Particle Size Analysis Flashcards
Particle size distribution
Histogram
- Shows incramental distribution
- Showing number of falling within a given size increment
Gemetric mean
- Progression root of first x second
Cumulative distribution
- Shows how much material
lies above or below a
particular size
Normal Histogram analysis
- Particle diameter In normal distribution
- Mean = Median = Mode
- Symetrical about the mean
Positive skew Histogram
- Mean > median > mode
- Normalised by replotting
the equivalent particle diameters using a logarithmic scale
Bimodal histogram
- Has two modes of particle distribution
- Not normal or log
Cumulative median split of distribution
- 50% split by the median into two half
- Undersize or oversize
- Use for <5 micrometer (undersize)
Linear probability graph
- Undersize by particle size
- Straight line means normal distribution
Lognormal distibution
- Plot on a cumulative frequency on normal graph
- If curved then plot on a lognormal graph if linear then lognormal
Dispersion central tendancy
- Tendency of the particle size to cluster around a particular value
- Mean/mode/median
Sample standard deviation
- Must -1 from the sample population (sum of n)
Coefficient of variation
- Normalise the standard deviation through division by the mean
- Compare degree of varience between sample population
- SD/mean x 100
D90/D10 Ratio
- polydispersity of powders, regardless of the distribution
model - 90% / 10% of particle diameter (small closser to 1 more uniform dose)
Sieving
- Fill with the sieve pan with powder
- Seal and agitate then weigh
- Large to small mesh & mesh no measures number
- Measure using sive equivalent diameter
Possible overestimates of undersize limitation of sieve
- Rod shaped particle size pass through sive verticle
- Hydroscopic could clamp togeth from moisture
Microscopy
- Light microscope
- Scanning lectron microscope
- Atomic force microscope
What does microscope measure
- Projected area diameter he diameter of acircle having the same area as the particle viewed on surface
- Use martins and feret diameter
Limitations of microscope
- May not be representitive of a selection of particles
Andreasen pipette
- Stokes law used to determine stokes diameter of particles suspened in powder
- Measurement of settling velocity
- Use centifugation speeding up the measurement
Limitations to Andreasen pipette
- Aggregation in water clampring not representitive of size
Electrical sensing zone
- Large particle cause resistance and bending when passing through
- Current pulse is directly proportional to the volume of the particle
Limitation of electrical sensing zone
- Limited to those particles that can be suitably suspended in an electrolyte solution
Laser Diffraction in static light
- Light waves diffracted on the
particle surface change their direction of travel dependent upon particle size - Amount of light hitting outer circles used to calculate the ammount of diffracted light on detector
Limitations of Laser Diffraction in static light
- Non-spherical causes diffused scatter patterns wich is difficult to accurately interperate
Photon correlation spectroscopy
Dynamic light scattering
- Particles diffused in fluid
- Calculation of angle of incidence of scattered lazer can be detected
- Measurement of the brownian motion relates to the size
What does photon correlation spectroscopy
measure?
- Measurement of the Hydrodynamic diameter
- This measurement shows the diameter of a sphere that diffuses at the same rate in liquid as the particle
Mie Theory
The Mie model takes into account both diffraction and diffusion of the light around the particle in its medium
High intensity particle shown on spectroscopy graph
- A high intensity particle shows more scattered light with slow fluctuations
Low intensity particle shown on spectroscopy graph
- Low intensity causes rapid fluctuations as less light is scattered and movement is faster
Limitations of Photon correlation spectroscopy
- Small amounts of large aggregates or dust particles can disturb the
size determination - Small particles can aggregate together
Cascade impactor
Particles break free of the
air stream, then impact on
the collection plates
What does a cascade impactor measure
- For measuring particle size of inhaled products
- Corresponds to area in the respiratory tract
- Measurement of aerodynamic diameter of sphere with same terminal velocity
Limitations of cascade impactor
- Does to indaviduals having different inhalation rates of flow canot determin that all is inhaled homogenously
