A surfactant enhanced novel pencil graphite and carbon nanotube composite paste material as an effective electrochemical sensor for determination of riboflavin

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Original Article

A surfactant enhanced novel pencil graphite and carbon nanotube

composite paste material as an effective electrochemical sensor for

determination of ribo

flavin

Girish Tigari, J.G. Manjunatha

*

Department of Chemistry, FMKMC College, Madikeri, Constituent College of Mangalore University, Karnataka, India

a r t i c l e i n f o

Article history:

Received 11 September 2019
Received in revised form
25 October 2019
Accepted 1 November 2019
Available online xxx

Keywords:

Sodium lauryl sulphate
Carbon nanotubes

Pencil graphite paste electrode
Riboflavin

Dopamine

a b s t r a c t

A novel sensor fabrication using anionic surfactant sodium lauryl sulphate modified carbonnanotube and
pencil graphite composite paste electrode (SLSMCNTPGCPE) is prepared and characterized using Field
Emission Scanning Electron Microscope (FE-SEM) and Cyclic Voltammetry (CV). The devised
SLSMCNTPGCPE is a responsive electrode material for the determination of Riboflavin (RF) as compared
to carbon nanotube and pencil graphite composite paste electrode (CNTPGCPE) and bare pencil graphite
paste electrode (BPGPE). The fabricated sensor shows a linear current response to a diverse concentration
of RF in 0.2e0.8mM and 1e5mM with a low detection limit of 1.16
108_{M by applying differential pulse}
voltammetry (DPV). The stability, reproducibility, repeatability, interference and concurrent investigation
with dopamine (DA) have been done with satisfactory outcomes. The new sensor was applied for the RF
estimation shows good recovery in B-complex pill and natural food supplement.

© 2019 The Authors. Publishing services by Elsevier B.V. on behalf of Vietnam National University, Hanoi.
This is an open access article under the CC BY license ( />

1. Introduction

Vitamins and neurotransmitters are biologically active
mole-cules and play a vital role in the humanoid biochemistry and
metabolism. RF (vitamin B2) is aqueous soluble and a principal

component offlavoenzymes. It assists the conversion of
carbohy-drates, fats, and proteins into energy and supports the body during
anxiety [1e3]. RF cannot be formed in the human body, so it has to
be obtained from nutritional sources such as milk, eggs, green
vegetables, tea, wine, liver, etc. The lack of RF in the human body
may lead to eye and skin disorders [4e6]. Dopamine (DA) is a
neurotransmitter molecule in the mammalian central nervous
system and plays a substantial role in operating the central
ner-vous, hormonal, renal and cardiac systems. Abnormal levels of DA

in the human brain cause brain diseases, such as Parkinson's and
Schizophrenia [7e13].

RF is determined using different analytical procedures such as
high-performance liquid chromatography [14], spectrophotometry
[15], Flow injection analysis [16], mass spectrometry [17], etc. These
analytical techniques are expensive and time-consuming. Also,

some voltammetric methods for quantification of RF are reported in
the previous literature such as: mercury drop electrode [18], ZnO/
Manganese hexacyanoferrate nanocomposite/glassy carbon
elec-trode [19], Highly dispersed multiwalled carbon nanotubes coupled
manganese salen nanostructure [20], pre-treated GC [21],
Manga-nese (III) Tetraphenyl porphyrin Modified Carbon Paste Electrode
[22], pencil graphite [23], Reduced graphene oxide [24], Poly
(3-methyl thiophene) Modified Glassy Carbon Electrode [25], etc.

Electroanalytical approaches are active and gifted analytical
practices having a strong impact on human health and
environ-mental monitoring. The electrochemical methods are strongly
recognized due to low cost, simple preparations, rapid analyzing
time with the outstanding analytical performance [26e32]. Pencil
graphite is known to be a multipurpose tool for electroanalysis of
bioactive molecules due to their sp2 hybridized carbon which
shows characteristics like excellent electrical conductivity,
adsorption, little background current, easy exterior modification
and mechanical stability [33_e35]. Carbon nanotubes (CNTs) are
frequently used in the fabrication of electrochemical sensors due to
their excellent electronic properties, rapid renewal, extensive
po-tential ranges, less residual noise with extreme stability [36e38].

Surfactants (SDS, TX-100, CTAB), nanomaterials, stainless steel
powder, ferrocene, etc can alter and regulate the characteristic
properties of electrode surfaces, which leads to changes in the

* Corresponding author.

