EXPERIMENT: PARTICLE SIZE AND SHAPE ANALYSIS USING MICROSCOPE

TITLE: Particles Size and Shape Analysis Using Microscope

OBJECTIVE:

1)  To analyse and interpret the shape of particles with five different samples.

2)  To observe and compare the size of particles for each sample.

INTRODUCTION:

     The need for particle size control in the manufacture of pharmaceuticals is becoming increasingly apparent as the pharmaceutical industry attempts to capitalize on some APIs with less-than-ideal solubility profiles. Also, significant advances in drug delivery have been made in which a finely divided API, with the concomitant increase in specific surface area, has resulted in increased bio-availability. Precise particle size control technologies have also assisted in the development of drug delivery platforms for the delivery of a medicament to the lung. As these trends have occurred, the need for highly reproducible particle size assessment techniques has grown significantly in the past decade. The interest in particle size   measurements will remain high, particularly in view of FDA trends toward recommending more thorough descriptions of particle size distributions in submissions in which the emphasis of a drug product claim is based in a tightly controlled particle size. When drug is synthesized and formulated, the particle size of drug and other powder is determined and this influences the subsequent physical performance of the medicine and the pharmacological of the drug.

     Powder with different particle sizes have different flow and packaging properties, which alter the volumes of powder during each encapsulation or tablet compression event. The particles which are having small dimensions will tend to increase the rate of solution.

     In order to obtain equivalent diameters with which to analyse and interpret the particle size of powder, it is necessary to carry out a size analysis using different methods. One of the methods for particle analysis is using microscope. The use of a microscope to examine and measure particle is very effective procedure and it is the only method in which direct measurement of the particles is made.

MATERIALS AND APPARATUS:
Electron Microscope, weighing boat, five (5) different size of sand  (A=850 microns, B=500 microns, C=355 microns, D=150 microns, E=various), MCC powder, Lactose powder and prepared slide

Prepared slide

Electron Microscope

EXPERIMENTAL PROCEDURE:

1. Microscope was set up.
   
2. Five different particle samples were labelled with A, B, C, D and E.
   
3. A pinch of sample A was taken and put on the slide. The particles were separated one with another to prevent from redundant particle on one place. This will prevent accurate analysis of size and shape of particles.
4. The sample was put on the slide and observed the particles size and shape using microscope with magnification x10.
   
5. The shape and size of particles had been drawn and analysed.
6. The experiment was repeated by changing the particles and used sample B, C, D , E , MCC powder and lactose powder.

RESULTS

TYPES OF SANDS AND POWDERS	IMAGE	CHARACTERISTICS
Sand 150 microns		rough edges due to the presence of attached material smallest size particle diameter different size particles  which include smaller and larger particle size shape cannot be indentified clearly
Sand 355 microns		rough edges due to the presence of attached material smaller particle diameter compared to 500 microns sand different size particles which include smaller and larger particle sizes non- spherical shape
Sand 500 microns		rough edges due to the presence of attached material larger diameter compared to 355 microns sand different size particles irregular shape
Sand 850 microns		defined edges and no attached material larger particle diameter compared to 500 microns sand same size particles non- perfect spherical shape
Various sand		rough edges due to the presence of attached material largest particle diameter different size particles spherical and irregular shape
Lactose		presence of attached material very fine particles shape cannot be identified clearly has projection
Microcrystalline cellulose (MCC)		presence of attached material particles size larger than lactose particles shape cannot be identified clearly has projection

