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PCT 411 > Micromeritics > Flashcards

Micromeritics Flashcards

1
Q

Define micromeritics.

A

Micromeritics is the science and technology of small particles.

It is the study of the fundamental and derived properties of individual particles as well as a collection of particles.

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2
Q

What is the importance of micromeritics?

A

i. It is related to the physical, chemical and pharmacological properties of drugs
ii. It affects drug release
iii. It is essential in achieving flow properties as well as mixing of granules and powders in tablet or capsule production.

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3
Q

Mention 4 applications of micromeritics.

A
  1. Physical stability of formulations e.g. suspensions, emulsions.
  2. Absorption and therapeutic activity e.g griseofulvin
  3. Release and dissolution e.g. capsules, tablets.
  4. Dose uniformity e.g solid, semi-solid, liquid preparations.
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4
Q

Mention 4 fundamental properties of a powder.

A
  1. Particle size
  2. Particle shape
  3. Surface area
  4. Particle size distribution
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5
Q

What is Equivalent Spherical Diameter?

A

It is a parameter used to describe the size of an irregularly-shaped particle by representing it with spheres with an equivalent diameter.

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6
Q

Define surface diameter (ds).

A

Surface diameter (ds) is the diameter of a sphere having the same surface area as that of the particle in question.

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7
Q

Volume diameter (dv) is _____.

A

The diameter of a sphere having the same volume as that of the particle in question.

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8
Q

Projected particle diameter (dp) is _____

A

The diameter of a sphere having the same observed area as the particle when viewed normal to the most stable plan.

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9
Q

What is Stoke’s diameter?

A

It is the diameter of an equivalent sphere undergoing sedimentation at the same rate as the asymmetric particle.

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10
Q

What are the important parameters for consideration in powder analysis?

A

i. Average particle size
ii. Particle size distribution
iii Surface area

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11
Q

What is the Edmundson equation for? State it.

A

It is used to determine average particle size.

((€ndp + f)/€ndf)^1/p

n=numberof particles in a size range
d=midpoint diameter
p=index related to an individual particle
ndf=frequency factor of particle in size range
f= frequency index.

If:
f=0, size frequency is expressed in terms of total number.
f=1, size frequency=length of particles
f=2, size frequency=surface of particles
f=3, size frequency=volume of particles

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12
Q

What is particle size distribution curve?

A

It is a frequency distribution curve obtained when the number or weight of particles lying within a certain size range is plotted against the size range or mean particle size.

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13
Q

What is the significance of the particle size distribution plot?

A

i. It helps differentiate between two or more powder batches with the same average diameter
ii. It shows particle size that occurs most frequently within the sample.

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14
Q

Mention 3 other useful particle size plots.

A

i. Log-normal distribution curve
ii. Log-probability curve
iii. Particle number of particles per unit weight

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15
Q

What are the methods for performing particle size analysis?

A

i. Microscopy
ii. Sieving
iii. Sedimentation
iv. Coulter counter (volume displacement method)
v. Beckman Coulter (proton correlation method)

i-iii are not direct as only 2 out of 3 dimensions can be seen.

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16
Q

What is the advantage of the microscopy method?

A

It helps to detect agglomerates or particles of more than one component.

17
Q

What are the disadvantages of the microscopy method?

A

i. Diameter can only be obtained from two dimensions, length and breadth.
ii. It is slow and tedious.

18
Q

What is the advantage of the sieving method?

A

It is faster and inexpensive.

19
Q

What is the disadvantage of the sieving method?

A

Reproducibility of results is affected by sieve loading, duration and intensity of agitation.

20
Q

What are the 3 types of sedimentation method?

A
  1. Pipette method
  2. Balance method
  3. Hydrometer method
21
Q

When is Stoke’s equation valid?

A

i. For spheres falling freely at constant rate without hindrance
ii. Asymmetric particles with the assumption that the sphere is falling at the same rate as the particle being considered.
iii. Deflocculating agent needed to keep particles free and separate as they fall through the medium
iv. Laminar flow of the dispersion medium around the settling particle.

22
Q

Explain the principle of the coulter counter method.

A

This method works on the principle that a particle suspended in a circulating liquid displaces a known volume of the liquid when passed through a small orifice.
The displaced volume causes a change in electrical resistance which is recorded by a pulse height analyser.

The suspension must be sufficiently dilute to allow particles pass through one at a time.

23
Q

Explain the principle of the Beckman Coulter method.

A

It uses photon correlation spectroscopy that senses the brownian motion of particles in suspension.
Laser beam passes through the sample and the sensor detects the light scattered by the particles in brownian motion. The smaller the particle, the faster the brownian motion.

24
Q

What are the methods used to determine surface area?

A

i. Air adsorption method: based on the principle that the amount of gas or liquid solute adsorbed to form a monolayer is a direct function of the surface area (SA).
**At high pressures, the adsorption is multilayer.

ii. Air permeability method: based on the principle that the rate at which a gas or liquid permeates a bed of powder is related to the SA exposed to the permeate.
**Permeability is inversely proportional to specific surface area

24
Q

Mention 3 derived properties of powders.

A
  1. Porosity
  2. Packing arrangement
  3. Dissolution rate
25
Q

What is the porosity of a powder?

A

It is the ratio of the void volume to the bulk volume of the packing.

26
Q

What are the two packing arrangements of an ideal powder system?

A

i. Rhombohedral (tightest)
ii. Cubic (loosest)

27
Q

What are the 3 types of particle density?

A
  1. True density: this excludes voids and intra-particle pores larger than atomic dimensions in crystal lattices.
  2. Bulk density: ratio of powder weight to bulk volume.
  3. Granule density: determined with mercury displacement. Does not penetrate into pores smaller than 10 micrometer at ordinary pressure.
28
Q

For a non porous powder system, true and granule densities are identical. It is obtained by the
displacement of either helium, benzene, mercury or water.

True or False

A

True

29
Q

Density obtained by displacement method is approximately equal to true density.

True or False

A

True

30
Q

What is Stoke’s equation?

A

V=h/t= ds((Ps-Po)/18n)g

Ps=density of the particles
Po=density of the dispersion medium
n=viscosity of the medium.

31
Q

Briefly explain how the Pipette method (Andreasen apparatus) is done.

A
  • Prepare a 1-2 % suspension of the particles in a medium with sufficient deflocculating agent and bring it to the 550ml mark.
  • Agitate the stoppered vessel to distribute the particles
  • Clamp pipette in position and place in a constant temp bath.
  • Withdraw 10 mL at 10 min intervals
  • Evaporate sample, weigh and analyse (with correction for deflocculating agent)
  • Particle diameter corresponding to each time period is obtained using Stoke’s equation.
32
Q

What is the BET equation for air adsorption method?

A

At monolayer adsorption, volume of nitrogen gas adsorbed by 1g of powder is given by the Brunaver, Emmett and Teller (BET) equation.

P/V(Po - P) = 1/Vmb + (b-1)p/VmbPo

Vm=volume of nitrogen gas (cm3) that 1g of powder can adsorb when monolayer is complete.
V=volume of gas (Cm3) absorbed per gram of powder at Pressure P
P= saturation vapour pressure of liquified nitrogen at experimental temp.
b=a constant, difference between heat of adsorption and heat of liquefaction of nitrogen.

PCT 411 (3 decks)

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