MWCNT-CTAB modified glassy carbon electrode as a sensor for the determination of paracetamol

Article abstract of DOI:10.1039/c5ra05802c

An electrochemical sensor for the sensitive detection of paracetamol (PCM) was developed by constructing a glassy carbon electrode (GCE) modified with multiwalled carbon nanotube-cetyltrimethyl ammonium bromide (MWCNT-CTAB). Modification improves the redox kinetics of PCM with increased current intensity. A similar modification at CTAB modified GCE did not result in an impressive charge transfer. The detection limit of PCM was determined from a differential pulse voltammetric (DPV) study and found to be 4.82 × 10^-9 M with a linear dynamic range of 4.0 × 10^-7 M to 4.0 × 10^-6 M. The interference studies showed that the modified electrode exhibits excellent selectivity in the presence of a large excess of interferents and the response is fast, stable, reliable, resistant to biofouling and can be applied for real sample analysis in medical, pharmaceutical and biotechnological sectors. Kinetic parameters were determined using electrochemical approaches. The practical analytical application of this electrode was demonstrated by measurement of the PCM content in a PYREMOL 650 tablet and real sample analysis.

Full text of DOI:10.1039/c5ra05802c

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Page 1 of 27
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DOI: 10.1039/C5RA05802C
MWCNT-CTAB modified glassy carbon electrode as a sensor for the
determination of paracetamol
Jayant I. Gowda, Danavva G. Gunjiganvi, Nagaveni B. Sunagar, Manjushree N. Bhat
and Sharanappa T. Nandibewoor*
P.G. Department of Studies in Chemistry, Karnatak University, Dharwad-580 003, India.
*Corresponding author: Tel.: +91 836 2215286; Fax: +91 836 2747884
E-mail : stnandibewoor@yahoo.com;
1

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DOI: 10.1039/C5RA05802C
MWCNTꢀCTAB modified glassy carbon electrode as a sensor for the
determination of paracetamol
Jayant I. Gowda, Danavva G. Gunjiganvi, Nagaveni B. Sunagar, Manjushree N. Bhat
and Sharanappa T. Nandibewoor*
P.G. Department of Studies in Chemistry, Karnatak University, Dharwad-580 003, India.
*Corresponding author: Tel.: +91 836 2215286; Fax: +91 836 2747884
Eꢀmail : stnandibewoor@yahoo.com;
Abstract
An electrochemical sensor for sensitive detection of paracetamol (PCM) was developed by
constructing the glassy carbon electrode (GCE) modified with multiwalled carbon nanotubeꢀ
cetyltrimethyl ammonium bromide (MWCNTꢀCTAB). Modification improves the redox kinetics
of PCM with increased current intensity. A similar modification at CTAB modified GCE did
not result in an impressive charge transfer. Detection limit of PCM was determined from
differential pulse voltammetric (DPV) study and found to be 4.82×10−9 M with a linear
dynamic range of 4.0×10−7 M to 4.0×10−6 M. The interference studies showed that the
modified electrode exhibits excellent selectivity in the presence of large excess of
interferents and response is fast, stable, reliable, resistant to biofouling and can be applied
for the real sample analysis in medical, pharmaceutical and biotechnological sectors.
Kinetic parameters were determined using electrochemical approaches. The practical analytical
application of this electrode was demonstrated by measurement of PCM content in
PYREMOL 650 tablet and real sample analysis.
Keywords: Voltammetry, Modified electrode, Paracetamol, Electroꢀoxidation, Pharmaceutical
analysis
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1. Introduction
Sensors based on multiꢀwalled carbon nanotubes (MWCNTs) were widely used in
various electrochemical applications in the last years, since they display numerous advantages,
such as great electrochemically accessible area, high electrical conductivity, extremely high
reactivity and selectivity, as well as great chemical stability[1]. Furthermore, it was recognized
that MWCNTs exhibit improved electric transport properties and electrocatalytic properties and
are capable to reduce the over potentials and to improve significantly the currents of redox
systems[2ꢀ4]. In addition, MWCNTs display high sensitivity and detection capability, and thus,
they improve the reaction rate and amplify the stability and reproducibility of electrode's
response[5]. Cetyltrimethylammonium bromide (CTAB), a cationic surfactant, often used as
an absorbent due to the strong hydrophobic interaction between the long alkyl chain of
CTAB. In this case, CTAB can be used as electrode modifier for enrichment of
MWCNTs on the electrode surface to improve sensitivity.
