GHK-Cu identity is confirmed by exact-mass measurement showing the copper isotope pair near m/z 402.1 and 404.1, MS/MS fragments that fix the Gly-His-Lys sequence, a chromatographic retention match against a reference, and a separate copper determination establishing stoichiometry. Purity percentages address none of that.
- GHK is C14H24N6O4 with monoisotopic mass 340.1859; the neutral 1:1 copper complex is C14H22CuN6O4 at 401.0999, average molecular weight 401.91.
- Copper's two stable isotopes produce a doublet near m/z 402.1 and 404.1 at roughly a 2.2 to 1 ratio, which is the clearest single indicator that copper is bound in the measured species.
- Exact mass cannot separate GHK from its sequence isomers; only MS/MS fragment ions such as b2 at 195.088 and y2 at 284.172 fix the residue order.
- Acidic reversed-phase conditions dissociate the complex on-column, so most published GHK-Cu purity figures describe the peptide rather than the chelate.
- Copper accounts for about 15.8% by mass of the 1:1 complex, the figure an ICP or atomic absorption result is checked against.
- There is no USP monograph and no FDA-approved drug product for GHK-Cu, which is why identity rests on orthogonal analysis rather than a compendial procedure.
Identity and purity are separate questions
A certificate that says 99.1% and nothing else has answered a question nobody asked. Purity by area percent describes how much of what eluted was the main peak. It says nothing about what that peak is. A vial of pure glycyl-L-lysyl-L-histidine, a sequence isomer of GHK, would return the same exact mass, a similar retention window on a generic gradient, and a purity figure just as flattering.
ICH Q6A is direct on this point: an identity test should be specific for the substance and capable of discriminating between compounds of closely related structure, and chromatographic retention time alone does not meet that bar. Retention becomes evidence only when it is a comparison against a characterized reference standard run in the same system on the same day. Most certificates in the research-chemical supply chain quote retention as a bare number with no reference injection, which makes it a system record rather than an identity test.
For GHK-Cu there is a second layer. The name describes a metal complex, so identity has to cover both the peptide and the copper, and the two are established by different measurements on different instruments. Confirming one is not confirming the other.
The molecule being confirmed
GHK is the tripeptide glycyl-L-histidyl-L-lysine, C14H24N6O4, monoisotopic mass 340.1859, first isolated from human plasma in the early 1970s. It binds copper(II) with high affinity through the N-terminal amine, the deprotonated amide nitrogen of the Gly-His bond and an imidazole nitrogen of histidine, leaving the lysine side-chain amine free. The fourth coordination position is taken by water, a carboxylate, or a donor from a second ligand depending on pH and on the copper-to-peptide ratio.
Deprotonation on chelation is the reason the complex is not simply peptide plus metal. The neutral 1:1 species is written C14H22CuN6O4, monoisotopic mass 401.0999, average molecular weight 401.91. Copper accounts for 63.546 ÷ 401.91 = 15.8% w/w in that stoichiometry, which is the number an elemental assay is checked against.
Solution speciation is more complicated than the single formula suggests, and the literature is not unanimous on which species dominates in a dried solid. Preparations sold as GHK-Cu vary between 1:1 and 2:1 peptide-to-copper, sometimes with residual copper salt or acetate along for the ride. Stoichiometry is therefore a certificate field, not an assumption. Two vials with identical labels can be materially different substances.
What the mass spectrum has to show
Copper is the gift here. It has two stable isotopes, 63Cu at 69.15% and 65Cu at 30.85% natural abundance, giving an intensity ratio near 2.24 to 1 and a two-mass-unit spacing. Nothing in an organic contaminant profile mimics that pattern. A pair of ions separated by 1.998 Da at the correct ratio is strong evidence that copper is bound in the species being measured, not merely present in the vial.
| Species | Monoisotopic m/z | What it establishes |
|---|---|---|
| [Cu(GHK−2H)+H]+, 63Cu | 402.107 | Intact 1:1 copper complex |
| [Cu(GHK−2H)+H]+, 65Cu | 404.105 | Isotope partner; ratio to 402.1 should approach 2.2:1 |
| [GHK+H]+ | 341.193 | Free peptide, from in-source demetallation |
| [GHK+Na]+ | 363.175 | Common adduct; useful as a sanity check on calibration |
| y1 (Lys) | 147.113 | C-terminal residue |
| y2 (His-Lys) | 284.172 | Fixes His at position 2 |
| b2 (Gly-His) | 195.088 | Fixes Gly at the N-terminus |
| Histidine immonium | 110.071 | Residue marker, not positional |
Seeing free peptide at 341.19 alongside the complex is normal and not a defect. Acidic mobile phases and the ion source both strip copper. What matters is that the complex ion is present at all, because a demetallated spectrum on its own is indistinguishable from a spectrum of plain GHK.
