Highly sensitive and efficient voltammetric determination of ascorbic acid in food and pharmaceutical samples from aqueous solutions based on nanostructure carbon paste electrode as a sensor

Article abstract of DOI:10.1016/j.molliq.2016.01.010

A square wave voltammetric method for the trace analysis of ascorbic acid was developed in this study. Carbon paste electrode was modified with NiO nanoparticle and 1-butyl-3-methylimidazolium tetrafluoroborate as a binder. Electro-oxidation behavior of ascorbic acid on the modified electrode was studied, which indicated that the nanostructure modified electrode could efficiently promote electrocatalytic oxidation of ascorbic acid. A fast, selective, high sensitive and simple electrochemical strategy was then developed for trace analysis of ascorbic acid using the constructed electrode. The catalytic oxidation signal exhibited a wide linear range from 0.08 to 380.0 μM toward the concentration of ascorbic acid with a sensitivity of 0.0158 μA/μM, and the limit of detection was as low as 0.04 μM. The suggested sensor was also used for quantitative determination of ascorbic acid in food and pharmaceutical samples.

Full text of DOI:10.1016/j.molliq.2016.01.010

Journal of Molecular Liquids 216 (2016) 387–391
Contents lists available at ScienceDirect
Journal of Molecular Liquids
journal homepage: www.elsevier.com/locate/molliq
Highly sensitive and efficient voltammetric determination of ascorbic
acid in food and pharmaceutical samples from aqueous solutions based
on nanostructure carbon paste electrode as a sensor
a
a,
a
b,c,
Abbas Pardakhty , Saeid Ahmadzadeh ⁎, Sanaz Avazpour , Vinod Kumar Gupta ⁎⁎
a
Pharmaceutics Research Center, Institute of Neuropharmacology, Kerman University of Medical Sciences, Kerman, Iran
Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee 247667, India
Department of Applied Chemistry, University of Johannesburg, Johannesburg, South Africa
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
A square wave voltammetric method for the trace analysis of ascorbic acid was developed in this study. Carbon
paste electrode was modified with NiO nanoparticle and 1-butyl-3-methylimidazolium tetrafluoroborate as a
binder. Electro-oxidation behavior of ascorbic acid on the modified electrode was studied, which indicated that
the nanostructure modified electrode could efficiently promote electrocatalytic oxidation of ascorbic acid. A
fast, selective, high sensitive and simple electrochemical strategy was then developed for trace analysis of ascor-
bic acid using the constructed electrode. The catalytic oxidation signal exhibited a wide linear range from 0.08 to
Received 14 December 2015
Received in revised form 2 January 2016
Accepted 4 January 2016
Available online xxxx
Keywords:
Ascorbic acid analysis
380.0 μM toward the concentration of ascorbic acid with a sensitivity of 0.0158 μA/μM, and the limit of detection
1
-Butyl-3-methylimidazolium
was as low as 0.04 μM. The suggested sensor was also used for quantitative determination of ascorbic acid in food
and pharmaceutical samples.
tetrafluoroborate
NiO nanoparticle
Modified electrode
© 2015 Elsevier B.V. All rights reserved.
1
. Introduction
Ascorbic acid is a naturally organic compound and as a water-soluble
greatly demanded. Until now numerous techniques have been reported
for quantitative determination of ascorbic acid including high perfor-
mance liquid chromatography [8,9], spectrophotometry methods [10,
11], fluorometry methods [12,13], solid phase analysis [14,15] and
chemiluminescence methods [16]. However, all mentioned methods
have major disadvantages including high cost, laborious in sample prep-
aration and time consuming, requiring large infrastructure back up and
expert knowledge, background interference for fluorometry and
destroying of sample for chromatography. Recently electrochemical
techniques provide accurate and rapid tools with high sensitivity for
routine and reliable determination of ascorbic acid in various matrices
[17–20].
Among all chemically modified electrodes, carbon paste electrodes
(CPEs) received high attention due to its ease of application and regen-
eration, cheapness, stable response and very low ohmic resistance.
