Peptides are supplied in two common physical forms — lyophilized (freeze-dried) powder and pre-mixed solution — and each has meaningfully different storage requirements. Understanding which form you're handling, and treating it accordingly, is one of the simplest ways to preserve sample integrity for research use.
Lyophilized powder
Freeze-drying removes water from a peptide solution, leaving a stable solid that is generally far more resistant to degradation than a liquid. Unopened lyophilized vials are typically stored frozen (commonly around -20°C), protected from light, and kept sealed until they're needed. In this state, most peptides maintain stability over a period of months to years, depending on the specific sequence.
Solution (reconstituted) form
Once a peptide is reconstituted with a diluent, it becomes far more susceptible to degradation from temperature, light, bacterial growth, and repeated freeze-thaw cycles. Reconstituted solutions are generally stored refrigerated (around 2-8°C), not frozen, and are typically used within a much shorter window — often weeks rather than months.
Why freeze-thaw cycling matters
Repeatedly freezing and thawing a reconstituted solution can physically disrupt the peptide's structure, reducing purity over successive cycles. Aliquoting a solution into single-use portions before freezing (where freezing is appropriate) avoids this problem, since each portion is only thawed once.
Light and moisture exposure
Many peptides are light-sensitive and should be stored in amber vials or opaque packaging away from direct light. Ambient humidity can also affect lyophilized powder if a vial's seal is compromised, which is why an intact, undamaged seal is worth checking on arrival.
Practical takeaway
Treat the transition from powder to solution as the point where your storage protocol needs to change — cold, dark, and used promptly, rather than assuming reconstituted material behaves the same as the sealed vial it came from.