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Journal ofMaterials Chemistry B
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Controlled electr
Department of Chemical Engineering and Bio
Technology, Taipei 10608, Taiwan. E-mail:
Electronic supplementary informa10.1039/c4tb01325e
These authors contributed equally.
Cite this: DOI: 10.1039/c4tb01325e
Received 10th August 2014Accepted 1st September 2014
DOI: 10.1039/c4tb01325e
www.rsc.org/MaterialsB
This journal is The Royal Society of
ochemical synthesis of new rareearth metal lutetium
hexacyanoferrate on reducedgraphene oxide and its application as a
salicylic acidsensor
Balamurugan Devadas, Rajesh Madhu, Shen-Ming Chen* and Huai-Tse
Yeh
The hexangular star building-like lutetium hexacyanoferrate
(LuHCF) structure with an average size of ca.
8.0 0.5 mm was synthesized using a simple, one-step
electrochemical method, and it was highlydispersed on to a reduced
graphene oxide (RGO) modified glassy carbon electrode (GCE) support
for the
first time. The size and shape of the as-synthesized LuHCF micro
stars were controlled by the deposition
time. The LuHCF/RGO samples were characterized by a variety of
analytical and spectroscopy
techniques, viz. scanning electron microscopy (SEM), infra-red
spectroscopy (IR), energy dispersive X-ray
spectroscopy (EDS), X-ray diffraction (XRD), and X-ray
photoelectron spectroscopy (XPS). In addition,
LuHCF/RGO/GCE was adopted for the novel electrochemical
detection of salicylic acid (SA) using cyclic
voltammetry (CV) and amperometry methods. The charge transfer
resistant value of LuHCF/RGO/GCE
was smaller than LuHCF and bare GCE, which exhibit a remarkable
electrocatalytic performance towards
SA. Notably, the SA sensor was found to exhibit a lower
detection limit and high sensitivity of ca. 0.49
mM and 77.2 mA mM1 cm2, respectively. The reported SA sensor
possesses an excellent real time
application with commercially purchased aspirin tablets and
salic ointment (which contains salicylic acid).
The excellent analytical parameters of the reported sensor,
surpasses the previously reported modified
electrodes, rendering practical industrial applications.
1. Introduction
Salicylic acid (SA) is a type of phenolic acid, which is also
knownas 2-hydroxybenzoic acid. SA has been found in plants,
andplays a signicant role in the development of plant
growth,photosynthesis, and transpiration. However, the treatment
ofSA has grateful consideration toward the synthesis of
patho-genesis-related proteins and alfalfa mosaic virus
infectedplants.1 Owing to unique properties such as keratolytic,
bacte-riostatic, fungicidal, and photo protective activity, SA is
bene-cial for a wide range of applications, namely, topical
use,dermatologic conditions, reducing the rate of
keratinocyteproliferation.2 Moreover, SA is used to heal several
skin prob-lems such as acne, hyperpigmentation, oily skin, large
pores,and surface roughness.3 Therefore, SA has been widely used
inthe preparation of cosmetics and ointment due its peeling
andexible nature.4 Hence, the effective and sensitive
technology, National Taipei University of
[email protected]
tion (ESI) available. See DOI:
Chemistry 2014
determination of SA is very important in pharmaceuticals
andother cosmetic industries.
Owing to the numerous activities of pharmaceutical analysis,it
is highly signicant to develop sensitive and selective
sensingsystems for the detection of SA. Previously, P. Trinder et
al.,reported the determination of salicylate in biological
uidsusing a ferric salt spectrophotometer.5 Nevertheless, there
havebeen several reports on the detection of SA using
differenttechniques including spectrophotometry,6 Raman
spectros-copy,7 ultraviolet spectrometry,8 gas
chromatography-massspectrometry (GC-MS),9 colorimetric
techniques,10 liquid chro-matography-tandem mass spectrometry,11,12
and gasliquidchromatography.13 The aforementioned methods have
disad-vantages such as high cost and the need of expensive
instru-ments and technical operators. In contrast to these
methods,electrochemical techniques are more convenient, cost
effectiveand easy to operate. However, there are few reports on the
use ofelectrochemical methods for SA detection.14,15 Interestingly,
wehave developed a simple and convenient amperometric methodfor the
electrochemical determination of SA.
