How to read a Certificate of Analysis
A Certificate of Analysis (CoA) is a supplier’s test report for one specific batch of material. It is the definitive record of what a vial contains and how pure it is. A CoA is only as good as what it actually shows, and a serious one goes well beyond a bare headline figure such as “99%”. This guide explains what to look for and how to recognise a weak or template certificate.
A good CoA answers two separate questions with two separate methods: is it the right molecule, and how much of the vial is that molecule. Purity and identity are not the same thing, and a certificate that gives only one of them is incomplete.
Identity by mass spectrometry
Identity is proven by mass spectrometry (MS), which weighs the molecule. A credible identity result prints two numbers side by side: the expected (theoretical) mass calculated from the sequence and formula, and the observed mass the instrument actually measured. The two should match.
How close is close enough depends on the instrument, and the CoA should state which mass it quotes. Most research-peptide certificates report an average mass on a standard-resolution ESI or MALDI instrument, where a match within roughly plus or minus 1 Dalton (about 0.1% of the molecular weight) is the normal expectation. A certificate that claims high-resolution MS should show a correspondingly tighter match measured in parts per million.
A mismatch of many Daltons is a red flag. It can mean the wrong sequence, the wrong salt form, an oxidation (which adds 16 mass units per oxygen), a missing residue, or a copy-and-paste error. This is exactly why identity matters: two very different molecules can ship under the same trade name, and only the observed mass tells you which one is in the vial.
The salt form
A thorough CoA states the salt form, for example acetate, trifluoroacetate (TFA) or free base. This matters because the counterion changes how much actual peptide sits in each milligram of powder, and it changes the molecular weight the observed mass should be compared against. A certificate that gives only a trade name with no salt form and no formula has left out information you need. Our guide on salt forms and net peptide content covers this in full.
Purity by HPLC, with the chromatogram
Purity is proven by reversed-phase high performance liquid chromatography (RP-HPLC). The sample is separated on a column and each component appears as a peak; purity is reported as area percent, the area of the main peak divided by the total area of all peaks. A stated “greater than or equal to 98%” means at least 98% of the material the detector sees is the target peptide.
The single most important thing to insist on is the actual chromatogram, not just the headline number. A bare “99%” with no trace behind it cannot be checked. A strong purity section shows:
- One tall, sharp, symmetric main peak that dominates the trace.
- A flat, quiet baseline with no large unexplained humps.
- An integration table listing retention time and area percent for each peak, so the headline number can be checked against the picture.
- The method stated: column, mobile phase, gradient, flow rate and detection wavelength (usually 210 to 220 nm). Without the method the number cannot be reproduced.
A few small impurity peaks near the main peak are normal and honest synthesis by-products. For research peptides the market norm is greater than or equal to 98% by RP-HPLC. Metal-complexed peptides such as GHK-Cu behave differently and carry extra identity checks, so always read the number against the molecule.
The safety panel
- Heavy metals. Screening for metallic contaminants such as lead, arsenic, cadmium and mercury.
- Endotoxin. Bacterial endotoxin measured by the Limulus Amebocyte Lysate (LAL) test, reported in endotoxin units per milligram (EU/mg). Purified research material described as substantially endotoxin free typically sits at or below 100 EU/mg, with better material lower still. Many research-only certificates omit endotoxin entirely, which is a gap worth noting.
- Net peptide content and water. The proportion of the powder that is genuinely peptide as opposed to counterion and residual water. A vial can read 99% pure by HPLC yet be only 70 to 85% peptide by weight, so this is the number that governs real content.
Batch number and independent verification
The batch or lot number is the key that ties the certificate to the physical vial and to any independent testing. It should be present on the certificate and match the vial label. A recent analysis date tied to that batch matters too. The strongest signal of all is independent, third-party testing: a certificate from a named external laboratory, traceable by batch number, that you can verify rather than take on trust. Axyn publishes batch documentation on our lab results page and explains our approach on the testing page, with a QR code on the vial linking to the live certificate.
How to spot a weak or template CoA
| Element | Strong CoA | Weak or template CoA |
|---|---|---|
| Product identity | Exact name, formula or sequence, and salt form | Just a trade name, no salt form, no formula |
| Batch / lot number | Present, and matches the vial | Missing, or a generic specimen reused across products |
| Analysis date | Recent, tied to the batch | None, or older than the stock |
| Purity | Number plus the chromatogram, integration table and method | A bare headline “99%” with no trace |
| Identity | Expected vs observed mass by MS | No mass spectrum, or a claim with no numbers |
| Laboratory | Named lab, independently verifiable | Unnamed, or an unbranded template |
In short, distrust any certificate that is a generic template with no named laboratory, no batch number and no dates, or that offers a single purity figure with no chromatogram behind it. A trustworthy certificate shows the batch, the named laboratory, and all three dimensions of identity, purity and safety.
For research use only. Not for human consumption. Not a medicine, supplement or cosmetic. No therapeutic use is stated or implied.