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Determination of Esters


Learn how to determine the Esters in Pharmaceutical preparations.
Boil a convenient quantity of ethanol (95 percent) thoroughly to expel carbon dioxide and neutralize it to phenolphthalein solution. Unless otherwise stated in the individual monograph, weigh accurately about 2 g or other suitable quantity of the substance under examination so that the volume of 0.5 M ethanolic potassium hydroxide added is at least twice that theoretically required, dissolve it in 5 ml of the neutralised ethanol contained in a hard-glass flask and neutralise the free acid in the solution with 0.1 M ethanolic potassium hydroxide using 0.2 ml of phenolphthalein solution as indicator. Add 25.0 ml of 0.5 M ethanolic potassium hydroxide and boil under a reflux condenser on a water-bath for 1 hour. Add 20 ml of water and titrate the excess of alkali with 0.5 M hydrochloric acid using a further 0.2 ml of phenolphthalein solution as indicator. Repeat the operation without the substance under examination. The difference between the titrations represents the alkali required to saponify the esters.
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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