Fe2MoO4 magnetic nanocomposite modified screen printed graphite electrode as a voltammetric sensor for simultaneous determination of nalbuphine and diclofenac

Abstract

This study applied screen printed graphite electrode (SPGE) modified with the Fe2MoO4 magnetic nanocomposite for simultaneously determining nalbuphine and diclofenac to fabricate a sensitive simple electrochemical sensor. A simple process was designed for preparing Fe2MoO4 magnetic nanocomposite. In addition, electrochemical features of the modified electrodes were characterized by differential pulse voltammetry (DPV), chronoamperometry (CHA) and cyclic voltammetry (CV). According to the analysis, very good electrocatalytic activities towards nalbuphine were shown by the modified electrode (PBS at a pH of 7.0). According to DPV measurements, the linear response to detect nalbuphine ranged between 0.02 and 250.0 μM. Furthermore, limit of detection (LOD) equaled 8.0 nM (S/N = 3). DPV was employed for the simultaneous determination of nalbuphine and diclofenac, which showed a significant peak potential difference equal to 0.14 V. Therefore, this new sensor exhibited acceptable repeatability, reproducibility and stability. Finally, the functional utility of the sensor was examined in the real samples, followed by attractive findings to detect nalbuphine and diclofenac.

Full text

Fe
2
MoO
4
magnetic nanocomposite modified screen
printed graphite electrode as a voltammetric sensor
for simultaneous determination of nalbuphine
and diclofenac
Halimeh Yaghoubian
1,
* , Somayeh Tajik
2
, Hadi Beitollahi
3
, Hamid Sarhadi
4
, and
Iran Sheikhshoaie
5
1
Department of Chemistry, Bam Branch, Islamic Azad University, Bam, Iran
2
Research Center of Tropical and Infectious Diseases, Kerman University of Medical Sciences, Kerman, Iran
3
Environment Department, Institute of Science and High Technology and Environmental Sciences, Graduate University of
Advanced Technology, Kerman, Iran
4
Department of Food Science, Bam Branch, Islamic Azad University, Bam, Iran
5
Department of Chemistry, Faculty of Science, Shahid Bahonar University of Kerman, 76175-133 Kerman, Iran
Received: 11 April 2021
Accepted: 21 May 2021
ÓThe Author(s), under
exclusive licence to Springer
Science+Business Media, LLC,
part of Springer Nature 2021
ABSTRACT
This study applied screen printed graphite electrode (SPGE) modified with the
Fe
2
MoO
4
magnetic nanocomposite for simultaneously determining nalbuphine
and diclofenac to fabricate a sensitive simple electrochemical sensor. A simple
process was designed for preparing Fe
2
MoO
4
magnetic nanocomposite. In
addition, electrochemical features of the modified electrodes were characterized
by differential pulse voltammetry (DPV), chronoamperometry (CHA) and cyclic
voltammetry (CV). According to the analysis, very good electrocatalytic activi-
ties towards nalbuphine were shown by the modified electrode (PBS at a pH of
7.0). According to DPV measurements, the linear response to detect nalbuphine
ranged between 0.02 and 250.0 lM. Furthermore, limit of detection (LOD)
equaled 8.0 nM (S/N= 3). DPV was employed for the simultaneous determi-
nation of nalbuphine and diclofenac, which showed a significant peak potential
difference equal to 0.14 V. Therefore, this new sensor exhibited acceptable re-
peatability, reproducibility and stability. Finally, the functional utility of the
sensor was examined in the real samples, followed by attractive findings to
detect nalbuphine and diclofenac.
Address correspondence to E-mail: h_yaghoubian@yahoo.com
https://doi.org/10.1007/s10854-021-06244-3
J Mater Sci: Mater Electron

