Practicle 3: Sieving

Date

17th November 2014

Objectives

To determine the particle size and the size distribution of both powders.

Introduction

A sieve is a device for separating wanted elements from unwanted material or for characterizing the particle size distribution of a sample, typically using a woven screen such as mesh or net. Sieves are the most commonly used devices for particle size analysis. The sieving process is comparatively inexpensive, simple in concept and easy to use. In sieving process, we use lactose and microcrystalline cellulose (MCC) by using sieve nest.

Apparatus and Materials

Lactose

 microcrystalline cellulose (MCC)

 weighing machine

 mechanical sieve shaker with stack of sieves

Procedures

1. 100g of lactose was weighed

2. A 'sieve nest'  was prepared in ascending order and assigned appropriate sieve size.

3. The lactose powder was put into the sieve.

4. Then, lactose powder was sieved for 20 minutes.

5. The results obtained was recorded and a graph on powder particle size distribution was built.

6. The process was repeated with MCC.

Results

Size (diameter) of aperture  (µm)	Particle size range (µm)	MCC		Lactose
		Weight (g)	Frequency (%)	Weight (g)	Frequency (%)
<50	0<x≤50	60.0473	59.9483	4.9536	4.9675
50	50<x≤150	34.1569	34.1006	93.1901	93.4518
150	150<x≤200	3.2373	3.2320	1.2056	1.2090
200	200<x≤300	1.7847	1.7818	0.3625	0.3635
300	300<x≤425	0.9293	0.9278	0.0082	0.0082
425	>425	0.0096	0.00958	0.0000	0.0000
Total		100.1651	100	99.7200	100

Graph

Discussion

Two types of materials which are lactose and microcrystalline cellulose (MCC) have been used in this experiment. Sieving methods is used to determine the particle size distribution. The stack of sieve nest, which have larger opening size above the smaller opening sizes, have the diameter of aperture of 50µm, 150µm, 200µm, 300µm, and 425µm.

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 of the experiment, the frequency of the MCC is higher at the range of particle size 0<x≤50 µm which is 59.9483. While the particle range for the lactose 50<x≤150 µm with the frequency 93.4518. This show that the particle of the lactose is bigger compared to the particle size of the MCC. This is also due to MCC and lactose is two different materials and it has different physical properties.

During the experiment, there is some error happen. The weight of the lactose and MCC is changed after the sieving process is done. The amount of the lactose is decreasing and this can be cause by the little amount of powder still left in the sieves and some of it is spilled out from the sieve nest when the powder was pouring into the weighing boat. The amount of the MCC is increasing might be due to the left powder at the sieve nest by the other group. This can affect the result obtained.


To avoid this happen, the container must be clean by the brush before using it again. The machine must be set up correctly to avoid the error along the process happen so that the experiment can be carried out without any problems.

Questions

1. What are the average particle size for both lactose and MCC?

The average particle size for both lactose and MCC are <50µm, 50µm, between 50µm and 150µm, between 150µm and 200µm, between 200µm and 300µm, between 300µm and 425µm, and >425µm.

2. What other methods can you use to determine the size of particle?

The other methods to determine the size of particle are:
• Laser light scattering method
Light scattering is a non-invasive technique for characterizing macromolecules and a wide range of particles in solution. In contrast to most methods for characterization, it does not require outside calibration standards. In this sense it is an absolute technique.

• Dynamic light scattering method
Dynamic Light Scattering (DLS) is nowadays used on a routine basis for the analysis of particle sizes in the sub-micrometer range. It provides an estimation of the average size and its distribution within a measuring time of a few minutes.

• Coulter counter
A coulter counter is an apparatus for counting and sizing particles suspended in electrolytes. It is used for cells, bacteria, prokaryotic cells and virus particles.  A typical Coulter counter has one or more micro channels that separate two chambers containing electrolyte solutions. As fluid containing particles or cells is drawn through each micro channel, each particle causes a brief change to the electrical resistance of the liquid. The counter detects these changes in electrical resistance.

• Sedimentation methods
Sedimentation method is a widely used analysis method that produces extremely high resolution size distributions of microscopic to sub-microscopic particles. The normal measurement range for the method is from about 0.02 micron (20 nanometers) to about 30 microns (30,000 nanometers), though it is possible with some types of materials to extend the range to below 0.01 micron or to 50 microns or more.

3. What are the importance of particle size in pharmaceutical formulation?

The particle size distribution of active ingredients and excipients is an important physical characteristic of the materials used to create pharmaceutical products. The size, distribution and shape of the particles can affect bulk properties, product performance, process ability, stability and appearance of the end product.


The link between particle size and product performance is well documented with regards to dissolution, absorption rates and content uniformity. Reducing particle size can aid the formulation of NCE’s with poor water solubility. Proper matching of active ingredient and excipient particle size is important for several process steps. Particle size analysis is an integral component of the effort to formulate and manufacture many pharmaceutical dosage forms.

Conclusion

Sieving process can be used as one of the method to determine the size of particles. After conducting the experiment, the distribution of particles can be known and the optimum production of drugs in medicine can be achieved in pharmaceutical phase.

References

1. http://images.alfresco.advanstar.com/alfresco_images/pharma/2014/08/22/f88b360d-1d82-4141-8d33-1643a3ec6357/article-40975.pdf

2. https://www.sympatec.com/EN/Science/Characterisation/13_DynamicLightScattering.html

3. http://www.wyatt.com/theory/theory/understandinglaserlightscatteringtheory.html

The particle size range of lactose and MCC is being weighed: