Lab Report : Practical 4(a) Sieving

TITLE

Sieving

 

OBJECTIVES

(i.)   To determine the particle size of lactose and microcrystalline cellulose (MCC).

(ii.)  To determine the size distribution of lactose and microcrystalline cellulose (MCC).

 

DATE OF EXPERIMENT

19 November 2015

 

INTRODUCTION      

Sieves are commonly used to break down agglomerates and determine the size and size distribution of a particular powder. Sieving is probably the most frequently used method of analysis because the equipment, analytical procedure, and basic concepts are simple. The particle size distribution is defined via the mass or volume. Sieve analysis is used to divide the particulate material into size fractions and then to determine the weight of these fractions. In this way a relatively broad particle size spectrum can be analyzed quickly and reliably.

During sieving the sample is subjected to horizontal or vertical movement. This causes a relative movement between the particles and the sieve; depending on their size, the individual particles either pass through the sieve mesh or are retained on the sieve surface. The likelihood of a particle passing through the sieve mesh is determined by the ratio of the particle size to the sieve openings, the orientation of the particle and the number of encounters between the particle and the mesh openings.

 

Sieve analyses in the laboratory and for quality assurance are carried out with sieve shakers. Modern sieve shakers are characterized by the fact that their mechanical parameters, such as sieving time and amplitude or speed, are carried out with exact reproducibility. In the laboratory a differentiation is made between horizontal sieve shakers and throw-action sieve shakers. The basic analytical method involved stacking the sieves on top of one another in descending order (largest diameter to the smallest, from top to bottom) and placing the test powder on the top sieve.

In this practical, students are given two common excipients used in tablet formulations, namely lactose and microcrystalline cellulose (MCC). Using sieve shaker, the particle size and size distribution of both powders are determined.

LIST OF APPARATUS

 

sieve shaker and stack of sieves

 

 

weighing scale

 

LIST OF CHEMICALS

 

 

lactose

 

 

microcrystalline cellulose (MCC)

 

 

EXPERIMENTAL PROCEDURES

1.  100g of lactose was 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 collected at every sieve was weighed and the particle size

     distribution was plotted in the form of a histogram.

 

 

 



5.  The above process was repeated using MCC.



 

 

RESULTS

Lactose

Sieve diameter (µm)	Particle size (µm)	Mass of lactose retained in the sieve (g)	% lactose retained  = (weight of lactose in sieve / total weight) × 100%	Cumulative percentage retained (%)	% passing = 100% - cumulative percentage retained
< 53	0 < x ≤ 53	7.3190	7.3190	7.3190	92.6810
53	53 < x ≤ 150	80.1245	80.1245	87.4435	12.5565
150	150 < x ≤ 212	1.1823	1.1823	88.6258	11.3742
212	212 < x ≤ 300	10.5231	10.5231	99.1489	0.8511
300	300 < x ≤ 500	0.3421	0.3421	99.4910	0.5090
500	x > 500	0.0267	0.0267	99.5177	0.4823

 

Microcrystalline cellulose (MCC)

Sieve diameter (µm)	Particle size (µm)	Mass of MCC retained in the sieve (g)	% MCC retained  = (weight of MCC in sieve / total weight) × 100%	Cumulative percentage retained (%)	% passing = 100% - cumulative percentage retained
< 53	0 < x ≤ 53	0.5412	0.5412	0.5412	99.4588
53	53 < x ≤ 150	92.3256	92.3256	92.8668	7.1332
150	150 < x ≤ 212	2.0101	2.0101	94.8769	5.1231
212	212 < x ≤ 300	4.5673	4.5673	99.4442	0.5558
300	300 < x ≤ 500	0.0445	0.0445	99.4887	0.5113
500	x > 500	0.0267	0.0267	99.5154	0.4846



 

QUESTIONS

1.  What are the average particle size for both lactose and MCC?
     The average particle size for both lactose and MCC is in the range of 53µm - 150µm. It is
     because the percentage of lactose and MCC retained is the highest.

2.  What other method can you use to determine the size of particle?
The other methods to determine the size of particle include LA - 960 laser diffraction technique,  SZ - 100 dynamic light scattering technique, PSA300 and CAMSIZER image analysis technique, microscopy, sedimentation, optical and electrical sensing zone method.

 

       (i.)  LA - 960 laser diffraction technique

The LA-960 combines the most popular modern sizing technique with state of the art refinements to measure wet and dry samples measuring 10 nanometers to 5 millimeters. The central idea in laser diffraction is that a particle will scatter light at an angle determined by that particle’s size. Larger particles will scatter at small angles and smaller particles scatter at wide angles. A collection of particles will produce a pattern of scattered light defi ned by intensity and angle that can be transformed into a particle size distribution result.

              

       (ii.)  SZ - 100 dynamic light scattering technique

              The SZ-100 nanoPartica Dynamic Light Scattering (DLS) system measures particle        size, zeta potential, and molecular weight from 0.3 nm to 8 μm at concentrations ranging from 0.1 mg/mL of lysozyme to 40% w/v.