1 Introduction
Attractive information of the pharmacokinetic
research, as well as clinical diagnosis is provided by
drug analysis in the biological systems and pharma-
ceutical compounds. Nalbuphine is a member of the
opioid class of analgesic medicines with a structure
as the same as naloxone and oxymorphone. Nal-
buphine has the antagonist and agonist features at
mu and kappa receptors [1] with the analgesic
effectiveness of nearly two-thirds of morphine [2].
Nevertheless, nalbuphine is administered at lower
risks in comparison with morphine [3]. Experts in the
field prescribe it to treat moderate to severe pain
related to the chronic and acute medical dysfunctions
like cancer, vascular or migraine headache, surgical
pain and renal colic or biliary colic [4]. Moreover, its
use has been reported in the course of obstetric
analgesia. Intra-muscular and intravenous adminis-
trations exhibited greater bioavailability than the oral
administration of nalbuphine; hence, this drug would
not be so efficient to relieve pain, which is largely
caused by the first-pass metabolism in liver or the
gastrointestinal-mucosa [5]. As the other opioid
analgesic compounds, it also suffers from several
consequences like dizziness, dry mouth, sweatiness,
sedation, nausea, vertigo, vomiting, headache and
clamminess [3]. In order to treat several diseases like
rheumatoid arthritis, osteoarthritis, sport injuries and
ankylosing spondylitis, one of the popular non-ster-
oidal anti-inflammatory drugs (NSAIDs) called
diclofenac is consumed [6]. This drug enjoys power-
ful anti-inflammatory, analgesic as well as antipyretic
features [7] but is strongly detrimental to living
organisms like high blood pressure (hypertension),
intensive hepatic metabolism and stroke [8]. More-
over, because of poor degradation, its ubiquity in the
environment disturbs the quality of water and fish
health [9]. Therefore, simultaneous detection of nal-
buphine and diclofenac would help improve anal-
gesia. As stated in Krenn et al.’s study, analgesia
considerably improved by consuming nalbuphine as
well as supplemented doses of diclofenac so that it
did not have any effects on the differences in the
consequences and vital signs [10]. For this reason, it
would be vital for designing one of the simple, rapid,
cheap ad sensitive sensors to simultaneously deter-
mine nalbuphine and diclofenac.
In addition, the concentration of drug can be
detected in the drug and biological samples by useful
instruments like analytical procedures, which enjoy
high performance liquid chromatography (HPLC),
spectroscopy and electrochemical methods [11–20].
Out of the analytical procedures utilized for drug
analysis, research has demonstrated more benefits of
the electrochemical procedures due to portability,
more rapid responses, affordability and higher sen-
sitivity [21–25]. Nonetheless, analytes are rarely
detected by the bare electrode because of remarkable
over-potential and poor responses at the bare elec-
trode. Thus, the most essential step with the direct
effects on the detection signal is to modify the elec-
trode for fabricating the electrochemical sensors
[26–30].
Chemically modified electrodes (CMEs) over the
last decade play an important role in analytical
chemistry with respect to electrocatalysis and devel-
opment of new electrochemical sensors [31–34].
CMEs exhibit, better over redox potentials, fast elec-
tron transfer kinetics, good electro-optical properties,
and stable electrode surfaces in electro analysis
[35–39]. Various conductive materials have been used
to prepare CMEs for analysis of various types of
inorganic and organic compounds in pharmaceutical,
biological and environmental samples [40–44].
Numerous methods have been developed to immo-
bilize species onto a variety of electrode surfaces.
These modification techniques include covalent
attachment, drop-casting, spin coating, dip coating,
electrochemical deposition, electropolymerization,
and others [45].
Nanomaterials are chemical substances or materi-
als that are manufactured and used at a very small
scale. Nanomaterials are developed to exhibit novel
characteristics compared to the same material with-
out nanoscale features [46–52].
Nanomaterials have been highly attracted for con-
structing modern electrochemical sensors due to the
very good electrical conductivity, acceptable biocom-
patibility as well as larger surfaces [27,53–57]. Fur-
thermore, one of the attractive approaches to enhance
the electrochemical sensors’ sensitivity and trace
analysis of the drug and biological samples has been
proposed to be electrochemical sensors modified
with conductive nanomaterials [58–60]. Currently,
experts in the field have focused on binary metal
oxides due to the respective good physico-chemical
features like environment benignity, higher chemical
stability, greater electrical conductivity and lower
toxicity than that of the mono metal oxides [61].
J Mater Sci: Mater Electron

