Hydrophilic–Lipophilic Balance Concept, HLB classification and MCQs for GPAT, NIPER, Pharmacist and Drug Inspector exam

Hydrophilic–Lipophilic Balance Concept: The HLB concept was introduced by Griffin in 1947 to classify nonionic surfactants but has since been applied to ionic surfactants as well. In this system, each surfactant is assigned a number between 1 and 20, representing the relative proportions of lipophilic and hydrophilic parts of the molecule.

1. The higher the HLB number, the more hydrophilic is the surfactant.
2. The lower the HLB number, the more lipophilic is the surfactant.
3. Exceptions to HLB scale exist such as sodium lauryl sulphate with an HLB value of 40.

Table 1  – Application of surfactants based on HLB value

HLB values                            Surfactants

15–18          Solubilizing agents (sodium lauryl sulphate)

13–15           Detergents (sodium stearate)

8–16            O/W emulsifer (Tween)

7–9             Wetting agents (Acacia)

3–6              W/O emulsi¿er (Span)

1–3              Antifoaming agents (simethicone)

Calculation of HLB value:

1. HLB values of surfactants based on polyhydric alcohol fatty acid esters such as glyceryl monostearate, sorbitan monooleate and polyoxyethylene sorbitan monooleate may be estimated by the following equation:

HLB = 20(1-S/A)

where S is the saponification number of the ester and A is the acid number of the fatty acid.

2. For materials such as beeswax and lanolin derivatives with which it is not possible to obtain good saponification number, the HLB value is estimated by the following:

HLB = E + P/5

where E is the weight percentage of oxyethylene chain and P is the weight percentage

of polyhydric alcohol groups (e.g. glycerol or sorbitol) in the material.

3. For materials whose hydrophilic region is polyoxyethylene, the HLB value is calculated by the following:

HLB = E/5

4. In another method for calculating the HLB values, the component groups of the surfactant molecules are assigned group numbers and these are then added to give the HLB value of the surfactant molecule.

HLB = Ɛ (hydrophilic group numbers) − Ɛ (lipophilic group numbers) + 7

Required HLB- Generally, a single emulsifier cannot yield the desired type of emulsion. More often, stable emulsions can be prepared by utilizing a combination of a hydrophilic and a lipophilic surfactant. Such combinations produce mixed interfacial phases of high surface coverage as well as of sufficient viscosity to prevent creaming.

HLB values of combinations of surfactants A (HLBA) and B (HLBB) are calculated by the following equation:

HLB_mixture = f_A X HLB_A + (1-f_A) X HLB_B

Multiple choice questions (MCQs)

1.The HLB concept was introduced by 

a)Sorensen

b)Griffin

c)Arhenius

d)Seydler

2.The HLB concept was introduced in 

a)1947

b)1950

c)1951

d)1955

3.The higher the HLB number, the more _____ is the surfactant

a)Hydrophilic

b)Lipophilic

c)Amphiphilic

d)All of the above

4.The lower the HLB number, the more _____ is the surfactant.

a)Hydrophilic

b)Lipophilic

c)Amphiphilic

d)All of the above

5.Sodium lauryl sulphate has an HLB value of 

a)3

b)12

c)18

d)40

6.Solubilizing agents have HLB value

a)15–18

b)8–16

c)7–9

d)3–6

7.Detergents have HLB value

a)15–18

b)8–16

c)7–9

d)13–15

8.O/W emulsifer have HLB value

a)15–18

b)8–16

c)7–9

d)13–15

9.Wetting agents have HLB value

a)15–18

b)8–16

c)7–9

d)13–15

10.W/O emulsifier have HLB value

a)8–16

b)7–9

c)13–15

d)3-6

11.Antifoaming agents have HLB value

a)8–16

b)7–9

c)13–15

d)1-3

12.HLB values of surfactants based on polyhydric alcohol fatty acid esters such as glyceryl monostearate, sorbitan monooleate and polyoxyethylene sorbitan monooleate may be estimated by which of the following equation?

a)HLB = 20(1-S/A)

b)HLB = E + P/5

c)HLB = Ɛ (hydrophilic group numbers) − Ɛ (lipophilic group numbers) + 7

d)All of the above

13.For materials such as beeswax and lanolin derivatives with which it is not possible to obtain good saponification number, the HLB value is estimated by which of the following?

a)HLB = 20(1-S/A)

b)HLB = E + P/5

c)HLB = Ɛ (hydrophilic group numbers) − Ɛ (lipophilic group numbers) + 7

d)All of the above

14.For materials whose hydrophilic region is polyoxyethylene, the HLB value is calculated by which of the following?

a)HLB = 20(1-S/A)

b)HLB = E + P/5

c)HLB = Ɛ (hydrophilic group numbers) − Ɛ (lipophilic group numbers) + 7

d)All of the above

15.HLB values of combinations of surfactants A (HLBA) and B (HLBB) are calculated by which of the following equation?

a)HLB = 20(1-S/A)

b)HLB = E + P/5

c)HLB = Ɛ (hydrophilic group numbers) − Ɛ (lipophilic group numbers) + 7

d)HLB_mixture = f_A X HLB_A + (1-f_A) X HLB_B

Solutions:

1. b)Griffin
2. a)1947
3. a)Hydrophilic
4. b)Lipophilic
5. d)40
6. a)15–18
7. d)13–15
8. b)8–16
9. c)7–9
10. d)3-6
11. d)1-3
12. a)HLB = 20(1-S/A)
13. b)HLB = E + P/5
14. c)HLB = Ɛ (hydrophilic group numbers) − Ɛ (lipophilic group numbers) + 7
15. d)HLB_mixture = f_A X HLB_A + (1-f_A) X HLB_B

References:

1. GAURAV KUMAR JAIN – THEORY & PRACTICE OF PHYSICAL PHARMACY, 1st edition 2012 Elsevier, page no. 104-107.

2. Martins Physical Pharmacy, 6th edition 2011, page no. 671-676.

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