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Pharm 124 > Emulsions > Flashcards

Emulsions Flashcards

(60 cards)

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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
Examples of non-ionic surfactants
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
What are disadvantages of naturally occurring emulsifying agents
batch to batch variation | susceptible to bacterial/mold growth (not good for products needed long shelf life)
27
Examples of naturally occurring materials
polysaccharides (acacia - o/w) methylcellulose - o/w lanolin - w/o
28
What are finely divided solids
accumulate on surface of droplet and stabilize them
29
Examples of finely divided solids
colloidal clays bentonite veegum
30
What are 3 emulsion additives
antioxidants, preservatives, humectants
31
what are antioxidants
prevent auto-oxidation of oil/lipid in emulsion
32
examples of antioxidants
BHA and BHT - true antioxidants (synergistic with chelating agents) ascorbic acid
33
what are preservatives
prevent growth of microorganisms - usually lipid and water preservatives combined (methylparabens (water) and propylparabens (oil)) - some emulsions inactivate preservatives, more required (ex. Tween)
34
what are humectants
absorb water from air to reduce evaporation of water phase
35
examples of humectants
propylene glycol, glycerol, sorbitol
36
what is interfacial tension
exists at the surface between two immiscible liquids | = force/length
37
Graph of micellization - what happens to interfacial tension as concentration increases
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
What is aggregation number
the number of surfactant molecules that form a micelle
39
what happens if an emulsion has a low CMC
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
What is Gibbs Adsorption Equation
the relationship between interfacial tension and adsorption of molecules (review - page 42)
41
What is the HLB scale
hydrophile - lipophile balance
42
What is HLB 10-20 indicative of
hydrophilic | form o/w
43
What does HLB 0-10 represent
lipophilic | w/o
44
What are the 3 types of interfacial films
``` monomolecular film (ionic, non-ionic surfactants) multimolecular film (hydrocolloids - acacia, gelatin) solid particle film (finely divided solids - bentonite) ```
45
what is a stable emulsion
droplets remain uniformly distributed throughout the continuous phase
46
what are the 3 phenomena of unstable emulsions
1. creaming or sedimentation 2. flocculation 3. coalescence
47
what is creaming/sedimentation
- creaming = droplets move upwards - sedimentation = droplets move downwards - movement depends on density of droplets compared to external phase - reversible - increases probability of coalescence
48
What factors decrease the rate of creaming/sedimentation (Stokes Law)
- decreasing droplet size - decreasing density difference btwn phases - increasing viscosity of external phase - smaller concentration of dispersed phase
49
what is flocculation
aggregation of droplets into loose clusters | - increases rate of creaming (increased particle unit size)
50
what is coalescence (breaking, cracking)
- complete fusion of droplets - separation of immiscible phases - irreversible
51
How to formulate an emulsion
1. using HLB calculations 2. In situ soap formulation 3. Wet gum and dry gum method
52
Calculations for a single surfactant for a multicomponent oil phase
1. calculate the required HLB (review - page 43) | 2. choose the surfactant with the closest HLB
53
Calculation of surfactant if a mixture of surfactants are used
Have a desired HLB but using 2 different surfactants | - use alligation to determine quantity of each surfactant to use
54
In Situ soap formation emulsions
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
What is the dry gum method
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
what is the wet gum method
4: 2:1 (oil:water:gum) 1. water is added to acacia in small portions 2. oil is slowly added
57
How does the surfactant determine the type of emulsion formed
more water soluble surfactant - O/W emulsion | more lipid soluble - W/O
58
What is phase inversion
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
What types of equipment are used for emulsification
- mechanical stirrers (large scale, low viscosity) - homogenizers - ultrasonifiers (makes a uniform emulsion) - colloid mills (most used, reduces particle size)
60
How is shelf life of emulsions tested
employing stress conditions: 1. aging and temp 2. centrifugation 3. agitation

Pharm 124 (4 decks)

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