SUMMARY
Particle size characterization is one of the key areas involved in quality assurance. The concept of particle size and size characterization acts as a foundation for all the processes involved in theproduction of a formulation; from manufacturing to quality control operations. Particle size characterization dictates many properties of the finished product. Particle size characterization of samples is important to make a better quality product, improve its appearance, taste, texture and shelf-life. There are many instruments for particle size characterization that are available commercially. Each instrument is based on a different technique and each technique is based on a different principle. Selecting the right particle size characterization technique for the given sample is a challenging decision. The choice of technique is made according to the sample. Sometimes even a combination of techniques is used to obtain accurate results. There are several factors upon which choice of technique depends like size range, sample quantity, cost effectiveness etc. To ensure appropriate quality standards in the field of particle sizing and particle size characterization, ICH and US-FDA have recently insisted on including Quality-by-design approach in thepharmaceutical industry. Application of QBD approach to particle size characterization techniques ensures a resilient method which gives reproducible results. It aids in reducing result and method variations and promotes productivity and quality. The main objectives of this review are first, to understand the principle, instrumentation, and working of commercially used techniques and to compare their pros and cons; secondly, to study the factors which govern the choice of technique and lastly, to understand the concept of Quality by design and its role in particle size characterization through some example.Keywords: Particle size characterization; techniques; factors;QBD