If you formulate with a copper peptide, you will be shown a purity figure before you are shown anything else. It is almost always a high one. The figure is not usually wrong; it is usually undefined. In this category a single percentage can be a chromatographic ratio, a peptide mass fraction, or the mass fraction of the whole complex, and those three numbers for one and the same powder do not agree with each other. At Demeter Biotech we supply cosmetic-grade GHK-Cu as a lyophilized powder in 1 g bottles, and every lot leaves with a certificate that states which definition each figure rests on. This note sets out the arithmetic behind that habit: what the percentage can mean, what the molecular formula allows, and what to ask for so that two quotations can be compared at all.

1. One number, three definitions

A percent sign is not a definition. It only says “per hundred of something”, and the useful question is what the something is. For a copper peptide three denominators are in routine use, and a document can carry any of them without ever naming it.

Read the third row against the second and the reason for two separate figures becomes obvious: the complex is a peptide plus a metal, so its content cannot be read off a peptide peak alone. Read the first row against the second and the reason for a method statement becomes obvious: an area share and a mass share answer different questions, and only one of them tells you how much peptide is in the bottle.

2. The ceiling: 84.2% is the most peptide the complex can contain

This is the single most useful piece of arithmetic in the category, and it needs nothing but the molecular formula already on the certificate. The free tripeptide Gly-His-Lys has a molecular weight of 340.38. When it binds one copper(II) ion it loses two amide protons and becomes C₁₄H₂₂CuN₆O₄, molecular weight 401.91. So in the anhydrous complex the peptide portion is (340.38 − 2.02) ÷ 401.91, which is 84.2%, and the copper portion is 63.55 ÷ 401.91, which is 15.8%.

Composition of the anhydrous complex, by mass

Peptide 84.2% · Copper 15.8% — and nothing else, because the two parts account for the whole molecule.

Two consequences follow, and both are checkable in a few seconds. First, a figure above roughly 84% presented as peptide content by mass of the complex is not possible, so it must be resting on a different basis — an area share, a salt-free calculation, a reference standard that is not the complex, or material that is not wholly complexed in the first place. None of those is automatically a problem; an unstated basis is. Second, water, an acetate counter-ion and any residual solvent can only push the peptide figure down from 84.2%, never up, which is why a well-dried lot and a poorly dried lot of the same material carry different peptide numbers without either being out of specification.

A set of figures consistent with all of this might read: peptide 70.0%, copper 13.1%, complex content 83.1%, with water, counter-ion and a small residual fraction making up the remainder. That is an arithmetic illustration of how the three rows fit together, not a batch record from anyone’s file.

3. What an area percentage does and does not see

Reversed-phase HPLC with ultraviolet detection separates what is in solution by hydrophobicity and integrates the peaks. At the low wavelengths used for peptides — typically 210 to 220 nm — the detector responds to the amide backbone, which is why even a short, non-aromatic sequence produces a usable peak. That is also its limitation: the detector reports what absorbs, not what weighs. Water does not absorb meaningfully at those wavelengths. Neither does an acetate or trifluoroacetate counter-ion. So the denominator of an area percentage is the set of UV-visible species that the method separated, and the mass of the powder is not in it.

The size of that gap is not a rounding error, and the cleanest demonstration comes from metrology rather than from marketing. When a national measurement institute assigned a purity value to a candidate certified reference material for the peptide angiotensin II, the assignment combined quantitative NMR, isotope-dilution amino acid analysis and a mass-balance calculation, and the three independent routes agreed. The assigned value was 691 ± 9 mg/g. In other words, a reference material held to the highest standard available in the field was about 69% peptide by mass, and the trifluoroacetate counter-ion alone accounted for nearly 25% of the sample (Melanson et al., 2018). A document reporting 99% chromatographic purity and a document reporting 69% peptide content can therefore describe one and the same solid, with neither figure being false.

Two more limits are worth keeping in mind. An area share is semi-quantitative at best, because different species do not absorb in proportion to their mass, and a number computed from integration rules is only as reproducible as those rules. And chromatographic purity does not confirm identity: two sequences can share a retention time. That is why identity sits on its own line of a certificate, from a mass measurement, separate from the purity figure.

4. This raw material now has its own written standard

Until recently the numbers in this category were conventions rather than requirements, which is precisely how three meanings of one percentage could coexist. That changed with a dedicated standard: YY/T 10005-2026, Cosmetic ingredients — Copper tripeptide-1, published on 3 April 2026 and taking effect on 1 May 2027. It is a recommended industry standard, its scope covers the copper tripeptide-1 complex and its salts, and its own introduction notes that no national or industry standard for this raw material existed when it was drafted — which is exactly why market figures were not comparable.

