Expected stability for sealed lyophilised vials versus reconstituted solution, and how storage temperature changes the usable window.
Bacteriostatic water is not a stabiliser
The preservative inhibits microbial growth. It does nothing to prevent hydrolysis, oxidation or deamidation of the peptide itself, so solution shelf life stays short.
Sealed lyophilised vials
Stored sealed, dry, dark and cold, lyophilised peptides are stable for extended periods — commonly quoted in years at −20 °C and in months at 2–8 °C for typical sequences. The limiting factors are moisture ingress and temperature, not time on its own, which is why desiccant and a stable freezer matter more than the calendar.
Reconstituted solution
In solution the usable window shortens dramatically, from years to days or weeks depending on the compound, concentration, diluent and temperature. Bacteriostatic water contains a preservative that inhibits microbial growth, but it does nothing to prevent chemical degradation of the peptide itself. Plan preparations around the experiment rather than storing large reconstituted stocks.
What shortens the window
- Repeated freeze-thaw cycles.
- Warm ambient storage, or a fridge door rather than a shelf.
- Light exposure, particularly for sequences containing tryptophan or tyrosine.
- Repeated septum entry, introducing air, moisture and potential contamination.
- Sequences prone to oxidation or deamidation, which age faster in solution than robust ones.
Judging whether material is still fit for use
- Lyophilised: intact white cake, no discolouration, no clumping or visible moisture.
- In solution: completely clear, no haze, no particulates, no precipitate at the base.
- Any doubt in quantitative work: re-analyse or replace rather than proceed.
- Where an endpoint is sensitive, prepare fresh from a sealed vial as a matter of routine.
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