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Determination of the Saponification Value (S.V.)
2.202 Determination of the Saponification Value (S.V.) (Fifth Edition : Method II.D.2) 1.
SCOPE
This Standard describes two methods for the determination of the saponification value of animal and vegetable oils and fats. The indicator method should be preferentially chosen to the potentiometric method when it is applicable. 2.
FIELD OF APPLICATION
This Standard is applicable to animal and vegetable oils and fats. waxes. 3.
It is not applicable to
DEFINITION
The saponification value (S.V.) is the number of mg of potassium hydroxide required to saponify 1 g of fat. 4.
INDICATOR METHOD
4.1.
Principle
Boiling of the sample under reflux condenser with ethanolic potassium hydroxide solution, and titration of the excess potassium hydroxide with hydrochloric acid in the presence of an indicator. 4.2.
Apparatus
4.2.1.
250-ml round-bottomed flasks, or conical flasks, made of alkali-resistant glass.
4.2.2.
1-m reflux tubes, or 30 cm minimum in length reflux condensers, to fit the round-bottomed flasks or conical flasks (4.2.1).
4.2.3.
25-ml volumetric pipette.
4.2.4.
50-ml burette, graduated in 0.1 ml.
4.2.5.
Boiling chips.
4.2.6.
Heating device (water bath, electric hot-plate,...).
4.3.
Reagents
4.3.1.
Potassium hydroxide, approximately 0.5 N solution in 95 per cent (V/V) ethanol. Use a solution prepared at least 5 days previously and decanted into a bottle of brown glass, provided with a rubber stopper. The solution should be colourless or straw yellow {note 1).
4.3.2.
Hydrochloric acid, 0.5 N aqueous solution, accurately standardized.
4.3.3.
Phenolphthalein, 10 g/1 solution in 95 per cent (V/V) ethanol.
4.4. Procedure Prepare the sample according to 2.001, "Preparation of the sample". Into the round-bottomed or conical flask (4.2.1) weigh to the nearest 0.005 g about 2 g of the prepared sample. With the pipette (4.2.3) add 25 ml of the ethanolic potassium hydroxide solution (4.3.1) and some boiling chips (4.2.5). Fit a reflux tube or reflux condenser (4.2.2). Boil gently with occasional shaking, After 60 minutes, stop heating.
Add to the hot solution 0.5 to 1.0 nl of phenolphthalein (4.3.3) 56
57
and titrate with the hydrochloric acid solution (4.3.2) until the colour of the indicator changes. Carry out two determinations with the same prepared sample. Carry out a blank test in the same way. 4.5.
Expression of Results
The saponification value (S.V.) is given by the formula : .
56.1 χ Γ χ (Vn - ?,) m
where V0 is the number of ml of the standardized hydrochloric acid solution (4.3.2) used for the blank test, V\ is the number of ml of the standardized hydrochloric acid solution (4.3.2) used for the test with the fat, T is the exact normality of the standardized hydrochloric acid solution (4.3.2) used, m is the mass, in g, of the test portion. Take as the result the arithmetic mean of the two determinations, provided that the requirement of repeatability 4.6 is satisfied. 4.6.
Repeatability
The difference between the results of two determinations carried out simultaneously or in rapid succession by the same analyst should not exceed 0.5 per cent of the mean value. 5.
POTENTIOMETRIC METHOD
5.1.
Foreword
This method should be employed instead of method 4 for the determination of the saponification value of highly coloured oils and fats. 5.2.
Principle
Reflux boiling of the sample with an isopropanolic potassium hydroxide solution and potentiometric titration of the excess of potassium hydroxide by hydrochloric acid in a non-aqueous medium. 5.3.
Apparatus
5.3.1.
100-ml flasks with ground joints, made of alkali-resistant glass.
5.3.2.
1-m reflux tubes, or 30 cm minimum in length reflux condensers, to fit the flasks (5.3.1).
5.3.3.
150-ml tall form beakers.
5.3.4.
1000-ml volumetric flasks.
5.3.5.
