Particle size distribution and its methods

PARTICLE SIZE DISTRIBUTION
AND ITS METHODS

PARTICLE SIZE DISTRIBUTION AND
ITS METHODS
presented by
MD JAHA SULTANA,
M. Pharmacy
(pharmaceutics)
137N1S0308.
Under the Guidance of
Mr. S.SELVA RAJ, M. Pharm
Assistant Professor,
Department of Pharmaceutics.
VIJAYA INSTITUTE OF PHARMACEUTICAL SCIENCES
FOR WOMEN
Enikepadu, Vijayawada-521108

CONTENTS
Introduction
Particle size expression
Particle size distribution
Methods for determination of particle size
Calculation of average particle size
Conclusion

A particle is a small localized object through which
several physical or chemical properties such as volume
or mass are described.
Particle size, also called grain size, refers to the
diameter of individual grains of sediment.
The Particle-size distribution is defines the relative
amount of particles present according to size. PSD is
also known as grain size distribution.
INTRODUCTION

Spherical particles – Diameter
Non spherical particles – Surface area,
volume or diameter of spherical particles
SIZE OF PARTICLES MAY BE
EXPRESSED

Surface diameter (ds): Having same
surface area of asymmetric particles.
Volume diameter (dv): Having same
volume of asymmetric particles.
Volume - surface diameter: Having
same volume to the surface area ratio of
particles.

Sieve diameter: Passed through the
sieve aperture as the particle.
Stocke’s diameter: Having same density
of asymmetric particles.
Projected diameter: Having same
observed area of asymmetric particles.

It is determine in two ways
I. Microscopic technique (number)
II. Sieving method (weight)
1. Frequency distribution curve:
It is obtained by plotting a graph between number (or) weight
of the particles Vs size range (or) mean particle size
PARTICLE SIZE DISTRIBUTION

2. Normal and Weight
distribution:
Due to large variation in size
of powders normal distribution
is not seen. Such distributions is
termed as unsymmetrical or
skewed.
3. Log Normal
distribution curves:
It is shown by powders which
obtained by crystallization and
milling methods.
Graph is plotted against log
mean particle size and %
frequency.

4. Cumulative frequency distribution curve:
It is obtained by plotting particle size against cumulative %
frequency.
A sigmoid curve is obtained by plotting the data values and then
joining them.

Microscopic method
Sieving method
Sedimentation method
Coulter – counter method
METHODS FOR DETERMINING
PARTICLE SIZE

I. Optical microscopy (1-150µm)
II. Electron microscopy (0.001 - 5µ)
For submicron particles it is necessary to use either
TEM (Transmission Electron Microscopy) or
SEM (Scanning Electron Microscopy).
TEM and SEM (0.001-5µm)

Calibration of the
eye piece
micrometer using
standard stage
micrometer.
A dilute suspension of
powder particles
whose sizes are to be
determined is
prepared in liquid
vehicle in which it is
insoluble.
A drop of
suspension is taken
and mounted on a
glass slide which is
then observed
under the
microscope.
On an average of
about 300
particles are
counted through
eye piece
micrometer.
The data can be
scientifically
represented by size
frequency
distribution.
From that data
the average
particle size is
determined.
Procedure:

ADVANTAGES:
Relatively inexpensive.
Each particle individually examined - detect aggregates, 2D
shape, colour, melting point etc.
Small sample sizes required.
DISADVANTAGES:
Time consuming.
High operator fatigue - few particles examined.
Very low output.
No information on 3D shape.
MANUAL OPTICAL MICROSCOPY

TRANSMISSION AND SCANNING ELECTRON
MICROSCOPY
ADVANTAGES:
Particles are individually examined.
Visual means to see sub-micron specimens.
Particle shape can be measured.
DISADVANTAGES:
Very expensive.
Time consuming sample preparation.
Materials such as emulsions difficult/impossible to prepare.
Not for routine use.

This method is used for particle size having range from
50 - 1500µm.
This method directly gives weight distribution.
Sieve number is defined as number of pores per linear
inch.
Generally the pore size is ranging from 90 µm to 5 µm.
Based on sieve number particles may be classified as:
Passage of all
particles through
sieves
Passage of particles
not more than 40%
through sieves
Grade of powdered
particles
10 44 Coarse
22 60 Moderately coarse
44 85 Moderately fine
85 - Fine
120 - Very fine

Procedure:
A series of standard
sieves calibrated by the
National Bureau of
Standards are taken and
stacked on one another.
Sieve with less
number must
be arranged on
the top.
Certain specified
mass of the substance
is placed on the
stacked sieves of
different sizes.
The setup is
agitated for a
specified period of
time.
The powder that
remains on the top
of each sieve is
collected and
weighed.
Data is
recorded and
calculated.