On the other hand, progress on new materials using
elec-trochemical technique is still a challenging task for
manyresearchers. In spite of the overwhelming activity on
metalhexacyanoferrate, rare earth metalHCFs have also been
widely
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used in electrochemical sensor applications.1620 To date,several
rare earth metalHCFs such as dysprosium,21,22
samarium,23,24 and lanthanum HCF,25 respectively, have
beenreported for preparation and characterization. Nonetheless,rare
earth metalHCFs have fascinating morphologies such asower and
christmas tree-like CeHCF,26 diamond-like NdHCF,27
LaHCF,28 and parabola-like HoHCF.29 Moreover, we
havedemonstrated microstar-like DyHCF and ower-like YHCF forsensor
applications in our previous reports.30,31 Among them, inthe order
of rare earth metal, lutetium is one of the signicantmaterials for
electrochemical sensor applications.32 In recentdecades,
electrochemical properties and the applications oflutetium
phthalocyanines have been investigated.3336 More-over, reduced
graphene oxide (RGO) is an inspiring materialdue to its unique
electrical, thermal and mechanical properties,which can be used as
an efficient substrate material. Hence,RGO modied electrodes have
been widely used for biofuelcells, energy storage devices and
biosensor applications.3741
Moreover, RGO is more favorable to prevent the
uncontrollablegrowth of the MHCF, hence, favorable for catalytic
reactions.42,43
In contrast to earlier reports on electrochemical methods
byJiang et al., and M. A. Raj et al., the reported
electrochemicalreduction of GO was performed with a 0.1 M solution
of KClcontaining the metal and ferricyanide. Moreover, only
10consecutive CV cycles were scanned for the
electrochemicalreduction.44,45 Interestingly, RGO can retain the
electrochemicalbehaviour of the hexacyanoferrate (HCF) lm and
enhances theelectron transfer ability between the HCF and GCE.
Hencecomposites of graphene with HCF have prevalent
considerationfor different applications.46,47Owing to the
distinctive propertiesof RGO-HCF it has received a lot of attention
for applications inelectrocatalysis in recent years.31,48,49 To the
best of our knowl-edge using an extensive literature survey, there
is no report forthe LuHCF/RGO hybrid material. Hence, the
electrochemical,structural and morphological characterisation, and
wideapplications of LuHCF are still intriguing. Therefore, in
thiswork, we have developed an amperometric method for
theelectrochemical preparation of LuHCF for the rst time.
Herein, we demonstrate a novel electrochemical route for
thepreparation of the LuHCF/RGO composite material for appli-cation
as a SA sensor. The LuHCF micro star particle structurewas achieved
by controlling the deposition time. The as-syn-thesised LuHCF/RGO
composite material was characterizedusing a range of analytical and
spectroscopic techniques. Thedetermination of SA was carried out
using a amperometricmethod, and the real time application of the
reported SA sensorwas performed with aspirin tablets and salic
ointment samples.
2. Experimental section2.1 Materials and methods
Lutetium(III) chloride hexahydrate was obtained from
SigmaAldrich. K3Fe(CN)6 and KCl were purchased from Wako
purechemical industries, Ltd. Salicylic acid was purchased
fromYakuri Chemicals. Co. Ltd. Sodium hydroxide was purchasedfrom
Sigma Aldrich. All other chemicals were of analytical gradeand used
as received. The supporting electrolyte 0.1 M KCl and
J. Mater. Chem. B
all reagents were prepared using doubly deionized
distilledwater. Prior to electrochemical experiments, pure nitrogen
gaswas purged through the experimental solution.
The entire electrochemical measurements were carried outusing a
CHI 1205A work station using a three electrode systemconsisting of
a glassy carbon electrode as the working electrode,Ag/AgCl as the
reference electrode and Pt wire as the counterelectrode in the
electrochemical cell. Amperometric studieswere carried out using a
rotating ring disk electrode (RRDE-3A),BAS instrument made in
Japan. The morphological studies werecarried out using a Hitachi
S-3000H scanning electron micro-scope (SEM). Energy dispersive
X-ray (EDX) spectra was recor-ded with a HORIBA EMAX X-ACT.
