How to read a certificate of analysis
A certificate only counts as evidence if it is the certificate for the vial you received. The five checks, the three dates that get confused, and what a COA cannot tell you.
A certificate of analysis is the only document that connects the vial in your hand to a measurement someone actually made. Read properly it takes about a minute. Read carelessly it tells you almost nothing.
Every batch of material we supply is sent to an independent analytical laboratory before it is listed, and the resulting certificate is published against the lot it covers. This page explains what is on that document, which parts matter, and the one check almost nobody performs.
What a certificate of analysis is
A certificate of analysis — COA — is a laboratory’s record of what it found when it tested a specific quantity of material. It is tied to a lot: a single production run, analysed once. It is not a statement about the compound in general, not a statement about a supplier, and not transferable between batches. A certificate for lot A says nothing whatsoever about lot B, even if both carry the same compound name.
This is the detail that makes certificates worth reading at all. A supplier can publish an impressive certificate and ship you different material. The certificate is only evidence if it is the certificate for the vial you received.
The five checks
- Find the lot number on the vial. It is printed on the label, usually as an alphanumeric code. On our labels it appears as the batch reference — for example a code beginning EBL. Write it down or photograph it before you go looking for the certificate.
- Open the certificate for that lot. Not the product page, not a certificate the supplier showed you before you ordered — the one filed against that specific lot number. If a supplier publishes a single certificate for a product rather than one per batch, you are looking at marketing, not analysis.
- Check the lot matches character for character. This is the step people skip. Suffixes matter: 001 and 002 are different production runs analysed on different days. If the certificate’s lot does not match the vial exactly, the certificate does not describe your material, however good the numbers on it look.
- Check who performed the analysis. The laboratory’s name and contact details should be on the document. An independent laboratory has no commercial interest in the result. A certificate issued by the manufacturer that made the material is a supplier grading its own homework — it may be perfectly accurate, but it is not independent evidence, and it should not be presented as though it were.
- Read the result against what was measured. A number is meaningless without the method beside it. Purity determined by HPLC means one thing; identity confirmed against a reference standard means another. The next article covers what each measurement actually proves.
The verification step most people miss. Several independent laboratories, including the one we use, publish results against a report or task number that can be checked directly on the laboratory’s own website. If that facility exists, use it. It confirms the document you are reading came from the laboratory and has not been edited between the laboratory and you.
Dates: three different ones
Certificates carry dates, and they are routinely confused with one another.
| Date | What it means |
|---|---|
| Date received | When the laboratory took delivery of the sample. Not when the material was made. |
| Date of analysis | When the measurement was performed. This is the date the result describes. |
| Date of manufacture | Often absent entirely. Where it appears it comes from the manufacturer, not the testing laboratory, and is not something the certificate verifies. |
None of these is a dispatch date or an expiry date. A certificate characterises material as it was when a sample was taken. How that material has been stored and handled since is a separate question, and no certificate answers it.
What a certificate does not tell you
This is as important as what it does tell you, and it is where most supplier marketing quietly overreaches.
- It does not describe the whole batch. It describes the sample that was submitted. Whether that sample represents the batch depends entirely on how it was selected.
- It does not describe the vial in front of you specifically — only the lot that vial belongs to.
- It says nothing about biological behaviour, suitability for any particular experiment, or performance of any kind. It is an analytical document about a chemical, and nothing more.
- It is not a safety assessment. That is what a safety data sheet is for.
Where ours are
Every certificate we hold is published in the COA Library, filed by compound and by lot, with the current lot marked. Each product page links directly to the certificate for the lot currently shipping, and each certificate links back to the product and to its safety data sheet.
If you have received material from us and cannot match its lot to a published certificate, that is worth an email rather than a guess — tell us the lot number and we will send the document.