What matters for your reading of a certificate is how the document splits the quantities. The standard sets out identification, purity and peptide content by high-performance liquid chromatography, and its normative appendix determines three separate quantities: copper, tripeptide-1, and the complex itself. Three determinations, because no single peak can report all three. Purity is a chromatographic area figure — the share of total integrated peak area carried by the copper and the peptide peaks — while peptide content and complex content are mass figures, with the moisture correction applied, and both the peptide and the copper are quantified against external standards rather than inferred from one another.

The practical point is not the document’s jurisdiction. It is that a standard written for this material confirms what the arithmetic already told us: on a compliant certificate, purity and content are two different rows, and a bare percentage is a summary of the file rather than the file. We are writing from outside the standard’s own market and it does not bind a lot sold elsewhere, but its definitions are the clearest public statement of how these figures relate, which makes it a useful yardstick wherever you buy.

5. Copper is the cross-check on the peptide figure

Because the two parts of the complex stand in a fixed mass ratio, the copper figure audits the peptide figure. From the numbers above, copper divided by peptide in the pure complex is 15.8 ÷ 84.2, or about 0.19. If a certificate reports copper well below that ratio for the peptide it reports, part of the peptide is probably not carrying copper; if it reports copper well above it, some copper may be present outside the complex. Neither reading is a verdict — both are reasons to ask how each figure was obtained. Measuring copper itself is a different analytical question with its own methods and its own traps, and we keep it in a separate note in this series.

6. Five lines to request before you compare quotations

The fix for all of this costs one email and belongs at quotation stage, not after the goods have landed. Ask for five things, and ask for them in writing.

7. The comparison that actually holds: price per gram of peptide

Once the figures carry definitions, the pricing conversation gets simpler and less pleasant for loose numbers. The unit you formulate against is the peptide, not the powder, so divide before you decide. One gram of powder at 70% peptide delivers 0.70 g of peptide; one gram at 84% delivers 0.84 g. Same bottle, same 1 g label, a fifth more material in the second case. A quotation that looks lower per gram can easily be higher per gram of peptide, and a figure that looks better can simply be measured on a friendlier basis.

Two habits keep the comparison honest. Convert everything to peptide mass and compare that. And never compare across methods: a number produced at one wavelength, on one column, against one reference standard is not the same measurement as a number produced under another set, no matter how similar the two percentages look on paper.

8. How Demeter documents GHK-Cu

At Demeter Biotech we supply Copper Tripeptide-1, CAS 89030-95-5, as a cosmetic-grade lyophilized powder in 1 g bottles, for topical cosmetic formulation. Each lot is released against a certificate of analysis that carries identity (INCI name and CAS number), chromatographic purity with the method behind it, peptide content with its basis, copper content, heavy metals, microbiology, date of manufacture and the lot number. Where a figure could be read two ways, we state which reading applies rather than leaving the higher one to speak for itself. Tell us the basis your specification needs — as-is or anhydrous, which salt form, which method — and we will confirm the lot figures against it before the order is packed, including the chromatogram if your file requires one.

Blue Copper Peptide GHK-Cu Powder — Copper Tripeptide-1, Water-Soluble Cosmetic-Grade Active

Cosmetic-grade GHK-Cu supplied as a 1 g lyophilized bottle. Copper Tripeptide-1 (INCI), CAS 89030-95-5, water-soluble, released against a batch certificate covering identity, purity with its method, peptide and copper content, heavy metals and microbiology.

View the specification →

Pure Blue Copper Peptide Powder GHK-Cu (CAS 89030-95-5) — Cosmetic Grade Tripeptide-1

High-purity cosmetic-grade GHK-Cu in a 1 g lyophilized bottle. Copper Tripeptide-1 (INCI), water-soluble; the batch certificate states the purity definition, peptide content with its basis, copper content and the analytical method used.

View the bulk specification →

None of this requires distrust. It requires one line of definition per figure. Once that line is present, a high number and a low number can both be true, and you can finally tell which quotation is the cheaper one.

This article discusses analytical measurement, specification language and the supply form of a raw material only. It makes no statement about the effect of the ingredient on any person, and it describes no application other than use as a cosmetic raw material. Molecular weights and the resulting mass fractions are arithmetic on the formula. The three illustrative figures in section 2 are a worked example, not a batch record. Standards are described as published by the issuing authority in April 2026 and their text governs; the figures that bind a lot are those on its own certificate of analysis.