QUESTIONS

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

Many methods are available for determining particle size such as microscopy, sedimentation sieving, Coulter counter, adsorption, elutriation and laser spectrometer. Although the microscope allows the observer to view the actual particles, the results obtained are probably no more “direct” than those resulting from other methods because only two of three particle dimensions are ordinarily seen. The sedimentation methods yield a particle size relative to the rate at which particles settle through a suspending medium, a measurement important in the development of emulsions and suspensions. Sieving is the method that uses a series of standard sieves calibrated by the National Bureau of Standards. Sieves are made up of wire mesh with opening of known size. To determine particle size by this method, a nest of sieves with the coarsest on top is placed on the shaker and the powder sample placed on the top of sieve. Particle diameter is considered as the size of the opening in the larger or finer sieve or as the size of the arithmetic or geometric mean of the opening of the two sieves. The measurement of particle volume, using an apparatus called the Coulter counter, allows one to calculate an equivalent volume diameter. The Coulter Counter determines the particle volume distribution of materials suspended in an electrolyte- containing solution. This instrument utilizes an electrical sensing zone and measure electrical pulses caused by the passage of particles through the zones. Adsorption of a solute from solution or of a gas at low temperatures onto powdered material serves as a measure of the particle surface area that can determine its diameter. In elutriation, the particles are suspended in a moving fluid, generally water or air. In vertical elutriation at any particular velocity of the fluid, particles of a given size will move upwards with the fluid, while larger particles will settle out under influence of gravity. In horizontal elutriation, a stream of suspended particles is passed over a settling chamber. Particles that leave the stream are collected in the bottom of the chamber. Other methods of measuring particle diameter size include a laser diffraction. It is a common, and fully automated, in-line method of measuring the particle size distribution of a sample. The light-scattering effect caused by the interaction of a laser beam with particles is measured by an array of detectors. The size distribution of the particles can then be calculated using the principle that the angle of diffraction of the light is inversely proportional to the particle size. Every method has a suitable size range for measurement. Since the particle size measurements obtained by methods differing in principle will yield different results, it is necessary to be aware of and to understand the method and size characteristic involved in any particular method. For the measurement diameter of particle, therefore, one should select the method most suitable for the purpose of the measurement after considering the history of the powder sample and deciding upon the appropriate size characteristics.

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

Sedimentation is the best statistical method. The application of ultracentrifugation to the determination of the molecular weight of high polymers has already been discussed. The particle size in the subseive  range can be obtained by gravity sedimentation as expressed in Stoke’s law, The equation holds exactly only for spheres falling freely without hindrance and at a constant rate. The law is applicable to irregularly shaped particles of various sizes as long as one realizes that the diameter obtained is a relative particle size equivalent to that of sphere falling at the same velocity as that of the particles under consideration. The particles must not be aggregated or clumped together in the suspension because such clumps would fall more rapidly than the individual particles and erroneous results would be obtained. The proper deflocculating agent must be found for each sample that will keep the particles free and separate as they fall through the medium. There are two common sedimentation methods which are integral sedimentation and differential sedimentation. Integral sedimentation can be applied to particles lower in density than the fluid in which they are suspended. In this case, the particles have a net buoyancy, so they sediment toward the surface of the fluid rather toward the bottom. In differential sedimentation, a sample of particles to be analyzed is placed on top of column of clear liquid at the start of the analysis, and the particles settle according to Stoke’s Law, just as in integral sedimentation.

DISCUSSION:

          In this experiment, five different types of sands and powders with particular emphasis on the size and shape of particles are analysed. For the analysis of particle size by using microscope, it is carried out on two-dimensional images of particle. It is normally assumed to be oriented randomly in three dimensions. This assumption is considered valid for most of the cases. 
However for dendrites, fibres or flakes it is very unlikely that the particles will orient with their minimum dimensions in the plane of measurement. Therefore, the size analysis is carried out by assuming they are viewed in their most stable orientation. Thus, overestimation of size occurs as the largest dimensions of the particle will be observed as the smallest dimension will most often orientate vertically.
     The two dimensional images are analysed according to the desired equivalent diameter. Disadvantages of this method include it is not suitable for quality control, elaborate sample preparation and slow and rapid operator fatigue.

CONCLUSION:

In conclusion ,different types of particles (sand or powder) have different properties in terms shape,size and diameter. 

REFERENCES:

1) https://books.google.com.my/books?id=jayzqzefqUsC&pg=PA65&lpg=PA65&dq=size+and+particle+analysis+experiment&source=bl&ots=e25EbMF6Ul&sig=F4p8qDCk4nn6AukyK2WEi3PdJ3g&hl=en&sa=X&ei=3aCNVOPZAsfJuATGu4KgBw&sqi=2&ved=0CGcQ6AEwCA#v=onepage&q=size%20and%20particle%20analysis%20experiment&f=false

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