Storing lyophilised peptides: temperature, light, humidity

What lyophilisation does

In freeze-drying a frozen solution is placed under vacuum so that the ice sublimes, passing from the solid state to vapour without melting. What remains is a porous cake with very little residual moisture. Because the mobile water that drives hydrolysis and microbial growth has been removed, a lyophilisate is far more stable than the same substance in solution, which is why research peptides are supplied in this form and remain stable for months to years when kept correctly.

Unopened vials

• Short term (weeks): refrigerator, 2–8 °C.
• Long term: freezer, −20 °C or colder.
• Always: protected from light in the original box, and dry. Not in the refrigerator door, where the temperature fluctuates every time the door is opened.

The vials are closed with a stopper under a crimped cap, so the powder is shielded from ambient air for as long as that seal is intact.

What a storage temperature does and does not say

A temperature specification is a condition, not a shelf life. Chemical degradation slows as the temperature falls, but it never stops entirely. Short excursions – a transport leg, a few minutes on the bench – matter far less than repeated cycling between cold and warm, because every cycle moves water inside the vial.

Before opening a cold vial

Bring the vial fully to room temperature before breaking the seal. If a cold vial is opened, humid room air condenses on the cold glass and on the powder itself; the water introduced this way accelerates degradation and distorts every weighing that follows. For a small vial taken from a freezer this means roughly twenty to thirty minutes on the bench, not a few seconds in the hand. Condensation is the most common storage mistake and it leaves no visible trace.

Solutions in the laboratory

In solution a peptide loses the protection the dry state provides: hydrolysis, adsorption to the container wall and, where sterility is not maintained, microbial growth resume. Solutions are kept refrigerated at 2–8 °C and used within the period the stability data for that substance support. Repeated freezing and thawing is avoided; where a solution has to be kept longer, it is divided into aliquots once and frozen, so that each aliquot is thawed only once. Vials, filters and solvents are listed under accessories, including bacteriostatic water.

Light and humidity

Ultraviolet and strong visible light promote oxidation, in particular at methionine, tryptophan and cysteine residues; the original carton is the simplest protection against this. Humidity is the second factor. Lyophilisates are hygroscopic, and a cake that has drawn water may shrink, collapse or turn sticky. Absorbed water does not change the chromatographic purity determined in the test report, but it does change how much peptide a given weight of powder contains.

What to check

1. Discolouration of the powder, or a cake that has collapsed, shrunk or become sticky.
2. Turbidity, fibres or particles in a solution that was clear before.
3. A stopper that no longer sits tightly, or a damaged crimp cap.
4. A label that has become illegible or detached.

If one of these applies, stop using the material and contact us, quoting your order number. The reports that are available are collected in the lab area; every certificate of analysis names the material it refers to, and how material reaches that point is set out in the quality-control guide.

Storage as part of the record

Every vial carries its own label, applied at goods receipt. Keeping that label with the vial is part of storage: without it the material can no longer be matched to its report.

How the vials travel before they reach the cold store – packaging, transit times and what to check on arrival – is covered in the guide on shipping and packaging.