Freeze-drying Flashcards
Dr. Ubani
1
Q
What is freeze-drying?
A
Freeze-drying, also known as lyophilization, is a dehydration process that removes moisture from a substance by freezing the material and then subjecting it to a vacuum to allow the frozen water in the material to sublimate directly from the solid phase to the gas phase.
It is used to dry extremely heat sensitive materials e.g. Proteins, peptides, blood products, hormones, vaccines, without excessive damage.
2
Q
Draw the phase diagram of water showing the triple point.
A
[Learn it]
3
Q
What are the stages of the freeze-drying process?
A
- Freezing stage: The solution is cooled to below the normal freezing temperature for pure water, between -10℃ to -30℃, but typically below -18℃.
- Vacuum application stage: The frozen material is connected to a vacuum to reduce the pressure below the triple point and remove the large volumes of vapour formed during drying.
- Sublimation stage: In this stage primary drying occurs by supplying latent heat of sublimation. Secondary heating is applied to completely remove the residual moisture in the container.
4
Q
What are the advantages of freeze-drying?
A
- Drying occurs at very low temperature, so enzyme action is inhibited and chemical decomposition is minimised.
- Freeze dried products are light and porous and therefore dissolve rapidly.
- Concentration of the product is avoided in free drying, hence proteins are not denatured.
- The process is carried out under high vacuum, which minimises contact with air, thus oxidation is minimised.
5
Q
What are the disadvantages of freeze-drying?
A
- Porosity, easy dissolution and complete dryness of the product result in it being very hygroscopic.
- The process is very slow and uses expensive and complicated equipment.
6
Q
What are the pharmaceutical applications of freeze-drying?
A
- It is used for products which cannot be dry satisfactually by any other heat method e.g., some antibiotics, blood products, vaccines, enzymes and microbiological cultures.
- It is used in formulating fast dissolving tablets.
- Stabilisation of novel drug delivery systems e.g., liposomes, microparticles and nanoparticles.
