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Pharmaceutics > Mixing > Flashcards

Flashcards in Mixing Deck (21)
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1

What is the aim of mixing?

To rearrange particles to distribute them homogeneously.

2

Positive Mixture is

mixes spontaneously, energy input required to separate to components

3

Negative Mixture is

segregates spontaneously, energy required to mix and keep mixed

4

Neutral Mixture is

components neither mix nor segregate, energy required to mix or segregate.

5

Mixing in Liquids types (3)

bulk transport
- large degree of mixing in short period of time

turbulent mixing
- group of molecules move with constant velocity changes

molecular diffusion
- movement down a conc gradient

6

Mixing in Solids types (3)

connective mixing
- like bulk transport in liquids

shear mixing
- like turbulent in liquids

diffusive mixing
- like MD in liquids

7

What is a free flowing powder, is it easy to mix?

easy to mix especially if monosize

susceptible to segregation if different size or density

8

What is a cohesive powder, is it easy to mix?

Fine particles which are cohesive

need high energy de-agglomeration for adequate mixing but need to consider the friability of particles.

9

Is a perfect mixture attainable in powders?

No.

Random mixture is most likely.

10

What is the random mixture?

Probability of selecting a particle type is the same in all positions of the mixture and equal to the proportion of the particles in the totalmixture.

11

Equation for theoretical standard deviation of a random mixture =

O R = Square root of p(1-p) /n

p = proportion go drug/tracer in mixture
n = total number of particles in mixture

12

Mixing index =

o (standard deviation) / theoretical standard deviation

13

If mixing index is 1...

mixing complete - homogenous sample attained.

14

What is the scale of scrutiny?

the amount of powder per sample for assessing the extent of mixing = amount in 1 dosage unit e.g. 1 tablet.

15

If you sample too little..

you will mistakenly believe that the powder is not mixed enough

16

if you sample too much...

you will mistakenly believe the powder is mixed enough

17

What is an ordered mixture?

where the micronised particles are adsorbed on the surface of larger carrier particles.

18

Segregation is likely if... (3)

particle size non uniform

particle density non-uniform

spherical shape - free flowing.

19

Mechanisms of segregation:

Percolation segregation
- small particles fall through voids.

Trajectory segregation
- larger particles go further as they have more mass based inertia

Elutriation segregation
- fine particles settling on top after motion has ceased

20

Minimising segregation: (4)

ordered mixture

reduce vibration

inform particle size

excipients of similar density

21

mechanism of mixing in a powder is:

convective mixing