PRACTICAL 4 :  PART B - MICROSCOPIC                                                    SIZE ANALYSIS                                  

TITLE :

Analysis of Particle Size and Shape under Light Microscope

DATE OF EXPERIMENT :

17^th of November 2014

OBJECTIVES :

   
     
                   To analyse the various shapes and sizes of particles under a light microscope.
                   To describe the distribution of particles’ sizes and shapes.

 

INTRODUCTION:

The size and shape of particle can be analysed using various method. In this experiment, we used microscope as the method to achieve our objectives. There are three types of microscope that can be used to analyse size and shape of the samples which are light microscope, transmission electron microscope (TEM) and scanning electron microscope (SEM). We used light microscope which function for the particles or samples to disperse on a microscope slide to avoid analysis of agglomerated particles. The analysis using this type of microscope is to determine the diameter, shape, and surface area of a particle. We are using various kind of sizes of sand, which are 150 µm, 355 µm, 500 µm, 850 µm, sand with all of this sizes that already been mixed together, lactose and microcrystalline cellulose (MCC)  as samples for this experiment. Some batches of samples may differ by such a small amount that this difference is lost during the translation to a circle equivalent or spherical-equivalent diameter.  In this experiment, we observe different sizes of particles under a microscope, draw and take picture of the particles’ observed.

MATERIALS:

Sand (150 µm, 355 µm, 500 µm, 850 µm, mixture of various size)LactoseMicrocrystalline cellulose (MCC)
 

APPARATUS:

Light microscope, Weighing boat

EXPERIMENTAL PROCEDURES :

Particle size and shape analysis using microscope

1) 5 different types of sands (150 μm, 355μm, 500μm, 850μm and mixture of various sizes of sand     particles) and powders (MCC and lactose) were analyzed with particular emphasis on the size and shape of the particles by using a microscope.

2) The particles observed microscopically were sketched and the general shape for particular material was determined. The magnification used in this experiment was 10x.

RESULTS:

Items to be observed	Observed under microscope	Drawing
1. Mixture of various size of sand particles
2. Sands (150μm)
3. Sands (355μm)
4. Sands (500μm)
5. Sands (850μm)
6. Lactose
7. Microcrystalline Cellulose ( MCC)

 DISCUSSION :

Particle size is one of the most important parameters in materials science and technology as well as many other branches of science and technology, from medicine, pharmacology and biology to ecology, energy technology and the geosciences. The theoretical backbone is the statistics of small particles.Except for sieve classification (which has lost its significance for particle size analysis today, although it remains an important tool for classification) the most important particle size analysis methods are treated in some detail, in particular are the sedimentation methods, laser diffraction, microscopic image analysis  dynamic light scattering, electrozone sensing, optical particle continuing, XRD line profile analysis, adsorption techniques and mercury intrusion.

If describing a 3D particle size is complex then quantifying shape is even more complicated. There are an almost infinite number of ways to describe a complex shape and in doing so we seem to be deviating from our stated objective of reducing a sample to one quantifiable number. Measuring size alone is sometimes insufficiently sensitive to identify important but subtle differences between samples. Some batches of samples may differ by such a small amount that this difference is lost during the translation to a circle equivalent or spherical-equivalent diameter.

Particle size, in the sense commonly used, is a linear length measure, measured in SI unit [m].In this sense it can be uniquely defined only for spheres, where it is the diameter (or radius). For all other shapes, particle size must be clearly defined via the measuring procedure. So called derived diameters are determined by measuring a size-dependent property of the particle and relating it to a single linear dimension. The most widely used of these are the equivalent diameters, in particular the equivalent spherical diameters. Important equivalent diameters are volume equivalent sphere diameter, surface equivalent sphere diameter, hydrodynamic sphere diameter, sieve diameter, laser diffraction equivalent diameter, projected area diameter and volume surface diameter.

