Saponification value
The saponification value is the number of mg of potassium hydroxide required to neutralize the free acids and saponify the esters contained in 1.0 g of the substance.[1]
Method
The saponification value was originated by Koettsdorfer and sometimes known by this name. The saponification is the process by which the fatty acids in the glycerides of the oil are hydrolysed by an alkali; to evaluate this, a known quantity of wax is refluxed with an excess of alcoholic potassium hydroxide, after the reflux the remaining KOH is estimated by titrating it against a standard acid. Since each molecule of fat, regardless of its size, requires three molecules of KOH to saponify, it is evident that the saponification number really indicates the number of fat molecules per gram of fat. The larger fat molecule, the fewer number will be per gram of fat.[2]
USP 401
Place 1.5 to 2.0 g of the substance in a tared, 250 mL flask, weight accurantely, and add to it 25.0 mL of 0.5 N alcoholic potassium hydroxide. Heat the flask on a steam bath, under a suitable condenser to maintain reflux for 30 minutes, frequently rotating the contents. Then add 1 mL of phenolphthalein, and titrate the excess potassium hydroxide with 0.5 N hydrochlorirc acid. Perform a blank determination under the same conditions. 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 56.1 and the exact normality of the 0.5N hydrochloric acid VS, and dived by the weight in g of specimen taken, is the Saponification Value.