Lyophilized means freeze-dried
Lyophilized means freeze-dried. Lyophilization is a drying process: a solution is frozen, and the ice is then removed under vacuum so that the water passes directly from solid to vapour without melting. What remains is a dry solid, called a lyophilisate or, from its shape in the vial, a cake. Lyophilized, freeze-dried and lyophilisate all describe material dried this way.
These words describe how a material was dried. They say nothing about its identity, purity or amount, and freeze-drying does not make a material sterile. Those questions are answered by the lot documents and test reports.
How lyophilization works
Lyophilization runs in three stages, each controlled by temperature and chamber pressure. The settings are chosen for the material being dried.
- Freezing: the solution is cooled until the water and the dissolved material are completely solid.
- Primary drying: the pressure is lowered and gentle heat is supplied, so the ice sublimes and leaves a porous structure behind.
- Secondary drying: the temperature is raised to remove water still bound to the solid, down to a low residual moisture.
Why peptides are supplied lyophilized
In solution, many peptides change over time. Water takes part in hydrolysis of the peptide chain and in deamidation of asparagine and glutamine residues, dissolved oxygen can oxidize methionine, cysteine and tryptophan, and solutions can support microbial growth. Removing the water slows most of these reactions considerably. A dry solid therefore generally keeps its composition longer than the same peptide in solution, and it is easier to ship and store.
A lyophilized peptide is rarely peptide alone. Synthetic peptides are usually isolated as salts with counter-ions such as acetate or trifluoroacetate (TFA), and the dried solid keeps some residual water. The weight of solid in a vial and the amount of peptide in it can therefore differ; the guide on peptide purity and net peptide content explains why.
Terms on labels and documents
Documents for lyophilized materials use a small set of terms. Read each one for what it states, and keep it separate from results such as purity.
| Term | Meaning | What it does not tell you |
|---|---|---|
| Lyophilized, freeze-dried | Dried by freezing and removing the ice under vacuum. | Identity, purity or amount. |
| Lyophilisate, cake | The dry solid in the vial; it may stay in one piece or break into powder. | The amount of material in the vial. |
| Residual moisture | Water left in the solid after drying, often measured by Karl Fischer titration. | How much of the solid is peptide. |
| Hygroscopic | Readily takes up water from the air once the vial is open. | The storage temperature, which the lot documents state. |
| Counter-ion (acetate, TFA) | The ion paired with the peptide in its salt form; it adds weight without being peptide. | The purity of the peptide. |
| Net peptide content | The share of the solid’s weight that is peptide. | Purity, which compares the peptide with other detected components. |
Receiving a lyophilized vial
Because the ice leaves without melting, the dried solid keeps roughly the shape and volume of the frozen fill. A few milligrams of material can therefore look like a small cake, a loose powder or a thin film on the glass, and a vial may appear almost empty.
On arrival, compare the vial label and lot number with the quote and the lot documents before judging appearance. Lyophilized peptides are often white or off-white, but some are coloured: copper peptides such as GHK-Cu are blue. The cake may have shrunk, cracked or broken into powder in transit. Appearance does not show identity or purity, so record what you see and ask us if it differs from the lot documents.
Ask for the documents for the exact lot in your quote. A report describes only the batch it tested, so check that its lot number matches the lot you receive.
Storing lyophilized material
Lyophilized material keeps best when it stays dry and protected from light. Follow the storage conditions in the lot documents, and build these points into your laboratory routine:
- Keep the vial sealed and protected from moisture and light, under the storage conditions in the lot documents.
- Let a cold vial reach room temperature before opening, so that moisture does not condense on the solid.
- Open the vial as few times as possible, and record the lot number with each use.
For laboratory research. Not for human or animal use.