According to a research, inorganic metal molybdates
are the members of the family of binary metal oxides
because of attractive physical and physicochemical
features [62]. In fact, researchers introduced them as
the potential materials for a variety of utilizations like
phosphors [63], supercapacitors [64], sensors [65],
photo-catalysis [66] and scintillators [67]. Moreover,
concurrence of the transitional metals with molyb-
denum in such structures largely improves their
features and approves their significance. Therefore,
iron molybdate may be one of the important keys in
sensors.
Other studies have shown a special focus on the
electrochemical sensors based on the screen printed
electrodes (SPEs) as the analytical devices for elec-
troanalysis due to the special benefits of the SPEs,
which result in the superior features of such sensors.
The properties include simplified application and
modification of the surfaces, portability and inex-
pensiveness [68–71]. Ultimately, screen printed tech-
nology largely involves in transition from the
traditional unwieldy electrochemical cells to the
portable and miniaturized electrodes for meeting the
needs for on-site analyses [72,73].
The present study was conducted for designing
and constructing a new voltammetric sensor (Fe
2-
MoO
4
/SPGE) to detect nalbuphine. We used this new
sensor substantially for simultaneous detection of
nalbuphine and diclofenac and assessed its analytical
uses for detecting both drugs in the real specimens.
2 Experimental
2.1 Chemicals and apparatus
According to the research design, we utilized an
Autolab potentiostat/galvanostat Model PGSTAT
302N provided by Eco Chemie from the Netherlands
for performing electrochemical experiments. In
addition, a general purpose electrochemical system
software was used to monitor this system.
SPE (DropSens: DRP-110: Spain) includes three
traditional electrodes known as silver pseudo-refer-
ence electrode, unmodified graphite working elec-
trode, and graphite counter electrode. We applied pH
for measuring Metrohm 710 pH meter.
In addition, nalbuphine, diclofenac, and each
reagent are of the analytical grade and we selected
Merck Co. from Darmstadt in Germany to buy the
reagents. For procuring buffers, orthophosphoric acid
was applied and the salts to provide pH ranged from
2.0 to 9.0.
2.2 Synthesis of Fe
2
MoO
4
magnetic
nanocomposite
According to the research design, 5.000 g of
FeSO
4
.7H
2
O was used to prepare Fe(II) solution, and
dissolution was done in 35 mL of the deionized water
in a 50 mL 2-necked round bottom flasks under
nitrogen gas (solution a). Then, in another flask, we
dissolved 2.800 g of KOH and 0.400 g of KNO
3
in
15 mL deionized water (solution b) in an oil bath at
90 °C. After that, we poured solution b drop-wise for
five minutes in solution a under nitrogen gas when it
yielded a black solution. This black solution was also
shaken at 90 °C for one hour and put aside overnight
at the mentioned temperature for ensuring the solu-
tion homogeneity. Finally, we washed it with 30 mL
deionized water 6 times and isolated it magnetically
and dried it in an oven of 95 °C.
Then, we distributed 0.0004 mol (100 mg) of the
nanosized Fe
3
O
4
in the above round bottom flask,
which contains 50 mL ethylene glycol and added a
solution of 0.0004 mol (i.e., 617 mg) of (NH
4
)
6-
Mo
7
O
24
4H
2
O in 10 mL deionized water into the flask
to reflux the mixture at 160 °C for 12 h. After that, we
filtered the black products and applied distilled
water and absolute ethanol for washing it several
times in order to eliminate any impurities and used
an oven of 60 °C to dry it for 4 h.
2.3 Preparing the electrode
In this stage, the bare SPE was coated with regard to
the above simplified process. Therefore, 1 mg Fe
2-
MoO
4
magnetic nanocomposite was distributed in
1 mL aqueous solution in a 45 min ultrasonication
period. Then, we dropped 3 lL of this suspension
onto the surface of the carbon working electrode and
kept at the room temperature for drying.
2.4 Preparing the real samples
In this step, we diluted 1 mL of a nalbuphine
ampoule (20 mg/mL, Rusan Healthcare Pvt Ltd.) to
10 mL with 0.1 M PBS at a pH of 7.0 and transported
different volume of the diluted solution into 25 mL
volumetric flasks to the mark with PBS. Moreover,
J Mater Sci: Mater Electron

