Extraction and Spectrophotometric Determination of Diclofenac in ...

356 Journal of the Chinese Chemical Society, 2008, 55, 356-361
Extraction and Spectrophotometric Determination of Diclofenac in
Pharmaceuticals
Zh.O.Kormosh, a * I. P. Hunka a and Ya. R. Bazel b,c
a Volyn State University, Voliav., 13, 43025 Lutsk, Ukraine
b Uzhgorod National University, Pidgirna str., 46, 88000 Uzhgorod, Ukraine
c P.J. Safarik University, Moyzesova str., 11, 04154 Kosice, Slovakia
A new simple, rapid and sensitive spectrophotometric method has been developed for the determination
of diclofenac sodium (Dicl) in pharmaceutical preparations. This method is based on the reaction of
diclofenac sodium with an analytical reagent 1,3,3-trimethyl-5-thiocyanato-2-[3-(1,3,3-trimethyl-3-
H-indol-2-ylidene)-propenyl]-indolium cloride (TIC) at pH 8.0-11.0 and the extraction of ion associate
colored complex. Optimal conditions for the complex formation between Dicl and TIC were studied. This
ion associate complex (1:1) was detected and extracted with toluene and an absorption maximum at 566.2
nm against a blank reagent. The calibration graph was linear from 0.9-11.0 µg/mL of diclofenac and the
detection limit was 0.86 µg/mL.
Keywords: Diclofenac; Ion associates; Determination; Spectrophotometry.
INTRODUCTION
The determination of small amounts of diclofenac in
pharmaceutical preparations is very important for medical
and pharmaceutical needs where it is used for the treatment
of various diseases. Therefore it is crucial to develop a simple,
selective and cost-effective method of determining the
microamounts of diclofenac in different pharmaceutical
formulations.
Diclofenac [2-(2,6-dichloroamino)phenyl]acetic acid
is a non-steroidal anti-inflammatory drug. It is usually
found as a sodium or potassium salt (Fig. 1(a)). It is used
for the treatment of rheumatoid arthritis, ankyllosing spondylitis,
osteoarthritis and sport injuries. 1
Several types of analytical procedures have been proposed
for the analysis of diclofenac in pharmaceutical formulation.
These procedures include potentiometry, 2–4 fluorimetry,
5–7 HPLC, 8 gravimetry, 9 UV spectrophotometry
Fig. 1. Structures of diclofenac sodium or potassium
salt (a) and TIC (b).
and partial least squares regression (PLS) 10–13 and other
methods. Some of these procedures are cumbersome and
too costly for routine analysis.
The spectrophotometric method provides sensitivity,
precision and accuracy of analysis, thus it offers practical
and economical advantages over other techniques. There
are methodologies developed for the spectrophotometric
determination of diclofenac. 14–17 Some of them describe
the spectrophotometric determination of diclofenac after
the extraction of a created complex. 15,17,18
There are numerous publications 16,19 dedicated to the
determination of small amounts of pharmaceutical compounds
with the help of base coloring agents. Base dyes are
often used as reagents for the extractive spectrophotometric
determination of many inorganic and organic substances.
20–22 The merits of a base coloring agent include
high molar absorptive values and stability in solution over
a wide pH range. But some of the systems still lack a definitive
study, therefore triggering further interest in detailed
study of conditions and peculiarities of creation and extraction
of ionic associates with new coloring agents. This
trend of analytical chemistry is of current interest and holds
much promise.
In this work we describe a new analytical form by using
1,3,3-trimethyl-5-thiocyanato-2-[3-(1,3,3-trimeth-
* Corresponding author. Tel: +38-03322-48427; Fax: +38-03322-41007; E-mail: kormosh@univer.lutsk.ua

Spectrophotometric Determination of Diclofenac J. Chin. Chem. Soc., Vol. 55, No. 2, 2008 357
yl-3-H-indol-2-ylidene)-propenyl]-indolium cloride (TIC)
(Fig. 1(b)) for the spectrophotometric determination of
diclofenac in different pharmaceutical form.
EXPERIMENTAL
Materials
All chemicals were of analytical-reagent grade. Distilled
water was used to prepare all solutions and in all experiments.
Universal buffer solution (pH = 9.6) was prepared by
mixing 100 mL of a mixture of 0.04 mol/L H 3 BO 3 ,0.04
mol/L CH 3 COOH, 0.04 mol/L H 3 PO 4 and75mL0.20
mol/L NaOH.
TIC was used as a 1 × 10 -3 mol/L solution.