2.2 Synthesis of graphene oxide
Graphene oxide (GO) has synthesized by Hummers method.Briey,
graphite oxide was synthesized by treating raw graphitewith sodium
nitrate and potassium permanganate in an icebath. Then, aer the
addition of 3% hydrogen peroxide toreduce the permanganate and
manganese dioxide. Theobtained brownish graphite oxide was washed
with warm waterand the graphite oxide collected by centrifugation.
Further,graphite oxide was dispersed in water in the ratio of 1 mg
mL1
using sonication to obtain a GO solution.
2.3 Fabrication of modied electrode
Prior to the fabrication of the electrode, the GCE was well
pol-ished with alumina powder, ethanol and DD water and dried inan
air atmosphere and 5 mL of the as-synthesized GO solutionwas
drop-casted onto the GCE surface and dried. The GOmodied GCE was
placed in a supporting electrolyte KCl solu-tion containing equal
amounts of LuCl3$6H2O and K3Fe(CN)6.Then 10 consecutive CV scans
were performed at the GO/GCE,and amperometric deposition performed
on the same solutionwith a constant applied potential of 0.2 V for
500 s.
3. Result and discussion3.1 Amperometric deposition of LuHCF on
RGO/GCE
Fig. 1 depicts the 10 consecutive CV cycles of the
electro-chemical reduction of GO. As shown in Fig. 1, in the rst
cycle alarge cathodic peak appears at 1.0 V, which was attributed
tothe reduction of oxygen functionalities in GO. Meanwhile, theGO
lm was stabilized with the ferricyanide solution, and RGO/GCE was
turned back to the amperometric deposition ofLuHCF. At a constant
potential of 0.2 V, the amperometricscan was performed for 500 s.
The positively charged Lu3+ ionsare consequently adsorbed on to the
negatively charged hex-aycanoferrate (HCF) particles, which formed
the LuHCF parti-cles. Here GO has acted as a substrate material for
the efficientdeposition of LuHCF. Based on a previously reported
mecha-nism, the formation of LuHCF particles can be expressed
usingeqn (1).
Fe(CN)64 + Lu3+ + K+ + H2O / KLu[Fe(CN)6]$H2O (1)
This journal is The Royal Society of Chemistry 2014
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Fig. 1 CVs of the electrochemical reduction of graphene oxide
(GO) ina 0.1 M solution of KCl containing 5 mM of K3Fe(CN)6 and
LuCl3$6H2Oat a scan rate of 50 mV s1.
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Scheme 1 represents the mechanism of nucleation andgrowth of the
LuHCF on RGO at different deposition times. Toprovide a clear
insight into the mechanism of formation of theLuHCF particles, we
monitored the nucleation and growth ofthe particles formed at
different deposition times throughamperometry. As shown in Scheme
1, distorted spherical sha-ped particles with sizes (1.5 0.5 mm)
were formed on thesurface of RGO at 100 s. The growth of petals
occurred from theadjacent facets of the particles. At 300 s,
increased nucleation ofthe particles from the side facets occurred
on the surface of theRGO, leading to the formation of gooseberry
shaped particleswith sizes two times that of the star shaped
petals. When thedeposition time increased to 500 s, the nucleation
of theparticles at the adjacent star shaped petals increased
greatly,
Scheme 1 Electrochemical growth and nucleation mechanism ofLuHCF
on RGO.
This journal is The Royal Society of Chemistry 2014
resulting in the formation of well-dened petals that are
sepa-rated through dened edges. The as-formed particles
resembledthat of hexangular star-fruit shaped particles. It has to
be notedthat the deposition time played a key role in controlling
thenucleation of the particles, the shape of the petals and
themorphology of the particles.50
3.2 Characterization of RGO
The FT-IR spectra of GO and RGO is shown in Fig. 2A.
