Difference between revisions of "Ester value"
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==USP 401== | ==USP 401== | ||
| + | Place 1.5 g to 2 g of the substance in a tared, 250 mL flasks, add 20 mL to 30 mL of neutralized alcohol and shake. Add 1 mL of phenolphthalein, and titrate with 0.5 N alcoholic potassium hydroxide until the free acid is neutralized. Add 25.0 mL of 0.5N alcoholic potassium hydroxide. Heat the flask on a steam bath, under a suitable condenser to maintain reflux for 30 minutes, frequently rotating the contents titrate the excess potassium hydroxide with 0.5 N hydrochloric acid. Perform a blank determination under the same conditions. Calculate the ester value by the formula: | ||
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| + | It is possible to perform this test using the sample at the end of determination of acid value, adding 15 mL of potassium hydroxide 0.5 N and heat the flask under a suitable condenser to maintain reflux for 3-4 h. Titrate the excess potassium hydroxide with 0.5 N hydrochloric acid (until the sample turns white). Perform a blank determination under the same conditions. Register the volume of hydrochloric acid consumed for the sample as the well blank. Calculate ester value by the formula: | ||
Revision as of 16:19, 14 August 2013
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, add 20 mL to 30 mL of neutralized alcohol and shake. Add 1 mL of phenolphthalein, and titrate with 0.5 N alcoholic potassium hydroxide until the free acid is neutralized. Add 25.0 mL of 0.5N alcoholic potassium hydroxide. Heat the flask on a steam bath, under a suitable condenser to maintain reflux for 30 minutes, frequently rotating the contents titrate the excess potassium hydroxide with 0.5 N hydrochloric acid. Perform a blank determination under the same conditions. Calculate the ester value by the formula:
It is possible to perform this test using the sample at the end of determination of acid value, adding 15 mL of potassium hydroxide 0.5 N and heat the flask under a suitable condenser to maintain reflux for 3-4 h. Titrate the excess potassium hydroxide with 0.5 N hydrochloric acid (until the sample turns white). Perform a blank determination under the same conditions. Register the volume of hydrochloric acid consumed for the sample as the well blank. Calculate ester value by the formula: