Experiment 2 :Seiving

Objective:

To determine the particle size distribution of a powder and the size of the particles.

Introduction:

Sieving is used to classify powders by particle size distribution. Sieving is most suitable where the majority of the particles are larger than about 75µm although it can be used for some powders having smaller particle sizes where the method can be validated. In pharmaceutical terms, sieving is usually the method of choice for classification of the coarser grades of single powders. It is a particularly classify the powder based on particle size and in most cases the analysis can be carried out in the dry state. Among the limitations of the sieving method are the need for an appreciable amount of sample (normally at least 25g) and difficulty in sieving oily or other cohesive powders that tend to clog the sieve openings. The method is essentially a two-dimensional estimate of size because passage through the sieve aperture is frequently more dependent on maximum width and thickness than on length.

Analytical test sieves are constructed from a woven-wire mesh which is of simple weave that is assumed to give nearly square apertures and is sealed into the base of an open cylindrical container. The basic analytical method involves stacking the sieves on top of one another in ascending degrees of coarseness and then placing the test powder on the top sieve. The nest of sieves is subjected to a standardized period of agitation and then the weight of material retained on each sieve is accurately determined. The test gives the weight percentage of powder in each sieve size range. This sieving process for estimating the particle size distribution of a single pharmaceutical powder is generally intended for use where at least 80%of the particles are larger than 75µm.The size parameter involved in determining particle size distribution by analytical sieving is the length of the side of the minimum square aperture through which the particle will pass.

During this experiment, lactose and microcrystalline cellulose were used to allow sieving process. Basically, a selection of highly consistent lactose products suitable for most of your Oral Solid Dose Form (OSDF) applications where as microcrystalline cellulose is one of the most important and widely-used of all excipients. Microcrystalline cellulose is a key diluent for drug formulations and an essential component for almost every kind of oral dosage including tablets, capsules, sachets, pellets and others.

Apparatus:

1)      Balance                                              

2)      Sieve nest

3)      Weighing boat

4)      Beakers

5)      Spatula

6)      Microscope slide

7)      Specimen

8)      Microscope

Material:

1)      Lactose

2)      Microcrystalline cellulose (MCC)

3)      5 different types of sands

Method (part A):

1.      100g of lactose was weighed.

2.      The sieve nest was preparing in descending order in which from largest diameter to the smallest and from top to bottom.

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

4.      Upon completion, the powder collected at every sieve was weighed and the particle size distribution in the form of histogram was plotted.

5.      The process above was repeated using microcrystalline cellulose.

Method (part B):

1.      5 different types of sands and powders such as microcrystalline cellulose and lactose were prepared.

 

2.      The sand that put under the microscope with specimen and slide was observed. 

3.      The structure and shape of the sand particles was captured.

4.      The experiment was repeated by using another four sands, microcrystalline cellulose and lactose which same magnification which is multiplied by forty times so that the approximate habit of the particles can be determined.

Results:

Part A

MCC

NO	SIEVE DIAMETER (RANGE)	MASS OF WEIGHING BOAT AND MCC	MASS OF WEIGHING BOAT	MASS OF MCC
1	0<x≤45	2.7936	2.7887	39.8085
2	45<x≤150	2.5931	2.4902	54.9343
3	150<x≤300	5.1424	3.3012	3.3412
4	300<x≤425	6.3262	2.9850	1.8412
5	425<x≤500	57.8043	2.8700	1.1029
6	>500	43.1416	3.2731	0.0049

 

FIGURE 1: GRAPH OF SIEVE DIAMETER AGAINST THE MASS OF MCC

LACTOSE

NO	SIEVE DIAMETER (RANGE)	MASS OF WEIGHING BOAT AND MCC	MASS OF WEIGHING BOAT	MASS OF LACTOSE
1	0<x≤45	0.2114	0.1196	0.0918
2	45<x≤150	23.0573	1.0121	22.0452
3	150<x≤300	27.4139	3.3010	24.1129
4	300<x≤425	56.7855	2.9550	53.8305
5	425<x≤500	3.1125	3.1004	0.0121
6	>500	0.2014	0.1918	0.0096

 

