Determination of Ester Value of Oil
Ester value: Ester value (EV) represents combined (with glycerol) fatty acids in a fat, and therefore,
when expressed in milligrams of potassium hydroxide.
The Ester Value is the number of mg of potassium hydroxide required to saponify the esters in 1.0 g
of the substance.
Ester Value = Saponification Value – Acid Value
9.0 Determination of Saponification Value
9.1 Definition: The saponification value is the number of mg of potassium hydroxide required to
saponify 1 gram of oil/fat.
Saponification is a process that involves the conversion of fat, oil, or lipid, into soap and alcohol by
the action of aqueous alkali
9.1.1 Principle: The oil sample is saponified by refluxing with a known excess of alcoholic potassium
hydroxide solution. The alkali required for saponification is determined by titration of the excess
potassium hydroxide with standard hydrochloric acid.
9.1.2 Analytical importance: The saponification value is an index of mean molecular weight of the
fatty acids of glycerides comprising a fat. Lower the saponification value, larger the molecular
weight of fatty acids in the glycerides and vice-versa.
9.1.3 Apparatus: a. 250 ml capacity conical flask with ground glass joints. b. 1 m long air condenser,
or reflux condenser (65 cm minimum in length) to fit the flask (a). c. Hot water bath or electric hot
plate fitted with thermostat.
9.1.4 Reagents: (i) 4% ethanolic potassium hydroxide solution-weight 1.67g KOH pellets and place it
into a distillation flask. Now, weigh 1g granulated Aluminum or Aluminum foil and transfer it into
the distillation flask. Measure 200ml absolute ethanol and pour into the same flask. Attach the
reflux condenser with the flask. Now heat the flask and reflux the alcohol with KOH and Al foil for 30
mins. Now remove the reflux condenser and set a distillation unit. Distil and collect 180 ml ethanol
after discarding first 10ml. after that turn off the heating of the distillation unit. Crush 6g of KOH in a
clean mortar and pestle and add in the 150 ml distilled solution collected from the distillation
column. Mix and dissolve KOH in ethanol, keeping the flask into cold water (150C).
ii) Phenolphthalein indicator solution - Dissolve 2.0 g of phenolphthalein in 100 ml rectified spirit.
iii) Standard hydrochloric acid: approximately 0.5N- Dilute 4.1 ml of conc. HCl with distilled water to
make the total volume of 100 ml. Standardize newly prepared 0.5N HCl with standard NaOH
solution and find the actual normality.
9.1.5 Procedure: Melt the sample if it is not already liquid and filter through a filter paper to
remove any impurities and the last traces of moisture. Make sure that the sample is completely dry.
Mix the sample thoroughly and weigh about 1.5 to 5.0 g of dry sample into a 250 ml Erlenmeyer
flask. Pipette 50 ml of the alcoholic potassium hydroxide solution into the flask. Conduct a blank
(50ml of alcoholic KOH only) determination along with the sample. Connect the sample flasks and
the blank flask with air condensers, keep on the water bath, boil gently but steadily until
saponification is complete, as indicated by absence of any oily matter and appearance of clear
solution. Clarity may be achieved within one hour of boiling. After the flask and condenser have
cooled somewhat wash down the inside of the condenser with about 10 ml of hot ethyl alcohol
neutral to phenolphthalein. Titrate the excess potassium hydroxide with 0.5N hydrochloric acid,
using about 1.0 ml phenolphthalein indicator.
9.1.6 Calculation:
Saponification Value = 56.1 (B-S) N/W
Where, B = Volume in ml of standard hydrochloric acid required for the blank.
S = Volume in ml of standard hydrochloric acid required for the sample
N = Normality of the standard hydrochloric acid and
W = Weight in gm of the oil/fat taken for the test.
