The three storage variables
Storage stability is governed by three factors: temperature, light, and humidity. Lower temperature slows degradation, light promotes oxidation, and humidity reintroduces the water that lyophilization removed.
- Temperature: store dry solid desiccated at −20°C to −80°C.
- Light: protect from direct light, especially for oxidation-sensitive residues.
- Humidity: keep vials sealed and desiccated until use.
Freeze-thaw and prepared material
Once a material is dissolved for an in vitro assay, its stability drops. Repeated freeze-thaw cycles of a prepared solution accelerate degradation, so prepared material should be aliquoted into single-use fractions before freezing.
Sequence-dependent stability
Stability is not uniform across peptides. Sequences containing oxidation-prone residues (such as methionine or tryptophan) degrade faster under light and oxygen, while others are limited mainly by hydrolysis. The COA and handling guidance for each material reflect these differences.
Protein storage temperature: −20°C or −80°C?
Lyophilized peptides and proteins are commonly stored at −20°C for routine work and at −80°C for longer-term storage or for sequences known to be less stable. The right choice depends on the material, the intended storage period, and the guidance issued with its certificate. What matters most is a stable temperature: a freezer that cycles through frost-free defrost periods is a worse home for a vial than a slightly warmer freezer that holds a constant temperature.
Bring a vial to room temperature before opening it. A cold vial opened straight from the freezer can draw moisture onto the material, and moisture is the variable lyophilization was used to remove. Wipe any condensation from the outside of the vial before it goes back into storage.
Protein storage in solution
Once a material is dissolved, its stability window narrows. Prepare the working solution at the concentration the assay needs, aliquot it into single-use fractions, and freeze the fractions rather than the master stock. Keep prepared solutions cold during use and avoid repeated warming and cooling.
Some proteins and peptides are sensitive to agitation and foaming. Mix gently, avoid vigorous vortexing where the material's guidance says so, and follow the handling notes that accompany the lot.
Humidity, light, and the vial
Store vials sealed and desiccated. A desiccant in the storage container absorbs the moisture that enters each time the container is opened. Protect light-sensitive sequences from direct light, particularly those containing oxidation-prone residues. If a vial is stored in a secondary container, label the container as well as the vial so the lot number stays readable.
A storage routine that stays traceable
Storage conditions are part of the experimental record, not housekeeping. A routine that records where a vial is and what was done to it is what lets a later result be tied back to a specific lot.
- Keep the vial sealed until it has equilibrated to room temperature.
- Use a desiccant and a stable, non-cycling freezer.
- Aliquot prepared solutions; avoid repeated freeze-thaw.
- Record lot, preparation date, and storage location.
Labeling and logbook practice
Label every aliquot with the lot number and the date it was prepared, and log storage conditions. Consistent labeling is what makes a batch traceable months later.