Fig. 1 The XRD pattern of synthesized Fe
2
MoO
4
nanocomposite
Fig. 2 aSEM image used for
EDX analysis. EDX elemental
mapping of bO, cFe, and d
Mo in Fe
2
MoO
4
nanocomposite
Fig. 3 The TEM image of synthesized Fe
2
MoO
4
nanocomposite
J Mater Sci: Mater Electron

our new method was used to analyze the content of
nalbuphine through the standard addition method.
We purchased diclofenac tablets with the label of
value diclofenac = 50 mg/tablet, (Darou Pakhsh
Company, Iran) and powdered them completely and
homogenized prior to the preparation of 15 mL of
0.1 M stock solution. Then, sonication of the solution
was performed to achieve a very good dissolution. In
the next step, it was filtered and a certain volume of
the transparent filtrate was added into an electro-
chemical cell, which contains 10 mL of 0.1 M PBS at a
pH of 7.0 to record DPV voltammogram.
Then, we maintained the urine specimens in a
refrigerator and centrifuged 10 mL of the specimens
at 2000 rpm for 15 min. After that, we used a 0.45 lm
filter to filter the supernatant and diverse contents of
the solution were transported into a 25 mL volu-
metric flask. Afterward, dilution was performed to
the mark with PBS at a pH of 7.0. Consequently,
different amounts of nalbuphine and diclofenac were
employed for spiking the diluted urine specimen and
contents of both drugs were examined by the sug-
gested procedure through the standard addition
procedure.
3 Results and discussion
3.1 Characterization of Fe
2
MoO
4
nanocomposite
It is notable that patterns of XRD on a Bruker
Advance-D8 equipped with X’Pert Pro filtered by Cu
Karadiation ((k= 1.54 A
˚). Figure 1shows the XRD
pattern of synthesized Fe
2
MoO
4
nanocomposite.
Notably, the presence of miller indices of Fe
2
MoO
4
(111), (220), (311), (222), (400), (422), (511), (440), (622),
and (444) in 2hrange of 17.978, 29.655, 34.879, 36.511,
42.423, 52.618; 56.103; 61.526; 73.796; 77.699 would
approve the cubic crystal system with reverse spinel
structure (2FeO MoO
2
) for the nanocomposite. It is
also possible to quantitatively evaluate the
nanocomposite size from XRD data with the help of
Debye–Scherre equation. This compound diameter
equaled 47.93 nm.
The energy-dispersive X-ray spectroscopy (EDX)
elemental mapping has been analyzed for the Fe
2-
MoO
4
nanocomposite for the control of distributing
the elements found in the nanocomposite (Fig. 2).
According to the results, outputs verify the presence
of Mo, Fe and O in the synthesized nano-compound.
Moreover, we investigated Fe
2
MoO
4
morphology
through TEM on the EO912AB electron microscope.
Fig. 4 The FE-SEM image of
Fe
2
MoO
4
nanocomposite
J Mater Sci: Mater Electron

