Particle size

Question 1

Why is particle size measurement important?

Answer 1

• Size influences physical properties of pharmaceutical materials
• It tells us if a process has been successful
• Gives an indication of product stability
• Quality control of product
• Indicative of in-vitro behavior

Question 2

What is equivalent diameter?

Answer 2

-The diameter of a sphere that is in some unique way similar to the particle in question

Question 3

What is volume equivalent diameter?

Answer 3

-The diameter of a sphere that has the sam volume as the irregular particle

Question 4

What techniques are used for measuring particle size?

Answer 4

• Sieving
• Sedimentation
• Microscopy
• Light scattering

Question 5

The choice of technique used for measuring particle size is depend on?

Answer 5

• Applicable size range for sample
• Cost
• Time taken
• Skill required
• Precision
• Quantity of material needed

Question 6

Sieving seperates fine material from course material by means of a series of woven or perforated surfaces. TRUE OR FALSE?

Answer 6

TRUE

Question 7

What are some of the errors in sieving?

Answer 7

• Sieve hole may vary in size due to manufacture or damage
• Powder may coat the wires leading to sieve apertures being reduced
• Particles may be cohesive
• Vibration from shaking may damage the particles leading to erroneous fines
• Sieve may be overloaded

Question 8

Settling velocity is not measured directly. TRUE OR FALSE?

Answer 8

TRUE

Question 9

What are the advantages and disads of sedimentation

Answer 9

ADS
- measures relatively few particles
Disdas
-One of the few methods getting shape information

Question 10

What are the advantages of particle size analysis by light scattering?

Answer 10

• Rapid
• Easy to use
• Wide applicability
• Wide size range

Question 11

How does light scattering phenomena work?

Answer 11

• If we shine light through a suspension of particles we can see its track
• When light hits a particle, it is scattered in all directions
• The diffraction pattern is determined by the particle size and shape
• If there are lots of particle in suspension, then we see the scattering from each one adding up, because the particles are different sizes the various patterns usually smear out.

Question 12

Given the scattering pattern we cannot directly compute the particle size. TRUE OR FALSE?

Answer 12

TRUE

Question 13

How does the calculation work for laser diffraction sizer?

Answer 13

• It guesses the size distribution
• It calculates the scattering pattern of the trial distribution
• It compares the trial distribution scattering with the measured scattering pattern
• It adjusts the trial distribution
• Recalculates scattering pattern of trial distribution

Question 14

What instrument is used for particle counting?

Answer 14

-Coulter counter or elcetrical zone sensing technique

Question 15

How does optical particle counting work?

Answer 15

• Particles in dilute suspension are passed through a narrow beam of light
• As they pass they cast a shadow which is measured by a photodetector
• This is the principle of the hiac counter which is the method used in pharmacopoeil tests for particles in injections

Question 16

The width can be diefined as the standard deviation. TRUE OR FALSE?

Answer 16

TRUE

Question 17

What is a cumulative frequency representation?

Answer 17

-The % of particles above or below a given size

Question 18

Sieving is the oldest method used, it is inexpensive and widely available. TRUE OR FALSE?

Answer 18

TRUE

Question 19

Sieves seperate fine materials from course material by means of a series of woevn or perforated surfaces. TRUE OR FALSE?

Answer 19

TRUE

Question 20

The smallest size for a sieve is 50 micrometers. TRUE OR FALSE?

Answer 20

TRUE

Question 21

Fine meshes are readily damages and clogged. TRUE OR FALSE?

Answer 21

TRUE

Question 22

What is the sieve equivalent diameter?

Answer 22

-The size of the sphere which will pass through the square hole

Question 23

The conection between particle size and sedimentation velocity is given by stokes law. TRUE OR FALSE?

Answer 23

TRUE

Question 24

Sedimentation can measure the amount of materials settled in a particular time. TRUE OR FALSE?

Answer 24

TRUE

Question 25

Sedimentation can measure the amount remaining in suspension vs time by passing a beam of light and x-rays through the sample. TRUE OR FALSE?

Answer 25

TRUE

Question 26

What is a centrifugal sedimentation used to speed up?

Answer 26

-Settling particles

Question 27

How does Andreasen pipette work?

Answer 27

-Removes samples over time and anylse particle content; calculate size distribution

Question 28

How does a laser diffraction sizer work?

Answer 28

• Particles in dilute suspension scattering is measured from many particles
• Laser light source (high intensity, single colour and direction)
• Array detector - measures light intensity at ecah point

Question 29

How does the calculation work for laser diffraction sizer?

Answer 29

• It guesses the size distribution
• It calculates the scattering pattern of the trial distribution
• It compares trial distribution to measured scattering pattern
• It adjusts trial distribution

Question 30

What is hydrodynamics?

Answer 30

-The size of a sphere that moves at an identical rate to particle

Question 31

How does electrical zone sensing work?

Answer 31

• Suck a known amount of suspension through apertures and the instrument willcount the number of times teh current has been blocked
• Through this blockage we can measure the size of each particle and the instrument can build up the size distribution

Question 32

How does an optical particle counting work?

Answer 32

• Particles in dilute suspensio pass through a narrow beam of light
• As they pass they leave a shadow which is measured by a photodectector
• This is hte principle of the hiac counter which is used for pharmacopeial tests