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Assay of Paracetamol tablet by UV spectrophotometer
Experiment Findings · April 2023
DOI: 10.13140/RG.2.2.29867.11048
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Kailas K Mali
Adarsh College of Pharmacy, Vita
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Adarsh College of Pharmacy, Vita
Experiment No.
Date:
Aim: To perform the assay of Paracetamol tablet by UV spectrophotometer at specific
absorbance.
Objectives:
1. To understand the application of A 1% 1cm by spectrophotometer.
2. To develop skill of handling of UV- visible spectrophotometer.
3. To perform assay calculations.
4. To find out percentage purity of paracetamol tablet.
Principle
UV-Visible spectrophotometry is one of the most frequently employed
techniques in pharmaceutical analysis. It involves measuring the amount of ultraviolet
or visible radiation absorbed by a substance in solution. In qualitative analysis, organic
compounds can be identified by use of spectrophotometer, if any recorded data is
available, and quantitative spectrophotometric analysis is used to ascertain the quantity
of molecular species absorbing the radiation. Spectrophotometric technique is simple,
rapid, moderately specific and applicable to small quantities of compounds. The
fundamental law that governs the quantitative spectrophotometric analysis is the Beer
-Lambert law. Beer's law: It states that the intensity of a beam of parallel
monochromatic radiation decreases exponentially with the number of absorbing
molecules. In other words, absorbance is proportional to the concentration. Lambert's
law. It states that the intensity of a beam of parallel monochromatic radiation decreases
exponentially as it passes through a medium of homogeneous thickness. A combination
of these two laws yields the Beer-Lambert law. Beer-Lambert law: When beam of light
is passed through a transparent cell containing a solution of an absorbing substance,
reduction of the intensity of light may occur. Mathematically, Beer Lambert law is
expressed as:
A=abc
Where,
A= absorbance or optical density.
a = absorptivity or extinction coefficient.
b = path length of radiation through sample (cm)
c = concentration of solute in solution.
Adarsh College of Pharmacy, Vita
Theory:
Moleculer formula : C₈H₉NO₂
Moleculer weight : 151.2
IUPAC Name : N-(4- hydroxyphenyl) acetamide
Usual strengths : 300mg – 500mg.
Storage : Store in well closed, light resistant containers.
Standard: Paracetamol tablet contain not less than 95.0 percent and not more than
105.0 percent of the stated amount of paracetamol.
Requirements
Apparatus: Volumetric flask (200mL, measuring cylinder, pipette, beaker, glass rod,
funnel, weighing balance, glass mortar pastel, spatula, Whatman filter paper etc.
Chemicals: Paracetamol tablet, Sodium hydroxide, Distilled water.
Prepration of 0.1M sodium hydroxide
Take about 100 ml of distilled water in clean and dry 1000ml volumetric flask. Add
about 4gm of sodium hydroxide with continues stirring. Makeup the volume at 1000ml
with distilled water.
Procedure:
1. Weigh and powder 20 tablets.
2. Weigh accurately a quantity of the powder equivalent to about 0.15 g of
Paracetamol.
3. Take clean 200ml volumetric flask and place clean funnel on it.
4. Transfer carefully weighed quantity of powder into funnel.
5. Add 50 ml of 0.1M sodium hydroxide into funnel so as to all powder gets transferred
to volumetric flask.
6. Dilute the resulting mixture with 100 ml of distilled water and shake for 15 minutes.
7. Finally add sufficient quantity of water to produce 200ml.
8. Filture resulting solution from whatman filter.
Adarsh College of Pharmacy, Vita
9. Take 10 mL of filtrate and dilute to 100 mL with water.
10. Take 10 mL resulting solution in 100 mL volumetric flask and add 0.1M sodium
hydroxide.
11. Adjust the volume of solution using distilled water and mix.
12. Measure the absorbance of the resulting solution at the maximum at about 257 nm.
13. Calculate the content of, C₈H₉NO₂ taking 715 as the value of A(1%, 1 cm) at the
maximum at about 257 nm.
Absorbance of paracetamol solution at 257nm:
Paste UV Spectra of Paracetamol
Calculations
1. Theoretical concentration of Paracetamol in solution
0.75mg
750μg
𝑜𝑟
ml
ml
75μg
𝐒𝐞𝐜𝐨𝐧𝐝 𝐝𝐢𝐥𝐮𝐭𝐢𝐨𝐧: 10ml in 100 ml →
ml
𝐅𝐢𝐫𝐬𝐭 𝐝𝐢𝐥𝐮𝐭𝐢𝐨𝐧: 0.15gm in 200ml →
𝐓𝐡𝐢𝐫𝐝 𝐝𝐢𝐥𝐮𝐭𝐢𝐨𝐧: 10ml in 100ml → 7.5μg/ml (7.5 × 10 g/ml)
𝐓𝐡𝐞𝐨𝐫𝐞𝐭𝐢𝐜𝐚𝐥 𝐀𝐛𝐬𝐨𝐫𝐛𝐚𝐧𝐜𝐞 (𝐀)
= Specific Absorbance (a) × Path length (b)
× Concentration (c) g/100ml
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Adarsh College of Pharmacy, Vita
A = abc
A = 715 × 1 × 7.5 × 10
A = 0.5362
Practical Absorbance =
------------------------ nm
% Purity of paracetmol tablet =
% Purity of paracetmol tablet =
Practical absorbance
× 100
Theoratical absorbance
.
0.5362
× 100
% Purity of paracetamol tablet = ------------------%
Result
The percentage purity of paracetamol tablet was found to be -----------------%w/w.
Conclusions
The given sample of paracetamol tablet complies / dose not complies as per IP 1995.