Diclofenac sodium (Sigma-Aldrich): a freshly prepared
1 × 10 -3 mol/L aqueous solution was used as a standard
solution for analytical purposes. It was standardized
using the method proposed by the Ukrainian State Pharmacopoeia.
1
The following commercial dosage forms were analyzed
with TIC: capsules, labeled to contain 75 mg of diclofenac
(sodium salt) per tablets, injectable ampoules, 75 mg
of diclofenac (sodium salt) per ampoule. Ointment, 10% of
diclofenac (sodium salt). The working standard 1 × 10 -3
mol/L solutions were prepared by dilution the stock solution
from capsules, injections and ointments with buffer
solution.
Instruments
A SF-2000 spectrophotometer (LOMO, Russia) was
used to obtain spectra, with 0.3 cm matched glass cells used
to perform analyses. All pH measurements were made with
an I-160 Model pH meter (AKVILON, Russia).
All experiments were performed at room temperature,maintainedat25±1°C.
Procedure for the determination of diclofenac sodium
in pharmaceutical preparations
An aliquot of standard diclofenac sodium solution
0-0.2 × 10 -3 mol/L was transferred into a 10 mL funnel, and
0.5 mL of universal buffer solution of pH 9.6 and 0.5 mL of
1×10 -3 mol/L TIC were added. The solution was mixed
well and diluted to 5 mL with distilled water. Toluene (5
mL) was added to the funnel and was shaken for exactly 1
min. The absorbance of the separated toluene layer was
measured at 566.2 nm against that of the blank test. The
amount of diclofenac sodium in the capsules, ampoules and
ointment present was calculated from a calibration graph.
Two capsules were weighed and powdered. The
quantity of powder equivalent to 150 mg of diclofenac sodium
was mixed with 1 mL of ethanol and then 20 mL of
universal buffer solution of pH 9.6. This was filtered into a
50 mL glass, the powder washed three times with 7 mL of
distilled water, filtered, and the combined filtrate mixed
well. The solution was transferred into a 50 mL calibrated
flask and brought to volume with distilled water. The concentration
of diclofenac sodium solution was 1 × 10 -2
mol/L. The working 1 × 10 -3 mol/L and 1 × 10 -4 mol/L solutions
were prepared by the dilution of the stock solution
with 20 mL of buffer solution. 0.3, 0.6, 0.9 mL aliquots of 1
×10 -4 mol/L solution were assayed as described above.
The contents of five ampoules were mixed. 12.7 mL
of this solution were transferred into a 100 mL calibration
flask and 20 mL of universal buffer solution of pH 9.6 were
added. The concentration of diclofenac sodium was 1 ×
10 -2 mol/L. The working 1 × 10 -3 mol/L and 1 × 10 -4 mol/L
solutions were prepared by dilution of the stock solution
with 20 mL of buffer solution. The same aliquots were assayed
as described above.
10% of ointment was weighed and mixed well. The
quantity of ointment of diclofenac sodium was mixed in 20
mL of universal buffer solution of pH 9.6. The concentration
of diclofenac sodium was 1 × 10 -3 mol/L. The working
1×10 -4 mol/L solution was prepared by the dilution of the
stock solution with 20 mL of buffer solution. The same
aliquots were assayed as described above.
RESULTS AND DISCUSSION
Absorption spectra
Absorption spectra were recorded under optimal
complexation and extraction conditions. The absorption
spectra from the dye and from the ion associate of diclofenac
are not different in practice. Changes in the position
of the maximum help to explain the solvatochromatic effect
observed, which provides evidence of the formation of
complex compounds of the ion associate type. It was determined
by different methods 23 that the molar ratio Dicl - :
TIC + in the formed ion associate (IA) is 1:1. This means
that the ion associate contain singly charged diclofenac and
dye cations. Therefore, the reaction mechanism can be
expressed by the following equations:
Dicl - Na + (aq) Dicl - (aq) +Na + (aq)
R + Cl - (aq) R + (aq) +Cl - (aq)
Dicl - (aq) +R + (aq) + k S (org) [Dicl × R] × k S (org)

358 J. Chin. Chem. Soc., Vol. 55, No. 2, 2008 Kormosh et al.
where Dicl - is the diclofenac anion, R + is the TIC, S is the
organic solvent, aq is the aqueous phase, and org is the organic
phase.