Modified CPEs overcome on large over potential required for oxidation
of electroactive compounds by modification of electrode surface using
nanostructure materials and high conductive binder to increase the
conductivity of the electrode [21]. Nanostructure materials received
considerable attention due to their distinctive and unique behavior
with outstanding electrical, chemical, mechanical and structural prop-
erties that make them a very attractive material for large range of appli-
cations in pharmaceutical, biological and industrial procedure [22–25].
Metal nanoparticles have been used commonly in electrochemical tech-
niques owing to its high catalytic activity in chemical reactions and
high surface area for increasing current density [26]. Since metal
vitamin has been widely applied in large quantities to food products,
drinks, animal feed, pharmaceutical formulations and cosmetics due to
its valuable properties such as pH regulating and antioxidant features
[1,2].
Ascorbic acid participates as a key component in biological metabo-
lism such as reducing agent in various metabolic pathways, synthesis
and maintenance of collagen, blood vessels, cartilage, bones and ten-
dons and reacts with reactive oxygen species or free radicals and prob-
ably reducing cholesterol level [3,4]. Furthermore, ascorbic acid as a
vital nutrient is commonly used in therapeutical fields such as improv-
ing immunity, preventing and healing of catarrh, infertility, skin disor-
ders, amelioration of injuries and burns, cancer, aids and clinical
diagnostic applications [5,6]. Besides, in food processing industries
ascorbic acid is used as an antioxidant to prevent changes in color,
taste and odor of products [7].
Therefore, due to biological importance of ascorbic acid, its accurate
determination in pharmaceutical, clinical and food industries samples is
⁎
Correspondence to: S. Ahmadzadeh, Pharmaceutics Research Center, Institute of
Neuropharmacology, Kerman University of Medical Sciences, Kerman, Iran.
Correspondence to: V.K. Gupta, Department of Chemistry, Indian Institute of
⁎
⁎
Technology Roorkee, Roorkee 247667, India.
E-mail addresses: chem_ahmadzadeh@yahoo.com (S. Ahmadzadeh),
vinodfcy@gmail.com, vinodfcy@iitr.ac.in (V.K. Gupta).
http://dx.doi.org/10.1016/j.molliq.2016.01.010
0167-7322/© 2015 Elsevier B.V. All rights reserved.

388
A. Pardakhty et al. / Journal of Molecular Liquids 216 (2016) 387–391
described above to prepare BMITB/NiO/NPs/CPE. When necessary, a
new surface of BMITB/NiO/NPs/CPE was obtained by pushing an excess
of the paste out of the tube and polishing it on a white paper.
2.4. Real sample preparation
Vegetable and fruit juices were obtained using a mechanical squeez-
er. The juices obtained were filtered into a beaker and acidified (pH =
) using citric acid. A 2.0-mL portion of the filtrate was added to the
2
phosphate buffer solution pH = 7.0 in voltammetric cell. Standard addi-
tion method was used for determination of ascorbic acid in the juice
samples.
Ten tablets of ascorbic acid powdered in mortar and then dissolved
in 100 mL water with ultrasonication. Then, 1.0 mL of the solution
plus 9.0 mL of the buffer (pH 7.0) was used for the analysis with stan-
dard addition method.
Fig. 1. SEM image of synthesized NiO nanoparticles.
Liposomes containing ascorbic acid were prepared using film hydra-
tion method. Lecithine and cholesterol were dissolved in chloroform
solvent with three different compositions of 70:30, 60:40 and 50:50, re-
spectively. Rotary evaporator was used to evaporate the solvent, until
an oily concentrated mixture was obtained and then known amount
of ascorbic acid which is dissolved in di-water, was added to the mixture
and for 30 min rotary evaporating process was continued until milky
color suspensions containing liposomes were formed. To prevent the
oxidation of Lecithine the procedure was carried out under inert
atmosphere. To determine the amount of ascorbic acid loading in all for-
mulations, the non-entrapped compounds were separated from encap-
sulated ones by centrifuge. The supernatant phase which contains the
non-trapped ascorbic acid was separated. Standard addition method
was used to determine the percentage of non-trapped ascorbic acid
using proposed sensor.
nanoparticles revealed biocompatible properties, they could be applied
in fabrication of electrochemical sensors to determine electroactive
compound in pharmaceutical and food samples. Furthermore, using
ionic liquids as a high conductive binder with specific characteristics
such as good chemical and thermal stability, wide electrochemical win-
dows and high ionic conductivity greatly benefited the fabricated elec-
trode [27–29].