25-ml volumetric pipette.
5.3.6.
50-ml burette, graduated in 0.1 ml.
5.3.7.
pH meter equipped with glass and calomel electrodes {note 2). Contact between the saturated potassium chloride solution and the test solution is made across a sintered glass or porcelain disc at least 0.3 cm thick.
5.3.8.
Stirrer, preferably a magnetic stirrer.
5.3.9.
Boiling chips.
5.4.
Reagents
5.4.1.
2-Propanol (isopropanol), analytical reagent quality.
5.4.2.
Ethanediol, analytical reagent quality.
5.4.3.
Acetic acid, analytical reagent quality.
5.4.4.
Sodium carbonate, analytical reagent quality.
58 5.4.5.
Potassium hydroxide, approximately 0.5 N solution in 2-propanol (5.4.1) : dissolve 35 g of potassium hydroxide pellets in 1000 ml of 2-propanol (5.4.1).
5.4.6.
Hydrochloric acid, 0.5 N accurately standardized solution in 2-propanol (5.4.1). Pour 42 ml of hydrochloric acid (p =* 1.18) into a volumetric flask (5.3.4) and make up to the mark with 2-propanol (5.4.1). Standardization of the solution : e.g. weigh accurately to within 0.0002 g about 0.35 g of sodium carbonate (5.4.4), which has been previously calcined to constant weight at 270-300°C. Transfer to a beaker (5.3.3). Add gradually and cautiously a slight excess of acetic acid (5.4.3) to decompose the sodium carbonate completely. When the evolution of carbon dioxide has ceased, add sufficient distillated water to dissolve the sodium acetate formed and evaporate the solution to dryness on a water bath. Dissolve the residue in 20 ml of 2-propanol (5.4.1). Add 20 ml of ethanediol (5.4.2). Titrate by whichever of the two methods described below is preferred : (a)
Insert the electrodes of the pH meter (5.3.7) and start the stirrer (5.3.8). Titrate with the ^sopropanolic solution of hydrochloric acid (5.4.6) to the equivalent point {note 3).
(b) Add 2 drops of a 10 g/1 solution of thymol blue in 2-propanol (5.4.1) and titrate with the isopropanolic solution of hydrochloric acid (5.4.6) until the colour changes from yellow to pink. 1000 x m0 Ί. Normality = —=-r *· 53 x aQ where aQ is the number of ml of the tsopropanolic solution of hydrochloric acid (5.4.6) used, mQ is the mass, in g, of sodium carbonate taken. 5.5. Procedure Prepare the sample according to 2.001. Into a ground-necked flask (5.3.1) weigh to within 0.002 g about 2 g of the prepared fat. Add with the pipette (5.3.5) 25 ml of the istfpropanolic potassium hydroxide solution (5.4.5). Fit the tube or the condenser (5.3.2) and boil gently, with occasional shaking, until the solution become homogeneous. Stop heating after 60 minutes. In order to avoid solidification of the saponified solution, transfer it quantitatively, while still warm, into a beaker (5.3.3) with the aid of three 10-ml portions of ethanediol (5.4.2). Finish rinsing with 5 ml of 2-propanol (5.4.1). Insert the electrodes of the pH meter (5.3.7) and start the stirrer (5.3.8). Titrate with the -ksopropanolic hydrochloric acid solution (5.4.6) to the equivalence point of the neutralization curve (note 3). Carry out two determinations on the same prepared sample. Carry out a blank test in the same way. 5.6.
Expression of Results
The saponification value (S.V.) is given by the formula : S.V
« 56.1 x T x (V0 m
-
νλ)
where VQ is the number of ml of the standardized isopropanolic hydrochloric acid solution (5.4.6) used for the blank test, V\ is the number of ml of the standardized isöpropanolic hydrochloric acid solution (5.4.6) used for the test with the fat," T is the exact normality of the tsopropanolic hydrochloric acid solution (5.4.6) used, m is the mass, in g, of the test portion. Take as the result the arithmetic mean of the two determinations, provided that the requirement of repeatability 5.7 is satisfied.