E-mail address:(J.G. Manjunatha).

Peer review under responsibility of Vietnam National University, Hanoi.

Contents lists available atScienceDirect

Journal of Science: Advanced Materials and Devices

j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / j s a m d

/>

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reaction rates and pathways. Surfactant-modified electrodes have
been extensively applied in the organic electroanalysis, including
nutrition, medicinal, and bio-samples assessment [39e46]. The
present effort is the fabrication of a surfactant modified carbon
nanotube and pencil graphite powder composite paste electrode
for the electroanalysis of RF in the presence of DA.

2. Experimental

2.1. Apparatus

The Electroanalytical experiments were carried out through
CHI-6038E (electrochemical workstation - USA). It is assembled

with a standard three-electrode arrangement with a computer for
information storage and selection of analytical parameters. The
fabricated bare and chemically modified electrodes were executed
as a working electrode, a saturated calomel electrode (SCE) and a
platinum wire were executed as a reference electrode and counter
electrode correspondingly. Field emission scanning electron
mi-croscopy (FE-SEM) was obtained using the instrument operating at
5.00 kV (DST-PURSE Laboratory, Mangalore University). All current
measurements were taken with background current. All
experi-ments were done at lab temperature.

2.2. Reagents and chemicals

RF (99%) was purchased from Molychem, India. DA (99%)
and CNTs were bought from Sigma Aldrich, US. Silicone oil
(99%) was bought from Nice Chemicals, India. 8B pencil is
purchased from the local market. Other chemicals are of assay
98.5%, A.R grade used as received. The RF and DA standard
so-lution of 2.5 mM was prepared just before the experiment with
distilled water. 25 mM SLS was prepared using distilled water.
The 0.1 M Phosphate buffer solutions (PBS) of different pH values
were prepared by mixing the suitable quantity of 0.1 M Na2HPO4

and 0.1 M NaH2PO4.

2.3. Preparation of pencil graphite powder

The acid-treated pencil graphite, polymer, and surfactant
modified pencil graphite are previously reported for electroanalysis
of electroactive species. The present effort of sensor fabrication

provides advantages like less impurity electrode, easy surface
renewal as like carbon paste, simple procedure, easy activation
approach, low cost with good sensitivity and selectivity. The 8B
pencil lead is cut into small pieces and crushed in an agate mortar
to afine pencil powder and the obtained powder is stirred with
2 N H2SO4(1:5 ratio) for 30 min, kept 12 h for digestion at 30C and

then washed with dilute acid followed by distilled water. The
washed product is dried in the oven at 60C [47e49].

2.4. Development sodium lauryl sulphate modified carbon
nanotube and pencil graphite composite paste electrode

The carbon nanotube and pencil graphite composite electrode
was equipped by hand mixing of 55% pencil graphite powder, 15%
carbon nanotube, 30% silicone oil in a mortar and grounded well
for 20 min to get an homogenous paste; the obtained paste was
filled into a hollow tube of Teflon and it was smoothed out by a
tissue paper. The electrical connection was provided through a
wire of copper joined to the end of the tube. The surface
modi-fication of the electrode was done by immobilization 10

m

L SLS
surfactant on the carbon nanotube and pencil graphite composite

3. Result and Interpretations

3.1. FE-SEM and electrochemical characterization of BPGPE,
CNTPGCPE, SLSMCNTPGCPE

Fig. 1(a), (b) and (c) depict the FE-SEM images of BPGPE,
CNTPGCPE, and SLSMCNTPGCPE. The BPGPE morphology appears

flat whereas CNTPGCPE shows spheres and a fibrous morphology,
therefore it was successfully modified with CNTs. SLSMCNTPGCPE
shows an agglomerated surface with white patches which indicates
that the electrode surface is modified with SLS. The three electrodes
having different topographical properties show different
electro-chemistry with electroactive species.

An electroanalytical description of BPGPE, CNTPGCPE,

SLSMCNTPGCPE for the standard 1 mM K4[Fe(CN)6] in 0.1 M KCl is

presented in Fig. 1(d). The SLSMCNTPGCPE (curve c) senses
K4[Fe(CN)6] oxidation at 0.268 V, and reduction at 0.204 V, with

elevated current signals and a lesser

D

Ep value (0.064V). But in case
of BPGPE (Curve a) and CNTPGCPE (curve b) the

D

Ep values are
0.173, 0.154 V, respectively, with lower current responses. So,
SLSMCNTPGCPE exhibits higher electrochemical amplification with

a small

D

Ep value as compared to CNTPGCPE and BPGPE.

