How long does reconstituted peptide last?

Not long. Manufacturers' guidance gives up to about a week in the fridge (2–8 °C) and a few weeks frozen in single-use portions. Dry, sealed powder keeps for years; a solution does not.

Storage

Keep it refrigerated (2–8 °C), protected from light, and avoid repeated freeze-thaw cycles. Bacteriostatic water (with its preservative) gives a longer usable window than plain sterile water.

What manufacturers' stability guidance says

• Sigma-Aldrich (Merck): peptide solutions are generally stable for up to a week at 4 °C. Storage at −20 °C or colder is best.
• Bachem: frozen solutions may be kept for a few weeks. Long-term storage in solution is not recommended, especially for peptides containing asparagine, glutamine, cysteine, methionine or tryptophan.
• GenScript: the shelf life of a peptide in solution is very limited, much shorter than that of the dry powder, and freeze-thaw cycles degrade it.

Bacteriostatic water contains a preservative that limits microbial growth. It protects the solution against contamination, not the peptide against chemical breakdown. Label every portion with the compound, the concentration and the date.

Sources: Sigma-Aldrich (Merck) · Bachem · GenScript

When to discard

Discard if the solution turns cloudy, changes colour or shows particles. Sealed, dry lyophilized powder lasts far longer — often 2+ years frozen.