Spectrophotometric and spectrofluorometric methods for the determination of non-steroidal anti-inflammatory drugs: A review

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Abstract
Non-steroidal anti-inflammatory drugs (NSAIDs) are the group most often used in human and veterinary medicine, since they are available without prescription for treatment of fever and minor pain. The clinical and pharmaceutical analysis of these drugs requires effective analytical procedures for quality control and pharmacodynamic and pharmacokinetic studies. An extensive survey of the literature published in various analytical and pharmaceutical chemistry related jour-nals has been conducted and the instrumental analytical methods which were developed and used for determination of some non-steroidal anti-inflammatory, coxibs, arylalkanoic acids, 2-arylpropi-onic acids (profens) and N-arylanthranilic acids (fenamic acids) in bulk drugs, formulations and biological fluids have been reviewed. This review covers the time period from 1985 to 2010 during which 145 spectrophotometric methods including UV and derivative; visible which is based on for-mation of metal complexation, redox reactions, ion pair formation, charge-transfer complexation and miscellaneous; flow injection spectrophotometry as well as spectrofluorometric methods were
REVIEW ARTICLE
Spectrophotometric and spectrofluorometric methods
for the determination of non-steroidal anti-inflammatory
drugs: A review
Ayman A. Gouda
a,
*
, Mohamed I. Kotb El-Sayed
b
, Alaa S. Amin
c
,
Ragaa El Sheikh
a
a
Chemistry Department, Faculty of Science, Zagazig University, Zagazig, Egypt
b
Organic Chemistry Department (Pharmaceutical Biochemistry), Faculty of Pharmacy, Sana’a University, Sana’a, Yemen
c
Chemistry Department, Faculty of Science, Benha University, Benha, Egypt
Received 27 June 2010; accepted 6 December 2010
KEYWORDS
Review;
Non-steroidal
anti-inflammatory;
Spectrophotometry;
Spectrofluorometry
Abstract Non-steroidal anti-inflammatory drugs (NSAIDs) are the group most often used in
human and veterinary medicine, since they are available without prescription for treatment of fever
and minor pain. The clinical and pharmaceutical analysis of these drugs requires effective analytical
procedures for quality control and pharmacodynamic and pharmacokinetic studies. An extensive
survey of the literature published in various analytical and pharmaceutical chemistry related jour-
nals has been conducted and the instrumental analytical methods which were developed and used
for determination of some non-steroidal anti-inflammatory, coxibs, arylalkanoic acids, 2-arylpropi-
onic acids (profens) and N-arylanthranilic acids (fenamic acids) in bulk drugs, formulations and
biological fluids have been reviewed. This review covers the time period from 1985 to 2010 during
which 145 spectrophotometric methods including UV and derivative; visible which is based on for-
mation of metal complexation, redox reactions, ion pair formation, charge-transfer complexation
and miscellaneous; flow injection spectrophotometry as well as spectrofluorometric methods were
*
Corresponding author. Tel.: +2 055 242 3346; fax: +2 055 230
8213.
E-mail address: aymangouda77@gmail.com (A.A. Gouda).
1878-5352 ª 2011 King Saud University. Production and hosting by
Elsevier B.V. All rights reserved.
Peer review under responsibility of King Saud University.
doi:10.1016/j.arabjc.2010.12.006
Production and hosting by Elsevier
Arabian Journal of Chemistry (2011) xxx, xxxxxx
King Saud University
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www.ksu.edu.sa
www.sciencedirect.com
Please cite this article in press as: Gouda, A.A. et al., Spectrophotometric and spectrofluorometric methods for the determination
of non-steroidal anti-inflammatory drugs: A review. Arabian Journal of Chemistry (2011), doi:10.1016/j.arabjc.2010.12.006
reported. The application of these methods for the determination of NSAIDs in pharmaceutical for-
mulations and biological samples has also been discussed.
ª 2011 King Saud University. Production and hosting by Elsevier B.V. All rights reserved.
Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00
2. Spectrophotometric and spectrofluorometric methods for determination of coxibs. . . . . . . . . . . . . . . . . . . . . . . . . . . 00
2.1. Celecoxib . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00
2.2. Valdecoxib . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00
2.3. Rofecoxib . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00
2.4. Etoricoxib . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00
3. Spectrophotometric and spectrofluorometric methods for determination of arylalkanoic acids . . . . . . . . . . . . . . . . . . 00
3.1. Aceclofenac . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00
3.2. Diclofenac . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00
3.3. Etodolac . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00
3.4. Ketorolac. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00
4. Spectrophotometric and spectrofluorometric methods for determination of N-arylanthranilic acids derivatives (fenamic
acids) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00
4.1. Mefenamic acid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00
4.2. Flufenamic acid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00
4.3. Enfenamic acid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00
4.4. Tolfenamic acid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00
5. Spectrophotometric and spectrofluorometric methods for determination of arylpropionic acids (profens) . . . . . . . . . . 00
5.1. Ibuprofen. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00
5.2. Ketoprofen. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00
5.3. Flurbiprofen. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00
5.4. Naproxen. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00
5.5. Tiaprofenic acid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00
6. Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00
7. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00
1. Introduction
Non-steroidal anti-inflammatory drugs (NSAIDs) are a group
of drugs of diverse chemical composition and different thera-
peutic potentials having a minimum of three common features:
identical basic pharmacological properties, similar basic mech-
anism of action as well as similar adverse effects. Moreover, all
drugs in this group exhibit acidic character. Most NSAIDs are
weak acids, with a pK
a
values in the range of 3.0–5.0 (acids of
medium strength).
NSAID molecules contain hydrophilic groups (carboxylic
or enolic group) and lipophilic ones (aromatic ring, halogen
atoms). In accordance with their acidic character, NSAIDs oc-
cur in the gastric juice in the protonated (lipophilic) form. Also
in the small intestine, there are conditions favorable for
absorption of weak acids. NSAID exist in highly ionized forms
Abbreviations: NSAIDs, non-steroidal anti-inflammatory drugs; COX, cyclooxygenase; HPLC, high-performance liquid chromatography; RP-
HPLC, reversed phase high-performance liquid chromatography; LC, liquid chromatography; TLC, thin layer chromatography; GC, gas
chromatography; IR, infrared; AAS, atomic absorption spectrophotometry; NMR, nuclear magnetic resonance;
1
H NMR, proton nuclear
magnetic resonance; MS, mass spectrometry; FIA, flow injection analysis; CE, capillary electrophoresis; r, correlation coefficient; R, intensity ratio;
CZE, capillary zone electrophoresis; MEKC, micellar electrokinetic capillary chromatography; UV, ultraviolet; k, wavelength; Abs, absorbance;
LOD, limit of detection; LOQ, limit of quantitation; mol L
1
, concentration;
1
D, first derivative spectrophotometry;
1
DD, first derivative of the
ratio spectra; SD, standard deviation; RSD, relative standard deviation; SPE, solid-phase extraction; T
1/2
, half life time; K, reaction rate constant;
MBTH, 3-methyl-2-benzothiazolinone hydrazone hydrochloride;
3
D, third-derivative spectrophotometry; PDAC, p-dimethylaminocinnamalde-
hyde; DPPH, 2,2-diphenyl-1-picrylhydrazyl; DPPH2, 2,2-diphenyl-1-picrylhydrazine; PDAB, p-dimethylaminobenzaldhyde; TG, thermogravime-
try; DSC, differential scanning calorimetry; TIC, 1,3,3-trimethyl-5-thiocyanato-2-[3-(1
0
,3
0
,3
0
-trimethyl-3
0
-H-indol-2
0
-ylidene)-propenyl]-indolium
chloride; p-chloranil, tetrachloro-p-benzoquinone; DCNP, 2,4,dichloro-6-nitrophenol; o-phen, o-phenanthroline; Bipy, bipyridyl; CT, charge
transfer; TCNE, tetracyanoethylene; DDQ, 2,3-dichloro-5,6-dicyano-p-benzoquinone; DCNP, 2,4,dichloro-6-nitrophenol;
2
D, second-derivative
spectrophotometry; PLS, partial least squares regression; GA-PLS, genetic algorithm-par tial least squares regression; l, ionic strength; a-CD,
a-cyclodextrin; b-CD, b-cyclodextrin; DH, enthalpy change; DS, entropy change; DG, free energy change; IUPAC, international union of pure
and applied chemistry; PHP, phenolphthalein.
2 A.A. Gouda et al.
Please cite this article in press as: Gouda, A.A. et al., Spectrophotometric and spectrofluorometric methods for the determination
of non-steroidal anti-inflammatory drugs: A review. Arabian Journal of Chemistry (2011), doi:10.1016/j.arabjc.2010.12.006
in plasma. Low values defining NSAIDs distribution volume
(from 0.1 to 1.0) in tissues may be a proof of poor distribution
of these drugs in extra vascular systems. A very high degree of
binding with plasma proteins (>97%) is the result of favorable
amiliphilic properties and accounts for the fact of displacing
other drugs from protein binding of NSAIDs. Most NSAIDs
are metabolized in the liver by oxidation and conjugation to
inactive metabolites which are typically excreted in the urine,
although some drugs are partially excreted in bile. Metabolism
may be abnormal in certain disease states, and accumulation
may occur even with normal dosage (Starek and Krzek, 2009).
NSAIDs are classified according to their chemical structure
into the following groups: salicylic acid derivatives (i.e. acetyl-
salicylic acid, salicylamid, sodium salicylate); aniline and
p-aminophenol derivatives (i.e. paracetamol, phenacetyne);
pyrazolone derivatives (i.e. phenylbutazone, propyphenazone);
oxicams (i.e. piroxicam, meloxicam, tenoxicam, lornoxicam,
droxicam); arylalkanoic acids derivatives (i.e. aceclofenac,
diclofenac, etodolac, indometacin, nabumetone, sulindac,
tolmetin); 2-arylpropionic acids derivatives (profens) (i.e. flur-
biprofen, ibuprofen, ketoprofen, naproxen, tiaprofenic acid);
N-arylanthranilic acids (fenamic acids) (i.e. mefenamic acid,
tolfenamic acid, flufenamic acid, meclofenamic acid); enolic
acid derivatives, and coxibs (i.e. celecoxib, rofecoxib, etoricox-
ib, parecoxib, valdecoxib); naphtylbutanone derivatives (nab-
umetone); sulphonamides (nimesulide); benzoxazocine
derivatives (nefopam). Four groups of NSAIDs only were cho-
sen in the present work due to more spectrophotometric and
spectroflourometric methods done.
Most NSAIDs act as non-selective inhibitors of the enzyme
cyclooxygenase, inhibiting both the cyclooxygenase-1 (COX-1)
and cyclooxygenase-2 (COX-2) isoenzymes. Cyclooxygenase
catalyzes the formation of prostaglandins and thromboxane
from arachidonic acid (itself derived from the cellular
phospholipid bilayer by phospholipase A
2
). Prostaglandins
act (among other things) as messenger molecules in the process
of inflammation.
NSAIDs are easily available and effective and thus are
extensively used by patients. The growing demand for these
agents stimulate a search for new even more effective drugs,
but also calls for higher level of quality control of these thera-
peutic substances and preparations, so that they are in the
highest possible degree free from any impurities that may come
from the production process, as well as from decomposition
products of active or auxiliary substances. Therefore, it seems
appropriate to develop new analytical methods regarding their
qualitative and quantitative analysis (Sherma, 2000; Rao et al.,
2005; Ferenczi-Fodor et al., 2001).
The progress of analytical chemistry in the scope of instru-
mentalisation of the methods of chemical analysis is reflected
in the use thereof in pharmacopoeia monographs as well as in
the standards adopted by manufacturers. A constant place is
occupied by chromatographic methods [high-performance li-
quid chromatography (HPLC), thin layer chromatography
(TLC), and gas chromatography (GC)]. Unification of the
equipment used necessitates preparation of a very accurate
and detailed description of conditions for carrying out the anal-
ysis. Other meaningful methods having a big meaning are also
ultraviolet–visible (UV–vis) and infrared (IR) spectropho-
tometry, atomic absorption spectrophotometry (AAS), nuclear
magnetic resonance (NMR), mass spectrometry (MS) or
spectrofluorometry. Among the analytical methods used for
determining NSAIDs are also electromigrational (capillary
electrophoresis (CE), capillary zone electrophoresis (CZE),
and micellar electrokinetic capillary chromatography (MEKC))
and voltamperometric methods. One that has been gaining
more and more applications is the flow injection analysis
(FIA), whose main advantage is the full automation of the anal-
ysis, which considerably minimizes the effects of side reactions
and thus increases the sensitivity and selectivity of this method.
