The COA Is a Snapshot
When a lab tests a peptide and issues a COA showing 99% purity, that number is accurate for that sample at that moment. From the instant the test is complete, the peptide begins to change. How much it changes depends entirely on how it is stored and handled between testing and use.
This is not a theoretical concern. Peptides are chains of amino acids held together by peptide bonds that are susceptible to hydrolysis (breakdown by water), oxidation, and aggregation. A product that tested at 99% purity can degrade to 90% or lower if stored improperly — and nothing on the COA will tell you that happened.
How Peptides Degrade
Hydrolysis
Water molecules attack peptide bonds, breaking the chain into shorter fragments. This is the primary degradation pathway once a peptide is reconstituted (dissolved in solution). The rate of hydrolysis increases with temperature. A reconstituted peptide stored at room temperature degrades significantly faster than one refrigerated at 2–8°C.
Oxidation
Amino acids containing sulfur (methionine, cysteine) or aromatic rings (tryptophan) are susceptible to oxidation when exposed to air or light. Oxidized peptides often have reduced or altered biological activity. This is why peptides are typically packaged under nitrogen or argon atmosphere and stored protected from light.
Aggregation
Peptide molecules can stick together (aggregate) under certain conditions, particularly at high concentrations, elevated temperatures, or extreme pH. Aggregated peptides may lose activity and can also pose safety concerns for injectable preparations.
Deamidation
Asparagine and glutamine residues can spontaneously lose their amide group, particularly in solution at elevated temperatures or non-optimal pH. This changes the peptide's charge and can affect its biological activity.
Two States, Two Sets of Rules
Lyophilized (dry powder)
Most stable form. Without water present, hydrolysis cannot occur. Lyophilized peptides stored properly can maintain their purity for months to years.
- • Store at -20°C (freezer) for long-term
- • 2–8°C (refrigerator) acceptable for shorter periods
- • Protect from light and moisture
- • Keep sealed until ready to reconstitute
- • Avoid repeated freeze-thaw of the sealed vial
Reconstituted (in solution)
Degradation clock starts. Once dissolved in water or bacteriostatic water, the peptide is exposed to hydrolysis and the stability window shortens dramatically.
- • Refrigerate at 2–8°C immediately
- • Use within weeks, not months
- • Never leave at room temperature
- • Minimize repeated freeze-thaw cycles
- • Protect from light
- • Use bacteriostatic water (contains preservative) over plain sterile water
The Shipping Gap
Between testing and delivery, a peptide may sit in a warehouse, travel through a shipping network, and wait on a doorstep. Each stage introduces potential exposure to heat, light, and mechanical stress. This is a gap that no COA addresses.
Was the product stored at the correct temperature between testing and shipping?
Was it shipped with cold packs or temperature-controlled packaging?
How long was it in transit, and what temperatures was it exposed to?
Did the package sit in a hot mailbox or on a doorstep in direct sunlight?
These are questions a COA cannot answer. Suppliers who ship with insulated packaging and cold packs are addressing a real quality concern, not just adding a premium feature.
Compound-Specific Considerations
Not all peptides degrade at the same rate. Some are more sensitive than others:
The Bottom Line
A COA tells you what was in a sample at the moment it was tested. Everything after that — warehouse storage, shipping conditions, time on a shelf, reconstitution, and refrigeration — determines whether the product you use matches the product that was tested. Store lyophilized peptides at -20°C, reconstituted peptides at 2–8°C, and protect everything from light, heat, and moisture. The COA is the starting point, not the finish line.