59
5.7.
Repeatability
The difference between the results of two determinations carried out simultaneously or in rapid succession by the same analyst should not exceed 0.5 per cent of the mean value. 6.
TEST REPORT
The test report should show the method used. 7.
NOTES
2.
A stable colourless solution of potassium hydroxide can be prepared in the following manner: reflux 1000 ml of ethanol with 8 g of potassium hydroxide and 5 g of aluminium pellets for 1 hour, then distil immediately. Dissolve the required amount of potassium hydroxide in the distillate. Allow the whole to stand for several days and decant the clear supernatant liquid from the deposite potassium carbonate. The solution can also add 4 ml of aluminium several days. Decant potassium hydroxide.
2.
be prepared without distillation in the following manner : butylate to 1000 ml ethanol and allow the mixture to stand for the supernatant liquid and dissolve therein the necessary amount of The solution is ready for use.
It is advisable to store the glass electrode in water or, better still, in a 6/1 (V/V) mixture of ethanediol (5.4.2) and 2-propanol (5.4.1) for 12 hours preceding the titration. Dry it very gently with a piece of filter paper before use. Immediately after the titration, rinse with ethanediol, then with 2-propanol, and finally with distilled water. If the electrode does not function satisfactorily, it may be possible to regenerate it by immersion for 24 hours in a 1 N solution of hydrochloric acid in 2-propanol. After this treatment the electrode should be washed with distilled water, then with 2-propanol and with a 6/1 (V/V) mixture of ethanediol and 2-propanol. A thick sintered glass or porcelain disc between the saturated potassium chloride solution and the test solution prevents diffusion currents and parasitic potentials.
3,
Equivalence point/inflexion point The equivalence point usually corresponds approximately to the reading 10 on the pH scale, and can be determined graphically by observing the inflexion point on the neutralization curve. Alternatively, it can be calculated as the figure for which the first differential of the variation of pH as a function of the amount of isopropanolic hydrochloric acid solution added reaches a maximum, or the value for which the second differential becomes zero.
S.M.A.O.M).-- F
SCOPE
This Standard describes two methods for the determination of the saponification value of animal and vegetable oils and fats. The indicator method should be preferentially chosen to the potentiometric method when it is applicable. 2.
FIELD OF APPLICATION
This Standard is applicable to animal and vegetable oils and fats. waxes. 3.
It is not applicable to
DEFINITION
The saponification value (S.V.) is the number of mg of potassium hydroxide required to saponify 1 g of fat. 4.
INDICATOR METHOD
4.1.
Principle
Boiling of the sample under reflux condenser with ethanolic potassium hydroxide solution, and titration of the excess potassium hydroxide with hydrochloric acid in the presence of an indicator. 4.2.
Apparatus
4.2.1.
250-ml round-bottomed flasks, or conical flasks, made of alkali-resistant glass.
4.2.2.
1-m reflux tubes, or 30 cm minimum in length reflux condensers, to fit the round-bottomed flasks or conical flasks (4.2.1).
4.2.3.
25-ml volumetric pipette.
4.2.4.
50-ml burette, graduated in 0.1 ml.
4.2.5.
Boiling chips.
4.2.6.
Heating device (water bath, electric hot-plate,...).
4.3.
Reagents
4.3.1.
Potassium hydroxide, approximately 0.5 N solution in 95 per cent (V/V) ethanol. Use a solution prepared at least 5 days previously and decanted into a bottle of brown glass, provided with a rubber stopper. The solution should be colourless or straw yellow {note 1).
4.3.2.
Hydrochloric acid, 0.5 N aqueous solution, accurately standardized.
4.3.3.
Phenolphthalein, 10 g/1 solution in 95 per cent (V/V) ethanol.
4.4. Procedure Prepare the sample according to 2.001, "Preparation of the sample". Into the round-bottomed or conical flask (4.2.1) weigh to the nearest 0.005 g about 2 g of the prepared sample. With the pipette (4.2.3) add 25 ml of the ethanolic potassium hydroxide solution (4.3.1) and some boiling chips (4.2.5). Fit a reflux tube or reflux condenser (4.2.2). Boil gently with occasional shaking, After 60 minutes, stop heating.