Figure 3demonstrates TEM images for this nano
sized sample. As seen, the synthesized Fe
2
MoO
4
resembles a sphere with *40 nm diameter.
In addition, we applied FE-SEM for analyzing
morphology of the synthesized sample and a Zeiss-
Sigma operating at 26 kV for recording the obtained
images. Figure 4shows the SEM images of the Fe
2-
MoO
4
nanocomposite.
3.2 Electrochemical behavior
of nalbuphine on the Fe
2
MoO
4
/SPGE
The optimum pH value for accurate output should be
calculated to investigate the pH-dependent electro-
chemical properties of nalbuphine. The modified
electrodes were tested at different pH values (2.0 to
9.0), the result of which showed that the maximum
output was acceptable at pH 7.0 for nalbuphine
electrooxidation. The CV responses from electro-
chemical oxidation (150.0 lM) for nalbuphine in
0.1 M PBS (pH 7) on unmodified SPGE (curve a)
surface were compared with Fe
2
MoO
4
/SPGE (curve
b) surface using electrochemical tests, as shown in
Fig. 5. The voltammograms exhibited a main differ-
ence in the shift of background current magnitude
and potential value. The peak potential of nalbuphine
oxidation on unmodified SPGE surface was elevated
than that on Fe
2
MoO
4
/SPGE surface. Moreover, the
anodic peak current for nalbuphine oxidation on
unmodified SPGE surface was significantly declined
than that on Fe
2
MoO
4
/SPGE surface. No cathodic
peaks were found in the reverse scan for nalbuphine
at the pH value of 7.0 on the both unmodified and
Fig. 5 The cyclic voltammogram of aSPGE and bFe
2
MoO
4
/
SPGE in 0.1 M PBS (pH 7.0) in the presence of 150.0 lM
nalbuphine at the scan rate 50 mV s
-1
Fig. 6 The LSVs of Fe
2
MoO
4
/SPGE in 0.1 M PBS (pH 7.0)
consisting of 100.0 lM nalbuphine at diverse scan rates. a–g10,
25, 50, 75, 100, 200 and 300 mV s
-1
. Inset: variation of anodic
peak current vs. m
1/2
Fig. 7 LSV (at 10 mV s
-1
) of electrode in 0.1 M PBS (pH 7.0)
containing 100.0 lM nalbuphine. The points are the data used in
the Tafel plot (inset)
J Mater Sci: Mater Electron

modified SPGE surface. The catalytic impact of Fe
2-
MoO
4
nanocomposite was confirmed by the
improved electrochemical activity for nalbuphine
oxidation.
3.3 Effects of the scan rates on the results
The cyclic voltammetry method was performed to
assess the scan rate effect on electrochemical behavior
of 100.0 lM nalbuphine in 0.1 M PBS (pH 7.0). As
seen in Fig. 6. A shift of the scan rate for nalbuphine
from 10 to 300 mV/s caused an oxidation current
elevation and a slight positive change of oxidation
peak potential. The plot of oxidation peak current (I
p
)
versus scan rate square root (m
1/2
) was drawn for the
nalbuphine. A diffusion-controlled oxidation process
was verified for nalbuphine based on the linear
relationship observed between the anodic peak cur-
rent and m
1/2
.
In the next step, the Tafel plot that corresponded to
the linear sweep voltammetric curve with the
increased sharp at 10 mV s
-1
scan rate is depicted in
Fig. 7. Moreover, the numbers of electron involved in
the rate determining step may be approximated
according to the Tafel-slope under rapid de-proto-
nation step of nalbuphine. This Tafel slope has been
specified as 0.1269 V, revealing that the rate deter-
mining step contains 1 electron in the electrode pro-
cedure, considering 0.53 for charge transfer
coefficient (a).
3.4 Chronoamperometric analyse
The scan rate findings confirmed a diffusion process
for nalbuphine electrooxidation on modified elec-
trode surface, which made us to calculate the diffu-
sion coefficient by chronoamperometric technique for
the nalbuphine. As shown in Fig. 8, a potential of
450 mV as a potential step was selected to record the
chronoamperograms. In addition, Cottrell equation is
proposed in the case of the chronoamperometric
analyses of electroactive moiety in the basis of the
mass transfer restricted states [74]:
Fig. 8 Chronoamperograms
achieved at Fe
2
MoO
4
/SPGE in
0.1 M PBS (pH 7.0) for
distinct concentration of
nalbuphine. a–e refer to 0.1,
0.7, 1.2, 1.6 and 2.0 mM of
nalbuphine. Insets: (A) I plot
vs. t
-1/2
achieved from
chronoamperograms ato
e. (B) The slope plot of
straight lines versus
nalbuphine concentration
J Mater Sci: Mater Electron