SLSMCNTPGCPE might deliver a conducting track through the
surfactant layer for quicker electron transfer kinetics. Hence,
SLSMCNTPGCPE acts as an electron exchange negotiator.

The effective surface area of SLSMCNTPGCPE, CNTPGCPE, BPGPE
can be calculated by using the Randles-Sevcik equation [50].

Ip¼ 2.69
105_n3/2_{A D}1/2_C
0

y

1/2

where Ip is the anodic/cathodic peak current in A, Co is the

concentration of electroactive species (mol cm3), n is the number
of electrons interchanged, D is the coefficient of diffusion (cm2_/s),

_y

is the potential scan rate (V/s), A is the effective surface area (cm2).
The surface area is found to be extremely large for SLSMCNTPGCPE
(0.04 cm2) as compared to CNTPGCPE (0.025 cm2), BPGPE
(0.016 cm2).

3.2. Optimization of the quantity of carbon nanotubes and SLS

The amount of carbon nanotubes used for the preparation of
CNTPGCPE effects the electrochemical response of RF (0.1 mM).
So, it was optimized by varying the magnitude of carbon
nano-tubes from 5 mg to 25 mg using CV in 0.1 M PBS of pH 6.5 at a
sweep rate of 0.1 V/s as shown inFig. 2(a). The highest
electro-chemical activity for RF (0.1 mM) is obtained at the 15 mg carbon
nanotube amount, so it is an optimized carbon nanotube amount
for electrode fabrication throughout the experiment. The
sur-factant amount optimization is an essential parameter in
elec-troanalysis. The surfactant optimization from 5 to 20

m

L at
CNTPGCPE for the detection of RF (0.1 mM) was performed using
CV in 0.1 M PBS of pH 6.5 at a sweep rate of 0.1 V/s as shown in

Fig. 2(b). The elevated current is reached at 10

m

L SLS because at
10

m

L SLS the critical aggregation concentration was reached. At
any further increase in the amount of SLS, the cathodic peak
current decreases.

3.3. Electroanalysis of RF at different electrodes

The electrocatalytic behavior of RF (0.1 mM) at BPGPE,
CNTPGCPE and SLSMCNTPGCPE was investigated in 0.1 M PBS of pH
6.5 at a sweep rate of 0.1 V/s and is presented inFig. 3(a). At BPGPE
(curve a) the cyclic voltammogram for 0.1 mM RF reveals poor
oxidation and reduction responses at 0.445 V and 0.579 V,

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Fig. 1. FE-SEM Depiction of (a) BPGPE (b) CNTPGCPE (c) SLSMCNTPGCPE (d) Electrochemical performance of BPGPE (curve a), CNTPGCPE (curve b) SLSMCNTPGCPE (curve c) for
1 mM K4[Fe (CN)6] in 0.1 M KCl at sweep rate of 0.1 V/s.

Fig. 2. (a) Calibration of carbon nanotube weight for the preparation of CNTPGCPE for reduction of RF (0.1 mM) (b) Effect SLS quantity for RF (0.1 mM) electroanalysis.

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activity of RF was increased at CNTPGCPE (curve b) with
quasi-reversible behavior. The anodic and cathodic potential for RF at
CNTPGCPE were detected at - 0.464 V and0.577 V, respectively,
with elevated current responses. The current sensitivity obtained at
CNTPGCPE was two times higher than that at BPGPE. The
SLSMCNTPGCPE (curve c) creates further enhancement in the
cur-rent signal for 0.1 mM RF with anodic and cathodic detection
po-tentials of 0.467 V and 0.678 V, respectively. The current
produced at SLSMCNTPGCPE for 0.1 mM RF is four times higher
than the current signal produced at CNTPGCPE. The results show
that the electrochemical response is amplified at each step of
modification. The CV analysis in the presence and absence of RF was
performed at the optimal condition as shown inFig. 3(b). In the
absence of RF (curve a) the characterized CV portrays no peak at
SLSMCNTPGCPE. But under parallel conditions in the presence of RF
(0.1 mM), the sharp oxidation and reduction were observed

at0.467 V and 0.678 V, respective;y, with an excellent current
response (curve b).

