A certificate of analysis is a factual record: these tests were run, on this batch, by this laboratory, on this date, and these were the results. It is the document that connects the vial in your hand to a set of measurements.
That sounds obvious. It matters because a large share of what circulates as a COA in the research chemical trade is not one.
Batch-specific, or it is not a COA
The defining property is that it applies to one batch. A batch is a discrete quantity of material made in one run, from one set of starting materials, purified together and filled together. Its properties are its own. The next batch of the same compound is a different batch with a different certificate.
A document describing what a compound should meet — target purity, expected appearance, storage conditions — is a specification sheet. It is a useful document, but it certifies nothing, because it was written before the material existed. If a supplier's certificate carries no batch code, no analysis date and no measured values, that is what you are looking at.
Who issues it
There are three arrangements, and they carry different weight.
- Manufacturer's certificate — issued by the laboratory that made and released the material. Standard practice and entirely legitimate.
- Third-party certificate — the supplier sends samples to an independent contract laboratory. Adds independence, at cost and delay.
- Supplier-reissued certificate — the trader passes on a certificate from further up the chain, sometimes rebranded. The measurements may be sound, but the chain of custody between that analysis and your vial may not be documented.
None of these is disqualifying. But you should know which you have been given. A reissued certificate from an unnamed manufacturer, for a batch code that does not appear on your vial, is close to worthless as evidence.
What belongs on one
- Product name and, where assigned, CAS number
- Batch or lot code — matching the vial label exactly
- Date of manufacture and date of analysis
- Appearance, against a stated reference description
- Chromatographic purity, with the method named
- Identity by mass spectrometry, with observed and theoretical values
- Water content, by Karl Fischer
- Counter-ion identity and level
- Net peptide content
- Storage conditions and retest date
- The name of the laboratory and an authorised signature
A certificate carrying most of that is doing its job. One carrying a product name and a purity percentage is not.
Common failures
Four patterns come up repeatedly, and all are visible without any analytical expertise.
The batch code does not match. The certificate is for RYZ-XXXX-24011 and the vial says 24019. Either the wrong document was sent or the certificate is generic. Ask before opening the vial.
No date. A certificate without an analysis date cannot be placed in time relative to the material's retest interval, which makes it impossible to know whether the result is still meaningful.
Methods absent. 'Purity: 99.2%' with no method stated could be area percent by RP-HPLC at 214 nm, or it could be something considerably less demanding. Without the method the number cannot be interpreted.
Impossible precision. Purity reported as 99.99% for a synthetic peptide should prompt a question. Analytical methods have limits, and figures at that level generally indicate the number was chosen rather than measured.
Using one properly
Check the batch code against the vial before you open it. Record the certificate reference in your notebook alongside the experiment, so results can be traced back to specific material later. Keep the document; if a result is questioned two years on, the certificate is what lets you rule the material in or out.
And use the net peptide content, not the chromatographic purity, when you calculate concentration. That single habit removes the most common systematic error in peptide work.
The companion guide walks through an annotated certificate line by line, if you want to see this applied to a real document.
This guide is written for laboratory practitioners and describes analytical and handling practice. It is not medical advice, and it contains no dosing or administration guidance. Material supplied by Ryzen Research Ltd is for research use only and is not for human or veterinary use.