The Golden Rule: Refrigerate Immediately
Once a peptide is reconstituted, the clock starts. Water reintroduces hydrolysis as a degradation pathway, and dissolved oxygen enables oxidation. Refrigerating at 2-8°C slows both processes dramatically. Transfer reconstituted vials to the refrigerator immediately after use — do not leave them at room temperature on the bench.
How Long Do Reconstituted Peptides Last?
As a general guideline, most reconstituted peptides maintain acceptable purity for 3-4 weeks at 2-8°C when reconstituted in bacteriostatic water. Some more stable peptides may last longer; some fragile sequences may degrade faster. The benzyl alcohol in bacteriostatic water provides antimicrobial protection but does not prevent chemical degradation.
If you need to keep reconstituted peptides longer than 4 weeks, consider aliquoting and freezing (see below).
To Freeze or Not to Freeze
Freezing reconstituted peptides at -20°C can extend shelf life to 2-3 months, but introduces risks. Ice crystal formation during freezing can damage peptide structure. Freeze-thaw cycles are particularly harmful — each cycle causes additional damage.
If you freeze: aliquot into single-use volumes BEFORE freezing. Never refreeze a thawed aliquot. Thaw at room temperature or in a 2-8°C refrigerator — do not heat.
Light Protection
Light accelerates oxidation of tryptophan, tyrosine, and phenylalanine residues. If your peptide contains these amino acids, store in amber vials or wrap clear vials in aluminum foil. Even refrigerator lights can cause gradual photodegradation over weeks of storage.
Container Selection
Glass vials are preferred over plastic. Peptides can adsorb to plastic surfaces, reducing the effective concentration in solution. If using plastic tubes for aliquots, low-binding polypropylene tubes (such as those marketed for protein work) minimize surface adsorption.
When to Discard
Discard reconstituted peptides if you observe cloudiness or visible particles, color changes, unusual odor, or if the reconstitution date is more than 4 weeks ago. When in doubt, start fresh — the cost of a new vial is far less than the cost of unreliable experimental results.
Documentation
Label every reconstituted vial with the peptide name, concentration, reconstitution date, solvent used, and lot number. This takes 30 seconds and saves hours of troubleshooting when results are inconsistent.
