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Methods and objects of chemical analysis, 2021, Vol. 16, No. 2, 103–111
Voltammetric Determination of Paracetamol in Pharmaceutical
Formulations at Iodine-Coated Polycrystalline Platinum Electrode
† ‡ §
Mohammad Amayreh* , Wafa Hourani , Mohammed Khair Hourani
† Department of Chemistry, Faculty of Science, Al-Balqa Applied University, P.O. Box 19117, Al-Salt, Jordan; *e-mail:
mohammad.amayreh@bau.edu.jo
‡ Faculty of Pharmacy, Philadelphia University, Amman, Jordan
§ Department of Chemistry, the University of Jordan, Amman, Jordan
Recieved: April 05, 2021; Accepted: May 31, 2021
DOI: 10.17721/moca.2021.103-111
Copyright © 2021 Amayreh Mohammad et al. Open access article distributed under the Creative Commons
Attribution License CC BY 4.0.
In this work the modified iodine-coated polycrystalline platinum electrode was used to develope a voltammetric
sensor for paracetamol determination in pharmaceutical formulations. The optimized experimental parameters for
the determination of paracetamol were using 0.5 M H SO as a supporting electrolyte with a scan rate of 50 mV/s.
2 4
The anodic peak related to paracetamol oxidation was centered at about +0.60 V. The extended calibration graph
2
was constructed between 1 ppm and 500 ppm. The anodic current showed excellent linearity with R = 0.9985. The
limit of detection (LOD) and limit of quantitation (LOQ) were 0.046 and 0.139 ppm, respectively, which attests to
the sensitivity of the method. The investigation for the effect of potential interferences from the content of tablet
matrices indicated a specific selectivity toward paracetamol and the absence of any electrochemical response
toward these components. The developed method was successfully applied to analysis paracetamol in three
brands of pharmaceutical formulations and the obtained results were in good agreement with the labeled values,
besides that, the statistical tests indicated no significant difference at p = 0.05 with a 95 % confidence level.
Keywords: paracetamol, pharmaceutical formulation, voltammetric analysis, iodine-coated platinum electrode,
modified platinum electrode
Determination of paracetamol in pharmaceutical surface. Where the adsorbed iodine monolayer at
formulations is of great importance. Paracetamol platinum electrode surface transforms the highly
(acetaminophen) is one of the most common drugs reactive surface to an apparent passive electrode with
around the world used for relief fever, headaches, a low current background [25].
and minor pain [1]. Also, paracetamol is renowned Iodine is one the anions simply adsorbed to
as multimodal analgesia with excellent safety profile electrode surface. The chemisorptions process can be
except in significant overdoes [2] .Since paracetamol achieved by two ways; from solution or from vacuum to
found solely or in combination in pharmaceutical form stable chemisorbed mono layers even the iodine
formulation, it is a paramount important to have a coated electrode would be rinsed or evacuated [26].
simple, fast, sensitive, and selective analytical method The iodine is adsorbed at potential 0.2 V (double layer
for routine analysis of this compound. potential) vs. Ag/AgCl or SCE reference electrodes
A numerous analytical methods have been [27]. At the surface of polycrystalline platinum
reported for paracetamol determination in pharma- electrode an oxidation reaction of iodine anions
ceutical formulations. These methods include, from solution leads to spontaneous chemisorption of
potentiometry [3-7], high performance liquid iodine anion to form stable neutral iodine atoms at
chromatography [8-13], and spectrophotometry [14] . the electrode surface accompanied by hydrogen gas
These reported methods have some limitations such evolution. The adsorbed iodine is less reactive toward
as instruments, skills, cost, and the environment. electrochemical oxidation compared with the free
In contrast to these traditional methods, the iodine anion in solution [28]. The chemisorbed iodine
electrochemical methods have attracted much can be desorbed from platinum electrode surface if
attention due to the low sensitivity toward the matrix the potential scanned lower than - 0.2 V which lead to
effects compared to other analytical techniques reduction of hydrogen ions and generation hydrogen
[15]. Also, the electroanalytical methods offer many gas [28]. Also the rate of iodine desorption from
advantages such as simple analysis procedures, electrode surface increase as the potential become
environmentally–friendly chemical reagents. Many more negative [29]. At the positive direction, the
voltammetric methods based on modified electrodes chemisorbed iodine begins to be desorbed at potential
have been reported for paracetamol determination 1.0 [27]. Carbon monoxide is completely desorbed
in pharmaceutical tablets [16-24]. The Iodine-coated iodine from platinum electrode surface at potential
platinum electrode considers as a typical example for lower than 0.35 V while at higher potential incomplete
the modification of a highly reactive platinum electrode desorption is occurred [30].
