Practical 2: Sieving
Aim:
To
determine the particles size distribution of lactose and microcrystalline
cellulose (MCC) by using the sieving
method.
Introduction:
The
particle-size distribution (PSD) of a powder, or granular material, or
particles dispersed in fluid, is a list of values or a mathematical function
that defines the relative amount, typically by mass, of particles present
according to size. PSD is also known as grain size distribution. The way PSD is
usually defined is by the method by which it is determined. The most easily understood
method of determination is sieve analysis, where powder is separated on sieves
of different sizes. In this experiment we are using the sieving method via the
help from the sieving shaker’s machine. The use of sieves with different sized
mesh is one of the oldest, most reliable, and most commonly used methods for
providing an analysis of particle size distribution. Although sieve shakers
have limitations based on the assumption that all particles are spherical, they
work well for a wide variety of applications, and because it is relatively
inexpensive, is generally the first method employed by companies when a
particle size distribution analysis program is initiated.
Moreover, sieving, microscopy, computerized
image analysis, laser diffraction, sedimentation, and centrifugation, are some
of the particle size analysis methods by which a samples particle
characterization may be established.
Procedure:
1) A
100g of lactose is weighed by using the weighing balance.
2) A
set of sieve nest is prepared according
to descending order from top to below the size must be from larger to smallest
diameter of the sieve plate.
3) Then
the lactose is placed into the top of the sieve nest. The set of the sieve nest
is then being set up to the sieve shaker’s machine.
4) The
machine is start and the time is set up at 15 minutes.
5) After
the sieving is done, the remaining lactose that is left at every stage of the
sieve is weighed and a graph of particle size of distribution is plotted.
6) The
process is repeated by using microcrystalline cellulose (MCC).
Results:
<45 mic
|
45 mic
|
46-150
mic
|
151-300
mic
|
301-425
mic
|
426-500
mic
|
WEIGHED
Size of
Sieve nest (µm)
|
lactose
(g)
|
MCC
(g)
|
(%)
lactose
|
(%)
MCC
|
||
sieve
1 (UP) (426-500)
|
0.0162
|
0.0035
|
0.0162
|
0.0035
|
||
sieve
2 (301-425)
|
0.0267
|
0.0043
|
0.0267
|
0.0043
|
||
sieve
3 (151-300)
|
0.016
|
0.0787
|
0.016
|
0.0787
|
||
sieve
4 (46-150)
|
30.5684
|
4.9485
|
30.5684
|
4.9485
|
||
sieve
5 (45)
|
57.515
|
51.8688
|
57.515
|
51.8688
|
||
sieve
6 ( <45 )
|
11.1436
|
42.1931
|
11.1436
|
42.1931
|
||
Total %
|
99.2859
|
99.0969
|
||||
Calculation:
% of particles passing through the sieve nest=
weighed of substance after
sieving x 100
total weight of substance before sieve
example1, lactose (sieve 1): 0.0162x100
100
=0.0162
%
Size of particles (µm) vs percentage of
lactose/MCC passing through the sieve nest
Discussion:
In
this experiment, we are using the sieve method in order to determine the
particles size distribution between lactose and microcrystalline cellulose by
using the sieving shaker machine. Note that we row the sieve stack from the top
to the bottom according to the size of the sieve nest that is from largest size
(top) to the smallest size (bottom). From the result we can say that the MCC
have a smaller size of molecules because it can pass through the bottom of the
sieve more than lactose. Moreover we can predict that the size of MCC is <45µm
because it can pass through the sieve nest of the size of <45 µm. While for the lactose, we can
predict that the size of particles of lactose is approximately 45µm because
mostly lactose are well distributed until at the size of sieve of 45µm.
Thus this supports the theory as we can
determine the particle size distribution by using sieving method. If we notice
that the total percentage of particles passing through the sieve nest are not
exactly 100%, supposedly we should get both lactose and MCC 100% but due to
some errors we only get 99.2859% of lactose and 99.0969% of MCC. This might be
due to some errors during the experiment. For examples, there might be errors
during transferring of substance from sieve nest to weighing boat; maybe not
all of the substances are perfectly being transferred, thus this will effects
the results.
Question:
1. What
are the average particle size for lactose and MCC?
Even there still have a small
portion of particle size for lactose and MCC between size 150µm and 500µm, the
overall average particle size for lactose and MCC are found within less than
150µm. Based on the result, MCC have a smaller size of molecules because it can
pass through the bottom of the sieve more than lactose.
2.
What are the other
method that can be used to identify the size of
a particle rather than sieving method?
The other method that can be used
to identify the size of a particle
rather than sieving method are microscopy methods, laser light scattering
method, dynamic light scattering method, backlight imaging, direct imaging,
sedimentation method and electrical stream sensing zone method (coulter
counter).
3.
What are the importance
of particle size in a certain formulation?
The particle size of a substance is
important to make a certain formulation. The size of a particle can affect bulk
properties, product performance, processibility, stability and appearance of
the end product. The link between particle size and product performance is well
documented with regards to dissolution, absorption rates and content
uniformity. Reducing particle size can aid the formulation of NCE’s with poor
water solubility. Proper matching of active ingredient and excipient particle
size is important for several process steps. Particle size analysis is an
integral component of the effort to formulate and manufacture many
pharmaceutical dosage forms
Conclusion:
From
the result of the experiment we can say that microcrystalline cellulose has a
greater distribution of particles compare to lactose as its size much smaller
than lactose that is <45µm thus make it more reliable to pass through the
sieve nest. And we can agree that sieve method also can be used in order to
determine the particle size distribution although it may have some limitations
as compared to the other method.
References:
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