Introduction of new methods, enabling carrying out deter-
minations with maximum accuracy, contributes to increased
interest in analytical methods as such. They should enable to
simultaneously determine the individual components in multi-
component preparations and in biological material. Range of
guidelines, standardizing requirements concerning the quality
of drugs, have been issued. Fulfillment confirms them the
appropriate quality of the product and of the analytical meth-
od used. These are numerical parameters that validate reliabil-
ity of the results and enable comparing efficiency of the
methods used. The process that is used to determine the above
parameters is the so-called method validation (Harmonised
Tripartite Guideline, 1996).
Development and validation of analytical methods are of
basic importance to optimize the analysis of drugs in the phar-
maceutical industry and to guarantee quality of the commer-
cialized product. Several techniques like AAS (Khuhawar
et al., 2001; Salem et al., 2000, 2001; Alpdogan and Sungur,
1999), HPLC (Hassan et al., 2008; Pavan Kumar et al.,
2006; Jaiswal et al., 2007; Vinci et al., 2006; Sun et al., 2003),
SPE-LC (Hirai et al., 1997 ), LC (Rouini et al., 2004 ), GC
(Thomas and Foster, 2004; El Haj et al., 1999; Gonza
´
lez
et al., 1996), CE (Makino et al., 2004; Ahrer et al., 2001; Pe
´
r-
ez-Ruiz et al., 1998), potentiometric (Santini et al., 2007), con-
ductometric (Aly and Belal, 1994) and voltammetric methods
(Liu and Song, 2006) have been used for the determination
of NSAIDs. Chromatographic methods have been extensively
used and recommended. However, these methods generally re-
quire complex and expensive equipment, provision for use and
disposal of solvents, labour-intensive sample preparation pro-
cedures and personal skills in chromatographic techniques.
Spectrophotometric and spectrofluorometric methods for
the determination of drugs can be used in laboratories where
modern and expensive apparatuses such as that required for
GLC or HPLC are not available. However, spectrophotomet-
ric and spectrofluorometric methods are versatile and econom-
ical particularly for developing countries. Spectrophotometric
and spectrofluorometric methods have several advantages such
as being easy, less expensive and less time consuming com-
pared with most of the other methods. Spectrophotometric
and spectrofluorometric methods are simple and rapid; so
these methods can be successfully used for pharmaceutical
analysis, involving quality control of commercialized product
and pharmacodynamic studies. These methods are mostly
based on the formation of coloured complexes between NSA-
IDs and the reagent which can be determined by visible spec-
trophotometry. The complexes formed are mostly due to
charge transfer reaction between the drug and the reagent or
due to formation of ion-pair complexes. The spectrophotomet-
ric methods are simple and rapid but less sensitive. UV- and
derivative spectrophotometric methods have also been widely
used for NSAIDs and are covered under this review.
In the last few years, there was no review published cover-
ing all different spectrophotometric techniques like (ion pair,
Spectrophotometric and spectrofluorometric methods 3
Please cite this article in press as: Gouda, A.A. et al., Spectrophotometric and spectrofluorometric methods for the determination
of non-steroidal anti-inflammatory drugs: A review. Arabian Journal of Chemistry (2011), doi:10.1016/j.arabjc.2010.12.006
charge transfer, metal complexes, flow injection, derivative)
used for the determination of NSAIDs. The high importance
of this class of drugs prompted us to review the most impor-
tant recent spectrophotometric methods for their analysis in
pure forms, in different pharmaceutical dosage forms and in
biological fluids reported so far in the literature. Because of
the large number of references that appeared as individual
methods or as part of clinical and pharmacological studies, it
is possible to make reference only to the most important pa-
pers. The present review comprises references covering the per-
iod from 1985 to 2010.
2. Spectrophotometric and spectrofluorometric methods for
determination of coxibs
2.1. Celecoxib
The official method of celecoxib was potentiometric titration
method with perchloric acid (Pharmacopoeia, 2004).
UV spectrophotometric methods have been developed for
the determination of celecoxib and tizanidine hydrochloride in
its pure and in its pharmaceutical formulations. Celecoxib hav-
ing absorption maximum at 251.2 nm in 0.1 mol L
1
sodium
hydroxide (Sankar, 2001). New UV spectrophotometric meth-
ods for the quantitative estimation of celecoxib, a selective
COX-2 inhibitor, in pure form and in solid dosage form were
developed in the present study. The linear regression equation
obtained by least square regression method, was Abs = 4.949 ·
10
2
. Conc. (lgmL
1
) + 1.110 · 10
2
. The detection limit was
found to be 0.26 lgmL
1
(Saha et al., 2002). Ultraviolet spec-
trophotometric method for the determination of celecoxib in
bulk and its pharmaceutical formulation (dispersible tablets
and capsules) has been developed. The absorbance maxima of
celecoxib in a mixture of methanol and 0.01 N sodium hydrox-
ide (1:1 v/v) were determined at 253.1 nm. Beer’s law is obeyed
over concentration range of 8–22 lgmL
1
with correlation
coefficient r > 0.999 (Sahu et al., 2009).
Two simple and sensitive spectrophotometric methods have
been developed for the quantitative estimation of celecoxib
from its capsule formulation. The first method is a UV spectro-
photometric method using methanol as solvent; the drug
showed absorption maximum at 253.2 nm in methanol and lin-
earity was observed in the concentration range of 5.0–
15 lgmL
1
. The second method is a visible spectrophotomet-
ric method, based on formation of red coloured complex of
drugs with o-phenanthroline and ferric chloride, the complex
showed absorbance maximum at 509.2 nm and linearity was
observed in the concentration range of 50–400 lgmL
1
(Pillai
and Singhvi, 2006).
A simple fluorescence method was developed for the direct
determination of celecoxib in capsules. The capsules were emp-
tied, pulverized and dissolved in either ethanol or acetonitrile,
sonicated and filtered. Direct fluorescence emission was mea-
sured at 355 ± 5 nm (exciting at 272 nm). The method was
fully validated and the recoveries were excellent, even in pres-
ence of excipients (Damiani et al., 2003).
2.2. Valdecoxib
The official method of valdecoxib was potentiometric titration
method with perchloric acid (Pharmacopoeia, 2004).
Two simple, rapid, accurate and economical methods have
been developed for the estimation of valdecoxib and tizanidine
HCl in the mixture. Valdecoxib has an absorbance maximum
at 243 nm in methanol: 0.1 mol L
1
HCl (1:1) mixture. The lin-
earity was observed in the concentration range 5.0–
30 lgmL
1
. First method is based on Q absorbance ratio
and second method is based on the simultaneous equations
(Sankar et al., 2007). Two methods for simultaneous estima-
tion of valdecoxib and tizanidine in combined dosage form
have been described. The first method; involves formation of
Q-absorbance equation at 239.6 (isoabsorptive point) and at
241 nm, while the second method; involves formation of simul-
taneous equation at 241 and 229 nm, using methanol as sol-
vent (Devarajan and Sivasubramanian, 2006). A reproducible
method for simultaneous estimation of valdecoxib and para-
cetamol in two-component tablet formulation has been devel-
oped. The method of analysis is derivative spectroscopy to
eliminate spectral interference by measuring analytical signals
or dA/dk value at 284 nm (Aditya et al., 2006). Analytical
method for the simultaneous estimation of valdecoxib and par-
acetamol in combined tablet dosage form by Vierodt’s UV
spectrophotometric method was validated. The k
max
value of
valdecoxib in 0.1 mol L
1
NaOH was 244 nm. Beer’s law is va-
lid in the concentration range of 1.0–6.0 lgmL
1
. The A1%
1 cm values for valdecoxib at 244 nm were 520 and 420
(Nagulwar et al., 2006). UV spectrophotometric method has
been developed for the simultaneous estimation of valdecoxib
and tizanidine in pharmaceutical dosage form. The proposed
method is based on the Vierodt’s simultaneous equations. Val-
decoxib absorption maxima at 239.0 nm in methanol. The lin-
earity was observed in the concentration range of 2–
18 lgmL
1
(Sharma et al., 2009). UV method was used for
bulk form as well as the formulation of the valdecoxib and
was expanded to study the dissolution profile of valdecoxib
tablets. The measurements were done at 241 nm, linear con-
centration range was observed to be 3–17 lgmL
1
. The per-
centage recovery was found to be between 99.52 and 100.32
(Baviskar et al., 2009).
A spectrophotometric method has been developed for the
determination of valdecoxib in pure and pharmaceutical dos-
age forms. The method is based on the reaction of valdecoxib
with potassium permanganate to form a bluish green coloured
chromogen with an absorption maximum at 610 nm. Beer’s
law was obeyed in the range of 5.0–25 lgmL
1
. The molar
absorpitivity is 7.1437 · 10
3
L mol
1
cm
1
(Suganthi et al.,
2006).
2.3. Rofecoxib
The official method of rofecoxib was potentiometric
titration method with perchloric acid (Pharmacopoeia,
2004).
Two different UV spectrophotometric methods were devel-
oped for the determination of rofecoxib in bulk form and in
pharmaceutical formulations. The first method, a UV spectro-
photometric procedure, was based on the linear relationship
between the rofecoxib concentration and the k
max
amplitude
at 279 nm. The second one, the first derivative spectrophotom-
etry, was based on the linear relationship between the rofecox-
ib concentration and the first derivative amplitude at 228, 256
and 308 nm. Calibration curves were linear in the concentration
range using peak to zero 1.5–35 lgmL
1
(Erk and Altuntas,
4 A.A. Gouda et al.
Please cite this article in press as: Gouda, A.A. et al., Spectrophotometric and spectrofluorometric methods for the determination
of non-steroidal anti-inflammatory drugs: A review. Arabian Journal of Chemistry (2011), doi:10.1016/j.arabjc.2010.12.006
2004). Rofecoxib has been determined in the presence of
its photo-degradation product using first derivative spectro-
photometry (
1
D) and first derivative of the ratio spectra
(
1
DD) by measuring the amplitude at 316.3 and 284 nm for
1
D and
1
DD, respectively. Rofecoxib can be determined in
the presence of up to 70% and 80% of the photo-degradation
product by the
1
D and
1
DD, respectively. The linearity range
of both the methods was the same (5.8–26.2 lgmL
1
) with
mean percentage recovery of 100.08 ± 0.84 and 100.06 ±
1.06 for
1
D and
1
DD, respectively.
1
D method was used to
study kinetics of rofecoxib photo-degradation that was found
to follow a first-order reaction. The T
1/2
was 20.2 min while K
(reaction rate constant) was 0.0336 mol min
1
(Shehata et al.,
2004). Rofecoxib was assayed by UV spectrophotometry, the
concentration ranges were 2.0–30 lgmL
1
(Duran et al.,
2004). UV and visible spectrophotometric methods have been
developed for the determination of rofecoxib in pure and its
pharmaceutical formulations. In UV method rofecoxib solu-
tion in methanol medium showed absorption maximum at
285 nm, whereas in visible spectrophotometric method it reacts
with ferric chloride and 3-methyl-2-benzothiazolinone hydra-
zone hydrochloride (MBTH) reagent and forms a green col-
oured chromogen having absorption maximum at 625 nm
(Reddy et al., 2002).
A spectrofluorometric method was described to determine
rofecoxib at very low concentrations (25–540 ng mL
1
) where
rofecoxib is converted to its photo-degradate product, which
possesses a native fluorescence that could be measured (Sheh-
ata et al., 2004).
2.4. Etoricoxib
The official method of etoricoxib was potentiometric titration
method with perchloric acid (Pharmacopoeia, 2004).
A presented method was performed at 284 nm for the anal-
ysis of etoricoxib formulations. Extraction of etoricoxib from
tablet was carried out using methanol. The linearity range
was 5.0–35 lgmL
1
(Shakya and Khalaf, 2007). A simple,
rapid, precise spectrophotometric method for estimation of
etoricoxib in bulk drug, dosage forms and human plasma
was developed. Sample preparation for the developed method
employs 90% methanolic sodium hydroxide (0.1 mol L
1
)as
the solvent system for analyzing bulk drug and dosage forms,
while precipitation using acetonitrile (direct procedure) and
liquid–liquid extraction with ethyl acetate (indirect procedure)
was utilized for its determination in human plasma samples.
All samples were analyzed spectrophotometrically at 280 nm.
