Practical 1 - Particle Size and Shape Analysis Using Microscope

Introduction:

Microscopy is the technical field of using microscopes to view samples and objects that cannot be seen with the unaided eye. It is an excellent technique to look directly at the particles. Microscopic method can observe shape of particles clearly in good dispersion. There are 3 types of microscope can be used that are light microscope, transmission electron microscope and scanning electron microscope for measuring different sizes of particles. In this experiment, light microscope is used.

Apparatus:

Light microscope

Weighing boat

Material:

Sand with various sizes of 150, 355, 500 and 850 micrometres

Procedure:

1.      A light microscope is prepared and set up on the table.

2.      Sand with different sizes of 150, 355, 500 and 850 micrometres are took in small quantity using weighing boat.

3.      150 micrometres sand are scattered evenly with suitable amount on the glass slide to prevent agglomeration of particles.

4.      The glass slide is covered with lens and observed under light microscope with x 10 magnification power.

5.      Then, the observation proceed to x 40 magnification power.

6.      Observations are drew out on a piece of paper.

7.      The experiment is repeated using 355, 500 and 850 micrometres sand.

Results:

Discussion:

Light microscopy involves passing visible light transmitted through or reflected from the sample through a single or multiple lenses to allow a magnified view of the sample. The resulting image can be detected directly by the eye, imaged on a photographic plate or captured digitally. The single lens with its attachments, or the system of lenses and imaging equipment, along with the appropriate lighting equipment, sample stage and support, makes up the basic light microscope. 2-D image obtained are generally assumed to be randomly oriented in 3-D. Using conventional light microscope, particle size analysis can carried out using projector screen with screen distance related to particle dimensions. Each sizes of sand are observed up to x 40 magnification because higher power causing a blur image. Both x 10 and x 40 images for each sizes of sand are drew and compared.

Questions:

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

            1.  Sieve method

•      Carried out using dry powders, poor reproducibility for wet sieving

•      Using sieve diameter, ds – particle dimension

•      Lowest ds is 45 micrometres to maximum 1000 micrometres

2. Microscopic method

•      Directly look at particles size and shape

•      Equivalent diameters used are projected area diameter, projected perimeter diameter, Feret’s and Martin’s diameter

•      2-D image obtained

3. Coulter counter

•      Electrical stream sensing zone method

•      Measures any particulate material that can be suspended in electrolyte

•      Equivalent diameter : volume diameter

4. Laser light scattering method

•      Interaction of light with particles

•      Described using Fraunhofer or Mie theory

•      Entire sample is measured and have high resolution

5. Sedimetation method

•      Based on Stokes’s Law equation – expression of drag factor in a fluid, linked to the flow conditions

•      Comparison of particles settling rate to a sphere at the same rate

2. State the best statistical method for each of the samples that you have analysed.

Microscopic method is used in experiment to examine sand of different sizes.

Projected perimeter diameter – based on circle having same perimeter as the particle

Projected area diameter – based on circle of equivalent area to that of projected image of solid particle

Feret’s diameter – mean distance between 2 parallel tangents to projeced particle perimeter

Martin’s diameter – mean chord length of the projected particle perimater (boundary separating equal particle areas)

Conclusion:

Microscopic method is the best statistical method in analysing particle’s diameter and size.

References:
1. Pharmaceutics, The science of dosage form design (2nd Edition) Michael E.Alton Edinburgh               London New York Philadophia St Louis Sydney Toronto 2002.
2. http://www.en.wikipedia.org
3. http://www.jenike .com
4. Physicochemical Principals of Pharmacy (2nd Edition) AT Florence and D.Attwood, The                     Macmillan Press Ltd.