Other equivalent diameters which are less frequently used for example the perimeter equivalent diameter of a particle outline. Apart form the equivalent diameters there are other size measures which can be used to quantify particle size, mainly in microscopic image analysis of 2D particle outlines, among them the chord or intercept lengths (including the Martin diameter, for example the length of the chord dividing the projected particle area into two equal halves) and the caliper or Feret diameters (including the maximum and minimum Feret diameter)

Particle shape is a complex geometric characteristic. It involves the form and habit of the particle as well as features like convexity and surface roughness. The literature on shape characterization is enormous and so is the number of possible definitions of shape factors. Characterizing size and shape of particles is critical for the development of a drug product since most pharmaceutical processes such as granulation, mixing and compaction are affected by these properties. An ideal particle characterization technique should provide an accurate determination of the volume-weighted particle size distribution combined with a reliable definition of the particle shape. In addition, very few techniques directly measure particle shape. The goal was to use optical microscopy with image analysis to confirm the accuracy of the other particle size techniques.

Equivalent diameters from three particle size techniques including laser light scattering (LLS), focused beam reflectance (FBRM) and dynamic image analysis (DIA) were compared to optical microscopy with image analysis (OM/IA). Optical microscopy is considered the most accurate because the size and shape of the individual particles can be observed and measured .To do this comparison several factors were considered such as relative size (5μ, 50μ or 500μ) and shape (spherical or irregular) of the sample, objective and camera resolution sample size spherical volume calculation and accuracy of the system based on analysis of a standard.

In this experiment, five different types of sands and powders (MCC and lactose ) with particular emphasis on size and shape were analyzed using microscope. The particles which are observed microscopically were sketched and the general shape for each particle were determined. The general shape observed were spherical and irregular. The magnification that was used for all the particles that were observed was ×10. There were five different diameters for the sands which are namely (150 mic, 355 mic, 500 mic, 850 mic and various). Based on the observation, the sizes of all particles differs from each other. The methods used to determine the particle size analysis are sedimentation, laser diffraction and also microscopic image analysis. Method used for this experiment is microscopic image analysis. Type of the particle surface was namely coarse and fine surface.

There are some precautionary steps to be taken during experiment in order to obtain accurate results. Although microscopes may seem sturdy, they are actually quite fragile as evidenced by their glass lenses and delicate focusing mechanisms. Always pick up a microscope using both hands, one holding the arm of the microscope and the other supporting its base. Position the arm of the microscope toward you and the stage so that flat platform used for holding the specimen is directed away from you. When using your microscope at its highest magnification, some models require special preparation of the specimen or lens.

CONCLUSION:

 Based on the experiment, microscopic image analysis is one of the method used to determine shape and size of the particles. The general shape of the particles observed from the experiment were spherical and irregular. The size of the particles differ from each other. Surfaces of the particles were namely coarse and fine.

QUESTIONS:

1. Explain in brief the various statistical methods that you can use to measure the diameter of the particle.

Diameter of a particle can be measured based on a circle having the same perimeter as the particle, which known as projected perimeter diameter. Meanwhile, projected area diameter can be measured from a circle of equivalent area to that of the projected image of a solid particle. 

There are also methods called Feret's diameter and Martin's diameter. These two methods are dependent on both the orientation and the shape of the particles. The value of diameter is averaged over many different orientations produced for each particle. The only difference between these two is, Feret's diameter refers to the mean distance between two parallel tangents to the projected diameter. While Martin's diameter refers to the mean chord length of the projected particle perimeter which can be considered as the boundary separating the particle equally.

 2. State the best statistical method for each sample used in this experiment.

355 micron sand : Martin's diameter

500 micron sand : Martin's diameter

800 micron sand : Martin's diameter

Vary in Size sand : Martin's diameter

REFERENCES:

• http://www.particlesciences.com/docs/DDT-Particle_Size_Dist-May_09.pdf
• Michael E.Aulton, 2007, Aulton's Pharmaceutics The Design And Manufacture Of    Medicines, Third Edition, Churchill Livingstone Elsevier (page 122-134)
• http://www.nature.com/nature/journal/v162/n4113/abs/162329b0.html
• http://www.ncbi.nlm.nih.gov/pubmed/1437996

• 3.http://www.surfaceanalysis.ru/surface/categors/1f/74/content_128015234686.pdf