Storing and handling lyophilized research peptides: temperature, light and moisture

Lyophilization (freeze-drying) removes water by sublimation so the material is held as a dry solid. Wang's review of solid protein formulations explains why: chemical degradation pathways such as deamidation and hydrolysis depend on water and are slowed in the dry state. The goal of storage is therefore to keep the solid dry, cold and away from light and oxygen for as long as it is held.

Stability is sequence-dependent. Bachem notes that peptides containing asparagine, glutamine, methionine, cysteine or tryptophan have a more limited shelf life, and Sigma-Aldrich flags cysteine, methionine and tryptophan as prone to oxidation. Manning and colleagues' review of protein stability describes the main chemical (deamidation, oxidation) and physical (aggregation) routes that storage conditions are meant to slow.

USP General Chapter <659> gives the vocabulary used on labels: a freezer is -25 °C to -10 °C, a refrigerator is 2-8 °C, and controlled room temperature is 20-25 °C with excursions to 15-30 °C. When a supplier says 'store frozen', a standard laboratory -20 °C freezer meets the USP definition.

For long-term holding of lyophilized peptides, Sigma-Aldrich recommends -20 °C or preferably -80 °C, and Bachem recommends below -15 °C with -50 °C or lower preferred. Bachem also notes that peptides may be shipped at room temperature and stored in a refrigerator at 4 °C for short-term use, so a parcel that arrives at room temperature is not by itself a problem. Move it to cold storage on receipt and note the arrival time.

Keep the vial tightly capped whenever it is not in use (Sigma-Aldrich). A min/max thermometer or data logger in the freezer gives a record you can check if a result is ever questioned.

Bachem notes that peptides tend to be hygroscopic: they pull water from air, and absorbed moisture both lowers the peptide content of a weighed sample and can reduce stability. The single most useful habit is to let a cold vial warm to room temperature before opening it, preferably inside a desiccator, so that condensation forms on the outside of the container rather than on the solid. Sigma-Aldrich gives the same instruction.

When a portion has to be removed, weigh it quickly, reseal the vial promptly, and return it to cold storage. USP <659> defines a 'dry place' as not exceeding 40% average relative humidity at 20 °C, a useful target for the desiccator or storage box.

Sigma-Aldrich recommends storing peptides away from bright light. ICH Q1B, the guideline used for formal photostability studies, exposes samples to at least 1.2 million lux hours of visible light and 200 watt hours per square meter of near-UV, which shows how much light exposure is used to look for photodegradation. In practice, keep vials in their box or in amber or foil-wrapped containers and do not leave them on an open bench.

For sequences containing cysteine, methionine or tryptophan, Sigma-Aldrich suggests limiting air exposure, for example by gently overlaying the vial with dry nitrogen or argon before resealing.

Every time a stock vial is warmed, opened and refrozen it is exposed to condensation and temperature stress. Sigma-Aldrich recommends dividing material into single-use aliquots so the bulk stays sealed. Plan the split once, label every aliquot with the parent lot number and the date, and keep a count so the stock vial is opened as few times as possible.

A storage record ties handling to the lot's certificate of analysis. ICH Q1A(R2) frames stability around defined storage conditions and a re-test period; a simple log lets you show that the material stayed within the conditions it was tested under.

1. Receipt: date and time, lot number from the vial label, condition of the seal, and whether the COA lot matches (see the COA checklist).
2. Location: freezer or refrigerator ID and set point, with a min/max or logger reading at each check.
3. Openings: date, who opened it, approximate amount removed, and whether it was warmed in a desiccator first.
4. Aliquots: number made, labels used, and where each is stored.
5. Excursions: any time out of storage or temperature alarm, with duration.

Fine lyophilized powders disperse easily. Bachem advises wearing a dust respirator when handling larger amounts of lyophilized peptide. Follow the supplier's Safety Data Sheet and your institution's chemical hygiene plan under OSHA's laboratory standard (29 CFR 1910.1450).