I¼nFAD1=2Cbp1=2t1=2
where Iis current (A), Dis the diffusion coefficient
(cm
2
s
-1
), C
b
is the bulk concentration of analyte (mol
cm
-3
), Ais the surface area of the electrode (cm
2
), Fis
Faraday’s constant, tis the time (s), and nis the
number of electrons transferred.
Figure 8a demonstrated experimental outcomes of
Ivs. t
-1/2
, showing the most proper fit for various
concentrations of nalbuphine. Then, the resultant
straight lines slopes were drawn vs nalbuphine con-
centration (Fig. 8b). Hence, Dmean value equaled to
7.4 910
–6
cm
2
/s with regard to Cottrell equation and
resultant slopes.
3.5 Calibration curve
The DPV technique for modified electrode was per-
formed to measure the electrode activity of nal-
buphine detection (Fig. 9). Increasing the added
concentrations from 0.02 to 250.0 lM elevated the
characteristic peak current of nalbuphine in 0.1 M
PBS. In fact, increasing the nalbuphine concentrations
has enhanced the oxidation peak currents. Figure 9
(inset) shows the plot related to the relationship of
peak current as a function of nalbuphine
concentration, indicating an acceptable linearity
(Linear range: 0.02 to 250.0 lM) with a linear equa-
tion of I= 0.0744C
nalbuphine
?1.4395. Moreover, the
LOD of nalbuphine is 8.0 nM. In the case of diclofe-
nac peak currents of diclofenac oxidation at the sur-
face of Fe
2
MoO
4
/SPGE were linearly dependent on
the diclofenac concentrations, over the range of
1.0–400.0 lM and the detection limit was obtained
0.4 lM.
3.6 Simultaneous determination
of nalbuphine and diclofenac
The analysis was performed to assess the applica-
bility of Fe
2
MoO
4
/SPGE for simultaneous detection
of nalbuphine and diclofenac in 0.1 M PBS (pH 7.0).
The DPV oxidation peak currents were enhanced
linearly with co-elevation of nalbuphine and
diclofenac concentrations, almost with no change in
their oxidation peak potentials (Fig. 10). Moreover,
two distinct separated oxidation signals were found
for nalbuphine and diclofenac based on the differ-
ence in their pulse voltammograms at 400 and
540 mV respectively, which were enough for their
simultaneous detection on the modified electrode
surface. The analysis sensitivity was estimated at
0.0741 lAlM
-1
for nalbuphine, indeed very close to
pure nalbuphine solutions (0.0744 lAlM
-1,
see
Fig. 9), which means the method selectivity. In
addition, in the presence of both analytes (nal-
buphine and diclofenac) the linear dynamic ranges
were obtained in the ranges of 2.5 to 200.0 lM and 3.0
to 300.0 lM for determination of nalbuphine and
diclofenac, respectively. The LODs were obtained
0.6 lM and 0.8 lM for measurement of nalbuphine
and diclofenac, respectively.
3.7 Repeatability, reproducibility,
and stability of Fe
2
MoO
4
/SPGE
The peak currents of DPV tests of nalbuphine
(25.0 lM) for 15 times were calculated and compared
to assess the Fe
2
MoO
4
/SPGE repeatability. The
acceptable repeatability of the modified electrode was
proved in accordance with the relative standard
deviation (RSD) of 2.5%.
The Fe
2
MoO
4
/SPGE reproducibility for 25.0 lM
nalbuphine was examined by six sensors under the
same condition, the result of which showed the RSD
Fig. 9 Differential pulse voltammograms of Fe
2
MoO
4
/SPGE in
the 0.1 M PBS (pH 7.0) consisting of distinct concentrations of
nalbuphine. a–krefer to 0.02, 0.2, 2.5, 7.5, 15.0, 30.0, 70.0,
100.0, 150.0, 200.0 and 250.0 lM of nalbuphine. Inset: the peak
current plot as a function of nalbuphine concentrations ranging
between 0.02 and 250.0 lM
J Mater Sci: Mater Electron

