For coated particles to be suitable in a sustained release application, the quality of
the coating must be strictly controlled. This is done by establishing the optimum
operating conditions for a particular coating material and seed particle. An ability to
monitor the thickness and uniformity of the coating between particles and within an
individual particle is essential in assessing the suitability of any set of process
conditions. Although there are a number of ways to measure the particle size
distribution (PSD), many of these procedures may not be useful for determining
uniformity of the coating deposited on the original particles.