For analysis of dosage forms, the method was found to be lin-
ear in the range of 3.0–60 lgmL
1
(r
2
= 0.9997 and 0.9998);
for estimation of human plasma samples, the method was
found to be linear in the range of 0.1–20 lgmL
1
(r
2
=
0.9998 and 0.9994, respectively, for direct and indirect method)
(Vadnerkar et al., 2006). Sensitive UV spectrophotometric
methods for the determination of etoricoxib and ezetimibe
were having absorption maximum at 235 and 230 nm, respec-
tively, and these methods were extended to pharmaceutical
preparations (Sankar et al., 2005). Extractive spectrophoto-
metric methods for the determination of etoricoxib in tab-
lets through ion–association complexes with bromocresol
Table 1 Comparison between the spectrophotometric methods for determination of coxibs.
Drug Method k
max
(nm) Linear range
(lgmL
1
)
Ref.
Celecoxib UV methods 251.2 Sankar (2001)
––Saha et al. (2002)
253.1 8–22 Sahu et al. (2009)
253.2 5.0–15 Pillai and Singhvi (2006)
1,10-Phenanthroline/ferric chloride 509.2 50–400 Pillai and Singhvi (2006)
Spectrofluorometric method k
em
= 355 ± 5 Damiani et al. (2003)
k
ex
= 272
Valdecoxib UV methods 243 5.0–30 Sankar et al. (2007)
239.6 Devarajan and Sivasubramanian (2006)
241
284 Aditya et al. (2006)
244 1.0–6.0 Nagulwar et al. (2006)
239 2–18 Sharma et al. (2009)
241 3–17 Baviskar et al. (2009)
Potassium permanganate 610 5.0–25 Suganthi et al. (2006)
Rofecoxib UV methods 279, 228, 256 and 308 1.5–35 Erk and Altuntas (2004)
316.3 5.8–26.2 Shehata et al. (2004)
284
2.0–30 Duran et al. (2004)
285 Reddy et al. (2002)
Ferric chloride/(MBTH) 625 Reddy et al. (2002)
Spectrofluorometric method 25–540 ng/ml Shehata et al. (2004)
Etoricoxib UV methods 284 5.0–35 Shakya and Khalaf (2007)
280 3.0–60 Vadnerkar et al. (2006)
235 Sankar et al. (2005)
BCG 416 Shah et al. (2009)
BCP 408
Spectrophotometric and spectrofluorometric methods 5
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green (BCG) and bromocresol purple (BCP) were soluble in
chloroform. The complex of etoricoxib with BCG and BCP
showed k
max
at 416 and 408 nm, respectively. Molar absorptiv-
ity, 1.9331 · 10
4
and 1.6642 · 10
4
L mol
1
cm
1
for BCG and
BCP, respectively (Shah et al., 2009).
Table 1 shows comparison between the published spectro-
photometric and spectrofluorometric methods for coxibs.
3. Spectrophotometric and spectrofluorometric methods for
determination of arylalkanoic acids
3.1. Aceclofenac
The official method of aceclofenac was potentiometric titration
method with sodium hydroxide (Pharmacopoeia, 2004).
Four procedures for simultaneous estimation of paraceta-
mol and aceclofenac in tablet dosage form have been devel-
oped. The first method employs the formation and solving of
simultaneous equation using 273 nm as the wavelength for
forming equation. The second method employs first order
derivative spectroscopy to eliminate spectral interference.
The third method employs selection of area under curve in
wavelength region of 271–275 nm and solving the equation.
The fourth method employed 266 nm as k
1
(isobestic point)
and 244 nm as k
2
, which is the k
max
of paracetamol. The solu-
tion of drug in methanol obeys Beer’s law in the concentration
range 10–100 lgmL
1
for aceclofenac (Nikam et al., 2007). A
simultaneous equation and Q-analysis UV spectrophotometric
method has been developed for the simultaneous determina-
tion of aceclofenac and paracetamol from the combined tablet
dosage form. The method involves solving of simultaneous
equation value analysis based on measurement of absorptivity
at 276, 249 and 270 nm, respectively. Linearity was in the
range 2.0–25 lgmL
1
for aceclofenac (Jain et al., 2007). Three
accurate methods; multicomponent, two wavelength and
simultaneous equations using area under curve have been de-
scribed for the simultaneous estimation of aceclofenac and
paracetamol in tablet dosage form. Absorption maxima of ace-
clofenac in methanol diluted with glass double distilled water
was found to be 274.5 nm. Beer’s law was obeyed in the con-
centration range 2.0–20 lgmL
1
for aceclofenac (Mahaparale
et al., 2007). A derivative spectrophotometric procedure has
been developed for the simultaneous determination of individ-
ual combination of aceclofenac and tramadol with paraceta-
mol in combined tablet preparations. Tablet extracts of the
drugs were prepared in distilled water. The zero crossing point
technique and the compensation technique were used to esti-
mate the amount of each drug in the combined formulations,
and were compared. Calibration graphs are linear
(r = 0.9999), with a zero intercept up to 24 lgmL
1
of each
drug in combination with paracetamol. Detection limits at
the p = 0.05 level of significance were calculated to be
0.5 lgmL
1
(Srinivasan et al., 2007). An UV-spectrophoto-
metric method was developed for the estimation of aceclofenac
in tablets. In this method, aceclofenac is determined accurately
having absorbance maximum at 203 nm. Beer’s law is obeyed
in the concentration range 0.0–20 lgmL
1
(Saravanan et al.,
2006). A spectrophotometric method for the determination
of aceclofenac in its pharmaceutical dosage forms has been
developed. Aceclofenac shows absorption maximum at
273.5 nm and obeyed Beer–Lambert’s law in the concentration
range of 5.0–45 lgmL
1
in the 7.4 phosphate buffer (Dashora
et al., 2006). Two spectrophotometric methods for the determi-
nation of aceclofenac and paracetamol in tablets have been
developed. First method is based on the additivity of absor-
bances. Second method is based on the determination of
graphical absorbance ratio at two selected wavelengths; one
being the isoabsorptive point for the drug (230 nm). Beer–
Lambert’s law is obeyed in the concentration range 1.0–
10 lgmL
1
(Mishra and Garg, 2006). New methods for the
determination of aceclofenac in the presence of its degradation
product (diclofenac) were described. Method A utilizes third
derivative spectrophotometry at 242 nm. Method B is a
1
DD
spectrophotometric method based on the simultaneous use of
the first derivative of ratio spectra and measurement at
245 nm. Method C is a pH-induced difference (DA) spectro-
photometry using UV measurement at 273 nm. Regression
analysis of a Beer’s plot showed good correlation in the con-
centration ranges 5.0–40, 10–40, 15–50 lgmL
1
for methods
A, B and C, respectively (Hasan et al., 2003). Three methods
were developed for the determination of aceclofenac in the
presence of its degradation product, diclofenac. In the first
method, third-derivative spectrophotometry (
3
D) is used. The
3
D absorbance is measured at 283 nm where its hydrolytic
degradation product diclofenac does not interfere. The sug-
gested method shows a linear relationship in the range of
4.0–24 lgmL
1
with mean percentage accuracy of 100.05 ±
0.88. This method determines the intact drug in the presence
of up to 70% degradation product with mean percentage
recovery of 100.42 ± 0.94. The second method depends on
ratio-spectra first-derivative (RSD
1
) spectrophotometry at
252 nm for aceclofenac and at 248 nm for determination of
the degradation product over concentration ranges of 4.0–
32 lgmL
1
for both aceclofenac and diclofenac with mean
percentage accuracy of 99.81 ± 0.84 and 100.19 ± 0.72 for
pure drugs and 100.17 ± 0.94 and 99.73 ± 0.74 for labora-
tory-prepared mixtures, respectively (El-Saharty et al., 2002).
Two methods have been developed for the quantitative esti-
mation of aceclofenac from tablet formulation using Folin–
Ciocalteu reagent. Aceclofenac forms a blue coloured chromo-
gen with the reagent, which shows absorbance maxima at
642.6 nm and linearity in the concentration range of 80–
160 lgmL
1
of drug (Singhvi and Goyal, 2007). Two conve-
nient visible spectrophotometric methods have been developed
for the estimation of aceclofenac in tablet formulation. The
developed methods are based on the formation of chloroform
extractable complex of aceclofenac with orange G in acidic
medium and naphthol green in aqueous medium. The ex-
tracted complex with orange G shows absorbance maxima at
481 nm and linearity in the concentration range of 10–
80 lgmL
1
. The extracted complex with naphthol green
shows absorbance maxima at 633.6 nm and linearity in the
concentration range of 0.2–1.0 lgmL
1
(Goyal and Singhvi,
2006). A spectrophotometric method for the determination
of aceclofenac in its pharmaceutical dosage forms has been
developed. The method is based on the formation of a col-
oured complex of the drug with ferric nitrate in acidic medium,
which has absorption maximum at 470 nm. Beer’s law is
obeyed over concentration range of 75–200 lgmL
1
(Mishra
and Garg, 2006). Quantitative determination of aceclofenac
in pure form and in pharmaceutical formulation was pre-
sented. The method is based on the reaction between the drug
via its secondary aromatic amino group and p-dimethylamino-
6 A.A. Gouda et al.
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of non-steroidal anti-inflammatory drugs: A review. Arabian Journal of Chemistry (2011), doi:10.1016/j.arabjc.2010.12.006
cinnamaldehyde (PDAC) in acidified methanol to give a stable
coloured complex after heating at 75 C for 20 min. Absorp-
tion measurements were carried out at 665.5 nm. Beer’s law
is obeyed over concentration range 20–100 lgmL
1
with mean
recovery 100.33 ± 0.84 (Zawilla et al., 2002). A spectrophoto-
metric procedure for the assay of aceclofenac has been
developed. The method is based on the reaction of aceclofenac
with 2,2-diphenyl-1-picrylhydrazyl (DPPH). The latter is
employed to abstract a hydrogen atom from the drug thereby
promoting a process of radical coupling. This results in a
reduction of the violet colour of DPPH with the formation
of the yellow coloured 2,2-diphenyl-1-picrylhydrazine
(DPPH2). The decrease in the intensity of the violet colour is
used to measure the concentration of the drug. All measure-
ments are made at k = 520 nm on methanolic solutions of
the reagent and drugs. Beer’s law is obeyed in the range of
5.0–30 lgmL
1
(Salem, 2000). A spectrophotometric method
was adopted for the analysis of the anti-inflammatory drug,
aceclofenac. The method is based on the formation of coloured
complexes between the drug and p-dimethylaminobenzalde-
hyde reagent (PDAB) in the presence of sulfuric acid and ferric
chloride. Measurement of the absorbance was carried out at
545.5 nm. Regression analysis of Beer’s plots showed good
correlation in the concentration ranges 8.0–55 l gmL
1
. The
spectrofluorometric method in samples of aceclofenac in the
phosphate buffer pH 8.0 showed native fluorescence at
k = 355 nm when excitation was at 250 nm. The calibration
graph was rectilinear from 2.0 to 8.0 lgmL
1
. The proposed
methods are applied successfully for the determination of the
drug in bulk powder with a mean accuracy of 100.03 ± 0.38
in the PDAB method and of 99.88 ± 0.45 in the spectrofluoro-
metric method (El Kousy, 1999).
3.2. Diclofenac
The official method of diclofenac was potentiometric titration
method with perchloric acid (Pharmacopoeia, 2004).
Spectrophotometric methods were developed and validated
for quantitation of diclofenac potassium and tizanidine in tab-
let dosage form. Three new analytical methods were developed
based on the simultaneous estimation of drugs in a binary
mixture without previous separation. In multiwavelength tech-
nique, the binary mixture was determined by mixed standards
and three sampling wavelengths of 277, 295 (isobestic point),
and 320 nm. In the simultaneous equation method, the drugs
were determined by using the absorptivity values of diclofenac
potassium at selected wavelength, viz., 277 nm. The standard
deviation value for the validation parameters was found to
be between 0.08% for multiwavelength technique and between
0.069% for simultaneous equation method. The graphical
absorbance ratio method was performed by absorbances at 277,
295 (isobestic point), and 320.4 nm of their mixture (Sanjay
et al., 2006). Spectrophotometric methodology was applied
in order to determine benzyl alcohol and diclofenac in inject-
able formulations by applying a multivariate calibration meth-
od. By a multivariate calibration method such as partial least
squares, it is possible to obtain a model adjusted to the concen-
tration values of the mixtures used in the calibration range. In
this study, the concentration model is based on absorption
spectra in the 230–320 nm range for 25 different mixtures of
benzyl alcohol and diclofenac. Calibration matrix contains
1.0–50 lgmL
1
for diclofenac (Ghasemi et al., 2005a). Two
spectrophotometric methods were presented for simultaneous
quantitative determination of benzyl alcohol and diclofenac
in various pharmaceutical forms. The first method makes use
of a derivative of the double-divisor-ratio spectrum of optical
density. The linear determination range is 12–45 lgmL
1
.In
the second method, the analytical signals are measured at
wavelengths corresponding to either maxima or minima for
both drugs in the spectra of the first derivative of the ratio
of optical densities of the sample and the standard solution
of one of the drugs. In this case, the linear determination
ranges is 14–45 lgmL
1
(Ghasemi et al., 2005b). A procedure
for determination of diclofenac in the presence of B vitamins
was described, based on UV measurements and partial least
squares. The interference of thiamine and pyridoxine were
modeled using an experimental design constructed in the
ranges of 10–50 lmol L
1
for diclofenac (Sena et al., 2004).