Oxygenfunctional groups such as OH, epoxy, C]O and CO can beseen in
the spectrum of GO. The high intensity peak at 3400cm1 conrms the
presence of the stretching vibration of they(OH) group present in
GO. The sharp peak at 1720 cm1 wasattributed to y(C]O) and 1619 cm1
corresponding toy(C]C) groups were present in GO. The peak at 1068
cm1
indicated the y(CO) groups of GO. All these peak intensitieswere
ascribed to the stretching vibrations of the oxygen
func-tionalities in GO. Whereas, signicant peaks were
decreased,indicating reduction of oxygen functionalities in GO.
BesidesUV-Vis spectroscopy of the as-synthesized GO and RGO
weredemonstrated in Fig. 2B. As shown in the UV-Vis spectrum,
abroad absorption peak at 230 nm corresponding to the pp*
Fig. 2 (A) FT-IR and (B) UV-Vis spectra of GO and RGO.
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transition and shoulder peak at 295 nm for the n p*
transitionwas observed for GO (black colour). The spectrum of RGO
wasshown in red colour. The pp* transition peak was red shiedto 265
nm indicating the reduction of the oxygen functionalitiesin GO and
rearrangement of the electron conjugationstructure.51
3.3 Structural and morphological studies of LuHCF
The morphological studies of rare earth LuHCF particle are
veryinteresting to discern the size and shape of the particles
con-cerned. Fig. 3 elucidates the different morphologies of
LuHCFparticles. The deposition of LuHCF microparticles has
beenmonitored at different interval time of the
amperometricdeposition. As shown in Fig. 3A, the star fruit-like
structureformed at 100 s with each particle having an equal size of
1.5 0.5 mm. Further, the particles became gooseberry-like
structuresand the size of micro stars were increased two times at
300 s, asshown in Fig. 3B. Upon increasing the deposition time to
500 s,we obtained the closely packed star-like structure of
LuHCF(Fig. 3C). Every star-like particle has a diameter of 8.0 0.5
mmand was deposited on the electrode surface uniformly as shownin
Fig. 2D. Fig. 3E and F shows the LuHCF deposited on the GCEand RGO
surface. It can be seen that LuHCF was highlydistributed on RGO in
a manner similar to GCE.
3.4 Elemental analysis and FT-IR spectroscopy of LuHCF
Fig. 4A shows the EDX spectra of the as-deposited LuHCF. Asshown
in the EDX graph, the elements carbon, lutetium, iron,
Fig. 3 SEM of LuHCF at different deposition times (A) 100 s (B)
300 s(C) 500 s. (D) Single particle image of LuHCF. (E) LuHCF on
GCE and (F)LuHCF on the RGO surface.
Fig. 4 (A) EDX analysis and (B) FT-IR spectrum of LuHCF.
J. Mater. Chem. B
nitrogen and potassium were present in the deposited LuHCF,and
revealed that the LuHCF possessed a signicant weight% ofthese
elements. The EDX prole of a single LuHCF particlereveals the
presence of 27 wt% carbon, 28 wt% lutetium, 15 wt%potassium, 20 wt%
ferrous ion and 10 wt% nitrogen ion.Accordingly, the EDX result
conrms the LuHCF complex wasformed efficiently. The FT-IR spectrum
of the as-synthesizedLuHCF is displayed in Fig. 4B. According to
prussian blue (PB)and its analogues the corresponding peaks of
LuHCF arelocated in Fig. 3B. A very sharp peak with high intensity
wasobserved at 2080.9 cm1, which validates the stretching
vibra-tion of ferricyanide (y(CN)) present in LuHCF. The broad peak
at1597.93 cm1 corresponded to the HOH bending mode of theLuHCF
complex. Moreover, the two broad peaks at 2876 and2973 cm1 were
assigned to the stretching vibration of the twokinds of water
molecule present.
3.5 XRD and XPS analysis of LuHCF
Fig. 5A displays the XRD pattern of the as-deposited LuHCFmicro
star particles. As shown in the XRD pattern, the highestpeak
intensity of the LuHCF was described and mentioned forthe
corresponding hkl value. Moreover, there is no literatureavailable
for the KLu[Fe(CN)6] complex and its characteriza-tion.
Nevertheless, the properties and high intensity XRD
This journal is The Royal Society of Chemistry 2014
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Fig. 5 (A) XRD pattern and (B) XPS survey spectra of LuHCF.
