A validated RP-HPLC method for the simultaneous estimation of paracetamol and naproxen in bulk and tablet dosage forms

1. Krishanu Pal et al / Int. J. of Pharmacy and Analytical Research Vol-2(4) 2013 [184-193]
184
* Corresponding author: Krishanu Pal
E-mail address: krishanupal5227@gmail.com
IJPAR |Volume 2 | Issue 4 | Oct-Dec-2013 ISSN: 2320-2831
Available Online at: www.ijpar.com
[Research article]
A validated RP-HPLC method for the simultaneous estimation of
paracetamol and naproxen in bulk and tablet dosage forms
*Krishanu Pal1
, V.Murali Balaram2
, M.Bhagavan Raju3
*1
Dept. of Pharmaceutical Analysis, SriKrupa Institute of Pharmaceutical Sciences, Siddipet-
502276, AP.
2
Dept. of Pharmaceutical Analysis, Sultan-Ul-Ulum College of pharmacy, Hyderabad, AP.
3
Dept. of Pharmaceutical Chemistry, Gland Institute of Pharmaceutical Sciences, Hyderabad,
AP.
.
ABSTRACT
A simple, sensitive, accurate, precise, reproducible, specific and cost-effective RP-HPLC method was developed
and validated for the simultaneous estimation of Paracetamol (PCM) and Naproxen sodium (NPX) in the bulk
and pharmaceutical dosage forms. Chromatography was carried on a Nucleosil C8 (250 X 4.6 mm, 5μm) column
with mobile phase comprising of phosphate buffer pH-6.5 adjusted with 1N potassium hydroxide and
acetonitrile in the ratio of 70:30 v/v. The flow rate was adjusted to 1.0 ml/min with UV detection was carried
out at 240 nm, and column temperature of 30±0.50
C was maintained throughout the study. The retention times
for PCM and NPX were found to be 3.54 min and 4.59 min respectively. Linearity values were obtained in the
range of 2.5-15 µg/ml for PCM and 2-12 µg/ml for NPX with correlation coefficient (r2
) of 0.999 for both drugs.
The method was validated as per ICH guidelines for specificity, linearity, precision, accuracy, robustness, limit
of detection and limit of quantification. So the proposed method was found to be suitable for the routine quality
control analysis of these drugs in raw materials and also in pharmaceutical dosage forms.
Keywords: RP-HPLC, Paracetamol or PCM and Naproxen sodium or NPX, Nucleosil C8 column, phosphate
buffer pH 6.5, and acetonitrile.
INTRODUCTION
Non-steroidal anti-inflammatory drugs (NSAIDs)
are among the most frequently prescribed drugs
worldwide and are used for mainly analgesic,
antipyretic and anti-inflammatory actions. The
main mechanism of action behind the anti-
inflammatory activity of major NSAIDs is
blockage of prostaglandins (PGs), as generation of
PGs locally at the site of inflammation mediate
many of the inflammatory changes. Prostaglandins,
prostacyclin and thromboxane-A2 are produced
from arachidonic acid by the enzyme
cyclooxygenase which exists in a constitutive
(COX-1) and an inducible (COX-2) isoforms. Most
of the NSAIDs inhibit COX-1 and COX-2 non-
selectively, but some selectively inhibits COX-2.
PCM is a para-amino phenol derivative comes
under the classification of broad group of
nonsteroidal anti-inflammatory drugs which is
chemically N-(4-Hydroxyphenyl) acetamide
(Figure 1a). It is one of the most popular drugs

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185
under this category and has good analgesic and
antipyretic properties but mild anti-inflammatory
activity. It is commonly used for the relief
of headaches and other minor aches and pains, and
is a major ingredient in numerous
cold and flu remedies. It works by blocking the
action of the enzyme cyclooxygenase which is
responsible for the production of PGs. NPX is a
propionic acid derivative related to the arylacetic
acid group of nonsteroidal anti-inflammatory drugs
which is chemically (2S)-2-(6-methoxynaphthalen-
2-yl) propionic acid (Figure 1b). It is commonly
used to treat pain or inflammation caused by acute
masculo-skeletal pain, headaches and migraines,
and conditions such as arthritis, ankylosing
spondylitis, tendinitis, bursitis, gout, or menstrual
cramps.
