How to read a certificate of analysis
Every lot we sell ships with a certificate of analysis. It is the single most useful document in the box, and also the most commonly misread: a COA is a record of specific measurements on a specific batch, not a general guarantee about a substance.
What the header tells you
The top of a certificate identifies the batch, not the product. A lot number, a manufacturing date and a test date. If the lot number on the paper does not match the lot number on the vial, the certificate describes a different batch of material and tells you nothing about what you are holding.
The test date matters as much as the lot number. A certificate issued eighteen months ago describes the material as it was then. Purity is not a permanent property — it is a measurement with a date on it.
Identity versus purity
These are two different questions answered by two different instruments, and a certificate should answer both.
Identity asks whether the material is the compound named on the label. Mass spectrometry answers it by measuring molecular mass: the observed mass should match the theoretical mass for the sequence, usually within a fraction of a dalton.
Purity asks what proportion of the material is that compound rather than something else. High-performance liquid chromatography answers it by separating the sample and measuring the relative size of each peak.
A certificate with a purity figure but no identity confirmation is incomplete. It tells you the material is 99% something.
Who performed the test
A certificate produced by the same organisation that made the material carries less weight than one from an independent laboratory, for the obvious reason. The certificate should name the testing laboratory.
This is worth checking rather than assuming. In-house testing is common in this market and is not always disclosed prominently.
What a certificate does not establish
It does not establish sterility. Sterility is a separate test and is rarely performed on research-grade lyophilised material.
It does not establish endotoxin levels unless an endotoxin assay is listed explicitly.
It does not establish that the vial in your hand came from the lot described. That link is a matter of the supplier's traceability, not of the paper itself — which is why the lot number needs to appear on the vial, the certificate and the order.
And it does not establish suitability for any particular use. A certificate is a measurement record. Deciding what a measured material is appropriate for is the researcher's judgement, not the certificate's.