Storing peptides: lyophilized vs reconstituted

A peptide's stability depends directly on its storage. And the rules differ depending on whether it is still a lyophilized powder or already reconstituted into solution. Here is how to keep track.

Lyophilized peptide: long-term storage

As a dry powder, the peptide is stable for a long time. General recommendations:

• Freezer ideally (−20 °C) for prolonged storage; the refrigerator is fine for shorter durations.
• Away from light and moisture.
• Sealed vial as long as it is unused.

This is the state in which a peptide travels and stores best.

Reconstituted peptide: the refrigerator

Once back in solution (see How to reconstitute a peptide), things change:

• Refrigerator (2–8 °C), never at room temperature between handlings.
• Away from light.
• Reconstituted with bacteriostatic water, it generally keeps for several weeks thanks to the preservative.
• Note the reconstitution date on the vial.

The mistakes that degrade a peptide

• Heat: leaving a vial at room temperature or in direct sunlight.
• Light: prolonged storage without protection.
• Repeated freeze–thaw cycles: each cycle weakens the peptide. Better to split into portions if needed, rather than refreeze the same vial several times.
• Shaking a reconstituted solution (foam, degradation) — swirl gently instead.

A warning sign: a solution that has turned cloudy, colored or contains particles after an initially clear dissolution.

What about transport?

Over short durations, a lyophilized peptide tolerates room-temperature transport well — one of the benefits of freeze-drying. For an already-reconstituted solution, keeping the cold chain is preferable.

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In short: lyophilized → freezer, long term; reconstituted → refrigerator, a few weeks, away from light and without repeated freeze cycles. For the rest of the vocabulary, head to the glossary.