Objective :
1.
To analyse and
interpret the shape of particles with five different samples
2. To observe and compare the size of particles for each
sample.
Date of Experiment : 30 September 2014
Introduction :
The dimensions of
particulate solids are important in achieving optimum production of efficacious
medicines. When drug is synthesized and formulated, the particle size of drug
and other powder is determined and this influences the subsequent physical
performance of the medicine and the pharmacological of the drug.
Powder with
different particle sizes have different flow and packaging properties, which
alter the volumes of powder during each encapsulation or tablet compression
event. The particles which are having small dimensions will tend to increase
the rate of solution.
In order to obtain
equivalent diameters with which to analyse and interpret the particle size of
powder, it is necessary to carry out a size analysis using different methods.
One of the method for particle analysis is using microscope.
Material/Apparatus :
1.
Electron Microscope
2.
Five (5) different
samples (A=850mic, B=500mic, C=355mic, D=150mic,E=various size)
Procedure :
- 5 different types of samples were analysed by using microscope, by observing the size and shape of given particle.
- The samples were examined first by 4x10 magnification, followed by 10x10 magnification.
- The particle shape is sketched and the overall particle shape of that material is stated.
(Magnification:
10x for all observations)
Discussion :
The
ability to analyze and characterize particle size and shape can significantly
improve the manufacturing efficiency and product performance. Thus, we can use
of microscopy and image analysis as the most reliable technique to characterize
particle shape, size and volume distribution. From this practical, it is found
that the overall shape of the sand is asymmetrical. One of the methods used to
measure a particle is the projected area diameter which is based on the
equivalent area to that of projected image of the particle. Another method is
the projected perimeter diameter which is based on the circle having the same
perimeter as the particle. Both of the methods do not account the 3 dimensional
shape of particle (orientation). They only consider the 2 dimensions of the
particle, thus it is inaccurate for unsymmetrical particle.
During the experiment, we put
different types of sand on slide to be directly observed them using a light
microscope. The sand should be spread evenly and just thin layer to avoid
agglomeration that will affect the observation. We observed that the particles
are irregular in shape. The size analysis is carried out on two-dimensional
image of particles which are generally assumed to be randomly oriented in
3-dimensional and they are viewed in their most stable orientation.
Feret’s and Martin’s diameter that
considering the orientation of the particles is one of the methods to measure
the diameter of particle. Feret’s diameter is the mean distance between two
parallel tangents to the projected particle perimeter while Martin’s diameter
is the mean chord length of the projected particle perimeter. The best
statistical method is Feret’s and Martin’s diameter because both of them use
statistical diameter which are the average over many different orientations to
produce a mean value for each particle diameter. Besides, since it is accessing
the three-dimensinal image of particle, we can use the electron microscope that
considering the orientation and shape of the image.
Conclusion:
As a conclusion, each of the particles have different
shape and they are irregular. The shape is not fix. The size of particles also
various. This show that the granulation is important to ensure that flowability
of drug can be achieved.
Question :
1.
Explain in brief the
various statistical methods that you can use to measure the diameter of a
particle.
Equivalent diameter
|
Symbol
|
Definition
|
Equation
|
Drag diameter (or frictional drag diameter)
|
dd
|
Diameter of a sphere having the same
resistance to motion in a fluid as the particle in a fluid of the same
density (ύf) and same
viscosity (η), and moving at the same velocity (v) (ddapproximates to ds when the particle Reynolds number (Rep) is small and
particle motion is streamlined. i.e. Rep < 0.2)
|
FD=CDAύfv22
where CD A = f(dd) (i.e. FD = 3πddηv) |
Feret’s diameter
|
dF
|
The mean value of the distance between pairs
of parallel tangents to the projectedoutline of the particle. This can be considered
as the boundary separating equal particle areas.
|
None
|
Free-falling diameter
|
df
|
Diameter of a sphere having the same density
and same free-falling speed as the particle in a fluid of the same density
and viscosity
|
None
|
Hydrodynamic diameter
|
dh
|
Diameter calculated from the diffusion
coefficient according to the Stokes-Einstein equation
|
D=1.38×10−12T3πηdm2s−1
|
Martin’s diameter
|
dM
|
The mean chord length of the projected outline
of the particle
|
None
|
Projected area diameter
|
da
|
Diameter of a circle having the same area (A) as the projected area of the particle resting in a
stable position
|
A=π4da2
|
Perimeter diameter
|
dp
|
Diameter of a circle having the same perimeter
as the projected outline of the particle
|
None
|
Sieve diameter
|
dA
|
The width of the minimum square aperture
through which the particle will pass
|
None
|
Stokes diameter
|
dSt
|
The free-falling diameter (df, see above) of
a particle in the laminar flow region (Rep < 0.2)
|
Under these conditions
dst2=dv3dd
|
Surface diameter
|
ds
|
Diameter of a sphere having the same external
surface area (S) as the particle
|
S=πds2
|
Surface volume diameter
|
dsv
|
Diameter of a sphere having the same external
surface area to volume ratio as the particle
|
dsv=dv3ds2
|
Volume diameter
|
dv
|
Diameter of a sphere having the same volume (V) as the particle
|
V=π6dv3
|
2.
State the best
statistical method for each of the samples that you have analysed.
Martin’s diameter and Feret’s
diameter is the best statistical method to measure the diameter of particle.
Conclusion :
As a conclusion,
each of the particles have different shape and they are irregular. The shape is
not fix. The size of particles also various. This show that the granulation is
important to ensure that flowability of drug can be achieved.
References :
1.
Michael E.Aulton, 2007,
Aulton's Pharmaceutics The Design And Manufacture
Of Medicines,
Third Edition, Churchill Livingstone
Elsevier (page 122-134)
2.
http://www.horiba.com/fileadmin/uploads/Scientific/Documents/PSA/PSA_Guidebook.pdf
3.
http://www.tcd.ie/CMA/misc/particle_size.pdf
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