In
this work, the effect of crystallization parameters, i.e., supersaturation,
seeding, and temperature, on the polymorphism and crystal size of
a nonsteroidal anti-inflammatory drug, indomethacin (IMC), was investigated.
First, several crystallization solvents (ethanol, methanol, ethyl
acetate, acetone, acetonitrile, and dichloromethane) were screened
through the measurement of IMC solubility at different temperatures.
This was followed by the investigation of IMC nucleation through measurement
of induction times in selected solvents at two supersaturations. Finally,
seeded cooling crystallization of IMC in ethanol was performed with
different process parameters to investigate the influence on the polymorphism
and crystal size distribution. Remarkably long induction times were
observed for IMC in ethanol and ethyl acetate solutions, while a shorter
induction time was observed in acetone. Cooling crystallization of
IMC from ethanol confirmed that supersaturation, operating temperature,
and seeding do affect the polymorphism as well as crystal size distribution
of IMC. Fine needle-shaped crystals of metastable α-IMC were
obtained at 5 °C with high supersaturation even in the presence
of γ-IMC seeds, while rhombic platelike crystals of thermodynamically
stable γ-IMC were obtained in the remaining experiments. The
seed loading only marginally influenced the crystal growth rate and
median particle diameter. Particle size analysis of the crystals obtained
showed a bimodal distribution in all experiments, and a larger median
particle diameter was observed at 15 °C with high supersaturation.