It works by reducing PGs synthesis by inhibiting
the enzyme cyclooxygenase, both COX-1 and
COX-2 enzymes that cause inflammation and pain
in the body. It is clinically proven as the most
cardio safe NSAID with reduced side effects like
considerable hepatic and renal safety. This
combination of PCM and NPX exhibits anti-
inflammatory, analgesic and antipyretic activities.
PCM has central action and NPX has peripheral
action. Thus the combination is more effective
when individual drugs act by different mechanism
and act synergistically. By activating multiple pain
inhibitory pathways PCM and NPX combination
has more effective pain relief property and at the
same time decreased adverse effects.
Figure-1a: Structure of Paracetamol Figure-1b: Structure of Naproxen
Literature survey shows that there are several UV
spectrophotometric, HPLC, LC-MS and HPTLC
methods been reported for estimation of PCM and
NPX individually in bulk drugs and also in
respective formulations. Even there are many UV,
HPLC and HPTLC methods reported for estimation
of PCM and NPX in combination with other drugs
in various formulations. But there are three UV
spectrophotometric, one HPLC and one UPLC
method been reported till now for simultaneous
estimation of PCM and NPX in fixed dose
combination formulations. So in the present work
an attempt was made for developing a simple,
sensitive, accurate, precise, reproducible, specific
and cost-effective RP-HPLC method for the
simultaneous estimation of PCM and NPX in the
bulk drug and pharmaceutical dosage form, and
also to validate the same as per ICH guidelines.
EXPERIMENTAL
Instrumentation
A Waters Alliance 2695 Separation Module-HPLC
system comprising of quaternary, low pressure
mixing pump and inline vacuum degasser with
auto sampler and programmable temperature
control, and a PDA detector using Waters
(Alliance) Empower-2 software. For normal UV
absorbance estimations during trials were done by a
Lab India UV- VIS spectrophotometer UV 3000+
,
and weighing of drugs and chemicals were done by
a Shimadzu precision balance AUX-220.
Chemicals and reagents
Paracetamol and Naproxen sodium RSwere
obtained as a gift samples from Aurbindo Pharma
Ltd, Hyderabad. Due to unavailability of the Mkd.
formulation in the local market during the time of
experimentation PCM and NPX synthetic mixture
was prepared by placebo technique and formulated
as tablet. HPLC grade acetonitrile and water were
procured from Merck (Mumbai, India) and
potassium dihydrogen phosphate, dipotasssium
hydrogen phosphate and potassium hydroxide of
analytical grade were used for the studies. The
solvents and mobile phases after preparation were
filtered using Millipore 0.45 µm filter medium.
Chromatographic conditions
A Nucleosil C8 (250 X 4.6 mm, 5μm) column was
used as a stationary phase, and phosphate buffer

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pH-6.5 adjusted with 1N potassium hydroxide and
acetonitrile in the ratio of 70:30 v/v was used as a
mobile phase. With a flow rate of 1.0 ml/min,
detection wavelength at 240 nm and column
temperature was maintained at 300
C.
Preparation of mobile phase
1.36 gm of potassium dihydrogen phosphate and
0.6 gm of dipotasssium hydrogen phosphate were
dissolved in 500 ml of HPLC-grade water and
finally the volume was made upto 1000 ml with
same, and adjust pH 6.5 with 1 N potassium
hydroxide. Now mix the phosphate buffer pH-6.5
solution with HPLC-grade acetonitrile in the ratio
of 70:30 v/v, sonication was done for 15 minutes
to remove any dissolved gases and finally filter
with Millipore 0.22 µm filter.
Preparation of standard stock solutions
Weigh accurately about 100 mg of PCM and NPX
reference standards separately and transfer into
two different 100 mL volumetric flasks, and 50
mL of mobile phase was added as diluent. Shake
the mixtures for 15 minutes and sonicate the
solutions to remove any dissolved gases and
finally make up volume upto the neck mark with
same diluent.
Preparation of working standard solutions
Take 10 ml of the PCM and NPX stock solutions
from the respective containers and transfer into
two different 100 mL volumetric flasks and make
up volume upto the neck mark with diluent.
