What mass should a GHK-Cu COA show?

It depends on what the method measures. The free GHK peptide is 340.38 g/mol average and 340.19 Da monoisotopic in PubChem. PubChem lists the copper complex as prezatide copper at 402.92 g/mol, with related records at 400.90 and 401.91 that differ in hydrogen and charge. The certificate should say which species it identified and give a separate copper result.

How do I know if my GHK-Cu is real?

Ask for two measurements on a sample from your vial: the peptide by LC-MS or HPLC, confirming it is GHK, and copper by ICP-MS. Together they show whether both parts are present in a sensible proportion. Colour and solubility prove neither. A seller's certificate that reports only a purity percentage has not shown that the copper is there.

Can GHK-Cu contain free copper?

Yes, if more copper salt was added than the peptide can bind, or the peptide content is low. A peptide-only test will not see it, because copper is not a peptide. Measuring copper by ICP-MS and comparing it with the measured peptide content shows whether there is more copper than the GHK present could hold in a 1:1 complex.

What does a 50 mg GHK-Cu label actually measure?

That depends on the seller, which is the problem. It could mean 50 mg of copper complex, 50 mg of GHK peptide, or 50 mg of powder including counter-ions and water. These are different quantities. An amount test reports milligrams of a stated species against a reference, so ask which species the label and the report each refer to before comparing them.

One of the 30 compound testing profiles

GHK-Cu

GHK-Cu is a 3-amino-acid peptide, Gly-His-Lys, bound to one copper ion (PubChem lists prezatide copper as C14H23CuN6O4+, average mass 402.92 g/mol); a test should confirm the GHK peptide by mass, measure copper separately, and check that the two are present in the expected proportion.

GHK-Cu is the copper(II) complex of the tripeptide glycyl-L-histidyl-L-lysine (GHK), a peptide found in human plasma that binds copper with high affinity (Pickart et al., BioMed Research International, 2015).

Test your GHK-Cu

Identity card

Formula: C14H23CuN6O4+
Average mass: 402.92 g/mol
Monoisotopic mass: 402.11 Da
Length: 3 residues
Modifications: Copper(II) bound by the histidine imidazole nitrogen, the glycine alpha-amino nitrogen and the deprotonated nitrogen of the Gly-His peptide bond; Free C-terminal acid on lysine
Also sold as: Copper peptide, Copper tripeptide-1
Sequence: GHK
Note: PubChem represents the complex in several ways that differ by hydrogen count and charge. The record used here, CID 71587328 (prezatide copper, also listed as copper tripeptide-1 and GHK copper), is C14H23CuN6O4+ at 402.92 g/mol, monoisotopic 402.107675 Da (recorded as 402.11). Other records give C14H22CuN6O4 at 401.91 g/mol (CID 165429100), C14H21CuN6O4- at 400.90 g/mol (CID 139035031) and a 2:1 peptide to copper complex, C28H46CuN12O8 at 742.3 g/mol (CID 9831891). The copper-free peptide GHK is CID 73587, C14H24N6O4, average mass 340.38 g/mol, monoisotopic 340.19 Da.

Source: PubChem CID 71587328, Prezatide copper, PubChem CID 73587, Glycyl-L-histidyl-L-lysine (GHK), PubChem CID 139035031, GHK-Cu, Pickart L et al. GHK Peptide as a Natural Modulator of Multiple Cellular Pathways in Skin Regeneration. Biomed Res Int. 2015;2015:648108.

Compare the mass printed on a certificate with the values above. The mass checker explains charge states and which mass a lab usually reports.

What usually goes wrong with GHK-Cu. Documented failure modes, with sources.

Free copper, free peptide, or the wrong ratio

GHK-Cu is a peptide and a metal ion held together: copper(II) is bound by the histidine imidazole nitrogen, the glycine amino nitrogen and the deprotonated amide nitrogen of the Gly-His bond, and GHK can take copper from the high-affinity site on plasma albumin (Pickart et al., 2015). A product made with too little copper leaves uncomplexed GHK; too much leaves free copper salt. Neither shows on a peptide-only purity test. Measuring the peptide by LC-MS or HPLC and the copper by ICP-MS, then comparing the two, checks the proportion.

More than one valid mass on paper

PubChem holds 1:1 complex records at 400.90, 401.91 and 402.92 g/mol that differ in hydrogen count and charge, and a 742.3 g/mol record with two GHK peptides around one copper (PubChem, prezatide copper; PubChem CID 9831891). In solution GHK-Cu can also form binary and ternary structures (Pickart et al., 2015). A spectrum may show the free peptide, the complex or both, so a certificate should name the species it assigned and the reference mass it used; a bare "403" is not enough to judge.

