Objective:
To determine the particle size distribution of a
powder and the size of the particles.
Introduction:
Sieving is used to classify
powders by particle size distribution. Sieving is most suitable where the
majority of the particles are larger than about 75µm although it can be used
for some powders having smaller particle sizes where the method can be
validated. In pharmaceutical terms, sieving is usually the method of choice for
classification of the coarser grades of single powders. It is a particularly
classify the powder based on particle size and in most cases the analysis can
be carried out in the dry state. Among the limitations of the sieving method
are the need for an appreciable amount of sample (normally at least 25g) and
difficulty in sieving oily or other cohesive powders that tend to clog the
sieve openings. The method is essentially a two-dimensional estimate of size
because passage through the sieve aperture is frequently more dependent on
maximum width and thickness than on length.
Analytical test
sieves are constructed from a woven-wire mesh which is of simple weave that is
assumed to give nearly square apertures and is sealed into the base of an open
cylindrical container. The basic analytical method involves stacking the sieves
on top of one another in ascending degrees of coarseness and then placing the
test powder on the top sieve. The nest of sieves is subjected to a standardized
period of agitation and then the weight of material retained on each sieve is
accurately determined. The test gives the weight percentage of powder in each
sieve size range. This sieving process for estimating the particle size
distribution of a single pharmaceutical powder is generally intended for use
where at least 80%of the particles are larger than 75µm.The size parameter
involved in determining particle size distribution by analytical sieving is
the length of the side of the
minimum square aperture through which the particle will pass.
During this experiment, lactose and
microcrystalline cellulose were used to allow sieving process. Basically, a
selection of highly consistent lactose products suitable for most of your Oral
Solid Dose Form (OSDF) applications where as microcrystalline cellulose
is one of the most important and widely-used of all excipients.
Microcrystalline cellulose is a key diluent for drug formulations and an
essential component for almost every kind of oral dosage including tablets,
capsules, sachets, pellets and others.
Apparatus:
1)
Balance
2)
Sieve nest
3)
Weighing boat
4)
Beakers
5)
Spatula
6)
Microscope slide
7)
Specimen
8)
Microscope
Material:
1)
Lactose
2)
Microcrystalline cellulose
(MCC)
3)
5 different types of sands
Method
(part A):
1.
100g of lactose was
weighed.
2.
The sieve nest was
preparing in descending order in which from largest diameter to the smallest
and from top to bottom.
3.
The powder was placed at
the uppermost sieve and the sieving process was allowed to proceed for 10
minutes.
4.
Upon completion, the powder
collected at every sieve was weighed and the particle size distribution in the
form of histogram was plotted.
5.
The process above was
repeated using microcrystalline cellulose.
Method
(part B):
1.
5 different types of sands
and powders such as microcrystalline cellulose and lactose were prepared.
2.
The sand that put under the
microscope with specimen and slide was observed.
3.
The structure and shape of
the sand particles was captured.
Results:
Part
A
MCC
NO
|
SIEVE DIAMETER (RANGE)
|
MASS OF WEIGHING BOAT AND MCC
|
MASS OF WEIGHING BOAT
|
MASS OF MCC
|
1
|
0<x≤45
|
2.7936
|
2.7887
|
39.8085
|
2
|
45<x≤150
|
2.5931
|
2.4902
|
54.9343
|
3
|
150<x≤300
|
5.1424
|
3.3012
|
3.3412
|
4
|
300<x≤425
|
6.3262
|
2.9850
|
1.8412
|
5
|
425<x≤500
|
57.8043
|
2.8700
|
1.1029
|
6
|
>500
|
43.1416
|
3.2731
|
0.0049
|
FIGURE 1: GRAPH OF SIEVE DIAMETER
AGAINST THE MASS OF MCC
LACTOSE
NO
|
SIEVE DIAMETER (RANGE)
|
MASS OF WEIGHING BOAT AND MCC
|
MASS OF WEIGHING BOAT
|
MASS OF LACTOSE
|
1
|
0<x≤45
|
0.2114
|
0.1196
|
0.0918
|
2
|
45<x≤150
|
23.0573
|
1.0121
|
22.0452
|
3
|
150<x≤300
|
27.4139
|
3.3010
|
24.1129
|
4
|
300<x≤425
|
56.7855
|
2.9550
|
53.8305
|
5
|
425<x≤500
|
3.1125
|
3.1004
|
0.0121
|
6
|
>500
|
0.2014
|
0.1918
|
0.0096
|
FIGURE 2: GRAPH OF SIEVE DIAMETER
AGAINST THE MASS OF LACTOSE
Part B
Lactose
 |
MCC
 |
·
Total magnification =
40×
·
The particles are
spherical in shape
·
The size of particle
is smaller than the sand particles but smaller than the MCC powder.