Preparation of Sample solution
Twenty tablets each containing 500 mg of PCM
and 400 mg of NPX, were weighed accurately and
finely powdered. From this an amount equivalent
to 100 mg of PCM and 80 mg of NPX was
weighed and transferred to a 100 ml clean
volumetric flask. Around 50 ml of diluent was
added and the mixture was shaken for 15 minutes
for three times. The mixture was sonicated for 20
minutes to remove any dissolved gases and finally
make up volume upto the neck mark with same
diluent. Next filter the above solution with
Whatmann filter paper with pore size of 40 A0
.
From this 10 ml of the filtrate was diluted upto
100 ml in another volumetric flask. Finally 2 ml
of the previous solution was taken and transferred
to a 10 ml volumetric flask and the volume was
made upto the neck mark using same diluent.
METHOD DEVELOPMENT
Selection of suitable detection wavelength
As per literature survey methanol was found to be
the most suitable solvent for both PCM and NPX.
So suitable dilutions of 100 µg/ml were prepared
for both PCM and NPX and were scanned within
the range of 200-400 nm using a UV-Visible
spectrophotometer. From the obtained spectrums of
both drugs the isobestic point was found to be 240
nm, which was selected as the suitable detection
wavelength.
Optimized chromatographic conditions
Initially many trials were performed using
different combination of mobile phases, different
columns and varying chromatographic conditions
in attempt to obtain the best separation and
resolution between the PCM and NPX in
chromatograms. So finally a Nucleosil C8 (250 X
4.6 mm, 5μm) column was found to be best
suitable stationary phase, and phosphate buffer pH-
6.5 adjusted with 1N potassium hydroxide and
acetonitrile in the ratio of 70:30 v/v was found to
be best suitable mobile phase. Flow rate was
adjusted to 1.0 ml/min, detection wavelength at 240
nm and column temperature was maintained at
300
C, and the same chromatographic conditions
were maintained throughout the study.
System suitability
The system suitability parameters like theoretical
plate, asymmetric factor, capacity factor,
resolution, retention time and tailing factor were
calculated with Waters (Alliance) Empower
software. In order to establish system suitability for
the instrument, six consecutive injections of PCM
and NPX mixed standard were prepared from
working standard solutions, each having 10 µg/ml
and 8 µg/ml of PCM and NPX respectively, and
analyzed.
Method Validation
As per ICH guidelines, the method validation
parameters were performed for specificity,
linearity, accuracy, precision, limit of detection,
limit of quantification, robustness and ruggedness.
Specificity
The specificity of the method was established
through resolution factor of the drug peak from the
nearest resolving peak and also among all other
peaks. Specificity of the method was assessed by

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comparing chromatograms of blank, individual and
mixed reference standards and formulation tablets.
A blank solution (mobile phase) was injected and
the chromatogram showed no interfering peaks at
the retention time of both the drugs. The
chromatograms of PCM and NPX extracted from
the tablets were compared with the chromatograms
acquired from PCM and NPX reference standards;
correlation was found good in terms of Rt and peak
area which indicates specificity of method.
Linearity and Range
Aliquots of standard stock solutions of PCM and
NPX were taken in 10 ml volumetric flasks and
diluted with diluent to get final concentrations in
range of 2.5-15 μg/ml for PCM and 2-12 μg/ml for
NPX. Triplicate injections were made five times
for each concentration for each drug separately.
The peak areas of the chromatograms were plotted
against the concentrations for PCM and NPX both
to obtain the respective calibration curves.
LOD and LOQ
The limit of detection (LOD) and limit of
quantification (LOQ) were estimated from the set
of 5 calibration curves obtained from serial
dilutions of PCM and NPX working standard
solution in order to obtain signal-to -noise ratio of
3:1 for LOD and 10:1 for LOQ. The LOD and
LOQ may be calculated as –
LOD = 3.3XSD/Slope and
LOQ = 10XSD/Slope
Where,
SD= standard deviation of the Y-intercepts of the 5
calibration curves.
Slope= Average of slopes of the 5 calibration
curves.
Precision
The precision study was carried out as both system
and method precisions. The repeatability was
carried out by performing assay of six dilutions of
test sample preparation each having 10 µg/ml and 8
µg/ml of PCM and NPX respectively and from this
% RSD was calculated (intraday). Intermediate
precision of the method was checked by
performing same procedure on a different day
(interday) by another person under same
experimental conditions.