Spectrophotometric methodology was used in order to deter-
mine diclofenac and benzyl alcohol in injectable formulations
by applying, on the one hand, the first-derivative method of
crossing zero for diclofenac sodium and on the other, the sec-
ond derivative for benzyl alcohol (De Micalizzi et al., 1998 ).
Two methods for the determination of the diclofenac salts
[sodium or diethylammonium] in three pharmaceutical formu-
lations (tablets, suppositories and gel) are presented. In the
first, diclofenac salt is determined both by measuring the
absorbance of the solutions at a fixed wavelength (k =
276 nm) and using a multiwavelength computational program
to process the spectrophotometric data in a selected range
(k = 230–340 nm). In this case, the analysis is performed mea-
suring the peak-to-peak amplitude in the first-derivative UV
spectrum (
1
D 261.296). In the second method, diclofenac is
precipitated in acid medium and determined by the analysis
of the endothermic peak (t
p
= 182 C) in the DSC curve ob-
tained in nitrogen atmosphere. Finally, some aspects of chem-
ical (solubility, acid–base equilibria, redox reaction),
spectroscopic (UV, IR) and thermoanalytical (TG, DSC)
behaviour of DS and DH and the values of the parameters
which enable to calculate the UV spectrum of DS in aqueous
solution are reported (Bucci et al., 1998). A second derivative
spectrophotometric method (
2
D) has been developed for the
determination of the degradation products from diclofenac so-
dium in gel-ointment. The amplitudes in the second derivative
spectra at 260 and 265 nm were selected to determine oxindol.
The LOD of oxindol was estimated to be 0.01% with respect to
the gel-ointment ( Karamancheva et al., 1998). Three proce-
dures for simultaneous estimation of diclofenac sodium and
paracetamol in two component tablet formulation have been
developed. The methods employ first derivative ultraviolet
spectrophotometry, simultaneous equations and the program
in the multicomponent mode of analysis of the instrument
used, for the simultaneous estimation of the two drugs. In
0.02 mol L
1
sodium hydroxide, diclofenac sodium has max-
ima at 276 nm (Bhatia et al., 1996). A procedure for simulta-
neous estimation of diclofenac sodium, chlorzoxazone and
paracetamol in three component tablet formulations has been
developed. The method is based on the native ultraviolet
absorbance maxima of the three drugs in 0.02 mol L
1
sodium
hydroxide. Diclofenac sodium has absorbance maxima at
276 nm (Bhatia and Dhaneshwar, 1995). Spectrophotometric
methods for simultaneous estimation of diclofenac sodium
and rabeprazole in combined dosage form. Methanol was
used as a common solvent for both the drugs. Linearity was
Spectrophotometric and spectrofluorometric methods 7
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observed at both wavelengths in the concentration range of
10–50 lgmL
1
for each drug (Choudhary et al., 2010).
A new spectrophotometric method has been developed for
the determination of diclofenac sodium in pharmaceutical
preparations. This method is based on the reaction of diclofenac
sodium with an analytical reagent 1,3,3-trimethyl-5-thiocya-
nato-2-[3-(1
0
,3
0
,3
0
-trimethyl-3
0
-H-indol-2
0
-ylidene)-propenyl]-
indolium chloride (TIC) at pH 8.0–11.0 and the extraction of
ion associate coloured complex. This ion associate complex
(1:1) was detected and extracted with toluene and an absorp-
tion maximum at 566.2 nm against a blank reagent. The
calibration graph was linear from 0.9 to 11 lgmL
1
of diclofe-
nac and the LOD was 0.86 lgmL
1
(Kormosh et al., 2008).
An extractive-spectrophotometric method for the preconcen-
tration and determination of diclofenac was developed. In a
strong nitric acid medium, diclofenac produced a yellowish
compound in a water/tetrahydrofuran/perfluorooctanoic acid
homogeneous phase that could be extracted into a sedimented
microdroplet. The concentration of the extracted coloured
compound in the microdroplet was determined by measuring
its absorbance at 376 nm. The maximum absorbance was
achieved in 1.5 and 7.0 mol L
1
aqueous and methanolic solu-
tions of nitric acid. The absorbance of diclofenac solutions in
water and methanol obeyed Beer’s law, over the range of 1.0–
30 and 0.5–40 lgmL
1
, with molar absorptivities of 7.4 · 10
3
and 1.3 · 10
4
L mol
1
cm
1
, respectively. The LOD achieved
with the proposed method was 0.03 ng mL
1
(Ghiasvand
et al., 2008). A kinetic method based on a ligand-exchange
reaction for the determination of micro quantities of diclofe-
nac sodium was described. The reaction was followed spectro-
photometrically by monitoring the rate of appearance of the
cobalt diclofenac complex at 376 nm. The optimized condi-
tions yielded a theoretical LOD of 1.29 lgmL
1
based on
the 3S
b
criterion (Mitic
´
et al., 2007). An effective method for
the determination of sodium or potassium diclofenac is pro-
posed in its pure form and in their pharmaceutical prepara-
tions. The method is based on the reaction between
diclofenac and tetrachloro-p-benzoquinone (p-chloranil), in
methanol medium. This reaction was accelerated by irradiating
of reactional mixture with microwave energy (1100 W) during
27 s, producing a charge transfer complex with a maximum
absorption at 535 nm. Beer’s law is obeyed in a concentration
range from of 1.25 · 10
4
to 2.00 · 10
3
mol L
1
with a corre-
lation coefficient of 0.9993 and molar absorptivity of
0.49 · 10
3
L mol
1
cm
1
. The LOD was 1.35 · 10
5
mol L
1
and the LOQ was 4.49 · 10
5
mol L
1
(Ciapina et al., 2005).
A spectrophotometric method was proposed for determination
of sodium diclofenac in pharmaceutical preparations based on
its reaction with concentrated nitric acid (63% w/v). The reac-
tion product is a yellowish compound with maximum absor-
bance at 380 nm. The corresponding calibration curve is
linear over the range of 1.0–30 lgL
1
, while the LOD is
0.46 lgL
1
(Matin et al., 2005). A modified procedure for
the visible spectrophotometric determination of diclofenac, in
pharmaceutical preparations using as reagent an aqueous solu-
tion of copper(II), is proposed. A green colour complex is
formed between copper(II) and diclofenac with a maximum
light absorption at 680 nm. The optimal conditions were found
to be 5.3 (pH of the solution to be extracted), 50.0 mg mL
1
(copper(II) acetate in 0.01 mol L
1
acetic acid solution) and
three extractions with chloroform using a total volume of
5.0 mL. The intrinsic RSD of the proposed method was about
2.3% for sodium diclofenac and 2.7% for potassium
diclofenac. The linear correlation coefficient, r, was 0.9984
for sodium diclofenac salt and 0.9993 for potassium diclofenac
salt. The linear range goes from 1.0 to 25.0 mg mL
1
in the
working solution. The LOD is 0.2 mg mL
1
and the LOQ is
0.7 mg mL
1
(De Souza and Tubino, 2005). A spectrophoto-
metric method for the determination of diclofenac sodium in
pure form and in pharmaceutical formulations was developed.
The method is based on the oxidation of diclofenac sodium by
iron(II) in the presence of o-phenanthroline. The formation of
tris(o-phenanthroline) iron(II) complex (ferroin) upon the
reaction of diclofenac sodium with an iron(III)-o-phenanthro-
line mixture in acetate buffer solution of pH 4.4, respectively,
was investigated. The ferroin complex is measured at 510 nm
against a reagent blank prepared in the same manner. The
optimum experimental parameters for the colour production
are selected. Beer’s law is valid within a concentration range
of 1.0–32 lgmL
1
. For more accurate results, Ringbom opti-
mum concentration ranges are 2.0–30 lgmL
1
. The molar
absorptivity is 1.15 · 10
4
L mol
1
cm
1
, whereas Sandell sensi-
tivity is 2.78 ng cm
2
. The method gave a mean percentage
recoveries 99.8 ± 1.2% (El-Didamony and Amin, 2004).
Spectrophotometric determination of diclofenac sodium using
2,2-diphenyl-1-picrylhydrazyl (Salem, 2000) was investigated.
Simple spectrophotometric methods are described (Agrawal
and Shivramchandra, 1991) for the determination of diclofe-
nac. In the first method diclofenac reduces iron(III) to iron(II)
when heated in aqueous solution. The ferrous ions produced
react with 2,2
0
-bipyridine to form a complex having a maxi-
mum absorbance at 520 nm. The reaction obeys Beer’s law
for concentrations of 10–80 lgmL
1
. In the second method,
diclofenac is treated with methylene blue in the presence of
phosphate buffer (pH 6.8) and the complex is extracted with
chloroform. The complex has a maximum absorbance at
640 nm and the graph of absorbance against concentration is
linear in the range 5–40 l gmL
1
. A multifactor optimization
technique was successfully applied to develop a new spectro-
photometric method in which diclofenac sodium is analyzed
and determined as it is Fe(III) complex. The effect of simulta-
neously varying the pH, ionic strength and concentration of
colour reagents in the reaction mixture were studied. A four-
variable two-level factorial design was used to investigate the
significance of each variable and interactions between them.
A response surface design was used to optimize complex for-
mation and extraction. It was established that diclofenac reacts
with Fe(III) chloride, in the presence of ammonium thiocya-
nate, in the pH range 4.2–6.5, forming a red chloroform
extractable (2:1) complex with maximum absorbance at
481 nm. By applying the methods of Sommer and Job involv-
ing non-equimolar solutions the conditional stability constant
of the complex, at the optimum pH of 6.0 and an ionic strength
l = 0.19 mol L
1
, was found to be 10
6.4
. Good agreement
with Beer’s law was found for diclofenac concentrations up
to 1.57–15.7 mmol L
1
(0.1–1.0 mg mL
1
). The nominal
percent recovery of diclofenac was 98.8% (n = 10). The lower
limit of sensitivity of the method was found to be
14.7 lgmL
1
(Agatonovic-Kus
ˇ
trin et al., 1997). A colorimetric
method for the quantitative determination of diclofenac so-
dium in pure form and in pharmaceutical preparations was
developed. It was based on the interaction of the secondary
aromatic amine with p-dimethylaminocinnamaldehyde in acid-
ified absolute methanol medium to form very stable red [k
max
8 A.A. Gouda et al.
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of non-steroidal anti-inflammatory drugs: A review. Arabian Journal of Chemistry (2011), doi:10.1016/j.arabjc.2010.12.006
at 538 nm] products. Beer’s law was obeyed over the range 10–
80 lgmL
1
. The reactants were heated on a boiling water bath
for 6.0 min (El Sherif et al., 1997). A validated method has
been developed for estimation of diclofenac diethylammonium
in bulk and formulation. The present method utilizes the reac-
tion of diclofenac diethylammonium with 1.0% w/v potassium
ferricyanide in presence of 0.5% w/v sodium hydroxide which
produces orange chromogen with maximum absorbance at
450 nm and obeys Beer’s law in the concentration range of
2.0–12 lgmL
1
. The chromogen is stable for more than
30 min (Validya and Parab, 1995). A spectrophotometric
method was described for the determination of diclofenac so-
dium in bulk samples and pharmaceutical preparations. The
method is based on the reaction of diclofenac sodium with p-
N,N-dimethylphenylenediamine in the presence of S
2
O
8
2
or
Cr(VI) whereby an intensely coloured product having maxi-
mum absorbance at 670 nm is developed. The reaction is sen-
sitive enough to permit the determination of 2.0–24 lgmL
1
(Sastry et al., 1989).
Two FI spectrophotometric methods were proposed for the
determination of diclofenac in bulk samples and pharmaceuti-
cals. Both methods are based on the reaction of diclofenac
with potassium ferricyanide in a sodium hydroxide medium.
