Particle size characterisation

Particle size characterisation is required in many aspects of drug delivery research, e.g., drug dissolution rates, powder inhaler carrier lactose, emulsion systems, micellar systems, liposomes, lipid digestion systems and non-viral DNA transfection agents. Size characterisation and size distribution analysis for particles less than about 1 mm in diameter falls into three classes, based on the methodology used. Large dry solid particles (45 - 1000 m) can be characterised by sieve shaking methodology, with manual weighing of sieved fractions, followed by construction of log diameter-probability plot. Solid particles or liquid droplets that extend this size range to smaller sizes (0.2 – 1000 m) can be dispersed in a non-dissolving liquid (water or organic solvents) and characterised by elastic laser scattering methodology using the Malvern MasterSizer S. This instrument can handle sample volumes ranging from 15 to 250 mL. Very small solid particles or liquid droplets (10 nm to 3000 nm) dispersed in liquids may be characterised by the combination of quasi-elastic laser scattering with photon correlation analysis, using the Malvern ZetaSizer 3000. This analysis may be performed on sample volumes as low as 150 L, using special cuvettes, although 3 mL sample volumes are more usual and larger volumes can be analysed with a flow cell. The ZetaSizer 3000 also allows zeta potential (surface charge) measurement for dispersed liquid droplets or solid particles. These methods of particle characterisation are convenient to use, but have the disadvantage that aggregation of particles cannot be detected. Aggregation is demonstrated using high quality microscopy with photographic or digital image analysis. Use of calibration graticles also allows size and size distribution measurements to be performed. The Zeiss microscope allows magnifications up to 1250x and samples can be examined under polarised light conditions on a temperature controlled stage (range, -80 to +350°C)