Why is a glass vial preferred over plastic for peptide solution?

I have the same lot stored correctly as a comparator, if a side-by-side test would help.

I keep seeing this stated as a fact with no explanation attached, and unexplained facts make me suspicious.

My background is quantitative but not chemical, so I can follow an equation more easily than a hand-wave.

What is the causal chain, and where does it stop being established?

The honest answer is that ordinary refrigeration handles almost every case people ask about.

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.

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.

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 27 Aug 2026 by ruaidhri_o_shea — updated for the 2026 guidance change

Answering this needs the intended duration, since a fortnight and two years call for different arrangements.

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.

Let a refrigerated or frozen vial equilibrate to room temperature before opening, so humid air does not condense water onto a cold cake.

Minus eighty buys very little over minus twenty for a dry solid.

edited 5 Aug 2026 by halvard_ness — tightened the wording; no substantive change

Start with the physical state, because lyophilised and reconstituted material have completely different storage answers.

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.

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.

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.

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.

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.

Nothing here is medical advice, and research-use compounds are not approved for human use.

Dry, cold, dark, still. Four words and you have the answer.