PRACTICAL 4 (Part A): Sieving

Title: Sieving

Objectives:

1. To determine the size and size distribution of a particular powder.

2. To classify and differentiate the powder based on its diameter.

Date of experiment: 16^th November 2015

Introduction

            Sieving is one of the oldest particle size analysis methods. This sieving method is used to classify powders and granules by particle size distribution. The sieves are arranged in decreasing order of the sieve number. The particle size that passes through the sieve also decreases from top to bottom. In this experiment, 100g of microcrystalline cellulose (MCC) is weighed and placed on the uppermost sieve. The sieves are shaken rigorously on a mechanical shaker for a certain period. The MCC powder collected at each sieve is weighed and recorded.

Apparatus:

1.      Mechanical sieve

2.      Sieve nests

3.      Large weighing boats

4.      Spatula

5.      Electronic balance

Materials:

1.      Microcrystalline cellulose (MCC)

2.      Lactose

Experimental Procedure:

1.      100g MCC and lactose were weighed.

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 at every sieve was collected and the weight is measured.

5.      The particle size distribution of MCC and lactose were plotted in the form of a histogram.

Results :

Lactose
Diameter of sieve nest (µm)	<150	150-212	213-299	300-354	355-425	>425
Weight (g)	0.3021	8.1646	6.46963	3.2764	48.3759	33.3162

MCC
Diameter of sieve nest (µm)	<53	53-149	150-199	200-299	300-500	500
Weight (g)	17.5855	76.8885	3.3547	1.8236	0.2216	0.1261

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. In this experiment, the sieve method is used.  There are two types of sieve analysis, dry sieving and wet sieving. Dry sieving can used in cement industry, fertilizer industry and building construction while wet sieving is special used in ceramic industry, pharmaceutical industry and cosmetic industry. Sieve is a device for separating particles of different sizes. Coarse particles which are in different particle size are separated by passing through the sieve nest with different diameters which arrange from largest diameter to the smallest diameter.

            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 and contain impurities. This alter the final results which is the average particle size of lactose and MCC.  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. The precaution of this error is do the experiment in a closed area and repeat the experiment to get the average result.

Questions:

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

Between 355-425µm lactose and 54-149µm MCC.

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

Microscope method-an excellent technique because we can look at the shape and size of the particles directly.

Coulter counter-it uses electrical stream sensing zone method where it measures the material that can be suspended in an electrolyte.

Laser light scattering method-it uses laser diffraction which results from interaction of light with particles.

Dynamic light scattering method-Brownian motion principle is used to measure particle size and the photon correlation spectroscopy (PCS) analyses the changing patterns of laser light scattered.

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

Particle size is important in pharmaceutical formulation because it has an effect on the absorption of drugs. Particle size also affects the disintegration time of the tablets. Besides, the particle size of a pharmaceutical semi-solid dosage influences the efficacy, safety and performance of the dosage form. It affects the penetration of the drug into the skin and also the flux rate of the active ingredient. 

Conclusion:

Sieving is one the methods that can be used to separate solids such as powders of different sizes. This experiment clearly shows that methylcellulose crystalline (MCC) and lactose have different particle size distribution and can be differentiated according to sizes by using a mechanical shaker of different apertures at each layer to sieve the powders. From the results, it can be concluded that the particle size distribution of lactose is larger than that of MCC because most of the lactose particles are accumulated at the sieve nest of diameter 355-425µm, while most of the MCC particles are accumulated at the sieve nest of diameter 54-149µm.

References:

http://www.pharmainfo.net/tegkmurthy/blog/influence-particle-size

http://www.pharmacopeia.cn/v29240/usp29nf24s0_c786.html