA was investigated and results are shown in Fig. 7.
In the absence of AA, oxidation peak current shifted to same
potential observed by modiꢀed GCE at PBS (pH 7) elec-
trolyte solution (Fig. 7a black line curve). After addition of
diꢁerent concentrations of AA from 5 to 25 µM, the oxida-
tion peak current increases proportionally with increasing
AA concentration. It demonstrated that the current response
increase due to CoTODAPc can catalyze the oxidation of
AA has good electrocatalytic activity towards AA oxida-
tion. The electrocatalytic mechanism of AA on the GCE
can be described by Eqs. (1), (2). CoPc (III) oxidizes AA to
dehydroascorbic acid (DHAA) by the Co ion at the central
of phthalocyanine structure and regenerates CoPc(II).
2
(
µA)=2.04 (UA) – 10.04 (R =0.9995) (Fig. 6B green line
−1
curve). The sensitivity and detection limit are 2.04 µA µM
−
1
and 1.671×10 M (S/N=3), respectively. Magniꢀed por-
tion of the amperometric response curve for addition of AA,
DA or UA solution with very low concentration is shown in
Fig. 6a (Shaopeng et al. 2015).
Selectivity studies
The selectivity of our catalyst (CoTODAPc/GCE) was stud-
ied in the presence of various interfering biochemicals like
glucose, L-cysteine, tyrosine, H O and glycine. Ampero-
2
2
metric response for CoTODAPc/GCE on addition of AA,
1
3

2952
Chemical Papers (2021) 75:2945–2956
Fig. 7 Cyclic voltammograms plot of CoTODAPc/GCE in PBS (pH=7) electrolyte solution at peaks; a modiꢀed GCE (black curve) and diꢁer-
ent concentrations of AA (2–25 µM); At scan rate 50 mV s−1 and b diꢁerent scan rates of AA (10–100 mV s
−1
)
−
CoPc(II) ↔ CoPc(III) + e + H
+
the diꢁerent concentrations. The study suggests that the
proposed sensor proved to be good electrocatalytic activity
towards DA oxidation; the positive peak current of DA at
CoTODAPc/GCE has a meagre increase than that of modi-
(1)
(2)
+
2
CoPc(III) + AA → 2CoPc(II) + DHAA + 2H
ꢀ
ed GCE (Fig. 8a black line curve). There were twofold
increases in peak current with electrochemical process
ΔEp≈ 270 mV). A pair of well-deꢀned redox peaks were
The AA predicting the oxidation peak potential (170 mV)
(
shows the linear responses of diꢁerent concentrations on
modified CoTODAPc/GCE, the linear regression equa-
also observed for CoTODAPc/GCE, indicating that the redox
reaction of DA occurred at the electrode surface. The modi-
ꢀed electrode was clear evidence of electrocatalytic eꢁect
towards DA oxidation (Łuczak et al. 2008; Huiying et al.
tion; Y = 0.8734 (AA) + 20.083 with correlation coef-
2
ꢀ
cient of R = 0.9991 (inset Fig. 7a). The diꢁerent scan
rates (10–100 mV/s) of AA display the well-deꢀned linear
and increases the scan rate with increasing positive cur-
rent (Fig. 7b), while a linear relationship was established
between the positive peak current and the square root of
scan rate. The linear equations are expressed as follows: AA:
2
006). The electrocatalytic mechanism of DA to the GCE
can be described by Eqs. (3), (4). CoPc(III) oxidizes DA to
dehydrodopamine (DHDA) by the Co ion at the central of
phthalocyanine structure and regenerates CoPc(II).
1
/2
−1
2
Ipa (µA)=0.28162 ʋ (mV s )+25.36, R =0.999 (inset
Fig. 7b); the above results indicate that the oxidation of AA
on CoTODAPc/GCE is a diꢁusion-controlled process and
good linearity, reproducibility (Saithip et al. 2014; Zuo et al.
−
CoPc(II) ↔ CoPc(III) + e + H
+
(3)
+
2
CoPc(III) + DA → 2CoPc(II) + DHDA + 2H
(4)
2
012).