Mohammad Amayreh, Wafa Hourani, Mohammed Khair Hourani 103
Voltammetric determination of paracetamol in pharmaceutical formulations at iodine-coated polycrystalline platinum electrode
Iodine-coated platinum electrodes have been in 0.5 M H SO + 10-2 M KI solution for five minutes
2 4
applied for the electrochemical quantification of under closed-circuit potentiostatic conditions in the
some species in aqueous solutions with and without double layer region (~ 0.2 V) to accomplish dosing
further modification. A furtherly modified iodine- of the platinum electrode surface with iodine. After
coated platinum electrode with quanternized poly(4- that the electrode was subjected to multiple rinses
vinylpyridine), qPVP by Cox and Kulesa was used for with water and 0.5 M H SO solution, and then
2 4
analysis of nitrite [31]. Amayreh and co-workers have the electrode potential was cycled in supporting
used the iodine-coated electrode for the analysis of electrolyte solution between -0.2 V and +0.8 V at
iron(II) [32, 33] and copper(II) [34]. 50 mv/s to confirm the completeness of the coating
Iodine-coated platinum electrode is characterized process (Fig.1). The absence of oxygen and hydrogen
by the simplicity in preparation, application, and adsorption/desorption peaks from the recorded
the absence of the need for environmentally cyclic voltammogram of an iodine-coated platinum
unfriendly chemical reagents. The simplicity of the electrode provides a conclusive evidence for the
instrumentations all stimulated the implementation complete coverage of platinum electrode surface with
of the present work. This work was undertaken with a monolayer of iodine.
the main objective of method development for Standard solution preparation. A 1000 ppm of
voltammetric analysis of paracetamol at iodine-coated paracetamol stock solution was prepared by dissolving
platinum electrode in pharmaceutical formulations. a 0.1g of paracetamol (151.163 g/mol) in 100mL of
0.5 M H SO . A working solution of different concen-
Experimental part 2 4
trations of paracetamol, 1, 10, 50, 100, 200, 300, 400,
Chemicals and reagents. The following reagents and 500 ppm in 0.5 M H SO were prepared through a
2 4
along with their suppliers were used in the present serial dilution procedure.
work: Sulfuric acid (95-97 %, Merck), paracetamol Sample preparation. The pharmaceutical
(99.8 %, Merck), potassium iodide (Sigma-Aldrich). formulation samples (Paracetamol commercial
Milli-Q water (Millipore) was used for preparation of tablets), Revanin (Jordan), Panda (Jordan),
all solutions. The nitrogen gas was a five-G grade, and Myogesic (Jordan) were purchased from
99.999 % minimum purity supplied from International Jordanian local drug stores. The selected brands of
Jordanian Gases Company (Amman, Jordan). All pharmaceutical formulations were analyzed for their
used chemicals and reagents were of analytical grade paracetamol content. The tablet of each brand was
and used without further purification. powdered using porcelain mortar and dissolved in
Apparatus. A potentiostat (PAR Model 362, warm 50.0 mL of 0.1 M H SO supporting electrolyte
2 4
EG & G) interfaced to a computer via GPIB interface to ensure complete dissolution of paracetamol.
(IEEE) equipped with a locally modified Labview® The solution of the samples was sonicated for
(IEEE) software was used for data acquisition and 5 minutes and left to equilibrate for 10 minutes. Then,
experimental control. A one-compartment electro- the solution was filtrated through a 0.45 µm Millipore
chemical cell with an inlet/outlet system for deo- filter and transferred to 100 mL volumetric flask and
xygenation and blanketing with highly pure nitrogen diluted to the mark. The stock solutions were kept in
was used. A 0.5 mm polycrystalline platinum wire the refrigerator for succeeding analysis. An aliquot
purchased from Aldrich (99.99 % minimum purity of this solution was diluted to 50.00 mL with 0.1 M
certified reagent) was used as a working electrode. The HSO to be within the constructed calibration curve
2 4
immersed end of the platinum electrode was curved concentrations’ range. A 10.00 mL of the diluted
at the end to make a mark for a consistent surface solution was placed in the electrochemical cell. The
area of the immersed part of the electrode. A silver/ solution was deaerated with nitrogen gas and kept
silver chloride wire was used as a quasi-reference under a nitrogen gas atmosphere during conducting the
electrode (QRE). The used auxiliary electrode was a voltammetric measurements. Voltammetric analysis of
0.5 mm polycrystalline platinum wire (Aldrich, certified the commercial tablets for their paracetamol content
99.99 % minimum purity). was conducted at the iodine-coated electrode within
Preparation of iodine-coated platinum electrode. a potential window -0.2 V to 0.8 V where the adsorbed
Preparation of iodine-coated platinum electrode was iodine is stable within this potential range.
