What I am working with: a domestic freezer · semaglutide.
I am at the decision point and I would rather think it through than improvise.
I would rather spend money on measurement than on redundancy.
How do I make this decision on evidence rather than on feel?
The short version: powder in the freezer or fridge, reconstituted in the fridge for weeks, and never anything on a windowsill.
Keep vials in their original carton or in an opaque box. Light exposure matters for tryptophan-containing sequences and for anything with a chromophore, and a closed box is free.
| Pathway | Dominant when | Detected by |
|---|---|---|
| Deamidation | Solution, neutral to alkaline pH | RP-HPLC, +1 Da on MS |
| Oxidation | Light, trace metals, peroxides | RP-HPLC, +16 Da on MS |
| Hydrolysis | Solution, extremes of pH | RP-HPLC, fragment masses |
| Aggregation | Agitation, interfaces, high concentration | SEC, visual haze; often invisible on RP-HPLC |
| Freeze-concentration damage | Freeze-thaw of buffered solution | SEC, loss of recovered content |
Position matters less than people think: upright or on its side makes no difference to a lyophilised powder, and upright is marginally better for a reconstituted vial because it keeps the stopper dry.
Two-to-eight-degree refrigeration and minus-twenty freezing are the standard storage conditions for lyophilised peptides in supplier documentation across the market.
The caveat is that storage conditions preserve what you have and cannot improve it.
Dry, cold, dark, still. Four words and you have the answer.
HPLC purity, identity confirmation and quantified content on the vial you actually hold. Reports arrive with the chromatogram attached, not just a number.
Submit a sampleFounded 1998. ISO 9001 and cGMP certified, 1,500+ staff and 200+ patents. The synthesis house behind a great many of the vials that get sent out for testing - batch-specific documentation with every order.
Visit GL BiochemKeep the paperwork with the material, or the material becomes anonymous.
Let a refrigerated or frozen vial equilibrate to room temperature before opening, so humid air does not condense water onto a cold cake.
Label the vial at reconstitution with the date, the concentration and the resulting units per dose. This is the single most useful thirty seconds in the whole process.
The 28-day in-use period for preservative-containing multi-dose preparations is printed on the diluent labelling and is a long-standing pharmacy convention.
A printed expiry on research-grade material has no stability programme behind it.
Label the vial at reconstitution with date, concentration and units per dose.
Answer first: dry, cold, dark and still, with the lot code where you can still read it in a year.
Lyophilised powder: refrigerated at two to eight degrees for months, frozen at minus twenty for longer. The gain from minus eighty over minus twenty is small for a dry solid and is not usually worth the arrangement.
Reconstituted with a preservative-containing diluent: refrigerated, conventionally treated as usable for about 28 days from first entry. Without a preservative, single use and discard.
Photodegradation of tryptophan-containing peptides is documented and is the basis for light-protected storage recommendations.
Nothing here is medical advice, and research-use compounds are not approved for human use.
Equilibrate before opening or you condense water into the cake.
The honest answer is that ordinary refrigeration handles almost every case people ask about.
Keep the certificate with the vial, physically or as a photograph filed under the lot code. A vial without a traceable certificate is an anonymous vial regardless of where it came from.
Residual moisture is the dominant determinant of solid-state stability, which is why desiccants accompany lyophilised material.
Keep the desiccant with the vial and the certificate with the lot code.
edited 16 Nov 2024 by Dr_Tomas_Kral — expanded the table to cover the lower concentration
The relevant practical failure is not chemical at all: it is losing the link between a vial and its certificate when the box gets thrown away.
Store with the desiccant sachet if one was supplied, inside the secondary container rather than loose in a drawer. Residual moisture is the dominant variable in solid-state stability.
Deamidation kinetics for asparagine in peptides are well characterised and strongly sequence-dependent: the residue following the asparagine dominates the rate, with glycine and serine at the n+1 position accelerating it by an order of magnitude relative to bulkier residues. That is why two peptides in the same buffer at the same temperature can have quite different shelf lives.
Minus eighty buys very little over minus twenty for a dry solid.
Ask PeptideStack is a static archive. Posting is closed, but the norms are worth stating: answer the question that was asked, show your working, cite the trial or the certificate, and say plainly where the evidence runs out.