PRACTICAL V : ANALYSIS OF PARTICLES' SIZE AND SHAPE USING MICROSCOPE

TITLE

Analysis of particles’ size and shape using microscope

OBJECTIVE

1. To analyse the different sizes and shapes of particles under microscope.

2. To describe the distribution of particle size and shape.

INTRODUCTION

Various methods have en used to determine particle sizes and shapes. Microscopic analysis is one of the most simple and widely used method in this case.  It can determine the diameter, shape, and surface area that cannot be determined with the unaided eye.  In this experiment, different sizes and shapes of sands are used. The various sizes of sands used includes 355 µm, 500 µm, 850 µm and lactose. It was observed carefully under the microscope and the observation were drawn at the end of the experiment.

Sand is a naturally occurring granular material composed of finely divided rock and mineral particles.  It exsits in various different sizes ranging from 0.0625 mm (or 1⁄16 mm) to 2 mm.  Fine sand is defined as particles between 0.02 mm and 0.2 mm while course sand as those between 0.2 mm and 2.0 mm. It is used in this experiment as it is inert, easy to obtain and economical. 

METHOD

Materials and Apparatus: Sand particles with size of 355 µm, 500 µm, 850 µm, lactose and a microscope.

PROCEDURE

1. 5 samples of different types of particles are analyzed based on the size and shapes of given particles under the microscope.

2. The samples are examined using the magnification of 4X10 and 10X10.

3. The shapes of particles are observed  and sketched. The overall shape of particles of each powder is described. 

OBSERVATION

355 µm sand

Characteristic: almost same size, small, irregular in shape

4 x 10 magnification                   10 x 10 magnification

500 µm sand

Characteristic: almost same size, larger than 355 µm, irregular in shape

4 x 10 magnification           10 x 10 magnification

                                      

850 µm sand

Characteristic: largest size among all sands, irregular, irregular shape

 4 x 10 magnification             10 x 10 magnification

                          

Various sizes sand

Characteristic: different sizes, irregular shape

4 x 10 magnification             10 x 10 magnification

                                            

Lactose

Characteristic: constant size, very small size, mostly round

4 x 10 magnification             10 x 10 magnification

QUESTIONS

1. Describe the various statistical methods that can be used to measure the diameter of a particle.
There are a few statistical method that can be used in this case, which includes the Feret's diameter (F),  Martin's diameter (M), Projected area diameter (d_a or d_p), perimeter diameter, maximum chord and longest dimension.  Feret's diameter (F) is the distance between two tangents on opposite sides of the particle and parallel to some fixed direction.  While Martin's diameter (M) is the length of the line which bisects the particle image.  The lines may be drawn in any direction which must be maintained constant for all image measurements.  The projected area diameter is the diameter of a circle having the same area as the particle viewed normally to the plane surface on which the particle is at rest in a stable position.  As for perimeter diameter, it is the diameter of a circle having the same circumference as the perimeter of the particle.  For maximum chord, it is a diameter equal to the maximum length of a line parallel to some fixed direction and limited by the contour of the particle.  Lastly, the longest dimension is a measured diameter equal to the maximum value of Feret's diameter.

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2. Name the best statistical method for every sample that has been used.

Feret’s diameter (F) is the best statistical method for the samples.  This is because the average diameter can be obtained over many orientations nd the mean value can be obtained for each particle diameter.  This in turn produce a more accurate average diameter as the it is taken in more orientations.

DISCUSSION

From the results of observation, it can be seen that there are various sizes and shapes of sands. The sizes of the sands increases from the 355 µm, 500 µm, to 850 µm respectively.  It is also observed that the shapes of the sands are irregular and has some sharp and pointy edges.  On the other hand, the lactose shows that the size of each particle is quite similar and constant.  Lactose also exhibit regular shapes and it is seen mostly to be round and do not have sharp edges.

In this experiment, light microscope is used to observe the sands and lactose for the particle size analysis.  The microscope used is a compound microscope normally used in the laboratory.  Light microscope allows passing visible light to be transmitted through or reflected from the sample through a single or multiple lenses to allow a magnified view of the sample.  The actual power or magnification of a compound optical microscope is the product of the powers of the ocular (eyepiece) and the objective lens. In this practical, we used objective lens of 4x and 10x and eyepiece of 100x.  Therefore, it can give us magnifications of 400 and 1000 respectively.  The observations were then drawn.

As for the analysis of the particle size, Feret’s diameter (F) and Martin’s diameter (M) are among the methods that can be used. In short, Feret's diameter (F) is the distance between two tangents on opposite sides of the particle and parallel to some fixed direction. As for Martin's diameter (M) it is the length of the line which bisects the particle image.  The lines may be drawn in any direction which must be maintained constant for all image measurements.  The longest dimension can also be used as a measurement by equalling to the maximum value of Feret's diameter.

CONCLUSION

There are various sizes for particles like sands. However, lactose exhibit a more constant sizes and shapes.

The particle size analysis can be done with the aid of a light microscope and later determined using Feret’s diameter and Martin’s diameter.

REFERENCE

Physicochemical Principals of Pharmacy (2nd Edition) AT Florence and D.Attwood, The Macmillan Press Ltd.

Pharmaceutics, The science of dosage form design (2nd Edition) Michael E.Alton Edinburgh London New York Philadophia St Louis Sydney Toronto 2002.

 http://en.wikipedia.org/wiki/Sand

http://www.nature.com/nature/journal/v162/n4113/abs/162329b0.html

http://en.wikipedia.org/wiki/Microscopy#Electron_microscopy