How to Read a Peptide COA

A certificate of analysis is the only document connecting the powder in a vial to a testable claim. Most arguments about peptide quality come down to a COA nobody actually read. This guide covers what each section means, what the numbers should look like, and the specific failures that indicate a certificate is decorative rather than real.

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What a certificate of analysis is for

A COA is a laboratory report on one specific synthesis run. It is not a description of a product line, not a marketing document, and not a general statement about a vendor's standards. It describes a batch — and only that batch.

This distinction is the root of most problems. A vendor can hold a genuinely excellent certificate for a batch synthesised two years ago and serve it to every customer indefinitely. Nothing on the document is false. It simply does not describe the vial you received.

Everything that follows is about determining whether the certificate in front of you describes your material, and whether the tests it reports are the right ones.

The two tests that matter

HPLC — how pure is it

High-performance liquid chromatography separates the contents of a sample by pushing it through a column and measuring what emerges, when. The output is a chromatogram: a trace with peaks, where the area under each peak corresponds to the relative quantity of that component.

Purity is reported as the target peak's area as a percentage of total peak area. A 99% result means the target compound accounts for 99% of the UV-absorbing organic material detected.

That qualifier matters enormously and is almost always omitted. HPLC with UV detection sees only what absorbs UV light. Water does not. Residual salts largely do not. Counterions such as acetate and trifluoroacetate do not appear as impurities. So a vial reported at 99% purity may still be a substantial fraction water and salt by mass — this is normal for lyophilised peptides, but it means the net peptide content is always lower than 99% of the fill weight.

Mass spectrometry — is it the right molecule

Mass spectrometry measures molecular weight. The reported value is compared against the theoretical weight calculated from the amino-acid sequence. If they match within tolerance, the molecule is what the label claims.

This is the test that catches substitution. HPLC will happily report 99% purity on a vial containing entirely the wrong peptide — the trace looks clean because the sample is clean, just clean of something else. Only the mass spec establishes identity.

This is precisely how a shorter synthetic fragment gets sold as a full-length protein without anything on the paperwork being technically false. It is a live issue for TB-500, where the fragment and the native 43-residue protein have very different molecular weights.

What the purity numbers should look like

Below 95% the impurity fraction is large enough that results stop being attributable to the named compound. Between 95 and 98% is workable for screening but inadequate for dose-response work. Most reputable research material sits at 98% or above, and 99%+ is the standard claim for anything sold as high-grade.

Treat implausibly high claims with the same suspicion as low ones. Purity above 99.9% for a synthesised peptide is unusual enough that it warrants looking hard at the chromatogram.

The rest of a complete certificate

Beyond purity and identity, a full certificate carries several fields that are easy to skip and worth checking:

• Batch or lot number — must match the vial label exactly. This is the single most important field on the document.
• Test date — an undated certificate cannot be tied to anything.
• Testing laboratory — named and identifiable. Independent analysis carries weight because the lab is accountable; in-house testing has an obvious incentive problem.
• Residual solvents — solid-phase synthesis leaves TFA, acetonitrile and DMF behind. A complete panel quantifies them.
• Water content — usually by Karl Fischer titration. Relevant because it determines how much of the fill weight is actually peptide.
• Counterion content — most synthetic peptides are supplied as acetate or TFA salts. This is part of the mass.
• Appearance — a white to off-white lyophilised cake is standard. Discolouration is worth questioning.

Accreditation of the testing lab, where stated, is a meaningful signal. ISO 17025 is the relevant standard for testing and calibration laboratories and indicates the lab's competence has been independently assessed.

Red flags, in order of seriousness

• Batch number missing, or not matching the vial. The certificate describes different material. Nothing else on it matters.
• The same certificate served to every buyer. If the document is undated and identical across orders, it is decorative.
• A purity figure with no chromatogram. The trace is the evidence. A bare percentage is an unverifiable assertion.
• No mass-spectrometry result. Purity alone cannot establish that the vial contains the named compound.
• No testing laboratory named. Anonymous testing is not testing.
• No residual-solvent panel. Synthesis leaves solvents behind; a certificate that ignores them is incomplete.
• Certificates supplied only on request, reluctantly. Vendors confident in their material publish them.

None of these individually proves bad material. Several together describe a supplier who has not done the work.

Applying this before a purchase

In practice the check takes a couple of minutes. Locate the certificate for the specific batch, confirm the batch number matches the vial, confirm both HPLC and mass-spec results are present, look at the chromatogram, and check the residual-solvent panel exists.

The discipline matters more in 2026 than it did previously. The supplier landscape shifted sharply over the past year — one of the largest vendors ceased trading in March, another was raided by the FDA, and a third's founders faced federal charges after products labelled as one compound were found to contain another. Vendor longevity is no longer a reliable proxy for quality, which puts the weight back on per-batch documentation.

This applies across a catalogue equally. Whether the material is BPC-157, Ipamorelin, Semax, Selank, Melanotan II, Epithalon, MOTS-c, GHK-Cu, NAD+ or a blend such as KLOW, the verification is the same and the failure modes are the same.

Related handling guidance is covered in our guides to reconstituting research peptides and peptide storage and stability.

Reading the chromatogram itself

The purity percentage is a summary of a picture, and the picture carries information the number discards.

An HPLC chromatogram plots detector response against retention time. The target compound appears as a dominant peak; impurities appear as smaller peaks at different retention times. Purity is the target peak's area as a fraction of total peak area.

Two features are worth examining beyond the headline figure. Peak shape should be roughly symmetrical — significant tailing or fronting can indicate column problems or sample issues that make the integration less trustworthy. Impurity distribution matters as much as impurity total: a single 1.5% impurity peak is a different situation from fifteen scattered 0.1% peaks. The first suggests one identifiable side product; the second suggests a messier synthesis.

Also check the baseline. A noisy or drifting baseline makes small peaks difficult to distinguish from background, and purity integration correspondingly less reliable.

None of this requires analytical chemistry training. It requires looking at the trace rather than only the number printed above it — which is precisely why certificates that omit the chromatogram deserve suspicion.

Frequently asked questions

Research use only. All products referenced on this page are sold strictly for laboratory and research purposes. They are not drugs, foods, cosmetics, or medical devices, and they are not intended to diagnose, treat, cure, or prevent any disease. They are not for human or veterinary consumption. Handling should be performed only by qualified individuals in an appropriate laboratory setting.