How to recognise peptide degradation
The visual signs worth acting on, the invisible degradation only analysis reveals, and a practical rule for when to discard a peptide stock.
Peptides do not announce that they have degraded. A stock solution can be chemically compromised while looking exactly as it did on day one, and equally a stock that looks alarming can be perfectly usable once you know what you are seeing. This note lists the visual signs worth acting on, the invisible degradation that only analysis reveals, and a practical decision rule for when to discard. All Alphex products are for laboratory and in-vitro research only.
Visual signs, and what each means
- Cloudiness or haze in a solution that was clear: aggregation, or a solubility limit reached as solvent evaporated or the temperature dropped. Some fraction of peptide has left solution. Discard for quantitative work; a gentle warm and swirl may redissolve a cold-precipitated peptide, but the stock is no longer trustworthy for concentration.
- Particles, threads or a film on the glass: aggregated peptide or, in unpreserved diluent, microbial growth. Discard.
- Colour change. GHK-Cu should be blue; a shift to green or a brown or grey precipitate means copper loss or oxidation. Colourless peptides that turn yellow have usually oxidised or become contaminated. Discard.
- Foam that will not settle after shaking or fast reconstitution: unfolded, surface-denatured peptide. The clear liquid beneath is at an unknown concentration.
- Loss of vacuum in the sealed vial (stopper no longer domed inward, no air rush on puncture): the powder may have taken up moisture in transit. Contact us before using.
Two things that are not degradation: a lyophilised cake that has broken into flakes or slid down the glass, and a very sparse film in a low-mass vial. Both are normal.
Degradation you cannot see
Most chemical degradation produces no visual change at all:
- Deamidation of asparagine and glutamine (mass +1 Da, often a small shift in HPLC retention).
- Oxidation of methionine, cysteine, tryptophan (mass +16 Da per oxygen).
- Hydrolysis at labile bonds, producing shorter fragments.
- Adsorption to plastic, which removes intact peptide from solution without any chemical change.
The compounds in the Alphex catalogue vary in susceptibility. BPC-157 has no Met, Cys or Trp and is comparatively robust. TB-500 has a glutamine that can deamidate on long storage. Ipamorelin's D-amino acids and Aib make it protease-resistant but its aromatic residues encourage adsorption at low concentration. GLP-3 (RT), large and lipidated, is the most prone to aggregation and adsorption. See deamidation and oxidation in stored peptides for the chemistry.
How to detect invisible degradation
- Assay drift. A positive control that weakens, or a standard curve that shifts, at unchanged nominal concentration is the most common first sign in a working laboratory.
- HPLC. Re-running the stock and comparing to the batch chromatogram is definitive: new peaks, a reduced main peak, or a shifted retention time. Benzyl alcohol from bacteriostatic water will show as its own peak; prepare the analytical sample accordingly.
- Mass spectrometry. Extra masses at +1, +16 or fragment masses.
A practical decision rule
- Any visible change: discard.
- No visible change, but past the working shelf life for that storage condition (see how long reconstituted peptides last): discard for quantitative work, or re-verify by HPLC if the assay is expensive.
- Within shelf life, no visible change, but assay behaviour has drifted: suspect the stock first, before the assay. Make fresh from a sealed vial and repeat.
- Record what you discarded and why. Patterns (one compound always failing at week three, for instance) tell you to shorten your own limits.
Preventing it
Reconstitute correctly, aliquot and freeze, keep dark, use low-binding plastic, and use bacteriostatic water for multi-sample stocks. The methods are in how to reconstitute research peptides and storage, reconstitution and shelf life.
Alphex research peptides are supplied for laboratory and in-vitro research by qualified researchers only. They are not authorised for human or veterinary use.
Research use only. Alphex products are supplied exclusively for laboratory and in-vitro research by qualified researchers. They are not authorised for human or veterinary use, and nothing in this note is advice on any such use.
Published 24 March 2026. Alphex reviews research notes when the testing method, the catalogue or UK guidance changes.