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Analyst, July, 1979, VoL 104, $9. 620-625
620
Downloaded by Duke University on 18 January 2013 Published on 01 January 1979 on http://pubs.rsc.org | doi:10.1039/AN9790400620
Spectrophotometric Determination of Acetaminophen, Salicylamide and Codeine Phosphate in Tablets M. Abdel-Hady Elsayed," Saied F. Belal, Abdel-Fattah M. Elwalily and Hassan Abdine Defiartment of Pharmaceutical Analytical Chemistry, Faculty of Pharmacy, University of Alexandria, Alexandria, Egypt
An accurate and simple method is proposed for the analysis of a threecomponent mixture composed of acetaminophen, salicylamide and codeine phosphate, without the necessity for the previous separation of any component. The first two components are determined directly by independent spectrophotometric measurements, based on the pH -induced spectral changes. Codeine phosphate is assayed by the formation of: an ion pair with methyl orange. The procedure has been applied successfully to the analysis of known mixtures and commercial tablets.
Keywords metry
Acetaminophen ; salicylamide ; codeine phosphate ; spectrophoto-
Acetaminophen (paracetamol; N-acetyl-p-amjnophenol) and salicylamide (o-hydroxybenzamide) occupy prominent positions among the extensively employed antipyretic analgesics. They are frequently prescribed in admixture with each other or with other related drugs. Prior to its spectrophotometric determination, acetaminophen was separated from combination with other antipyretic - analgesics by column chromatography using purified siliceous earth,1-3 a cation-exchange resin4-6 or an anion-exchange resin.' Recently, highperformance liquid chromatographp was utilised in the determination of an acetaminophen methaqualone (2-methyl-3-o-tolylquinazolin-4-one) mixture. Spectrophotometric methods9P for the determination of acetaminophen in Combination with acetylsalicylic acid (aspirin) have been proposed. In biological fluids, acetaminophen was extracted and determined by spectrophotometry,ll fluorimetry,12 differential spectrophotometry13J4and gas - liquid chromatography.16Js Spectrophotometric determinations have been described for salicylamide in combination with caffeine and phenacetin,l' papaverine, phenobarbitone and guaiphenesine carbamate (methocarbamol),l* acetaminophen and caffeine,19 chloroquine phosphate,20and phenacetin, caffeine and chlorpheniramine maleate.21 Salicylamide and acetaminophen, in combination, could be determined by the use of an ion-exchange thin-layer chromatography23or differentiating non-aqueous titration.24-26 Hence the independent spectrophotometric *analysisof a ternary mixture containing the strongly absorbing compounds acetaminophen and salicylamide and the weakly absorbing compound codeine phosphate is challenging. The problem is made more difficult when the dose ratio is not in favour of the codeine phosphate. In this instance the ratio of acetaminophen to salicylamide to codeine phosphate is 25 :30:1. In this investigation the orthogonal function method27,2* and the absorbance-difference m e t h 0 d ~ ~are ~ ~used 0 for the determination of strongly absorbing components without prior separation. Codeine phosphate is assayed by the ion-pair method.31 In the application of the orthogonal function method to spectrophotometric analysis, the absorbance A is replaced by the coefficient $j, which is proportional to concentration. In order to extract the coefficient of a given pcllynomial from an absorption graph, it is necessary to obtain absorbances at a number of equally spaced wavelengths. Thus, to extract the coefficient of a quadratic polynomial $, we need, for example, eight absorbances at eight equally spaced wavelengths [equation (3)]. By plotting the quadratic coefficient
* Present address : Department of
Pharmacy, University of Nigeria, Nsukka, Nigeria.
ELSAYED, BELAL, ELWALILY AND ABDINE
View Article Online
62 1
+
Downloaded by Duke University on 18 January 2013 Published on 01 January 1979 on http://pubs.rsc.org | doi:10.1039/AN9790400620
p 2 , or its substitute he2,at different intervals versus [whereA, = ()(initial hrina1)/2] a convoluted graph is obtained (Fig. 2). The absorbance-difference method is based on the absorbance measurement of the ionic form (in alkaline medium) against the molecular form (in neutral medium) of the drug. This permits the determination of the active components without any interference from other co-existing components, not sensitive to pH change.