Fig. 6 (A) CV of different modified films (a) LuHCF/RGO/GCE (b)
RGO/GCE (c) LuHCF and (d) bare GCE in a 0.3 M solution of NaOH
con-taining 1 mM of SA at a scan rate of 50 mV s1. (B) CV of
LuHCF/RGO/GCE in a 0.3 M solution of NaOH containing different
concentrationsof SA at a scan rate of 50 mV s1.
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peaks of LuHCF were similar to rare earth metal
hex-acyanoferrate. The high intensity peaks at 15.5, 19.2 and24.5
were common for all lanthanide metals based on thosein previously
reported literature (black colour).52 The broaddiffraction peak of
RGO appeared at 28 indicating LuHCFmicros stars were distributed
throughout the RGO sheets (redcolor). All the peaks were referred
according to JCPDS cards.The referred JCPDS card numbers were JCPDS
# 01-072-4771,JCPDS # 00-047-1329, JCPDS # 00-046-1089 and JCPDS #
01-071-8282. The presence of all peak intensities according to
theJCPDS cards suggest a orthorhombic (Cmcm space group)structure
model for the LuHCF complex. When compared tothe other rare earth
metal hexacyanoferrate complexes, thestructure model was similar to
the orthorhombic structure ofLuHCF.19,30,31,53 Furthermore, X-ray
photoelectron spectros-copy (XPS) is known to analyze the chemical
composition andbinding energy. Fig. 5B shows the XPS survey spectra
ofLuHCF, which exhibits the corresponding peaks appearing
forFeS3(CN)3, Fe 3s, Cl 2p, K 2p3/2 (chloride) and O 1s, which
isconsistent with the EDS results.5456
This journal is The Royal Society of Chemistry 2014
3.6 Cyclic voltammetric determination of SA
To evaluate the electrocatalytic activity of the various
electrodes,cyclic voltammograms (CVs) were recorded for: (a)
LuHCF/RGO/GCE (b) RGO/GCE (c) LuHCF and (d) bare GCE in a 0.3M
solutionof NaOH containing 1 mM of SA at a scan rate of 50 mV s1.
Asshown in Fig. 6A, the well-dened SA oxidation initiation peakwas
observed on (a) LuHCF/RGO/GCE at 0.45 V. Besides, othermodied
electrodes (b) RGO/GCE (c) LuHCF/GCE and (d) bareGCE show a very
poor SA oxidation initiation peak at 0.55 V, 0.6 Vand 0.65,
respectively. It is noteworthy that the oxidation peakpotential of
the LuHCF/RGO/GCE-modied electrode was 150and 230 mV less positive
than the LuHCF modied and bareGCE. Moreover, the oxidation peak
current of SA at LuHCF/RGO/GCE was several times higher than that
of other modied GCEs.
To assess the analytical performances of the proposed SAsensor,
the LuHCF/RGO/GCE-modied GCE was performed
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Scheme 2 The electro-oxidation process of Salicylic acid.
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using CV measurements. The cyclic voltammetric electro-chemical
determination of SA is shown in Fig. 6B. It can be seenthat the SA
oxidation peak current at 0.5 V increased linearlywith increasing
concentrations of SA, meanwhile no reductionpeak was observed,
which was attributed to a fast irreversibleelectrochemical
reaction. In the rst step, SA was adsorbed onthe LuHCF, causing the
formation of a phenoxy radical andfurther oxidized into a phenoxy
cation. Finally, the carboxylhydroquinone was obtained as the
product of this electro-chemical reaction. Here the supporting
electrolyte NaOH hasbeen used for the efficient oxidation of SA.
The SA oxidationmechanism can be expressed as shown in Scheme
2.
Fig. 7 (A) EIS of the different modified GCE bare, LuHCF and
RGO/LuHCF (B) CV of RGO/LuHCFmodifiedGCE in a 0.3 M solution of
NaOHcontaining 100 mM of SA at different scan rates (100 to 1000 mV
s1).