The absorption spectra of the extracted IA colored
complex of diclofenac with TIC in toluene were measured
over 400-750 nm. The complex shows the maximum absorbance
at 566.2 nm (Fig. 2) which can therefore be used
for analytical purposes. This wavelength was used for all
subsequent measurements. The maximum production and
extraction of complex was attained after 1 min.
Effect of pH
One needs to create the conditions for the IA components
to form and extract the IA.
To establish the optimum pH range, diclofenac sodium
was mixed with TIC in aqueous solution with pH values
from 2.0 to 11.0, and the IA extract absorbance measured.
Fig. 3 shows that the absorbance increases and
reaches a maximum plateau at 8.0-11.0 pH range. Hence, a
pH of 9.6 was used in all the subsequent experimental
work. As the shape of the absorption curve and the position
of the absorption maximum do not vary with pH, it was assumed
that only one type of complex formed in this pH
range.
Effect of TIC concentration
The dye concentration has a significant effect on the
formation and extraction of the diclofenac ion pair.
To establish the optimum TIC content, the solution
absorbance was plotted as a function of TIC concentration.
The absorbance of the system increased in the concentration
range of (0.0-1.6) 10 -4 mol/L and was practically
constant in the (1.0-1.6) 10 -4 mol/L range. Thereafter, 1.0
10 -4 mol/L TIC solution was used as the optimum concentration.
Effects of salting-out agent
Salting-out agents are known to improve extraction
by organic solvents. 24 The influence of such salting-out
agents as Na 2 SO 4 ,MgSO 4 ,(NH 4 ) 2 SO 4 on the IA complex
formation was studied. The results show that all these compounds
have no salting-out properties in the investigated
system.
Effects of organic solvents miscible with the aqueous
phase
The publications on the determination of small amounts
of different inorganic compounds with the help of base coloring
agents 22,25 show that in some cases an addition of the
organic solvent that dissolves in the aqueous phase increases
the analytical signal of the created ion-association
complex in the system and at the same time lowers the signal
of blank reagent. This phenomenon is very important
because it promotes the sensitivity of the system.
The addition of donor solvents to the aqueous phase
leads to a considerable improvement in the extraction of
Fig. 2. Absorption spectra of the solution Dicl (1), TIC
in OH - form (2), TIC in the ion form (3) and of
the extracted Dicl × TIC IA colored complexes
in toluene (4).
Fig. 3. The effect of pH on IA colored complex formation
and extraction. Diclofenac concentration;
4 10 -5 mol/L; 1 10 -4 mol/L of TIC.

Spectrophotometric Determination of Diclofenac J. Chin. Chem. Soc., Vol. 55, No. 2, 2008 359
diclofenac ion pairs (synergistic effect) and to the simultaneous
suppression of the extraction of simple salts of dyes
(antagonistic effect).
Donor solvents may conditionally be divided into
groups by their water toluene distribution constants: 26,27
the donor solvents that readily extracted into toluene (K d >
0.01) (acetone, ethanol, pyridine, dioxane, and other solvents
that hardly cross into the toluene phase (K d < 0.01)
(DMFA, DMSO, HMPA etc.). In practice, the effect of the
concentration should also be taken into account. However,
in our case, this division explains the antagonistic effect
observed in the extraction of simple salts of dyes reasonably
well.
We tested this division in our system for the determination
of the organic ion of diclofenac. For this test DMFA,
DMSO, acetone, 1,4-dioxane were used.
Assuming that dye solvates are formed in the aqueous
phase according to the equation
R + ×Dicl - + kS [R + ×Dicl - ]×S k ,
where R + is a dye cation, and S is the molecule of a donor
solvent, and taking into account the fact that the unsolvated
species of the dye predominantly go into the organic phase,
we can write the distribution ratio (D) for a simple dye salt
as follows:
Table 1. The main characteristics of extracted IA of Dicl with
TIC (A k absorbance of IA, A 0 absorbance of blank test,
R efficiency of IA extraction)
Organic solvent , nm 10 -4 À k /A o R(%)
butyl acetate
benzene
toluene
558.1
566.2
566.2
2.2
6.0
7.7
1.4
7.0
9.5
83.0
97.8
98.9
Effects of organic solvents
We investigated the influence of the nature of extragents
on the formation and extraction of the ion associates
of diclofenac with TIC.
Such organic solvents as toluene, benzene, butylacetate,
chloroform were examined for the extraction of the IA
complex. The best results were obtained for benzene and
toluene. Toluene was chosen over benzene because the latter
is a known carcinogen. Table 1 shows the main spectrophotometric
characteristics of these systems.