Experimental Materials and Reagents All reagents were of analytical-reagent grade and the solvents were of spectroscopic grade. Acetaminophen standard solution, 1 mg ml-1. Obtained from the Alexandria Company, Egypt. Salzcylamide standard solution, 1 mg ml-1. Obtained from the CID Company, Egypt. Codeine phosphate standard solution, 1 mg ml-1. Obtained from E. Merck, Darmstadt, Germany. Codacetine tablets. Obtained from Elkahira Co., Egypt. Each tablet contained 0.25 g of acetaminophen, 0.3 g of salicylamide and 0.01 g of codeine phosphate. Methyl orange solution. A 0.1%m/V solution in 20% V / V aqueous ethanol. B u f e r solz&ion. Prepared by mixing 1 M sodium acetate solution (63.7 ml) with 1 M hydrochloric acid (36.3 ml) and diluting to 100 ml with water. The pH 3.5 of the prepared solution is adjusted potentiometrically (using a Pye pH meter). Sodium hydroxide solution, 0.1 M. Apparatus A Prolabo photoelectric spectrophotometer with 1-cm silica cells was used. Analysis of Codacetine Tablets Twenty tablets were powdered and mixed. An accurately weighed mass equivalent to one tablet was extracted with three 60-ml portions of hot water. The extracts were collected and diluted to 200 ml with water (solution X). Determination of acetaminophen component Two equal volumes of solution X were accurately measured and identical dilutions were made. One volume was diluted with water and the other with 0.01 M sodium hydroxide solution, so as to obtain a concentration of approximately 1.0% m/m. The absorbance of the alkaline solution was measured at 262.5nm using the aqueous solution as a blank (AA method). The absorbance of the alkaline solution was measured in the range 256-270 nm, at 2-nm intervals using 0.01 M sodium hydroxide solution as a blank. The absorbance of the aqueous solution was measured in the range 256-270 nm at 2-nm intervals using water as a blank. The coefficients p , for the alkaline and the aqueous solution were calculated and A$, (p2alk- Pzaq)was then computed (Ap2method). Determination of salicylamide component Two aliquots of solution X were accurately measured and identical dilutions were made with water and 0.01 M sodium hydroxide solution to give concentrations of approximately 1.8% m/m. The absorbance of the alkaline solution was measured at 329nm using the aqueous solution as blank ( A A method). Both solutions (alkaline and aqueous) were measured in the wavelength range 324-338nm at 2-nm intervals using 0.01 M sodium hydroxide solution or water, respectively, as the blank. The coefficient9, for each solution was calculated and Ap2 (p2alk- Pz,,) was then computed. Determination of codeine Phosphate component An aliquot (5.0 ml) of solution X was accurately measured and transferred into a 100-ml separating funnel, containing 3 ml of the 0.1% m/V methyl orange solution and 3 ml of pH 3.5 acetate buffer solution. The mixture was extracted three times with chloroform (10, 10 and then 5 ml). The extracts were pooled in a 25-ml calibrated flask and diluted to
622
ELSAYED et
al. : SPECTROPHOTOMETRIC DETERMINATION
OF
View Article Online Analyst, VOl. 104
Downloaded by Duke University on 18 January 2013 Published on 01 January 1979 on http://pubs.rsc.org | doi:10.1039/AN9790400620
volume with chloroform. The absorbance of the combined extracts was measured at 418 nm against a blank, prepared in a similar manner to that described above but omitting the addition of drug solution.
Results and Discussion The assay of acetaminophen and salicylamide: in combination with codeine phosphate in the ratio 25: 30: 1 is based on the use of their pH-induced spectral changes.19 Codeine phosphate shows negligible interference, as it exists as a minor component and its differential curve exhibits negligible absorbance (Fig. 1).
I
230
250
270
290
310
330
Wavelength/nm
Fig. 1. A A curves of 1% xn/m acetaminophen (solid line), 1% m / m salicylamide (broken line) and 10% m / m codeine phosphate (dotted line).
From the differential curve (Fig. 1) acetaminophen and salicylamide can be determined at 262.5 and 329 nm, respectively. Salicylamide shows an isosbestic point of zero absorbance a t 262.5 nm, acetaminophen (in a concentration equal to salicylamide) exhibits no absorbance at 329 nm. The calibration graphs for acetaminophen and salicylamide were prepared by the application of the procedure mentioned above, using a concentration range of 0.2-2.0% m/mof the former and 0.3-2.4y0 m/mof the latter. Using the method of least squares,32 the data from the absorbance measurements give the following regression equations :
+ 0.3863C . . = 0.0043 + 0.3856C . .