|
·
Total magnification =
40×
·
The particles are
needle like in shape
·
The size of particle
is smaller than the sand particle but bigger than the
|
|
|
500 micron
 |
·
Total magnification = 40×
·
The particles are irregular in shape
·
Large in size compare to the other
types of sand particles and the powder particles.
|
·
Total magnification = 40×
·
The particles are irregular in shape
·
Smaller than the type 1 sand particles
but bigger than the other types of sand particles
|
Mixed sand
|
|
·
Total magnification =
40×
·
The particles are
irregular in shape
·
Smaller than the type 1 and 2 sand
particles but bigger than the other types of sand particles
|
·
Total magnification =
40×
·
The particles are
irregular in shape
|
150 micron
 |
·
Total magnification =
40×
·
The particles are
irregular in shape
·
Sand particle is small
in size but bigger than the particles found in powder
|
Discussion:
Sieving
is the process by which the particles of various sizes passed through the
perforations of the sieve to separate them from coarser to finer. In this
experiment , MCC and lactose were observed. The sieve stack was placed from top
to bottom according to the size of the sieve nest that is from largest size to
the smallest. The sieve that have
diameter of aperture of 500 µm will be placed at the above followed by 425 µm,
300 µm, 150 µm, 45 µm and less than 45
µm.
According
to the results obtained , MCC has particle size of around 45µm as the highest amount of MCC powder remained at the sieve while
lactose has size particles of range 151µm-300µm
as the highest amount of lactose powder remained at the sieve. From here, we
can conclude that MCC powder is finer than lactose powder.
This
experiment also cannot be considered very accurate as there are some errors
during the experiment. There is still some amount of MCC or lactose powder that
stuck at the gaps of the sieve where the exact amount of powder cannot be
determined. Besides , the particles are very light and easily loss to the
surroundings during handling of the sample. Furthermore , the sieve might be
contaminated by other powder of MCC or lactose where it is done by the previous
group.
Some
precautions need to be taken in order to minimise the errors of the experiment.
Before we start the sieving process, clean the sieve thoroughly using brush to
avoid any foreign powder stick on the sieve that might affect the results. Next
, make sure that we cover the powder before taking it to another place so that
the powder would not be blown out and try to carry out the experiment in a non
windy area.
The
light microscope is used to observe the sands and powders (MCC, lactose) with
40X magnification. The sands and powder need to be dispersed on the slide until
a thin layer is formed. From the observation, there are various sizes and
shapes of sands. The sizes are observed from the smaller ones to the bigger
size. The shape of the sands are irregular with sharp and pointy edges. As for
powder of MCC and lactose, the particles have regular shape; round, averagely
similar sizes and smooth edges.
1.
There are various statistical
method that can be used to measure the diameter of a particle, which are the
Feret's diameter (dF), Martin’s diameter (dM), Projected area diameter (da) and
perimeter diameter (dp). Feret's
diameter is the perpendicular distance between parallel tangents touching
opposite sides of the profile. In other words, the boundary separating equal
particle areas. Next, Martin's diameter, which is the mean chord length of the
projected outline of the particle. The
lines may be drawn in any direction which must be maintained constant for all
image measurements. While the projected area diameter is the diameter of a
circle having the same area as the projected area of the particle resting in a
stable position. As for perimeter
diameter, it is the diameter of a circle having the same circumference as the
perimeter or projected outline of the particle.
2. The best statistical method for each
sample is the Feret's diameter (dF). The measure can be done in a few
orientation for randomly oriented particles and the average or mean value can
be calculated for the accurate diameter.
Conclusion:
1)
The size of MCC particles are in the range between 45um to 150um.
2)
The size of lactose particles are in the range between 300um to 425um
3)
MCC has finer particle size than lactose
4)
All samples of sand particles in this experiment have irregular shape under 40x
magnifications and the type 5 sand has the smallest in size particles than
others
Reference:
W.
H. Walton, Feret‘s Statistical Diameter as a Measure of Particle Size
http://www.nature.com/nature/journal/v162/n4113/abs/162329b0.html
http://www.nature.com/nature/journal/v162/n4113/abs/162329b0.html
