DATE OF EXPERIMENT: 22 /11 /2016
PRACTICAL 4(A)
TITLE: SIEVING
OBJECTIVE(S):
· To determine the particle size distribution of a powder
· To determine the size of a particle
INTRODUCTION:
Sieve is a device with meshes or perforations through which finer particles of a mixture (as of ashes, flour, or sand) of various sizes may be passed to separate them from coarser ones, through which the liquid may be drained from liquid-containing material, or through which soft materials may be forced for reduction to fine particles and commonly used to break down agglomerates, and determine the size and size distribution of a particular powder. In this practical, students are given two common excipients used in tablet formulations, namely lactose and microcrystalline cellulose (MCC). Students are required to use a sieve nest to determine the particle size and the size distribution of both powders.
APPARATUS AND MATERIALS:
Lactose
Microcrystalline cellulose (MCC)
Weighing boat
Spatula
Sieve nest
PROCEDURES:
1. 100g lactose was weighed in the beaker.
2. The sieve nest was prepared in descending order (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 20 minutes.
4. Upon completion, the powder collected at every sieve was weighed and the particle size distribution was plotted in the form of a histogram.
5. The above process was repeated using MCC.
RESULTS:
Lactose 20 minutes.
Particle size (µm)
|
Mass of Lactose retained in the sieve (g)
|
% retained = (w sieve/w total)
x 100%
|
Cumulative percentage retained
|
% passing = 100% - cumulative percentage retained
|
500
|
27.9594
|
28.071
|
28.071
|
71.929
|
355
|
47.1532
|
47.342
|
75.413
|
24.587
|
300
|
6.2833
|
6.308
|
81.721
|
18.279
|
212
|
2.5117
|
2.522
|
84.243
|
15.757
|
200
|
0.0088
|
0.008
|
84.251
|
15.749
|
150
|
0.0766
|
0.077
|
84.328
|
15.672
|
45
|
13.8096
|
13.865
|
98.193
|
1.807
|
<45
|
1.7984
|
1.807
|
100.000
|
0
|
Lactose 10 minutes.
Particle size (µm)
|
Mass of Lactose retained in the sieve (g)
|
% retained = (w sieve/w total)
x 100%
|
Cumulative percentage retained
|
% passing = 100% - cumulative percentage retained
|
500
|
26.2340
|
26.56
|
26.56
|
73.44
|
355
|
45.7467
|
46.31
|
72.87
|
27.13
|
300
|
8.6832
|
8.79
|
81.66
|
18.34
|
212
|
8.9177
|
9.03
|
90.69
|
9.31
|
200
|
0.0672
|
0.07
|
90.76
|
9.24
|
150
|
2.6130
|
2.65
|
93.41
|
6.59
|
45
|
6.2178
|
6.29
|
99.70
|
0.30
|
<45
|
0.2968
|
0.30
|
100.00
|
0
|
MCC 20 minutes.
Particle size (µm)
|
Mass of Lactose retained in the sieve (g)
|
% retained = (w sieve/w total)
x 100%
|
Cumulative percentage retained
|
% passing = 100% - cumulative percentage retained
|
710
|
3.0839
|
4.20
|
4.20
|
95.8
|
600
|
2.7706
|
3.77
|
7.97
|
92.03
|
425
|
3.1839
|
4.34
|
12.31
|
87.69
|
300
|
3.1520
|
4.29
|
16.60
|
83.40
|
150
|
6.9298
|
9.44
|
26.04
|
73.96
|
53
|
44.4114
|
60.48
|
86.50
|
13.5
|
50
|
9.9029
|
13.48
|
100
|
0
|
MCC 10 minutes
Particle size (µm)
|
Mass of Lactose retained in the sieve (g)
|
% retained = (w sieve/w total)
x 100%
|
Cumulative percentage retained
|
% passing = 100% - cumulative percentage retained
|
710
|
0.0036
|
0.005
|
0.005
|
99.995
|
600
|
0.0007
|
0.001
|
0.006
|
99.994
|
425
|
0.0485
|
0.075
|
0.081
|
99.919
|
300
|
0.1148
|
0.177
|
0.258
|
99.742
|
150
|
4.9990
|
7.706
|
7.964
|
92.036
|
53
|
50.6871
|
78.134
|
86.098
|
13.902
|
50
|
9.0179
|
13.902
|
100
|
0
|
DISCUSSION:
Size reduction process is also termed as comminution or pulverization. The importance of particle size reduction is to aid efficient processing of solid particles by facilitating powder mixing or the production of suspensions, exposing cells prior to extraction and reducing the bulk volume of a material to improve transportation efficiency. Sieves are used to determine the particle size and the size distribution of both powders (MCC and Lactose). The method of using sieves is by putting MCC and Lactose powder in the most upper sieve. Then switch the plug and it will vibrate the sieve stack for 10 minutes. Each sieve can filter the powder to a smaller diameter. The highest diameter for the sieve is >500 µm followed by 355-500 µm, 300-355 µm, 212-300 µm, 200-212 µm, 150-200 µm, 45-150 µm and the lowest sieve diameter is <45 µm. After the sieving is finished, the result is obtained and recorded. The mass of powder for each sieve is measured by analytical balance. The mass obtained in different sieve indicates different size analysis of Lactose and MCC. The distribution of particle size of MCC and lactose is demonstrated experimentally.
