What to Check on a GHK-Cu COA Before You Buy

A certificate of analysis for an ordinary peptide answers three questions: is it the right molecule, how pure is it, and how should it be stored. A copper-peptide COA has to answer more, because the active is a coordination complex. A GHK-Cu COA that reads like a generic peptide COA is missing the line items that define the lot. Here is what to look for, and what an absence should tell you.

Identity and peptide purity (necessary, not sufficient)

The COA should confirm peptide identity (the GHK sequence) and peptide purity by HPLC-UV, with the method and wavelength stated. This is the baseline every peptide COA carries — and for a copper peptide it is necessary but not sufficient, because it says nothing about the copper.

Copper content and the bound fraction

This is where a copper-peptide COA earns its name. Look for total copper quantified by ICP-MS or atomic absorption, and evidence of how much of that copper is actually bound to the peptide rather than free.

• Total copper (ICP-MS or AAS) — confirms the labelled copper content is in the vial.
• Bound-copper evidence (HPLC-DAD on the complex peak) — separates peptide-bound copper from free copper.
• Cu²⁺ : peptide molar ratio — the single number that summarises coordination; target 1.00, clean lots 0.95–1.05.
• A bound fraction at or above ~0.95 of total copper indicates a clean complex; materially lower means part of the copper is uncoordinated.

Coordination and colour evidence

Because the copper coordination geometry is what makes the molecule active, the COA should carry evidence that the geometry is intact, not just that copper atoms are present.

• UV-Vis d-d band — a single broad peak near 620 nm, λmax close to the master reference, confirms square-planar Cu(II) in its proper pocket.
• Colour / CIELAB ΔE against a master reference — a quantitative, reproducible check that the lot matches the expected blue, with the illumination and observer geometry stated (D65 / 10° is the cosmetic standard).

Stability, water, and counter-ion

Round out the packet with the handling-relevant data: solution stability across the working pH window, water content, counter-ion form (acetate is typical), and storage / retest conditions. For a copper peptide the pH-stability data matters more than for most actives, because the complex dissociates outside a narrow window.

The tell of a serious copper-peptide COA is not length — it is whether total copper, the bound fraction, the Cu²⁺ : peptide ratio, and the d-d band are all present. If those four are missing, the COA is describing a peptide, not a copper complex.