PRACTICAL – DETERMINATION OF HLB NUMBER (HYDROPHILLIC-LYPOPHILLIC BALANCE)

Object – To determine the HLB number (Hydrophillic-Lipophillic Balance number) of a surfactant by saponification method.

Reference – Mohanta G.P. & Manna P.K., Physical pharmacy – Practical Text, Pharma Book Syndicate, Hyderabad, 2006, 30-33

Materials required –

Chemicals – polyoxyethylene sorbitan monolaurate (Tween 20), alcoholic potassium hydroxide (2.82%), phenolphthalein, lauric acid, standard N/2 hydrochloric acid, standard N/10 Potassium hydroxide, alcohol, ether.

Glasswares & Apparatus – round bottom flask, condenser, waterbath, burette, burette stand, pipette, beaker, measuring cylinder, conical flask

Theory – The hydrophilic-lipophillic balance (HLB) of a surfactant is a measure of its polarity. The HLB value of nonionic surfactant can be calculated using the formula –

HLB = 20 (1-S/A)

Where S= Saponification number of ester and A = Acid number of fatty acid.

Saponification number is defined as number of milligram of potassium hydroxide required to neutralize the acid present in one gram of substance.

Acid number is defined as the number of milligram of potassium hydroxide required to neutralize the free acid present in one gram of substance.

The normal values of tween 20 (polyethelene sorbitan monolaurate) are Saponification number (S) = 45.5, Acid number (A) = 276 and Hydrophillic-Lypophillic balance number  (HLB) = 16.7

Procedure – Determination of saponiofication number – First of all, 1 gram of sample (Tween 20) was accurately weighed and taken in a round bottom flask. Then 30 ml of alcoholic potassium hydroxide (2.82%) was added and refluxed on boiling water bath for 1 hour. A blank experiment was performed in the same way but without sample. The reaction mixtures were cooled down to room temperature and titrated against standard N/2 hydrochloric acid using phenolphthalein as indicator taking color change from pink to colorless or slightly yellow as end point.

Determination of acid number – First of all, 500 milligram of lauric acid was accurately weighed and taken in a conical. Then 10 ml of alcohol and 10 ml ether were added. It was heated slightly to dissolve the lauric acid. The above mixture was titrated against standard N/10 potassium hydroxide using phenolphthalein as indicator.

Observation & Calculation – Saponification number-

Weight of sample taken for saponification number determination = ……………. gram

Let the titre value of sample = V1 ml

Titre value of blank = V2 ml

(V2-V1) ml of N/2 hydrochloric acid equivalent potassium hydroxide was required to neutralize the sample taken

(V2-V1) ml of N/2 HCl = (V2-V1) ml of N/2 KOH

1000 ml N KOH = 56000 x N/2 x V2-V1/1000 mg KOH

Saponification number = 56000 x N/2 x V2-V1/1000 whole divided by amount of sample in gram.

Acid number-

Let the titre value of N/10 KOH = V3 ml

V3 ml of N/10 KOH was required to neutralize the free acid in taken sample

Acid number (A) =

V3 X  Eq. weight of KOH / weight of sample taken in gram x normality of KOH / Weight of sample in gram

HLB = 20 X (1-S/A)

Result – The HLB value of polyoxyethelene sorbitan monolaurate (Tween 20) was ……………..

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