3.4. Influence of potential sweep rate

The impact of the potential scan rate on the RF oxidation/
reduction was analyzed to identify the electrode kinetics. By
altering the sweep rate from 0.1 to 0.3 V/s in 0.1 M PBS of pH 6.5, the
voltammograms are found as inFig. 4(a). As the sweep rate
in-creases the peak current also inin-creases and the anodic potential
shifts to the more positive side and the cathodic peak potential
shifts to the more negative side with a signi_{ficant change in}

D

Ep
values. It shows that the RF process is quasi-reversible. The
po-tentialfluctuations were due to the kinetic limitation of diffusion
layers, which is formed at the upper current density.

The plot of Ipcvs. v1/2(Fig. 4(b)) is found to be linear and it is

stated by the linear regression equation Ipc

(A)ẳ 2.49
105ỵ3.39
104v1/2(V/s)1/2with a value for the
correlation coefficient of 0.99. This discloses that the process is
diffusion rather than adsorption-controlled, so it is the ideal
instance for a quantitative assessment.

3.5. Effect of pH

pH is a key factor that affects the electrocatalytic sensing
phe-nomena and is helpful in the prediction of biomolecular reaction
pathways.Fig. 5(a) illustrates the cyclic voltammograms of 0.1 mM

RF at various pH ranging from 5.5 to 7.5 of 0.1 M PBS at a sweep rate

of 0.1 V/s. A plot of Ipcvs. pH (Fig. 5(b)) confirms that the reduction

peak current was maximum at pH 6.5. At a further increase and
decrease in pH, the reduction peak current values decrease and so a
pH value of 6.5 was preferred to complete the electrochemical
experiments. Meanwhile, at this pH, a swift electron transfer
re-action will occur. The basic pH is not appropriate for an estimate of
RF since it may be influenced by the creation of unstable lumiflavin
molecules with irradiation of light.

A plot of Epcvs. pH (Fig. 5(c)) demonstrates the impact of pH on

the cathodic peak potential of 0.1 mM RF over the range of
5.5e7.5. The plot shows that the electrocatalytic peak is lifted
towards a more negative potential with an increase in pH
ac-cording to the equation Epc(V)¼ 0.0574 pH-0.31. The slope value

of 0.0574 is close to the accepted value 0.059 which indicates that
the electrons and protons involved in the electrochemical
reac-tion are in the ratio 1:1. So the sequence of reducreac-tion/oxidareac-tion of
RF comprises two electrons and two protons as revealed in

Scheme 1.

3.6. Linearity, limit of detection and quantification

For the quantitative estimate of RF, the more responsive DPV
technique was executed. The effect of change in RF concentration

vs. oxidation peak current was obtained at SLSMCNTPGCPE using
0.1 M PBS of pH 6.5 as presented inFig. 6(a) and (b). Thesefigures
indicate that, under optimal conditions, the change in
concen-tration of RF is directly proportional to the oxidation peak current
values in the concentration domain 0.2e0.8

m

M and 1e5

m

M. We
considered the_{fine linear range 1e5}

m

M. The linearity is described
by an equation as Ipc(A)¼ 8.60
106ỵ 0.733 (M) and LOD and

LOQ were calculated as 3sd/m and 10sd/m [51], respectively Here,

‘sd’ is the standard deviation of the buffer solution current values

(5 replicates) and‘m’ is the slope of the calibration graph. The LOD
and LOQ were found to be 1.16
108 M and 3.87
108 M
(±0.065), respectively.Table 1[52e56] depicts the comparison of
the established electrode with previously reported electrodes.
The SLSMCNTPGCPE yields higher detection values as compared

to modified glassy carbon with PdeCuNPS, MBeSO3HeMSM

[52,53], detection values that are near to those of GCE/
AuNPS@PDA-RGO [54] and a smaller detection limit value as
compared to that of SnO2/RGO/GCE, CreSnO2/GCE [55,56].

Comparatively, the fabricated sensors provide advantages such as
low cost, non-toxic nature, simple sensor development with good
biosensing ability.

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Fig. 5. (a) Cyclic voltammetric characterization of RF (0.1 mM) at various pH from 5.5 to 7.5 at SLSMCNTPGCPE with a potential scan rate of 0.1 V/s (b) Plot of cathodic peak current
vs. pH (c) Plot of cathodic peak potential vs. pH.

Scheme 1. The Electron transfer mechanism of RF.

