Estimation of Paracetamol content in tablet.

Resonance March 12, 2026


Aim

To estimate the amount of paracetamol present in a given tablet formulation using UV–Visible spectrophotometry.

Principle

Paracetamol absorbs ultraviolet radiation at 257 nm. The absorbance of the solution is proportional to the concentration of the drug according to Beer–Lambert’s law.

A=εcl

Where

  • A = Absorbance

  • ε = Molar absorptivity

  • c = Concentration

  • l = Path length of the cell

The absorbance of the diluted tablet solution is measured at 257 nm, and the concentration is calculated using the absorptivity constant.

Apparatus

  • UV–Visible spectrophotometer

  • 200 ml volumetric flask

  • 100 ml volumetric flasks

  • 10 ml pipette

  • Mortar and pestle

  • Beakers

  • Glass funnel

  • Filter paper

Chemicals / Reagents

  • Paracetamol tablets

  • 0.1 M NaOH solution

  • Distilled water

Procedure

1. Preparation of Tablet Powder

  1. Weigh 20 paracetamol tablets accurately.

  2. Calculate the average weight of one tablet.

  3. Grind the tablets into a fine powder using mortar and pestle.

2. Weighing the Sample

  1. From the powdered tablet, weigh a quantity equivalent to 0.15 g of paracetamol.

3. Preparation of Solution A

  1. Transfer the weighed powder into a 200 ml volumetric flask.

  2. Add 50 ml of 0.1 M NaOH.

  3. Dilute with distilled water to 100 ml and shake for 15 minutes.

  4. Make the volume up to 200 ml with distilled water.

  5. Label this as Solution A.

4. Filtration

Filter Solution A using filter paper to obtain a clear filtrate.

5. Preparation of Solution B

  1. Pipette 10 ml of filtrate into a 100 ml volumetric flask.

  2. Make up the volume to 100 ml with distilled water.

  3. Label this as Solution B.

6. Preparation of Solution C

  1. Pipette 10 ml of Solution B into another 100 ml volumetric flask.

  2. Dilute to 100 ml with distilled water.

  3. Label this as Solution C.

7. Measurement

  1. Set the UV spectrophotometer at 257 nm.

  2. Use distilled water as blank.

  3. Measure the absorbance of Solution C.

Observations

  • Absorbance of solution C = 0.620

  • Weight of 20 tablets = 12.36 g

  • Weight of tablet powder taken = 0.185 g

Result

The percentage of paracetamol in the given tablet formulation was found to be approximately 115.4% of the labeled claim.

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