PRACTICLE 4A:
Sieving
DATE:
16th
November 2015
OBJECTIVES:
1.
To determine the particle size
distribution of the powders, lactose and microcrystalline cellulose (MCC)
2.
To determine the different size of
particles containing fine and coarse aggregates by sieving.
INTRODUCTION:
Sieving
is the method that had been used not only by pharmacists, but also by a chefs,
housewives, gardeners and contractors. Sieving is the process of separating the
particles or solids substances from a mixture of solids or from the liquid
solution which cannot be conducted by hand-picking. This type of particles
separating methods is simple in concept, easy to use and is comparatively
inexpensive. In ancient times, the Egyptian used sieve to separate grain. But
in recent times, sieve are the most commonly used devices for separating the
particles according to their respective sizes in the range of 5µm to 125 000µm,
which were then are used to determine the distribution of the particle size and
this methods also used to break
down agglomerates in the
pharmaceutical practices.
In
this practical, we are given two common excipients which are used in tablet
formulations named lactose and microcrystalline cellulose (MCC). We are
required to use a sieve nest and sieve shaker in order for us to determine the
particle size and the particle size distribution for both of the powders.
EXPERIMENTAL
METHODS:
Apparatus:
Balance, weighing board,
spatula, sieve metal
Chemicals:
Lactose, Microcrystalline
cellulose (MCC)
Experimental
Procedures:
1.
100 g of MCC was weighed.
2.
The sieve nest was prepared in descending
order, the largest diameter to the smallest, from top to bottom.
3.
The powder was placed at the uppermost
sieve and the sieving process was allowed to proceed for 15 minutes.
4.
Upon completion, the powder collected at
every sieve was weighed.
RESULTS
AND CALCULATIONS:
Diameter (µm)
|
53
|
150
|
200
|
300
|
500
|
|
Weight (g)
|
40.3951
|
3.1585
|
1.6559
|
0.0978
|
0.0000
|
 |
||||||
QUESTIONS |
1.
What are the average particle size for both lactose and MCC?
The overall particle size for both lactose and
MCC is between 53 µm and 150 µm.
2.
What other methods can you use to determine the size of particle?
One
of the other methods that be used to determine the particles’ size is by using
microscopy. This method can helps in examining each particle individually and
distinguish aggregates from the single particles. Coupling to image analysis
computers, each fields can be examined hence a distribution can be obtained.
Furthermore, sedimentation methods is a method that depends to the velocity of
the particle in a fluid. The size distribution of the particle can be
determined by examining the suspension of the powder. Next is the coulter
counter. This methods is used to measure any particulate materials that are
suspended in an electrolyte. When the particles pass through the orifice of the
coulter counter, there will be disruptions in the electric impedance which is
proportional to the volume diameter and this volume is directly proportional to
the volume of the particles. In light scattering method, the particle size
distribution is determined by measuring the angular variation in the intensity
of the light scattered of a laser beam that pass through a dispersed
particulate sample. A bigger size particle will scattered light at small angles
while the small particles scattered light at big angles. The size of particles
will the can obtained by calculating the volume of equivalent sphere diameter
in the Mie Theory.
3.
What are the importance of particle size in a pharmaceutical formulation?
In
the Noyes-Whitney equation, the dissolution rates is directly proportional to
the surface area of the particles, which means that, the smaller the size
particles, the bigger the particles’ surface area exposed to the solvent, the
higher the rate of dissolution of the solute. Besides, the rate of drying up the
solids can also be reduced. This is due to the distance travelled by the
moisture particles to reach the surface is decreased. Other than that, the
reducing size of particles can helps in increasing the rate of combustion as
the area exposed to the air is bigger. In addition, for suspension type of
solution, the stability of the active ingredients is important and it is
reflected based on the distribution of the particles. A narrow distribution due
to the smaller size particles produces more uniform in solution. Based in
Stokes’ Law, the smaller the particles size, the lower the velocity of the
particles, the higher the stability of the suspensions as the sedimentation of
the suspension had been retarded. Last but not least, decreasing in particles’
size helps in increasing the bioavailability of the drug which is in the other
words, the ratio of the area calculated for oral route of administration to the
intravenous route of administration would be increased.
DISCUSSION:
In this experiment, we are required
to observe the distribution of particle size of lactose and microcrystalline
cellulose, MCC. To achieve this requirement, the method used is sieve analysis
which is the practice used to assess the particle size distribution of granular
materials. Sieve shaker and a set of sieve nest are the main apparatus that
were used to conduct this method. The
aperture of the sieve plates that we used had the range of diameter around 53
µm up to 425 53 µm and 53 µm up to 500 µm. The sieve plate with the biggest
diameter is placed the upper part of the sieve plate arrangement while the
smallest diameter of aperture of the sieve plate would be at the bottom of the
arrangement. These sieve nest will be then placed on the sieve shaker. After 15
minutes, each of the powder on each sieve plate are weighed to obtain the
distribution of size particles.
From the experiment conducted, the
result shows that most of the lactose particles’ size are in the range between
355 µm up to 25 µm, weighed 61.3789g out of 100g, which is also 61.38% of the
total weight. While for the MCC, most of its particles’ size are in the range
of less than 53 µm which is 53.6404 and 53.64% of the total weight. These
result proves that the particles size of lactose is much smaller and finer than
MCC. After each of the powder at each sieve plate are weighed, all the powders
are combined and weighed again. Unfortunately, both lactose and MCC total
weight before and after the sieving process are not same as 11% of MCC powder
is lost but 13.22% excess of lactose is obtained after the experiment.
This inaccuracy are due to several
reasons. Firstly, the sieve nest is not completely cleaned from foreign
substances. For example, dust or the residue of the powder left in the sieve
plate by the previous group that used the same apparatus. This error could
affect the final weight of the lactose. Secondly, the loss some of the powder
might due to the incorrect setting up of the sieve shaker or some of the powder
might escape to the air due to the air movement when the machine is operating
as the powder is light and fluffy. Next, the incorrect method of using the
electric balance is also one of the errors that contributes to an inaccurate
reading. Other than that, a finer particles are prone to attach to the sieve
nest and it is hard to ensure that all of the particle are completely weight.
So this would probably decrease the actual weight of the particles of the
powder. Last but not least, prolong duration of the sieving process could also
lead to an inaccuracy of the results as more of the fine particles are leaks
out of the machine and thus decrease the end weight of the powder.
To
avoid these errors, ensure that each of the sieve plate are from any dust or
residue of the powder. Besides, set up the sieve plates on the sieve shaker and
closed the lid tightly to prevent the leaking of powder during the sieving
process. In addition, use a brush and shakes the sieve plate slightly to ensure
that all of the powder are transferred completely to the weighing boat.
Finally, set a constant time taken for each of the experiment to decrease the
amount of the powder lost. In conclusion, the particle size of MCC is much more
smaller and finer than lactose as most of the MCC particles have sizes around
less than 53 µm while for lactose is around 355 µm up to 425µm.
CONCLUSION:
Sieving method is used to
determine the size of particles. Each of the particles have different and
irregular shapes. The size of particles were also different. Lastly, the errors
made in this experiment should be avoided in the future in order to obtain an
accurate result.
