Bepaling van de onverzeepbare rest
The term "unsaponifiable matter" is applied to the substances non-volatile at 100 �C to 105 �C obtained by extraction with an organic solvent from the substance to be examined after it has been saponified. The result is calculated as per cent m/m.
Use ungreased ground-glass glassware.
Introduce the prescribed quantity of the substance to be examined (m g) into a 250 ml flask fitted with a reflux condenser. Add 50 ml of 2 M alcoholic potassium hydroxide R and heat on a water-bath for 1 h, swirling frequently. Cool to a temperature below 25 �C and transfer the contents of the flask to a separating funnel with the aid of 100 ml of water R. Shake the liquid carefully with three quantities, each of 100 ml, of peroxide-free ether R. Combine the ether layers in another separating funnel containing 40 ml of water R, shake gently for a few minutes, allow to separate and reject the aqueous phase. Wash the ether phase with two quantities, each of 40 ml, of water R then wash successively with 40 ml of a 30 g/l solution of potassium hydroxide R and 40 ml of water R; repeat this procedure three times. Wash the ether phase several times, each with 40 ml of water R, until the aqueous phase is no longer alkaline to phenolphthalein. Transfer the ether phase to a tared flask, washing the separating funnel with peroxide-free ether R.
Distil off the ether with suitable precautions and add 6 ml of acetone R to the residue. Carefully remove the solvent in a current of air. Dry to constant mass at 100 �C to 105 �C. Allow to cool in a desiccator and weigh (a g).
Unsaponifiable matter = 100 a / m per cent
Dissolve the residue in 20 ml of alcohol R, previously neutralised to phenolphthalein solution R and titrate with 0.1 M ethanolic sodium hydroxide. If the volume of 0.1 M ethanolic sodium hydroxide used is greater than 0.2 ml, the separation of the layers has been incomplete; the residue weighed cannot be considered as "unsaponifiable matter". In case of doubt, the test must be repeated.
10 september 1999