In the current work a great attempted have been done to fabricate a
novel modified carbon ionic liquid paste electrode using NiO nanoparti-
cles and 1-butyl-3-methylimidazolium tetrafluoroborate (BMITFB) as a
binder. The electrochemical behavior of ascorbic acid was investigated
and the obtained results demonstrate the advantage of BMITFB/NiO/
NPs/CPE in compare to the bare carbon paste electrode in terms of
higher sensitivity and reliability. The well fabricated BMITFB/NiO/NPs/
CPE revealed an extraordinarily low background current, an extensive
operating potential window, convenient modification, reproducibility,
renewability and low cost. The analytical performance of the fabricated
electrochemical sensor was evaluated by determination of ascorbic acid
in liposome dope with ascorbic acid and food samples.
2.5. Synthesis of NiO nanoparticles
To prepare the nanoparticles (NiO), 0.25 M aqueous solution of
NiO(NO
in distilled water. The NiO(NO
slowly for 3.0 h) to the above solution under high-speed stirring. The
3
)
2
⋅6H
2
O and a 0. 5 M aqueous solution of NaOH was prepared
)
3 2
⋅6H O solutions were added drop wise
2
(
2
. Materials and methods
beaker was sealed at this condition for 3 h. The precipitated Ni(OH)
2
2
.1. Chemical and reagents
Ascorbic acid, NaOH, mineral oil, methanol and graphite powder
were obtained from Merck. 1-butyl-3-methylimidazolium tetrafluoro-
borate was purchased from Sigma-Aldrich. Phosphate buffer solution
(
0
PBS) with various pH was prepared by mixing the stock solution of
.1 M H
PO . The doubly distilled water was used in all solution prepa-
3
4
rations. All of the other chemicals were purchased in analytical grade
from Merck.
2
.2. Apparatus
Voltammetric measurements were performed on a Sama-500 elec-
trochemical workstation (Isfahan, Iran). A three-electrode system was
employed with a modified or unmodified carbon paste electrode as
working electrode, a Pt wire as counter electrode, and a Ag/AgCl/KClsat
electrode as reference electrode.
Microstructure and surface morphology of nanoparticles were iden-
tified by a scanning electron microscope (SEM, Philips).
2
.3. Preparation of BMITB/NiO/NPs/CPE
BMITB/NiO/NPs/CPE was prepared by mixing 0.2 g of BMITB, 0.8 g of
paraffin, 0.1 g of nanoparticles and 0.9 g of graphite powder. Then the
mixture was mixed well for 1 h until a uniformly wetted paste was ob-
tained. A portion of the paste was filled firmly into a glass tube as
Scheme 1. Eelectrochemical mechanism for electro-oxidation of ascorbic acid.

A. Pardakhty et al. / Journal of Molecular Liquids 216 (2016) 387–391
389
1
/2
Fig. 4. Plot of Ipa versus ν for the oxidation of ascorbic acid BMITFB/NiO/NPs/CPE. Inset
shows cyclic voltammograms of ascorbic acid at BMITFB/NiO/NPs/CPE at different scan
rates of (a) 20, (b) 50, (c) 100, (d) 150, (e) 200 and (f) 300 mV s− in 0.1 M phosphate
buffer, pH 7.0.
Fig. 2. Plot of potential, E, vs. pH for the electro-oxidation of 500 μM ascorbic acid at a
surface of BMITFB/NiO/NPs/CPE. Inset: influence of pH on cyclic voltammograms of
ascorbic acid at a surface of the modified electrode (pH 5–8, respectively).
1
was cleaned with deionized water and ethanol then calcined at 400 °C
for 1.5 h for synthesis of NiO/NPs.
data in this investigation, we selected pH = 7.0 as the optimum condi-
tion for the ascorbic acid determination.
Cyclic voltammetry was used for investigation of electrochemical
oxidation signal of ascorbic acid on the different modified electrode
3
. Results and discussion
(
Fig. 3). BMITB/NiO/NPs/CPE exhibited large oxidation current with
3
.1. Morphological investigation by SEM
the oxidation peak current of 163.5 μA (curve a). On the other hand,
weak electrochemical oxidation activity peak was observed at CPE
Morphology of NiO nanoparticles was characterized by SEM (Fig. 1).