3.7 Electrochemical impedance spectroscopy
EIS has been employed to distinguish the electron
transferbehavior of the fabricated electrode. Fig. 7A shows the
Nyquistplot of the real component (Zre) and imaginary
component(Zim). The inset gure represents the Randles circuit
parameters(inset gure) corresponding to the charge transfer
resistance(Rct), solution resistance (Rs) and double layer capacity
(Cdl) ofthe lms. It can be seen that in Fig. 7A, bare GCE has the
lowercharge transfer resistance than LuHCF/GCE, RGO/GCE
andLuHCF/RGO/GCE. Though the LuHCF and RGO modied GCEhas a lower
semicircle value than bare GCE, and a comparativelyhigher charge
electron transfer resistance than the fabricatedLuHCF/RGO/GCE.
Therefore, the modied GCE reported has anexcellent electron
transfer capacity when compared to LuHCF,RGO modied and bare
GCE.
3.8 Different scan rate
The CVs of RGO/LuHCF modied GCE in the presence of 100mM of SA
in a 0.1 M solution of NaOH at different scan rates (10to 100 mV
s1) are shown in Fig. 7B. The linear increase in bothredox peaks at
0.2 V corresponding to the LuHCF and SAoxidation peaks around 0.4 V
were observed when increasingthe scan rates from 10 to 100 mV s1.
The inset of Fig. 6Bdisplays the calibration plot of log scan rate
(log y) vs. logcurrent (log Ipa). The linear regression equation of
the calibra-tion plot can be expressed as Ipa (mA) 0.489 log y (mV
s1) 1.053, R2 0.9901. As shown in the regression equation, thevalue
of scan rate was observed at 0.489 log y, which is very nearto the
theoretical value of 0.500, which reveals that the elec-trochemical
reaction occurred on the electrode surface and wasa diffusion
controlled process. Moreover, the redox peak of
J. Mater. Chem. B
LuHCF at 0.2 V increased linearly with scan rate indicating
asurface conned process.
3.9 Amperometric determination of SA
To further assess the analytical performance of the proposed
SAsensor, electrocatalytic activities of the
LuHCF/RGO-modiedrotating ring disk electrode (RRDE) were evaluated
using theamperometry method at an applied potential (Eapp) of +0.55
V,as shown in Fig. 8A. At constant regular intervals (50 s) 50 mm
ofSA was injected while the RRDE (1500 rpm) rotates
continuouslyinto the solution of NaOH. The excellent and sharp SA
amper-ometric responses were observed within a 5 s. of every
addition.The inset to Fig. 8A shows the calibration plot of SA
concen-tration vs. current. It can be seen that the SA oxidation
currentswere linearly increased with increasing concentrations of
SA.The linear regression equation can be expressed as, I
0.0605C(mM) + 0.1802, R2 0.9863. The low limit of detection for
thereported lm modied GCE for the SA sensor has been
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Fig. 8 (A) Amperometric response of LuHCF/RGO/GCE for
thesequential addition of SA at an applied potential (Eapp) of
+0.55 V. (Inseta) Calibration plot of concentration vs. current (b)
amperometricresponse of the interference compound. (B) CV of
LuHCF/RGO/GCEin salic ointment (500 mg/10 mL).
Table 1 A comparison of analytical parameters for the detection
of SA o
Modied electrodesa Detection limit (mM)
Well-aligned MWCNTs 0.8BDD in a sodium sulphate medium 1DNA/PPy
nanober modied electrode 0.8BDD 2HPLC with uorescence detection
0.02, 0.2 (mg kg1)Ni/GCE 0.5PNP/Pt disk electrode 6.4Co/Al
hydrotalcite coated-Pt 6LuHCF/RGO/GCE 0.49
a MWCNTs multi-walled carbon nanotube; BDD boron-doped
diamondmodied GCE; Co/Al cobalt hydrotalcite-like.
This journal is The Royal Society of Chemistry 2014
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calculated using the formula of LOD 3s/S, where s is thestandard
deviation of the three blank and S is the sensitivity.The
calculated LOD and sensitivity of the SA sensor were 0.491mM and
77.2 mA mM1 cm2, respectively. The obtainedanalytical parameters
are more feasible when compared tovarious modied electrodes
available in the literature (Table 1).
