PARTICLE SIZE ANALYSIS

Why measure particle size of pharmaceuticals??? Since particle size can affect micromeritics of specimen substance,,,, like 1- “Processability” of powder 2-Final formulation

Methods for Determining Particle Size 1-Microscopy 2-Sieving 3-Sedimentation

Microscopy 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…….

Advantages : Relatively inexpensive Each particle individually examined Detect aggregates Permanent record – photograph Small sample sizes required For submicron particles, Electron microscopy can be performed.

DISADVANTAGES : Time consuming High 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.

SIEVING It is based upon WEIGHT DISTRIBUTION. 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. Approx. size range : 5μm - ~3mm

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

ADVANTAGES : Easy to perform Wide size range Inexpensive

DISADVANTAGES : Known problems of reproducibility Wear/damage in use or cleaning Irregular/agglomerated particles Rod-like particles : overestimate of under-size Labour intensive

Sedimentation Techniques: It is based upon WEIGHT DISTRIBUTION. These methods depend on the fact that the terminal velocity of a particle in a fluid increases with size. It follows Stoke’s Law,, states;

METHOD:

ADVANTAGES: Equipment required can be relatively simple. Inexpensive Can measure a wide range of sizes with accuracy and reproducibility.

DISADVANTAGES: 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.