FIGURE 2: GRAPH OF SIEVE DIAMETER AGAINST THE  MASS OF LACTOSE

Part B

Lactose	MCC
·         Total magnification = 40× ·         The particles are spherical in shape ·         The size of particle is smaller than the sand particles but smaller than the MCC powder.	·         Total magnification = 40× ·         The particles are needle like in shape ·         The size of particle is smaller than the sand particle but bigger than the

800micron	500 micron
·         Total magnification = 40× ·         The particles are irregular in shape ·         Large in size compare to the other types of sand particles and the powder particles.	·         Total magnification = 40× ·         The particles are irregular in shape ·         Smaller than the type 1 sand particles but bigger than the other types of sand particles

Mixed sand	355micron
·         Total magnification = 40× ·         The particles are irregular in shape ·         Smaller than the type 1 and 2 sand particles but bigger than the other types of sand particles	·         Total magnification = 40× ·         The particles are irregular in shape ·         Smaller than the type 1, 2 and 3 sand particles but bigger than the other type of sand particles

150 micron

·         Total magnification = 40× ·         The particles are irregular in shape ·         Sand particle is small in size but bigger than the particles found in powder

Discussion:

Sieving is the process by which the particles of various sizes passed through the perforations of the sieve to separate them from coarser to finer. In this experiment , MCC and lactose were observed. The sieve stack was placed from top to bottom according to the size of the sieve nest that is from largest size to the smallest.  The sieve that have diameter of aperture of 500 µm will be placed at the above followed by 425 µm, 300 µm, 150 µm,  45 µm and less than 45 µm.

According to the results obtained , MCC has particle size of  around 45µm as the highest amount of  MCC powder remained at the sieve while lactose has size particles  of range 151µm-300µm as the highest amount of lactose powder remained at the sieve. From here, we can conclude that MCC powder is finer than lactose powder.

This experiment also cannot be considered very accurate as there are some errors during the experiment. There is still some amount of MCC or lactose powder that stuck at the gaps of the sieve where the exact amount of powder cannot be determined. Besides , the particles are very light and easily loss to the surroundings during handling of the sample. Furthermore , the sieve might be contaminated by other powder of MCC or lactose where it is done by the previous group.

Some precautions need to be taken in order to minimise the errors of the experiment. Before we start the sieving process, clean the sieve thoroughly using brush to avoid any foreign powder stick on the sieve that might affect the results. Next , make sure that we cover the powder before taking it to another place so that the powder would not be blown out and try to carry out the experiment in a non windy area.

The light microscope is used to observe the sands and powders (MCC, lactose) with 40X magnification. The sands and powder need to be dispersed on the slide until a thin layer is formed. From the observation, there are various sizes and shapes of sands. The sizes are observed from the smaller ones to the bigger size. The shape of the sands are irregular with sharp and pointy edges. As for powder of MCC and lactose, the particles have regular shape; round, averagely similar sizes and smooth edges. 

1.         There are various statistical method that can be used to measure the diameter of a particle, which are the Feret's diameter (dF), Martin’s diameter (dM), Projected area diameter (da) and perimeter diameter (dp).  Feret's diameter is the perpendicular distance between parallel tangents touching opposite sides of the profile. In other words, the boundary separating equal particle areas. Next, Martin's diameter, which is the mean chord length of the projected outline of the particle.  The lines may be drawn in any direction which must be maintained constant for all image measurements. While the projected area diameter is the diameter of a circle having the same area as the projected area of the particle resting in a stable position.  As for perimeter diameter, it is the diameter of a circle having the same circumference as the perimeter or projected outline of the particle. 

2.         The best statistical method for each sample is the Feret's diameter (dF). The measure can be done in a few orientation for randomly oriented particles and the average or mean value can be calculated for the accurate diameter.

Conclusion:

1) The size of MCC particles are in the range between 45um to 150um.

2) The size of lactose particles are in the range between 300um to 425um

3) MCC has finer particle size than lactose

4) All samples of sand particles in this experiment have irregular shape under 40x magnifications and the type 5 sand has the smallest in size particles than others

Reference:

W. H. Walton, Feret‘s Statistical Diameter as a Measure of Particle Size
 http://www.nature.com/nature/journal/v162/n4113/abs/162329b0.html