A.O.C.S Official Method Cd 3b-76
Reapproved 1989

    Saponification Value

    Definition:
    The saponification value is the amount of alkali necessary to saponify a definite quantity of the sample. It is expressed as the number of milligrams of potassium hydroxide (KOH) required to saponify 1 gram of the sample.

    Scope: Applicable to vegetable oil deodorizer distillates and sludges.
    Apparatus:
  1. Erlenmeyer flasks, alkali resistent, 250 or 300 mL, with T 24/40 ground glass joint.
  2. Air condensers, minimum 65 cm long, with T 24/40 ground glass joint to fit Erlenmeyer flasks.
  3. Water bath, or a hot plate with variable heat control.
  4. Distillation flask, 2 liter, with T ground glass joint, fitted with water cooled condenser, for refluxing and distilling 95% ethyl alcohol as noted in Reagents, 2.

    Reagents:
  1. Hydrochloric acid, 0.5 N, accurately standardized. See AOCS Specification H 14-52.
  2. Alcoholic potassium hydroxide (KOH), prepared by placing 5 to 10 g of reagent grade KOH (see Notes, Caution) pellets in a 2 liter flask and adding 1 liter to 1.5 liters of 95% ethyl alcohol (see Notes, Caution) and boil on a water bath under reflux for 30 to 60 minutes. Distill and collect the alcohol in a clean, glass stoppered receiver. Dissolve 40 g of potassium hydroxide, low in carbonate, in 1 liter of the distilled alcohol (see Notes, Caution) with cooling to keep the temperature at or below 15 C. This solution should remain clear.
  3. Phenolphthalein indicator solution, 1.0% in 95% ethyl alcohol.
  4. Toluene, reagent grade (see Notes, Caution).
    Procedure:
  1. Heat the sarmple (see Notes, 1) at 100 C until liquid and then mix thoroughly.
  2. Accurate weigh about 2g +- 0.1 mg of the melted sample into the Erlenmeyer flask.
  3. Add 25 mL of toluene and heat gently to dissolve the sample.
  4. Add 50 mL of the alcoholic KOH with a pipet and allow the pipet to drain for a definite period of time (see Notes, 2).
  5. Prepare and conduct blank determinations simultaneously with the sample and similar in all respects, except omitting the fat or oil.
  6. Add several boiling chips to the flask and connect the air condenser. Boil gently, but steadily, until the sample is completely saponified. This usually requires about 1 hour for normal samples. Make certain that the vapor ring in the condenser does not rise to the top of the condenser, or loss may occur.
  7. After the flask and condenser have cooled somewhat, but not sufficiently to form a jell, wash down the inside of the condenser with a small quantity of distilled water. Disconnect the condenser, add about 1 mL of phenolphthalein indicator and titrate with 0.5 N HCl until the pink color just disappears. Record the volume of 0.5 N HCl required for the titration (see Notes, 3).
    8.
    Calculations:
    Saponification value = [(B - S) x (N)]/ W x 56.1

    Where -
    B = mL 0.5 N HCl required to titrate blank
    S = mL 0.5 N HCl required to titrate sample
    N = normality of HCl solution
    W = weight of sample in grams

    Precision:
  1. Two single determinations performed in one laboratroy should not differ by more than 3.2 units.
  2. Two single determinations performed in different laboratories should not differ by more than 6.4 units.
    Notes:
    Caution
    Potassium hydroxide, like all alkalies, can burn skin, eyes, respiratory tract severely. Wear heavy rubber gloves and face shield to protect against concentrated alkali liquids. Use effective fume removal device or gas mask to protect respiratory tract against alkali dusts or vapors. When working with extremely caustic materials like potassium hydroxide, always add pellets to water and not vice versa. Alkalies are extremely exothermic when mixed with water. Take precautions to contain the caustic solution in the event the mixing container breaks from the extreme heat generated.
    Ethyl alcohol (ethanol) is flammable. Use a fume hood when heating or evaporating this solvent. Toluene is flammable and a dangerous fire risk. Explosive limits in air are 1.27 to 7%. It is toxic by ingestion, inhalation and skin absorption. The TLV is 100 ppm in air. A fume hood should be used at all times when using toluene.
    Numbered Notes
  1. When the saponification value is required on the fatty acids, the preparation and separation are performed as directed in AOCS Official Method Cd 6-38.
  2. For consistent results, a 50 mL class A volumetric pipet, calibrated "To Deliver" should be used. The pipet should be allowed to drain for the time specified.
  3. Some samples may yield a, solution too dark in color to permit satisfactory endpoint detection. To overcome this problem, use a smaller sample size, about 1 g.
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