(
curve d) over the same condition. The ascorbic acid oxidation peak cur-
The dark spots correspond to NiO/NPs, which were only synthesized in
our synthesis condition. Nanoparticles with nearspherical shapes were
synthesized.
rent at NiO/NPs/CPE and at CPE was observed around 960 and 1000 mV
with the oxidation current of 58.5 and 21.5 μA, respectively. Also, at the
surface of BMITB/CPE, the oxidation peak current was 101.5 μA (curve
b), which indicated that the presence of BMITB in CPE could enhance
ascorbic acid oxidation peak currents. The results indicated that the
presence of synthesized NiO nanoparticles and BMITB on BMITB/NiO/
NPs/CPE surface had great improvement with the electrochemical oxi-
dation response of ascorbic acid.
3
.2. Electrochemical investigation
Scheme 1 shows electro-oxidation mechanism for ascorbic acid in
aqueous buffer solution. According to Scheme 1, we found that
electro-oxidation of ascorbic acid is relative to pH value in buffer solu-
tion. So, this parameter optimized in the first step of ascorbic acid anal-
ysis. The influence of the buffer solution pH on electrochemical
oxidation of ascorbic acid for the BMITB/NiO/NPs/CPE was investigated
at various pH values ranging from 5.0 to 8.0 (Fig. 2 insert). As can be
seen the oxidation peak potentials shifted toward negative potential
with the increase in pH values that confirm proposed mechanism in
Scheme 1. On the other hand, the maximum catalytic peak current
was obtained at pH 7.0 for ascorbic acid analysis. According to obtained
Investigation of scan rate can be useful for study of electrochemical
mechanisms and kinetic characteristics of ascorbic acid. Fig. 4 insets
showed the cyclic voltammograms of ascorbic acid on BMITB/NiO/
NPs/CPE between −0.1 and 0.8 V at various scan rates. As can be seen
1
/2
in Fig. 4, the oxidation peak currents (Ip) increased linearly vs. ν
from 20 to 300 mV s
−
1
indicating that the oxidation of ascorbic acid
on BMITB/NiO/NPs/CPE was a diffusion controlled process.
To obtain further information on the rate determining step, a Tafel
plot was developed for the ascorbic acid at a surface of BMITB/NiO/
NPs/CPE using the data derived from the raising part of the current–
Fig. 5. (A) Chronoamperograms obtained at BMITFB/NiO/NPs/CPE in the presence of
(a) 100; (b) 200; (c) 300 and (d) 400 μM ascorbic acid in the buffer solution (pH 7.0).
(B) Cottrell's plot for the data from the chronoamperograms.
Fig. 3. Cyclic voltammograms of (a) BMITFB/NiO/NPs/CPE, (b) BMITFB/CPE, (c) NiO/NPs/
CPE and (d) CPE in the presence of 500 μM ascorbic acid pH 7.0, respectively.

390
A. Pardakhty et al. / Journal of Molecular Liquids 216 (2016) 387–391
Table 1
Determination of ascorbic acid in real samples (n = 3).
Sample
Ascorbic acid
Found (ascorbic acid)
Found (ascorbic acid)
F
ex
F
tab
t
ex
t
tab(95%)
added (μM)
proposed method (μM)
published method (μM) [30]
Tablet
10.0
9.86 ± 0.56
20.68 ± 0.75
10.45 ± 0.74
20.83 ± 0.95
8.9
19.0
–
2.2
–
3.8
–
20.0
–
Fruit Juices
Orange
Lemon
–
–
–
201.65 ± 1.51
187.55 ± 1.48
20.65 ± 0.85
200.98 ± 1.65
188.01 ± 1.42
19.99 ± 0.79
11.8
10.7
9.1
19.0
19.0
19.0
3.1
3.0
2.4
3.8
3.8
3.8
Apple
±
Shows the standard deviation.
Fex is calculated F-value; Ftab is the F-value obtained from one-tailed table of F-test; tex is calculated value of t-student test; ttab is the t-value obtained from the table of student t-test.
voltage curve (not shown). The slope of the Tafel plot is equal to n(1 −
method revealed 83.5% efficiency of encapsulation in composition
of 70:30 (Lecithine:cholesterol) which is the best compositions in
compare to the others.