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3.7. Analytical applicability

The devised SLSMCNTPGCPE was applied to estimate the
amount of RF in the B-complex pill and in a natural food
supple-ment solution, using the DPV technique at optimal conditions. A
suitable quantity of the B-complex powder and food supplement to
a standard solution of a concentration of 1.0
104_{M was prepared}

using distilled water. The determination of RF was performed using
the standard addition method in a 0.1 M PBS solution. The
re-coveries in the B-complex pill and food supplement were about
95e100.7%. The estimates and recovery assessments are tabulated
inTable 2So, the electrochemical sensor offers good recovery in

both B-complex tablets and natural food supplements, which
shows the practicability of the developed sensor.

3.8. Determination, repeatability and stability of the devised sensor

Repeatability for the detection of 0.1 mM RF was assessed
through CV in 0.1 M PBS (pH 6.5) with sweep rate 0.1 V/s at
SLSMCNTPGCPE. The fabricated electrode yields an admirable
repeatability for 5 distinct measurements with the relative
stan-dard deviation (RSD) of 1.81%. The stability of the proposed sensor
for the electrochemical detection of 0.1 mM RF was investigated by
30 uninterrupted cycles. It has been noticed that 95% of the primary
current signal was retained even after 30 cycles, so the established

sensor has a high stability.

3.9. Electrochemical behavior DA (0.1 mM) and sweep rate effects

The electrochemical enhancement of DA (0.1 mM) behavior was
inspected by CV at SLSMCNTPGCPE, CNTPGCPE and BPGPE in 0.1 M
PBS of pH 6.5 as shown in Fig. 7(a). The DA detection using
SLSMCNTPGCPE (curve c) was achieved with oxidation and

Table 1

Comparison of the proposed electrochemical sensor with previously reported sensor for voltammetric quantization of RF.

Working Electrode Modifier Method of analysis Linear range (mM) LOD (M) Reference

Porous carbon PdeCuNPS DPV 0.02 to 9 7.6
1012 _[₅₂_]

Glassy carbon MBeSO3HeMSM DPV 0.010e15 & 15e50 5.0
109 [53]

Glassy carbon AuNPs@PDA-RGO DPV 0.02e60.0 9.0
109 _[₅₄_]

Glassy carbon SnO2/RGO SWV 0.1e150 34
109 [55]

Glassy carbon Cr/SnO2nanoparticle LSV 0.2e100 107
109 [56]

CNTPGCPE SLS DPV 0.2e0.8 & 1e5 11.6
109 _{Present work}

PdeCuNPS - palladium-copper nanoparticles, DPV- differential pulse voltammetry, MBeSO3HeMSM- Methylene blue incorporated mesoporous silica microsphere,

AuNPs@PDA-RGO- gold nanoparticle/polydopamine/reduced graphene oxide, SnO2/RGO- reduced graphene oxide, SWV-square wave voltammetry, LSV- linear sweep

voltammetry.

Table 2

Estimate of RF in the B-complex pill and in the natural food supplement.

Sample Added (mM) Detected (mM) Recovery (%) RSD

B-complex pill 1.0 0.95 95.0 1.25%

3.0 3.023 100.7%

Natural food 1.0 0.96 96.0 2.0%

supplement 3.0 2.91 97.0%

RSD-relative standard deviation.

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reduction potentials of 0.231 V and 0.165 V, respectively, with a
swift current response. Whereas in CNTPGCPE (curve b), DA was
characterized at 0.221 V and 0.118 V with less current as compared
to SLSMCNTPGCPE. At BPGPE (curve a) the DA voltammetric
sensing was very poor with oxidation and reduction potentials of
0.230 V and 0.139 V, respectively. So, the cyclic voltammetric
sensing of DA was enhanced at SLSMCNTPGCPE.

The scan rate effect from 0.1 V/se 0.3 V/s on DA oxidation/
reduction was studied using CV in 0.1 M PBS of pH 6.5 displayed in

Fig. 7(b). The graphical plot of Ipcvs v1/2(Fig. 7(c)) gives a straight

line and it is expressed using a linear equation as

Ipc(A)¼ 3.16
105ỵ1.48
104v1/2(V/s)1/2, Rẳ 0.99. This

illu-minates that the electrochemical DA interaction with the electrode
surface was diffusion controlled.