Paracetamol (Nꢀacetylꢀpꢀaminophenol or acetaminophen, PCM) is the most widely
used antipyretic and analgesic drug in the world[6]. It is not only an effective and safe
analgesic agent used for the relief of mild to moderate pain associated with headache,
arthritis, backache, toothaches and postoperative pain, but also used for reduction of
fevers of viral and bacterial origin[7,8]. Generally, paracetamol does not exhibit any harmful
side effects. However, abnormal level of paracetamol is believed to be associated with the
formation of some liver and nephrotoxic metabolites[9,10]. In addition, the use of
acetaminophen in children younger than one year may cause an increase in
hinoconjunctivitis, asthma, and eczema[11]. Therefore, determination of PCM in biological
samples and quality control in pharmaceuticals is very important considering the enormous
interest of PCM for therapeutic purposes.
Many analytical methodologies based on different principles, such as titrimetry[12],
spectrophotometry[13],
chromatography[14],
capillary
electrophoresis[15],
chemiluminescence[16] and flowꢀinjection analysis[17] have been developed for the analysis
of PCM. However, these methods require expensive instruments, long analysis time, highly
skilled technician and laborious sample pretreatment, which make them unsuitable for
routine analysis. Taking the above mentioned lacune and the high electroactivity of PCM
into consideration, electrochemical analytical techniques for PCM determination has been
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widely explored method due to simplicity, high sensitivity, low cost, easy operation and
possibility to miniaturization[18ꢀ21]. However, at traditional working electrodes, PCM
exhibit poor voltammetric response due to sluggish electrode kinetics[22]. Another problem
commonly encountered at bare electrode is that they get poisoned by several species and
decrease sensitivity and reproducibility. Hence, considerable efforts have been devoted to
modify the electrode for enhancing its voltammetric response and analytical performance [23ꢀ
36]. In the present work, the dispersion of multiwalled carbon nanotubes in the presence of
CTAB surfactant modified glassy carbon electrode was used as suitable sensor for the
determination of PCM. The proposed method was applied to pharmaceutical sample and real
samples.
2. Materials and methods
2.1. Reagents and chemicals
Paracetamol was purchased from s.d. fine Chem limited and multi walled carbon
nanotubes (MWCNTs) powders was purchased from Sigma Aldrich. Cetyltrimethylammonium
bromide was from Merck. A solution of paracetamol was prepared by dissolving an appropriate
amount of powdered sample in double distilled water. Double distilled water was used
throughout the work. All other solvents and materials used were of analytical grade.
2.2. Instrumentation and analytical procedure
The electrochemical experiments were performed with a CHI630D Electrochemical
analyzer with a three electrode system. A MWCNTꢀCTAB/GCE serves as the working electrode,
a platinum wire as the auxiliary electrode, and an Ag/AgCl (3.0 MKCl) as the reference
electrode, respectively. pH measurements were performed with Elico LI120 pH meter (Elico
Ltd., India). Experiments were carried out at room temperature.
The parameters for differential pulse voltammetry (DPV) were initial potential: 0.4V;
final potential: 1.4; increase potential: 0.004 V; amplitude: 0.05 V; frequency: 15 Hz; with time:
2 s; sensitivity:1×10ꢀ4 A\V.