Linearity
A calibration curve was obtained under optimum conditions
(pH 9.6, diclofenac concentration of 2 × 10 -5 mol/L,
1×10 -4 mol/L TIC solution). The absorbance response is
linear in relation to the calculated concentration of diclofenac
sodium over the range of 0.9-11.0 µg/mL. The cali-
D =[R×Dicl] org /([R × Dicl] aq +[RL k × Dicl] aq ).
After simple transformations (at [Dicl - ] = const), we
obtained the linear equation
log(K d /D-1) = log K s +klog [S],
which allowed us to calculate K s (solvation constants of IA)
for different donor solvents.
The logarithm of salvations constants (log K s )are
1.18 for DMFA, 1.79 for DMSO, 1.12 for acetone but only
0.42 for 1,4-dioxane.
Fig. 4 shows that the addition to aqueous phase of the
DMSO, DMFA, acetone, 1,4-dioxane don’t increase the
analytical signal. At the same time, one should take into account
that when the concentrations of these solvents in the
aqueous phase are higher than 0.07-0.15 vol. %, they suppress
the extraction of not only simple dye salts but diclofenac
ion pairs as well.
Fig. 4. Variation in absorbance of the Dicl × TIC ion
associate complex in the presence of acetone
(1), DMSO (2), DMFA (3) and 1,4-dioxane (4)
in aqueous phase. pH 9.6; diclofenac concentration
4 10 -5 mol/L; 1 10 -4 mol/L of TIC
(absorbance was recorded at 566.2 nm ).

360 J. Chin. Chem. Soc., Vol. 55, No. 2, 2008 Kormosh et al.
Table 2. Comparison of main chemistry-analytical parameters of different spectrophotometric methods for the determination of
diclofenac sodium
Analytical
reagent
Copper acetate
[17]
Methylene
Violet [19]
Methylene
Blue [18]
Proposed
method
pH range , nm 10 -4 Sensitivity,
Sandell
g/mL
Range Beer’s
law
Detection
limit,
g/mL
Disadvantages
1.00 Some important parameters
72.00 Low sensitivity
0.37 Selectivity was not studied
5.3 680 – 0.010 1.0-25.0
mg mL -1 are unknown
7.4-8.0 540 3.1 – 1.0-8.0
mg mL -1
9.2-9.4 653 5.7 0.006 0.8-6.4
mg mL -1
8.0-11.0 566.2 7.7 1.08 0.9-11.0 0.86 –
g/mL g/mL
Table 3. Determination of diclofenac sodium in different dosage
forms (n = 5, average)
Sample
Labeled amount
(mg)
Amount found (mg)
Dicloberl Retard 100.00 capsule -1 99.68 0.33
Dicloberl 75.00 ampoule -1 74.77 0.42
Dicloran ® CP 100.00 tablet -1 99.33 0.68
Sodium Diclofenac 25.00 capsule -1 24.75 0.40
Naclofen 75.00 ampoule -1 74.91 0.22
Naclofen 75.0 capsule -1 75.16 0.38
Diclofenac retard 75.0 capsule -1 74.81 0.22
bration equation for the representative curve is: A 0.03058
×10 -4 + 0.05496C, where A and C correspond to the absorbance
and the calculated concentration of diclofenac sodium
(g/mL), respectively. The molar absorptivity coefficients
for different solvents were shown in Table 1, the
detection limit of 0.86 µg/mL.
Table 2 shows that the method reported here has
higher sensitivity than other similar methods, in which copper
acetate, 17 methylene violet 19 and methylene blue 18 are
employed as analytical reagents.
Application
Some pharmaceutical dosage forms were analyzed by
the proposed method. Table 3 shows the results of diclofenac
sodium determination in pharmaceutical preparations
by the spectrophotometric method with the reagent
TIC.
CONCLUSIONS
On the basis of obtained data, we found a new analytical
form and developed a new methodology for determining
micro amounts of diclofenac in pharmaceutical formulations
using the base coloring agent TIC. The technique
has good metrological characteristics, high sensitivity, and
is simple to use.
ACKNOWLEDGMENTS
This work has been supported by the Ministry of Education
and Science of Ukraine and International Visegrad
Fund (Grant 997015), the Scientific Grant Agency of the
Ministry of Education of the Slovak Republic and the Slovak
Academy of Sciences (Grant VEGA No 1/4450/07)
and Slovak Research and Development Agency (Project
APVV SK-UA-0002-07).
Received June 7, 2007.
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