Specify by registry number. GHK-Cu, the copper complex of Gly-His-Lys, is CAS 89030-95-5 with formula C14H21CuN6O4 and molecular weight 400.91, supplied as a blue powder. Free GHK is CAS 49557-75-7, the tripeptide without copper. They are different substances with different masses, so they cannot be treated as two grades of one material. One condition applies to the whole comparison: the identifier tells you what is in the pack, while the binding limits come from the signed batch COA.
Why do the two names get confused?
Both are shortened to "GHK peptide" in catalogue titles, and some pages use the copper-complex name while quoting the free-peptide registry number. We have even seen a FAQ answer describe the copper complex as the copper-free form. A buyer who copies the title into a purchase order can therefore receive a material that matches the words but not the number.
What does the mass difference mean in practice?
It changes the arithmetic of a formulation. At molecular weight 400.91, 1.00 g of the copper complex is about 2.49 mmol. If a brief is written in millimoles and the person ordering converts using the free tripeptide mass instead, the weighed quantity will be wrong by the ratio of the two molecular weights. Take an illustrative 0.25 mmol target: that is about 100 mg of the copper complex, but roughly 85 mg if calculated with a 340 g/mol free-peptide value. These numbers are an example of unit conversion, not a recommended inclusion rate; the point is that the registry number and the molecular weight must travel together.
Which checks separate the two materials?
Check: registry number on the COA, molecular formula and weight, colour of the powder, and a copper-content or complex-confirmation result with its method. What to confirm: that the LC-MS identity trace matches the stated sequence, that the copper result is reported against an agreed method, and that the document list names the correct substance. A blue powder labelled with the free-peptide CAS deserves a written clarification before a sample ships.
What should a comparison sheet contain?
Put the two substances in two columns and fill, for each, the registry number, sequence, formula, molecular weight, appearance, solubility in the intended matrix, storage, analytical method and document list. Leave the result fields blank until the batch COA arrives. This is also the structure we use on our product pages, so a buyer can copy it straight into a supplier audit.
Can a supplier substitute one for the other?
Not without a new agreement. Changing the substance changes the molecular weight, the appearance and the identity trace, so the approved sample no longer represents the offered material. Ask for a fresh sample and a revised specification if the substance changes.
What about finished-product claims?
We describe ingredients and identifiers, not finished-product performance. Formulation testing and any claims made for a finished cosmetic product sit with the manufacturer who puts it on the market.
References
[1] CAS Common Chemistry, entries 89030-95-5 and 49557-75-7. [2] General practice for peptide identity confirmation by LC-MS. [3] INCI naming convention, Personal Care Products Council.
Request the documentation
See our GHK-Cu product page and email sales@yaxbio.com to request a COA, a sample or a bulk quotation for the substance you actually need.