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AIM - Determination of saponification Value and Unsaponifiable Matter Give with reference Principles Requirement - 1 reagent/ chemicals 2 apparatus Procedure Observation table and calculations Results

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Here is a complete, well-referenced practical write-up for the Determination of Saponification Value and Unsaponifiable Matter, following the standard format used in pharmaceutical/analytical chemistry practicals.

PRACTICAL: Determination of Saponification Value and Unsaponifiable Matter

AIM

To determine the Saponification Value and Unsaponifiable Matter of a given fixed oil/fat sample.

REFERENCES

  • Indian Pharmacopoeia (IP) 2022, Volume I, Appendix 2.14 - Fats and Oils
  • British Pharmacopoeia (BP) 2023, Appendix X B - Saponification Value; Appendix X C - Unsaponifiable Matter
  • United States Pharmacopoeia (USP 35), ⟨401⟩ Fats and Fixed Oils
  • IS:1448 [P:55]-1963 (Indian Standards for Petroleum Products - Saponification Value)
  • Ranganna S., Handbook of Analysis and Quality Control for Fruits and Vegetable Products, TATA McGraw-Hill
  • Vogel's Textbook of Practical Organic Chemistry, 5th Ed.

PART A: SAPONIFICATION VALUE

PRINCIPLE

Saponification value (SV) is defined as the number of milligrams of potassium hydroxide (KOH) required to neutralize the free acids and completely saponify the esters present in 1 gram of the oil or fat.
The fat (triglyceride) is refluxed with a known excess of alcoholic KOH. The ester linkages are hydrolyzed (saponified):
Triglyceride + 3 KOH → Glycerol + 3 Fatty Acid Potassium Salts (Soap)
The excess unreacted KOH is back-titrated against standard hydrochloric acid (HCl) using phenolphthalein as indicator. A blank is run simultaneously under identical conditions.
The difference in titration volumes between the blank and the sample directly corresponds to the amount of KOH consumed in saponification.
A higher saponification value indicates lower average molecular weight of the fatty acids (shorter chain length), e.g., coconut oil (SV ~ 248-265). A lower SV indicates longer chain fatty acids.
Formula:
SV (mg KOH/g) = [(B - S) × N × 56.1] / W
Where:
  • B = Volume (mL) of HCl consumed in blank titration
  • S = Volume (mL) of HCl consumed in sample titration
  • N = Normality of HCl solution
  • 56.1 = Molecular weight of KOH (g/mol)
  • W = Weight (g) of sample taken

REQUIREMENTS

1. Reagents / Chemicals

S. No.ReagentSpecification / Preparation
1Alcoholic KOH solutionDissolve ~40 g KOH in 1 L of 95% ethanol; standardize; approx. 0.5 N
2Standard HCl (0.5 N)Standardized against Na₂CO₃ or borax
3Phenolphthalein indicator1% w/v in 95% ethanol
495% Ethyl alcohol (neutralized)Neutralize with 0.1 N KOH before use
5Oil/fat sampleGroundnut oil / castor oil / coconut oil
6Distilled waterFor blank & rinsing

2. Apparatus

S. No.ApparatusSpecification
1Flat-bottom / round-bottom flask250 mL, borosilicate glass
2Reflux condenser (air condenser)Fitted to flask
3Water bath / hot plateTemperature-controlled
4Burette50 mL, graduated
5Pipette25 mL (for KOH delivery)
6Weighing balanceAnalytical, 0.0001 g sensitivity
7Conical flask250 mL
8Measuring cylinder25 mL, 50 mL

PROCEDURE

  1. Weigh accurately 1.5 - 2.0 g of the oil/fat sample into a clean, dry 250 mL flat-bottom flask. Label this as "Sample Flask."
  2. Prepare a blank flask under identical conditions with no sample.
  3. Using a pipette, add 25.0 mL of 0.5 N alcoholic KOH to both the sample flask and the blank flask.
  4. Connect both flasks to air condensers to prevent evaporation of alcohol.
  5. Heat both flasks on a boiling water bath for 60 minutes with occasional swirling, until saponification is complete. The solution should become clear and homogeneous (no oil droplets).
  6. Test for complete saponification: Take 1-2 drops of the saponified mixture; no oily drops should appear when diluted with hot water.
  7. After cooling, add 1 mL of phenolphthalein indicator to each flask.
  8. Back-titrate the excess KOH in both flasks with standard 0.5 N HCl from a burette until the pink color just disappears (endpoint).
  9. Note the volume of HCl used for blank (B mL) and sample (S mL).

OBSERVATION TABLE

ParameterBlankSample
Weight of oil taken (W)-______ g
Volume of KOH added25.0 mL25.0 mL
Burette initial reading (mL)
Burette final reading (mL)
Volume of HCl used (mL)B = ______S = ______
(B - S) in mL______ mL

CALCULATIONS

Saponification Value (SV) =
$$SV = \frac{(B - S) \times N \times 56.1}{W}$$
Example (specimen calculation):
  • B (blank) = 24.5 mL, S (sample) = 13.2 mL
  • N (HCl) = 0.5 N
  • W = 2.0 g
$$SV = \frac{(24.5 - 13.2) \times 0.5 \times 56.1}{2.0} = \frac{11.3 \times 0.5 \times 56.1}{2.0} = \frac{317.0}{2.0} = \mathbf{158.5 \text{ mg KOH/g}}$$

RESULT

The Saponification Value of the given oil sample = ______ mg KOH/g
(Acceptable range for common oils - Groundnut oil: 188-196, Coconut oil: 248-265, Castor oil: 176-187 mg KOH/g)