−
1
α)F/2.3RT which comes up to 0.3006 V decade . We obtained α as 0.9.
Chronoamperometric measurements of ascorbic acid at BMITB/NiO/
NPs/CPE were carried out by setting the working electrode potential at
7
50.0 mV for the various concentrations of ascorbic acid in PBS
4. Conclusion
(
Fig. 5A). Using the obtained slopes and Cottrell equation (Fig. 5B) the
−
5
2 −1
mean value of the D was found to be 8.56 × 10 cm s
.3. Calibration plot and limit of detection
Since square wave voltammetry (SWV) was used for determination
.
The novel voltammetric sensor was developed for the fast and rapid
determination of ascorbic acid. The BMITB/NiO/NPs/CPE showed great
improvement to the electrode process of ascorbic acid compare to the
carbon paste electrode. Under the optimum conditions, the oxidation
peak current was proportional to the ascorbic acid concentration in
the range of 0.08–380 μM with the detection limit of 0.04 μM. Finally,
the BMITB/NiO/NPs/CPE was successfully used for the determination
of ascorbic acid in real samples.
3
of ascorbic acid in this work. The SW voltammograms clearly show that
the plot of oxidation peak current versus ascorbic acid concentration is
linear for 0.08–380 μM of ascorbic acid. The detection limit was deter-
mined at 0.04 μM ascorbic acid according to the definition of YLOD
+ 3σ.
=
Y
B
Acknowledgments
3
.4. Effect of interference
The authors express their appreciation to Kerman University of
Medical Sciences, Kerman, Iran for supporting the current Pharm. D.
dissertation.
Interference of various inorganic and organic compounds in the de-
termination of ascorbic acid was investigated. 150 fold concentration of
glucose, fructose, lactose, sucrose, urea, thiourea, phenol, 100 fold con-
centration of Na , SO
and 75 fold concentration of histidine, methionine, cysteine, lysine, phe-
nyl alanine, glycine had almost no influence at the peak current of 50 μM
ascorbic acid with a change of less than 5%, which suggested good selec-
tivity of the method.
References
+
2−
−
2+
2+
2+
2+
−
+2
4 3
, Cl , Mg , Ca , Pb , Zn , NO , and Ni
[
1] S. Sharifian, A. Nezamzadeh-Ejhieh, Modification of carbon paste electrode with Fe
III)-clinoptilolite nano-particles for simultaneous voltammetric determination of
acetaminophen and ascorbic acid, Mater. Sci. Eng. C 58 (2016) 510–520.
(
[2] H.-J. Ahn, C. Li, H.-B. Cho, S. Park, P.-S. Chang, Y.-W. Kim, Enzymatic synthesis of 3-O-
α-maltosyl-L-ascorbate using an engineered cyclodextrin glucanotransferase, Food
Chem. 169 (2015) 366–371.
[
3] E. Ergün, Ş. Kart, D.K. Zeybek, B. Zeybek, Simultaneous electrochemical determina-
tion of ascorbic acid and uric acid using poly (glyoxal-bis(2-hydroxyanil)) modified
glassy carbon electrode, Sensors Actuators B Chem. (2015) (DOI).
3
.5. Stability and reproducibility
[
4] K. Tyszczuk-Rotko, I. Bęczkowska, M. Wójciak-Kosior, I. Sowa, Simultaneous
voltammetric determination of paracetamol and ascorbic acid using a boron-
doped diamond electrode modified with nafion and lead films, Talanta 129
(2014) 384–391.
The repeatability and stability of BMITB/NiO/NPs/CPE were investi-
gated by SWV measurements of 50.0 μM ascorbic acid. The relative stan-
dard deviation (RSD%) for fifteen successive assays was 2.1%. When
using four different electrodes, the RSD% for fifteen measurements
was 1.9%. When the electrode stored in the laboratory, the modified
electrode retains 97% of its initial response after 10 days and 92% after
[
5] L. Chen, X. Guo, B. Guo, S. Cheng, W. Fei, Electrochemical investigation of a
metalloporphyrin–graphene composite modified electrode and its electrocatalysis
on ascorbic acid, J. Electroanal. Chem. (2015) (DOI).