2.3. Preparation of modified electrode
To get reproducible results, great care was taken in the electrode preꢀtreatment. The GCE
was preꢀtreated in two ways: (i) mechanical polishing over a velvet microꢀcloth with 0.3 and
0.05 m alumina slurry and (ii) electrochemical treatment by applying a potential of 1.25 V for 2
s. The electrochemical preꢀtreatment was done in the same supporting electrolyte solution in
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which the measurement was carried out. Solution containing 0.3 g/L MWCNTs and 0.2 g/L
CTAB was sonicated for 60 min. 10 µL of the sonicated solution was placed on the GCE surface
º
and then evaporating in an oven at 50 C. The ultrasonication of MWCNTs via CTAB will lead
to the dispersion of nanotubes, and fix the surfactants on the surface of MWCNTs (Possible
arrangements of CTAB on MWCNTs are illustrated in Supplementary Fig. S1[37]. It is
described that the cationic surfactant make the nanotubes positively charged; these charged
MWCNTs are driven toward cathode to form a thin layer at the electrode surface.
Eventually, the coated electrodes (MWCNTsꢀCTAB/GCE) were immersed in the
bicarbonate solution (0.01 M) for 30 min in order to extract the residual surfactants from the
surface of electrode. The modified electrodes were washed with distilled water and dried in room
temperature (MWCNTs–GCE). Fig. 1 shows surface morphology of photography AFM images
of MWCNT and MWCNTꢀCTAB.
“Here Figure 1”
2.4. Pharmaceutical sample preparation
Three tablets of containing paracetamol were weighed, powdered and then placed into a
250 ml of conical flask; warm water was added into the flask. The sample was swirled to
dissolve for 30 minutes in sonicator and left cool. The sample solution was filtered through a
filter paper (Whatman No.42) into 100 ml volumetric flask. The filtrate was make up to the
volume with 0.2 M phosphate buffer pH 7.4 for the direct calibration method and standard
addition method, respectively.
2.5. Plasma sample preparation
Human plasma sample was prepared as described in the earlier report of our work[38].
Human blood samples were collected in dry and evacuated tubes (which contained saline and
sodium citrate solution) from a healthy volunteer. The samples were handled at room
temperature and were centrifuged for 10 min at 1500 rpm for the separation of plasma within 1 h
of collection. The samples were then transferred to polypropylene tubes and stored at ꢀ20 ºC until
analysis. The plasma samples, 0.2 mL, were deprotonised with 2 mL of methanol. After
vortexing for 15 min, the mixture was then centrifuged for 15 min at 6000 rpm, and supernatants
were collected.
3. Results and discussion
3.1. Electrocatalytic response of PCM at the MWCNT-CTAB modified glassy carbon electrode
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Cyclic voltammetry was used to investigate the electrochemical behavior of paracetamol
on a MWCNTꢀCTAB/GCE in the phosphate buffer solution (0.2 M, pH 7.4) at a scan rate of 50
mV s−1. It can be seen that paracetamol shows a quasiꢀreversible redox behavior with relatively
weak redox peaks at the bare GCE, which indicates that the direct electron transfer of
paracetamol at the bare GCE is very slow. The redox peak currents are higher than that at the
bare GCE with Ipa/Ipc ≈ 1. The redox performs a quasiꢀreversible process because the
nanocomposite film of MWCNTꢀCTAB can accelerate the electrochemical reaction. It can be
seen from Fig. 2. that there is a large background current at the MWCNTꢀCTAB modified GCE,
which is caused by a larger surface area of the nanocomposite film on the GCE.
“Here Figure 2”
3.2. Effect of amount of MWCNT-CTAB suspension
We examined the effect of MWCNTꢀCTAB suspension amount on the electrochemical
behavior of PCM. The results suggested that amount of MWCNTꢀCTAB suspension influenced
the current responses of PCM. Supplementary Fig. S2 demonstrates the relationship between the
oxidation peak current of PCM and the amount of MWCNTꢀCTAB suspension used for coating
GC electrode. As can be seen, the peak current gradually increased with increasing the amount of
MWCNTꢀCTAB suspension from 0 to 10 ꢁL, owing to the increased effective electrode surface
area for PCM oxidation. Further increasing the amount of MWCNTꢀCTAB suspension, the peak
current almost remained stable. However, when it exceeded 14 ꢁL, the peak current slightly
decreased. When the coating film was too thick, the film no longer adhered tightly to the glass
carbon, reducing conductivity and part of the MWCNTꢀCTAB left the electrode surface. More
excessively coated amount of MWCNTꢀCTAB suspension led to less adherent film.
