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PMP 102 > Stability > Flashcards

Stability Flashcards

1
Q

What interaction do lyophobic systems have with the solvent?

A

Poor

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2
Q

What physical stability do suspensions have?

A

Coarse

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3
Q

Why are large particles sedimenting problematic?

A

Not mixed evenly
Uneven distribution

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4
Q

What governs sedimentation, enabling redispertion?

A

Stokes’ Law

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5
Q

What does homogeneous dose mean?

A

Mixed dose

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6
Q

What does heterogeneous dose mean?

A

Not a well dispersed dose

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7
Q

What are the main instability phenomenas of macro particles?

A

Aggregation
Coagulation
Flocculations
Sedimentation
Caking
Ostwald ripening

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8
Q

What is aggregation?

A

Particles in groups

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9
Q

What is coagulation?

A

Closely aggregated and difficult to redisperse

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10
Q

What is flocculation?

A

Aggregates have an open structure with particles a small distance apart, attracted by a weak force to form flocs or flakes

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11
Q

What is sedimentation?

A

Process of settling or being deposited as a sediment

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12
Q

What is caking?

A

Defloculatted particles form cakes which can be difficult to re-suspend

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13
Q

What is Ostwald ripening?

A

Dissolution of small crystals

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14
Q

What does physical instability result in?

A

Poor dosing

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15
Q

What are the main factors affecting stability?

A

Kinetic properties
Size/shape
Electrical properties

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16
Q

What does the brownian motion and diffusion mean?

A

Particles diffuse from a high concentration

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17
Q

What law is diffusion rate based on?

A

Fick’s first law

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18
Q

What is the diffusion rate equation?

A

dm=-DA dc
dt. dx

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19
Q

What does dm over dt mean?

A

Mass of substances

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20
Q

What does D mean in Fick’s first law?

A

Diffusion coefficient

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21
Q

What does A mean in Fick’s first law?

A

Area

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22
Q

What does dc over dx mean in Fick’s first law?

A

Concentration gradient

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23
Q

What does viscosity relate to?

A

Molecular weight of suspended particles/suspending agents

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24
Q

How do we prevent sedimentation?

A

Form smaller particles
Decrease the density difference

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25
What are the names of each layer in the electrical double layer of ions?
Stern layer Diffuse layer
26
What does zeta potential stand for?
Magnitude and type of the electrical potential at the slipping plane
27
What does low zeta potential mean?
Prone to aggregate
28
What does high zeta potential mean?
Tend to remain dispersed
29
What are the factors affecting zeta potential?
Ion concentration - determines magnitude pH of continuous phase- alters the ionisation
30
What does the DLVO graph show?
Quantitative approach to the stability of lyophobic systems
31
What does the DLVO graph assume?
That the only interactions involved are van Der walls (VA) and electrostatic repulsive forces (VR)
32
What is the equation for DLVO?
VT=VA+VR
33
What is the instability phenomena?
Not redispersable
34
What is emulsion stability?
Droplets can retain their initial character and remain uniformly distributed throughout the continuous phase.
35
When can emulsion stability occur?
Phase inversion Creaming Flocculation Coalescence Ostwald ripening
36
What is phase inversion?
Oil in water emulsion stabilised by ionic surfactant/ co-surfactant
37
What is creaming?
Different density between oil and water, the oil droplets tend to concentrate at the top of the emulsion.
38
What is flocculation?
When two or more emulsion droplets aggregate without losing their individual identity
39
What is coalescence?
When two or more droplets collide me form one larger droplet and is irreversible
40
What is Ostwald ripening?
Collision between two droplets may cause one bigger droplet and one smaller droplet
41
What does the van der waals forces in the DLVO graph explain?
Explains why some colloidal particles aggregate Eva use energy attraction varies with the distance between the pairs of atoms or molecules or neighbouring particles with the inverse of the 6th power. A=1 H*6
42
What does the electrostatic repulsive forces explain in the DLVO graph?
Explains why some colloidal particles stay separated Arrives from the interaction of the electronic double layers surrounding pairs of particles Depends on zeta potential
43
What does low zeta potential mean?
Flocculated
44
What does high zeta potential mean?
Stable
45
What are the factors in the secondary minimum on the DLVO graph?
Forces of attraction are weak Flocculation Minimum attraction at large distances of separation
46
What are the factors of the primary maximum on the DLVO graph?
Particles come closer so there are some repulsion Height of this repulsion determines the stability of the system (vmax)
47
What are the factors of the primary minimum in the DLVO graph?
At close approach van der waals forces always dominate over repulsive electrostatic forces Coagulation that’s irreversible
48
What are the two ways non-ionic surfactants interact with each other?
Entropic (steric) effects Osmotic (salvation) forces
49
What happens when entropic effects happens?
The polymer chains on non-ionic surfactants start to overlap Which leads to a loss of freedom of motion This situation is thermodynamically unfavourable and forces the droplets apart again
50
What happens when there are osmotic forces in non-ionic surfactants?
When two particles come in close contact the polymer chain starts to overlap effectively, leading to concentrated polymer solution Induces osmotic gradient Water enters the concentrated region and forces the polymer chains apart.
51
What are the 4 main types of forces?
Van der waals (attractive) Electrostatic (repulsive) Steric forces (repulsive) Salvation forces (repulsive)
52
What types of forces do charged colloids use?
Van der waals Electrostatic
53
What types of forces do uncharged colloids use?
Van der waals Steric Solvation
54
What does stability stand for in medicines?
Capacity of a product to remain within specifications to ensure potency, quality or purity
55
What are the 3 types of degradation of medicines?
Chemical degradation Physical degradation Microbial degradation
56
What is chemical degradation?
Decomposition of chemical moiety
57
What is physical degradation?
Formulation specific E.g. caking is suspensions, phase separations, hardness and brittleness in tablets
58
What is microbial degradation?
Microbial contamination
59
What can drug instability cause?
Inconsistent dosing Undesired change in performance Changes in physical appearance Product failures
60
What are the 4 chemical degradation reactions?
Hydrolysis Oxidation Photochemical degradation Polymerisation
61
How do we reduce hydrolysis reaction for chemical degradation?
Dry formulations Adjusting pH to maximum stability Storage temperature Coating Choice of packaging
62
How can we reduce oxidation reaction in chemical degradation?
Remove initiators Exclude O2 Add free radical scavengers
63
How do we reduce photochemical degradation in chemical degradation?
Hide from light Black out containers/ packaging
64
How can we reduce polymerisation reaction in chemical degradation?
Hide from UV
65
What are the different reactions in chemical degradation classified?
Zero order+ pseudo zero order First order+ pseudo first order Second order reactions
66
What is a zero order reaction?
The rate of degradation of A is independent of the concentration of the reactants [A]t= [A]o -kt
67
What are first order reactions?
The rate of degradation of A is directly proportional to its contraction [A] In[A]t=In [A]o-kt
68
What are pseudo zero order reactions?
Observed rate constant is an expression for a zero order reaction.
69
What are second order reactions?
The rate of degradation of A is directly proportional to its concentration and the concentration of the reactant B 1. =. 1. +kt [A]t. [A]o
70
What are pseudo first order reactions?
Observed rate constant is an expression for a first order reaction
71
How much degradation is allowed?
5-10% loss over 5 years

PMP 102 (29 decks)

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