Determination of Unsaponifiable Matter

The unsaponifiable matter consists of substances present in oils and fats which are not saponifiable by alkali hydroxides and are determined by extraction with an organic solvent of a solution of the saponified substance under examination.

Method

Unless otherwise specified in the individual monograph, introduce about 5 g of the substance under examination, accurately weighed, into a 250-ml flask fitted with a reflux condenser. Add a solution of 2 g of potassium hydroxide in 40 ml of ethanol (95 percent) and heat on a water bath for 1 hour, shaking frequently.

Transfer the contents of the flask to a separating funnel with the aid of 100 ml of hot water and, while the liquid is still warm, shake very carefully with three quantities, each of 100 ml, of peroxide-free ether. Combine the ether extracts in a second separating funnel containing 40 ml of water, swirl gently for a few minutes, allow to separate and reject the lower layer. Wash the extract with two quantities each of 40 ml, of water and with three quantities, each of 40 ml, of a 3 percent w/v solution of potassium hydroxide, each treatment being followed by a washing with 40 ml of water.

Finally, wash the ether layer with successive quantities, each of 40 ml, of water until the aqueous layer is not alkaline to phenolphthalein solution. Transfer the ether layer to a weighed flask, washing out the separating funnel with peroxide-free ether. Distill off the ether and add to the residue 6 ml of acetone. Remove the solvent completely from the flask with the aid of a gentle current of air. Dry at 100° to 105° for 30 minutes. Cool in a desiccator and weigh the residue.

Calculate the unsaponifiable matter as percent w/w. Dissolve the residue in 20 ml of ethanol (95 percent), previously neutralized to phenolphthalein solution and titrate with 0.1 M ethanolic potassium hydroxide. If the volume of 0.1 M ethanolic potassium hydroxide exceeds 0.2 ml, the amount weighed cannot be taken as the unsaponifiable matter and the test must be repeated.

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