R. Mangaiyarkarasi, S. Premlatha, R. Khan et al.
Journal of Molecular Liquids 319 (2020) 114255
beneficial features such as high sensitivity, lower over potential and anti-
fouling properties [23]. For instance, Hadi Beitollahi et al. reported studies
on IL and Au NPs modified CPEs for sensing thyroid-stimulating hormone
[24]. ILCs have close resemblance to the properties of ILs such as negligible
vapour pressure, good thermal stability, wide electrochemical window
and also possess interesting properties of LCs namely self-assembling
ability, molecular order and anisotropic properties [6,7,25]. ILC modified
CPE surface is expected to have a layered morphology, which can induce
more edge-plane sites on the electrode surface. A high density of edge-
plane-like defects on the surface can increase the kinetics of electrode
for many redox reactions, reduce the passivation effects, impart the
anti-fouling property and improve the reproducibility, stability and sensi-
tivity of the electrode [26,27]. Owing to these remarkable properties, ILC
modified CPEs have been explored for the electrochemical sensing of
drugs and neurotransmitters [28,29].
Paracetamol or acetaminophen is a well-known analgesic, antipy-
retic and anti-inflammatory drug widely administered for the viral/bac-
terial fevers and mild to moderate pain relief associated with headache,
toothaches, arthritis, backaches, and post-operative pains. The pKa
value of paracetamol is 9.5 which easily get absorbed by the cells and
excreted in the urine [30]. In general, paracetamol intake does not man-
ifest any harmful side effects in therapeutic doses but, the overdose of
this drug could lead to inflammation of pancreas, glutathione depletion,
fulminating hepatic necrosis, kidney damage and hepatotoxicity [31].
The oral administration of paracetamol in children above one year can
cause an increase in asthma, and rhinoconjunctivitis [32]. Therefore,
the detection of paracetamol is necessary and has gained extensive at-
tention among the researchers worldwide.
Since paracetamol is electrochemically active, electrochemical de-
tection is emerging as better method due to its key advantages such as
cost effectiveness, extreme sensitivity, ease of preparation, and minia-
turization possibilities for electroanalysis of paracetamol. However, on
conventional electrodes, paracetamol is not easily oxidized and exhibit
poor response because of its sluggish electrode kinetics. Hence, chemi-
cally modified electrodes were developed in recent years, which were
successfully utilized in electrochemical sensor fabrication [33–37]. Re-
cently, carbon paste electrodes modified with ILCs were explored as
electrochemical sensors for the determination of drugs and compounds.
For instance, Galal, and his co-workers reported studies on piperidinium
based ILC modified CPE for electroanalysis of antihypertensive drug
[38,39] and described commercial ILCs/Au NPs/carbon nanotubes mod-
ified CPE for paracetamol sensing applications [40]. Moreover, the same
research group reported cyclodextrin and ILC modified graphene com-
posite electrode for detection of some neurotransmitters [41].
Herein, we reported the synthesis of a new imidazolium based ILC
compound, its mesomorphic behaviour and application of this ILC as
an electrode material in combination with carbon paste for the detec-
tion of paracetamol. The ILC is dimesomorphic and exhibited a high
temperature uniaxial SmA and a low temperature biaxial SmA phase
with a wider phase range. Composite electrodes were prepared by
employing the ILC and carbon paste (30:70 wt%) by heating the ILC to
different temperatures (rt, 90 °C, 120 °C) and the electrochemical per-
formance of the resulting ILC-CP composite electrodes was evaluated.
The ILC-CPE electrode displayed an improved response compared to
the unmodified CPE. Further, the detection of paracetamol using the
newly fabricated electrode, studies on stability, sensitivity and selectiv-
ity of the electrode for the sensing of paracetamol are presented. Real
sample analysis of the paracetamol in pharmaceutical drug formulation
was also conducted.
(NP), dopamine (DA), buffer tablets (pH =7) and 1-methyl imidazole
were obtained from Sigma Aldrich. Glucose (Glu), uric acid (UA), ascor-
bic acid (AA) and potassium chloride (KCl) were bought from TCI
chemicals. All the chemicals were used as purchased, except 1–
methylimidazole, which was distilled prior to conduct the reaction.
The solvents were purified and dried using conventional methods.
