Diclofenac Sodium Assay Method

Methanol Dissolution and Titration Method

Principle

Diclofenac Sodium is dissolved in methanol and titrated with 0.1 M sodium hydroxide (NaOH). The amount of Diclofenac Sodium present in the sample is calculated from the volume of NaOH consumed.

Factor:
1 mL of 0.1 M NaOH = 0.03181 g of Diclofenac Sodium

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Reagents Required

1. Diclofenac Sodium sample
2. Methanol
3. 0.1 M Sodium hydroxide solution
4. Phenolphthalein indicator or suitable indicator
5. Distilled water, if required

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Apparatus Required

1. Analytical balance
2. Burette
3. Pipette
4. Conical flask
5. Volumetric flask
6. Measuring cylinder
7. Funnel

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Step-by-Step Procedure

Step 1: Sample Weighing

Accurately weigh the required quantity of Diclofenac Sodium sample using an analytical balance.

Step 2: Transfer

Transfer the weighed sample into a clean and dry conical flask.

Step 3: Dissolution

Add sufficient quantity of methanol to the conical flask.

Step 4: Mixing

Swirl the flask gently until the sample dissolves completely in methanol.

Step 5: Indicator Addition

Add 2–3 drops of phenolphthalein indicator to the solution.

Step 6: Burette Preparation

Fill the burette with 0.1 M NaOH solution. Remove air bubbles from the burette tip and note the initial burette reading.

Step 7: Titration

Titrate the sample solution with 0.1 M NaOH while continuously swirling the conical flask.

Step 8: Endpoint Detection

Continue titration until a faint pink colour appears and persists for about 30 seconds.

Step 9: Reading

Record the final burette reading and calculate the volume of NaOH consumed.$$\text{Volume used} = \text{Final reading} – \text{Initial reading}$$Volume used=Final reading−Initial reading

Step 10: Blank Correction

Perform a blank titration using methanol and indicator without sample, if required. Subtract the blank volume from the sample titration volume.

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Calculation

$$\text{Amount of Diclofenac Sodium} = V \times F \times 0.03181$$Amount of Diclofenac Sodium=V×F×0.03181

Where:

V = Volume of 0.1 M NaOH used in mL
F = Molarity correction factor of 0.1 M NaOH
0.03181 = Diclofenac Sodium equivalent in grams per mL of 0.1 M NaOH

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Percentage Assay Formula

$$\% \text{Assay} = \frac{V \times F \times 0.03181 \times 100}{W}$$%Assay=WV×F×0.03181×100​

Where:

W = Weight of sample taken in grams

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Example Calculation

If:

Sample weight = 0.500 g
Volume of 0.1 M NaOH = 15.70 mL
Factor = 1.000$$\% \text{Assay} = \frac{15.70 \times 1.000 \times 0.03181 \times 100}{0.500}$$%Assay=0.50015.70×1.000×0.03181×100​ $$\% \text{Assay} = 99.88\%$$%Assay=99.88%

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Precautions

Use dry and clean glassware. Dissolve the sample completely before titration. Fill the burette carefully without air bubbles. Add NaOH slowly near the endpoint. Record readings accurately. Follow the current pharmacopoeial monograph or approved SOP for official QC testing.