Accepted answer
Whatever the refrigerated figure is, freezing does not simply extend it. minus 80 °C is 85 kelvin below a refrigerator, and below the glass transition of a lyophilised cake the ten-degree rule of thumb stops applying at all — solid-state chemistry is not slow liquid chemistry, it is a different regime, and the failure modes that survive it are mechanical rather than chemical. A frozen solution is not a slow solution: ice excludes solute, so the unfrozen fraction concentrates, the pH of the buffer shifts as one component crystallises first, and the damage happens during the transitions rather than during the hold. "Within specification" also needs a specification: purity, content, or both, and at what limit. Without that the question has no numerical answer at all.
Start with the sequence, because which pathways are available depends on which residues are present.
Oxidation targets methionine, cysteine and tryptophan, adding sixteen daltons per oxygen. It is catalysed by trace metals and promoted by dissolved oxygen and by light.
Aggregation is physical: peptides unfold at air-liquid interfaces and associate. Shaking maximises that interface, which is why swirling and shaking produce visibly different outcomes on the same vial.
Metal-catalysed oxidation of methionine is documented across peptide and protein formulations and is why chelators appear in some formulations.
Swirl, never shake. Aggregation is a handling problem more than a time problem.
edited 23 Jul 2024 by coldpack_88 — fixed an arithmetic slip in the third paragraph
8Adding for future readers: the domestic leg after delivery is the part you control. – nkem_obiora 2 months ago Confirming that opening a cold vial in a humid room is a genuinely bad idea. – gradient_slope 4 months ago add a comment