described in one of our earlier publications [32], These Results and discussions
preparation steps include a cyclization of a platinum
electrode placed in of 0.5 M H SO between - 0.25V and Electrochemical oxidation of paracetamol and
2 4
1.3 V until getting a reproducible cyclic voltammogram method validation
of polycrystalline platinum electrode with the well- Initially, as presented in Figure 1-a, a reproducible
known oxygen and hydrogen adsorption/desorption cyclic voltammogram for polycrystalline platinum
features, which is indicative of the cleanliness of the electrode was obtained which confirms the cleanness
electrode surface and electrochemical cell contents of all components of the electrochemical system. On
(Fig.1). the other hand, the cyclic voltammogram of the iodine-
Thereafter, the clean electrode was immersed coated electrode (Fig.1-b) indicates a complete and
104 Methods and objects of chemical analysis, 2021, Vol. 16, No. 2, 103–111
Mohammad Amayreh, Wafa Hourani, Mohammed Khair Hourani
successful as witnessed by absence of any surface 150
activity in the scanned potential range (- 0.2 – 0.80 V).
The complete absence of hydrogen and oxygen 100
reduction features is the main evidence for complete A 50
coverage of the platinum surface. The potential scan µ
/
was limited to the above-mentioned range to avoid t 0
n
desorption of iodine from the platinum surface. The rre
adsorbed iodine is stable toward rinsing with acidic or Cu-50
neutral supporting electrolytes. Also, the iodine-coated -100
platinum electrode does not need to regenerate before 0.1 M KCl 0.1 M H2SO4 Phosphate Buffer, pH=3.5
each measurement where scanned potential window -150
should between -0.2 and 1.0 V, which indicates to -0.2 0 0.2 0.4 0.6 0.8
reliability of using the electrode for daily routine Potential/V vs. Ag/AgCl
analysis.
140
800 120 117.7±1.73
600 100.31±1.83
100 87.82±3.56
A 400 µA
µ A / 80
nt/200 ent
e r 60
r 0 ur
ur B C 40
C -200
20
-400
-600 0
0.5M H2SO4 Phosphate 0.1M KCl
-800 buffer
-1 -0.5 0 0.5 1 1.5 Fig. 2. Effect of type of supporting electrolyte on the
Potential /V vs. Ag/AgCl electrochemical signal of paracetamol at iodine-
Fig. 1. Cyclic voltammogram curves of (a) poly- coated platinum electrode, Paracetamol; 100 ppm,
crystalline platinum electrode and(b) the same HSO; 0.5 M, phosphate buffer; pH=3.5; KCl, 0.1 M;
-2 2 4
electrode after adsorption of iodine from 1x10 MKI in n = 3; scan rate, 50 mV/sec.
0.5 M H SO solution.
2 4 The effect of scan rate from 10 mV/s to 100 mV/s
The effect of pH on the iodine coating on platinum on the paracetamol peak current was evaluated. As
electrode has been reported elsewhere [35] where it presented in Figure 3, there is a linear relationship
has been found that iodine coating is unstable upon between the square root of scan rate and the oxidation
cyclization in basic solution [36] . This fact limits usage peak current of paracetamol: y = 14.798 x - 10.932;
2
of iodine-coated electrode to acidic solutions only. The (R = 0.9976), which indicates that the oxidation
effect of the pH in the acidic range was investigated by process is a diffusion-controlled process.
following the effect of pH change on the peak current 200
for paracetamol oxidation. Three representative pH ―10mv/sec
values; 7, 3.5 and 0.3 were selected to demonstrate 150 ―20 mv/sec
the effect of solution acidity on the analytical signal
(peak current). Paracetamol standard solution was A 100 ―50 mv/sec
analyzed in 0.5 M H SO (pH = 0.3), phosphate µ
/
2 4 t
buffer (pH = 3.5), and 0.1M KCl (pH = 7) media. n 50
Figure 2 shows the effect of pH on the paracetamol rre
oxidation current peak. As displayed in Figure 2, the Cu 0
value of the oxidation peak current of paracetamol -50
decreases with increasing pH. Thereafter, 0.5 M
HSO was considered as a supporting electrolyte -100
2 4
for determination of paracetamol the following -150
study. This might be attributed to the experimentally -0.2 0 0.2 0.4 0.6 0.8
evidenced observation that the protonated form of Potential /V vs. Ag/AgCl
the paracetamol is more easily oxidized than the
deprotonated form [37].The ease of oxidation of the Fig. 3. Cyclic voltammograms of iodine-coated
protonated form of paracetamol is revealed by the platinum electrode in 0.5M H SO containing 50 ppm
2 4
shift in paracetamol peak potential with increasing pH of paracetamol at various scan rates: 10, 20, 50, and
of the medium. 100 mv/s.