Histidine racemisation and short deletions

Histidine has historically been a notoriously racemisation-prone residue in Fmoc peptide synthesis (Behrendt et al., Journal of Peptide Science, 2016), and in GHK it sits in the middle of the chain. A D-His version has the same mass as GHK, so only chromatography can show it. Deletion sequences, which arise from inefficient Fmoc deprotection (D'Hondt et al., 2014), would here be dipeptides such as Gly-His or His-Lys, easy to see by mass because the target is so small.

Counter-ions on a very small peptide

GHK has three sites that can carry a positive charge: the N-terminal amine and the histidine and lysine side chains. The number of trifluoroacetate counter-ions in synthetic peptides tracks the number of positive charges, and in one study trifluoroacetate reached 35% of the total weight of the peptide salts tested (Erckes et al., Pharmaceuticals, 2025). On a 340 g/mol peptide every counter-ion is a large fraction of the weight, so a label based on salt weight can overstate the peptide considerably.

What we check in GHK-Cu. Silent, with captions.

Which tests matter most

LC-MSConfirms the GHK peptide (340.38 g/mol free, or the complex if the method preserves it) and shows deletion dipeptides by mass.
ICP-MS (elemental impurities)Measures copper directly, the only way to check the copper to peptide proportion and spot free copper salt.
HPLC-UVGives the purity of the peptide part and is the routine way to see a D-histidine form with the same mass as GHK.
Counter-ion contentOn a 340 g/mol peptide, counter-ions can be a large share of the weight; this test lets the amount be stated as peptide.

Reading GHK-Cu results

A GHK-Cu certificate needs two findings: a peptide line naming GHK with a mass near 340.38 g/mol average or 340.19 Da monoisotopic for the free peptide (PubChem CID 73587), or near a complex mass if the method kept the copper attached, and a measured copper content. A purity percentage alone tells you about neither. The label amount also needs a stated basis, complex, peptide or powder, as the net peptide content lesson explains.

The US FDA names the potential for aggregation and peptide-related impurities among its concerns for compounded GHK-Cu for some routes of administration (FDA, bulk substances with safety risks).

Public Tested.ph results

No public GHK-Cu records yet

Each public GHK-Cu record will appear here with its identity, HPLC purity and measured amount against the label, once the first vial is tested.

FIG 13Amount against the label

Questions about testing GHK-Cu

What mass should a GHK-Cu COA show?: It depends on what the method measures. The free GHK peptide is 340.38 g/mol average and 340.19 Da monoisotopic in PubChem. PubChem lists the copper complex as prezatide copper at 402.92 g/mol, with related records at 400.90 and 401.91 that differ in hydrogen and charge. The certificate should say which species it identified and give a separate copper result.
How do I know if my GHK-Cu is real?: Ask for two measurements on a sample from your vial: the peptide by LC-MS or HPLC, confirming it is GHK, and copper by ICP-MS. Together they show whether both parts are present in a sensible proportion. Colour and solubility prove neither. A seller's certificate that reports only a purity percentage has not shown that the copper is there.
Can GHK-Cu contain free copper?: Yes, if more copper salt was added than the peptide can bind, or the peptide content is low. A peptide-only test will not see it, because copper is not a peptide. Measuring copper by ICP-MS and comparing it with the measured peptide content shows whether there is more copper than the GHK present could hold in a 1:1 complex.
What does a 50 mg GHK-Cu label actually measure?: That depends on the seller, which is the problem. It could mean 50 mg of copper complex, 50 mg of GHK peptide, or 50 mg of powder including counter-ions and water. These are different quantities. An amount test reports milligrams of a stated species against a reference, so ask which species the label and the report each refer to before comparing them.

Sources

Pickart L et al. GHK Peptide as a Natural Modulator of Multiple Cellular Pathways in Skin Regeneration. Biomed Res Int. 2015;2015:648108, BioMed Research International (PMC)
PubChem CID 71587328, Prezatide copper, National Library of Medicine
PubChem CID 9831891, GHK copper 2:1 complex, National Library of Medicine
PubChem CID 73587, Glycyl-L-histidyl-L-lysine (GHK), National Library of Medicine
Behrendt R, White P, Offer J. Advances in Fmoc solid-phase peptide synthesis. J Pept Sci. 2016;22(1):4-27, Journal of Peptide Science (PMC)
D'Hondt M et al. Related impurities in peptide medicines. J Pharm Biomed Anal. 2014;101:2-30, PubMed
Erckes V et al. Towards a Consensus for the Analysis and Exchange of TFA as a Counterion in Synthetic Peptides. Pharmaceuticals. 2025;18(8):1163, Pharmaceuticals (PMC)
Certain bulk drug substances for use in compounding that may present significant safety risks, US Food and Drug Administration

Last reviewed 6 Oct 2026.