Lyophilisation
In short Freeze-drying under vacuum, which turns a peptide solution into a stable dry powder.
In lyophilisation the peptide solution is frozen, then placed under vacuum so that the ice turns directly into vapour without melting. A final drying stage removes most of the remaining bound water. What is left in the vial is a dry, porous cake or powder.
Peptides in solution can degrade through several routes: hydrolysis of peptide bonds, oxidation of sensitive residues such as methionine or cysteine, and aggregation. Removing the water slows all of these considerably, which is why research peptides are supplied lyophilised rather than as ready-made solutions.
Lyophilised vials are best kept at −20 °C and protected from light. Left at room temperature for the short time of a delivery they are generally stable, but long-term storage should be cold. Once a peptide is returned to solution (reconstitution), it should be kept at 2 to 8 °C and the clock on its stability starts again.
Manufacturers sometimes add an excipient such as mannitol before freeze-drying to give the cake structure. Where a lot contains one, the certificate says so.