Does light exposure matter for a peptide in an amber vial?

I have continuous temperature data for the period in question, which is unusual and I would like to use it.

I suspect the usual explanation for this is wrong, or at least incomplete.

I am aware this may have a boring answer. I would still like the boring answer stated clearly.

What is actually going on here, physically?

Answer first: dry, cold, dark and still, with the lot code where you can still read it in a year.

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.

Degradation pathway by condition

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.

Two-to-eight-degree refrigeration and minus-twenty freezing are the standard storage conditions for lyophilised peptides in supplier documentation across the market.

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

This is the tag where the advice is cheapest to follow and most often ignored.

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

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.

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.

Keep the desiccant with the vial and the certificate with the lot code.

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

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.

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.

Residual moisture is the dominant determinant of solid-state stability, which is why desiccants accompany lyophilised material.

Equilibrate before opening or you condense water into the cake.

edited 26 Jul 2024 by loss_on_drying — reworded for clarity after a comment

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

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.

Photodegradation of tryptophan-containing peptides is documented and is the basis for light-protected storage recommendations.

The caveat is that storage conditions preserve what you have and cannot improve it.

Label the vial at reconstitution with date, concentration and units per dose.

edited 26 Jul 2024 by leonid_marchuk — added the method parameters

The short version: powder in the freezer or fridge, reconstituted in the fridge for weeks, and never anything on a windowsill.

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.

Appearance does not indicate stability; a normal-looking cake can be substantially degraded.

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