Dr. Professor
Paracetamol is crystalline white power with the scientific name N-(4- Hydroxyphenyl) acetamide. The chemical formula is C8H9NO2 and its structure is
Properties
The melting range of paracetamol is 168 to 172oC and its solubility is 14.3g / dm3 of water and ethanol’s 100g / dm3. It is insoluble in ether and dissolves quickly in chloroform. It dissipates uv absorption minimum in aqueous acidic medium at 245 nm and has uv absorption maximum in aqueous alkaline medium.
Assay
Through titration, paracetamol is analyzed using ceric ammonium sulphate. In the titration, Ferroin plays the role of indicator. It is also assayed using methods of uv spectrophotometric and high performance liquid chromatography.
Storage
It has to be stored away from light.
Uses
It is used as analgesic and antipyretic agent. It is also proven to be effective for rheumatic and arthritic and neuralgias, myalgias and dysmenorrhoea. Paracetamol is administered to patients who are intolerant to aspirin.
This experiment is conducted to assess the paracetamol result obtained through the experiment with the content of paracetamol specified by British Pharmocopoiea. The experiment involves assay of paracetamol using method of titration, uv method with calibration line and chromatography.
Aim
The aim of this experiment is to compare and contrast the methods adopted by pharmaceutical practices for the analysis of Paracetamol and to compare these results with the observed results in experiment.
Method
Titration
0.150 g of paracetamol was dissolved in mixture of 5 ml of water and 15 ml of dilute sulphuric acid was added to it. The solution was boiled under the reflex condenser for an hour and was cooled down. The solution was then diluted to quantity 50 ml with water. 20 ml of solution was taken and 20 ml of water, 20 g of ice and 7.5 ml of dilute hydrochloric acid was added. A drop of ferroin indicator was added to the solution. This solution was titrated with 0.1 M cerium ammonium sulphate and readings were recorded when the solution turned greenish-yellow. The experiment was conducted three times and readings were recorded. Blank titration was also performed that didn’t use paracetamol and readings were recorded.
UV Method with Calibration Line
Pure paracetamol standard were weighed and each amount was weighed twice for duplicates. The amounts weighed were 50, 100, 150, 200, 250 and 300 mg. The paracetamol xmg was dissolved in methanol, diluted to 100 ml in a 100 ml volumetric flask. 1 ml of this solution was taken and transferred to another 100 ml volumetric flask. 0.5 ml of 0.3 M hydrochloric acid was added to solution and was diluted to 100 ml with methanol. The absorbance was measured immediately at 249nm in a quartz cell. Blank was also measured with the same procedure that didn’t have paracetamol. The calibration line was plotted in excel.
Thin Layer Chromatography of Paracetamol
3 paracetamol solutions were prepared with concentration of 95%, 100% and 105%. To prepare 95% solution that is 4.75 g/l, 46 mg of paracetamol standard was added to 9.68 ml of methanol and similarly, 100% solution that is 5 g/l, 1/5 paracetamol tablet in 20 ml methanol and 105% solution that is 5.25 g/l, 46 mg of paracetamol standard in 8.76 ml of methanol was used. The eluent for chromatography was prepared with ratio of 2: 17:1 of methanol : ethyl acetate : concentrated ammonium hydroxide. Using the pipette, 5 µl of each solution was spotted along with component of eluent along the origin of silica plate in pencil. The silica plate was placed into the TLC development tank and was left to develop. The silica plate was removed and solvent was traced. This was allowed to dry in the fume cupboard and the plate was viewed under a UV light and spots were traced. The Rf values were calculated and recorded for each of the solution.
Calculation
Factor of 0.1 M Cerium Ammonium Sulphate = 0.9969
Titration of tablet paracetamol with Cerium Ammonium Sulphate;
The average pure paracetamol titer volume = 3.4+ 3.5 + 3.6 / 3 = 3.5
Blank average titer volume = 0.1 + 0.2 / 2 = 0.15
Volume of ammonium sulphate which reacted with pure paracetamol;
= (3.5 ml – 0.15 ml) = 3.35 ml
The amount of paracetamol actual = (0.007560 g x 3.35)/1 ml
= 25.32 mg
The percentage content of standard paracetamol pure = Actual amount / nominal amount
= 25.32 mg / (150 mg x (20/100))\
The percentage purity of pure paracetamol = 84.4
Titration of pure paracetamol with Cerium Ammonium Sulphate;
The average tablet paracetamol titer volume = 3.1+ 3.3 + 3.4 / 3 = 3.26
Blank average titer volume = 0.1 + 0.2 / 2 = 0.15
Volume of ammonium sulphate which reacted with pure paracetamol;
= (3.26 ml – 0.15 ml) = 3.11 ml
The amount of paracetamol actual = (0.007560 g x 3.11)/1 ml
= 23.51 mg
The percentage content of standard paracetamol pure = Actual amount / nominal amount
= 23.51 mg / (150 mg x (20/100))\
The percentage purity of pure paracetamol = 78.36
UV method with calibration line
y = 99.21 x + 10.63
- 50mg paracetamol. (1940/1900)x 50 = 51.05mg.