ADVANTAGES:
Easy to perform.
Wide size range.
Inexpensive.
DISADVANTAGES:
Weight changes while loading and unloading.
Irregular particles.
Attrition occur.
Labour intensive.

Based on sedimentation principle various methods are available for
determination of particle diameter.
 Pipette method
 Balance method
 Hydrometer method
Pipette method is most widely used because of ease of analysis,
accuracy and economy.
Particle size is expressed in stokes diameter (dst).
SEDIMENTATION METHOD

ANDREASEN PIPETTE
Construction:
10 ml Andreason pipette.
550 ml vessel.
Pipette is sealed with glass stopper.
The lower tip of pipette is placed 20cm below the
surface of suspension.
Method:
1 – 2 % of suspension of the particles in a suitable
medium is prepared and placed into the vessel.
The medium should have deflocculating agents in order
to separate any aggregates if present.
A stopper is placed onto the vessel and shaken
vigorously.
The entire set up is placed in a water bath maintained at
constant temperature.
Each 10ml of the sample is withdrawn into a weighed
china dish.
Then the samples are evaporated and weighed
separately.

The particle diameter can be determined using stoke’s equation
and rate of sedimentation.
Where,
d = Stoke’s diameter.
η1 = Viscosity of the medium.
ρ = Density of the powder.
ρ1 = Density of the medium.
g = Acceleration due to gravity.

ADVANTAGES:
Equipment is simple and inexpensive.
Accurate results can be obtained if standard method is
followed.
DISADVANTAGES:
Laborious method.
Careful temperature control is necessary to suppress
convection currents.
Chance of re-aggregation of particles during extended
measurements.
Determination of smaller sized particles is inaccurate.

Construction:
Two electrodes : One electrode is dipped into a container
containing electrolyte and particles.
Other electrode is immersed in a tube
containing the electrolyte solution.
Tube : Holds second electrolyte.
Orifice : Present between the tube and the container
which connects them.
Container : Contains electrolyte solution
Amplifier : Electrodes are connected to amplifier
through their terminals.
Mercury tube : Connected to the counter drive.

Method:
A predetermined
volume of dilute
suspension in an
electrolyte
solution is taken
and kept into a
container.
Dispersion
electrolyte +
particles from the
container is forced
into the tube
through the orifice.
Suspension should
be very dilute such
that only a single
particle passes
through the orifice
each time.
Electrodes are
kept at constant
voltage.
As the particle passes
through the orifice
increased electrical
resistance is observed
and voltage pulse is
generated.
Finally particle
size is
determined.

Advantages:
Accurate results.
Less time consuming.
Automatic.
Volume of very small particles in the size range of 0.5 – 1000
µm can be obtained.
Disadvantages:
Sample has to be suspended in predetermined volume of
electrolytic solution.
Aggregation of particles.

Edmundson has given a mathematical equation
for average particle size.
Where,
n = number of particles in each range.
d = equivalent diameter
p = size index
f = frequency
CALCULATION OF AVERAGE
PARTICLE SIZE

Examples:
Drug Particle Size Requirement
Hydrocortisone (o/w) 90% of the particles should be in
the range of 5 – 50 µm
Insulin Zinc amorphous
form (Injection)
< 2 µm
Betamethasone (tablets) 90% of the particles should be < 5
µm

Powders and particles are used in a wide variety of fields either they can
be used directly as pharmaceuticals, catalysts, additives, or binders while
in other formulations they are used as raw ingredients. In both the cases,
particle size distribution have major effects on performance and quality of
a final product.
In suspension, particle size distribution effects the rate of sedimentation,
which inturn effects physical stability of the product.
In tablets dosage forms, particle size distribution effects flow property
which inturn effects uniformity of product.
So from this, I conclude that measuring the particle size distribution is
essential for stabilizing the quality of products.
CONCULSION

Alfred Martin; A text book of Physical Pharmacy; fifth edition ; Page No:
533-546.
Aultons; Pharmaceutics The Design & Manufacture of Medicines; third
edition; Page No: 121-135.
Manavalan. Ramasamy; Physical Pharmaceutics; Page No: 313-326.
D.V.Derle; Essentials of physical pharmacy; Page No:182-194.
Cooper and Gunn’s; Tutorial pharmacy;Page No:174-182 .
en.wikipedia.org/wiki/Particle-sizedistribution
www.horiba.com/fileadmin/uploads/.../PSA/PSA_Guidebook.pdf
www.inventi.in/Article/ppt/587/12.aspx
www.tcd.ie/CMA/misc/particle.ppt
terpconnect.umd.edu/~sehrman/particle-class/PSA-05-1-and2.ppt
http://www.authorstream.com/Presentation/javadsameni-231114-particle-
size-analysis-pharmaceutics-particles-science-technology-ppt-powerpoint/
www.rci.rutgers.edu/~moghe/PSD%20Basics.pdf
REFERENCE

Particle size distribution and its methods

Particle size distribution and its methods

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