Determination of Unsaponifiable Matter in Oil

In this determination of unsaponifiable matter in oil post we briefly summarise about: principle, reagents requirements, unsaponifiable matter procedure, result, application and limitations of unsaponified matter.

The unsaponified 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.

Unsaponifiable Matter Principle

Unsaponifiable matter is defined as the substances soluble in the oil, which after saponification are insoluble in water but soluble in the solvent used for the determination.

It includes lipids of natural origin such as sterols, higher aliphatic alcohols, pigments, vitamins, and hydrocarbons as well as any foreign organic matter non-volatile at 100°C e.g. (mineral oil).

Light Petroleum or diethyl ether is used as a solvent but in most cases results will differ according to the solvent selected and generally the use of diethyl ether will give a higher result.

Unsaponifiable Matter Requirements

Materials

1. Flat bottom flask

2. Conical flask

3. Air condenser

4. Separating funnel

5. Weighing balance

Reagents

1. Alcoholic potassium hydroxide

2. Ethyl alcohol

3. Phenolphthalein indicator

4. Petroleum ether

5. 10% aqueous alcohol

6. Sodium hydroxide

7. Acetone

8. Anhydrous sodium sulphate

Unsaponifiable Matter Procedure

1. For unsaponified matter test procedure weigh accurately 5 gm of well mixed oil/fat sample into a 250 mL conical flask. Add 50 mL of alcoholic potassium hydroxide solution.

2. Boil the content under reflux air condenser for one hour or until the saponification is complete (complete saponification gives a homogeneous and transparent medium).

3. Take care to avoid loss of ethyl alcohol during the saponification. Wash the condenser with about 10 mL of ethyl alcohol.

4. Transfer the saponified mixture while still warm to a separating funnel, wash the saponification flask first with some ethyl alcohol and then with cold water, using a total of 50 mL of water to rinse the flask.

5. Cool to 20 to 25°C. Add to the flask 50 mL of petroleum ether, shake vigorously, and allow the layers to separate. Transfers the lower soap layer into another separating funnel and repeat the ether extraction 3 times, using 50 mL portions of petroleum ether.

6. Some oils high in unsaponifiable matter, e.g., marine oils, may require more than three extractions to completely remove Unsaponifiable matter. Wash the combined ether extract three times with 25 mL portions of aqueous alcohol followed by washing with 25 mL portions of distilled water to ensure ether extract is free of alkali.

7. Transfer washed ether extract to 250 mL beaker, rinse separator with ether, and add rinsing to main solution. Evaporate to about 5mL and transfer quantitatively using several portions of ether to a previously dried and weighed 50 mL Erlenmeyer flask. 

8. When all ether has been removed add 2-3 mL acetone and while heating on steam or water bath completely remove solvent under a gentle air.

9. To remove last traces of ether, dry at 100°C for 30 minutes till constant weight. Dissolve residue in 50 mL of warm ethanol, which has been neutralised to a phenolphthalein end point. Titrate with 0.02N Sodium hydroxide.

Unsaponifiable Matter Calculation

Weight in g of the free fatty acids = ——- V/N

Where,

V = Volume in mL of standard sodium hydroxide solution

N = Normality of standard sodium hydroxide solution

Unsaponifiable Matter

Where,

A = Weight of the residue in gm

B = Weight of free fatty acids in the extract in gm

W = Weight of the sample in gm

We hope determination of unsaponifiable matter in oil article helps you understand about principle, reagents requirements, procedure, result, application and limitations of unsaponification value determination. Learn more biochemical reactions at NotesHippo.com.

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