Determination of Saponification Value : Pharmaceutical Guidelines

Determination of Saponification Value

Learn how to determine the Saponification Value in Pharmaceutical substances.
The saponification value is the number of milligrams of potassium hydroxide necessary to neutralise the free acids and to saponify the esters present in 1 g of the substance.

Method

Unless otherwise specified in the individual monograph introduce about 2 g of the substance under examination, accurately weighed, into a 200-ml flask of borosilicate glass fitted with a reflux condenser. Add 25.0 ml of 0.5 M ethanolic potassium hydroxide and a little pumice powder and boil under reflux on a water-bath for 30 minutes. Add 1 ml of phenolphthalein solution and titrate immediately with 0.5 M hydrochloric acid (a ml). Carry out a blank titration omitting the substance under examination (b ml). Calculate the saponification value from the expression
Saponification value = 28.05 (b - a)/w
where, w = weight of the substance in g .
NOTE - If the oil has been saturated with carbon dioxide for the purpose of preservation, gently reflux the solution of the oil in ethanol (95 per cent) and ether for 10 minutes before titration. The oil may be freed from the carbon dioxide by exposing it in a shallow dish in a vacuum desiccator for 24 hours before weighing the sample.





Ankur Choudhary is India's first professional pharmaceutical blogger, author and founder of Pharmaceutical Guidelines, a widely-read pharmaceutical blog since 2008. Sign-up for the free email updates for your daily dose of pharmaceutical tips.
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