Assay study
After observing a steady base line with the
optimized chromatographic conditions, three mixed
drug dilutions of PCM and NPX bulk drugs each
having 10 µg/ml and 8 µg/ml of PCM and NPX
respectively were prepared and injected and the
chromatograms were recorded. The procedure was
repeated for the tablet sample dilutions having 10
µg/ml and 8 µg/ml of PCM and NPX respectively.
Finally using the peak area values of PCM and
NPX standard drug dilutions the % purity of the
bulk drug and tablet formulation was calculated.
Accuracy
To ensure the reliability (accuracy) of the method,
recovery studies were carried out by mixing
standard quantity of standard drug with the pre-
analyzed sample formulation and the contents were
reanalyzed by the proposed method. The accuracy
of the method was determined by calculating
recoveries of PCM and NPX by standard addition
method. In this known amount of standard
solutions of PCM and NPX (50%, 100% and 150%
spike level) added to previously spiked tablet
sample dilutions containing PCM and NPX were
prepared in triplicate. A mixed standard dilution of
5: 4 µg/ml of PCM and NPX was prepared, and
50%, 100% and 150% from this solution was
individually added to diluted sample formulation
having 5: 4 µg/ml of PCM and NPX respectively,
and analyzed.
Ruggedness
The ruggedness of an analytical method is the
degree of reproducibility of the test results
Obtained by the analysts of the same samples under
a variety of normal test conditions such as different
laboratories, different analysts using same
operational and environmental conditions that may
differ but are still within the specified parameters
of the assay. Ruggedness of the proposed method
was determined by analysis of aliquots of the
sample solution having 10 µg/ml and 8 µg/ml of
PCM and NPX respectively by two analysts using
same operational conditions.
Robustness
Robustness of the method was determined by
small, deliberate changes in flow rate, mobile phase
ratio and detection wavelength. Typical changes
include flow rate changing to 1.0±0.1 ml/min,
column temperature change ±20
C and detection
wavelength change to 240±1 nm.

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188
Result and discussion
The present study was carried out with a view to
develop a simple, accurate, precise and
economical RP-HPLC method for simultaneous
estimation of PCM and NPX in bulk drugs and
pharmaceutical dosage forms. In order to achieve
optimum separation of the component peaks,
mixture of acetonitrile with phosphate and acetate
buffer with different combinations were tested on
a C-18 type stationary phase. Finally a mixture of
phosphate buffer pH-6.5 adjusted with 1N
potassium hydroxide and acetonitrile in the ratio of
70:30 v/v was selected as the most suitable mobile
phase, as the chromatographic peaks were well
defined and resolved with no tailing. The retention
times were obtained 3.550±0.003 for PCM and
4.595±0.004 for NPX with flow rate of 1.0 ml/min
and detection wavelength at 240 nm. With the
optimized chromatographic conditions method
validation parameters were performed for
specificity, linearity, accuracy, precision, limit of
detection, limit of quantification, robustness and
ruggedness, and analyzed.
Specificity
Specificity of the method was assessed by
comparing chromatograms of blank, individual and
mixed reference standards and formulation tablets,
having a concentration of 10 µg/ml of PCM and 8
µg/ml of NPX. Respective chromatograms were
compared for retention time, resolution factor and
purity.
Figure-2: A typical chromatogram showing peaks of PCM and NPX in mixed standard solution
Table no-1: Specificity study for PCM and NPX in reference and tablet drug.
S.
No.
Sample
type
Concentration
of Drug in
µg/ml
Rt Peak Area Resolution USP
Plate Count
Tailing
Factor
PCM NPX PCM NPX PCM NPX PCM NPX PCM NPX PCM NPX
1. Blank 0 0 - - - - - - - - -
2. PCM_RS 10 0 3.552 - 264699 - - 4069 - 1.13 -
3. NPX _RS 0 8 - 4.595 - 240560 - - 4523 - 1.10
4. Mixed
Standard
10 8 3.552 4.593 268932 240352 4.09 4008 4558 1.14 1.10
5. Tablet
Drug
10 8 3.551 4.590 269132 239894 4.11 4013 4569 1.13 1.10
% RSD 0.0162 0.0548 0.9356 0.1418 0.3449 0.8404 0.5279 0.5095 0
Linearity
The method shows linearity in the range of 2.5-15
μg/ml for PCM and 2-12 μg/ml for NPX. From the
respective concentrations and peak areas of both
drugs calibration curves were plotted, the
correlation coefficient values were found to be
linear (r2
= 0.999) and slope and intercept values
were calculated.