- 100mg paracetamol. (1940/1900)x100 = 102.10mg
- 200mg paracetamol. (1940/1900)x200 = 204.21mg
- 250mg paracetamol. (1940/1900)x 250 = 255.26mg
- 300mg paracetamol. (1940/1900)x 300 = 306.31mg
*(3838mg/3500) x X = 114.1mg X = 114.1/(3838mg/3500)=104.05mg
Thin Layer Chromatography of Paracetamol
Rf value for 95% = 8.2/9.9 = 0.83
Rf value for 100% = 8.3/9.9 = 0.84
Rf value for 105% = 8.5/9.9 = 0.86
Discussion
Titration
Assay of paracetamol with titration using ceric ammonium sulphate and ferroin gives greenish-blue solution. The equation of the reaction which takes place are as follows;
C8H9NO2
C6H7NO + CH3COOH
Titrating the 4-Aminophenol formed in heating reaction
2Ce4+ + C6H7NO
C6H5NO + 2Ce3+ + 2H+
The conversion of 4-Aminophenol to iminoquinone follows the reduction to ferriin blue of ferroin
2Ce4+ + Fe2+
2Fe2+ + 2Ce3+
The conversion of red ferroin to blue ferrin completes the titration of paracetamol.
The titration of paracetamol with cerium ammonium sulphate yields greenish-blue solution. British pharmacopeia specifies the content of paracetamol to be 99 per cent to 101 per cent of dried substance. In this experiment, the paracetamol content of pure paracetamol and tablet paracetamol is ascertained to be compared and contrasted with the specified content limit by British pharmacopeia. The calculation shows that the paracetamol content in pure paracetamol is 84.4 per cent and in tablet paracetamol is 78.36 per cent. The percentage calculated for pure and tablet paracetamol through the experiment is lower than the content specified by British Pharmacopeia. The variation in the observed result and the expected result based on British Pharmacopeia implies that some error occurred while performing the titration. The titration values obtained for pure and tablet paracetamol are lower than the expected values of 6 or 7 which would have lead to acceptable results. The reason for this error could be accorded to potential error in preparing the solution and recording the readings.
UV method with calibration line
UV method with calibration line was performed for pure paracetamol and powder of paracetamol tablet. The result for 100 mg of pure paracetamol and paracetamol tables was 102.10 mg and 104.05 mg respectively. The result of the experiment for paracetamol is content is coherent with the British Pharmacopeia stating the content to be 99.0 per cent to 101.00 per cent. The result for the calibration of pure paracetamol for 100 mg varied and was not in the acceptable range. During performing the experiment, there could have been variance in adding the hydrochloric acid which must have resulted in the outlier result. The absorbance at 249nm from the assay could be equated to the absorbance of the contributing compound that is paracetamol multiplied by its concentration which contributed in that absorbance. Therefore, specific absorbance of paracetamol at 249nm and paracetamol concentration leads to the absorption equation. The absorbance of the paracetamol at 249nm is used to calculate the amount of paracetamol in the specific mg sample of paracetamol. The result obtained for tablet powder paracetamol is slightly above than the approved content by BP. Therefore, UV method for calibration line has provided the results which are slightly more than the pharmaceutical practice guidelines.
Thin Layer Chromatography of Paracetamol
The retention factor or Rf of the paracetamol solutions of concentration 95%, 100% and 105% were performed and the results were observed. The Rf value varies between 83 per cent to 86 per cent and these results are not coherent with the content for pharmaceutical practices specified by British Pharmacopeia. This result is not lower than the specified content which could be because of methanol not taken in appropriate quantity. This is one source of error as the measurement might have differed slightly leading to lower reading.
Conclusion
The experiment performed to compare and contrast the quantity of paracetamol in pure paracetamol and paracetamol tablet with British Pharmacopeia by using techniques of Titration, UV method with calibration line, and Thin Layer Chromatography. The results obtained in the experiment with these tests varied and didn’t exactly adhere to the content specified by British Pharmacopeia. The variation in the results has been identified because of some potential sources of error like measurement and titration readings.
Anon., 2009. British Pharmacopoeia. British Pharmacopoeia Commission.
Osborne, C., 2002. Paracetamol: a curriculum resource. London: Royal Society of Chemistry.
Tomlin, M., 2010. Pharmacology and Pharmacokinetics: A Basic Reader. Southampton: Springer.
