A Certificate of Analysis, almost always shortened to COA, is the single most useful document attached to a research peptide. It is not marketing material and it is not a general product description. It is the analytical record for one specific batch: what was tested, by which method, on which date, and what the instrument reported.
That distinction matters. A supplier can write anything on a product page. A COA ties a physical vial to a measurement. If you learn to read one properly, you can evaluate a supplier in about ninety seconds.
The fields that should always be present
| Field | What it should tell you |
|---|---|
| Product name | The compound identity, written in full, matching the vial label exactly. |
| Batch or lot reference | A unique code for this production run. This is the key that links document to vial. |
| Vial size / fill weight | The nominal quantity in the vial, e.g. 10 mg or 50 mg. |
| Appearance | A physical description, typically a white to off-white lyophilised powder or cake. |
| Identity result | Confirmation that the material is the compound named, and the method used to confirm it. |
| Purity result | The purity reported by the stated analytical method, with the method named. |
| Test date | When the analysis was performed. Not the date you received the document. |
| Testing laboratory | Who performed the analysis, and whether they are independent of the seller. |
| Storage statement | The conditions under which the material should be held. |
Start with the batch reference, not the purity number
Most people read a COA from the purity line down. Read it from the batch reference out instead. The batch code is what makes the rest of the document meaningful, because it is the only field that connects the certificate to the vial in your hand.
Take the code printed on the vial label and compare it, character for character, with the code on the certificate. If they match, the analytical results apply to your material. If the certificate carries no batch code, or carries a code that does not appear anywhere on the packaging, then whatever the purity line says, it is not a statement about your vial. It is a statement about some other vial, at some other time.
Reading the identity result
Identity answers a simple question: is this actually the compound named on the label? It is usually confirmed by mass spectrometry, where the measured molecular mass is compared with the theoretical mass calculated from the peptide sequence. A COA that reports identity properly will show both numbers, or will state the observed mass and confirm it is consistent with the expected structure.
A certificate that asserts identity without naming a method has told you nothing verifiable. "Identity: conforms" with no supporting data is an opinion formatted to look like a result.
Reading the purity result
Purity is almost always determined by high performance liquid chromatography, or HPLC. The important thing to understand is that a purity figure has no meaning detached from its method. Two laboratories running different gradients, columns or detection wavelengths can report different figures for the same material, and both can be correct within their own method.
So the purity line should never be a bare percentage. It should name the technique, and ideally the detection wavelength. A useful COA also attaches the chromatogram itself, which lets you see the shape of the main peak and whether the baseline is clean, rather than trusting a single summary figure.
Check the date, then check the gap
Two dates matter. The test date tells you when the analysis was run. The batch or manufacture date tells you how old the material is. A wide gap between manufacture and testing, or a test date several years in the past, is worth a question, particularly for material that has been held in stock.
Neither date being present is a stronger signal than either one being unflattering.
Who signed it
A COA produced by the seller's own quality function is not automatically untrustworthy, but it is a different kind of document from one produced by an independent laboratory. In-house testing is a control step. Third-party testing is a check on that control step. The distinction is significant enough that we wrote about it separately.
A ninety-second checklist
- Does the batch code on the certificate match the vial label exactly?
- Is the product name on the certificate identical to the product name on the label?
- Is the identity method named, with observed and expected mass?
- Is the purity method named alongside the purity figure?
- Is a chromatogram attached, or available on request?
- Is there a test date, and is it recent relative to the batch?
- Is the testing laboratory named?
- Are storage conditions stated?
If a supplier cannot answer all eight for the specific batch they are about to ship you, the certificate is decorative.
Frequently asked questions
What is a Certificate of Analysis for a peptide?
It is the analytical record for one specific production batch. It documents the identity and purity results for that batch, the methods used to obtain them, the date of testing and the laboratory that performed it. It applies only to the batch whose reference it carries.
Should a COA batch number match the vial?
Yes. The batch reference is the only field that links the certificate to the physical material. If the code on the certificate does not match the code on the vial label, the results on that certificate do not describe your vial.
Is a COA the same as third-party testing?
No. A COA can be issued by the manufacturer's own quality department or by an independent laboratory. Both are certificates of analysis. Only the second is third-party testing, and the certificate should name which one it is.
Can I request the COA before I order?
You should be able to. Eluvyne makes batch documentation available on request through the COA library, and any reputable supplier of research materials should do the same.