Title
– Particle Size and Shape Analysis using Microscope
Date : 16 November 2015
Objectives
1)
To analyse and compare the various size
and shapes of the prepared samples of 150, 355, 500 and 850 µm and various
sizes of sand as well as the sample of lactose and MCC (Microcrystalline
Cellulose) under the microscope.
2)
To describe the distribution particle
size and shape.
3)
To determine the percentage of different
grain sizes contained within a soil.
Introduction
Particle size analysis
or dimensions of particulates are important in the field of pharmaceutical
science in order to achieve optimum production of efficacious medicine. The
particle size and shape analysis are involved in the physical and
pharmacological performance of drug, the production of formulated medicines as
solid dosage forms and the drugs dissolution in the human body in conjunction
with its release properties from the human body. Different particle sizes of
powder have different flow and packing properties which alter the volume of
powder during each tablet compression event. The particles that have small
dimension will tend to increase the rate of dissolution.
As for example, MCC
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 particle shape and
size can be analysed by many methods. One of it is by using a microscope. This
analysis can be used to determine the diameter, shape, and surface area of a
particle by dispersing the samples on a microscope slide to avoid analysis of
agglomerated particles and looking directly at the particle in a microscopic
vision.
The equivalent
diameters measured for microscope method are projected area diameter, projected
perimeter diameter, Feret’s diameter and Martin’s diameter.
Material
Five different
types of sands of 150, 355, 500, 850 µm and various size, as well as powders of
MCC and lactose.
Apparatus
Microscope,
slide, spatula and weighing boat.
Procedures
1. Seven different types of samples are put on different slides and labelled.
2. The microscope
is set up and the first slide sample is observed and examined by 4x10
magnification.
3. The particles
shape and size are analysed and sketched.
4. The experiment
is repeated using the other particle samples.
Results
Discussion
After observing and analysing the
particles shape, it is found that the overall shape of the particles is
irregular or asymmetrical. In order to measure the particle size, the method
used is the equivalent diameter, in which the projected area diameter which is
measured based on the circle of equivalent area to that of projected image of
that particle and the projected perimeter diameter which is based on the circle
having the same perimeter as the particle. Both of the diameters are
independent of particle orientation. They only consider the two dimensions of
the particle, thus it is inaccurate for unsymmetrical particle.
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.
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. The
size analysis is carried out on two-dimensional image of particles which are
generally assumed to be randomly oriented in 3-dimensional and they are viewed
in their most stable orientation.
Feret’s and Martin’s
diameter is dependent on both orientation and shape of the particles is another
one of the methods to measure the size of particle. These are the statistical
diameters which are averaged over many different orientations to produce a mean
value for each particle diameter. Feret’s diameter is the mean distance between
two parallel tangents to the projected particle perimeter while Martin’s
diameter is the mean chord length of the projected particle perimeter, which is
the boundary separating equal particles.
Besides, since
it is accessing the three-dimensional image of particle, we can use the
electron microscope that considering the orientation and shape of the image.
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.
Light microscope
method is not suitable for quality control, elaborate sample preparation and
slow and rapid operator fatigue. However, the ability to analyse and
characterize particle size and shape can significantly improve the
manufacturing efficiency and product performance. Thus, we can use of
microscopy and image analysis to characterize particle shape, size and volume
distribution.
There are some
precaution steps taken while carrying out the experiment that the students wear
goggles and mask all the time to avoid the samples unintendedly get contacted
with the eyes. Besides, the experiment is carried out in an open space with a
non-windy condition to avoid the sand and powder from distributing everywhere.
The careful handling and transferring of the particles from the weighing boat
to the slide for microscopy by using spatula is taken into account in order to
prevent the particles from mixing with other particles not under study such as
dirt and dust and affect the accuracy of result. Next, only small amount of
sand and powder is put on the slide and is spread evenly to get a clear image.
Conclusion
We are able to
determine the overall distribution of shape and size of this particle that are
asymmetrical and irregular. In conclusion, different types of samples have
different shape and size analysis. Microscope method is an excellent technique to
be used where the light microscope allows the direct observation of the
particles in order to analyse the shape and size of particles depending on the
presence of agglomeration. The understanding of the characteristic of
particularly the active ingredients and excipients as the
pharmacologically inactive substance is always being used in the formulation of
drugs is thus indeed important.
Questions
1. Explain in brief the various statistical methods that you can
use to measure the diameter of a particle.
Various measures of the size of irregular shaped particles as
seen under the microscope have been used, chosen according to their theoretical
significance or practical ease of measurement.
These include, using Heywood’s notation, which measures the
diameter of the particle using projected perimeter diameter, dp, or
projected area diameter, da. The projected perimeter diameter is
based on a circle having the same perimeter as the particle. The projected area
diameter is based on a circle of equivalent area to that of the projected image
of a solid particle. Unless the particles are unsymmetrical in three
dimensions, then these two diameters will be independent of particle
orientation.
Feret’s and Martin’s diameters, where these methods are
dependent on both the orientation and the shape of the particles. These are the
statistical diameters which are averaged over many different orientations to
produce a mean value for each particle diameter. Feret’s diameter refers to the
mean distance between two parallel tangents to the projected particle perimeter.
Martin’s diameter is the mean chord length of the projected particle perimeter
which can be considered as the boundary separating equal particle areas (asymmetry
line).
Sieve diameter is defined as the width of the minimum square
aperture through which the particle will pass. A common sizing device
associated with this definition is a series of sieves with square woven meshes.
The surface diameter, ds, volume diameter, dv,
and Sauter’s diameter, d32, are defined such that each of them reflects a 3D
geometric characteristic of an individual particle. The concept of surface
diameter may be mostly used in the field of adsorption and reaction
engineering, where the equivalent surface exposure area is important. The volume
diameter of a particle may be useful in applications where equivalent volume is
of primary interest, such as in the estimation of solids holdup in a fluidized
bed or in the calculation of buoyancy forces of the particles. The volume of a
particle can be determined by using the weighing method. Sauter’s diameter is
widely used in the field of reacting gas-solid flows such as in studies of
pulverized coal combustion, where the specific surface area is of most
interest.
The dynamic response of a particle in gas-solid flows may be
characterized by the settling or terminal velocity at which the drag force
balances the gravitational force. The dynamic diameter is thus defined as the
diameter of a sphere having the same density and the same terminal velocity as
the particle in a fluid of the same density and viscosity.
2. State the best statistical method
for each of the samples that you have analysed.
The best statistical
method for each of the samples analysed is by Feret’s and Martin’s diameter
because both of the parameters give the average diameter over many different
orientations to produce a mean value for each particle diameter. This will give
an average value which is more accurate.
References
ReplyDeleteScientific Instruments