AA262.5 = 0.0147 AA,,,
.. ..
.. ..
(1) *
(2)
for which the percentage fiW3 are 99.87% and 99.94y0, respectively. Alternatively, the A$2 method can be applied to the determination of acetaminophen and salicylamide. The absorbances A,, A,, A,, . . ., A8 of the compound in different solvents (0.01 M sodium hydroxide solution and water11 were measured at 2-nm intervals. The coefficient pz for each solution was calculated using the following equation:
View Article Online
July, 1979 ACETAMINOPHEN, SALICYLAMIDE AND CODEINE PHOSPHATE 623 The subscripts 1-8 refer to A&,, respectively. The figures in parentheses are given in standard books3*and 168 is the normalisation factor. Apz ($2,1k - p2,,) was computed. A graph of Afi, versZts Am [where h, = (A1 &)/2] was a convoluted curve35 (Fig. 2). From the curve, a of 263nm (i.e., the absorbance measurement from the wavelength range 256-270 nm a t 2-nm intervals) was chosen for the determination of acetaminophen without the interference from salicylamide. The latter can be determined, with no interference from the co-existing components, by absorbance measurement in the wavelength range 324-338 nm at 2-nm intervals (A, = 331 nm). Using the procedure mentioned above, a linear relationship between AP2 and C is obtained in a concentration range 0.2-1 .6y0 m/m of acetaminophen and 0.3-2.4% m/m of salicylamide. The corresponding curves can be described by the following regression equations:
Downloaded by Duke University on 18 January 2013 Published on 01 January 1979 on http://pubs.rsc.org | doi:10.1039/AN9790400620
+
Ap, x lo3 = -0.1713 - 4.8881C
..
A$2 x lo3 = 0.0643 - 3.2253C
..
..
..
..
*
-
*.
(4) (5)
for which the percentage fits are 99.56% and 99.Slyo,respectively.
6.0
3.0
0.0 I I
z
E)
I
I I
X
I
&d
I
4 -3.0
\
I
\
-6.0
I 1
\ \ \ \
\ \
I I
I
270
I '
'.=
Analyst, July, 1979, VoL 104, $9. 620-625
620
Downloaded by Duke University on 18 January 2013 Published on 01 January 1979 on http://pubs.rsc.org | doi:10.1039/AN9790400620
Spectrophotometric Determination of Acetaminophen, Salicylamide and Codeine Phosphate in Tablets M. Abdel-Hady Elsayed," Saied F. Belal, Abdel-Fattah M. Elwalily and Hassan Abdine Defiartment of Pharmaceutical Analytical Chemistry, Faculty of Pharmacy, University of Alexandria, Alexandria, Egypt
An accurate and simple method is proposed for the analysis of a threecomponent mixture composed of acetaminophen, salicylamide and codeine phosphate, without the necessity for the previous separation of any component. The first two components are determined directly by independent spectrophotometric measurements, based on the pH -induced spectral changes. Codeine phosphate is assayed by the formation of: an ion pair with methyl orange. The procedure has been applied successfully to the analysis of known mixtures and commercial tablets.
