Practical 4A

TITLE:

Sieving

OBJECTIVES:

• To determine particle size distribution of powder and the size of solid particle of  lactose and microcrystalline cellulose (MCC) by sieve nest.
• To determine the size of particles.  

DATE OF EXPERIMENT:

22 November 2016

INTRODUCTION:

Sieves are commonly used to break down agglomerates, and determine the size and size distribution of a particular powder. 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 vibrate, the sample is segregated onto the different sized sieves. The weight of sample retained on each sieve is then used to determine the particle size distribution as well as the mean diameter of the sample. In this practical, students are given two common excipients used in tablet formulation, namely lactose and the microcrystalline cellulose (MCC). Students are required to use a sieve nest to determine the particles size and the size distribution of both powders.

APPARATUS:

Mechanical sieve, sieve nest, large weighing boats, spatula, electronic balance

MATERIALS:

Microcrystalline Cellulose (MCC), Lactose

PROCEDURE:

1. 100g of lactose is weighed. 

 

2. The sieve nest is prepared in descending order, from largest diameter to the smallest, from top to bottom.

3. The lactose powder is placed at the uppermost sieve and the sieving process is allowed to proceed for 20 minutes and 10 minutes.

4. After that, the powder collected at every sieve is weighed and the particle size distribution in the form of a histogram is plotted.

5. The above procedures are repeated using MCC.

RESULT:

LACTOSE
DIAMETER OF SIEVE NEST (μm)	WEIGHT (g)
	20 MINUTES	10 MINUTES
356 - 500	27.9594	26.2340
301 - 355	47.1532	45.7467
213 - 300	6.2833	8.6832
201 - 212	2.5117	8.9177
151 - 200	0.0088	0.0672
46 - 150	0.0766	2.6130
0 - 45	13.8096	6.2178

MCC
DIAMETER OF SIEVE NEST (μm)	WEIGHT (g)
	20 MINUTES	10 MINUTES
601 - 710	3.0839	0.0036
426 - 600	2.7706	0.0007
301 - 425	3.1839	0.0485
151 - 300	3.1510	0.1148
54 - 150	6.9298	4.9990
51 - 53	44.4114	50.6871
0 - 50	9.9029	9.0179

DISCUSSION:

Particle size analysis is a particle size measurement, using variety of name of the technical procedure or laboratory techniques which determine the range of particle size or the average particle size of the size in the powder or liquid form. As a stack of sieves were prepared, the sieve that has larger opening size are placed above the ones that having smaller opening sizes.This means, the sieve that have diameter of aperture of 710µm will be placed above and followed by 600-50µm for MCC while diameter sieve for lactose from 500-45µm. From this experiment, the highest weight for MCC is 44.4114g at 53µm in 20 minutes while for lactose, the most particles accumulated at 355µm which have a weight around 45.7467g in 10 minutes.

There are many factors that lead to this result. As the lactose and MCC are two different materials, so both of them have different physical properties. It seems that MCC has been affected more than lactose due to the physical vibration that applied on the particles since the hardness surface of particle is the one that contribute to the reduction of particle size.

However, this experiment is not considered to be accurate because the loss of lactose may due to the error in weighing the lactose after sieving. There is possible that we did not tared the weighing machine properly before weighing our products. So the precaution that we need to take is by  make sure the weighing machine is tared properly before weighing the products. Next, the sieving nest itself is contaminated with other powder and it is not clean when we used the machine. This may affected our results. We need to make sure that the sieving nest is clean and dry before conducting the experiment to obtain accurate results. Then, the result might be inaccurate as the vibration of the sieving nest is not significant or strong enough in sieving the particles through the sieve diameter. So the precaution is we need to calibrate the sieving vibrator machine before using it for the experiment as to provide an accurate results.

QUESTIONS

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

The average particle size for lactose  is 301 μm to 355 μm while for MCC is 51 μm to 53 μm.

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

The other method that can be used for determine the size of particle is elutriation. The material can be separated by means of elutriator, which consists of a vertical tube up which the fluid is passed at controlled velocity.  Next, optical counting method, which is the materials, can be measured optically by sizing against a graticule and counting. But for a statically valid analysis, millions of particle must be measured. Electro resistance counting method and laser diffraction methods also can be used for determine the particles size. Other method is sedimentation techniques which is need a longest time to determine the finest particles. So this technique is capable for determining the particles size below 10 µm. Optical granulometry, time of transition and acoustic spectroscopy are the other methods for determining the size of particles. 

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

Particle size is important because it can affect the bulk properties, product performance, process ability, stability, and appearance of the end of product. For solid or suspension system, particle size is important in controlling the dissolution or solubility properties. Dissolution rate is directly proportional to particle surface area. Particle size distribution is also relevant as a narrow distribution produces more uniform dissolution. Formulations with even a small number of relatively large particles may take some time to dissolve completely. For suspensions, stability is an important issue because if the active ingredient settles there is a greater chance of non-uniform delivery. Particle size also affects the formulation's behaviour.  Particle size also can influence segregation behaviour. 

CONCLUSION:

In conclusion, many natural and manufactured materials occur in a diverse form, which means that they consist of differently shaped and sized particles. The particle size distribution is responsible for important physical and chemical properties such as mechanical bulk behavior, surface reaction, taste, miscibility, filtration properties and conductivity. Only a continuous monitoring of the particle size distribution can guarantee a constant product quality. This experiment clearly shows that methylcellulose crystalline (MCC) and lactose have different particle size distribution and can be differentiated according to the sizes by using a mechanical shaker of different apertures at each layer to sieve the powders. It can be concluded that the particle size distribution of lactose is larger than that of MCC. This is because most of the lactose particles are accumulated at the sieve nest of diameter 500-350µm while most of particles are accumulated at the sieve nest of diameter 53-50µm.

REFERENCES:

1. http://www.ninolab.se/fileadmin/Ninolab/pdf/retsch/documents/af_sieving_basics_2004_en.pdf
2. https://www.innopharmalabs.com/tech/applications-and-processes/particle-size-monitoring
3. http://www.dfepharma.com/en/excipients/lactose/sieved-lactose.aspx