Title:
Sieving
Objective:
To determine particle
size distribution of powder and the size of solid particle of lactose and
microcrystalline cellulose (MCC) by using sieve nest.
Introduction:
Particle size and shape characteristics
are critical properties for a large number of pharmaceutical processes. There
exist many methods of particle size characterisation of materials. These
methods include microscopy, sieve analysis, laser diffraction, backlight
imaging and direct imaging.
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A sieve test is performed by first assembling a stack of interlocking sieves. In this stack the sieve with the largest openings is at the top each lower sieve will have a smaller opening than the one above it. A pre-weighed sample of the material to be tested is placed in the top sieve. This sieve stack is the shaken until all the material has either been retained on a sieve or passed through. The weight of sediment retained on each sieve is measured and converted into a percentage of the total sediment sample. This method is quick and sufficiently accurate for most purposes. A sieve test analysis or distribution is calculated which shows the proportion of each particle size category in the sample.
Materials:
·
Lactose
·
Microcrystalline
cellulose (MCC)
Apparatus:
·
Sieve
nest
·
Spatula
·
Weighing
boats
·
Electronic
balance
Procedure:
1.
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100G lactose was weighed.
2. The
sieve nest is prepared in descending order (largest diameter to the smallest,
from top to bottom)
3. The
powder is placed at the uppermost sieve and the sieving process is allowed to
proceed for 20 minutes.
4. Upon
completion, the powder collected at every sieve is weighed and the particle
size distribution is plotted in the form of a histogram.
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5. The
above process is repeated using MCC.
Results and
calculation:
|
Particle size range
(µm)
|
Lactose
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|
Mass of lactose
retained in each sieve nest (g)
|
% retained =
(W sieve/W total )x
100%
|
Cumulative % retained
|
% passing =
100% -cumulative %
retained
|
|
|
x >425
|
0.0171
|
(0.0171/99.5442)x
100% = 0.0172 %
|
0.0172
|
100- 0.0172 =99.9828
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|
300<x≤425
|
0.1443
|
(0.1443/99.5442)x
100% = 0.145%
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0.0172 + 0.145 = 0.1622
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100-0.1622 =99.8378
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200<x≤300
|
1.0212
|
(1.0212/99.5442)x 100%
= 1.0259%
|
0.1622+ 1.0259 = 1.1881
|
100-1.1881 =98.8119
|
|
150<x≤200
|
32.4183
|
(32.4183/99.5442)x
100% = 32.5667%
|
1.1881 + 32.5667
= 33.7548
|
100- 33.7548 =66.2452
|
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50<x≤150
|
62.4312
|
(62.4312/99.5442)x
100% = 62.7171%
|
33.7548 +62.7171 = 96.4719
|
100- 96.4719 =3.5281
|
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0<x ≤50
|
3.5121
|
(3.5121/99.5442)x
100% = 3.5282%
|
96.4719 + 3.5282 =100.00
|
100-100 =0
|
Initial
weight of lactose: 100g
After
sieving, weight of lactose:
3.5121+62.4312+32.4183+1.0212+0.1443+0.0171=
99.5442g
Percentage
of mass loss during sieving: (100 – 99.5442) / 100 x 100% = 0.4558%
|
Particle size range
(µm)
|
MCC
|
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|
Mass of MCC retained
in each sieve nest (g)
|
% retained =
(W sieve/W total )x
100%
|
Cumulative % retained
|
% passing =
100% -cumulative %
retained
|
|
|
x >425
|
0.0503
|
(0.0503/99.559)x 100%
= 0.0505%
|
0.0505
|
100- 0.0505 =99.9495
|
|
300<x≤425
|
0.1382
|
(0.1382/99.559)x 100%
= 0.1388%
|
0.0505 + 0.1388 = 0.1893
|
100-0.1893 =99.8107
|
|
200<x≤300
|
1.7704
|
(0.17704/99.559)x100%
= 1.7782%
|
0.1893 + 1.7782 = 1.9675
|
100 – 1.9675 =98.0325
|
|
150<x≤200
|
3.8783
|
(3.8783/99.559)x 100%
= 3.8955%
|
1.9675 + 3.8955 = 5.8630
|
100- 5.8630 =94.137
|
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50<x≤150
|
92.576
|
(92.576/99.559)x 100%
= 92.9816
|
5.8630 + 92.9816 =98.8446
|
100- 98.8446 =1.554
|
|
0<x ≤50
|
1.1502
|
(1.1502/99.559)x 100%
= 1.1553%
|
98.8446 + 1.1553 =99.9993
|
100-99.9993 =0.0007
|
Initial
weight of MCC: 100g
After
sieving, weight of MCC:
0.0503+0.1382+1.7704+3.8783+92.5716+1.1502
= 99.559g
Percentage
of mass loss during sieving: (100 – 99.559) / 100 x 100% = 0.441%
Discussion
In this experiment, the particle
size distribution of lactose and microcrystalline cellulose (MCC) are
determined using sieving method. The sieve nest are arranged in descending
order from 425µm, 300µm, 200µm, 150µm to 50µm so that particle with size larger
than the diameter of aperture can retained in the sieve nest while the smaller
one can pass through it.