The fragment ions carry the part that exact mass cannot. GHK, GKH, HGK and KHG all weigh 340.1859. Only the b and y series separate them. An identity claim built on a single-stage mass measurement has demonstrated elemental composition and stopped there, which is a real result and a partial one.
Why the chromatography is awkward
Reversed-phase HPLC of a copper peptide complex fights the method. The standard peptide gradient uses 0.1% trifluoroacetic acid, and at that pH the imidazole and the amide nitrogen are protonated, so the complex dissociates on-column. Free copper ions then interact with residual silanols and with any metal surfaces in the flow path, producing tailing, split peaks and retention that drifts between injections.
The practical consequence is that most purity numbers reported for GHK-Cu are purity numbers for GHK. That is worth knowing rather than hiding. A chromatogram run under acidic conditions measures peptide-related impurities: truncated sequences, deletion peptides, D-amino acid diastereomers where the method resolves them, residual protecting-group adducts from synthesis. It cannot see whether the copper is bound, and it cannot quantify a copper species.
Laboratories that want the complex intact through the column move to a near-neutral mobile phase with a volatile buffer, use hardware with an inert flow path, and accept worse peak shape than a peptide chemist would tolerate. Either approach is defensible. What is not defensible is a certificate presenting an acidic RP-HPLC purity figure as evidence about the complex. Ask which method was run and at what pH; the answer tells you what the number covers. Sample preparation matters for the same reason. Diluting into a chelating buffer, or into anything carrying EDTA or citrate, competes the copper away before the injection.
Confirming the copper
The metal needs its own measurement. Three approaches appear on legitimate certificates, in descending order of how often you will actually see them.
- ICP-MS or ICP-OES after acid digestion. Gives total copper as mass fraction, compared against the 15.8% expected for the 1:1 complex. Precise, and blind to whether the copper is coordinated or sitting there as sulfate.
- Flame atomic absorption. Older, cheaper, adequate for the same total-copper question.
- UV-visible spectrophotometry. The Cu(II) d-d transition puts a broad, weak band in the 600 to 640 nm region, which is what makes the material blue. Molar absorptivity is low, so this needs millimolar concentrations, and the band position responds to the donor set. It is the one measurement that reports on coordination rather than on total metal.
Read total copper and the visible band together. Copper high against the expected fraction with a normal absorption band suggests free copper salt riding along. Copper on target with a weak or shifted band suggests the peptide is not doing the coordinating you think it is. Neither result is visible in an HPLC trace.
Colour is a crude but honest first look. Lyophilized GHK-Cu is deep blue to blue-violet. A pale, grey or greenish cake is a reason to hold the lot and ask questions before any instrument time is booked.
The orthogonal tests that fill the gaps
Mass spectrometry and chromatography leave specific holes. Amino acid analysis after acid hydrolysis returns a Gly:His:Lys ratio that should sit near 1:1:1 and catches gross composition errors that a clean single peak can hide. Chiral analysis, usually by derivatization with Marfey's reagent followed by RP separation, addresses the stereochemistry that mass cannot see; glycine is achiral, so the question is confined to histidine and lysine, and D-content arises from racemization during synthesis rather than from substitution.
Peptide content is the field most often missing and most often assumed. Net peptide content by quantitative amino acid analysis or nitrogen determination tells you what fraction of the weighed powder is the substance rather than water, counterion and salt. Karl Fischer or loss-on-drying covers water; a lyophilized copper peptide is hygroscopic enough for that to matter to any gravimetric preparation. Residual acetate or trifluoroacetate belongs on the certificate as well, since TFA counterion can be several percent by mass and shifts every concentration you calculate from a weight.
None of this is exotic. It is the ordinary orthogonal panel that a competent contract laboratory quotes as a package, and its absence is information about the supplier.