Methods and objects of chemical analysis, 2021, Vol. 16, No. 2, 103–111 105
Voltammetric determination of paracetamol in pharmaceutical formulations at iodine-coated polycrystalline platinum electrode
The obtained cyclic voltammograms for iodine- 700
coated platinum electrode in a series of paracetamol Y = 1.1517X+1.0592
2
standard solutions show that the oxidation current 600 R = 0.9985 572 ± 10
increases linearly with paracetamol concentration.
Three voltammograms were recorded for each 500
standard solution and the dimensions of each point A 465 ± 2
were displayed in Figure 4. The anodic peak current µ400
/
was extracted for each cyclic voltammogram. nt 355 ± 2
e
r
ur300
600 C
―50 ppm 200 212 ± 3
500 ―100 ppm
100 113 ± 2
400 ―200 ppm 56 ± 2
A —300 ppm 12 ± 1
µ 300 0 6 ± 1
/ ―400ppm 0 100 200 300 400 500 600
nt
e 200 Concentration (ppm)
r
Cur100 Fig. 5. An extended calibration curve shows the
0 relationship between paracetamol concentration
in ppm and the oxidation peak current measured
-100 from cyclic voltammograms for paracetamol in
0.5 M H SO at iodine-coated platinum electrode.
-200 2 4 -1
-0.2 0 0.2 0.4 0.6 0.8 Scan rate = 50 mv.s .
Potential /V vs.Ag/AgCl Where paracetomol is a phenolic compound that
Fig. 4. Cyclic voltammograms of iodine-coated undergoes electrochemical oxidation by electrolytic
platinum electrode in 0.1 M H SO solution containing etching on the aromatic ring with irreversible removal
2 4 of two electrons and two protons, producing N-ace-
50, 100, 200, 300 and 400 ppm of paracetamol. All the tyl-p-quinoneimine according to the mechanism
scans were recorded at a scan rate of 50 mV/s.
shown in equation [37] :
Figure 5 shows a representative part of the cyclic
voltammograms recorded for a standard solutions O OH O
of paracetomol used for construction calibration +2e- +2H+
curve. The established calibration curve between H C N + 2e- + 2H+
HC N 3
concentrations of 50, 100, 200, 300 and 400 ppm 3 H
and the current values extracted from the recorded
cyclic voltammograms shows a linear relationship with
2
regression value of R = 0.986. O
Plotting the anodic peak current variation against
paracetamol concentration give a straight and The inter-and intra-day precision was estimated
extended dynamic range with a concentration ranging by extracting the current values for four different
from 1.0 ppm to 500.0 ppm. The calibration curve paracetamol standard solutions sample between 10
displayed in Figure 5 shows remarkable linearity;
2 and 200 ppm. The standard deviation was found to be
R = 0.9985, and the calibration equation is given by within 0.49 and 2.79 for five successive determinations
I = (µA) = 1.1517 Cparacetamol+ 1.0592 for each concentration. The measured values of
where I represents the anodic peak current, which standard deviation attest to the high repeatability for
attributed to the paracetamol oxidation. both of inter-and intra-day measurements.
The limit of detection based on the formula
The 95 % confidence intervals (α = 0.05, 6 degrees LOD = 3.3Ϭ/S, and limit of quantitation based on the
of freedom) for the slope and y-intercept are formula LOQ = 10Ϭ/S, where Ϭ represents the blank
β1=b ± ts = 1.15 ± 2.5 x 0.0232 = 1.152 ± 0.057 signal (background current) and S represents the
1 b1 sensitivity of the calibration curve was calculated
β2=b ± ts = 1.059 ± 2.5 x 5.90 = 1.0 ± 14 [38]. The estimated limits were 0.046 ppm and 0.139
0 b0
ppm respectively. Acceptable sensitivity of the applied
method with high precision was obtained. A higher
sensitivity can be achieved by application of a more
sensitive technique like differential pulse voltammetry.
Differential pulse voltammetry, however, was not
106 Methods and objects of chemical analysis, 2021, Vol. 16, No. 2, 103–111
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