3.9.1. Instantaneous analysis of RF in the presence of DA using CV
and DPV

The electrochemical separation of RF (0.1 mM) and DA (0.1 mM)
at SLSMCNTPGCPE is achieved using CV in 0.1 M PBS of pH 6.5, with
a 0.1 V/s scan rate as displayed inFig. 8(a). At BPGPE (curve a) RF

oxidation and reduction peaks were detected at 0.473 V

and0.576 V, respectively, with a low current value. But after bulk
modi_{fication with CNT i.e. CNTPGCPE (curve b) the RF oxidation and}
reduction peaks appeared at0.490, 0.608 V and DA anodic and
cathodic potential peaks were detected at 0.165 V and 0.037 V,
respectively, with an improved current response as compared to
BPGPE. However, a clear separation and current enhancement was
achieved at SLSMCNTPGCPE (curve c), the RF anodic and cathodic

peaks were characterized at 0.377 V, 0.699 V and DA

characteristic oxidation and reduction potentials appeared at
0.247 V and - 0.017 V, respectively, with enriched current signals.

So, the electrochemical separation is amended at SLSMCNTPGCPE.
The concurrent study of RF and DA at different electrodes

using DPV were performed as depicted in Fig. 8(b). At

SLSMCNTPGCPE (curve c) the RF and DA detection potentials
were at0.536 and 0.080 V with a peak separation of 0.456 V and
with high current responses in contrast to CNTPGCPE and BPGPE.
The RF and DA separation at CNTPGCPE (curve b) were
charac-terized at the potentials 0.536 and 0.063 V with less current
as compared to SLSMCNTPGCPE. At BPGPE (curve a) minor

sep-arations were detected at 0.540 and 0.072 V with poor

current sensitivity.

3.9.2. Determination of RF in the presence of DA using DPV
The feasibility of RF (0.1 mMe0.110 mM) determination in the
presence of DA was analyzed by using DPV technique in 0.1 M PBS
of pH 6.5 at a sweep rate of 0.05 V/s in the potential domain1.0 to
0.4 V as demonstrated inFig. 9(a). The RF concentration was varied
from 0.1 mM to 0.110 mM while the DA concentration was kept
constant as 0.1 mM. For each successive addition of RF, there is a
rise in current values without affecting much to the DA peak. So, it
may be concluded that SLSMCNTPGCPE is the dominant
electro-chemical sensor for the estimate of RF in the presence of DA. The
plot of the concentration variation of RF from 100

m

M to 110

m

M
against the peak current (Fig. 9(b)) gives a straight line. It follows
the linear regression equation Ipc(A)ẳ 8.14
106ỵ 0.21 (M) with

a coefcient of correlation of 0.99. It underlines the feasibility of RF
determination in the presence of DA.

Fig. 8. (a) CV concurrent analysis of RF and DA at BPGPE (curve a), CNTPGCPE (curve b) and SLSMCNTPGCPE (curve c) at sweep rate of 0.1 V/s in 0.1 M PBS of pH 6.5 (b)
Instantaneous separation of RF and DA at BPGPE (curve a), CNTPGCPE (curve b) and SLSMCNTPGCPE (curve c) at a 0.05 V/s sweep rate in 0.1 M PBS of pH 6.5 using DPV.

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3.9.3. Anti-interference ability analysis

The effects of diverse species that can have interference with
the 0.1 mM RF electroanalysis, such as folic acid, ascorbic acid,
biotin, pyridoxine, alanine, glycine, estriol, tartrazine (0.1 mM)
were evaluated at optimal conditions using the DPV technique.
The results showed that there was no significant effect on peak
potential and peak current value of 0.1 mM RF. So, the proposed
sensor has an excellent selectivity with low interference effects
(below±3%).

4. Conclusion

The established electrode is a low cost and an active sensor for
the determination of RF in the presence of DA. The projected sensor
offers a low detection limit, good linearity, comparable with
pre-vious sensores reported in literature. The presented sensing
strat-egy was applied to pharmaceutical and food samples with an
excellent recovery. So, the demonstrated sensor can be applied to
routine analysis of RF in real samples. Moreover, the electrode
ex-hibits a high stability, low interference effects, good repeatability
and is eco-friendly. From these discussions, we conclude that the
devised sensor is the best alternative for the electrochemical
quantification of RF in the presence of DA.

Declaration of Competing Interest

The authors declare no conflict of interest.

Acknowledgement

We gratefully acknowledge the financial support from the
VGST, Bangalore under Research Project No.
KSTePS/VGST-KFIST(L1)2016e2017/GRD-559/2017-18/126/333, 21/11/2017.

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