Ester value
The ester value is the number of mg of potassium hydroxide required to saponify the esters in 1.0 g of the substance. [1]
Contents
Wax esters
Wax esters are oxoesters of long-chain fatty acids esterified with long-chain alcohols. The ester value shows the amount alkali consumed in the saponification of the esters[2] and is possible identify and differentiate the waxes with this value; for example beeswax ester value is 72 to 79 mg KOH/ g, candelilla wax ester value is 31 to 43 mg KOH/g and carnauba wax ester value is 74 to 78 mg KOH/g.
Method
In ester value determination, the sample is hydrolysed to alcohol and using excess of standar potassium hydroxide solution. The excess of alkali is back titrated. USP-NF monographs presents a general procedure of ester value apply to fats, fixed oils and waxes.
USP 401
Place 1.5 g to 2 g of the substance in a tared, 250 mL flasks, weigh accurately, add 20 mL to 30 mL of neutralized alcohol and shake. Add 1 mL of phenolphthalein TS, and titrate with 0.5 N alcoholic potassium hydroxide VS until the free acid is neutralized. Add 25.0 mL of 0.5N alcoholic potassium hydroxide VS, and proceed as directed under Saponification Value, beginning with “Heat the flask” and omitting the further addition of phenolphthalein TS. The difference between the volumes, in mL, of 0.5 N hydrochloric acid consumed in the actual test and in the blank test, multiplied by 28.05 and divided by the weight in g of the specimen taken, is the Ester Value.