[6] B. Liu, L. Luo, Y. Ding, X. Si, Y. Wei, X. Ouyang, D. Xu, Differential pulse voltammetric
determination of ascorbic acid in the presence of folic acid at electro-deposited NiO/
graphene composite film modified electrode, Electrochim. Acta 142 (2014)
6
5 days. These results indicate that BMITB/NiO/NPs/CPE has good stabil-
ity and reproducibility, and could be used for ascorbic acid.
336–342.
[
[
[
7] M.P. Kingsley, P.B. Desai, A.K. Srivastava, Simultaneous electro-catalytic oxidative
determination of ascorbic acid and folic acid using Fe 3 O 4 nanoparticles modified
carbon paste electrode, J. Electroanal. Chem. 741 (2015) 71–79.
8] M. Szultka, M. Buszewska-Forajta, R. Kaliszan, B. Buszewski, Determination of ascor-
bic acid and its degradation products by high-performance liquid chromatography-
triple quadrupole mass spectrometry, Electrophoresis 35 (2014) 585–592.
9] B. Tsvetkova, I. Pencheva, A. Zlatkov, P. Peikov, Simultaneous high-performance liq-
uid chromatography determination of paracetamol and ascorbic acid in tablet dos-
age forms, Afr. J. Pharm. Pharmacol. 6 (2012) 1332–1336.
3
.6. Real sample analysis
To evaluate the applicability of the BMITB/NiO/NPs/CPE for the food
and tablet sample applications, the BMITB/NiO/NPs/CPE was employed
for the analysis of ascorbic acid in food juice and tablet samples. Stan-
dard addition method was used for measuring ascorbic acid concentra-
tion in the real samples. The results are given in Table 1, confirm that the
modified electrode retained its efficiency for the determination of ascor-
bic acid in real samples.
Moreover, the encapsulation efficiency of formed liposome
containing ascorbic acid was calculated by determination of the
non-entrapped ascorbic acid which is remaining in supernatant
phase by proposed fabricated sensor. Using standard addition
[10] R. Săndulescu, S. Mirel, R. Oprean, The development of spectrophotometric and elec-
troanalytical methods for ascorbic acid and acetaminophen and their applications in
the analysis of effervescent dosage forms, J. Pharm. Biomed. Anal. 23 (2000) 77–87.
11] N.E. Llamas, M.S. Di Nezio, B.S.F. Band, Flow-injection spectrophotometric method
with on-line photodegradation for determination of ascorbic acid and total sugars
in fruit juices, J. Food Compos. Anal. 24 (2011) 127–130.
12] T. Maki, N. Soh, K. Nakano, T. Imato, Flow injection fluorometric determination
of ascorbic acid using perylenebisimide-linked nitroxide, Talanta 85 (2011)
1730–1733.
[
[

A. Pardakhty et al. / Journal of Molecular Liquids 216 (2016) 387–391
391
[
[
[
[
[
13] Y. Matsuoka, M. Yamato, T. Yamasaki, F. Mito, K.-i. Yamada, Rapid and convenient
detection of ascorbic acid using a fluorescent nitroxide switch, Free Radic. Biol.
Med. 53 (2012) 2112–2118.
14] M. Adam, P. Pavlíková, A. Čížková, P. Bajerová, K. Ventura, Microextraction by
packed sorbent (MEPS) as a suitable selective method for l-ascorbic acid determina-
tion in beverages, Food Chem. 135 (2012) 1613–1618.
15] H. Filik, D. Aksu, D. Giray, R. Apak, Colourimetric solid-phase extraction coupled with
fibre optic reflectance spectroscopy for determination of ascorbic acid in pharma-
ceutical formulations, Drug Test. Anal. 4 (2012) 493–499.
16] Y.P. Dong, T.T. Gao, X.F. Chu, J. Chen, C.M. Wang, Flow injection-chemiluminescence
determination of ascorbic acid based on luminol–ferricyanide–gold nanoparticles
system, J. Lumin. 154 (2014) 350–355.
