TITLE:
Sieving
OBJECTIVES:
- To determine the particle size.
- To determine the size distribution of both powders
APPARATUS:
mechanical sieve, sieve nests, large weighing boats, spatula, brush, electronic
balance, label
CHEMICALS:
microcrystalline cellulose (MCC), lactose
INTRODUCTION:
Sieving is basically a method used to assess the particle size distribution (also called gradation) of a granular
material. It is one of the extremely old technique where the sieve stack is
usually comprises of 6 to 8 sieves. The powder is loaded on the coarsest sieve
and are subjected to mechanical vibration for 20 minutes or less according to
the desired time range. Just like any other method, the sieve method do have
its own advantages and disadvantages. Sieving benefits in the terms of cost as
it is cheap not to mention that it is readily usable for large particles. The
disadvantages can be seen where the method is unable to measure sprays and
emulsions. Besides, sieving is a very poor reproducibility for wet sieving. In
this experiment, the sieve method is used to sieve MCC and also lactose for 20
minutes and 10 minutes respectively.
PROCEDURE:
- 100g
of lactose are weighed
the picture shows 100g of lactose powder in weighing boat - The sieve nests are prepared and arranged in descending order ( start from bottom: smallest diameter, top part: largest diameter)
-
The
lactose powders are poured into uppermost sieve and proceed to sieving process
for 20 minutes.
- After
finished sieving process, the powders are collected from each sieve and then
weighed each powder obtained from different sieve.
- The particle size distributions are plotted in the form of histogram.
- All the steps above are repeated using MCC powder.
RESULTS:
1.
LACTOSE
SIZE OF THE SIEVE NEST (µm)
|
PARTICLE SIZE RANGE (µm)
|
LACTOSE
|
|||
10 MINUTES
|
20 MINUTES
|
||||
WEIGHT (g)
|
FREQUENCY (%)
|
WEIGHT (g)
|
FREQUENCY (%)
|
||
710
|
x<710
|
16.6162
|
16.7560
|
3.32
|
2.71
|
600
|
600<x≤710
|
44.2657
|
44.6382
|
3.01
|
2.45
|
425
|
425<x≤600
|
0.6282
|
0.6335
|
2.70
|
2.20
|
300
|
300<x≤425
|
26.4944
|
26.7174
|
18.15
|
14.79
|
150
|
150<x≤300
|
0.8332
|
0.8402
|
23.79
|
19.39
|
53
|
53<x≤150
|
10.0649
|
10.1496
|
54.00
|
44.01
|
50
|
50<x≤53
|
0.2128
|
0.2146
|
12.57
|
10.24
|
<50
|
x≤50
|
0.0501
|
0.0505
|
5.26
|
4.29
|
TOTAL
|
99.1655
|
100
|
122.71
|
100
|
|
2.
MCC
SIZE OF THE SIEVE NEST (µm)
|
PARTICLE SIZE RANGE (µm)
|
MCC
|
|||
10 MINUTES
|
20 MINUTES
|
||||
WEIGHT (g)
|
FREQUENCY (%)
|
WEIGHT (g)
|
FREQUENCY (%)
|
||
710
|
x<710
|
0.0126
|
0.0127
|
2.8085
|
2.3018
|
600
|
600<x≤710
|
0.1159
|
0.1167
|
2.7503
|
2.2541
|
425
|
425<x≤600
|
0.1267
|
0.1276
|
3.0490
|
2.4989
|
300
|
300<x≤425
|
1.2817
|
1.2906
|
3.9029
|
3.1988
|
150
|
150<x≤300
|
0.4695
|
0.4728
|
3.1775
|
2.6042
|
53
|
53<x≤150
|
3.4532
|
3.4773
|
5.4994
|
4.5072
|
50
|
50<x≤53
|
60.1720
|
60.5912
|
42.5846
|
34.9018
|
<50
|
x≤50
|
33.6766
|
33.9112
|
58.2404
|
47.7331
|
TOTAL
|
99.3082
|
100
|
122.0126
|
100
|
|
DISCUSSION:
Lactose
and microcrystalline cellulose are used in this experiment. The method that is
used to determine the particle size is sieving method. The diameter of the
sieve nest are from 710 µm to <50 µm.
The sieves are stacked on top of each other in ascending degrees of
coarseness, and the powder to be tested is placed on the top sieve. The nest of
sieves is completed by a well-fitting pan at the base and a lid at the top. The
literature provides additional sources of information about the performance of
sieving analysis. The nest of sieves is subjected to a standardized period of
agitation, which causes the powder sample to distribute between the sieves.
Agitation can be conducted using vibration, rotation–tapping, or ultrasound.
The horizontal sieve motion loosens the powder packing and permits sub sieve
particles to pass through. Vertical motion mixes the particles and brings more
of the sub sieve particles to the screen surface. The sieving analysis is
complete when the weight on any of the test sieves does not change by more than
5% of the previous weight on that sieve.
Based on the result obtained for the
experiment, the frequency of lactose sieved for 10 minutes is higher at the
range of 600<X≤710, while sieving for 20 minutes the frequency of lactose is
higher at the range 53<X≤150. The frequency of MCC sieved for 10 minutes is
higher at the range 50<X≤53, while the frequency of MCC sieved for 20
minutes is higher at the range X≤50 µm. From the result we can see that lactose
has bigger size of particle compared to MCC. This is because different
materials have different particle size and different physical properties.
