The short answer
"GHK-Cu" is not one unambiguous substance. Public chemical databases index the free GHK tripeptide near 340 Da, a 1:1 copper complex near 402 Da, and a 2:1 peptide-to-copper species near 742 Da under overlapping names. A certificate of analysis therefore has to state which species and stoichiometry it measured.
One name, several substances
GHK is a naturally occurring tripeptide — glycine, histidine, lysine — found in human plasma, which binds copper(II) with high affinity. The copper-bound form is what most people mean by GHK-Cu, and it is used as a cosmetic ingredient under the INCI name Copper Tripeptide-1.
The complication is that the name is applied loosely. Public chemical databases index the free tripeptide at about 340 Da, a 1:1 peptide-to-copper complex at roughly 402 Da, and a 2:1 species in the 742 Da region — all findable under GHK-Cu or closely related names. These are chemically different materials.
This is not a marketing quibble invented to sell a testing story. It is a genuine ambiguity present in the reference data itself, which means a certificate that reports a purity percentage without saying what was measured has left the most important question open.
What a complete GHK-Cu certificate specifies
The first thing to look for is an explicit statement of species and stoichiometry: free peptide or copper complex, and if a complex, the peptide-to-copper ratio. A mass result then either supports that statement or contradicts it, which is exactly what identity testing is for.
Copper content is the second element. For a copper coordination complex, the metal is part of the substance rather than a contaminant, so its quantity is a specification rather than an impurity limit — and it is what distinguishes a 1:1 from a 2:1 material analytically.
That creates a wrinkle worth understanding when reading elemental-impurity results. Heavy-metal screening under USP ⟨233⟩ exists to catch unintended metals; copper here is intentional. A well-constructed certificate distinguishes the two rather than presenting a copper figure without context.
The visual check, and its limits
Copper complexes of GHK are deep blue to violet solids, whereas the free peptide is white to off-white. Colour is therefore a crude but genuine first indication of whether copper is present at all — and one of the few cases in peptide supply where appearance carries real information.
Its limits are equally real. Colour indicates that copper is present; it does not establish stoichiometry, purity, or that the peptide portion is the correct sequence. A blue powder can still be the wrong ratio or contain the wrong tripeptide.
So the visual observation belongs where certificates usually put it — as an appearance note recorded alongside the analysis, not as a substitute for it. The analytical work still has to answer which species, at what purity, in which lot.
There is a second reason to read GHK-Cu paperwork carefully, which is that the compound has a substantial life outside research supply. It is an established cosmetic ingredient, indexed under an INCI name, and cosmetic-grade material is manufactured and documented to the expectations of that industry rather than to the analytical standards applied to research reference materials. Neither is inherently better made. But the documentation traditions differ, and a certificate written for a cosmetic supply chain may simply not report the attributes a laboratory needs — which is a reason to read what a certificate covers rather than assume a standard panel.
Questions researchers ask
Is GHK-Cu the same thing as GHK peptide?
No. GHK is the free tripeptide at about 340 Da; GHK-Cu refers to its copper complex, indexed near 402 Da for the 1:1 form. Because both circulate under overlapping names, a certificate should state explicitly which species it measured rather than leaving it to the product title.
Why is my GHK-Cu blue and not white?
Because copper is present. GHK copper complexes are deep blue to violet, while the free GHK peptide is white to off-white. Colour is a reasonable first indication that a copper complex was supplied, but it says nothing about stoichiometry, purity or sequence.
How do I verify GHK-Cu is 1:1 and not 2:1?
By mass and copper content read together. The 1:1 complex sits near 402 Da and the 2:1 species in the 742 Da region, and the copper specification differs accordingly. A certificate that states stoichiometry and reports copper content answers this; one reporting only purity does not.
Should copper show up as a heavy-metal impurity?
Not in the same sense. Elemental-impurity screening under USP ⟨233⟩ targets unintended metals, whereas in a copper complex the copper is part of the substance. A well-constructed certificate separates the intentional copper specification from the impurity screen rather than conflating them.
At a glance
- Class
- Gly-His-Lys tripeptide as a copper(II) coordination complex
- Free peptide mass
- ≈ 340 Da (GHK, white to off-white)
- 1:1 complex mass
- ≈ 402 Da (deep blue to violet)
- Also indexed
- 2:1 peptide-to-copper species in the ≈ 742 Da region
- Status
- Research use only — not an approved therapeutic peptide drug
How our GHK-Cu lots test
Applying the same standard described above to our own material. Each certificate below opens on the issuing laboratory's portal— not a PDF hosted here — so you are reading the lab's record, not ours.
Sources
Written from primary literature and published standards — never from other suppliers' marketing copy.
- PubChem CID 73587 — glycyl-L-histidyl-L-lysine (free GHK), 340.38 Da ↗
- PubChem CID 71587328 — prezatide copper / Copper Tripeptide-1, 402.92 Da ↗
- Pickart L, Margolina A — GHK peptide as a natural modulator of multiple cellular pathways (PMC) ↗
- USP General Chapter ⟨233⟩ Elemental Impurities — Procedures ↗
Written by Ivory Science. Scientific review: pending appointment of a named reviewer. Until then this page cites its sources directly so every claim can be checked at origin.
Related notes
For research use only. Not for human or veterinary use, ingestion or administration. Nothing here is medical advice, and no statement on this page has been evaluated by the FDA. GHK-Cu is not an approved medicine.