Lactose and MCC have different material properties. These differences contribute to different size distribution as shown in Figure 3. For Y axis for the graph is percentage of mass powder (MCC or Lactose) retained in the sieve (g) per total mass of powder inserted times 100. (% retained = (w sieve/w total) x 100%). For X axis is Particle size (µm). Based on data collected in the experiment particle size (µm) for MCC is >500 and the percentage retained is 0.0051% while for Lactose is 0.0395%. For 425-500 particle size (µm) the percentage retained is 0.0071% (MCC) while for Lactose is 0.0046%. For 355-425 the percentage retained is 0.1473% (MCC) while Lactose 4.5437%. For 150-355 is 6.6879% (MCC) while lactose 26.8064%. For 45-150 is 90.1897% (MCC) while lactose 68.3500%. For <45 is 2.9629% (MCC) while lactose 0.2558%. From comparison of MCC and Lactose in the graph (Figure 3) we can deduce that MCC has finer and smaller particle size as compared to Lactose because the percentage retained of MCC in particle size (µm) >500, 355-425, 150-355 is lower than Lactose. This shows that particles of MCC is smaller than Lactose so that the tendency to pass through the sieves hole is higher, making the percentage retained lower in particle size (µm) >500, 355-425, 150-355 sieves.
The total mass retained in sieves for Lactose is 99.601 g. The mass of lactose when put in the sieves stack is 100.0064 g. There is lack of 0.4054 g in total mass retained. While handling this experiment after sieving is finished, we collect the total mass retained in each of the sieve but some of the powder is split. This lead to reduce of total Lactose mass retained in the sieve. The precaution can be made by more caution when handling this experiment to avoid error.
There are some sources of errors occurred during the experiment. First and foremost, apparatus used in the experiment contains impurities. Since the sieve nest is repeated used by several groups in the experiment, the sieve nest is not clean which contains impurities and might change the result. Therefore, we must wash and dry the sieve nest before use in other to obtain more accurate result. Next, the weight of lactose and MCC are different before and after the experiment. This is due to the dispersed and spilled of the tiny size and light powder to the surrounding. In order to get an accurate weight of lactose, do this experiment in a closed area and repeat the experiment.
CONCLUSION:
Sieving process is one of the methods to determine the size of particles. The distribution of particles size are able to be analyzed after conducting this experiment especially in achieving optimum production of efficacious medicines in pharmaceutical phase. The particles size of MCC is smaller than lactose.
REFERENCE(S):
1. Physicochemical Principles of Pharmacy, 3rd edition (1998). A.T. Florence and D.Attwood. Macmillan Press Ltd.
3. jsedred.sepmonline.org/content/35/3/750.abstract
QUESTIONS:
1. What are the average particle size for both lactose and MCC?
The average particle size for both lactose and MCC is in the range of 53µm - 150µm. It is
because the percentage of lactose and MCC retained is the highest.
The average particle size for both lactose and MCC is in the range of 53µm - 150µm. It is
because the percentage of lactose and MCC retained is the highest.
2. What other method can you use to determine the size of particle?
The other methods to determine the size of particle include LA - 960 laser diffraction technique, SZ - 100 dynamic light scattering techniques, PSA300 and CAMSIZER image analysis technique, microscopy, sedimentation, optical and electrical sensing zone method.
The other methods to determine the size of particle include LA - 960 laser diffraction technique, SZ - 100 dynamic light scattering techniques, PSA300 and CAMSIZER image analysis technique, microscopy, sedimentation, optical and electrical sensing zone method.
i. LA - 960 laser diffraction technique
The LA-960 combines the most popular modern sizing technique with state of the art refinements to measure wet and dry samples measuring 10 nanometers to 5 millimeters. The central idea in laser diffraction is that a particle will scatter light at an angle determined by that particle’s size. Larger particles will scatter at small angles and smaller particles scatter at wide angles. A collection of particles will produce a pattern of scattered light defined by intensity and angle that can be transformed into a particle size distribution result.
ii. SZ - 100 dynamic light scattering technique
The SZ-100 nanoPartica Dynamic Light Scattering (DLS) system measures particle size, zeta potential, and molecular weight from 0.3 nm to 8 μm at concentrations ranging from 0.1 mg/mL of lysozyme to 40% w/v.
iii. PSA300 and CAMSIZER image analysis technique
Two types of image analysis exist, namely static image analysis and dynamic image analysis. The samples measured by static image analysis typically rest on a slide that is moved by an automated stage. With the PSA300 static image analysis system a microscope and digital camera collect images of the particles as the slide is scanned. For dynamic image analysis, sample preparation is completely different since the sample itself is moving during the measurement. Sample preparation steps could include an ionizer to mitigate static interactions between particles thus improving flow ability or a sample director to specifically orientate particles through the measurement zone.
3. What is the importance of particle size in a pharmaceutical formulation?
Particle size is important in a pharmaceutical formulation because particle size is directly related to drug dissolution and drug solubility. Referring to Per Noyes-Whitney equation, dissolution rate is directly proportional to particle surface area. Smaller solid particles suspended in the liquid will be more uniform and no agglomerates will be formed. This can increase the uniformity and efficacy of drugs produced. Besides, smaller size of solid particles will have larger surface area to come into contact with the medium. This can ensure that the medicine produced can dissolve easily in the body system and function effectively when consumed. Furthermore, when the drugs are injected into the body system, small particle size can ensure that the drug particles will not block the blood vessels.
