A certificate of analysis records what a laboratory measured on a specific batch of material, on a specific date, using stated methods. That is a narrow claim, and its narrowness is the point. A certificate is not a description of a product line, not a guarantee of future batches, and not a substitute for your own incoming inspection.
The three fields that decide whether a certificate is usable
Before reading any result, check three identifiers. If any one of them fails, the rest of the document is not evidence about the material in front of you.
- Lot or batch number. This must match the number printed on the container you received, character for character. A certificate issued against a product code rather than a lot describes a category, not your material.
- Product identity. The name and catalog number on the certificate must match what you ordered, including any modification — a certificate for the unmodified sequence does not cover the acetylated analogue.
- Issue or release date, and the retest or expiry date if one is stated. A certificate with no date cannot be placed in time relative to the storage history of the material.
Generic documents are the most common substitution
The failure mode to watch for is not a forged certificate; it is a real document for a different batch, or a specification sheet presented as a certificate. A specification states the limits a product is manufactured to. A certificate states what was found in one batch. They look similar and they are not interchangeable.
Method matters as much as the number
A purity figure is meaningless without the method that produced it. Purity by reversed-phase HPLC at one wavelength, purity by area normalisation across a gradient, and purity determined against a reference standard are three different measurements that can be reported with the same units. A certificate should state the method, the column or detection conditions in enough detail to be reproducible in principle, and the acceptance limit the result is being judged against.
Where a result is reported as conforming rather than as a number, the specification limit should still be visible. "Conforms" against an undisclosed limit is not a result you can act on.
Purity is not the only identity check
Chromatographic purity says how much of the detected material is the main peak. It does not confirm that the main peak is the molecule you ordered. Identity is established separately, usually by mass spectrometry, and a certificate that reports purity without an identity determination has left the more important question open.
What a certificate cannot tell you
- How the material was stored between release and delivery. Cold-chain evidence is separate from the certificate.
- How the material will behave in your assay system. Performance in a specific assay is a property of the assay, not of the batch.
- Whether a future batch will match. Lot-to-lot consistency is demonstrated across certificates over time, not asserted within one.
Scope of this article
This article covers documentation practice for laboratory materials. It does not address preparation, administration, or use of any material in humans or animals, and no material described in this catalog is supplied for those purposes.
References
- ISO/IEC 17025:2017 — General requirements for the competence of testing and calibration laboratoriesInternational Organization for Standardization
- ICH Q2(R2) — Validation of Analytical ProceduresInternational Council for Harmonisation
- USP General Chapter <1225> — Validation of Compendial ProceduresUnited States Pharmacopeia
References are cited as the standards and guidance this note is written against. Citing a standard is not a claim of conformance to it.
Scope
This note covers documentation, procurement, storage, and analytical practice for laboratory and manufacturing materials. It is not guidance for preparing or using any material in a person or an animal, and nothing in this catalog is supplied for that purpose.
More on documentation
- Lot traceability in practice
Traceability is a records problem before it is a supplier problem. What to capture on receipt so that a result eighteen months from now can still be tied to a batch.