[28] M. Elyasi, M.A. Khalilzadeh, H. Karimi-Maleh, High sensitive voltammetric sensor
based on Pt/CNTs nanocomposite modified ionic liquid carbon paste electrode for
determination of Sudan I in food samples, Food Chem. 141 (2013) 4311–4317.
[29] H. Karimi-Maleh, S. Rostami, V.K. Gupta, M. Fouladgar, Evaluation of ZnO nanoparti-
cle ionic liquid composite as a voltammetric sensing of isoprenaline in the presence
of aspirin for liquid phase determination, J. Mol. Liq. 201 (2015) 102–107.
[30] S. Gheibi, H. Karimi-Maleh, M.A. Khalilzadeh, H. Bagheri, A new voltammetric sensor
for electrocatalytic determination of vitamin C in fruit juices and fresh vegetable
juice using modified multi-wall carbon nanotubes paste electrode, J. Food Sci.
Technol. 52 (2015) 276–284.
17] M. Keyvanfard, R. Shakeri, H. Karimi-Maleh, K. Alizad, Highly selective and sensitive
voltammetric sensor based on modified multiwall carbon nanotube paste electrode
for simultaneous determination of ascorbic acid, acetaminophen and tryptophan,
Mater. Sci. Eng. C 33 (2013) 811–816.
Further Reading
[31] R. Jain, V.K. Gupta, N. Jadon, K. Radhapyari, Anal. Biochem. 407 (2010) 79–88.
[32] R.N. Goyal, V.K. Gupta, S. Chatterjee, Sensors Actuators B Chem. 149 (2010)
252–258.
[33] V.K. Gupta, I. Ali, Water Res. 35 (2001) 33–40.
[34] V.K. Gupta, S. Sharma, I.S. Yadava, D. Mohan, J. Chem. Technol. Biotechnol. 71 (1998)
[
18] A.A. Ensafi, H. Karimi-Maleh, S. Mallakpour, Simultaneous determination of ascorbic
acid, acetaminophen, and tryptophan by square wave voltammetry using N-(3, 4-
dihydroxyphenethyl)-3, 5-dinitrobenzamide-modified carbon nanotubes paste
electrode, Electroanalysis 24 (2012) 666–675.
[
19] M. Bijad, H. Karimi-Maleh, M.A. Khalilzadeh, Application of ZnO/CNTs nanocompos-
ite ionic liquid paste electrode as a sensitive voltammetric sensor for determination
of ascorbic acid in food samples, Food Anal. Methods 6 (2013) 1639–1647.
20] H. Karimi-Maleh, F. Tahernejad-Javazmi, M. Daryanavard, H. Hadadzadeh, A.A.
Ensafi, M. Abbasghorbani, Electrocatalytic and simultaneous determination of
ascorbic acid, nicotinamide adenine dinucleotide and folic acid at ruthenium (II)
complex-ZnO/CNTs nanocomposite modified carbon paste electrode, Electroanaly-
sis 26 (2014) 962–970.
180–186.
[35] V.K. Gupta, I. Ali, V.K. Saini, T.V. Gerven, B.V. der Bruggen, C. Vandecasteele, Ind. Eng.
Chem. Res. 44 (2005) 3655–3664.
[36] T.A. Saleh, S. Agarwal, V.K. Gupta, Appl. Catal. B Environ. 106 (2011) 46–53.
[37] H. Khani, M.K. Rofouei, P. Arab, V.K. Gupta, Z. Vafaei, J. Hazard. Mater. 183 (2010)
402–409.
[38] V.K. Gupta, R. Kumar, A. Nayak, T.A. Saleh, M.A. Barakat, Adv. Colloid Interf. Sci. 193–
194 (2013) 24–34.
[39] T.A. Saleh, V.K. Gupta, J. Colloid Interface Sci. 371 (2012) 101–106.
[40] F. Najafi, O. Moradi, M. Rajabi, M. Asif, I. Tyagi, S. Agarwal, V.K. Gupta, J. Mol. Liq. 208
(2015) 106–113.
[
[21] H. Karimi-Maleh, P. Biparva, M. Hatami, A novel modified carbon paste electrode
based on NiO/CNTs nanocomposite and (9, 10-dihydro-9, 10-ethanoanthracene-
11, 12-dicarboximido)-4-ethylbenzene-1, 2-diol as a mediator for simultaneous de-
termination of cysteamine, nicotinamide adenine dinucleotide and folic acid,
Biosens. Bioelectron. 48 (2013) 270–275.