Add to the hot solution 0.5 to 1.0 nl of phenolphthalein (4.3.3) 56
57
and titrate with the hydrochloric acid solution (4.3.2) until the colour of the indicator changes. Carry out two determinations with the same prepared sample. Carry out a blank test in the same way. 4.5.
Expression of Results
The saponification value (S.V.) is given by the formula : .
56.1 χ Γ χ (Vn - ?,) m
where V0 is the number of ml of the standardized hydrochloric acid solution (4.3.2) used for the blank test, V\ is the number of ml of the standardized hydrochloric acid solution (4.3.2) used for the test with the fat, T is the exact normality of the standardized hydrochloric acid solution (4.3.2) used, m is the mass, in g, of the test portion. Take as the result the arithmetic mean of the two determinations, provided that the requirement of repeatability 4.6 is satisfied. 4.6.
Repeatability
The difference between the results of two determinations carried out simultaneously or in rapid succession by the same analyst should not exceed 0.5 per cent of the mean value. 5.
POTENTIOMETRIC METHOD
5.1.
Foreword
This method should be employed instead of method 4 for the determination of the saponification value of highly coloured oils and fats. 5.2.
Principle
Reflux boiling of the sample with an isopropanolic potassium hydroxide solution and potentiometric titration of the excess of potassium hydroxide by hydrochloric acid in a non-aqueous medium. 5.3.
Apparatus
5.3.1.
100-ml flasks with ground joints, made of alkali-resistant glass.
5.3.2.
1-m reflux tubes, or 30 cm minimum in length reflux condensers, to fit the flasks (5.3.1).
5.3.3.
150-ml tall form beakers.
5.3.4.
1000-ml volumetric flasks.
5.3.5.
25-ml volumetric pipette.
5.3.6.
50-ml burette, graduated in 0.1 ml.
5.3.7.
pH meter equipped with glass and calomel electrodes {note 2). Contact between the saturated potassium chloride solution and the test solution is made across a sintered glass or porcelain disc at least 0.3 cm thick.
5.3.8.
Stirrer, preferably a magnetic stirrer.
5.3.9.
Boiling chips.
5.4.
Reagents
5.4.1.
2-Propanol (isopropanol), analytical reagent quality.
5.4.2.
Ethanediol, analytical reagent quality.
5.4.3.
Acetic acid, analytical reagent quality.
5.4.4.
Sodium carbonate, analytical reagent quality.
58 5.4.5.
Potassium hydroxide, approximately 0.5 N solution in 2-propanol (5.4.1) : dissolve 35 g of potassium hydroxide pellets in 1000 ml of 2-propanol (5.4.1).
5.4.6.
Hydrochloric acid, 0.5 N accurately standardized solution in 2-propanol (5.4.1). Pour 42 ml of hydrochloric acid (p =* 1.18) into a volumetric flask (5.3.4) and make up to the mark with 2-propanol (5.4.1). Standardization of the solution : e.g. weigh accurately to within 0.0002 g about 0.35 g of sodium carbonate (5.4.4), which has been previously calcined to constant weight at 270-300°C. Transfer to a beaker (5.3.3). Add gradually and cautiously a slight excess of acetic acid (5.4.3) to decompose the sodium carbonate completely. When the evolution of carbon dioxide has ceased, add sufficient distillated water to dissolve the sodium acetate formed and evaporate the solution to dryness on a water bath. Dissolve the residue in 20 ml of 2-propanol (5.4.1). Add 20 ml of ethanediol (5.4.2). Titrate by whichever of the two methods described below is preferred : (a)
Insert the electrodes of the pH meter (5.3.7) and start the stirrer (5.3.8). Titrate with the ^sopropanolic solution of hydrochloric acid (5.4.6) to the equivalent point {note 3).
