Disperse Systems part 1

Question 1

What is a dispersed system?

Answer 1

Un-dissolved globules (liquid) or particels (solid) mixed throughout another phase

Question 2

What do disperse systems consist of?

Answer 2

2 or more components in a heterogenous mixture

Question 3

What is a heterogenous mixture?

Answer 3

A non-uniform mixture of smaller constituent parts

Question 4

What are the phases in a dispersed system and what do they mean?

Answer 4

DISPERSED PHASE: small droplets/particles that are seperated and dispersed throughout
CONTINUOUS PHASE or DISERSANT is the remainder of the formulation in which the small droplets or particles are dispersed in.

Question 5

What can the continuous or disperse phases be?

Answer 5

Solid, liquid or gas

Question 6

What type of disperse system is solid particles dispersed in a liquid continuous phase?

Answer 6

A solution

Question 7

What type of disperse system is liquid globules in a liquid continuous phase?

Answer 7

An Emulsion

Question 8

What is a liquid or solid phase dispersed in gas?

Answer 8

A liquid or solid AEROSOL.

Question 9

How do we want the dispersed particles to be?

Answer 9

We want the dispersed particles to be of the same size, and be very small to reduce the effect of gravity (take longer for the dispersed particles to fall to the bottom.)

Question 10

What is the name on dispersed particles of different size, and what happens to the particles?

Answer 10

Poly-dispersed - not likely to be seen in pharmacy. The small particles get squished by the large particles causing them to stick together.

Question 11

What happens if the particles in the dispersed phase are very large?

Answer 11

The gravity will have a greater effect, and cause the particles to fall to bottom (sedimentation)

Question 12

There are two different sizes of dispersions:

Answer 12

Colloidal and coarse

Question 13

What is the size of colloidal dispersions?

Answer 13

Tiny particle size about 1nm to 1µm

Question 14

What is the size of coarse dispersions?

Answer 14

Bigger particle size of more than 1µm

Question 15

Properties of an ideal disperse system (list 5)

Answer 15

1) Uniform particle size (not poly-dispersed)
2) Small particle size
3) Particles must not sediment too rapidly (will do eventually)
4) Any sediment must be easily re-dispersed
5) Must easily flow out of the container (will need a balance between being too thick to flow out and too thin that sediments too quickly)

Question 16

How do we want the surface are of the drug to be in a dispersed system? What does nature want?

Answer 16

We want to break the drug up for larger surface area to reduce sedementation, but nature doesn’t like lots of energy in the system so will try to reduce the surface area by clumping the particles together to decrease the surface area.

Question 17

What are the advantages of a dispersed system?

4

Answer 17

1) Drugs that are susceptible to aqueous degredation (break down when in contact with water) may be formulated as a suspension
2) Improved bioavailibility compared to a solid due to the smaller particle size and therefore increased surface area for metabolism.
3) Particle size can control absorption rates so if extended absorption was required, then could create a poly-dispersed system where the small molecules would be absorbed quickly and the larger molecules slower.
4) Allows flexibility of formulation e.g. masking bitter taste.

Question 18

Why is it possible to formulate a suspension with drugs susceptible to aqueous degredation?

Answer 18

The drug is put into the water as solid particles and therefore the chemistry of the molecule is less likely to be damaged by hydrolysis. The outside of the ‘clump’ of particles may be effected, but the inside won’t.

Question 19

Why can’t drugs susceptible to aqueous degredation be in a solution?

Answer 19

Because the particles would be evenly distributed and the chemistry of the molecules will be damaged by hydrolysis.

Question 20

What are the diadvantages of Disperse systems?

2

Answer 20

1) If not shaken or re-dispersed when shaken, accurate dosing cannot be assured.
2) It is a liquid medicine so there is water present so must be careful of contamination.

Question 21

Optical Properties of disperse systems:

Answer 21

They are too small to be visible to the human eye, but are large enough to interfere with the path of light travelling through.

Question 22

What will happen when light passes through a suspension?

Answer 22

The light will pass through if it doesn’t come to contact with any particles, but will be scattered if it comes to contact with particles.

Question 23

What will effect the degree of light scattering?

Answer 23

The size of the particles:
Small particles = scater (“bend”) the light more
Large particles = Scater the light less

Question 24

What property can be used to determine thr Molecular weight , and give information on particle size and shape?

Answer 24

The degree of light scattering, and the fact that small particles will “bend” the light more than large particles.

Question 25

What is turbidity?

Answer 25

The cloudiness of the fluid

Question 26

What causes a dispersion to appear turbid?

Answer 26

Light scattering causes the dispersion to be turbid

Question 27

How can turbidity be used to measure concentration?

Answer 27

the more concentrated the dispersion, the more light is scattered and the more turbid the dispersion looks.

Question 28

What is Laser Diffraction?

Answer 28

Similar to light, but laser only has ONE WAVELENGTH. If nothing is in the way of a laser beam then the laser will pass through and hit the detector in the middle.
If the laser beam will come to contact with a particle, the beam will be sacttered, and won’t hit the middle of the detector.

Question 29

What does the amount of bending from a laser beam predict about the particles?

Answer 29

It predicts the size of the paricles - the further from the middle of the detector the beam is, the smaller the particle size (the smaller the particle size, the more bending of the laser beam).

Question 30

What does the laser beam tell about poly-dispersement?

Answer 30

Because the laser beam is a single wavelength, if it hits the detector at different sites, then we know that the particle sizes are different so poly-dispersed.

Question 31

What will affect laser beam scattering other than particle size?

Answer 31

The wavelength (colour) of the light - Blue light has a short wavelength and is scattered more than red light which has a long wavelength.