GHK-Cu test: what a full panel shows, why the copper ratio matters and how samples fail

What a GHK-Cu test should show

GHK-Cu is a small peptide, glycyl-histidyl-lysine (GHK), with a copper ion bound to it, so a useful test covers both parts. LC-MS shows that the peptide is GHK, HPLC shows how pure it is, and a content assay gives the mg in the vial. The amount of copper, and the copper per peptide molecule, need a separate elemental measurement that standard peptide tests do not include.

Test	What it answers for GHK-Cu	Reported as
Identity (LC-MS)	Is the main peptide GHK?	Observed and calculated m/z, error in ppm
Purity (HPLC)	The peptide’s share of UV peak area	% area, with impurity peaks
Content per vial	mg in the vial against a reference standard	mg per vial, basis, % of label
Copper content and ratio	mg of copper, and copper per peptide molecule	mg of copper, molar ratio
Endotoxin (LAL)	Bacterial endotoxin in the sample	EU per mg and EU per vial
Sterility (USP <71>, 14 days)	Microbial growth from the tested units	Growth or no growth, units tested

PubChem lists the compound, as prezatide copper, with one copper per GHK molecule (average mass 402.92 Da); the free peptide weighs 340.38 Da. The GHK-Cu compound page gives the formula and calculated masses.

GHK-Cu test results: how published samples fail

Finnrick, a US platform that sends community-submitted samples to partner labs and publishes the results, gives pass and fail counts per product. In its data to 20 September 2026, GHK-Cu had 807 published tests: 695 passed and 104 failed its default standard. That is about 13% of classifiable samples, the lowest fail share among widely tested peptides in our peptide fail rates table. Finnrick’s later summary, read on 4 October 2026, listed 939 GHK-Cu tests from 140 vendors with 123 fails, still about 13%.

That standard, Purity Focus, passes a sample only if the identity is right, HPLC purity is at least 99.5% and the fill is within ±35% of the label. Finnrick’s GHK-Cu page lists the 200 most recent tests, dated 23 June to 25 September 2026, and each test page states the reason for a fail. We counted them on 4 October 2026:

Result	Tests
Pass	152
Fail: fill outside ±35% only	30
Fail: purity below 99.5% only	7
Fail: purity and fill both out	2
Fail: not the labelled substance	4
Incomplete	5

Four points stand out:

• Recent samples failed more often. 43 of 195 classifiable tests failed, about 22%, against about 13% over the whole history.
• Fill is the main failure. 32 of the 43 fails involved fill. All 30 fill-only fails read 99.6% pure or higher.
• Most fill fails were short. 24 vials held less than the label and 8 held more. Seven read 86% to 88% below the label, about an eighth of the stated amount.
• Purity fails were mostly near misses. Six of nine read between 98.3% and 99.3%. Three read 67.9%, 79.3% and 82.9%.

The test pages show purity, fill and identity but no copper result, so these counts say nothing about the copper. See how Finnrick works for its standards and their limits.

Copper content and the copper-to-peptide ratio

A complete GHK-Cu result gives two amounts, mg of peptide and mg of copper, and from them the molar ratio:

ratio = (mg of copper ÷ 63.55) ÷ (mg of GHK ÷ 340.38)

A ratio near 1.0 fits the 1:1 complex that PubChem describes. Below 1, part of the peptide carries no copper. Above 1, there is more copper than the peptide can hold as a 1:1 complex. GHK binds copper through three nitrogen atoms, and with extra peptide present a second complex, with two GHK molecules per copper, forms as well, according to a 2020 study of copper and GHK by Bossak-Ahmad and colleagues. So two vials with the same mg can hold different products.

The arithmetic also explains why labs can report different mg for one vial. By calculated mass, copper is about 15.8% of the 1:1 complex. A vial that holds exactly 50 mg of complex contains about 42.2 mg of GHK and 7.9 mg of copper. A lab that reports the complex prints 50 mg. A lab that reports the peptide prints about 42 mg, 16% lower, and neither is wrong. Salts and water add weight that is neither peptide nor copper. The guide to net peptide content explains the basis question, and a counter-ion test measures the salt.

Ethos Analytics publishes a GHK-Cu sample certificate on its verification page. It reports 53.16 mg per vial against a 50 mg claim, measured against a certified reference standard, with purity given as >99%. The figure is labelled GHK-Cu; there is no separate copper result or ratio. One figure shows whether a vial is near its label, but it cannot answer the ratio question.

Colour is not a copper test

Copper bound to GHK absorbs orange light; the 2020 study tracked its absorbance band at 605 nm. That is why GHK-Cu looks blue. A blue colour shows that copper is present. It cannot show how much, whether the ratio is 1:1, or whether the peptide is pure. Our September 2026 market research found no home kit for the identity or purity of GHK-Cu; see peptide test kits.

How a lab confirms GHK-Cu identity

GHK is a tripeptide, so its mass is easy to measure. The calculated [M+H]+ ion of free GHK is m/z 341.19. The copper complex appears at m/z 402.11 with copper-63, with a partner peak 2 Da higher from copper-65. Natural copper is about 69% copper-63 and 31% copper-65, so the partner peak stands a little under half as tall. That twin-peak pattern is a sign of copper.

The binding depends on pH: in the 2020 study, free copper ions were among the species in acid, and the complex formed as the pH rose. Depending on the method’s conditions, a spectrum can show the free peptide, the complex, or both. Either can confirm GHK; neither measures how much copper the vial holds. As for every peptide, retention time alone is not proof of identity; see LC-MS identity.

Purity, blends and safety tests

HPLC purity is the main peak’s share of UV peak area. For GHK-Cu it describes the peptide; it does not measure copper, salts or water. GHK-Cu is also sold in blends with other peptides, which need identity and mg for each component; see peptide blend testing. If the vials are for injection research, endotoxin and Sterility (USP <71>, 14 days) answer separate questions, and each needs its own unopened vials.

“Lab tested” also appears on GHK-Cu creams and serums. Their other ingredients can add peaks, and a method built for a freeze-dried vial may not work on them. Tell the lab the form and ingredients first, and ask whether results are per gram or per mL.

What HK Analytical does for GHK-Cu

We test GHK-Cu with any mix of identity (LC-MS), purity (HPLC), content per vial, endotoxin (LAL), Sterility (USP <71>, 14 days), residual solvents, counter-ion (TFA, acetate), water content (Karl Fischer) and vial-to-vial consistency. We do not offer copper content or the copper-to-peptide ratio, so our report gives no copper result. We do not offer blend analysis per component. Results within days of receipt. Sterility (USP <71>, 14 days) is the one test that takes 14 days, because the method incubates for 14 days. Every number comes with its raw data, the report is a signed record you can check at hkanalytical.com/verify, and it carries our photo of the vial as received. See the example report or request a quote.