Reading the certificate
| Field | Acceptable | Flag |
|---|---|---|
| Lot identifier | Matches the vial label exactly | Blank, generic, or a different lot than shipped |
| Identity method | Named technique with the observed value | The word "conforms" with no data |
| Observed mass | 402.1 with the 404.1 partner, or 401.10 as neutral monoisotopic | Only 340.4 or 341.2 quoted, with no copper species |
| MS/MS or sequence data | Fragment table or annotated spectrum attached | Absent, so sequence isomers remain untested |
| Copper determination | ICP or AAS result with a mass fraction | No metal assay anywhere on the page |
| Stoichiometry | Stated, for example 1:1 peptide to copper | Unstated |
| HPLC conditions | Column, mobile phase, pH, gradient, detection | A purity number with no method |
| Water and counterion | Reported values | Omitted, making net content unknown |
| Date, analyst, laboratory | All three present | Undated, or typical values rather than lot results |
The distinction between lot-specific results and typical values is the one that catches people. A page headed "typical analysis" is a marketing document describing what the process usually produces. It is not a measurement of the vial on your bench, and it cannot be traced back if a result goes sideways. Our quality standard page sets out which documents accompany a lot and in what form.
Attached raw data is worth more than a summary table. A chromatogram with a visible baseline and a spectrum with an axis let a reader check the claim; a table of pass marks only lets them trust it.
Documenting what happens after receipt
Identity confirmed on arrival is identity at one point in time. A copper peptide in solution has more ways to change than a plain peptide: the complex can dissociate as pH drifts, copper can redistribute onto chelators introduced with the diluent, and copper(II) catalyses oxidation of susceptible residues in anything else sharing the container. Record the diluent and its lot alongside the concentration, since choice of diluent is part of the chemistry here rather than a detail. Notes on diluent selection sit in our guide to bacteriostatic water for peptides, and the general storage reasoning for lyophilized peptides is set out in the storage and stability guide.
Concentration arithmetic deserves the same care as the identity work. A 50 mg vial taken into 5 mL gives 50 mg ÷ 5 mL = 10 mg/mL of as-supplied powder. That is not 10 mg/mL of the complex unless water and counterion are zero, which they are not. Where a protocol works in molar terms, dividing by the 401.91 average molecular weight of the 1:1 species requires that the stoichiometry on the certificate is the stoichiometry in the vial. The vial concentration calculator handles the mass-per-volume step; the correction for net content is a judgement call that belongs in the notebook with its reasoning attached.
Regulatory position
GHK-Cu appears in cosmetic formulations under the INCI designation copper tripeptide-1. There is no FDA-approved drug product containing GHK-Cu, and no United States Pharmacopeia monograph specifying identity or purity criteria for it. That absence is why identity testing falls back on general chapters and on orthogonal analysis rather than on a monograph procedure.
Material supplied for laboratory use is not a cosmetic ingredient release and is not a pharmaceutical grade. It carries a certificate covering identity and purity for research purposes, which is a narrower claim than either of those categories.
Status verified 26 August 2026.
FOR LABORATORY AND IN-VITRO RESEARCH USE ONLY. NOT FOR HUMAN OR ANIMAL CONSUMPTION. NOT FOR PERSONAL, MEDICAL, DIAGNOSTIC, THERAPEUTIC, OR RECREATIONAL USE.
Common questions
Can a purity percentage confirm that a vial contains GHK-Cu?
Why do I see free peptide at m/z 341 instead of the complex?
What does the copper isotope pattern prove?
Is an ICP copper result enough on its own?
Which certificate fields matter most for GHK-Cu specifically?
Does chiral purity need separate testing?
Sources
- ICH Q6A, Specifications: Test Procedures and Acceptance Criteria for New Drug Substances and New Drug Products. Establishes that identity tests must be specific and able to discriminate between closely related structures, and that chromatographic retention time alone is not sufficiently specific.
- United States Pharmacopeia general chapter on chromatography (<621>). Defines system suitability and the conditions under which a retention comparison against a reference standard constitutes evidence; supports the treatment of bare retention numbers as system records.
- CIAAW / IUPAC isotopic composition of the elements. Source for the natural abundances of copper-63 and copper-65 used to derive the expected doublet spacing and intensity ratio in the mass spectrum.
- PubChem records for glycyl-L-histidyl-L-lysine and its copper(II) complex. Molecular formulas, monoisotopic and average masses used for the exact-mass and copper mass-fraction calculations in this article.