PRACTICAL II : SIEVING

TITLE

Sieving

OBJECTIVES

i. To determine the size of particles.

ii. To break the agglomerate.

THEORY

Sieving classified material not only according to the size but also according to the shape and the roundness of the particles. The accurate particle-size measurement by sieving requires that consideration is given to particles shape and screen opening size variations. A mathematical sieving theory stemming from the idea of particle passing probability is developed.

METHODLOGY

i.  Material and apparatus

Lactose, microcrystalline cellulose (MCC), sieve nest

ii.  Procedure

a. 100g of lactose was weighted using electronic balance.

b. Sieve nest was prepared according to the given size of the sieve.

c. The lactose powder was poured into the sieve nest.

d. The sieve nest was sieved for 20 minutes.

e. The powder was weighted separately from each sieve and a graph was plotted regard to the particle size of the powder.

f. The experiment was repeated using MCC.

RESULT

Sieve opening	Mass of lactose remained in each sieve/ g ( W sieve)	% retained = (W sieve/ W total) x 100%	Cumulative % retained	% passing= 100% - cumulative % retained
425 - 500µm	0.0162	(0.0162/100) x 100% = 0.016%	0.0162	100 – 0.0162 = 99.9838
300 - 425µm	0.0170	(0.0170/100) x 100% = 0.017%	0.0162 + 0.0170 = 0.0332	100 – 0.0332 = 99.9668
151 - 300µm	0.0267	(0.0267/100) x 100% = 0.027%	0.0332 + 0.0267 = 0.0599	100 – 0.0599 = 99.9401
46 - 150µm	11.5400	(11.5400/100) x 100% = 11.540%	0.0599 + 11.5400 = 11.5999	100 – 11.5999 = 88.4001
45µm	30.5777	(30.5777/100) x 100% = 30.578%	11.5999 + 30.5777 = 42.1776	100 – 42.1776 = 57.8224
< 45µm	57.5240	(57.5240/100) x 100% = 57.52%	42.1776 + 57.5240 = 99.7016	100 – 99.7016 = 0.2984

Sieve opening	Mass of MCC remained in each sieve/ g ( W sieve)	% retained = (W sieve/ W total) x 100%	Cumulative % retained	% passing= 100% - cumulative % retained
425 - 500µm	3.5x 10-3	(3.5x 10-3/100) x 100% = 0.004%	3.5x 10-3	100 – 0.0035 = 99.9965
300 - 425µm	4.3x 10-3	(4.3x 10-3/100) x 100% = 0.004%	3.5x 10-3+ 4.3x 10-3 = 7.8x 10-3	100 – 0.0078 = 99.9922
151 - 300µm	0.0787	(0.0787/100) x 100% = 0.079%	7.8x 10-3+ 0.0787 = 0.0865	100 – 0.0865 = 99.9135
46 - 150µm	4.9485	(4.9485/100) x 100% = 4.949%	0.0865+ 4.9485 = 5.0350	100 – 5.0350 = 94.9650
45µm	42.1931	(42.1931/100) x 100% = 42.193%	5.0350 + 42.1931 = 47.2281	100 – 47.2281 = 52.7719
< 45µm	51.8688	(51.8688/100) x 100% = 51.867%	47.2281 + 51.8688 = 99.0969	100 – 99.0969 = 0.9031

Graph I

Graph II

DISCUSSION

Sieve analysis is used to obtain the particle size distribution of a solid material by determining the amount of powder retained on a series of sieves with different sized apertures. A sample is added to the top of a nest of sieves arranged in decreasing size from top to bottom. As the sieves are vibrated, the sample is segregated onto different sized sieves. The weight of sample retained on each sieve is then used to determine the particle size distribution.

Theoretically, the smaller the size aperture of the sieve nest, the more the powder we can get from the sieve nest. From the mass of powder remained in each sieve nest, we can calculate the retained percentage as well as passing percentage. By comparing the both graph of MCC and lactose, we know that the particle size of MCC is smaller than lactose.

In the formulation, the uniformity of the particle size of the powder and also the roundness play an important role in the pharmacodynamics properties of the medicine. It will affect the absorption rate and stability of the formulation.

CONCLUSION

From the graph, we can conclude that the particles size of MCC is smaller than lactose.  Proven the cumulative percentage retained for lactose is 99.7016%. While the cumulative percentage retained for MCC is 99.0969%.

QUESTIONS

1. What is the overall size particles of lactose and MCC?

Less than 45µm for both lactose and MCC. This is because most of the lactose and MCC powder were found in the sieve nest which the size of aperture is less than 45µm.

2. What is other method can be used to measure the size of particular particles?

Electron microscope analysis can be used to measure particles size.

3. What are the importance of size particles in the formulation?

The particle size will affect the dissolution rate, absorption rate, content uniformity and stability of the medicine in the body. 

REFERENCE

i. Theory of sieving [Online]

Available from: jsedred.sepmonline.org/content/35/3/750.abstract

ii. Particle shape and inference of size from sieving [Online]

Available from: onlinelibrary.wiley.com/doi/10.1111/j.1365-3091.1968.tb00853.x/abstract