The linear response of CoTODAPc/GCE towards the
diꢁerent concentrations of DA vs. cathodic peak current
Detection of DA
(
Ipc); Y = 0.936(DA)+ 24.804 with correlation coeꢃcient
2
of R = 0.999 (inset Fig. 8). Figure 8b shows the diꢁerent
scan rates for DA with well-defined peak potential and
intermediate peaks at same positive current and a linear
relationship was established between the positive peak cur-
rent and the square root of scan rate. The linear equations
The electrocatalytic activities of CoTODAPc modiꢀed GCE
towards various concentrations of DA are depicted by cyclic
−
1
voltammograms at a scan rate of 50 mV s . Figure 8a dis-
plays the concentration dependence of DA at CoTODAPc/
GC electrode. As expected, no redox peaks can be observed
in pH 7 blank solution. After addition of diꢁerent concentra-
tions of DA from 5 to 25 μM, a well-deꢀned and reversible
pair of redox peaks located at 350 mV versus SCE appeared
with the linear relationship between the peak currents and
1
/2
were expressed as follows: DA: Ipa (µA) = 0.28161 ʋ
−
1
2
(
mV s )+20.99152, R =0.999 (inset Fig. 8b); the above
results indicate that the oxidation of DA on CoTODAPc/
GCE was a diꢁusion-controlled process and good linearity,
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3

Chemical Papers (2021) 75:2945–2956
2953
Fig. 8 Cyclic voltammograms plot of CoTODAPc/GCE in PBS (pH=7) electrolyte solution at peaks; a modiꢀed GCE (black curve) and diꢁer-
ent concentrations of DA (2–25 µM); At scan rate 50 mV s− and b diꢁerent scan rates of DA (10–150 mV s
1
−1
)
reproducibility and comparatively diꢁerent literature of DA
detection as shown in Table 1 (Wei et al. 2013; Cheng et al.
1.1678 µA µM/L (inset Fig. 9a). The analytic parameters
namely: linearity range, sensitivity, detection (DOL) and
quantiꢀcation limits (QOL) were shown in Table S1. The
observed results with the modiꢀed GCE (Fig. 9a black
line curve) were more sensitive towards the UA. Fig-
ure 9b shows the increasing scan rates with increasing
peak current (Ip)(10–100 mV/s), while a linear relation-
ship was established between the positive peak current
and the square root of scan rate. The linear equations
2
012).
Detection of UA
Figure 9 shows the CVs plots for the modiꢀed CoTODAPc/
GCE at PBS (pH 7) electrolyte at diꢁerent concentrations
(
5–25 µM) of UA (Fig. 9a) predicting the well-deꢀned
1
/2
cathodic peak potential (550 mV) and there was a linearity
with concentration of UA. The UA could be electrochem-
ically quantiꢀed when they are not mixed with another
analytes. The linearity of UA; Y = 1.1678 (UA) + 24.985
were expressed as follows: UA: Ipa (µA) = 0.40217 ʋ
−
1
2
(mV s ) + 22.12667, R = 0.999 (inset Fig. 9b); the above
results indicate that the oxidation of UA on CoTODAPc/
GCE was a diꢁusion-controlled process with good linear-
ity, reproducibility, low detection limit for UA.
2
with correlation coeꢃcient and sensitivity R = 0.999 and
Table 1 Comparative study of CoTODAPc/MWCNTs/GCE modiꢀed electrode with other modiꢀed electrodes in the detection of dopamine
Sl. no
Modiꢀed electrodes
Method
LOD
Sensitivity
References
a
4.8 µA nM L−1 cm−2
1
2
3
4
5
6
7
AuNPs@SiO2-MIP sensor
PDEs-PAD
CV
CV
CV
DPV
SWV
DPV
CV
DPV
CA
200 nM
0.04 µM
6.7 µM
0.2 µM
0.07 µM
0.12 µM
40 nM
Yu et al. (2012)
b
−1
−2
6.91 nA µM L cm
Weibo et al. (2016)
Alarco-Angeles et al. (2008)
Zheng et al. (2013)
Fabio et al. (2017)
Wang et al. (2007)
This Work
c
−1
−2
GCE/MWCNT/β-CD
116.63 nA mM L cm
d
−1
−2
GNF/GCE
0.022 µA µM L cm
e
−1
−2
GNPs/MWCNTs
2.06 µA µM L cm
f
−1
−2
−2
−2
−2
AuNPs/Ch/GCE
1.741 µA µM L cm
0.045 µA nM L− cm
1
CoTODAPc/MWCNTs/GCE
−
1
30 nM
30 nM
0.065 µA nM L cm
0.154 µA nM L− cm
1
a
AuNPs@SiO2-MIP, Gold nanoparticles @ silicon dioxide molecularly imprinted polymer microsensor; PDEs-PAD, pencil-drawn electrodes;
c
d
e
GCE/MWCNT/β-CD, β-cyclodextrin/multiwalled carbon nanotubes/GCE; GNF, Gold nanoꢂower; GNPs/MWCNTs, Gold nanoparticles with
f
multiwalled carbon nanotubes; AuNPs/Ch/GCE, gold nanoparticles/Choline; CA, Chrono-amperometry
1
3

2954
Chemical Papers (2021) 75:2945–2956
Fig. 9 Cyclic voltammograms plot of CoTODAPc/GCE in PBS (pH=7) electrolyte solution at peaks; a modiꢀed GCE (black curve) and diꢁer-
ent concentrations of UA (2–25 µM); At scan rate 50 mV s− and a diꢁerent scan rates of UA (10–100 mV s
1
−1
)
Determination of real sample analysis
UA, the 30 and 40 µM urine samples used for detection were
diluted two times with PBS (pH 7). The results are listed
in Table S2. The recovery of the spiked samples ranged
between 96.7% indicating the detection procedures are free
from interferences of the urine sample matrix.