Accordingly, 10 ꢁL of MWCNTꢀCTAB suspension solution providing the maximum current
response was used in further experiments, while the amount of suspension of MWCNTꢀCTAB
had little effect on the oxidation potential of PCM.
3.3. Effect of pH
The electrochemical response of PCM at MWCNTꢀCTAB/GCE was generally dependent
on pH. The voltammograms of PCM were recorded at 0.2 M phosphate buffer solution of
different pH by cyclic voltammetric method. Fig. 3(a) demonstrates the pH dependence of PCM
at MWCNTꢀCTAB/GCE at sweep rate of 50 mV sꢀ1. Both anodic and cathodic peak potentials
were shifted to less positive side with increasing in the pH values. The anodic peak potential of
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PCM shifted from 0.547 to 0.238 mV with increase in the pH 3.0 –11.2. The potential diagram
was constructed by plotting the graph of Epa vs. pH of the solution (Fig. 3(b)). The graph shows
good linearity with a slope of 51 mV/pH this behavior is nearly obeyed the Nernst equation for
equal number of electron and proton transfer reaction[39, 40]. From the graph of Ipa vs. pH,
maximum current was obtained at pH 7.4 (Fig. 3(c)) and for further studies pH 7.4 was selected
for PCM determination.
“Here Figure 3 (a), 3(b), 3(c)”
3.4. Effect scan rate
The effect of scan rate on the electroꢀoxidation of PCM at the MWCNTꢀCTAB/GCE was
investigated by cyclic voltammetry to acquire information about electrochemical mechanism
from the relationship between peak current and scan rate of potential. The cyclic voltammograms
of 0.1 mM PCM at MWCNTꢀCTAB/GCE (Fig. 4(a)) were recorded at different scan rates from
0.025 to 0.4 V s−1, as well. The anodic (Ipa) and cathodic (Ipc) peak currents are found to be
linearly dependent on v at scan rates of 0.025 to 0.4 V s−1. A linear correlation is obtained
between the peak current and the scan rate, indicating that the redox process is controlled by
adsorption. The regression equations are Ipa(10ꢀ4A) = 1.764 + 55.401v (V s −1); R2= 0.991
and Ipc (10ꢀ4A) = 1.306 + 36.88 v (V s−1); R2 = 0.993 (Fig. 4(b)). From the plot of log Ip vs
log scan rate the slope values are nearly equal to the 0.5 of purely diffusion controlled process.
Hence the process is diffusion controlled (Supplementary Fig. S3).
The anodic and cathodic peak potentials are found to be linearly dependent on log v at
scan rates of 0.025 to 0.40 V s−1 (Fig. 4(c)). Two straight lines were obtained with two linear
regression equations as Epa(V) = 0.087 log v + 0.384; R2= 0.9916 and Epc (V) = −0.089 log v +
0.180; R2= 0.9918. Under these conditions, the ks can be obtained according to the
following equations[41];










2.303RT
(1ꢀαnF)
2.303RT
(1ꢀαnF)
nF(1ꢀα)
RTks
Epa = E0' +
logv+
log
(1)








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









2.303RT
(αnF)
2.303RT
(αnF)
α
RTks
nF
Epc = E0' −
logv ꢀ
log
(2)
(3)








α(1ꢀα)nFꢂEp
2.3RT
RT
logks = αlog(1ꢀα) + (1ꢀα)logα ꢀ log
ꢀ
nFv
According to the slopes of two curves (Epa vs. log v and Epc vs. log v) and Eq. (1) and Eq. (2), α
was calculated to be 0.51 and number of electrons (n) was 1.92 ≈ 2.0. With the Eq. (3), a value
of ks= 2.397 × 10ꢀ5 s−1 was obtained from all the extracted experimental data.
