Every formulation has a critical temperature, below which it should be cooled for complete solidification and maintained below during primary drying in order to prevent processing defects.
In R&D, the glass transition temperature of the maximally freeze concentrated solute (Tg`) is often used as the critical temperature, although Tg` and the collapse temperature (Tc) are frequently reported to show a bias of 1-5 degrees C for the same formulation.
An informative new presentation (www.genevac.com/freeze-drying) is available from Genevac that provides you with the best ways to achieve the critical formulation temperature in order to develop an optimised freeze-drying process.
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