3.9.1 Selectivity. The selectivity of the reported sensor
isextremely important for practical applications. So we
haveperformed the selectivity of SA sensor in the presence of
somecommon co-existing interference compounds such as ascorbicacid
(AA), dopamine (DA), uric acid (UA), glucose and para-cetamol (PA)
using the amperometric technique. The rightbottom inset of Fig. 8A
shows the selectivity of the SA sensor atthe RGO/LuHCFmodied GCE.
As shown in the inset of Fig. 8A,the well-dened amperogram
responses were observed at each100 mM addition of SA (a). But no
remarkable response wasobserved for each addition of 100 mM of (b)
glucose, (c) AA, (d)DA, (e) UA and (f) PA. However, a signicant
response wasobserved by subsequent addition of SA, validating the
selectivityof the reported sensor. Thus, SA could be determined
selectivelyat the RGO/LuHCF modied GCE without interference from
co-existing species.
3.9.2 Real sample applications. To investigate the
versatileapplication of the SA sensor for practical analysis of
realsamples, the fabricated GCE was tested with
commerciallyavailable tablets (aspirin) and ointment (salic
ointment con-taining salicylic acid). The results are shown in
Table 2 andFig. 8B, respectively. The 3 aspirin tablets were
weighed on ananalytical balance and crushed using a cleaned mortar,
andprepared for the required concentration. The CV technique
wasemployed for the tablet sample analysis. Three
differentconcentration of samples were analysed using the
LuHCF/RGO
ver various modified electrodes
Concentrationrange (mM)
Sensitivity(mA mM1 cm2) Reference
23000 59.25 1410100 24.17 570.12 582.5105 58.66 59 602550 63.78
6120500 0.219 6210500 6351000 77.2 This work
electrode; PPy polypyrrole; PNR platinum nanoparticles; Ni
nickel
Table 2 Performance of LuHCF/RGO/GCE for the determination
ofsalicylic acid (SA) in real samples
S. no. Tablet sample Added (mM) Found (mM) Recovery %
1 Sample 1 200 199.45 99.72 Sample 2 400 377.26 94.33 Sample 3
700 692.72 98.96
J. Mater. Chem. B
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modied GCE under the same conditions. From the amount ofadded
and found SA in the tablet samples, the calculatedrecoveries are
summarized in Table 2. It is found that a satis-factory recovery
rate exceeding ca. 99.7% for the 3 samples maybe inferred for these
real samples, indicating the promisingperspective application of
the proposed SA sensor for theanalysis of real samples.
Further, to widen the applications of the reported SA sensor,the
CV technique was employed for the determination of SA inSalic
ointment. The 1 g sample of Salic ointment containsstandard
salicylic acid of 25 mg. We squeezed out all of the Salicointment
into an empty bottle. Then 500 mg of ointment wasweighed and
dissolved in a solution of NaOH with stirring andultrasonication.
The 500 mg/10 mL solution of ointment wasplaced in an
electrochemical cell and the CV recorded at theLuHCF/RGO/GCE. As
shown in Fig. 8B, the SA oxidation peakwas observed at 0.55 V at a
scan rate of 50 mV s1. It is notingthat the reported modied GCE
would be worthy to reach up theprototype level sensor for the
determination of SA.