Keywords metry
Acetaminophen ; salicylamide ; codeine phosphate ; spectrophoto-
Acetaminophen (paracetamol; N-acetyl-p-amjnophenol) and salicylamide (o-hydroxybenzamide) occupy prominent positions among the extensively employed antipyretic analgesics. They are frequently prescribed in admixture with each other or with other related drugs. Prior to its spectrophotometric determination, acetaminophen was separated from combination with other antipyretic - analgesics by column chromatography using purified siliceous earth,1-3 a cation-exchange resin4-6 or an anion-exchange resin.' Recently, highperformance liquid chromatographp was utilised in the determination of an acetaminophen methaqualone (2-methyl-3-o-tolylquinazolin-4-one) mixture. Spectrophotometric methods9P for the determination of acetaminophen in Combination with acetylsalicylic acid (aspirin) have been proposed. In biological fluids, acetaminophen was extracted and determined by spectrophotometry,ll fluorimetry,12 differential spectrophotometry13J4and gas - liquid chromatography.16Js Spectrophotometric determinations have been described for salicylamide in combination with caffeine and phenacetin,l' papaverine, phenobarbitone and guaiphenesine carbamate (methocarbamol),l* acetaminophen and caffeine,19 chloroquine phosphate,20and phenacetin, caffeine and chlorpheniramine maleate.21 Salicylamide and acetaminophen, in combination, could be determined by the use of an ion-exchange thin-layer chromatography23or differentiating non-aqueous titration.24-26 Hence the independent spectrophotometric *analysisof a ternary mixture containing the strongly absorbing compounds acetaminophen and salicylamide and the weakly absorbing compound codeine phosphate is challenging. The problem is made more difficult when the dose ratio is not in favour of the codeine phosphate. In this instance the ratio of acetaminophen to salicylamide to codeine phosphate is 25 :30:1. In this investigation the orthogonal function method27,2* and the absorbance-difference m e t h 0 d ~ ~are ~ ~used 0 for the determination of strongly absorbing components without prior separation. Codeine phosphate is assayed by the ion-pair method.31 In the application of the orthogonal function method to spectrophotometric analysis, the absorbance A is replaced by the coefficient $j, which is proportional to concentration. In order to extract the coefficient of a given pcllynomial from an absorption graph, it is necessary to obtain absorbances at a number of equally spaced wavelengths. Thus, to extract the coefficient of a quadratic polynomial $, we need, for example, eight absorbances at eight equally spaced wavelengths [equation (3)]. By plotting the quadratic coefficient
* Present address : Department of
Pharmacy, University of Nigeria, Nsukka, Nigeria.
ELSAYED, BELAL, ELWALILY AND ABDINE
View Article Online
62 1
+
Downloaded by Duke University on 18 January 2013 Published on 01 January 1979 on http://pubs.rsc.org | doi:10.1039/AN9790400620
p 2 , or its substitute he2,at different intervals versus [whereA, = ()(initial hrina1)/2] a convoluted graph is obtained (Fig. 2). The absorbance-difference method is based on the absorbance measurement of the ionic form (in alkaline medium) against the molecular form (in neutral medium) of the drug. This permits the determination of the active components without any interference from other co-existing components, not sensitive to pH change.
Experimental Materials and Reagents All reagents were of analytical-reagent grade and the solvents were of spectroscopic grade. Acetaminophen standard solution, 1 mg ml-1. Obtained from the Alexandria Company, Egypt. Salzcylamide standard solution, 1 mg ml-1. Obtained from the CID Company, Egypt. Codeine phosphate standard solution, 1 mg ml-1. Obtained from E. Merck, Darmstadt, Germany. Codacetine tablets. Obtained from Elkahira Co., Egypt. Each tablet contained 0.25 g of acetaminophen, 0.3 g of salicylamide and 0.01 g of codeine phosphate. Methyl orange solution. A 0.1%m/V solution in 20% V / V aqueous ethanol. B u f e r solz&ion. Prepared by mixing 1 M sodium acetate solution (63.7 ml) with 1 M hydrochloric acid (36.3 ml) and diluting to 100 ml with water. The pH 3.5 of the prepared solution is adjusted potentiometrically (using a Pye pH meter). Sodium hydroxide solution, 0.1 M. Apparatus A Prolabo photoelectric spectrophotometer with 1-cm silica cells was used. Analysis of Codacetine Tablets Twenty tablets were powdered and mixed. An accurately weighed mass equivalent to one tablet was extracted with three 60-ml portions of hot water. The extracts were collected and diluted to 200 ml with water (solution X). Determination of acetaminophen component Two equal volumes of solution X were accurately measured and identical dilutions were made. One volume was diluted with water and the other with 0.01 M sodium hydroxide solution, so as to obtain a concentration of approximately 1.0% m/m. The absorbance of the alkaline solution was measured at 262.5nm using the aqueous solution as a blank (AA method). The absorbance of the alkaline solution was measured in the range 256-270 nm, at 2-nm intervals using 0.01 M sodium hydroxide solution as a blank. The absorbance of the aqueous solution was measured in the range 256-270 nm at 2-nm intervals using water as a blank. The coefficients p , for the alkaline and the aqueous solution were calculated and A$, (p2alk- Pzaq)was then computed (Ap2method). Determination of salicylamide component Two aliquots of solution X were accurately measured and identical dilutions were made with water and 0.01 M sodium hydroxide solution to give concentrations of approximately 1.8% m/m. The absorbance of the alkaline solution was measured at 329nm using the aqueous solution as blank ( A A method). Both solutions (alkaline and aqueous) were measured in the wavelength range 324-338nm at 2-nm intervals using 0.01 M sodium hydroxide solution or water, respectively, as the blank. The coefficient9, for each solution was calculated and Ap2 (p2alk- Pz,,) was then computed. Determination of codeine Phosphate component An aliquot (5.0 ml) of solution X was accurately measured and transferred into a 100-ml separating funnel, containing 3 ml of the 0.1% m/V methyl orange solution and 3 ml of pH 3.5 acetate buffer solution. The mixture was extracted three times with chloroform (10, 10 and then 5 ml). The extracts were pooled in a 25-ml calibrated flask and diluted to
622
ELSAYED et
al. : SPECTROPHOTOMETRIC DETERMINATION
OF
View Article Online Analyst, VOl. 104
Downloaded by Duke University on 18 January 2013 Published on 01 January 1979 on http://pubs.rsc.org | doi:10.1039/AN9790400620
volume with chloroform. The absorbance of the combined extracts was measured at 418 nm against a blank, prepared in a similar manner to that described above but omitting the addition of drug solution.