2.2. Methods
Chemical structure of the synthesized compounds was characterized
using infrared (IR), nuclear magnetic resonance (NMR) spectroscopy
and mass spectrometry techniques. IR spectra were recorded on a
Bruker Tenser 27 FTIR spectrometer (Bruker Optic GmbH, Germany)
using KBr pellets. 1H NMR spectra were recorded on a Bruker Avance
400 MHz spectrometer (Bruker, Switzerland) using tetramethylsilane
as an internal standard. Liquid crystalline behaviour of ILC, A was exam-
ined using a combination of differential scanning calorimetry (DSC), po-
larizing optical microscopy (POM) and X-ray diffraction studies (XRD).
Phase transition temperatures were obtained from thermograms re-
corded on a Perkin Elmer DSC (DSC 6000, Perkin Elmer, US) with a
heating and cooling rate of 10 °C/min. Textural observations were car-
ried out using a Olympus BX50 POM (Olympus Co., Japan) equipped
with a Linkam LTS 420E (Linkam, UK) heating stage having a T95-HS
Link controller. The X-ray diffraction patterns of the sample were col-
lected from PANalytical, (Model-Empyrean, Netherlands) X-ray diffrac-
tometer by employing Cu-Kα (λ = 1.54 Å) radiation. Molecular mass of
ILC was determined using a JEOL GCMATE II GC–MS, USA. Moreover,
Scanning electron microscope (SEM) observations were carried out
using FEI Quanta 250 (FEI Corporation, Japan) instrument. ILC dissolved
in chloroform was drop-casted on indium tin oxide (ITO) plate, dried at
room temperature and viewed under the SEM. Electrochemical studies
were performed using an AutolabPGSTAT30 Potentiostat/Galvanostat
electrochemical workstation (EcoChemi, Netherlands) with a three
electrode system consisting of Ag/AgCl as a reference electrode, plati-
num wire as a counter electrode and ILC modified CP as a working elec-
trode. A PBS buffer solution having pH = 7.0 was used as an electrolyte
for sensor studies.
For the interference studies, differential pulse voltammetry (DPV)
experiments were conducted in phosphate buffer solution (PBS) at a
scan rate of 50 mVs−1. Initially, 50 μM of paracetamol solution was
added to PBS (pH = 7) and the corresponding DPV curve was recorded.
Soon after, 5-fold increased concentration of other possible interferents
such as dopamine, ascorbic acid, KCl, nitrophenol, uric acid, glucose
were added one by one to the same electrolyte and their corresponding
DPV current response was recorded.
2.3. Synthesis of 4′-(decyloxy)-[1,1′-biphenyl]-4-ol, b
4,4′-Dihyroxy biphenyl (3 g; 16.1 mmol) was dissolved in dry
ethanol (30 mL), sodium hydroxide (0.644 g; 16.1 mmol) was added
to the reaction mixture and then refluxed until colour of the solution
was changed to dark green. Subsequently, 1-bromodecane (3.4 mL;
16.1 mmol) was added and continuously refluxed for 3 h at 80 °C.
After that, the reaction mixture was cooled to room temperature. The
reaction mixture was acidified with 5 mL of con. HCl to get a precipitate
which was then washed with ethanol and dried under vacuum. The res-
idue was dissolved in ethanol: acetic acid (1:1) and then undissolved
impurities were removed by filtration. Further, the product was purified
by column chromatography on silica gel using dichloromethane
(CH2Cl2) and ethyl acetate as an eluent (9:1) to get compound b as a
white powder. Yield: 40%
2. Experimental
FTIR (KBr) ʋmax: 3304, 2944, 2855, 1874, 1610, 1498, 1455, 1386,
2.1. Materials
1252, 1127, 1036, 803, 725, 648, 561, 510 cm−1
.
1H NMR (400 MHz, CDCl3) δ (ppm): 9.82 (s, OH, 1H), 7.51 (d, Ar-H,
2H, 3J = 8.4 Hz). 7.45 (d, Ar-H, 2H, 3J = 8.4 Hz) 6.97 (d, Ar-H, 2H, 3J =
8.4 Hz), 6.91 (d, Ar-H, 2H, 3J = 8.4 Hz), 4.05(t, -O-CH2, 2H, 3J = 6.8 Hz),
11-Bromoundecanoic acid, 4-(dimethylamino) pyridine (DMAP), N,
N′-diisopropyl carbodiimide (DIC), acetaminophen (PA), nitrophenol
2