How to read a peptide COA — and spot one that proves nothing

Nearly every peptide certificate reports high purity. Almost nothing that changes your dose is in that number. Here is what each field actually proves, and which ones a fake certificate always gets wrong.

A COA is a lab report, not a marketing asset

A certificate of analysis is what an independent analytical laboratory sends back after testing a sample of one specific batch. The vendor pays for the test. The vendor does not run it, and should not be the entity signing it. That is the entire point of the document: it is evidence only because someone other than the seller did the measuring.

A certificate worth trusting names the laboratory, names the product, carries a report number, carries a batch or lot number, and carries a test date. Methods should be stated for each result; if they are not, treat the numbers as unqualified. If the first five are missing, you are looking at a graphic, not a result.

The fields that matter

Identity — mass spectrometry

Mass spectrometry measures the molecular weight of the material in the vial and compares it against the theoretical weight of the peptide it claims to be. Each peptide has a specific mass. If the measured mass doesn't match, nothing else on the certificate matters. A match is necessary but not sufficient: peptides with the same amino acids in a different order share an identical mass, so confirming the actual sequence takes MS/MS fragmentation rather than intact weight alone.

Purity testing cannot do this job. A chromatogram can show one clean, dominant peak for a compound that is not the compound you ordered. The peptide quality-control recommendations published in Clinical Chemistry put it plainly: a single major peak may or may not correspond to the desired product. Identity and purity are two questions and they need two tests.

Purity — HPLC

High-performance liquid chromatography separates the peptidic material into peaks and reports the target peak as a percentage of total peak area. Well-made synthetic peptide typically comes back at 98-99% or better. Across the nearly 2,200 certificates in our registry that report a purity figure, the median is 99.74%.

That median is the useful fact here. Purity is not where vendors actually differ any more. A vendor advertising "99%+ purity" is advertising the middle of the pack.

Measured mass or content — how much peptide is actually there

This is the field that changes your dose, and it is the field most often absent. It goes by several names: measured mass, content, quantity, assay, or net peptide content. It answers a different question from purity — not "what fraction of this powder is peptide" but "how many milligrams of peptide are in this vial". It requires a quantitative method: amino acid analysis is the reference approach, with quantitative HPLC or mass spectrometry against a certified reference standard as alternatives. Compare the result to the mg printed on the label.

Water content

Lyophilized powder holds residual moisture, usually measured by Karl Fischer titration. That water is part of the powder's weight and none of your dose.

Counterion — acetate or TFA

Synthetic peptides are salts. Reversed-phase purification typically uses trifluoroacetic acid, so the product arrives as a TFA salt unless it has been exchanged to acetate. Either way the counterion is real mass sitting in the vial that is not peptide. Bachem defines net peptide content as the fraction of peptidic material relative to counterions and residual water; the worked example in their own documentation comes out at 85%. Counterion and water are the ordinary reason a vial weighing 10 mg contains less than 10 mg of peptide.

Endotoxin

Endotoxins are lipopolysaccharide fragments from the outer membrane of Gram-negative bacteria. They survive sterilisation, they are not removed by filtration, and they cause fever and inflammatory response when injected. The reference method is USP General Chapter <85>, Bacterial Endotoxins Test. Limits are product-specific and calculated from the dose: FDA uses K/M, where K is 5 EU per kg of body weight for non-intrathecal routes and M is the maximum human dose per kg in one hour. Results appear as EU/mg or EU/vial. For anything going into a body, this line is not optional.

Sterility and heavy metals

Sterility is a separate test from endotoxin, and passing one says nothing about the other — sterile material can carry endotoxin, and endotoxin-free material can be contaminated. Heavy metals (lead, arsenic, cadmium, mercury) are covered by USP <232> and <233>, typically by ICP-MS or ICP-OES. Neither appears on most peptide certificates. Both are meaningful when they do.

Purity is not mass. This is the one that costs you.

Purity is a ratio. Mass is a quantity. A vial can be 99.5% pure and contain 8.4 mg where the label says 10 mg — the 0.5% impurity is trivial, the 16% shortfall is not. Purity says nothing at all about your dose. Measured mass is the only field that does.

If you want to run the numbers for a vial in front of you, the dose calculator takes vial mg plus water volume and returns the unit mark.

A certificate covers one batch and nothing else

The batch or lot number is the link between the paper and the object. A COA is evidence for the material that was sampled, on the date it was sampled. It is not evidence for the vendor, the product line, or next month's production run.

So check the lot on the vial against the lot on the certificate. If they differ, the certificate describes someone else's vial. If the vial carries no lot number at all, the certificate cannot be tied to it by any means, and the document is decorative regardless of how good the numbers look.

Red flags

• No laboratory name. An unattributed result is an assertion.
• No test date, or a test date that predates the batch. Material cannot be tested before it exists.
• No batch or report number. Nothing to match, nothing to verify.
• Issued by the seller. In-house QC is a legitimate internal process. It is not third-party evidence.
• A purity figure with no method stated. "99.2% pure" with no mention of HPLC is a number, not a result.
• A chromatogram with no axis labels, no scale, or no retention times. Also worth checking: the same trace appearing under two different products.
• An image with no verification path. A JPEG is editable. A lab-hosted record is not.
• Purity reported, mass absent. Common, and the omission that actually affects you.

How to verify

Do not stop at the PDF the seller sent you. Several analytical labs used in this space — Janoshik among them — publish a lookup portal where a report number and a unique key printed on the certificate return the original record. Check the number at the lab, not in the file. A forged PDF is a few minutes of work; a matching entry in the lab's own database is not.

If the report number returns nothing, or the seller cannot supply one, treat the certificate as unverified. That is different from fraudulent, and it is also not proof of anything.

We keep a public registry of more than 2,400 certificates at lab results, searchable by compound, so you can compare what a given batch reported against what the rest of the market reports. Our free tracking app ties a vial to its certificate, so the mg your syringe math uses is the tested figure rather than the printed one.

The short version

Mass spec tells you it is the right molecule. HPLC tells you the material is clean. Measured mass tells you your dose. Endotoxin tells you the material is not pyrogenic. It is one line among several — sterility, identity and particulates are separate questions, and none of them make an unapproved research compound safe to inject. The batch number tells you all of that applies to the vial in your hand. Miss any one of those and the certificate is a document about something else.

Frequently asked

Sources

• USP General Chapter <85> Bacterial Endotoxins Test
• FDA Inspection Technical Guide: Bacterial Endotoxins/Pyrogens
• Recommendations for the generation, quantification, storage and handling of peptides used for mass spectrometry-based assays (Clinical Chemistry) — 2016
• Liquid Chromatography-High Resolution Mass Spectrometry for Peptide Drug Quality Control — 2015
• Bachem: What does net peptide content mean?
• USP <233> Elemental Impurities—Procedures (PDG harmonized chapter)

For research peptide users tracking their own protocol. Not medical advice. Peptides referenced here are research chemicals, not FDA-approved drugs. Consult a qualified clinician for medical decisions.