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189
Table no-2: Linearity values of PCM and NPX in mixed standard dilutions.
Serial No. Concentration of Drug in µg/ml Retention time (Rt) Peak Area
PCM NPX PCM NPX PCM NPX
1.
2.
3.
4.
5.
6.
2.5
5.0
7.5
10
12.5
15
2
4
6
8
10
12
3.545
3.541
3.548
3.553
3.559
3.590
4.606
4.587
4.590
4.599
4.604
4.676
65971
134197
203598
269967
337045
415282
58220
119645
180001
240927
300212
369206
Figure-3a: Calibration curve of PCM Figure-3b: Calibration curve of NPX
Table no-3: Statistical report of linearity study of PCM and NPX.
Statistical Parameters PCM NPX
Correlation coefficient (r2
) 0.999 0.999
Slope 27674 30822
Intercept -4470 -4387
Precision
Six dilutions each having 10 µg/ml and 8 µg/ml of
PCM and NPX respectively were selected for
performing both repeatability (intraday) and
intermediate precision (interday). The % RSD
values were found to be less than 2% which falls
within the acceptance criteria.
Table no-4: Repeatability study of PCM and NPX in mixed standard dilutions.
Serial No. Concentration of Drug in µg/ml PCM NPX
PCM NPX Rt Peak Area Rt Peak Area
1.
2.
3.
4.
5.
6.
10
10
10
10
10
10
8
8
8
8
8
8
3.548
3.549
3.549
3.553
3.553
3.550
266577
266909
270154
271218
270165
269846
4.591
4.593
4.595
4.599
4.599
4.595
239985
239990
240247
240122
241029
239998
Avg. 3.5503 269144.83 4.5953 240228.50
SD 0.0022 1920.496 0.0032 405.411
% RSD 0.062 0.713 0.070 0.169
y = 27674x - 4470.
R² = 0.999
0
100000
200000
300000
400000
500000
0 10 20
y = 30822x - 4387.
R² = 0.999
0
100000
200000
300000
400000
0 5 10 15

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Assay
The assay study for PCM and NPX was performed for bulk and tablet formulations, and % purity values were
calculated, which were found to be within the acceptance limit of 97-103%.
Figure-3: A typical chromatogram showing peaks of PCM and NPX in tablet sample dilution
Table no-5: Assay results of PCM and NPX in bulk and tablet formulation dilutions.
Accuracy
Method accuracy was achieved by performing
standard addition method with 50%, 100% and
150% spike level. From the results obtained the %
recovery and %RSD values were calculated and
found to be within the acceptance criteria (< 2).
Table no-5: Recovery study of PCM and NPX by standard addition method.
Serial
No.
% Spike
Level
Mean
Peak Area
(µg/ml)
Actual
Amount
(µg/ml)
Amount
Added
(µg/ml)
Amount
Recovered
(µg/ml)
% Recovery % RSD
PCM
1.
2.
3.
50%
100%
150%
203400
269002
336961
5
5
5
2.5
5
7.5
5.034±0.003
4.964±0.001
4.982±0.003
100.68±0.06
99.29±0.01
99.63±0.05
0.7256
NPX
1.
2.
3.
50%
100%
150%
179941
240166
299684
4
4
4
2
4
6
3.975±0.005
3.975±0.004
3.951±0.023
99.37±0.13
99.36±0.11
98.76±0.56
0.3522
Serial
No.
Concentration of
Drug in µg/ml
Peak Area Amount
Obtained
% Purity % RSD
PCM NPX PCM NPX PCM NPX PCM NPX PCM NPX
Bulk
Drug
1.
2.
3.
10
10
10
8
8
8
271218
271323
270427
242099
241988
241027
10.046
10.050
10.017
8.039
8.035
8.003
100.46
100.50
100.17
100.49
100.44
100.04
0.1794 0.2458
Formulat
ion
1.
