29-09-2016, 04:38 PM
Simultaneous Determination of Paracetamol and Codeine Phosphate in Combined
Tablets by First-Order Derivative and Ratio Spectra First-Order Derivative UV
Spectrophotometry
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ABSTRACT
Two simple, accurate and reproducible UV spectrophotometric techniques have been developed for the simultaneous
determination of paracetamol and codeine phosphate in combined tablets. The first one is based on the measurement of
first-order derivative amplitudes at zero-crossing points, 263.5 nm and 218.4 nm for the assay of paracetamol (5.0 –
25.0 mgL-1) and codeine phosphate (1.25 – 10.0 mgL-1) respectively. The second one uses the amplitudes of ratio
spectra first-order derivatives at 255.3 nm and 221.4 nm to quantify paracetamol (5.0 – 30.0 mgL-1) and codeine
phosphate (0.625 – 10.0 mgL-1), respectively. Both techniques have been extensively validated and compared to an
official HPLC method showing their applicability in the routine analysis.
INTRODUCTION:
Paracetamol or Acetaminophen (Figure 1 a) is an
analgesic and antipyretic drug commonly prescribed as
well as being available without prescription for treating
mild to moderate pains. Whereas, codeine (Figure 1 b) is
the traditional choice for the treatment of moderate to
moderate opioid-sensitive pains. Combinations of
codeine with paracetamol produce a significant increase
in analgesia compared with paracetamol alone. These
pharmaceutical formulations accounted for a further 6.4
million prescriptions (i.e. 20% of total non-opiate
analgesics) during the last decade in the UK 1
. Their
quality control is thus of paramount importance,
especially the determination of paracetamol in
pharmaceuticals has been critically reviewed since its
overdose can cause fulminating hepatic necrosis and
other toxic effects 2
.
Derivative spectrophotometry is one of the advanced
modern spectrophotometric techniques, which offers a
useful means for extracting both qualitative and
quantitative information from spectra composed of
overlapped bands. It is based on using the first- or
higher- order derivatives of absorbance with respect to
wavelength from parent zero-order ones.
Although the differentiation can degrade the signal-tonoise
ratio, this disadvantage can be substantially
overcome by smoothing algorithms available with builtin
spectra processing software.
Due to the fact that the derivatisation can lead to the
separation of unresolved signals and reduction of
spectral background interferences, this technique permits
the quantification of one analyte in the presence of
others without initial separation or purification. The
application of derivative spectrophotometry in
pharmaceutical analysis has been critically reviewed 3-5.
In particular, this technique was much used by
researchers to quantify paracetamol in multi-component
pharmaceutical formulations 6-18.
In an effort to develop a simple and accurate method for
routine analysis, this study describes two UV
spectrophotometric techniques, first-order derivative and
ratio spectra first-order derivative, for the simultaneous
determination of paracetamol and codeine phosphate in
their combined tablets. The spectrophotometric techniques
were also compared with the official HPLC method
specified in British Pharmacopoeia 2005 19 as a referee
method to validate further their applicability.
EXPERIMENTAL:
Apparatuses and conditions:
A UNICAM UV 300 double beam spectrophotometer with
a fixed slit width (1.5 nm) connected to an IBM computer
loaded with Thermo Spectronic VISION32 software and 1-
cm quartz cell were used for the registration and treatment
of absorption spectra. For all solutions, zero-order spectra
were recorded over the range from 200.0 to 300.0 nm
against a blank (Ethanol 96º) at Intelliscan mode to enhance
the signal-to-noise ratio of absorbance peaks without
extended scan duration with a Δλ = 0.1 nm (i.e. 30-120
nm/min). In order to get a best signal to noise ratio and
resolution, spectra and their corresponding derivative ones
were further smoothed by using Savitzky – Golay filter
(order 3, number of coefficients 25).
High performance liquid chromatogram (HPLC) analysis
was performed on an Agilent 1100 Series Diode-ArrayDetector
chromatograph at ambient temperature. A
reversed-phase Apollo C18 (150×4.6 nm, 5μm particle
size) was used. The mobile phase with a flow rate of 1.5
mLmin-1 was composed of 0.01 M sodium
pentasulphonate in a mixture of water – methanol (78:22,
v:v) being adjusted to pH 2.8 with HCl 2M. Injection
volume was 20μL and detection wavelengths were 220
nm and 243 nm for codeine phosphate and paracetamol,
respectively. Under this condition, the elution times for
paracetamol and codeine phosphate were 11.8 min and
18.1 min, respectively.
Sample solutions:
Two commercial products, Efferalgan Codeine effervescent
tablet (produced by UPSA, France containing 500 mg
paracetamol and 30 mg codeine phosphate per tablet) and
Paracetamol-Codeine tablet (produced by a domestic jointstock
pharmaceutical company containing 500 mg
paracetamol and 15 mg codeine phosphate per tablet) were
studied.
20 tablets were accurately weighed and powdered in a
mortar. A mass corresponding to one tenth of a tablet
was transferred to a 100-mL calibrated flask containing
about 30 mL water, swirled until effervescence ceased in
case of effervescent tablet. 30 mL codeine phosphate
1000 mgL-1 was then added to the flask and
ultrasonication followed for 15 minutes. After
dissolution process, the solution was filtrated in a 100-
mL calibrated flask through Whatman grade No. 42
filter paper. The residue was washed three times with 10
mL ethanol 96º and the volume completed to 100 mL
with ethanol 96º. The resulting solution was further
diluted to 1:25 in 25-mL calibrated flask with the same
solvent for UV spectrophotometric measurement.
RESULTS AND DISCUSSION:
The zero-order spectrum of paracetamol in ethanol 96º
exhibits two maxima at 206.1 and 249.5 nm and one
minimum at 218.4 nm, whilst codeine phosphate shows only
a band from 209.5 to 214.0 nm (Figure 2). It can be noted
that overlapping absorption zero-oder spectra of paracetamol
and codeine phosphate at the region 200.0 – 300.0 nm
hinders reliable direct determination of each compound by
ordinary UV spectrophotometry.
CONCLUSION:
Unlike the HPLC method, our study shows that the UV
spectrophotometric techniques enable the use of not only
simple sample preparation but also affordable instrument
and cheap solvent readily available in the laboratory.
The two developed UV spectrophotometric techniques,
first-order derivative and ratio spectra first-order
derivative, have proved to be suitable for the
simultaneous determination of paracetamol and codeine
phosphate in commercial tablets. These techniques are
free from interference by common excipients as
confirmed by their recovery study and statistical
comparison with the official HPLC method. In
conclusion, they are quite reproducible, simple and
accurate which can be used for the routine quality
control of pharmaceutical formulations.