From the experiment above, most
particle size of lactose are in the range of 50-150 µm which is 62.7171% followed
by 150-200µm which is 32.5667%, while for MCC, most particles size are in the
range of 50 -150 µm which is 92.9816%. This is because the particle size of MCC
is finer than lactose as more MCC powder can pass through the sieve nest with
150 µm aperture. The physical vibration that
exerted on the particles having greater effect on MCC compared to lactose. Besides,
different materials have different physical properties which include the
surface hardness of solids that will influence the reduction of size particles.
Initially, the mass of both lactose and MCC is 100g while
after sieving, the mass collected are 99.5442g and 99.559g respectively. The
weight after sieving is slightly less than the before which is 0.4558% for
lactose and 0.441% for MCC. This
may because some particles left in the sieve nest and some spilled out from the
container during preparation and sieving. Air movement in the laboratory may
also be one of the reasons causing the error of experiment as the particles is
light and fluffy. Hence, the particle size distribution obtained for both
lactose and MCC may not be accurate. To improve the accuracy of the result,
various precautions should be carried out such as clean the sieve nest with
brush to remove any residue in it before using and set up the machine correctly
and carefully to reduce the spilling out of particles.
Questions
1.
Explain in brief the various statistical methods that you can
use to measure the diameter of a particle.
·
Laser Diffraction
A laser beam is passed through a sample of particle.
Particles will scatter light at an angle that is directly related to their
size. Large particles scatter light at narrow angles with high intensity while
small particles scatter at wider angles with low intensity.
·
Dynamic Light Scattering
This method is
a non-invasive and sensitive technique used for measuring the size of molecules
and particles in the submicron region. It can measure particles, emulsions or molecules, which have been dispersed or
dissolved in a liquid. The Brownian motion of particles or molecules in
suspension causes laser light to be scattered at different intensities.
Analysis of these intensity fluctuations yields the velocity of the Brownian
motion and hence the particle size using the Stokes-Einstein relationship.
·
Sedimentation
Andreason
pipette or centrifuges and X-rays can be used in this method. The main
advantage of this technique is that it determines particle size as a function
of settling viscosity. However, as the density of the material is needed, this
method is not suitable for emulsions where the material does not settle or for
dense material that settles too quickly. It is also based on spherical
particles, so can give large errors for particles large aspect ratio.
·
Image Analysis
This
technology generates data by capturing direct images of each particle,
providing users with the ultimate sensitivity and resolution. Image analysis
systems are capable of high-resolution sizing ranging from 0.5µm – 1000µm. Subtle
differences in particle size and shape can be accurately characterised using
this method.
·
Coulter counter
This
instrument measures particle volume. The number and size of particles suspended
in an electrolyte is determined by causing them to pass through an orifice an
either side of which is immersed an electrode. The changes in electric
impedance (resistance) as particles pass through the orifice generate voltage
pulses whose amplitude are proportional to the volumes of the particles.
2.
State the best statistical method for each of the samples
that you have analysed.
Conclusion
Size of particles can be determined
using sieving process. After sieving, 62.7171%
of lactose are in the range of 50 - 150µm while as for MCC, 92.9816% are in the
range of 50 - 150µm. This shows that most particles in MCC is smaller than
those of lactose.
Reference
1.
Particle size: Sieves. http://www.cscscientific.com/particle-size/sieves
2.
Particle characterisation. http://www.innopharmalabs.com/tech/particle-characterisation
3.
An Overview of the Different Particle Size Measurement Techniques.
October 8th, 2010. http://www.atascientific.com.au/blog/2010/10/08/overview-particle-size-measurement-techniques/
4.
Dynamic Light Scattering (DLS) http://www.malvern.com/en/products/technology /dynamic-light-scattering/
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