Determination of AA in vitamin ‘C’ tablets
−
1
Vitamin ‘C’ tablet, containing 200 mg tablet AA, was
nely powdered and accurately weighed and dissolved in
00 mL of water. The mixture was shaken for 20 min and
ltered into a 100 mL volumetric ꢂask. The residue was
ꢀ
1
ꢀ
washed several times with water and the solution was diluted
to the mark. 10 µL of the sample was diluted to 10 mL with
PBS (pH 7) and then transferred to an electrolytic cell for
the determination of AA by CoTODAPc/GCE. The vitamin
C tablets of AA were analysed by the standard addition
method, Table S2.
Conclusion
In conclusion, a new CoTODAPc macromolecule was syn-
thesized and characterized by FT-IR, UV–Vis and MASS
spectra, electronic spectroscopy XRD and TGA. The
obtained compounds show maximum visible light absorption
from 200 to 700 nm and exhibit improved thermal stability.
The electrochemical sensor exhibits high electrochemical
sensing activity towards the detection of AA, DA and UA
with well-separated oxidation potentials. The constructed
sensor displays low detection limits, wide linear ranges and
outstanding sensing performance towards the detection of
AA, DA and UA. The CoTODAPc/GCE manifests an inter-
esting potential as the candidate for the construction of
electrochemical sensor for simultaneous detection of AA,
DA and UA, and determinations of real samples analysis of
AA in vitamin “C” tablet, DA in dopamine hydrochloride
injections and human urine in UA. The proposed sensor is
useful and suitable for the direct simultaneous determination
of AA, DA and UA in real samples by means of the DPV.
Determination of DA in dopamine hydrochloride injections
In order to verify the reliability of the method for analysis of
DA in pharmaceutical product, this CoTODAPc/GCE was
used to determine DA in dopamine hydrochloride injection
−
1
(
10 mg mL , 2 mL per injection). 25 µL of the dopamine
hydrochloride injection solution was injected into a 10 mL
volume ꢂask and made up to volume with PBS (pH 7). Then,
this test solution was placed in an electrochemical cell for
the determination of DA using DPV method. The analytical
results are listed in Table S2. The results were satisfactory,
showing that the proposed methods could be eꢃciently used
for the determination of DA in injections.
Supplementary Information The online version contains supplemen-
Determination of UA in human urine sample
tary material available at https://doi.org/10.1007/s11696-021-01547-5.
The utilization of the proposed method for real sample
analysis was also investigated by direct analysis of UA in
human urine sample. In order to ꢀt into the linear range of
Acknowledgement One of the authors Mounesh thankful for ꢀnan-
cially support by the Vijayanagara Sri Krishnadevaraya University
SC.ST fellowship.
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3

Chemical Papers (2021) 75:2945–2956
2955
MWCNTs on glassy carbon electrode sensitive detection of
hydrazine and L-cysteine. Anal Chem Lett 10(5):620–635
Mounesh Venugopala Reddy KR (2020a) Detection of nanomolar
concentrations H O Using cobalt(II) phthalocyanine modiꢀed
Compliance with ethical standards
Conflict of interest The authors declare that they have no conꢂict of
2
2
interest.
GCE with MWCNTs. Ana Chem Lett 10(1):33–48
Mounesh Venugopala Reddy KR (2020b) Electrochemical inves-
tigation of modiꢀed GCE on carboxamide-PEG -biotin-CoPc
2
using composite MWCNTs: sensitive detection for glucose and
hydrogen peroxide. New J Chem 44(8):3330–3340
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