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STANDARDISATION OF PARACETAMOL BY UV- SPECTROPHOTOMETRY. By. Jyotirmoy Das Choudhury M.Pharm 2 nd semester Phamacology Under the Guidance of Mr. Avik Das(M.S.), Lecturer, Pharmacology Department.


Contents: Aim of the Experiment. Description of Paracetamol. Pharmacokinetic Parameters. Theory. Principle of the Experiment. Requirements Procedure. Inference. References. 2

Aim of the Experiment.:

Aim of the Experiment. The main objective of the experiment is to construct a calibration curve of Paracetamol. 3

Description of Paracetamol:

Description of Paracetamol Chemically Paracetamol is N-(4-Hydroxyphenyl) acetamide . Its molecular formula is C 8 H 9 NO 2. Mol Wt. 151.2 gm. Appearance: White or almost white, crystalline powder. Solubility: Sparingly soluble in water, freely soluble in alcohol, very slightly soluble in methylene chloride. Action: Analgesic, Antipyretic. 4

Pharmacokinetic Parameters of Paracetamol:

Pharmacokinetic Parameters of Paracetamol Fractional absorption: 88 ± 15% Urinary excretion: 3 ± 1% Binding to plasma proteins: 0 Total clearance: 5.0 ± 1.4 ml/min per kg Volume of distribution: 0.95 ± 0.12 l/kg Half-life: 2.0 ± 0.4 hours 5

Theory :

Theory The metabolism and pharmacokinetics of paracetamol are very important aspects of the clinical pharmacology of this drug. Even the development of paracetamol was based upon studies on drug metabolism and pharmacokinetics. It was found that the old analgesics, acetanilide and phenacetin , are both converted largely to paracetamol . The subsequent confirmation of earlier work showing that paracetamol is an analgesic and questions about the renal toxicity of phenacetin led to the cessation of the use of phenacetin and its replacement by paracetamol . Paracetamol achieves high concentrations in plasma and urine. It is assayed easily, and is eliminated by several metabolic pathways. Therefore, like salicylate , paracetamol is used widely as a model drug in studies on the principles of drug metabolism, pharmacokinetics and drug interactions. 6

Principle of the Experiment::

Principle of the Experiment: The principle of the experiment is to plot a calibration curve between Abs & Conc. So that the unknown conc. of paracetamol can be determined in the sample solution. The sample solution can be salivary juice or urine or body fluid. To do so we have to construct the calibration curve of Paracetamol in different pH buffer. The pH of the different standard buffer solutions are 5.8, 6.4 & 7.4. 7


Requirements. Pottasium dihydrogen phosphate(KH 2 PO 4 ). Sodium hydroxide pellet ( NaOH ). Volumetric flask(10ml, 100ml, 500ml). UV-Spectrophotometer. 0.2m KH 2 PO 4 solution. 0.2m NaOH solution. 8


Procedure: Preparation of 0.2m KH 2 PO 4 solution: Preparation of 0.2m NaOH solution: 9


Cont…. Preparation of Phosphate buffer: 50 ml of 0.2m KH 2 PO 4 solution is taken in 200 ml of volumetric flask, add the specific volume of NaOH & then made the volume with d.w . pH Amt. of 0.2m NaOH soln. 5.8 3.6ml 6.4 11.6ml 7.4 39.1ml 10


Cont… 5mg of Paracetamol is dissolved in 500ml of Phosphate buffer of pH 5.8, 6.4 & 7.4 individually, so the conc. of the solutions will be 1000µg/ml. This is stock solution I. 10ml is taken from each solution & make the volume up to 100ml by phosphate buffer of pH 5.8, 6.4 & 7.4 respectively. So the conc. of the each solution will be 100µg/ml. This is stock solution II. 11


From each of the stock solution II, 1ml, 2ml, 3ml, 4ml, 5ml, 6ml, 7ml, 8ml, 9ml & 10ml is taken in different 10 ml volumetric flask & make up the volume by Phosphate buffer of pH 5.8, 6.4 & 7.4 respectively. So the conc. of the solutions will be 10, 20, 30, 40, 50, 60, 70, 80, 90 & 100 µg/ml. These are the sample solutions. Cont… 12


The absorbance is observed by UV- Spectrophotometry for each samle solution at ƛ max 249nm, 255nm & 257nm for pH 5.8, 6.4 & 7.4 respectively. A graph has been plotted between Abs. & Conc. The line intersecting the maximum no. of points is drawn. It will give us the calibration curve. Cont… 13


Calculation for 1000ml of buffer(Direct method) (Mol. Wt x strength x volume)/1000 Cont… 14


Infernce . The calibration curve helps us in quantitative determination of a sample. It is a useful method in Pharmacokinetic study which helps us to know about the conc. of the drug in urine, saliva or in blood. It is useful to know the half life, plasma binding ability of the drug & many more pharmacokinetic data. 15


References… British Pharmacopoeia 2009. Aspirin and Related Drugs. By K. D. Rainsford . 16

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