NAME: MASH’HOOD MAHMOOD KHAN SHAHID

TOPIC: PARTICLE SIZE DETERMINATION

----- PHARMACY DEPT--------

ASSIGNMENT OF PHARMACUETICS-I

PARTICLE SIZE ANALYSIS

Since particle size can affect micromeritics of specimen substance,,,, like

1- “Processability” of powder

2-Final formulation

WHY MEASURE PARTICLE SIZE OF PHARMACEUTICALS???

METHODS FOR DETERMINING PARTICLE SIZE

1-Microscopy2-Sieving 3-Sedimentation

In this method, small sample size is mounted on the stage of microscope and the particle size is measured using the

MICROMETER joined to it…….

MICROSCOPY

Size Range: 0.2 to about 100 Micrometer

Firstly, the powdered substance is placed over the stage and obseved through the lens.

The microscope eyepiece is fitted with a micrometer by which thesize of the particles can be estimated.

The field can be projected onto a screen where the particles are measured more easily, or a photograph can be taken from which a slide is prepared and projected on a screen for measurement.

PROCEDURE:

CONT’D

The particles are measured along an arbitrarily chosen fixed line, generally madehorizontally across the center of the particle.

Popular measurements are; Feret diameter -- Martin diameter -- Projected area diameter

These measurements can be stored as screenshot for long term use.

Relatively inexpensiveEach particle individually examined

Detect aggregatesPermanent record – photograph

Small sample sizes requiredFor submicron particles, Electron microscopy can be

performed.

ADVANTAGES

Time consumingHigh operator fatigue

No information about 3D,, just 2D info about specimen particles

In case of electron microscopy, materials such as emulsions difficult/impossible to prepare.

DISADVANTAGES

Sieve Analysis is performed using a nest or stack of sieves where each lower sieve has a smaller aperture size than that of the sieve above it.

SIEVING

Size Range: 5μm - ~3mm

It is based upon WEIGHT DISTRIBUTION.

Sieving may be performed wet or dry, by machine or by hand, for a fixed time or until powder passes through the

sieve at a constant low rate

METHODS

Machines:– Shaking– Vibration– Use a jet of air to clear the sieves– Ultra-sonics (wet sieving)

Mass of sample is placed on the proper sieve in a mechanical shaker.

The powder is shaken for a definite period of time, and the material that passes through one sieve and is retained on the next finer sieve is collected and weighed.

When a detailed analysis is desired, the sieves can be arranged in a nest of about fivewith the coarsest at the top.

PROCEDURE

Assuming a log-normal distribution, one plots the cumulative percent by weight of powder retained on the sieves on the probability scale against the logarithm of the arithmetic mean size of the openings ofeach of two successive screens.

Easy to performWide size range

Inexpensive

ADVANTAGES

Known problems of reproducibilityWear/damage in use or cleaningIrregular/agglomerated particles

Rod-like particles : overestimate of under-sizeLabour intensive

DISADVANTAGES

It is based upon WEIGHT DISTRIBUTION.

SEDIMENTATION TECHNIQUES

These methods depend on the fact that the terminal velocity of a particle in a fluid increases with size.

It follows Stoke’s Law.

STOKE’S LAW

Mathematically, Stoke’s Law states that;

METHODS

Pipette MethodBalancing Method

Hydrometer Method

Allow a homogeneous suspension to settle in a cylinder, take samples from the settling suspension at a fixed horizontal level at intervals of

time.• Each sample will contain a representative sample of the suspension, with the exception of particles greater than a critical size, all of which

will have settled below the level of the sampling point.• The concentration of solid in a sample taken at time t is determined

• This concentration expressed as a percentage of the initial concentration gives the percentage (w/w) of particles whose falling velocities are equal to or less than x/t. Substitution in the equation

above gives the corresponding Stokes' diameter.

PROCEDURE

PIPETTE METHOD

Equipment required can be relatively simple.Inexpensive

Can measure a wide range of sizes with accuracy and reproducibility.

ADVANTAGES

Large particles create turbulence, are slowed and are recorded undersize.

Particle re-aggregation during extended measurements.Particles have to be completely insoluble in the

suspending liquid.

DISADVANTAGES

THANKSTHE END