(b) Add 2 drops of a 10 g/1 solution of thymol blue in 2-propanol (5.4.1) and titrate with the isopropanolic solution of hydrochloric acid (5.4.6) until the colour changes from yellow to pink. 1000 x m0 Ί. Normality = —=-r *· 53 x aQ where aQ is the number of ml of the tsopropanolic solution of hydrochloric acid (5.4.6) used, mQ is the mass, in g, of sodium carbonate taken. 5.5. Procedure Prepare the sample according to 2.001. Into a ground-necked flask (5.3.1) weigh to within 0.002 g about 2 g of the prepared fat. Add with the pipette (5.3.5) 25 ml of the istfpropanolic potassium hydroxide solution (5.4.5). Fit the tube or the condenser (5.3.2) and boil gently, with occasional shaking, until the solution become homogeneous. Stop heating after 60 minutes. In order to avoid solidification of the saponified solution, transfer it quantitatively, while still warm, into a beaker (5.3.3) with the aid of three 10-ml portions of ethanediol (5.4.2). Finish rinsing with 5 ml of 2-propanol (5.4.1). Insert the electrodes of the pH meter (5.3.7) and start the stirrer (5.3.8). Titrate with the -ksopropanolic hydrochloric acid solution (5.4.6) to the equivalence point of the neutralization curve (note 3). Carry out two determinations on the same prepared sample. Carry out a blank test in the same way. 5.6.
Expression of Results
The saponification value (S.V.) is given by the formula : S.V
« 56.1 x T x (V0 m
-
νλ)
where VQ is the number of ml of the standardized isopropanolic hydrochloric acid solution (5.4.6) used for the blank test, V\ is the number of ml of the standardized isöpropanolic hydrochloric acid solution (5.4.6) used for the test with the fat," T is the exact normality of the tsopropanolic hydrochloric acid solution (5.4.6) used, m is the mass, in g, of the test portion. Take as the result the arithmetic mean of the two determinations, provided that the requirement of repeatability 5.7 is satisfied.
59
5.7.
Repeatability
The difference between the results of two determinations carried out simultaneously or in rapid succession by the same analyst should not exceed 0.5 per cent of the mean value. 6.
TEST REPORT
The test report should show the method used. 7.
NOTES
2.
A stable colourless solution of potassium hydroxide can be prepared in the following manner: reflux 1000 ml of ethanol with 8 g of potassium hydroxide and 5 g of aluminium pellets for 1 hour, then distil immediately. Dissolve the required amount of potassium hydroxide in the distillate. Allow the whole to stand for several days and decant the clear supernatant liquid from the deposite potassium carbonate. The solution can also add 4 ml of aluminium several days. Decant potassium hydroxide.
2.
be prepared without distillation in the following manner : butylate to 1000 ml ethanol and allow the mixture to stand for the supernatant liquid and dissolve therein the necessary amount of The solution is ready for use.
It is advisable to store the glass electrode in water or, better still, in a 6/1 (V/V) mixture of ethanediol (5.4.2) and 2-propanol (5.4.1) for 12 hours preceding the titration. Dry it very gently with a piece of filter paper before use. Immediately after the titration, rinse with ethanediol, then with 2-propanol, and finally with distilled water. If the electrode does not function satisfactorily, it may be possible to regenerate it by immersion for 24 hours in a 1 N solution of hydrochloric acid in 2-propanol. After this treatment the electrode should be washed with distilled water, then with 2-propanol and with a 6/1 (V/V) mixture of ethanediol and 2-propanol. A thick sintered glass or porcelain disc between the saturated potassium chloride solution and the test solution prevents diffusion currents and parasitic potentials.
3,
Equivalence point/inflexion point The equivalence point usually corresponds approximately to the reading 10 on the pH scale, and can be determined graphically by observing the inflexion point on the neutralization curve. Alternatively, it can be calculated as the figure for which the first differential of the variation of pH as a function of the amount of isopropanolic hydrochloric acid solution added reaches a maximum, or the value for which the second differential becomes zero.
S.M.A.O.M).-- F