Title: Determination Acid Value and Ester Value
1. Objective: To determine the Acid Value and Ester Value of the sample.
2. Principle:
- The Acid value is the number, which expresses in milligrams the amount of potassium hydroxide necessary to neutralise the free acids present in 1 g of the substance.
- The Ester value is the number of milligrams of potassium hydroxide required to saponify the esters present in 1 g of the substance.
3. Procedure:
- Method: Acid value
Unless otherwise specified in the individual monograph, dissolve about 10 g of the substance being examined, accurately weighed, in 50 ml of a mixture of equal volumes of ethanol (95 %) and ether. Previously neutralised with 0.1 M Potassium Hydroxide to Phenolphthalein solution. If the sample does not dissolve in the cold solvent, connect the flask with a reflux condenser and warm slowly, with frequent shaking, until the sample dissolves. Add 1 ml of Phenolphthalein solution and titrate with 0.1 M Potassium Hydroxide until the solution remains faintly pink after shaking for 30 seconds. Calculate the Acid Value from the expression.
Acid value = 5.61 n/w
Where, n = the number of ml of 0.1M potassium hydroxide required;
w = the weight in gram of the substance.
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 %) 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.
- Method: Ester Value
Determine the Acid Value as per above procedure.
Determine the Saponification Value as per Saponification Value test of the substance being examined. Calculate the Ester value from the expression.
Ester value = Saponification value – Acid value.