Difference between revisions of "Ester value"

From WaxPedia
Jump to: navigation, search
Line 15: Line 15:
  
 
==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:
  
.<ref name="multiple"></ref>
+
 
 +
 
 +
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]


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:


Referencia

  1. Warth, A. H.; The Chemistry and Technology of Waxes. Reinhold Publishing Corporation. Second Edition, p.586
  2. Pharmacopedia/National Formulary. US., Vol. 1, 2009, p. 150