The absorbance of the orange products obtained is measured
at 455 nm. The corresponding calibration graphs are linear
over the range 0.20–20 lgmL
1
, while the LOD were
0.05 lgmL
1
(Garci
´
a et al., 2001). A flow-through sensor
for the determination of diclofenac sodium was developed,
based on retention of the analyte on a Sephadex QAE A-25 an-
ion-exchange resin packed in a flow-cell of 1.0 mm of optical
path length, and monitoring of its intrinsic absorbance by
UV-spectrophotometry at 281 nm. Diclofenac could be deter-
mined in the concentration ranges 2.0–40.0, 1.0–22.0 and
0.5–14.0 lgmL
1
with RSD (%) ranging from 1.05 to 1.53
for sample volumes of 300, 600 and 1200 lL, respectively.
The proposed sensor was satisfactorily applied to the rapid
determination of diclofenac in commercial pharmaceutical
preparations and in semi-synthetic pharmaceuticals containing
diclofenac and paracetamol (Ortega-Barrales et al., 1999). A
FI spectrophotometric method for the determination of dic-
lofenac sodium based on the formation of coloured compound
with Ce(IV)–3-methyl-2-benzothiazolinone hydrazone hydro-
chloride (MBTH) in 3.0 · 10
2
mol L
1
H
2
SO
4
medium was
proposed. Using the peak height as a quantitative parameter
diclofenac was determined at 580 nm over the range 0.2–
8.0 lgmL
1
. The method was successfully applied to the
determination of diclofenac in pharmaceuticals and urine sam-
ples (Garci
´
a et al., 1998). Diclofenac sodium, famotidine and
ketorolac tromethamine were determined by FIA with spectro-
photometric detection. The sample solution 5.0–50 lgmL
1
of
diclofenac sodium, in methanol was injected into a flow system
containing 0.01% (w/v) of 2,4,dichloro-6-nitrophenol (DCNP)
in methanol. The colour produced due to the formation of a
charge transfer complex was measured with a spectrophoto-
metric detector set at 450 nm. A sampling rate of 40 per hour
was achieved with high reproducibility of measurements
(RSD 6 1.6%) Kamath et al., 1994.
The spectrophotometric determination of trace amounts of
diclofenac was carried out by liquid–liquid extraction using
acridine yellow with a flow system (Pe
´
rez-Ruiz et al., 1997).
The determination of diclofenac sodium in the range of 3.0–
80 lgmL
1
was possible with a sampling frequency of 40 sam-
ples h
1
. The spectrofluorometric determination of diclofenac
[2-(2,6-dichloroanilino)-phenylacetic acid] in pharmaceutical
tablets and ointments was described (Damiani et al., 1999).
It involves excitation at 287 nm of an acid solution (HCl
0.01 M) of the drug and measurement of the fluorescence
intensity at 362 nm. The linear range is 0.2–5.0 lgmL
1
.No
interference is observed from the excipients or from other
drugs which accompany diclofenac in certain formulations
(paracetamol or cianocobalamine).
The next study focuses on the complex formed between
a-cyclodextrin (a-CD) and diclofenac in aqueous solution
and also on its potential analytical applications. It was corrob-
orated that the fluorescence emission band of diclofenac is
significantly intensified in the presence of a-CD. From the
changes in the fluorescence spectra, it was concluded that
a-CD forms a 1:1 inclusional complex with diclofenac and
its equilibrium constant was calculated to be 1.20(3) ·
10
3
mol L
1
. With the purpose of characterizing the inclusion
complex, the acid–base behaviour of diclofenac in both the
presence and absence of a-CD was spectrophotometrically
investigated. From the results obtained, it was inferred that
both the carboxyl and the secondary amino groups of the guest
molecule remain outside the cyclodextrin cavity. Further de-
tails on the complex structure were obtained by
1
H NMR mea-
surements and semiempirical calculations. In addition to the
analysis of the a-CD-diclofenac interaction, a new approach
for the quantification of diclofenac in the presence of a-CD
is described in the range 0.0–5.0 lgmL
1
(Arancibia et al.,
2000). A spectrofluorometric method for the microdetermina-
tion of diclofenac sodium has been developed through its reac-
tion with cerium(IV) in an acidic solution and measurement of
the fluorescence of the Ce(III) ions produced. Under the opti-
mum experimental conditions for the oxidation reaction,
1.0 mol L
1
H
2
SO
4
with 90 min of heating time (100 C), the
range of application is 124.3–600 ng mL
1
and the limit of
detection is 72.7 ng mL
1
(Castillo and Bruzzone, 2006). A
new method has been devised for the determination of diclofe-
nac sodium in bulk and in pharmaceutical preparations using
Eu(III) ions as the fluorescent probe. The technique was built
around the hypersensitive property of the transitions of the
fluorescent probe ion, Eu(III), at 616 nm. This is normally a
forbidden transition, but the interaction with diclofenac so-
dium, which contains a carboxylic group, makes the transition
allowed and enhances the intensity of its fluorescence emission.
The Eu(III) fluorescence emission at 592 nm comes from a
non-hypersensitive transition and is not affected by ligation.
The intensity ratio, R, defined as I
592
/I
616
, was used as a mea-
sure of the percentage of bound probe ions. Diclofenac and
Eu(III) forms a (1:1) molar complex. The relative stability con-
stant of the complex was found to be 10
5
. A linear relationship
between bound Eu(III) and the concentration of diclofenac so-
dium was found for concentrations from 10 to 200 lgmL
1
,
with a recovery percentage of 100.22 ± 2.27 (Carreira et al.,
1995).
3.3. Etodolac
The official method of etodolac was potentiometric titration
method with tetrabutylammonium hydroxide (Pharmacopoeia,
2004).
Two spectrophotometric and spectrofluorometric methods
were adopted for the analysis of the anti-inflammatory drugs,
Spectrophotometric and spectrofluorometric methods 9
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Table 2 Comparison between the spectrophotometric methods for determination of arylalkanoic acids.
Name of drug Method k
max
(nm) Linear range
(lgmL
1
)
Ref.
Aceclofenac UV methods 273 10–100 Nikam et al. (2007)
276, 249 and 270 2.0–25 Jain et al. (2007)
274.5 2.0–20 Mahaparale et al. (2007)
up to 24 Srinivasan et al. (2007)
203 0.0–20 Saravanan et al. (2006)
273.5 5.0–45 Dashora et al. (2006)
230 1.0–10 Mishra and Garg (2006)
242 5.0–40 Hasan et al. (2003)
245 10–40
273 15–50
283 4.0–24 El-Saharty et al. (2002)
252 4.0–32
Folin–Ciocalteu 642.6 80–160 Singhvi and Goyal (2007)
Orange G in acidic medium 481 10–80 Goyal and Singhvi (2006)
Naphthol green in aqueous medium 633.6 0.2–1.0
Ferric nitrate in acidic medium 470 75–200 Mishra and Garg (2006)
p-Dimethylaminocinnamaldehyde (PDAC) 665.5 20–100 Zawilla et al. (2002)
2,2-Diphenyl-1-picrylhydrazyl (DPPH) 520 5.0–30 Salem (2000)
p-Dimethylaminobenzaldhyde reagent
(PDAB)/sulfuric acid/ferric chloride
545.5 8.0–55 El Kousy (1999)
Spectrofluorimetric method k
em
= 355 2.0–8.0 El Kousy (1999)
k
ex
= 250
Diclofenac UV methods 277, 295 (isobestic
point), and 320
Sanjay et al. (2006)
277
277, 295 and 320.4
230–320 1.0–50 Ghasemi et al. (2005a)
12–45 Ghasemi et al. (2005b)
14–45
10–50 lmol L
1
Sena et al. (2004)
276 Bucci et al. (1998)
260 and 265 Karamancheva et al. (1998)
276 Bhatia et al. (1996)
3,3-Trimethyl-5-thiocyanato-2-
[3-(1
0
,3
0
,3
0
-trimethyl-3
0
-H-indol-2
0
-ylidene)-propenyl]-
indolium chloride (TIC)
566.2 0.9–11 Kormosh et al. (2008)
Nitric acid in aqueous media 376 1.0–30 Ghiasvet al. (2008)
Nitric acid in methanol media 0.5–40
Kinetic method 376 Mitic
´
et al. (2007)
p-Chloranil, in methanol medium 535 1.25 · 10
4
–2
· 10
3
mol L
1
Ciapina et al. (2005)
Concentrated nitric acid (63% w/v) 380 1.0–30 Matin et al. (2005)
Copper (II) 680 1.0–25 De Souza and Tubino (2005)
Iron(II)/o-phenanthroline 510 1.0–32 El-Didamony and Amin (2004)
2,2-Diphenyl-1-picrylhydrazyl Salem (2000)
Fe
3+
/2,2
0
-bipyridine 520 10–80 Agrawal and Shivramchandra (1991)
Fe(III)/ammonium thiocyanate pH range (4.2–6.5) 481 Agatonovic-Kus
ˇ
trin et al. (1997)
p-Dimethyl-aminocinnamaldhyde 538 10–80 El Sherif et al. (1997)
potassium ferricyanide/NaOH 450 2.0–12 Validya and Parab (1995)
p-N,N-Dimethylphenylenediamine/S
2
O
8
2
or Cr(VI) 670 2.0–24 Sastry et al. (1989)
Flow injection with potassium
ferricyanide/sodium hydroxide
455 0.2–20 Garci
´
a et al. (2001)
Flow-through sensor 281 2.0–40 Ortega-Barrales et al. (1999)
Flow-injection with Ce(IV)–(MBTH)/H
2
SO
4
580 0.20–8.0 Garci
´
a et al. (1998)
Flow injection with 2,4,dichloro-
6-nitrophenol (DCNP) in ethanol
450 5.0–50 Kamath et al. (1994)
Spectrofluorimetric methods with -cyclodextrin 0.0–5.0 Arancibia et al. (2000)
with cerium(IV) in an acidic solution 0.1243–0.600 Castillo and Bruzzone (2006)
with Eu
3+
ions k
em
= 592 10–200 Carreira et al. (1995)
k
ex
= 616
10 A.A. Gouda et al.
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of non-steroidal anti-inflammatory drugs: A review. Arabian Journal of Chemistry (2011), doi:10.1016/j.arabjc.2010.12.006
etodolac and aceclofenac. The first method is based on the for-
mation of coloured complexes between the drugs and p-
dimethylaminobenzaldehyde reagent (PDAB) in the presence
of sulfuric acid and ferric chloride. Measurement of the absor-
bance was carried out at 591.5 nm for etodolac. Regression
analysis of Beer’s plots showed good correlation in the concen-
tration ranges 10–80 lgmL
1
. The second was the spectroflu-
orometric method in which samples of etodolac in ethanol
showed native fluorescence at a k = 345 nm when excitation
was at 235 nm. The calibration graph was rectilinear from 96
to 640 ng mL
1
. The proposed methods were applied success-
fully for the determination of the two drugs in bulk powder
with a mean accuracy of 100.48 ± 0.85 in the PDAB method
and of 99.88 ± 0.45 in the spectrofluorometric method (El
Kousy, 1999).
Gouda and Hassan have described (Gouda and Hassan,
2008) three spectrophotometric methods (A–C) for the deter-
mination of etodolac in pure form and in pharmaceutical for-
mulations. The first and second methods, A and B, are based
on the oxidation of the studied drugs by Fe(III) in the presence
of o-phenanthroline (o-phen) or bipyridyl (Bipy). The forma-
tion of tris-complex upon reactions with Fe(II)-o-phen and/
or Fe(III)-Bipy mixture in an acetate buffer solution of the
optimum pH-values was demonstrated at 510 and 520 nm with
o-phen and Bipy. The third method C, is based on the reduc-
tion of iron(III) by etodolac in acid medium and subsequent
interaction of iron(II) with ferricyanide to form prussian blue
and the product exhibits absorption maximum at 725 nm. The
concentration ranges are from 0.5 to 8.0, 1.0 to 10 and 2.0 to
18 lgmL
1
for methods A, B and C, respectively.
A spectrophotometric method for the determination of
etodolac was described. This method based on the etodolac
can reduce Fe(III) to Fe(II) in the presence of 2,2
0
-bipyridyl
(Bipy) and pH 3.5–6.0 acetate buffer medium. The Fe(II) can
react with Bipy to form a Fe(II)–Bipy coloured complex.
The maximum absorbance of the coloured complex is at
500 nm. Beer’s law is obeyed in the range of 0.5–25 lgmL
1
for etodolac. The method was applied to the determination
of etodolac in tablets without any interference from common
excipients. The RSD was 0.82% with recoveries 97–102%
(Hu et al., 2008).
Spectrophotometric method for the determination of etod-
olac was described. This method is based on the oxidation of
the studied drugs by Fe
3+
in the presence of o-phenanthroline
(o-phen) medium. The formation of tris-complex upon reac-
tions with Fe
3+
o-phen in an acetate buffer solution of the
optimum pH-values was demonstrated at 510 nm with o-phen.
