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Pharm 124 > Emulsions > Flashcards

Emulsions Flashcards

1
Q

What is an emulsion?

A

A dispersed system containing 2 immiscible liquids

Consists on an internal phase distributed throughout the external phase

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2
Q

What are droplet sizes in emulsions

A

0.1 - 100 micro metre

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3
Q

What are the 2 liquids in an emulsion

A

one is aqueous

other is oleaginous (oil based)

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4
Q

What are the 2 types of emulsions

A

O/W and W/O

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5
Q

What is a W/O/W emulsion

A

small water droplets enclosed in a large oil droplet which are dispersed in water

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6
Q

what are microemulsions

A

droplets are colloidal dimensions (1 nm - 1 microm)

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7
Q

What are the 3 tests to identify emulsion type

A

Dilution test, conductivity test, dye-solubility test

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8
Q

What is the dilution test

A

Dilution can only occur with the external phase (ex. O/W can be diluted with water)

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9
Q

What is the conductivity test

A

An emulsion will conduct electricity if water is the continuous/external phase

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10
Q

What is the dye-solubility test

A

Dyes can be used to determine the emulsion (ex. a water soluble dye would result in uniform colouring in a water based emulsion)

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11
Q

What type of emulsion is used in oral administration

A

o/w (better taste)

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12
Q

What type of emulsion is used in intravenous administration

A

o/w (or else embolization can occur)

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13
Q

What type of emulsion is used in intramuscular administration

A

w/o (sustained/slow release)

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14
Q

What emulsion is used for external administration?

A

can be either o/w or w/o depending on use
o/w - not greasy, water washable
w/o - greasy, occlusive, form water repellent film

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15
Q

Which oils can be used in oral administration

A

liquid paraffin
castor oil
cod liver oil
peanut oil

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16
Q

Which oils can be used in IV admin

A

cottonseed oil
soya bean oil
safflower oil

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17
Q

Which oils can be used for external admin

A

turpentine oil
benzyl-benzoate
various oils

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18
Q

Can ionic emulsifying agents be taken orally

A

No, irritant to GIT (both cationic and anionic)

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19
Q

Which emulsifying agents can be used parenterally

A

certain non-ionic (lecithin, polysorbate 80, poloxamers

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20
Q

What are the types of emulsifying agents

A

synthetic and semi-synthetic (anionic, cationic, non-ionic, amphoteric)
naturally occurring
finely divided solids

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21
Q

Structure of anionic surfactants

A

Hydrophobic tail

Hydrophilic head with negative charge

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22
Q

Examples of anionic surfactants

A

sodium stearate, calcium oleate, triethanolamine stearate, SLS

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23
Q

Structure of cationic surfactants

A

hydrophobic tail

hydrophilic head with positive charge

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24
Q

Structure and solubility of non ionic surfactants

A 
hydrophobic tail (carbon chain)
hydrophilic head (alcohol, etc)

if hydrophobic portion > hydrophilic - oil soluble
hydrophilic > hydrophobic - water soluble

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25
Q

Examples of non-ionic surfactants

A

glycol/glycerol
Sorbitan/Spans (hydrophobic)
Polysorbates/Tweens (hydrophilic)
poloxalcohols (poloxamers - can be used for IV)
higher fatty alcohols (cetyl/stearyl alcohol - used with other surfactants)

26
Q

What are disadvantages of naturally occurring emulsifying agents

A

batch to batch variation

susceptible to bacterial/mold growth (not good for products needed long shelf life)

27
Q

Examples of naturally occurring materials

A

polysaccharides (acacia - o/w)
methylcellulose - o/w
lanolin - w/o

28
Q

What are finely divided solids

A

accumulate on surface of droplet and stabilize them

29
Q

Examples of finely divided solids

A

colloidal clays
bentonite
veegum

30
Q

What are 3 emulsion additives

A

antioxidants, preservatives, humectants

31
Q

what are antioxidants

A

prevent auto-oxidation of oil/lipid in emulsion

32
Q

examples of antioxidants

A

BHA and BHT - true antioxidants (synergistic with chelating agents)
ascorbic acid

33
Q

what are preservatives

A

prevent growth of microorganisms
- usually lipid and water preservatives combined (methylparabens (water) and propylparabens (oil))

