PHM2213 practical
533558275
PHM2213 Physical Pharmacy 2
Particle size analysis: Sieves and Microscopy
Objective
To determine the size of powder/granule sample and the distribution, by using
both sieving and microscopic methods.
Introduction
Microscopy can be used to estimate the size of particles and their distribution. In
addition, through the microscope, one may be able to observe the shape of the
particle. This however, cannot be said when using the sieve method. However, the
sieve method is by far the cheapest technique available for the determination of
particle size. When the size distribution is great and when the shape of particle is
inconsistent, the results from both methods can be expected to be vastly different.
Microscopy will give the number average particle size whilst the sieve method
produces a weight average particle size.
Experimental procedure
A) Sieving method
1. Weigh 100 g of sample to 2 decimal places.
2. Weigh all the sieves one by one to 2 decimal places, Wi. Make sure that the
sieves are clean.
3. Arrange the sieves with the smallest size,X1, at the bottom. Note the sizes of
the sieves.
4. Pour the sample into the top sieve.
5. Using a vibrator/mechanical shaker, allow the sample to go through the sieves
for 15 minutes.
6. Weigh each sieve to 2 decimal places, Wf. Note the size of the sieve.
7. Tabulate your results. Refer to Table 1 and Table 2.
8. Plot the undersize distribution: size against % cumulative weight.
9. From the plot above, estimate the following:
a. d(0.5) or mean
b. d(0.1)
c. d(0.9)
d. polydispersity index: d(0.9) – d(0.1)/d(0.5)
10. From the undersize plot, plot particle size against % weight.
11. Answer the following in your discussion:
a. Does the plot in no. 10 show a normal distribution? If not, why?
b. Were the sizes of the sieves appropriate? Explain.
c. What are the advantages and disadvantages of the sieving method?
d. In which stage of production can this method be used?
Prepared by: Kausar Ahmad
Date created: 6-November-2004
Date of revision: 17-November-2004
Page 1 of 4
PHM2213 practical
533558275
Table 1 Sieving data – Sample A
Size of screen
Wo (g)
Wf (g)
(m)
bottom pan
X1
X2
X3
X4
X5
X6
Ws (g): Wf Wi
a
b
c
d
e
f
g
Total H g
particle size
(m)
<X1
X1-X2
X2-X3
X3-X4
X4-X5
X5-X6
>X6
Table 2 Size (weight) distribution using the sieve method – Sample A
Size
Cumulative weight % cumulative weight
X1
a
a/H x 100%
X2
a+b
a+b/ H x 100%
X3
a+b+c
a+b+c/ H x 100%
X4
a+b+c+d
a+b+c+d/ H x 100%
X5
a+b+c+d+e
a+b+c+d+e/ H x 100%
X6
a+b+c+d+e+f
a+b+c+d+e+f/ H x 100%
Prepared by: Kausar Ahmad
Date created: 6-November-2004
Date of revision: 17-November-2004
Page 2 of 4
% weight
a/H x 100%
b/H x 100%
c/H x 100%
d/H x 100%
e/H x 100%
f/H x 100%
g/H x 100%
PHM2213 practical
533558275
B) Microscopic method
1. Observe the sample under an optical microscope.
Refer to the operation manual.
Record the type of microscope and the magnification used.
2. Take a picture of a representative sample, consisting of at least 50 particles,
together with a scale.
3. Measure the size of all particles captured in the picture to 1 mm.
4. Tabulate your results. Refer to Table 3 and Table 4.
5. Based on your data (Table 4), plot the size distribution: size against % number.
6. Plot the undersize distribution: size against % cumulative number.
7. From the plot (no. 5), estimate the following:
a. d(0.5) or mean
b. d(0.1)
c. d(0.9)
d. Calculate the polydispersity index: d(0.9) – d(0.1)/d(0.5)
Table 3 Microscopy data – Sample A
Size
No. of Average size
particles
x1
n1
Standard deviation
x2
n2
Minimum size
x3
n3
Maximum size
x4
n4
Range, R
x5
n5
Number of divisions
x6
n6
Size interval, r
x7
n7
Smallest unit of measurement
Total no. particles
∑ni = N Start size, d1
∑xi ni / ∑ni
size max – size min
√N (round up to ODD no.)
R/√N
0.1 m
size min – (0.1 m/2)
Table 4 Size (number) distribution using the microscopic method – Sample A
Mid size
No.
%
% cumulative
Size range (m)
particles
number
number
(m)
d1- (d1+r)
d2 – d3
d2=d1+r
d3– d4
d3=d2+r
d4 – d5
d4+d5 /2
d5 – d6
d6 – d7
Total no. particles
N
Prepared by: Kausar Ahmad
Date created: 6-November-2004
Date of revision: 17-November-2004
Page 3 of 4
PHM2213 practical
533558275
Write a report and submit one week after the practical.
Include the following in your discussion:
1. Describe the plots obtained from the two methods.
2. Is there a difference between d(0.5) and the calculated average for both
methods. Explain.
3. Explain the difference in the results obtained from the two methods.
4. Why is it necessary to have a minimum of 50 particles for the microscopic
method to calculate the average particle size?
5. In your opinion which is the easiest method to use? Explain.
6. What are the advantages and disadvantages of each method?
7. Include copies of pictures taken in your report. Label them properly.
Prepared by: Kausar Ahmad
Date created: 6-November-2004
Date of revision: 17-November-2004
Page 4 of 4