PRACTICAL 4: SIEVING
PART B
Title
Particle Size and Shape Analysis Using Microscope.
Objective
1. To determine the percentage of different grain sizes contained within a soil.
2. To analyse and interpret the shape of particles with seven different samples.
2. To analyse and interpret the shape of particles with seven different samples.
3. To observe and compare the size of particles for each sample.
Date
17th November 2014.
Introduction
The analysis of particle size and shape is very important in the field of pharmaceutical science. The size and shape of the particles can give an effect to the bulk properties, product performance, processability, stability and appearance of the end product. Particle size analysis is an integral component of the effort to formulate and manufacture many pharmaceutical dosage forms. The understanding of the characteristic of particularly the active ingredients and excipients (pharmacologically inactive substance) always being used in the formulation of drugs is thus indeed important.
In this experiment, 5 different types of sands, MCC and lactose are being analysed to study the size and shape of the particles. Different types of particles have difference with respect to their sizes and shapes. MCC, or its full name, Microcrystalline Cellulose, is one of the most important and widely-used excipients. It acts as a key diluent for drug formulations and an essential component for almost every kind of oral dosage, including tablets, capsules, sachets, pellets and others, as well. Lactose, the milk sugar is another important excipient which is used to help form tablets due to its excellent compressibility properties. It can used to form a diluent powder for dry-powder inhalations as well. Lactose may be listed as lactose hydrous, lactose anhydrous, lactose monohydrate, or lactose spray-dried.
The analysis of particle size and shape can be done by several methods where each applying different working principle such as sieve method, laser light scattering method, dynamic light scattering method, sedimentation method and microscope method. The particle size and shape in this experiment are observed using microscope.
Experimental Methods
Chemicals
5 different types of sands and powders (MCC, Lactose).
Apparatus
Microscope, slide, spatula, beaker and weighing boat.
Procedures
1. A microscope was used to analyse 5 different types of sands and powders (MCC, Lactose) with particular emphasis on the size and shape of the particles.
2. The particles observed microscopically were sketched and the general shape for the particular material was determined.
3. The magnification that were used in sketching the particles were noted.
Results
Questions
1. Explain in brief the various statistical methods that you can use to measure the diameter of a particle.
Various measure of the size of irregularly shaped particles as seen in profile under the microscope have been used, chosen according to their theoretical significance or practical ease of measurement. Example of statistical diameters are useful measures of central size tendency and are computed from some measured property that is a function of size and related to a linear dimension. Irregular particles that has assigned size depends strongly on the method of measurement .Method of assignment of numerical value for the diameter, surface area or other perimeter has been established. Mean particles diameter is the most important single statistical parameter because if the proper diameter is chosen, the various other parameter of interest such as specific surface area, number, mean particle weight often may be calculated.
2. State the best statistical method for each of the samples that you have analysed.
The best statistical method for each of the samples that have been analysed is by histogram.
Discussion
In this experiment, the characteristic of different particles are observed and studied in regard to their size and shape using microscope. Particles being observed are sands with different size (150 micron, 350 micron, 500 micron, 850 micron and various size), lactose and microcrystalline cellulose (MCC). Microscopy is used as a sizing method as it allows the direct visualization and measurements of small particles. Light microscope is used where it works according to the principle of passing the visible light transmitted or reflected from the sample through a single or multiple lens to allow the magnification of sample’s view. In this case, 4 x 10 magnification (the product of objective-eyepiece combination) is chosen because it gives the best magnification view to observe the particles.
The shapes and sizes of different particles are distinct from each other. All the sand particles have irregular shape with pointed edges but their sizes vary. The size of sand particles increases following the sequence of 150 microns, 350 microns, 500 microns and 850 microns. The sand particles with various types have varying sizes. Meanwhile, the MCC and lactose have granular shape without sharp edges and they are far smaller than even the 150-micron sand particles. When comparing the MCC and lactose, some of the MCC particles are acicular while the lactose particles are more rounded. The particles are dispersed evenly on the slide when doing the microscopy to avoid agglomeration which may affect the observation. When doing the size and shape analysis using microscope, we are actually observing them as two-dimensional image whereby similar particles may appear to be different due to different orientation. However, we assume the particles are randomly oriented and viewed in their most stable orientation.
For the size analysis of non-spherical particle (which in our case are all the particles being observed), there are several equivalent diameters can be used to define them. Among the important and suitable ones are Feret’s diameter, Martin’s diameter and projected area diameter. They are diameters defined on the basis of the projected image or the two-dimensional image of particle. Martin's diameter is the averaged cord length of a particle which equally divides the projected area while Feret's diameter is the averaged distance between pairs of parallel tangents to the projected outline of the particle. The diameter of a sphere having the same projected area as the particle is termed the projected area diameter. Martin's diameter and Feret's diameter of a particle depend on the particle orientation under which the measurement is made. Thus, to obtain a statistically significant measurement for these diameters, a large number of randomly sampled particles which are measured in an arbitrarily fixed orientation is required.
One of the precautionary steps taken in the experiment is the careful handling and transferring of the particles from the weighing boat to the slide for microscopy by using spatula. This is to prevent the particles from mixing with other particles not under study such as dirt and dust and affect the accuracy of result.
Conclusion
In conclusion, different particles have different size and shape and these characteristics are indeed important to be understood well especially comes to the formulation of drugs in the field of pharmaceutical industry to allow the optimum efficacy of the drugs. To analyse particle size and shape, microscopy is a useful method to be used where the light microscope allows the direct observation of the particles being studied.
Reference
Reference
Anon. Chapter 1: Size and Properties of particles.
http://158.110.32.35/CLASS/IMP-
CHIM/PGSF21-42.pdf [1st December 2014].
Anon. Lactose. http://www.drugs.com/inactive/lactose-157.html [1st
December 2014].
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