What is Freeze Drying?

Freeze Drying is a process whereby a product is dried, that is water is removed, under low temperature and pressure. The water in the sample is first frozen to ice and then removed directly to vapor without passing through the liquid phase. This is carried out under vacuum.

 

Drying—what is drying?

Drying or dehydration is the process where the solvent in the sample in our case water, is physically removed from sample such that the solids are obtained in an essentially dry (eg. Wa- ter-free) condition.

 

Why Dry?

 • To increase stability of the sample.

 • To improve shelf life of pharmaceutical products.

 • To prepare sample of microscopic studies.

 • To prepare sample of future analysis.

 • To remover product from dissolved sample.

 • To reduce volume / weight.

Freeze drying is essentially a 3 steps process

1. Prefreezing

 During the Prefreeze step the sample is frozen so that all     the solvent    (normally water ) turns to solid (ice).

2. Primary Drying (Sublimation)

In Primary Drying, the ice sublimates or turns directly to     vapour under low pressure (vacuum).

3. Secondary Drying (Desorption)

   In secondary Drying the remaining water, not frozen but   bound by molecular bonding to the solute, is removed from    the sample.