Storage and stability

Peptides are shipped freeze-dried because removing water removes the main driver of degradation, making the dry material far more stable than a solution. Storage is about slowing chemistry: keep the material cold, dry and in the dark, minimise how often a vial is opened, and check the freeze-dried cake on arrival for any sign it has been compromised.

This page covers how research peptides should be stored as laboratory materials, why, and how to recognise a vial that has been damaged in transit or storage. It describes handling of the material, not any use of it.

Lyophilised versus solution

Material ships lyophilisedLyophilisationFreeze-drying — removing water from a frozen solution under vacuum by sublimation, leaving a dry, stable cake.Full definition → (freeze-dried) because water drives most peptide degradation. With the water removed, the dry cakeVial cakeThe solid, porous mass of freeze-dried material left in a vial after lyophilisation, whose appearance is a quality indicator.Full definition → is markedly more stableStabilityHow well a material retains its identity and purity over time under defined storage conditions.Full definition → for storage and transport than the same peptide in solution. This is why a vial arrives as a solid plug rather than a liquid, and why it is only returned to solution — reconstitutedReconstitutionDissolving a lyophilised (freeze-dried) material back into a liquid using a suitable solvent in the laboratory.Full definition → — in the laboratory when needed.

Storage temperatures for dry material

As a general laboratory practice, lyophilised peptides are held cold, with colder storage for longer horizons. The specific condition for any given material is set by its specification and certificate, but the usual pattern is:

• Short term (weeks): refrigerated, around 2–8 °C, is commonly adequate for dry material.
• Long term (months and beyond): a freezer at around −20 °C, or colder, slows degradation further.

Formal shelf-life is established through stability studies run under controlled conditions, following the principles in ICH Q1A(R2) ↗, which define how temperature, humidity and time points are chosen.

Reconstituted material

Once a peptide is in solution it is generally less stable than in its dry form, so a reconstitutedReconstitutionDissolving a lyophilised (freeze-dried) material back into a liquid using a suitable solvent in the laboratory.Full definition → solution is kept refrigerated and has a shorter usable window than the lyophilised source. SolubilitySolubilityThe extent to which a peptide dissolves in a given solvent, determining which reconstitution solvent is appropriate.Full definition → depends on the peptide and the solvent, so cloudiness or undissolved material after reconstitution is itself a signal worth noting.

Light, freeze–thaw and repeated entry

Three ordinary handling factors shorten stability:

• Light can promote oxidation, so material is stored in the dark or in protective packaging.
• Freeze–thaw cyclesFreeze–thaw cycleOne round of freezing and then thawing a solution, each cycle of which can physically stress a dissolved peptide.Full definition → physically stress a solution; each freeze and thaw can promote aggregation. Aliquoting before freezing limits the number of cycles a given portion sees.
• Repeated vial entry introduces moisture and potential contamination each time a stopper is pierced, which is why aseptic handling and minimal entries matter.

Degradation pathways

When peptides do degrade, the chemistry usually falls into a few recognised pathways, all accelerated by heat, moisture and time:

• Oxidation — reaction of susceptible residues with oxygen.
• DeamidationDeamidationA degradation reaction in which asparagine or glutamine side chains lose their amide group, altering the peptide's mass and charge.Full definition → — loss of an amide group from asparagine or glutamine, creating a new impurityImpurity peakAny peak on a chromatogram other than the main target peak, representing a component distinct from the intended compound.Full definition →.
• Hydrolysis — cleavage of bonds by water, which is why residual moisture matters.
• Aggregation — association of molecules into larger species, promoted by freeze–thaw and agitation.

Each pathway tends to produce new peaks on a chromatogramChromatogramThe plot produced by a chromatography run, showing detector signal over time as separated components pass through.Full definition →, which is how stability studies detect degradation over time.

Visual indicators of a compromised vial

Some checks need no instrument. On arrival, inspect the cakeVial cakeThe solid, porous mass of freeze-dried material left in a vial after lyophilisation, whose appearance is a quality indicator.Full definition → and vial:

• a collapsed, shrunken, cracked or melted-looking cake, rather than a uniform plug;
• discolouration compared with a normal white-to-off-white cake;
• cloudiness in any liquid, or a cake that looks wet;
• signs of moisture ingress — condensation inside the vial or a compromised stopper seal.

Any of these suggests a lyophilisation fault or later exposure to heat or humidity, and is a reason to set the vial aside rather than assume it is sound.

Cold chain and on-arrival checks

Cold chainCold chainThe unbroken sequence of temperature-controlled storage and transport that keeps a temperature-sensitive material within its specified range.Full definition → is the unbroken temperature-controlled path from storage through shipping to arrival. Lyophilised material tolerates brief excursions better than material in solution, but a badly broken cold chain can still accelerate degradation. The practical step on delivery is to inspect the cake and packaging, and to confirm the batch number on the vial matches the published certificate of analysis.