Quick answer: store lyophilized peptides sealed at -20°C, protected from light and moisture. Once reconstituted, keep the working solution at 2 to 8°C, split it into single-use aliquots, and avoid repeated freeze-thaw cycles.
Why storage decides your results
Peptides are chains of amino acids held together by bonds that are sensitive to heat, water, light, and oxygen. Degradation does not announce itself. The vial looks the same, but the fraction of intact molecules falls, and an assay run with a degraded stock produces a result that cannot be reproduced.
Lyophilized (dry) peptides
- -20°C is the standard for months of storage.
- -80°C for long-term archives, especially for sequences containing cysteine, methionine, or tryptophan, which oxidize more readily.
- Keep the vial sealed and dry. Desiccant in the storage box helps.
- Let the vial reach room temperature before opening so condensation does not form on cold powder.
Reconstituted peptides
- Refrigerate at 2 to 8°C and use within days.
- For longer holds, divide into single-use aliquots and freeze at -20°C. Thaw one, use it, discard the remainder.
- Every freeze-thaw cycle costs activity. Aliquoting exists to avoid that.
- Bacteriostatic water contains a preservative that limits microbial growth in multi-draw vials; sterile water does not.
Light and oxygen
Amber vials or an opaque box protect light-sensitive residues. Minimizing headspace in aliquots reduces oxidation. For sensitive sequences, purging with inert gas before sealing is common practice.
Signs a vial has degraded
- Cloudiness or particles after reconstitution
- Color change in the powder or solution
- Powder that has collapsed or looks wet
- Assay results drifting downward across a study
A simple storage log
Record the batch number, date reconstituted, solvent and volume, resulting concentration, and number of aliquots. When a result looks off, the log is the first place to look.
Sources
- Manning MC et al. Stability of protein pharmaceuticals: an update. Pharmaceutical Research, 2010.
- Lai MC, Topp EM. Solid-state chemical stability of proteins and peptides. Journal of Pharmaceutical Sciences, 1999.