Particle Size Analysis: A Glossary of Terms

In the fascinating world of particle size analysis, there are many difficult terms that you may need to get to grips with. Here we’ve provided a glossary of terms from Agglomeration through to Zeta Potential — it’s truly an A to Z of particle size analysis.

Agglomeration

A jumbled collection or mass of particles that have collected together; furthermore, the collection of these particles is known as “agglomeration”.

Aqueous solubility

Measured by weight, this refers to the maximum percentage of a substance that dissolves in a unit volume of water.

Bioavailability

The extent to which a living organism is able to absorb a drug into its systemic circulation. Bioavailability is important in ensuring drugs have their desired effect in the body.

Chromatography

A method of separating a mixture of compounds by passing them through a medium in which the components progress at different rates.

Coarse particle fraction

The percentage of a material which is composed of large particles.

Dose uniformity

The extent to which the active material within a sample of dosage units remains uniform. It is usually expressed as a percentage of the average content.

Hydrodynamic volume

The overall volume of a polymer when it is situated within a solution. The hydrodynamic volume can be measured by the way the polymer behaves in that solution.

Laser diffraction

A technique for measuring particle size which is predicated on the idea that particles moving through a laser beam will scatter light at an angle directly proportional to their own size. Laser diffraction is one of the most effective methods of particle size analysis.

Milling

The grinding of materials into smaller particles.

Oligomer

A molecule that consists of just a few repeating units, or monomers, which bind together chemically.

Particulate

Small subdivisions of matter that can be found suspended in a gas or liquid.

Percutaneous

Anything which is administered or absorbed through the skin, such as an injection or transdermal drug.

Polydisperity

The state of having a broad range of particle sizes within a semisolid; this stands in opposition to monodispersity, where the particles are all of the same size. Polydispersed materials tend to pack better than monidspersed materials.

Polymer

A large molecule composed of many repeating units, or monomers, which bind together chemically.

Rheology

The study of the deformation and flow of matter, usually in reference to the flow of liquids but also sometimes to semisolids.

Sedimentation

A naturally-occurring process whereby solid particles settle out of the fluid carrying them and come to rest against a barrier.

Semisolid drug

Otherwise referred to as simply a ‘semisolid’, it’s a pharmaceutical product that has some properties of solids and some properties of liquids. Common examples include creams, ointments or gels.

Shear rate

The rate that contiguous fluid layers move in relation to each other.

Size Exclusion Chromatography

A form of chromatography whereby molecules in a solution are separated based on their varying hydrodynamic volume.

Transdermal patch

A patch which is applied to the body in order to administer a certain amount of drugs through the skin and, subsequently, into the bloodstream.

Viscosity

The resistance that a liquid shows to being deformed by sheer stress.

Zeta potential

The effective charge on a particle that is immersed in a liquid.  This can have a significant effect on the stability of particles in suspension.