[41] D. Robati, B. Mirza, M. Rajabi, O. Moradi, I. Tyagi, S. Agarwal, V.K. Gupta, Chem. Eng. J.
284 (2016) 687–697.
[
22] N. Atar, T. Eren, M.L. Yola, H. Karimi-Maleh, B. Demirdögen, Magnetic iron oxide and
iron oxide@ gold nanoparticle anchored nitrogen and sulfur-functionalized reduced
graphene oxide electrocatalyst for methanol oxidation, RSC Adv. 5 (2015)
[42] M. Ghaedi, M. reza Rahimi, A.M. Ghaedi, I. Tyagi, S. Agarwal, V.K. Gupta, J. Colloid In-
terface Sci. 461 (2016) 425–434.
[43] V.K. Gupta, S.K. Srivastava, D. Mohan, S. Sharma, Waste Manag. 17 (1998) 517–522.
[44] V.K. Gupta, P. Singh, N. Rahman, J. Colloid Interface Sci. 275 (2004) 398–402.
[45] S. Karthikeyan, V.K. Gupta, R. Boopathy, A. Titus, G. Sekaran, J. Mol. Liq. 173 (2012)
153–163.
26402–26409.
[
[
[
23] T. Eren, N. Atar, M.L. Yola, H. Karimi-Maleh, A sensitive molecularly imprinted poly-
mer based quartz crystal microbalance nanosensor for selective determination of
lovastatin in red yeast rice, Food Chem. 185 (2015) 430–436.
24] B.J. Sanghavi, A.K. Srivastava, Adsorptive stripping differential pulse voltammetric
determination of venlafaxine and desvenlafaxine employing nafion–carbon nano-
tube composite glassy carbon electrode, Electrochim. Acta 56 (2011) 4188–4196.
25] H. Karimi-Maleh, F. Tahernejad-Javazmi, N. Atar, M.L.t. Yola, V.K. Gupta, A.A. Ensafi,
A novel DNA biosensor based on a pencil graphite electrode modified with polypyr-
role/functionalized multiwalled carbon nanotubes for determination of 6-mercapto-
purine anticancer drug, Ind. Eng. Chem. Res. 54 (2015) 3634–3639.
[46] V.K. Gupta, R. Jain, S. Agarwal, M. Shrivastava, Mater. Sci. Eng. C 31 (2011)
1062–1067.
[47] V.K. Gupta, A. Nayak, Chem. Eng. J. 180 (2012) 81–90.
[48] A. Asfaram, M. Ghaedi, S. Agarwal, I. Tyagi, V.K. Gupta, RSC Adv. 5 (24) (2015)
18438–18450.
[49] V.K. Gupta, B. Gupta, A. Rastogi, S. Agarwal, A. Nayak, Water Res. 45 (2011)
4047–4055.
[50] V.K. Gupta, A. Mittal, D. Jhare, J. Mittal RSC Adv. 2 (2012) 8381–8389.
[51] V.K. Gupta, A.K. Jain, G. Maheshwari, Talanta 72 (4) (2007) 1469–1473.
[52] V.K. Gupta, M.R. Ganjali, P. Norouzi, H. Khani, A. Nayak, and Shilpi Agarwal, Crit. Rev.
Anal. Chem. 41 (2011) 282–313.
[
26] B.J. Sanghavi, S.M. Mobin, P. Mathur, G.K. Lahiri, A.K. Srivastava, Biomimetic sensor
for certain catecholamines employing copper (II) complex and silver nanoparticle
modified glassy carbon paste electrode, Biosens. Bioelectron., 39 124–132.
27] M. Najafi, M.A. Khalilzadeh, H. Karimi-Maleh, A new strategy for determination of
bisphenol A in the presence of Sudan I using a ZnO/CNTs/ionic liquid paste electrode
in food samples, Food Chem. 158 (2014) 125–131.
[
[53] V.K. Gupta, A.K. Jain, S. Agarwal, G. Maheshwari, Talanta 71 (2007) 1964–1968.