Assay of Dapsone


To determine the percentage purity of a given sample of the tablet.


Dapsone is a diamino diphenyl sulphone. It is assayed by direct diazotization titration. The free primary amino group present in dapsone is
diazotized by nitrous acid and hydrochloric acid to form an arene diazonium compound. The endpoint can be determined by using an external indicator i.e. starch iodide paper, during titration with sodium nitrite an aromatic primary amine is diazotized. After the endpoint, the drug solution containing a slight excess of nitrite comes in contact with starch iodide paper. It oxidizes iodide into iodine which gives blue colour with starch indicating the endpoint.



Preparation of 0.1M Sodium nitrite solution

7.5g of sodium nitrite was dissolved insufficient water to be produced 1000ml.

Standardisation of 0.1M Sodium nitrite

0.3g of sulphanilic acid was dissolved in 50ml of 2M hydrochloric acid, 3g of potassium bromide was added, cool in ice and titrate with 0.1M sodium nitrite solution using starch iodide paper as an external indicator.
Each ml of 0.1M Sodium nitrite= 0.01732g of C6H7NO3S.

Assay of Dapsone tablet

20 tablets were weighed and powdered. Tablet powder equivalent to0.25gm dapsone was weighed and dissolved in a mixture of 15ml of 2M
hydrochloric acid. The solution was cooled to about 15oC and carry out sodium nitrite titration using starch iodide paper as an external indicator. The endpoint is the immediate appearance of blue colour.
Each ml of 0.1M sodium nitrite= 0.01241g of C12H12N2O2S.


The Molarity of 0.1M sodium nitrite = __________________
The percentage purity of given dapsone tablet was found to be = ________________

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