Caffeine — PIT (Process-induced transformation)
Process steps such as grinding, tablet pressing, etc., can affect the crystal structure of the solid API, both in its pure form or as a formulation component.
In the present example, caffeine form I with a melt onset temperature of approx. 136°C was stored 1 week at room temperature without any treatment (blue curve) and after compression (20 kN, red curve).
After compression, a small endothermal transformation effect at approx. 156°C (peak temperature) appears which indicates that pressing of the sample results (after a while) in the formation of form II that converts to form I during heating. Directly after the compression, only form I is present.
The measurements were carried out with sample masses of approx. 2.8 mg at 10 K/min heating rate in an
N2 atmosphere in Al crucibles with pierced lid.