“Here Figure 4(a), 4(b), 4(c)”
3.5. Mechanism
UV spectrum of 0.1 mM PCM in 0.2 M phosphate buffer solution in pH 7.4 before and
after electrolysis are shown in Fig. 5. One absorption peak was found at 243.5 nm before
electrolysis (curve a). The electrolysis was carried out for 6 h. After depleting electrolysis, the
absorption peak at 243.5 nm slightly vanishes (curve b). We speculate that electro oxidation
might have lead to destruction of the pi bond conjugate system in PCM. This was also
supported by the earlier report[42]. The number of electrons and hydrogen ions transferred was
2. With all the previous experimental results, a possible electrode reaction mechanism for
PCM might be expressed as shown in Scheme 1.
“Here Figure 5”
“Here Scheme 1”
3.6. Analytical performance
3.6.1. Linearity range and detection limit using voltammetry
Under the optimized experimental conditions, the quantitative analysis of PCM was
carried out by the fabricated sensor. Since a large capacitive current existed in CV
measurements, the differential pulse voltammetry (DPV) was applied in this assay because its
charging current contribution to the background current is quite low. Fig. 6(a) shows the
dependence of the DPV oxidation peaks on the concentrations of PCM. It is found that with the
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increase of the PCM concentrations, the DPV oxidation signals enhance gradually, and an
excellent linearity is observed over a wide concentration range from 4.0 × 10−7 M to 4.0 ×
10−6M, Ipa (10ꢀ4A) = 2.47 [PCM](ꢁM) + 6.534 (R2=0.9894) (Fig. 6(b)). Based on the signalꢀtoꢀ
noise ratio (S/N) of 3, the detection limit was estimated to be 4.82 ×10−9 M and limit of
quantification was 1.60×10ꢀ8 M as shown in Table 1. Referring to the analytical performances of
some recently published reports[43ꢀ58](Table 2), it is found that the obtained detection limit in
this work is lower than other modified electrodes, which is likely related that MWCNTꢀCTAB
have high electrocatalytic and surface area effects. But, compared with the electrode modified
with the other materials like SWCNTs, MWCNTs, CPB/CNTP and C60, our developed method
shows the lower detection limit and the wider kinetic range, suggesting that the developed sensor
in this work can be served as a promising platform for the sensitive detection of PCM in low
concentration.
“Here Figure 6(a) 6(b)”
“Here Table 1”
“Here Table 2”
Additionally, a relative standard deviation of 2.5% for 1.0×10−3 M PCM (n=5) suggests
that the MWCNTꢀCTAB/GCE modified electrode has good reproducibility. Six electrodes
fabricated independently were used to determine 1.0×10−4 M PCM, and the relative standard
deviation is 3.0%, revealing an excellent repeatability of the electrode preparation. The stability
of the film electrode was evaluated by measuring the peak current of 1.0×10−4M PCM
repeatedly. It is found that after 40ꢀtimes test, the peak current deviates from its original response
only 5%.
3.6.2. Linearity range and detection limit using UV data
The working standard solutions for the drug PCM having concentration 2 to 150 µM
were prepared with phosphate buffer 7.4 from the stock solution. The linearity was determined
by plotting standard calibration curves for the concentration range 2ꢀ150 µM at 248 nm as shown
in Fig. 7(a,b). The limit of detection (LOD) and limit of quantifications (LOQ) of paracetamol
were evaluated from the slope (m) of their respective calibration curve and the standard deviation
of the blank (s) using equations as:
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LOD = 3s/m; LOQ = 10 s/m
Using the detection limit was estimated to be 3.39 ×10−6 M and limit of quantification was
1.13×10ꢀ5 M as shown in Table 1. Comparing the LOD values obtained by means of
spectroscopic and voltammetric technique, we achieved a lower detection limit for PCM by
voltammetric technique.