  • some emulsions inactivate preservatives, more required (ex. Tween)
34
Q

what are humectants

A

absorb water from air to reduce evaporation of water phase

35
Q

examples of humectants

A

propylene glycol, glycerol, sorbitol

36
Q

what is interfacial tension

A

exists at the surface between two immiscible liquids

= force/length

37
Q

Graph of micellization - what happens to interfacial tension as concentration increases

A

increase in surfactant = decrease in interfacial temsion

  • interfacial tension decreases until CMC (when the surface layer is fully saturated) at which it becomes constant
  • when additional surfactant is added, it forms micelles
  • each surfactant has its own CMC
38
Q

What is aggregation number

A

the number of surfactant molecules that form a micelle

39
Q

what happens if an emulsion has a low CMC

A

the surfactant will form micelles before the oil/water droplets can be covered (therefore it is less efficient than a surfactant with higher CMC)
- more oil droplets covered = more stable emulsion (decreases interfacial tension)

40
Q

What is Gibbs Adsorption Equation

A

the relationship between interfacial tension and adsorption of molecules
(review - page 42)

41
Q

What is the HLB scale

A

hydrophile - lipophile balance

42
Q

What is HLB 10-20 indicative of

A

hydrophilic

form o/w

43
Q

What does HLB 0-10 represent

A

lipophilic

w/o

44
Q

What are the 3 types of interfacial films

A 
monomolecular film (ionic, non-ionic surfactants)
multimolecular film (hydrocolloids - acacia, gelatin)
solid particle film (finely divided solids - bentonite)
45
Q

what is a stable emulsion

A

droplets remain uniformly distributed throughout the continuous phase

46
Q

what are the 3 phenomena of unstable emulsions

A
  1. creaming or sedimentation
  2. flocculation
  3. coalescence
47
Q

what is creaming/sedimentation

A
  • creaming = droplets move upwards
  • sedimentation = droplets move downwards
  • movement depends on density of droplets compared to external phase
  • reversible
  • increases probability of coalescence
48
Q

What factors decrease the rate of creaming/sedimentation (Stokes Law)

A
  • decreasing droplet size
  • decreasing density difference btwn phases
  • increasing viscosity of external phase
  • smaller concentration of dispersed phase
49
Q

what is flocculation

A

aggregation of droplets into loose clusters

- increases rate of creaming (increased particle unit size)

50
Q

what is coalescence (breaking, cracking)

A
  • complete fusion of droplets
  • separation of immiscible phases
  • irreversible
51
Q

How to formulate an emulsion

A
  1. using HLB calculations
  2. In situ soap formulation
  3. Wet gum and dry gum method
52
Q

Calculations for a single surfactant for a multicomponent oil phase

A
  1. calculate the required HLB (review - page 43)

2. choose the surfactant with the closest HLB

53
Q

Calculation of surfactant if a mixture of surfactants are used

A

Have a desired HLB but using 2 different surfactants

- use alligation to determine quantity of each surfactant to use

54
Q

In Situ soap formation emulsions

A
  1. oleic acid (olive oil) + Ca(OH)2 (lime water) = ca-oleate (soap)
  2. stearic acid + NaOH or KOH = sodium or potassium stearate (soap)
  3. stearic acid + triethanolamine = triethanolamine stearate (soap)
55
Q

What is the dry gum method

A

4: 2:1 (oil:water:gum)
1. acacia is added to oil
2. water is added all at once (hard fast trituration)
3. should hear a crackling sound

56
Q

what is the wet gum method

A

4: 2:1 (oil:water:gum)
1. water is added to acacia in small portions
2. oil is slowly added

57
Q

How does the surfactant determine the type of emulsion formed

A

more water soluble surfactant - O/W emulsion

more lipid soluble - W/O

58
Q

What is phase inversion

A

used to achieve a more stable emulsion

ex. Wet gum method
2 parts water + 1 part gum -> + 4 parts oil = w/o emulsion 1st
add remaining water = o/w emulsion

59
Q

What types of equipment are used for emulsification

A
  • mechanical stirrers (large scale, low viscosity)
  • homogenizers
  • ultrasonifiers (makes a uniform emulsion)
  • colloid mills (most used, reduces particle size)
60
Q

How is shelf life of emulsions tested

A

employing stress conditions:

  1. aging and temp
  2. centrifugation
  3. agitation

Pharm 124 (4 decks)

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