There are some error that occur during the
experiment. One of it is the spillage of lactose and MCC during sieving,
transferring of the powder and weighing of the powder. Next, some of the powder
remains attached at the brush during transferring of the powder. Finally the
weighing boat are not clean thoroughly which causes the powder to be left in
the weighing boat and disturb the reading.
The precaution steps that must be taken are:
1. Make sure that the
weighing boat are clean before taking any reading.
2. Make sure the sieving
machine is tightly clamped in order to avoid spillage of the powder during
sieving.
3. Tapping the brush until
all the powders are completely fell off from it.
QUESTIONS:
- What are the average particle size for both lactose and MCC?
The average particle size
for lactose 20 minutes is between the range 53 μm to 150 μm where the average
particle size for lactose 10 minutes is between the range 600 μm to 710 μm.
The average particle size
for MCC 20 minutes is below 50 μm and for MCC 10 minutes is from range 50 μm to
53 μm.
2.What
other methods can you use to determine the size of particle?
Besides sieving
method, other techniques can also be used to determine the particle size of
particles. The methods are:
· Microscopic
method.
In microscopic
method, the types of microscope that can be used is the light microscope,
transmission electron microscope (TEM) and scanning electron microscope (SEM)
as well as automatic and image analysis microscope nevertheless it depends on
the size of the particles. Microscope method using light microscope is an
excellent technique as it allows us to directly look at the particle and
examine its shape which is in 2D, detect the presence of agglomeration or good
dispersion of the particles, colour and others. At the same time, microscopic
technique is relatively cheap and permanent record by photograph are obtained
as well as only small sample sizes are required. However, it is not suitable
for quality control as it highly depends on skill and time consuming.
Additionally, this method causes rapid operator fatigue and biased result.
Next, if microscopic method is done using TEM and SEM, the particles are
individually examined and detailed observation of the size and shape can be
obtained but TEM and SEM are highly expensive and time consuming. In addition,
it has low throughput. When automatic and image analysis microscope is used, it
is faster and give out an unbiased result but it is very expensive and have no
human judgment to help separate out the aggregates like semi-automatic
microscopes.
· Coulter
counter
The coulter
counter is a method that uses electrical stream sensing zone method. It
measures particle volume which can be expressed as Vd where the
equivalent diameter is the same as the particle’s volume diameter. To determine
the number and size of the particle, the particle must first pass through the
opening. As the particles pass through the opening, it causes impedance and
generates voltage amplitude that are proportional to the volumes of the
particles. Therefore, powder samples are first dispersed in an electrolyte to
form a very dilute suspension. Next, the suspension is subjected to ultrasonic
agitation to break up any aggregates and then dispersant is added to break more
aggregates. When electrical current flows in the circuit, the particles pass
through the opening and or sensing zone calculate the size of the particles
pass through by calculating the volume dispersed as volume dispersed is equal
to the volume of particle that pass through.
·
Laser light scattering
method
Laser light uses light diffraction to analyzes the
particle size and it is very flexible to be used for dry powders, aerosols,
suspensions, emulsions and sprays because it has a wide dynamic range of 0.2 to
2000 μm. The diffraction of the laser light results from the interaction of the
light with the particle. When a particle pass through the laser beam, it will
scatter light at an angle that is related to the particles’ size so particles
that have a bigger size will scatter more narrow light but with higher
intensity and vice versa for smaller size particle. Laser light scattering
method gives out rapid and high resolution results.
·
Dynamic light scattering
method
Photon
correlation spectroscopy (PCS) is usually for more fine particles and it uses
the Brownian motion particle to measure particle size. Brownian motion is the
random movement of small particles caused by collision with a smaller molecule
of the suspending liquid. PCS analyses the constantly changing patterns of
laser light scattered or diffracted by particles in Brownian motion and
monitors the rate of change of scattered light during diffusion meaning by
looking at the rate of fluctuation. The results are expressed as particle
hydrodynamic particle. The dynamic light scattering method is an accurate,
repeatable and reliable technique in determining particle size.
Besides,
other methods such as Sedimentation Techniques and Permeametry Technique can
also be used to analyse the size of particles.
3.What
are the importance of particle size in a pharmaceutical formulation?
Particle size is
important in the drug’s performance for example in its dissolution, solubility,
bioavailability, content uniformity, stability, or product appearance as well
as in the drug’s manufacturability for instance, in flowability, blend
uniformity, and compactibility. However the effect of particle size in
manufacturability is frequently not considered. The dimension of particles are
crucial in achieving optimum production of efficacious medicines.
In the formulation
of drugs, during drug synthesis, drugs need to have a small size, such as so
that it can fit into the receptors in the body. Furthermore, in the production
of formulated medicine, the drugs must be in uniform size that have uniformly
same content to make sure for the correct dosage of the medicine. Next, in the
administration of the medicine, injectible drugs should be in size smaller than
the blood capillaries to avoid blockage or burst in the capillaries.
Additionally, the particle size affects the solubility of the drug as the
smaller the size of the drug, the more surface area exposed and the higher the
solubility of the drug.
CONCLUSIONS:
REFERENCE:
- Alfred.N Martin. 2006. Martin’s Physical Pharmacy and Pharmaceutical Sciences: Physical Chemical and Biopharmaceutical principles in the Pharmaceutical Sciences. Patrick J. Sinko, Yashveer Singh, David B. Troy. 6th Edition. Maryland: Lippincott William & Wilkins.
- http://www.slideshare.net/HORIBA/essentials-of-particle-size-analysis
- Dr Haliza Katas. 2016. Particle Size Analysis. Slaid. Fakulti Farmasi Universiti Kebangsaan Malaysia.
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