“Here Figure 7(a) 7(b)”
3.7. Determination of PCM in pharmaceutical preparations and recovery test
The proposed method was validated for the determination of PCM in pharmaceutical
preparations in “PYREMOL 650” tablets (650 mg per tablet) as a real sample by applying DPV
using the standard addition method. PYREMOL 650 tablets (Shiva Biogenetics Pharmaceuticals
Pvt. Ltd., India) labeled as containing 650 mg of PCM per tablet were weighed and ground to a
homogeneous fine powder in a mortar. A portion equivalent to a stock solution of a
concentration of about 0.01 M was accurately weighed and transferred into a 100 mL calibrated
flask and completed to the volume with doubly distilled water. The contents of the flask were
sonicated for 15 min to affect complete dissolution. Appropriate solutions were prepared by
taking suitable aliquots of the clear supernatant liquor and diluting them with the phosphate
buffer solution. Each solution was transferred to the voltammetric cell and analyzed by standard
addition method. The differential pulse voltammograms were recorded between 0 and 0.5 V. The
oxidation peak current of PCM was measured at scan rate of 50 mV sꢀ1. To study the accuracy of
the proposed method and to check the interferences from excipients used in the dosage form,
recovery experiments were carried out. The concentration of PCM was calculated using the
standard addition method. The results are in good agreement with the content marked in
the label (Table 3).
“Here Table 3”
3.8. Interference study
The potential interference for the determination of PCM was also studied. Under the
optimized conditions, the oxidation peak of 1.0×10−6 M PCM was individually measured in the
presence of different concentrations of the common interferents, and then the change of peak
current was checked. It is found that glucose, citric acid, dextrose, gum acacia, oxalic acid,
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starch, tartaric acid almost have no influence on the detection of PCM since the peak current
change is below 5%, however gum acacia had apparent influence on the voltammetric signal of
PCM(Table 4), revealing that this sensor has good selectivity for PCM determination.
“Here Table 4”
3.9. Application to real matrices
To evaluate the applicability of the present method on real matrices, assays were
performed in serum and urine samples. To ascertain the validity of the results, the real samples
were spiked with certain amount of PCM. The results showed that satisfactory recovery for PCM
could be obtained (Table 5).
“Here Table 5”
4. Conclusion
A novel method is described for the determination of paracetamol which is simple, quick
and sensitive with a low cost analysis. A comparison of the voltammetric response of
paracetamol at bare GCE, MWCNT modified GCE and MWCNTꢀCTAB modified GCE clearly
revealed that MWCNT in presence of CTAB acts as a better surface modifier in comparison to
MWCNT at fixed concentration of nanotubes in mg/mL of the solvent. Such a deposition imparts
different effective surface areas to electrodes. The sensitivity at MWCNTꢀCTAB modified GCE
was found to be ∼1.5 times more in comparison to MWCNT modified GCE with a lower
detection limit. The quantitative evaluation of the compound was carried out in the range of 0.4–
4.0 µM with a detection limit of 4.92×10−9 M at MWCNTꢀCTAB modified GCE. To the best of
our knowledge, this limit of detection is the lowest value reported for paracetamol using
electrochemical techniques. The MWCNTꢀCTAB modified GCE exhibited a stable and
reproducible response for paracetamol determination without any influence of physiologically
common interferents. The usefulness of the method was demonstrated by applying it to the
analysis of pharmaceutical preparations and human urine and plasma samples. Thus, the
proposed method using differential pulse voltammetry is of beneficial use in analytical
applications and in fundamental studies of electrode mechanisms.