Results and Discussion The assay of acetaminophen and salicylamide: in combination with codeine phosphate in the ratio 25: 30: 1 is based on the use of their pH-induced spectral changes.19 Codeine phosphate shows negligible interference, as it exists as a minor component and its differential curve exhibits negligible absorbance (Fig. 1).
I
230
250
270
290
310
330
Wavelength/nm
Fig. 1. A A curves of 1% xn/m acetaminophen (solid line), 1% m / m salicylamide (broken line) and 10% m / m codeine phosphate (dotted line).
From the differential curve (Fig. 1) acetaminophen and salicylamide can be determined at 262.5 and 329 nm, respectively. Salicylamide shows an isosbestic point of zero absorbance a t 262.5 nm, acetaminophen (in a concentration equal to salicylamide) exhibits no absorbance at 329 nm. The calibration graphs for acetaminophen and salicylamide were prepared by the application of the procedure mentioned above, using a concentration range of 0.2-2.0% m/mof the former and 0.3-2.4y0 m/mof the latter. Using the method of least squares,32 the data from the absorbance measurements give the following regression equations :
+ 0.3863C . . = 0.0043 + 0.3856C . .
AA262.5 = 0.0147 AA,,,
.. ..
.. ..
(1) *
(2)
for which the percentage fiW3 are 99.87% and 99.94y0, respectively. Alternatively, the A$2 method can be applied to the determination of acetaminophen and salicylamide. The absorbances A,, A,, A,, . . ., A8 of the compound in different solvents (0.01 M sodium hydroxide solution and water11 were measured at 2-nm intervals. The coefficient pz for each solution was calculated using the following equation:
View Article Online
July, 1979 ACETAMINOPHEN, SALICYLAMIDE AND CODEINE PHOSPHATE 623 The subscripts 1-8 refer to A&,, respectively. The figures in parentheses are given in standard books3*and 168 is the normalisation factor. Apz ($2,1k - p2,,) was computed. A graph of Afi, versZts Am [where h, = (A1 &)/2] was a convoluted curve35 (Fig. 2). From the curve, a of 263nm (i.e., the absorbance measurement from the wavelength range 256-270 nm a t 2-nm intervals) was chosen for the determination of acetaminophen without the interference from salicylamide. The latter can be determined, with no interference from the co-existing components, by absorbance measurement in the wavelength range 324-338 nm at 2-nm intervals (A, = 331 nm). Using the procedure mentioned above, a linear relationship between AP2 and C is obtained in a concentration range 0.2-1 .6y0 m/m of acetaminophen and 0.3-2.4% m/m of salicylamide. The corresponding curves can be described by the following regression equations:
Downloaded by Duke University on 18 January 2013 Published on 01 January 1979 on http://pubs.rsc.org | doi:10.1039/AN9790400620
+
Ap, x lo3 = -0.1713 - 4.8881C
..
A$2 x lo3 = 0.0643 - 3.2253C
..
..
..
..
*
-
*.
(4) (5)
for which the percentage fits are 99.56% and 99.Slyo,respectively.
6.0
3.0
0.0 I I
z
E)
I
I I
X
I
&d
I
4 -3.0
\
I
\
-6.0
I 1
\ \ \ \
\ \
I I
I
270
I '
'.=
