Unsaponification Value

Definition:
Unsaponifiable matter includes those substances frequently found dissolved in fatty acids and drying oils which cannot be saponified by caustic treatment, but which are soluble in the normal fat solvents. Included are the higher aliphatic alcohols, sterols, pigments, and hydrocarbons.

Scope: Applicable to all fatty acids, drying oils and polymerized fatty acids.

Apparatus:

1. Glass stoppered extraction cylinder graduated at 40, 80, and 130 mL capacity, height about 300 mm, diameter about 35 mm.
   
2. Erlenmeyer or Soxhlet flasks, 100 to 200 mL.
   
3. Separation funnels, 500 mL.
   
4. Glass siphon (see paragraph 3 in Procedure, below).

Reagents:

1. Ethyl alcohol, 95% (U.S.S.D. Formula 30 and 3A are permitted).
   
2. Aqueous potassium hydroxide solution, 50% KOH by weight.
   
3. Petroleum either, AOCS Specification H 2-41.
   
4. Sodium hydroxide solution, 0.02 N, accurately standardized, see AOCS Specification H 12-52.
   
5. Phenolphthalein indicator solution, 1.0% in 95% alcohol.

Procedure:

1. Weigh accurately about 5 g of well mixed sample into an Erlenmeyer or Soxhlet flask. Add 30 mL of alcohol and 5 mL of aqueous KOH. Boil gently but steadily under a reflux condenser for 1 hour or until completely saponified. Complete saponification is essential.
   
2. Transfer to the extraction cylinder and wash to the 40 mL mark with alcohol. Complete the transfer with warm and then cold distilled water until the total volume is 80 mL. Wash out the flask with a little petroleum ether and add to the cylinder. Cool the cylinder and contents to room temperature (20 to 30 C), and then add 50 mL of petroleum ether.
   
3. Insert the stopper and shake vigorously for at least 1 min and allow to settle until both layers are clear. Use a glass siphon to remove the upper layer as completely as possible without including any of the lower portion.
   
4. The petroleum ether fractions are drawn into and accumulated in a 500 mL separator funnel containing 5 mL of 10% ethyl alcohol in order to minimize possibility of leakage of petroleum ether.
   
5. Repeat the extraction using 50 mL portions of petroleum ether each time, at least 6 more times, shaking vigorously with each extraction.
   Caution - There are some cases in which 7 extractions may not be sufficient. This is best judged by making another extraction and evaporating this separately. Extraction should be discontinued when a single extraction shows less than 0.005 g of residue.
   
6. Wash the combined extracts in the separatory funnel with 25 mL portions of 10% alcohol in distilled water, shaking vigorously and drawing off the alcohol layer after each wash. Washing should be discontinued when the wash water is neutral to phenolphthalein. Be careful not to remove any of the ether layer.
   
7. Transfer the ether extract to a tared beaker and evaporate to dryness on a water bath under a gentle stream of clear, dry air. Complete the drying to constant weight, preferably in a vacuum oven at 75 to 80 C, and an internal pressure of not more than 200 mm of mercury, or in an air oven at 105 C for 15 minute intervals. Cool in a desiccator and weigh.
   
8. Run a blank exactly as the sample, following from paragraph 1 through 6 in the Procedure Section.
   
9. After weighing both the residue from the samples and the residue from the blank, take up both in 50 mL of warm (50 C) 95% alcohol, containing indicator and previously neutralized to a faint pink color. Titrate with 0.02 N NaOH to same pink color.
   

Calculations:
Weight of fatty acids in sample residue and blank residue = mL x N x 0.282

1. Where -
   mL= mL of NaOH
   N = normality of NaOH determined by standardization
2. % Uncorrected Unsap = [Weight of sample residue x 100]/[Weight of sample, g]
3. % Unsap corrected for fatty acids =

	(Weight of sample residue - weight of fatty acids in sample residue) x 100
	Weight of sample, g

4. % Unsap corrected for fatty acids and blank =