What a COA tells you, and what it doesn't
A certificate of analysis is a vendor's document about one batch. What to look for on it, and the limits of what it can show. · 3 Oct 2026
Many vendors publish a certificate of analysis — a COA — for what they sell. It is useful information, and easy to read more into than it actually says.
What a COA is
A COA is a document reporting tests run on a sample from one production batch. The vendor, or the vendor's supplier, publishes it — usually as a PDF or an image on the product page.
What to look for
A COA you can make sense of usually shows:
- The batch or lot number. It should match the batch you would receive.
- The test date. A recent test of the current batch says more than an old one.
- The laboratory. The name of the lab that ran the test, and whether it is independent of the vendor.
- The method. For example HPLC for purity and mass spectrometry for identity.
- The results. Usually a purity percentage and a confirmation that the material is what the label says.
- The measured amount. Some COAs report the mg measured in a vial, which you can set against the label.
Reading a purity number
A purity figure such as 99.1% usually comes from HPLC: it is the share of the measured signal that belongs to the main compound. It says how clean the sample was, not how much material the vial holds — a vial can be very pure and still hold less than its label says, which is why a measured amount, when a COA gives one, is worth comparing with the label.
What a COA cannot tell you
- That your vial comes from the tested batch. Unless the lot number on the vial matches the COA, the document describes a different batch.
- How the product was stored and shipped. Peptides can degrade with heat and time after the test date.
- That the document is genuine. A COA is a PDF. Some independent labs let you confirm a report by its reference number on their own site.
- Anything about use. A COA is a lab result about a material. It is not a statement that a product is suitable or safe for any purpose.
Comparing COAs between vendors
When two vendors sell the same compound, their documents are only comparable if they answer the same questions. Check that both name a lab, a method and a date, and that both cover the batch on sale now. A recent report from a named, independent lab says more than an undated one from an unnamed source, whatever the purity figure on it.
When there is no COA
Not every vendor publishes one, and some publish one per compound rather than per batch. A missing COA is not proof of a problem, and a present one is not proof of quality. If a document matters to you, ask the vendor which batch it covers before you order.
What PepSpotter does and does not do
PepSpotter compares the prices vendors publish. It does not test products, does not verify lab reports and does not vouch for any vendor. Every product on the site is offered by its vendor for research use, and nothing on PepSpotter is advice about using any product.
See the FAQ for more on how prices are read, and the disclosure for how PepSpotter relates to the vendors it lists.
In short
- A COA describes one batch, tested once, by one lab.
- Match the lot number, and check the date and the lab.
- It is not a guarantee, and PepSpotter does not verify it.