Retest Date
Definition
The date by which stored material should be re-examined against its specification rather than discarded. It is used where stability data support continued use after confirmation, and it is a different claim from an expiry date.
Terms used in this definition
Other entries this definition refers to.
What this means for research sourcing
Correct storage preserves peptide integrity between experiments. Volta product pages list compound-specific storage conditions and shelf life.
Related Terms in Storage & Stability
Expiry Date
The date after which material is no longer considered to meet its specification. Unlike a retest date it is not extended by a further test, and it is only meaningful alongside the storage conditions it was established under.
Stability
Whether a material still meets its specification after storage, established by testing over time rather than assumed. A stability claim is only valid for the conditions it was measured under, which is why a temperature always accompanies it.
Freeze-Thaw Cycle
One round of freezing and thawing, during which ice crystal growth and the concentration of solutes at the freezing front push peptide molecules together. Repeated rounds degrade a material measurably, and aliquoting is the standard way to avoid them.
Aggregation
Peptide molecules associating into clumps under heat, agitation or repeated freezing. Aggregates lose activity, scatter light enough to make a solution look faintly cloudy, and are more immunogenic than the monomer.
Deamidation
A degradation route in which an asparagine or glutamine side chain loses its amide group, often via a cyclic intermediate that can also rearrange the backbone. Heat and alkaline pH speed it up and it shows on a chromatogram as a close-running impurity.
Oxidation
Reaction of methionine, cysteine or tryptophan side chains with oxygen, accelerated by light, air and trace peroxides. It costs activity, and a sequence containing none of those three residues has no oxidation liability to begin with.
Hydrolysis
Cleavage of the peptide backbone by water, which proceeds slowly in solution and faster at extremes of pH or temperature. It is the reason a lyophilised powder outlasts the solution made from it by a wide margin.
Desiccant
A moisture-absorbing material, usually silica gel, packed alongside a dry product to keep ambient humidity away from it. Residual moisture is what drives hydrolysis in a powder, so the sachet is doing real work.