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Fig. 1. AFM topography of (A) MWCNTs, (B) MWCNTꢀCTAB sample
(A). AFM image of GCE surface modified with MWCNTs
(B). AFM image of GCE surface modified with MWCNTꢀCTAB
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Fig. 2. Cyclic voltammograms obtained for 0.1 mM paracetamol at pH 7.4 at (a) bare GCE,
(b) MWCNT modified GCE and (C) MWCNTꢀCTAB modified GCE at 50 mV s−1.
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Fig. 3(a). Influence of pH (aꢀi : 3.0ꢀ11.2) on the shape of anodic peak of 1.0 ×10ꢀ4 M PCM on
MWCNTꢀCTAB/GCE at scan rate of 50 mV sꢀ1 in phosphate buffer.
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Fig. 3(b). Influence of pH on the potential of 1.0×10ꢀ4 M PCM on MWCNTꢀCTAB/GCE at
scan rate of 50 mV sꢀ1 in phosphate buffer.
0.6
0.5
0.4
0.3
0.2
y = ꢀ0.051x + 0.635
R² = 0.971
0.1
0
0
2
4
6
8
10
12
pH
Fig. 3(c). Variation of current with pH of 1.0 ×10ꢀ4M PCM on MWCNTꢀCTAB/GCE at scan
rate of 50 mV sꢀ1 in phosphate buffer.
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
2
3
4
5
6
7
8
9
10 11 12
pH
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Fig. 4(a). Cyclic voltammograms of 1.0 ×10ꢀ4 M PCM on MWCNTꢀCTAB/GCE with
different scan rates; (a) ꢀ (p), 25 ꢀ 400/mV sꢀ1, in phosphate buffer with pH 7.4.
Fig. 4 (b). Relationship between anodic and cathodic peak current vs. scan rate.
25
20
Anodic
15
Cathodic
10
5
0
0
0.1
0.2
0.3
0.4
0.5
v /Vsꢀ1
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Fig. 4(c). Relationship between anodic and cathodic peak potential vs. log of scan rate.
0.45
0.4
Anodic
0.35
0.3
0.25
0.2
Cathodic
0.15
0.1
0.05
0
ꢀ2
ꢀ1.5
ꢀ1
log v/Vsꢀ1
ꢀ0.5
0
Fig. 5. UVꢀvisible spectra of electrolyzed solution. (a) before electrolysis, (b) after
electrolysis.
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Fig. 6(a). DPV curves of different concentrations of PCM (1ꢀ17: 4.0 × 10−7 M ꢀ 4.0 × 10−6
M) in 0.2 M pH 7.4 phosphate buffer solution.
Fig. 6(b). Plot of peak current Ipa against concentration of PCM (µM).
18.0
16.0
14.0
12.0
10.0
8.0
6.0
4.0
2.0
0.0
0.0
10.0
20.0
30.0
40.0
50.0
[PCM]/µM
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Fig. 7(a). Overlay spectrum of paracetamol showing various spectra at different
concentration of drug(1)ꢀ(8): 2 µM to 150 µM.
Fig. 7(b). Calibration curve of paracetamol in phosphate buffer solution of pH 7.4 at λ max
248 nm.
0.5
y = 0.00546x + 0.347
R² = 0.954
0.45
0.4
0.35
0.3
0.25
0.2
0.15
0.1
0.05
0
0
50
100
150
200
Concentration (µM)
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Scheme 1. Probable electroꢀoxidation mechanism of PCM.
O
O
CH3
C
CH3
C
HN
N
O
ꢀ2eꢀ, ꢀ2H+
OH
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Table 1. Characteristics of PCM calibration plot using differential pulse voltammetry and
UVꢀvis spectroscopy at MWCNTꢀCTAB modified GCE.
DPV method
UVꢀvis method
2.0×10−6 M to 15.0×10−5
0.00546±0.00067
0.3475±0.0001
0.954
Linearity range
Slope of the calibration plot
Intercept
4.0×10−7 M to 4.0×10−6
2.444 ±0.00044
6.496±0.0062
0.972
Correlation coefficient(r)
RSD of slope (%)
1.609
1.116
RSD of intercept (%)
Number of data points
LOD (M)
0.869
0.437
10
08
4.82 ×10−9 M
1.60×10ꢀ8
2.5
3.39 ×10−6 M
1.13×10ꢀ5 M
LOQ(M)
Reproducibility of the electrode(%)
Repeatability of the electrode(%)
3.0
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Table 2. Summary of sensors reported by other authors for paracetamol detection
using CNTꢀelectrodes.
