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BACKGROUND
The hydrophilic-lipophilic balance of a surfactant is a measure of the degree to which it is hydrophilic or lipophilic, determined by calculating values for the different regions of the molecule, as described by Griffin in 1949 and 1954.
Griffin’s method
Griffin’s method for non-ionic surfactants as described in 1954 works as follows:
HLB = 20
Where S= Saponification number
A = Acid numberH L B = 20 ∗ M h / M {\displaystyle HLB=20*M_{h}/M}
where M h {\displaystyle M_{h}} is the molecular mass of the hydrophilic portion of the molecule, and M is the molecular mass of the whole molecule, giving a result on a scale of 0 to 20. An HLB value of 0 corresponds to a completely lipophilic/hydrophobic molecule, and a value of 20 corresponds to a completely hydrophilic/lipophobic molecule.1,2
Aim of the expt:
To determine the HLB value of a given surfactant.
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REQUIREMENTS
Chemicals: Distilled water,
Fatty acid ester e.g. Glyceryl monostearate (gms),
0.5n alcoholic potassium hydroxide (koh),
Stearic acid, ether,
0.5n hydrochloric acid,
0.1n sodium hydroxide
Phenolphthalein indicator.
Apparatus: Round bottom flask,
Reflux condenser,
Beakers,
Burette,
Pipette,
Conical flask, etc.
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PROCEDURE
Dissolve around 4 g of KOH in 3 to 5 ml distilled water in a vlumetric flask and make uo total volume to 100 ml with alcohol. Allow it to stand for about 24 hours and separate out clear liquid by decantation. Use this clear solution for experiment. Alcoholic KOH is used, because surfactantsare freely soluble in alcohol than in water. The solubility improved by alcohol hydrolysis is effective one.3
2. Determination of saponification number
Weigh accurately 0.5g of GMS and transfer into round bottom flask, add 15ml of alcoholic potassium hydroxide to it and reflux on boiling water bath for about half an hour.
Reflux separately 15 ml of alcoholic potassium hydroxide (without GMS) on boiling water bath for about an hour blank reading.
Cool both the solutions to rioom temperature and titrate separately against 0.5N hydrochloric acid using phenolphthalein as the indicator.
(End point: pink to colorless or slightly yellowish)
Let the titre reading for sample (GMS) be V1 and blank be as V2.
3. Determination of acid number
Weigh accurately 0.5g of stearic acid; add it to a mixture of 10ml of alcohol and 10ml of ether. If stearic acid does not dissolve in the solvent mixture, warm it on water bath until it dissolves. (Note:
take care while warming, since both ether and alcohol are highly inflammable liquids)
Titrate solution of stearic acid against 0.1N sodium Hydroxide using phenolphthalein as the indicator.
Let the titre reading be V3.
Observations
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Saponification number= ………
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Volume of 0.5N HCl consumed by sample (V1) = ……ml
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Volume of 0.5N HCl consumed by blank (V2) = ……ml
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Acid number=……
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Volume of 0.1N sodium hydroxide consumed (V3)=……ml
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Calculations
1. Calculations for Saponification number:
1000 ml of 1N KOH = 56000 mg of KOH
(V2-V1) ml of 0.5N KOH mg of KOH/0.5g GMS
Substitute values of V1 and V2 to determine saponification number
mg of KOH/g of GMS
Saponification value……….
2. Calculation for acid number:
V3 ml of 0.1N NaOH 0.5 g of stearic acid
2V3 ml of 0.1N NaOH 1 g of stearic acid
( 1000 ml of NaOH = 1000 ml of 1N KOH 56000 mg of KOH)
2V3 ml of 0.1N KOH
Substitute value of V3 and calculate acid number,
Acid number ……
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Calculation of HLB Value:
HLB = 20
S = Saponification number
A = Acid number
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CONCLUSION
The HLB value of given surfactant was found to be ___
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REFERENCES
- More HN, Hajare AA. Practical Physical Pharmacy. Career Publications. 2010: 194-195.
- Gaud RS, Gupta GD. Practical Physical Pharmacy. CBS Publisher and Distributors. 2009: 71-72.
- Mohanta GP. Physical Pharmacy Practical Text, Pharma Book Syndicate. 2006: 36-38.