Fig. 10 Differential pulse
voltammograms of Fe
2
MoO
4
/
SPGE in 0.1 M PBS (pH 7.0)
with diverse amounts of
nalbuphine and diclofenac.
Curves a–grelated to
2.5 ?3.0, 15.0 ?20.0,
30.0 ?50.0, 70.0 ?100.0,
100.0 ?150.0,
150.0 ?225.0, and
200.0 ?300.0 lMof
nalbuphine and diclofenac.
Insets: (A) plot of I
p
against
nalbuphine concentrations,
(B) plot of I
p
versus the
amount of diclofenac
concentrations
Table 1 Detection of nalbuphine and diclofenac in real samples. Whole considered concentrations are expressed in lM(n=5)
Sample Spiked Found Recovery (%) R.S.D. (%)
Nalbuphine Diclofenac Nalbuphine Diclofenac Nalbuphine Diclofenac Nalbuphine Diclofenac
Nalbuphine ampoule 0 0 4.0 – – – 3.5 –
1.0 5.0 4.9 5.1 98.0 102.0 2.7 1.9
2.0 7.0 6.1 6.8 101.7 97.1 2.4 3.1
3.0 9.0 7.3 8.9 104.3 98.9 1.9 2.3
4.0 11.0 8.1 11.1 101.2 100.9 3.0 2.8
Diclofenac tablet 0 0 – 5.0 – – – 2.7
5.0 1.0 5.1 5.8 102.0 96.7 3.6 2.1
7.5 2.0 7.4 7.1 98.7 101.4 1.7 3.3
10.0 3.0 10.1 7.8 101.0 97.5 2.6 1.9
12.5 4.0 12.2 9.3 97.5 103.3 2.3 2.8
Urine 0 0 – – – – – –
6.0 4.0 6.2 3.9 103.3 97.5 2.4 1.7
7.0 6.0 6.9 6.1 98.6 101.7 3.0 2.6
8.0 8.0 7.8 8.3 97.5 103.7 2.9 2.3
9.0 10.0 9.1 9.9 101.1 99.0 2.1 3.3
J Mater Sci: Mater Electron

value of 2.2%, indicating acceptable reproducibility of
the modified electrode.
The Fe
2
MoO
4
/SPGE stability in the PBS at pH 7.0
for 15 days was tested by recording the DPV of nal-
buphine solution (25.0 lM) in comparison with pre-
immersion DPV values. There was no change in
nalbuphine oxidation peak that was a less than 2.4%
reduction in signal in comparison with previous
responses to current, which means acceptable stabil-
ity of the modified electrode.
3.8 Analyzing the real samples
The Fe
2
MoO
4
/SPGE practically was used to estimate
applicability for detection of different concentrations
of nalbuphine and diclofenac in nalbuphine injection,
diclofenac tablet and urine using the DPV responses.
The standard addition method was applied for
quantitatively analysis of the solutions. The results
showed the recoveries of 96.7–104.3, as seen in
Table 1, indicating successfully practical applicability
of the fabricated electrode.
4 Conclusion
A novel voltammetric sensor based on Fe
2
MoO
4
magnetic nanocomposite was used for simultaneous
determination of nalbuphine and diclofenac. The
sensor was fabricated using Fe
2
MoO
4
nanocomposite
for modification of SPGE. The Fe
2
MoO
4
/SPGE
exhibited a synergetic impact on the oxidation of
nalbuphine. The peak current of oxidation was
raised, and the oxidation peak potential of nal-
buphine was declined on the prepared sensor sur-
face. Using the Fe
2
MoO
4
/SPGE, nalbuphine and
diclofenac could be measured simultaneously. Two
well-separated oxidation peaks were observed in a
mixed system containing nalbuphine and diclofenac;
the nalbuphine and diclofenac potential separation
was 140 mV, owing to the synergistic effect of Fe
2-
MoO
4
nanocomposite. Also, the prepared sensor
demonstrated acceptable stability, repeatability and
reproducibility. At finally, this sensor has been suc-
cessfully applied for detection of nalbuphine and
diclofenac in their pharmaceutical and biological
samples with satisfactory recoveries.
Acknowledgements
The authors sincerely thanks the Islamic Azad
University, Bam Branch, for the financial support of
this work.
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