Particle Size Analysis Flashcards
Why is particle size important
Affects Physicochemical and pharmacological properties
Affects processing properties of powders
Affects formulation performance
Martins diameter
Length of the line which bisects the image of a particle
Feret diameter
The distance between two tangents on opposite sides of the particle parallel to some fixed direction
Incremental histograms
Reflects the distribution of particle sizes
Presents an interpretation of the particles] size distribution
Leptokurtic
Distribution which is pointed
Platykurtic
Distribution which is flattened
Central tendency
The tendency of the particle size to cluster around a particular value
Averages or means
Types of particle size analysis
Sieve analysis
Microscopy
Sedimentation
Coulter counter
Laser diffraction
Dynamic light scattering
Sieve equivalent diameter
Defined as the minimum square aperture through which the particle will pass
Advantages of sieve analysis
Inexpensive easy to perform
Well established
Disadvantages of sieve analysis
Time consuming
Problems of reproducibility
Humidity, static electricity and powder cohesive can affect results
Particles may break or agglomerate during sieving
2D measurements
Advantages of microscopy
Inexpensive
Small sample size
Individual particles sized
Images can be captured
Disadvantage of microscopy
Expensive (electron)
Time consuming
Low throughput
2D measurement
Operator dependent
Sedimentation analysis
Particles with different size settle at different velocities
Advantages of sedimentation analysis
Lost cost
Useful for cases where sedimentation is key
Disadvantage of sedimentation analysis
Labour intensive
Particles must be insoluble in the dispersion medium
Temp control is required
Particle shape affects its settling rate
Coulter counter
Measurement by conductivity
Particles pass through the aperture opening, they bend the current flux lines around the particles
Longer length for the current to pass and a higher resistance to the current
Amplitude of current is directly proportional to the volume of the particle
Advantages of coulter counter
Rapid measurement
Large number of particles counted- reproducibility and reliable
Simple to use
Wide range of sizes measured
Disadvantages of coulter counter
Particles have to be suspended in an electrolyte liquid
Limited choice of liquid media
Blockage of orifice by oversized particles]needs calibration
Expensive
Laser diffraction
Technique based on laser diffraction derive particle size information from patterns of light scattering of the sample
Advantages of laser diffraction
Quick and simple
No calibration is required
High reproducibility
Testing is non destructive and non intrusive
Entire sample is measured
Suitable for a wide range of sample
Disadvantages of laser diffraction
Refractive index should be known
Refractive index difference required between particles and dispersion medium
Expensive
Dynamic light scattering
Used to measure nano particulate colloid systems using photon correlation spectroscopy
Advantages of DLS
Quick and simple
No calibration is required
High reproducibility
Testing is non destructive and non intrusive
Entire sample is measured
Nano particle size range
Disadvantages of DLS
Samples must be dispersed in liquid
Particle particle interaction at increased concentration
Multiple scattering at increased concentration
Expensive