The concentration ranges are from 0.5 to 20 lg/mL for this
method. The relative standard deviations were 60.76% with
recoveries 99–101% (Ye et al., 2009).
Charge transfer (CT) complexes of etodolac, which is elec-
tron donor with some p-acceptors, such as tetracyanoethylene
(TCNE), 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ), p-
chloranil (p-CHL), have been investigated spectrophotometri-
cally in chloroform at 21 C. The coloured products are mea-
sured spectrophotometrically at different wavelength
depending on the electronic transition between donors and
acceptors. Beer’s law is obeyed and colours were produced in
non-aqueous media. All complexes were stable at least 2.0 h
except for etodolac with DDQ stable for 5.0 min. The equilib-
rium constants of the CT complexes were determined by the
Benesi–Hildebrand equation. The thermodynamic parameters
DH, DS, DG were calculated by Van’t Hoff equation. Stoichi-
ometry of the complexes formed between donors and acceptors
were defined by the Job’s method of the continuous variation
and found in 1:1 complexation with donor and acceptor at the
maximum absorption bands in all cases (Duymus et al., 2006).
A method depends on complexation of etodolac with cop-
per(II) acetate and iron(III) chloride followed by extraction
of complexes with dichloromethane and then measuring the
extracted complexes spectrophotometrically at 684 and
385 nm in case of Cu(II) or Fe(III), respectively, was devel-
oped. Different factors affecting the reaction, such as pH, re-
agent concentration, and time were studied. By use of Job’s
method of continuous variation, the molar ratio method,
and elemental analysis, the stoichiometry of the reaction was
found to be in the ratio of 1:2 and 1:3, metal: drug in the case
of Cu(II) and Fe(III), respectively. The method obeys Beer’s
Table 2 (continued)
Name of drug Method k
max
(nm) Linear range
(lgmL
1
)
Ref.
Etodolac p-Dimethylaminobenzaldhyde reagent
(PDAB)/sulfuric acid/ferric chloride
591.5 10–80 El Kousy (1999)
Fe(III)/o-phenanthroline (o-phen) 510 0.5–8 Gouda and Hassan (2008)
Fe(III)
3+
/bipyridyl (Bipy) 520 1.0–10
Fe(III)/ferricyanide 725 2.0–18
Fe(III)/2,2
0
-bipyridyl 500 0.5–25 Hu et al. (2008)
TCNE Duymus et al. (2006)
DDQ
p-CHL
Copper(II) acetate 684 2.0–9.0 Amer et al. (2005)
Iron(III) chloride 385 0.5–2.0 mg mL
1
Spectrofluorometric method k = 345 k
ex
= 235 0.096–0.640 El Kousy (1999)
Ketorolac (MBTH)/Fe(III) 684 10–60 Shingbal and Naik (1997)
Flow injection analysis (FIA): 2,4,dichloro-
6-nitrophenol (DCNP) in methanol
450 10–120 Kamath et al. (1994)
Spectrofluorometry in cerium(IV)/H
2
SO
4
k
ex
= 255 0.1–0.8 Eid et al. (2007)
k
em
= 365
Spectrophotometric and spectrofluorometric methods 11
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law in a concentration range of 2.0–9.0 and 0.5–2.0 mg mL
1
in case of Cu(II) and Fe(III), respectively. The stability of
the complexes formed was also studied, and the reaction prod-
ucts were isolated for further investigation. The complexes
have apparent molar absorptivity of about 32.14 ± 0.97 and
168.32 ± 1.12 for Cu(II) and Fe(III), respectively (Amer
et al., 2005).
3.4. Ketorolac
The official method of ketorolac was potentiometric titration
method with tetrabutylammonium hydroxide (Pharmacopoeia,
2004).
A spectrophotometric method has been developed for the
estimation of ketorolac tromethamine and its dosage forms,
based on its reaction with 3-methyl-2-benzothiazolinone
hydrazone hydrochloride (MBTH) in presence of Fe(III) ion
yielding a green coloured chromogen with absorption maxima
at 684 nm. Beer’s law is obeyed in the concentration range of
10–60 lgmL
1
(Shingbal and Naik, 1997).
Ketorolac tromethamine was determined by FIA with
spectrophotometric detection. The sample solution 10–120
lgmL
1
in methanol was injected into a flow system containing
0.01% (w/v) of 2,4,dichloro-6-nitrophenol (DCNP) in metha-
nol. The colour produced due to the formation of a charge trans-
fer complex was measured with a spectrophotometric detector
set at 450 nm (Kamath et al., 1994).
A fluorometric method for determination of ketorolac tro-
methamine was studied. The method depends on oxidation of
the drug with cerium(IV) and subsequent monitoring of the
fluorescence of the induced cerium(III) at k
em
365 nm after
excitation at 255 nm. Different variables affecting the reaction
conditions, such as the concentrations of cerium(IV), sulfuric
acid concentration, reaction time, and temperature, were care-
fully studied and optimized. Under the optimum conditions, a
linear relationship was found between the relative fluorescence
intensity and the concentration of the investigated drug in the
range of 0.1–0.8 lgmL
1
(Eid et al., 2007).
Table 2 shows comparison between the published spectro-
photometric and spectrofluorometric methods for arylalkanoic
acids.
4. Spectrophotometric and spectrofluorometric methods for
determination of N-arylanthranilic acids derivatives (fenamic
acids)
4.1. Mefenamic acid
The official method of mefenamic acid was potentiometric
titration method with sodium hydroxide (Pharmacopoeia,
2004).
Two spectrophotometric methods for simultaneous estima-
tion of two-component drug mixture of ethamsylate and mefe-
namic acid in combined tablet dosage form have been
developed. The first developed method involves formation
and solving of the simultaneous equation using 287.6 and
313.2 nm as two wavelengths. The second developed method
is based on two wavelengths selected for estimation of
mefenamic acid which were 304.8 and 320.4 nm (Goyal and
Singhvi, 2008). The spectrophotometric methods for the deter-
mination of mefenamic acid and ethamsylate in pharmaceuti-
cal formulations have been developed. The methods are
based on the additivity of absorbances and the determination
of graphical absorbance ratio at two selected wavelengths,
one being the isoabsorptive point for the two drugs (301 nm)
and the other being the absorption maximum of mefenamic
acid (336 nm). The Beer–Lambert’s law is obeyed for
mefenamic acid in the concentration range 4.0–28 lgmL
1
(Garg et al., 2007). Two new, simple, accurate and economical
spectrophotometric methods have been developed for simulta-
neous estimation of drotaverine hydrochloride and mefenamic
acid in two-component tablet formulation. The methods em-
ployed are, first derivative spectrophotometry, using zero
crossing technique and multicomponent analysis. Both the
drugs obey the Beer’s law in the concentration range of
4–32 lgmL
1
. For quantitative estimation, absorbances were
measured at k
max
of both the drugs viz. 279 and 308 nm for
MA and DH, respectively. The assay values for tablets, were
in the range of 99.15–99.30% for MA (Dahivelkar et al.,
2007). A spectrophotometric method in the UV range has been
developed for the simultaneous determination of mefenamic
acid and paracetamol in bulk and in dosage forms. Mefenamic
acid shows three absorbance maxima at 219, 284 and 336 nm
in 0.1 mol L
1
sodium hydroxide (Dhake et al., 2001). A
simultaneous spectrophotometric procedure for the determina-
tion of mefenamic acid and paracetamol in two component
tablet formulations has been developed. The method is based
on the two-wavelength method of calculations. The difference
in absorbance at 217 and 285 nm was used for determination
of mefenamic acid (Gangwal and Sharma, 1996).
In the Vierordt’s spectrophotometric method, the drugs
were determined by using the absorptivity values of mefenamic
acid at selected wavelengths, viz., 216.8 nm, respectively. In Q-
analysis method, isoabsorptive point was found to be at
224.6 nm. The drug obeys Beer’s law in concentration range
of 4–18 lg/mL (Kumar et al., 2009).
A simple visible spectrophotometric method is described
for the determination of mefenamic acid in bulk sample and
pharmaceutical preparations. The method is based on the
reaction of mefenamic acid with p-N,N-dimethylphenylenedi-
amine in the presence of S
2
O
8
2
or Cr(VI) whereby an inten-
sely coloured product having maximum absorbance at 740 nm
is developed. The reaction is sensitive enough to permit the
determination of 0.25–4.0 lgmL
1
(Sastry et al., 1989). Spec-
trophotometric methods for the determination of mefenamic
acid, based on the formation of a coloured species with
MBTH on oxidation with Ce(IV) or Fe(III), are described
(Sastry and Rao, 1989). A method for the quantitative deter-
mination of mefenamic acid in pharmaceutical preparations
was proposed. The method is based on the formation of blue
complexes with Folin–Ciocalteu reagent (Sastry and Rao,
1988). A spectrophotometric method was developed for the
determination of mefenamic acid in the pure form and in
pharmaceutical dosage forms. The method depends on their
complexation with copper(II) ammonium sulphate. The com-
plex was extracted with chloroform and treated with diethyl-
dithiocarbamate solution, where upon another copper(II)
complex (k
max
430 nm) was formed. Beer’s law is followed
over the concentration range 6.0–48 lgmL
1
for mefenamic
acid (Khier et al., 1987). Spectrophotometric determination
of flufenamic acid, mefenamic acid, allopurinol and indo-
methacin using N-bromosuccinimide was studied (Hassib
et al., 1986). Spectrophotometric determination of mefenamic
acid with sodium cobaltinitrite was investigated (Sastry et al.,
12 A.A. Gouda et al.
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of non-steroidal anti-inflammatory drugs: A review. Arabian Journal of Chemistry (2011), doi:10.1016/j.arabjc.2010.12.006
1985). Mefenamic and flufenamic acids could be determined
colorimetrically after extraction as ion-pairs with methylene
blue (Issa et al., 1985). Extractive spectrophotometric deter-
mination of ibuprofen, ketoprofen, piroxicam, diclofenac
sodium, mefenamic acid and enfenamic acid with methylene
violet was illustrated (Sastry et al., 1989).
Low-cost spectrophotometric method for the determination
of mefenamic acid in its pure form and pharmaceutical prepa-
rations was developed. The method is based on the charge-
transfer complexation between mefenamic acid as an n-electron
donor and chloranil as a p-acceptor to form a violet chromo-
gen measured at 540 nm. Under the optimum conditions, a
linear relationship with a good correlation coefficient (0.9996)
was found between the absorbance and concentration of the
studied drug in the range of 10–60 lgmL
1
. The LOD was
2.16 lgmL
1
and LOQ was 7.15 lgmL
1
(Raza, 2008). Mefe-
namic acid reacts with p-dimethylaminobenzaldehyde to give a
bluish-green complex in acidic media after heating for 90 s at
90 C, having maximum absorbance at 597.5 nm. The reaction
is selective for mefenamic acid with 2.0 lgmL
1
as visual limit
of quantitation and provides a basis for a new spectrophoto-
metric determination. The reaction obeys Beer’s law from 2.0
to 25 lgmL
1
of mefenamic acid and the RSD is 0.50%
(Aman et al., 2005). A colorimetric method for the quantita-
tive determination of mefenamic acid in pure form and in
pharmaceutical preparations was developed. It was based on
the interaction of the secondary aromatic amine with p-dim-
ethylaminocinnamaldehyde in acidified absolute methanol
medium to form very stable blue product [k
max
at 665 nm].
Beer’s law was obeyed over the ranges 1.0–8.0 lgmL
1
. The
reactants were heated on a boiling water bath for 5.0 min. Op-
timization of the different experimental conditions were stu-
died. The mean percentage recoveries was found to be
100.73 ± 0.44%. The method was applied successfully for
the determination of some pharmaceutical formulations. (El
Sherif et al., 1997). Three simple, rapid and accurate spectro-
photometric methods were developed for the determination
of mefenamic acid. The first method (method I) is based on
the reaction of mefenamic acid as N-donor with p-chloranilic
acid as a p-acceptor. A red colour product shows peak at
520 nm and its absorbance is linear with concentration over
the range 10–300 lg/mL with correlation coefficient (n = 12)
of 0.9997. The second method (method II) involves oxidation
of mefenamic acid with N-bromosuccinimide. A yellow colour
product shows peak at 362 nm and its absorbance is linear
with concentration over the range 5–70 lgmL
1
with correla-
tion coefficient (n = 8) of 0.9999. The third method (method
III) is based on the formation of an oxidative coupling product
by the reaction of mefenamic acid with 3-methylbenzo-thiazo-
lin-2-one hydrazone as a chromogenic reagent in presence of
ferric chloride solution. A green colour product shows peak
at 602 nm and its absorbance is linear with concentration over
the range 1–6 lg/mL with correlation coefficient (n =6) of
0.9999 (Alarfaj et al., 2009).
