Pharmaceutical powders Flashcards
What is the principle of geometric dilution? (What is important when mixing powder with unequal quantities?)
- smallest weigh powder is titrated with an equal bulk of diluting powder
- 1st dilution is mixed with equal amount of diluents
- process goes on until all powder are intimately mixed
How does different particle size and different densities affect mixing powder?
for diff particle sizes reduce each powder size separately before mixing
for diff densities put lighter powder first then heavier powder on top
What is a powder?
- pool of solid particles
- particles can have the same composition or be mixture of chemical compositions
- usually <1000 micrometres
what are the two things powder particles tend to be?
1) irregular in shape
2) heterogeneously distributed
What does the equivalent sphere concept allow? However what does it provide?
- simplified size analysis for powder
- allows powder particles to be reimagined as a hypothetical sphere and using methods to then estimate its size
doesn’t provide true particle size but just an approx.
What is a common method to use to determine particle size?
sieving
- different size sieves are stacked on top of a receiver pan in decreasing order of mesh aperture size
- equivalent sphere diameter obtained Is calling sieving diameter; corresponds to min. aperture size
What is Martin’s diameter and Feret’s diameter? What does Ferets depend on?
Martins- length of a line that bisects the particle
Ferets- distance between drawn tangents (depends on particle orientation)
What changes if the particle size or the particle itself changes?
orientation diameter and tangent distance changes
What occurs when incident light hits a particle? What is this called?
It is
1) reflected; bounces off particle
2) absorbed; absorbed by particle
3) refracted; light changes direction pass through particle
4) diffracted; light changes direction hitting particle edge
light scattering
Size distribution is based on what?
- no of particles within each class size (number distribution)
- particles weight within each class size (weight distribution)
What happens to size distribution as variety of particle size is higher?
size distribution will become wider
this is obtained by frequency histogram/curve
For normal size distribution what does the curve look like?
curve is symmetrical on either side of the line
- mean, median and mode have the same value
What does +ve/-ve skewed size distribution graphs look like? Which has a higher mode and a higher mean
Positively skewed graphs go to the right and curve off to the right
Negatively skewed graphs shift to the left and curve off to the left
\+ve= mean> mode -ve= mode> mean
What will a log-normal distribution look like?
Why do we plot log scale?
- usually is skewed
- plotting on log normalises the size distribution
What is multimodal distribution and what does it look like?
- has two modes
- two peaks in the graph and two curves
- % frequency vs particle diameter on graph
What can you get from a cumulative frequency graph?
- you get the median but NOT the mean
- only get mean if distribution is normal
- look at particle diameter corresponding to % frequency of 50%
Flowability depends on?
Forces that drive flow:
- gravity
- particle mass
- angle of inclination
- applied mechanical force
Forces that resist flow:
- adhesion
- cohesion
- surface forces
- electrostatic interactions
when will a powder flow?
when the total flow-promoting forces > total drag forces
will a small or large particle have better flow properties with other parameters being equal?
a large particle
will have a spherical or irregular particle have better flow properties if all parameters being equal?
a spherical particle
For particles with <100um what happens to the adhesion/cohesion and flowability?
the adhesion and cohesion will increase
flowability will decrease
will particles with high or low density have better flow properties?
a powder with high density particles
- flow-promoting forces act more strongly and increase flow
what is porosity and at what percentage do powders aggregate?
porosity is a measure of how tightly/loosely particles are packed
aggregate- >50%
‘real’ powder- 30-50%
polydisperse - <26%
will powders with a high or low moisture content have better flow properties?
a low moisture content will have
- too low can backfire as moisture can prevent flow by becoming sticky