 

        (iii.) PSA300 and CAMSIZER image analysis technique

                Two types of image analysis exist, namely static image analysis and dynamic  image analysis. The samples measured by static image analysis typically rest on a slide that is moved by an automated stage. With the PSA300 static image analysis system a microscope and digital camera collect images of the particles as the slide is scanned. For dynamic image analysis, sample preparation is completely different since the sample itself is moving during the measurement. Sample preparation steps could include an ionizer to mitigate static interactions between particles thus improving flowability or a sample director to specifi cally orientate particles through the measurement zone.

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

      Particle size is important in a pharmaceutical formulation because particle size is directly
      related to drug dissolution and drug solubility. According to Noyes-Whitney equation, dissolution rate is directly proportional to particle surface area. Smaller solid particles suspended in the liquid will be more uniform and no agglomerates will be formed. This can increase the uniformity and efficacy of drugs produced. Besides, smaller size of solid particles will have larger surface area to come into contact with the medium. This can ensure that the medicine produced can dissolve easily in the body system and function effectively when consumed. Furthermore, when the drugs are injected into the body system, small particle size can ensure that the drug particles will not block the blood vessels

 

 





DISCUSSION

            Particle size influences many properties of particulate materials and is a valuable indicator of quality and performance. This is true for powders, suspensions, emulsions and aerosols. The size and shape of powders influences flow and compaction properties. Larger, more spherical particles will typically flow more easily than smaller or high aspect ratio particles. Smaller particles dissolve more quickly and lead to higher suspension viscosities than larger ones. Smaller droplet sizes and higher surface charge (zeta potential) will typically improve suspension and emulsion stability. Powder or droplets in the range of 2-5μm aerosolize better and will penetrate into lungs deeper than larger sizes. For these and many other reasons it is important to measure and control the particle size distribution of many products.

 

            Sieve analysis is performed to determine the particle size distribution of granular materials including sand, crushed rock, clays, feldspars, coal and grains. The most common method used for sieve analysis is sieving. In order to carry out sieving, sieve nest has to be prepared and they are arranged in descending order, from the largest diameter to the smallest diameter. The granular materials used in this experiment are lactose and microcrystalline crystal (MCC). 100g of lactose powder was placed at the uppermost sieve nest. The sieve shaker is then started and the sieving process is carried out for 10 minutes. Later, the lactose powder from each sieve is measured. The principle used to determine the particle size is that particles that cannot pass through a particular sieve nest has larger particle size compared to the diameter of the sieve nest. For example, particles that cannot pass through sieve with diameter 150µm but can pass through sieve with diameter 53µm has particle size range between 53µm and 150µm.

            From the result obtained, the particle size of lactose is estimated to be between 53µm and 150µm because the percentage of lactose retained at sieve with diameter 53µm is the highest. The particle size of MCC is estimated to be between 53µm and 150µm because the percentage of MCC retained at sieve with diameter 53µm is the highest. It can be deduced that lactose has larger particle size compared to MCC because the percentage of lactose retained at sieve with diameter less than 50µm is higher than the percentage of MCC retained at sieve with diameter less than 50µm.

            There are errors throughout the experiment because there is a loss in weight of lactose powder and MCC after the experiment compared to their weight before the experiment. The weight of both lactose and MCC are 100g initially. However, after the experiment, the weight of lactose powder is found to be 99.5177g. The weight of MCC is found to be 99.5154g. This may due to the lactose and MCC powder are not completely removed after the sieving process. Some powders may have been blown away during the vibration of sieve shaker, some of them may have sticked to the sieve nest, some may have spilt out from the sieve nest when we were transferring the powders from the sieve to weighing boat to be weighed. Some of the powders may have been contaminated with other powders as this experiment is carried out using both lactose and MCC.

            A few precautions have to be taken in order to minimise the error. First, the sieves have to be tightly closed when the sieve shaker is operating. The sieves should be cleaned thoroughly before repeating the experiment with another type of powders to prevent contamination. Besides, after the sieving process, the powders have to be removed from the sieve nest to the weighing boat slowly and carefully to prevent the spillage of the powders, causing inaccuracy in the weight of powders in each sieves.

CONCLUSION

In conclusion, the objectives of the experiment are achieved. The particle size and size distribution of lactose and microcrystalline cellulose (MCC) are successfully determined using sieving method. According to the result of the experiment, MCC has smaller particle size than lactose.

 

REFERENCES

Martin,A.N. 2006. Physical Pharmacy: Physical Chemistry Principles in Pharmaceutical     Sciences. 5th Edition. Philadelphia: Lea & Febiger.

Patrick J. Sinko, Yashveer Singh. 2011. Martins Physical Pharmacy and Pharmaceutical Pharmacy Sciences. Ed. ke6. China: Lippincott Williams & Wilkins.  

Jillavenkatesa A, Dapkunas S J, Lin-Sien Lum. 2001. Particle Size Characterization. NIST Special Publication.

https://www.horiba.com/fileadmin/uploads/Scientific/eMag/PSA/Guidebook/pdf/PSA_Guidebook.pdf

http://cma.tcd.ie/misc/particle_size.pdf