Storage considerations across the peptide lifecycle

Temperature

Sealed lyophilized material is normally held at -20 °C for long term storage, where degradation rates are low enough that shelf life is measured in years. Short-term storage at 2-8 °C is acceptable for weeks. Ambient storage of dry powder is tolerable for the duration of shipping but is not a storage strategy.

In solution the picture changes entirely. Aqueous stocks are typically held at 2-8 °C and used within days to a few weeks depending on the sequence, or frozen in aliquots at -20 °C or below for longer periods.

Light and oxygen

Residues with aromatic side chains — tryptophan, tyrosine and phenylalanine — absorb ultraviolet light and can undergo photo-oxidation. Methionine and cysteine oxidise readily even in the dark. Amber vials, foil overwrap or simply keeping stock in a closed box address both problems at no cost.

Vials sealed under nitrogen or argon arrive with the headspace already displaced. Once a stopper is pierced, that protection is partially lost, which is one more argument for aliquoting rather than repeatedly accessing a single vial.

Moisture

Lyophilized peptides are hygroscopic. Water absorbed from the atmosphere mobilises the solid state and permits hydrolysis and deamidation to proceed in what still looks like a dry powder. Keeping vials sealed, desiccated, and equilibrated to room temperature before opening addresses nearly all of this.

Container chemistry

Cationic and highly hydrophobic peptides adsorb onto glass and onto standard polypropylene, and at low concentrations the loss can be a substantial fraction of the sample. Low-binding tubes and tips, or the addition of a carrier protein where the assay allows, are the usual mitigations. This is a real effect and a frequent explanation for measured concentrations coming in below expectation.