Short-Term Storage: Days to Weeks

Short-term storage covers the periods between receiving material and putting it away for good, and between preparing a solution and using it up. These periods are where most handling mistakes happen, simply because they feel temporary.

Sealed powder in active use

A sealed lyophilized vial that will be opened again within a few weeks can be held at 2–8 °C in a closed box with desiccant. Returning it to −20 °C between uses is also fine, provided it is equilibrated before every opening. What matters most is the number of openings: each one lets in humid air. If a vial will be opened more than two or three times, consider dissolving it once and freezing aliquots instead.

Working solutions

A peptide in solution is far less stable than the same peptide dry. For a working solution that will be used over the next few days:

• Hold it at 2–8 °C, sealed, in an amber or covered tube.
• Use slightly acidic, sterile conditions where the experiment allows. Neutral and basic pH speeds deamidation.
• Label it with the preparation date and a use-by date set by your own procedure. Without stability data for the specific peptide and solvent, a conservative limit of a few days is common practice.
• Discard leftovers rather than refreezing them.

On the bench during an experiment

• Thaw aliquots just before use and keep them on ice or a cold block.
• Close tubes between withdrawals to limit evaporation and contamination.
• Keep material out of direct sunlight and away from heat sources such as instruments and lamps.
• Return or discard material promptly when the experiment ends; do not leave it for the next day.

Short holds at room temperature

Lyophilized peptides usually tolerate days at ambient temperature during shipping, which is why many suppliers do not ship them cold. That tolerance is not a reason to store powder on a shelf. Move received material into its storage band promptly.

Quick reference