3.9.3 Repeatability, reproducibility and stability.
Therepeatability of the fabricated GCE for the SA sensor
reportedwas performed by additional CV measurements using the
sameelectrolyte conditions. The electrochemical sensor
reportedshows good repeatability with a
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http://dx.doi.org/10.1039/c4tb01325eControlled electrochemical
synthesis of new rare earth metal lutetium hexacyanoferrate on
reduced graphene oxide and its application as a salicylic acid
sensorElectronic supplementary information (ESI) available. See
DOI: 10.1039/c4tb01325eControlled electrochemical synthesis of new
rare earth metal lutetium hexacyanoferrate on reduced graphene
oxide and its application as a salicylic acid sensorElectronic
supplementary information (ESI) available. See DOI:
10.1039/c4tb01325eControlled electrochemical synthesis of new rare
earth metal lutetium hexacyanoferrate on reduced graphene oxide and
its application as a salicylic acid sensorElectronic supplementary
information (ESI) available. See DOI: 10.1039/c4tb01325eControlled
electrochemical synthesis of new rare earth metal lutetium
hexacyanoferrate on reduced graphene oxide and its application as a
salicylic acid sensorElectronic supplementary information (ESI)
available. See DOI: 10.1039/c4tb01325eControlled electrochemical
synthesis of new rare earth metal lutetium hexacyanoferrate on
reduced graphene oxide and its application as a salicylic acid
sensorElectronic supplementary information (ESI) available. See
DOI: 10.1039/c4tb01325eControlled electrochemical synthesis of new
rare earth metal lutetium hexacyanoferrate on reduced graphene
oxide and its application as a salicylic acid sensorElectronic
supplementary information (ESI) available. See DOI:
10.1039/c4tb01325eControlled electrochemical synthesis of new rare
earth metal lutetium hexacyanoferrate on reduced graphene oxide and
its application as a salicylic acid sensorElectronic supplementary
information (ESI) available. See DOI: 10.1039/c4tb01325eControlled
electrochemical synthesis of new rare earth metal lutetium
hexacyanoferrate on reduced graphene oxide and its application as a
salicylic acid sensorElectronic supplementary information (ESI)
available. See DOI: 10.1039/c4tb01325eControlled electrochemical
synthesis of new rare earth metal lutetium hexacyanoferrate on
reduced graphene oxide and its application as a salicylic acid
sensorElectronic supplementary information (ESI) available. See
DOI: 10.1039/c4tb01325eControlled electrochemical synthesis of new
rare earth metal lutetium hexacyanoferrate on reduced graphene
oxide and its application as a salicylic acid sensorElectronic
supplementary information (ESI) available. See DOI:
10.1039/c4tb01325eControlled electrochemical synthesis of new rare
earth metal lutetium hexacyanoferrate on reduced graphene oxide and
its application as a salicylic acid sensorElectronic supplementary
information (ESI) available. See DOI: 10.1039/c4tb01325eControlled
electrochemical synthesis of new rare earth metal lutetium
hexacyanoferrate on reduced graphene oxide and its application as a
salicylic acid sensorElectronic supplementary information (ESI)
available. See DOI: 10.1039/c4tb01325eControlled electrochemical
synthesis of new rare earth metal lutetium hexacyanoferrate on
reduced graphene oxide and its application as a salicylic acid
sensorElectronic supplementary information (ESI) available. See
DOI: 10.1039/c4tb01325eControlled electrochemical synthesis of new
rare earth metal lutetium hexacyanoferrate on reduced graphene
oxide and its application as a salicylic acid sensorElectronic
supplementary information (ESI) available. See DOI:
10.1039/c4tb01325eControlled electrochemical synthesis of new rare
earth metal lutetium hexacyanoferrate on reduced graphene oxide and
its application as a salicylic acid sensorElectronic supplementary
information (ESI) available. See DOI: 10.1039/c4tb01325eControlled
electrochemical synthesis of new rare earth metal lutetium
hexacyanoferrate on reduced graphene oxide and its application as a
salicylic acid sensorElectronic supplementary information (ESI)
available. See DOI: 10.1039/c4tb01325eControlled electrochemical
synthesis of new rare earth metal lutetium hexacyanoferrate on
reduced graphene oxide and its application as a salicylic acid
sensorElectronic supplementary information (ESI) available. See
DOI: 10.1039/c4tb01325eControlled electrochemical synthesis of new
rare earth metal lutetium hexacyanoferrate on reduced graphene
oxide and its application as a salicylic acid sensorElectronic
supplementary information (ESI) available. See DOI:
10.1039/c4tb01325eControlled electrochemical synthesis of new rare
earth metal lutetium hexacyanoferrate on reduced graphene oxide and
its application as a salicylic acid sensorElectronic supplementary
information (ESI) available. See DOI: 10.1039/c4tb01325eControlled
electrochemical synthesis of new rare earth metal lutetium
hexacyanoferrate on reduced graphene oxide and its application as a
salicylic acid sensorElectronic supplementary information (ESI)
available. See DOI: 10.1039/c4tb01325eControlled electrochemical
synthesis of new rare earth metal lutetium hexacyanoferrate on
reduced graphene oxide and its application as a salicylic acid
sensorElectronic supplementary information (ESI) available. See
DOI: 10.1039/c4tb01325e