FI spectrophotometric method was proposed for the deter-
mination of mefenamic acid in bulk sample and pharmaceuti-
cals. The method is based on the reaction of mefenamic acid
with potassium ferricyanide in a sodium hydroxide medium.
The absorbance of the orange product obtained is measured
at 465 nm. The corresponding calibration graphs are linear
over the range 1.0–100 lgmL
1
for mefenamic acid, while
the limits of detection were 0.18 lgmL
1
(Garci
´
a et al., 2001).
A spectrofluorometric method was developed for determi-
nation of mefenamic acid in pharmaceutical preparation and
human urine. The procedure is based on the oxidation of
mefenamic acid with cerium(IV) to produce cerium(III), and
its fluorescence was monitored at 354 nm after excitation at
255 nm. Under the experimental conditions used, the calibra-
tion graphs were linear over the range 0.03–1.5 lgmL
1
. The
limit of detection was 0.009 lgmL
1
and the relative stan-
dard deviation for five replicate determinations of mefenamic
acid at 1.0 lgmL
1
concentration level was 1.72% (Tabrizi,
2006). Terbium sensitized fluorescence was used to develop
a sensitive and simple spectrofluorometric method for the
determination of the anthranilic acid derivatives (mefenamic
acid). The method makes use of radiative energy transfer
from anthranilates to terbium ions in alkaline methanolic
solutions. Optimum conditions for the formation of the
anthranilate–Tb(III) complexes were investigated. Under opti-
mized conditions, the LOD are 1.4 · 10
8
mol L
1
. The range
of application is 2.5 · 10
8
–5.0 · 10
5
mol L
1
. The method
was successfully applied to the determination of mefenamic
acid in serum after extraction of the samples with ethyl
acetate, evaporation of the organic layer under a stream of
nitrogen at 40 C and reconstitution of the residue with
alkaline methanolic terbium solution prior to instrumental
measurement. The mean recoveries from serum samples
spiked with mefenamic acid (3.0 · 10
6
, 9.0 · 10
6
and
3.0 · 10
5
mol L
1
) were 101 ± 5.0 (Ioannou et al., 1998).
Second-order advantage of excitation–emission fluorescence
measurements was applied to the simultaneous determination
of paracetamol (PC) and mefenamic acid (MF) in urine
samples. Two drugs were quantified by multivariate curve
resolution coupled to alternative least squares (MCR-ALS)
in micellar media of sodium dodecyl sulphate (SDS). Experi-
mental conditions including pH and SDS concentration
were optimized. Under the optimum conditions, pH 2.0 and
0.05 mol L
1
of SDS, mefenamic acid was determined in
concentration range 0.80–5.00 lgmL
1
, in urine samples
(Madrakian et al., 2009).
4.2. Flufenamic acid
The official method of flufenamic acid was potentiometric
titration method with sodium hydroxide (Pharmacopoeia,
2004).
A spectrophotometric method was developed for the deter-
mination of flufenamic in the pure form and in pharmaceutical
dosage forms. The method depends on their complexation with
copper(II) ammonium sulphate. The complex is extracted with
chloroform and treated with diethyldithiocarbamate solution,
whereupon another copper(II) complex (k
max
430 nm) is
formed. Beer’s law is followed over the concentration ranges
6.0–60 lgmL
1
for flufenamic acid (Khier et al., 1987).
Spectrofluorometric method for determination of flufen-
amic acid in bulk powder and capsule dosage forms was pre-
sented. The methods are based on the cyclization reaction of
flufenamic acid with concentrated sulfuric acid to produce
the corresponding acridone derivative and measurement of
the fluorescence intensity at 450 nm (k
ex
= 400 nm) and
peak-to-peak measurements of the first- (
1
D) and second-
derivative (
2
D) curves, respectively. Beer’s law is obeyed
over the concentration ranges of 2.0–20 ng mL
1
(Sabry and
Mahgoub, 1999).
Spectrophotometric and spectrofluorometric methods 13
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of non-steroidal anti-inflammatory drugs: A review. Arabian Journal of Chemistry (2011), doi:10.1016/j.arabjc.2010.12.006
4.3. Enfenamic acid
The official method of enfenamic acid was potentiometric
titration method with sodium hydroxide (Pharmacopoeia,
2004).
Spectrophotometric method for the quantitative determina-
tion of enfenamic acid and naproxen (after demethylation)
based on the formation of a coloured oxidative coupling prod-
uct with 2,6-dichloro- p-benzoquinone-4-chlorimine (Gibb’s re-
agent) in phosphate buffer (pH 7.0) was developed. The
reaction is sensitive to permit the determination of
0.25 lgmL
1
of enfenamic (Sastry et al., 1988).
A simple visible spectrophotometric method was described
for the determination of enfenamic acid in bulk samples and
pharmaceutical preparations. The method is based on the reac-
tion of enfenamic acid with p-N,N-dimethylphenylenediamine
in the presence of S
2
O
8
2
or Cr(VI) whereby an intensely col-
oured product having maximum absorbance at 720 nm is
developed. The reaction is sensitive enough to permit the deter-
mination of 0.125–2.0 lgmL
1
(Sastry et al., 1989).
4.4. Tolfenamic acid
The official method of tolfenamic acid was potentiometric
titration method with sodium hydroxide (Pharmacopoeia,
2004).
Terbium sensitized fluorescence was used to develop a sen-
sitive and simple spectrofluorimetric method for the determi-
nation of the anthranilic acid derivative (tolfenamic acid).
The method makes use of radiative energy transfer from an-
thranilates to terbium ions in alkaline methanolic solutions.
Optimum conditions for the formation of the anthranilate–
Tb(III) complexes were investigated. Under optimized condi-
tions, the LOD was 9.0 · 10
9
mol L
1
. The range of applica-
tion is 2.5 · 10
8
–5.0 · 10
5
mol L
1
. The method was
successfully applied to the determination of tolfenamic acid
in serum after extraction of the samples with ethyl acetate, eva-
poration of the organic layer under a stream of nitrogen at
40 C and reconstitution of the residue with alkaline methano-
lic terbium solution prior to instrumental measurement. The
mean recoveries from serum samples spiked with tolfenamic
Table 3 Comparison between the spectrophotometric methods for determination of N-arylanthranilic acids (fenamic acids).
Name of drug Method k
max
(nm) Linear range
(lgmL
1
)
Ref.
Mefenamic acid UV methods 336 nm 4.0–28 Garg et al. (2007)
219, 284 and 336 Dhake et al. (2001)
217 and 285 Gangwal and Sharma (1996)
p-N,N-Dimethylphenylenediamine/S
2
O
8
2
or
Cr(VI)
740 0.25–4.0 Sastry et al. (1989)
MBTH/Ce(IV) or Fe(III) Sastry and Rao (1989)
Folin–Ciocalteu Sastry and Rao (1988)
Copper(II) ammine sulphate/
diethyldithiocarbamate
430 6.0–48 Khier et al. (1987)
N-Bromosuccinimide Hassib et al. (1986)
Sodium cobaltinitrite Sastry et al. (1985)
Methylene blue Issa et al. (1985)
Methylene violet Sastry et al. (1989)
Chloranil 540 10–60 Raza (2008)
p-Dimethylaminobenzaldehyde 597.5 2.0–25 Aman et al. (2005)
p-Dimethylaminocinnamaldehyde 665 1.0–8.0 El Sherif et al. (1997)
p-Chloranilic acid 520 10–300 Alarfaj et al. (2009)
N-Bromosuccinimide 362 5–70
3-Methylbenzo-thiazolin-2-one hydrazone
as + ferric chloride
602 1–6
Flow injection with potassium ferricyanide/
sodium hydroxide
465 1.0–100 Garci
´
a et al. (2001)
Spectrofluorometric methods with cerium(IV)
in an acidic solution
k
em
= 354 0.03–1.5 Tabrizi (2006)
k
ex
= 255
with terbium Tb(III) 2.5 · 10
8
–5.0
· 10
5
mol L
1
Ioannou et al. (1998)
Flufenamic acid Copper(II) ammine sulphate/
diethyldithiocarbamate
430 6.0–60 Sabry and Mahgoub (1999)
Spectrofluorometry with concentrated sulfuric
acid
k
em
= 450 2.0–20 ng mL
1
Khier et al. (1987)
k
ex
= 400
Enfenamic acid 2,6-Dichloro-p-benzoquinone-4-chlorimine Sastry et al. (1988)
p-N,N-Dimethylphenylenediamine/S
2
O
8
2
720 0.125–2.0 Sastry et al. (1989)
Tolfenamic acid Spectrofluorometry with terbium Tb(III) 2.5 · 10
8
–5.0
· 10
5
mol L
1
Ioannou et al. (1998)
14 A.A. Gouda et al.
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of non-steroidal anti-inflammatory drugs: A review. Arabian Journal of Chemistry (2011), doi:10.1016/j.arabjc.2010.12.006
acid (3.1 · 10
6
, 12.5 · 10
6
and 2.5 · 10
5
mol L
1
) were
98 ± 7.0% (Ioannou et al., 1998).
Table 3 shows comparison between the published spectro-
photometric and spectrofluorometric methods for fenamic
acids.
5. Spectrophotometric and spectrofluorometric methods for
determination of arylpropionic acids (profens)
5.1. Ibuprofen
The official method of ibuprofen was potentiometric titration
method with sodium hydroxide (Pharmacopoeia, 2004).
The simultaneous determination of paracetamol, ibuprofen
and caffeine in pharmaceuticals by chemometric approaches
using UV spectrophotometry has been reported as a simple
alternative to using separate models for each component. Spec-
tra of paracetamol, ibuprofen and caffeine were recorded at
several concentrations within their linear ranges and were used
to compute the calibration mixture between wavelengths 200
and 400 nm at an interval of 1.0 nm in methanol: 0.1 mol L
1
HCl (3:1). Partial least squares regression (PLS), genetic algo-
rithm coupled with PLS (GA-PLS), and principal component-
artificial neural network were used for chemometric analysis of
data and the parameters of the chemometric procedures were
optimized. The analytical performances of these chemometric
methods were characterized by relative prediction errors and
recoveries (%) and were compared with each other (Khoshay-
and et al., 2008). A spectrophotometric method for the simul-
taneous and separate estimation of ibuprofen and paracetamol
in binary tablet formulation has been developed. This method
is based on the estimation of one drug in presence of another
drug by absorbance difference method. The ibuprofen and
paracetamol solution were scanned over a range of 200–
600 nm. In this method, two wavelengths 220 and 231 nm were
chosen for ibuprofen and at these wavelengths the absorbance
difference was almost zero while there was considerable absor-
bance difference in case of paracetamol, similarly. The amount
of ibuprofen was directly proportional to the absorbance dif-
ference between 241 and 255 mm (Omry et al., 2007). A simple
method was proposed for determination of paracetamol and
ibuprofen in tablets, based on UV measurements and partial
least squares. The procedure was performed at pH 10.5, in
the concentration range 2.4–12.0 lgmL
1
(ibuprofen). The
model was able to predict paracetamol and ibuprofen in syn-
thetic mixtures with root mean squares errors of prediction
of 0.17 lgmL
1
(Sena et al., 2007). Spectrophotometric meth-
ods were described for the simultaneous determination of
pseudoephedrine hydrochloride and ibuprofen in their combi-
nation. The obtained data were evaluated by using five differ-
ent methods. In the first method, ratio spectra derivative
spectrophotometry, analytical signals were measured at the
wavelengths corresponding to either maximums and mini-
mums for both drugs in the first derivative spectra of the ratio
spectra obtained by using each other spectra as divisor in their
solution in 0.1 mol L
1
HCl. In the other four methods using
chemometric techniques, classical least-squares, inverse least-
squares, principal component regression and partial least-
squares (PLS), the concentration data matrix were prepared
by using the synthetic mixtures containing these drugs in meth-
anol: 0.1 mol L
1
HCl (3:1). The absorbance data matrix cor-
responding to the concentration data matrix was obtained by
the measurements of absorbance in the range 240–285 nm in
the intervals with Dk = 2.5 nm at 18 wavelengths in their
zero-order spectra, then, calibration or regression was ob-
tained by using the absorbance data matrix and concentration
data matrix for the prediction of the unknown concentrations
of pseudoephedrine hydrochloride and ibuprofen in their mix-
ture. The procedures did not require any separation step. The
linear range was found to be 300–1300 lgmL
1
in all five
methods (Palabiyik et al., 2004). Two procedures for simulta-
neous estimation of ibuprofen and methocarbamol in two
component tablet formulation have been developed. Solutions
were prepared in 0.1 mol L
1
sodium hydroxide using all glass
double distilled water. Ibuprofen has an absorbance maximum
at 222 nm (Manikandan et al., 2001). The second-derivative
spectrophotometric method for the simultaneous determina-
tion of pseudoephedrine in the combinations with ibuprofen
was described. The second-derivative order of the spectra in
ethanol with the wavelength modulation was used. For the
quantitative assay for all of the investigated substances in the
laboratory mixture or in respective pharmaceutical dosage
forms, the ‘zero-crossing’ technique was applied (Ivanovic
et al., 2000). A spectrophotometric method requiring no prior
separation has been developed. The method employs first
derivative ultraviolet spectrophotometry for the simultaneous
estimation of ibuprofen and dextropropoxyphene hydrochlo-
ride. In aqueous methanol (10% v/v), ibuprofen has a maxi-
mum at 256 nm. In derivative spectroscopy, estimation of
ibuprofen was carded out in first order with N =6 at
232 nm (Sachan and Trivedi, 1998). Reproducible method
for estimation of ibuprofen and pseudoephedrine hydrochlo-
ride in combined dosage form has been developed. The method
involves two-wavelength calculation. The two wavelengths se-
lected for estimation of ibuprofen are 264.0 and 254.5 nm
(Singhvi and Chaturvedi, 1998a). Two methods for simulta-
neous estimation of ibuprofen and pseudoephedrine hydro-
chloride in combined dosage form have been developed.
