INTRODUCTION

The study of science and technology of small particles along with the fundamental and derived properties of indiviodual as well as a collection of particles is known as micromeritics. The micromeritic properties of a drug can be related in a significant way to the physical, chemical and pharmacological properties of a drug.

Clinically, the particle size of a drug can affect its release from dosage forms that are administered orally, parenterally, rectally and topically. Thus, the successful formulation of suspensions, emulsions and tablets, from the view points of both physcal stabilityand pharmacologic response, also depends on the particle size achieved in the product.

PRINCIPLE

The particle-size distribution (PSD) of a powder, or granular material, or particles dispersed in fluid, is a list of values or a mathematical function that defines the relative amount, typically by mass, of particles present according to size. Significant energy is usually required to disintegrate soil, etc. particles into the PSD that is then called a grain size distribution. Sieve analysis can be used for many measurements because of its simplicity, cheapness, and ease of interpretation. Methods may be simple shaking of the sample in sieves until the amount retained becomes more or less constant. Alternatively, the sample may be washed through with a non-reacting liquid (usually water) or blown through with an air current.

Advantages: This technique is well-adapted for bulk materials. A large amount of materials can be readily loaded into 8-inch-diameter (200 mm) sieve trays. Two common uses in the powder industry are wet-sieving of milled limestone and dry-sieving of milled coal.

Disadvantages: Mny PSDs are concerned with particles too small for separation by sieving to be practical. A very fine sieve, such as 37 μm sieve, is exceedingly fragile, and it is very difficult to get material to pass through it. Another disadvantage is that the amount of energy used to sieve the sample is arbitrarily determined. Over-energetic sieving causes attrition of the particles and thus changes the PSD, while insufficient energy fails to break down loose agglomerates.