how to dry samples

Freeze-Drying or Lyophilization is based on the physical phenomenon of the sublimation of water or of an organic solvent or of aqueous-organic mixtures that are frozen; the frozen solvent sublimates directly to vapor without passing through the liquid state. Usually, when working with food, protein or biological material, the solvent to be removed is water. 300K is optimizing this process to improve biological sample, conservation, storage and shipment.

The objective of lyophilization is to obtain a dry product, which when water or solvent is added again, presents the same characteristics as the original product (shape, color, aroma, flavor and texture). Freeze drying reduces quality losses due to deterioration of the sample due to chemical reactions and / or enzymatic degradation.

Lyophilization process have several advantages over other conservation methods:

• You get products that can be regenerated very quickly.
• The shape and characteristics of the final product are essentially the original ones.
• It is an ideal process for drying thermolabile substances.
• Oxidizable constituents are protected.
• The final moisture level is very low, less than 5 % of water content.

Freeze-Drying/Lyophilization process comprises three phases:

1. Freezing
2. Primary Drying (Sublimation)
3. Secondary Drying (Adsorption)

Freezing Phase

Freeze drying is easiest to accomplish using large ice crystals, which can be produced by slow freezing or annealing. However, with biological materials, when crystals are too large they may break the cell walls, and that leads to less-than-ideal freeze drying results. To prevent this, the freezing is done rapidly.

Primary Drying (Sublimation) Phase

Freeze drying’s second phase is primary drying (sublimation), in which the pressure is lowered and heat is added to the material in order for the water to sublimate. The vacuum speeds sublimation. The cold condenser provides a surface for the water vapor to adhere and solidify. The condenser also protects the vacuum pump from the water vapor. About 95% of the water in the material is removed in this phase. Primary drying can be a slow process.

Secondary Drying (Adsorption) Phase

Freeze drying’s final phase is secondary drying (adsorption), during which the ionically-bound water molecules are removed. Most materials can be dried to 1-5% residual moisture.