PART B: UNSAPONIFIABLE MATTER

PRINCIPLE

Unsaponifiable matter refers to those substances present in oils and fats which, after saponification with alkali, cannot be saponified under normal conditions but are soluble in ordinary fat solvents (diethyl ether/petroleum ether). These include:
  • Sterols (cholesterol, sitosterol, stigmasterol)
  • Hydrocarbons (squalene, mineral oil contaminants)
  • Fat-soluble vitamins (A, D, E, K)
  • Waxes, pigments (carotenoids, chlorophylls)
Method (Gravimetric - IP/BP/USP):
The oil is saponified with alcoholic KOH, the soap solution is extracted with diethyl ether to remove unsaponifiable matter. The ether layer is washed free of alkali, evaporated, and the residue weighed.
Formula:
$$%\text{ Unsaponifiable Matter} = \frac{W_R}{W_S} \times 100$$
Where:
  • W_R = Weight of dry residue (g)
  • W_S = Weight of oil/fat sample (g)

REQUIREMENTS

1. Reagents / Chemicals

S. No.ReagentSpecification
1Alcoholic KOH (2 N)40 g KOH in 500 mL 95% ethanol
2Diethyl ether (A.R. grade)Peroxide-free
3Ethanol (95%, neutralized)
4Sodium hydroxide solution (0.1 N)For washing ether layer
5Phenolphthalein indicator1% in ethanol
6Anhydrous sodium sulphate (Na₂SO₄)For drying
7Oil/fat sample
8Distilled water

2. Apparatus

S. No.ApparatusSpecification
1Round-bottom flask250 mL with reflux condenser
2Water bathBoiling
3Separating funnel250 mL or 500 mL
4Weighing balanceAnalytical
5OvenSet at 100-105°C
6DesiccatorWith silica gel/CaCl₂
7Tared evaporation flask/dishPre-weighed
8Rotary evaporator or water bathFor ether evaporation

PROCEDURE

Step 1 - Saponification:
  1. Weigh accurately 5 g of oil/fat (W_S) into a 250 mL round-bottom flask.
  2. Add 50 mL of 2 N alcoholic KOH.
  3. Reflux on a boiling water bath for 60 minutes until saponification is complete (solution is clear and homogeneous).
Step 2 - Extraction of Unsaponifiable Matter: 4. Cool the saponified solution and transfer to a separating funnel. 5. Rinse the flask with 50 mL of distilled water and add rinsings to the funnel. 6. Add 50 mL of diethyl ether, stopper, and shake gently (releasing pressure frequently). 7. Allow layers to separate; run off the lower aqueous (soap) layer into a conical flask. 8. Repeat ether extraction two more times with 50 mL ether each time. 9. Combine all ether extracts in the separating funnel.
Step 3 - Washing: 10. Wash the combined ether extract twice with 25 mL of 0.5 N NaOH (to remove fatty acids/soap). 11. Wash again 3-4 times with 25 mL of distilled water until wash water is neutral (no pink with phenolphthalein).
Step 4 - Drying & Weighing: 12. Drain the ether layer into a pre-weighed (tared) evaporation flask through a funnel containing anhydrous Na₂SO₄. 13. Evaporate the ether on a water bath at 40-50°C (in a fume hood). 14. Dry the residue at 100-105°C until successive weighings agree within 1 mg. 15. Cool in a desiccator and weigh accurately (W_R).

OBSERVATION TABLE

ParameterObservation
Weight of oil/fat sample (W_S)______ g
Weight of tared evaporation flask (W₁)______ g
Weight of flask + residue after drying (W₂)______ g
Weight of unsaponifiable residue (W_R = W₂ - W₁)______ g

CALCULATIONS

$$% \text{ Unsaponifiable Matter} = \frac{W_R}{W_S} \times 100$$
Example:
  • W_S = 5.0 g
  • W_R = 0.075 g
$$= \frac{0.075}{5.0} \times 100 = \mathbf{1.5%}$$

RESULT

The Unsaponifiable Matter in the given oil/fat = _______ %
(Typical values: Groundnut oil < 1%, Olive oil 0.4-1.1%, Coconut oil 0.1-1.4%, Shea butter 6-17%)

SUMMARY TABLE: Standard Values for Reference

Oil/FatSaponification Value (mg KOH/g)Unsaponifiable Matter (%)
Coconut oil248-2650.1-1.4
Palm oil190-209< 1.4
Groundnut oil187-1960.2-4.4
Olive oil184-1960.4-1.1
Castor oil176-187< 1.5
Linseed oil188-1960.1-2.0
Soybean oil187-1951.5-2.5
Corn oil187-1951.0-3.0

PRECAUTIONS

  1. Use peroxide-free diethyl ether to avoid explosion risk.
  2. Ether evaporation must be done in a fume hood away from open flames.
  3. Reflux must be performed with a proper condenser to prevent alcohol evaporation.
  4. Ensure complete saponification before extraction - no oily droplets should be visible.
  5. Wash the ether layer sufficiently to remove all soaps, which otherwise inflate the residue weight.
  6. Dry the final residue to constant weight (successive weighings within 1 mg) for accurate results.
  7. The alcoholic KOH solution must be freshly prepared and standardized.
  8. Release pressure from separating funnel during ether extraction to avoid pressure build-up.
References: IP 2022 (Appendix 2.14), BP 2023 (Appendix X B & C), USP 35 ⟨401⟩ Fats and Fixed Oils, IS:1448[P:55]-1963
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