First developed method employs formation and solving of
simultaneous equations using 263.8 and 257.6 nm as two wave-
lengths for formation of equations. Second method involves
first derivative ultraviolet spectroscopy. Two wavelengths se-
lected for this method are 265 and 257 nm (Singhvi and Cha-
turvedi, 1998b).
A new extractive spectrophotometric method for the deter-
mination of ibuprofen was developed. The method involves the
formation of coloured electron donor–acceptor complex be-
tween ibuprofen and safranine in the aqueous phase extract-
able into chloroform, which is measured at k
max
520 nm.
This method is extended to pharmaceutical dosage forms
(Babu, 1998). Kinetic spectrophotometric method for the
determination of ibuprofen in pharmaceutical formulations.
Ibuprofen was determined in an acidic ethanolic medium by
monitoring the rate of appearance of 1-nitroso-2-naphthol,
resulting from the displacement by ibuprofen of Co(III) from
the tris(1-nitroso-2-naptholato)cobalt(III) complex. The opti-
mum operating conditions regarding reagent concentrations
and temperature were established. The tangent method was
adopted for constructing the calibration curve, which was
found to be linear over the concentration range 0.21–1.44
and 1.44–2.06 lgmL
1
(Mitic
´
et al., 2008).
A spectrophotometric method was presented for the deter-
mination of ibuprofen by batch and flow injection analysis
methods. The method is based on ibuprofen competitive
Spectrophotometric and spectrofluorometric methods 15
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complexation reaction with phenolphthalein-b -cyclodextrin
(PHP-b-CD) inclusion complex. The increase in the absorbance
of the solution at 554 nm by the addition of ibuprofen was mea-
sured. Ibuprofen can be determined in the range 8.0 · 10
6
3.2 · 10
4
and 2.0 · 10
5
–5.0 · 10
3
mol L
1
by batch and
flow methods, respectively. The LOD and LOQ were 6.19 ·
10
6
and 2.06 · 10
5
mol L
1
for batch and 1.77 · 10
5
and
5.92 · 10
5
mol L
1
for flow method, respectively. The sam-
pling rate in flow injection analysis method was 120 ± 5.0
samples h
1
. The method was applied to the determination of
pharmaceutical formulations (Afkhami et al., 2007).
The inclusion complexation of ibuprofen with b-CD has
been examined by means of spectrofluorometry at both acid
and alkaline pH. The results suggest that stable 1:1 complexes
are formed in both media. The analysis of the pK
a
values for
ibuprofen in both the absence and presence of b-CD (4.12
and 4.66, respectively) suggests that in the inclusion complex
the carboxylic group is located outside the a-cyclodextrin (a-
CD) but interacting with it. Further structural characterization
of the complex was carried out by means of AM1 semiempiral
calculations. Based on the obtained results, a spectrofluoro-
metric method for the determination of ibuprofen in the pres-
ence of b-CD at 10 C was developed in the range of 4.7–
58 lgmL
1
. Better LOD (1.6 lgmL
1
) and LOQ
(4.7 lgmL
1
) were obtained in this latter case with respect
to those obtained in the absence of b-CD. The method was sat-
isfactorily applied to the quantification of ibuprofen in phar-
maceutical preparations. A novel spectrofluorometric
determination of ibuprofen in the presence of b-CD was also
developed for serum samples at concentration levels between
5.0 and 70 lgmL
1
(Hergert and Escandar, 2003).
The characteristics of host–guest complexation between b-
cyclodextrin (b-CD) and two forms of ibuprofen (protonated
and deprotonated) were investigated by fluorescence spectrom-
etry. Stoichiometry for both complexes were established to be
1:1 and their association constants at different temperatures
were calculated by applying a non-linear regression method
to the change in the fluorescence of ibuprofen that was brought
about by the presence of b-CD. The thermodynamic parame-
ters (DH, DS and DG) associated with the inclusion process
were also determined. Based on the obtained results, a sensitive
spectrofluorometric method for the determination of ibupro-
fen was developed with a linear range of 0.1–2.0 lgmL
1
with
LOD of 0.03 lgmL
1
(Manzoori and Amjadi, 2003).
The spectrofluorometric determination of ibuprofen in
pharmaceutical tablets, creams and syrup is described. It in-
volves excitation at 263 nm and emission at 288 nm. The linear
range is 2.0–73 lgmL
1
(Damiani et al., 2001).
Luminescence properties of the complexes of terbium(III)
with ibuprofen and orthofen were studied. It was demon-
strated that in the presence of organic bases (2,2
0
-dipyridyl
and o-phenanthroline) mixed-ligand complexes are formed
and the luminescence intensity of terbium(III) increases by a
factor of up to 250. The LOD are 2.0 and 0.05 lgmL
1
,
respectively (Teslyuk et al., 2007).
5.2. Ketoprofen
The official method of ketoprofen was potentiometric titration
method with sodium hydroxide (Pharmacopoeia, 2004).
A binary mixture of hyoscine butylbromide and ketoprofen
was determined by four different methods. The first involved
determination of ketoprofen was by using the ratio-spectra
first-derivative spectrophotometric technique at 234 nm over
the concentration ranges of 5.0–45 lgmL
1
. The second meth-
od utilized second-derivative spectrophotometry over the con-
centration ranges of 5.0–35 lgmL
1
with mean accuracies
99.55 ± 1.15%, respectively. The third method was based on
the resolution of the two components by bivariate calibration
depending on a simple and rapid mathematical algorithm and
quantitative evaluation of the absorbance at 254 nm over con-
centration ranges of 5.0–35 lgmL
1
; mean accuracies of
100.19 ± 1.07% were obtained for ketoprofen. The fourth
method was reversed-phase liquid chromatography using
0.05 mol L
1
ammonium dihydrogen phosphate–acetonitrile–
methanol (20 + 30 + 6, v/v) as the mobile phase with ultravi-
olet detection at 220 nm over concentration ranges of 1.0–90
and 5.0–70 lgmL
1
; mean accuracies were 99.92 ± 1.02%
and 99.61 ± 0.98%, for hyoscine butylbromide and ketopro-
fen, respectively (El-Saharty et al., 2007). Partial least-squares
calibration was used for the simultaneous UV spectrophoto-
metric determination of the active principle (ketoprofen) and
preservative (parabens) in a pharmaceutical preparation com-
mercially available in gel form. Calibration mixtures were pre-
pared by mixing pure solutions of the analytes (Blanco et al.,
1997). A second order derivative spectrophotometric method
was developed for the permeative determination of ketoprofen
in vitro. The method can avoid the disturbance of skin tissue
(Hu et al., 1997). The mean recovery of ketoprofen is
99.00 ± 1.51%.
A spectrophotometric determination of ketoprofen based
upon oxime formation followed by charge transfer complexa-
tion with o-chloranil has been developed. Different variables
affecting the complexation process have been studied. Beer’s
law is obeyed in the concentration range 10–80 lgmL
1
(El-
Sadek et al., 1993).
5.3. Flurbiprofen
The official method of flurbiprofen was potentiometric titra-
tion method with sodium hydroxide (Pharmacopoeia, 2004).
A UV spectrophotometric method for quantitative estima-
tion of flurbiprofen in pure form and in pharmaceutical dosage
forms was developed. The linear regression equations obtained
by least square regression method were Abs = 7.5906 · 10
2
concentration (lgmL
1
) ± 4.6210 · 10
2
for the UV method.
The detection limit as per the error propagation theory was
found to be 0.34 lgmL
1
for UV method (Sajeev et al., 2002).
5.4. Naproxen
The official method of naproxen was potentiometric titration
method with sodium hydroxide (Pharmacopoeia, 2004).
A second-derivative spectrophotometric method for the
determination of naproxen in the absence or presence of its 6-
desmethyl metabolite in human plasma is described. The meth-
od consists of direct extraction of the non-ionized form of the
drug with pure diethyl ether and determination of the naproxen
by measuring the peak amplitude (mm) in the second-order
derivative spectrum at a wavelength of 328.2 nm. The efficiency
of the extraction procedure expressed by the absolute recovery
was 94.6 ± 0.7% (mean ± SD) for the concentration range
tested, and the LOQ attained according to the IUPAC defini-
tion was 2.42 lgmL
1
(Panderi and Parissi-Poulou, 1994).
16 A.A. Gouda et al.
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of non-steroidal anti-inflammatory drugs: A review. Arabian Journal of Chemistry (2011), doi:10.1016/j.arabjc.2010.12.006
Naproxen reacts with 1-naphthylarnine and sodium nitrite
to give an orangish red colour having maximum absorbance
at 460–480 nm (working wavelength 480 nm). The reaction is
selective for naproxen with 0.001 mg mL
1
as visual LOQ
and provides a basis for a new spectrophotometric determina-
tion. The reaction obeys Beer’s law from 10 to 65 lgmL
1
of
naproxen and the relative standard deviation is 1.5%. The
quantitative assessment of tolerable amount of other drugs is
also studied (Khan et al., 1999). Spectrophotometric methods
for the determination of naproxen based on the formation of a
coloured species with MBTH on oxidation with Ce(IV) or
Fe(III), are described (Sastry and Rao, 1989). Spectrophoto-
metric method for the quantitative determination of naproxen,
after demethylation was developed based on the formation
of a coloured oxidative coupling product with 2,6-dichloro-p-
benzoquinone-4-ch lorimine (Gibb’s reagent) in phosphate
buffer (pH 7.0). The reaction is sensitive to permit the determi-
nation of 5.0 lgmL
1
(Sastry et al., 1988).
CT complexes of naproxen, which is electron donor with
some p-acceptors, such as tetracyanoethylene (TCNE), 2,3-di-
chloro-5,6-dicyano-p-benzoquinone (DDQ), p-chloranil, have
been investigated spectrophotometrically in chloroform at
21 C. The coloured products are measured spectrophotomet-
rically at different wavelength depending on the electronic
transition between donors and acceptors. Beer’s law is obeyed
and colours were produced in non-aqueous media. All com-
plexes were stable at least 2.0 h except for etodolac with
DDQ stable for 5.0 min. The equilibrium constants of the
CT complexes were determined by the Benesi–Hildebrand
equation. The thermodynamic parameters DH, DS, DG were
calculated by Van’t Hoff equation (Duymus et al., 2006).
5.5. Tiaprofenic acid
The official method of tiaprofenic acid was potentiometric
titration method with sodium hydroxide (Pharmacopoeia,
2004).
The spectrophotometric method for the determination of
tiaprofenic acid was described. The method depends on the
determination of the drug after extraction as an ion–associa-
tion complex with safranine-T in chloroform at pH 7.4 (Ali
et al., 1994).
Table 4 shows comparison between the published spectro-
photometric and spectrofluorometric methods for profens.
6. Applications
The above mentioned methods have applications in the deter-
mination of the studied drugs in various pharmaceutical for-
mulations like tablets, suppositories, injections, capsules and
oral solutions. These methods give results which are compara-
ble with the official pharmacopoeial methods used for the
determination of the