Particle size Flashcards
Why is particle size measurement important?
- 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
What is equivalent diameter?
-The diameter of a sphere that is in some unique way similar to the particle in question
What is volume equivalent diameter?
-The diameter of a sphere that has the sam volume as the irregular particle
What techniques are used for measuring particle size?
- Sieving
- Sedimentation
- Microscopy
- Light scattering
The choice of technique used for measuring particle size is depend on?
- Applicable size range for sample
- Cost
- Time taken
- Skill required
- Precision
- Quantity of material needed
Sieving seperates fine material from course material by means of a series of woven or perforated surfaces. TRUE OR FALSE?
TRUE
What are some of the errors in sieving?
- 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
Settling velocity is not measured directly. TRUE OR FALSE?
TRUE
What are the advantages and disads of sedimentation
ADS
- measures relatively few particles
Disdas
-One of the few methods getting shape information
What are the advantages of particle size analysis by light scattering?
- Rapid
- Easy to use
- Wide applicability
- Wide size range
How does light scattering phenomena work?
- 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.
Given the scattering pattern we cannot directly compute the particle size. TRUE OR FALSE?
TRUE
How does the calculation work for laser diffraction sizer?
- 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
What instrument is used for particle counting?
-Coulter counter or elcetrical zone sensing technique
How does optical particle counting work?
- 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
The width can be diefined as the standard deviation. TRUE OR FALSE?
TRUE
What is a cumulative frequency representation?
-The % of particles above or below a given size
Sieving is the oldest method used, it is inexpensive and widely available. TRUE OR FALSE?
TRUE
Sieves seperate fine materials from course material by means of a series of woevn or perforated surfaces. TRUE OR FALSE?
TRUE
The smallest size for a sieve is 50 micrometers. TRUE OR FALSE?
TRUE
Fine meshes are readily damages and clogged. TRUE OR FALSE?
TRUE
What is the sieve equivalent diameter?
-The size of the sphere which will pass through the square hole
The conection between particle size and sedimentation velocity is given by stokes law. TRUE OR FALSE?
TRUE
Sedimentation can measure the amount of materials settled in a particular time. TRUE OR FALSE?
TRUE
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?
TRUE
What is a centrifugal sedimentation used to speed up?
-Settling particles
How does Andreasen pipette work?
-Removes samples over time and anylse particle content; calculate size distribution
How does a laser diffraction sizer work?
- 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
How does the calculation work for laser diffraction sizer?
- 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
What is hydrodynamics?
-The size of a sphere that moves at an identical rate to particle
How does electrical zone sensing work?
- 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
How does an optical particle counting work?
- 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
