Tc and Tg points

Reagents and assays that are to be freeze-dried possess a critical temperature known as the collapse temperature, often denoted Tc, which it is essential not to cross during freeze-drying. It is important to maintain the temperature below Tc until drying is completed. If the product is maintained too far below this temperature it can lead to an unacceptably slow drying process.

The collapse temperature for commonly used cryo-preservatives in molecular assays is often found to be around 4oC higher that the products glass transition (Tg) point. Therefore, it is valuable to know this critical temperature for a formulation prior to lyophilisation, in order to create a suitable lyophilisation program. If required a suitable cryo-preservative solution can be developed to modify reagents for freeze-drying.

 

Many molecular assay formulations are amorphous in nature and for these the Tg and Tc correspond to the temperatures at which the material softens to the point of not being able to support its own structure and begins to collapse. Inappropriate cryo-preservatives and/or inappropriate critical lyophilisation temperatures may result in incomplete drying, collapse, and potential stability issues.