Electrode
Linear
range(µM)
0.2–150
LOD
Reference
1. singleꢀwalled carbon nanotubeꢀ
modified carbon–ceramic electrode
2. SWCNTꢀGraphene Sheet modified
GCE
0.2
29
30
0.05–64.5
0.038
3. MWCNT/GCE
26–340
0.5–100
0.074–230
0.25–5
0.029
0.42
0.040
0.032
0.16
0.5
31
32
4.MWCNTꢀcarboxylic acid/GCE
5. MWCNTꢀcarboxylic acid/GCE
6.MWCNTꢀpolyhistidine/GCE
7. MWCNTꢀchitosan/GCE
8. PDDAꢀPSS/GPE
33
34
2–250
35
25–400
36
9. DHPB/CNTP
15.0–270
3.0–600
2.0–400
39.4ꢀ136
0.01ꢀ0.1
0.25–1.50
7.80–110
5–250
10
37
10. DMBQ/CNTP
0.9
38
11.DHCA/CNTP
0.8
39
12. CPB/CNTP
2.1
40
13. BDDE
0.85
1.0
41
14. Redox polymer MWCN
15. Carbonꢀcoated Ni nanoparticles
16.Nefion@/Ru oxide
42
2.30
1.20
0.00482
43
44
17. MWCNTꢀCTAB/GCE
0.4ꢀ4.0
Present
Work
PSS: poly styrene sulfonate, PDDA: poly (diallyldimetheylammonium chloride), DHPB: Nꢀ(3,4ꢀ
dihydroxyphenethyl)ꢀ3,5ꢀdinitrobenzamide, DMBQ: 8,9ꢀdihydroxyꢀ7ꢀmethylꢀ12Hꢀbenzothiazolo[2,3ꢀ
b]quinazolinꢀ12ꢀone, DHCA: 3,4ꢀdihydroxycinnamic acid; CPB: cetylpyridinium bromide, BDDE:
Boron doped diamond electrode, CNTP: Carbon nanotube paste.
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Table 3. Results of the assay and the recovery test of PCM in pharmaceutical
preparations using DPV.
PYREMOL 650
Labeled claim (mg)
Amount found (mg)a
Recovery (%)
650
641.4
98.67
0.38
1.32
2
RSD (%)
Bias (%)
Amount of pure drug added (mg)
Amount found (mg)a
Recovery (%)
1.979
98.95
1.05
RSD (%)
a Average of five determinations
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Table 4. Influence of potential excipients on the voltammetric response of 1.0 × 10ꢀ6 M
PCM.
Excipients(1.0 mM) +
Drug (1.0 x 10ꢀ6)
Only paracetamol
Citric acid + PCM
Dextrose + PCM
Glucose + PCM
Potential observed
(V)
Signal change (%)
0.255
0
0.264
3.52
ꢀ1.17
ꢀ3.92
ꢀ27.84
2.74
ꢀ1.17
4.7
0.252
0.245
Gum acacia + PCM
Tartaric acid + PCM
Starch + PCM
0.184
0.262
0.252
Oxalic acid + PCM
0.267
Table 5. Determination of PCM in human plasma and urine samples.
Sample
Spiked
(10ꢀ6 M)
1.0
Founda
(10ꢀ6 M)
0.979
Recovery (%)
RSD(%)
Urine Sample 1
Urine Sample 2
Plasma Sample 1
Plasma Sample 2
97.9
99.2
0.085
5.0
4.96
0.044
0.087
0.014
3.0
2.921
97.36
101.3
8.0
8.104
a
Average of five determinations
26