2.
3.
10
10
10
8
8
8
268834
268929
270443
240344
241012
241326
9.958
9.961
10.018
7.981
8.003
8.013
99.58
99.61
100.18
99.76
100.04
100.16
0.3388 0.2053

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LOD and LOQ
Limit of detection and limit of quantification were
established by evaluating the five calibration
curves obtained from the five set of serial dilutions
of PCM and NPX working standard solutions. The
LOD values were found to be 0.572 µg/ml and
0.684 µg/ml for PCM and NPX respectively, and
LOQ values were found to be 1.733 µg/ml and
2.072 µg/ml for PCM and NPX respectively.
System suitability
System suitability was achieved by performing six
consecutive injections of PCM and NPX mixed
standard each having 10 µg/ml and 8 µg/ml of
PCM and NPX respectively, and analyzed for their
peak area, resolution, theoretical plates and tailing
factor. The results of system suitability study were
shown in the table-6, which shows within the
acceptance limit.
Table no-6: System suitability results for PCM and NPX mixed standard dilutions.
Ruggedness
Ruggedness of the proposed method was
determined by analysis of aliquots of the sample
solution having 10 µg/ml and 8 µg/ml of PCM and
NPX respectively by two analysts using same
operational conditions, and the data obtained was
given in the table-6.
Table no-6: Ruggedness study for PCM and NPX in sample dilutions.
Serial No. PCM NPX
Rt Peak Area Rt Peak Area
1.
2.
3.
4.
5.
6.
3.558
3.559
3.562
3.560
3.560
3.563
251376
255474
255890
254895
258905
260435
4.602
4.603
4.605
4.603
4.606
4.608
235469
239044
243265
243132
245648
244899
Mean 3.5603 256162.5 4.6054 241909.5
SD 0.0019 3188.76 0.0023 3897.09
%RSD 0.05 1.24 0.05 1.61
Robustness
Robustness was determined by analyzing same
sample at normal operating conditions but
deliberate change in some operational analytical
conditions such as temperature and flow rate. The
data obtained was given in the table-7.
Parameters PCM NPX Acceptance
Retention time (Rt)
in minutes
3.550±0.003 4.595±0.004 ˃2.5
USP Resolution (Rs) 4.29 ˃2
USP Tailing 1.13 1.10 0.8-1.2
USP Plate count (N) 4273.17±14.83 5136.83±6.17 ˃2000

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Table no-7: Robustness study for PCM and NPX in sample dilutions.
Operational
conditions
Retention
time
(Rt)
Peak Area USP
Resolution
(Rs)
USP Tailing USP Plate count
(N)
PCM NPX PCM NPX PCM NPX PCM NPX PCM NPX
Changein
Flowrate
(±0.2
ml/min)
F1 3.241 4.197 246529 219708 4.16 1.22 1.22 3947 5021
F2 3.937 5.100 303149 270351 4.45 1.24 1.23 4439 5436
Changein
Temperature
(±20
C)
T1 3.566 4.843 272702 243294 5.07 1.22 1.22 4026 5286
T2 3.619 4.408 278510 245541 3.23 1.22 1.24 4174 4801
CONCLUSION
In the proposed project work a RP-HPLC method
was developed and also successfully validated as
per ICH guidelines. So the proposed method was
found to be suitable enough for routine quality
control analysis for simultaneous estimation of
PCM and NPX in bulk drugs and as well as in
combination using isocratic mode of elution. The
results of linearity, precision, accuracy, and
specificity proved to be within the limit. The
method provides selective quantification of PCM
and NPX without interference from diluents and
placebo. The proposed method was found highly
sensitive, reproducible, reliable, rapid and also
has unique advantage of LC conditions being
compatible with MS detection. Therefore this
method can be employed in quality control to
estimate the amount of PCM and NPX in bulk and
combined dosage forms.
ACKNOWLEDGEMENT
The authors are grateful to Bio-Leo labs,
Hyderabad for permitting to carry out the research
work, Aurobindo Pharma, Hyderabad for
providing gift samples of PCM and NPX, and also
to SriKrupa Institute of Pharmaceutical Sciences,
Siddepet for project guidance and support.
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