Technical library
How to read a
Certificate of Analysis
A certificate is only useful if it can be tied to the vial in front of you and if someone has put their name to it. Most of the rest is detail.
The six fields
What a certificate must contain
| Batch or lot identifier | The single most important field. It ties the document to the physical vial. A certificate without one describes a product in general, not the thing you received. |
|---|---|
| Compound identity | Name, and where assigned, CAS number and molecular formula. Enough to confirm the certificate is for the compound you ordered. |
| Purity result | An actual figure for that batch. Not a range, not a specification, not a target. |
| Analytical method | Which method produced the figure. HPLC for purity is standard. Mass spectrometry confirms identity, which is a different question from purity. |
| Date of analysis | When the batch was tested. A certificate with no date cannot be aged against a retest interval. |
| Issuing party | Who ran the analysis and takes responsibility for it. An unsigned, unattributed result is a claim, not a certificate. |
Available before ordering. A redacted certificate is provided on request so the format is known before a first order is placed.
Warning signs
Six ways a weak certificate gives itself away
No batch number
The certificate cannot be matched to the vial. Everything else on it is unverifiable by definition.
A range instead of a result
'98 to 99 percent' is a specification, which describes intent. A result describes what was measured.
The same document every time
If consecutive orders return a byte-identical certificate, it is a template, not an analysis.
No method stated
A purity figure with no method behind it cannot be compared against anyone else's purity figure.
No issuer
Nobody has put their name to the result, so nobody can be asked about it.
Available only after purchase
A supplier confident in the documentation shows the format before the order, redacted if necessary.
In practice
What to do with it once you have it
Check the batch identifier against the vial before anything else. If they do not match, stop there; nothing further on the document applies to what you are holding.
Then read the purity figure alongside the method. A percentage without a method is not comparable across suppliers, because two laboratories can produce different figures for the same material using different approaches, and both can be honest.
Finally, file it against the batch, not against the order. Orders get consolidated and split. Batches do not. If a customer ever asks a question about a specific vial, the batch is the only key that reliably retrieves the right document.
Questions
Certificates, answered
What is the difference between a specification and a result?
A specification is what a batch is required to achieve. A result is what a specific batch actually achieved when it was measured. Certificates that quote only a specification are describing the intention rather than the outcome.
Does HPLC prove the compound is what it claims to be?
Not on its own. HPLC separates components and quantifies the proportion of the main peak, which is a purity question. Confirming identity is a separate analysis, typically mass spectrometry.
Should the certificate name a third-party lab?
It should name whoever performed the analysis, in-house or independent. Third-party analysis is stronger evidence because the party has no commercial interest in the result, but an honest in-house certificate beats an unattributed one.
Can a certificate be issued under our own brand?
Yes, and for distributors supplying their own trade customers it usually needs to be. Ask before the first order, because it is harder to retrofit once labelling is set.
How long should we retain certificates?
For as long as any product made from that batch could still be in a customer's hands, plus the retention period your own market requires. Certificates are the evidence trail if a batch is ever questioned.
Ask for a sample certificate
We will send a redacted Certificate of Analysis so you can see the format before you order.
| Working through a supplier decision? Tell us the compounds and the market. | Talk to us |
Also in the library
Related reference material
How to choose a peptide supplier
Eight checkable questions for vetting any wholesale supplier, including this one.
Procurement glossary
What the terms on a peptide quote mean, so two suppliers can be compared like for like.
Reconstitution concentration calculator
Work out the concentration of a reconstituted vial, how much compound sits in a given draw volume, and how many draws a vial yields.
Storage and stability
Lyophilised and reconstituted storage conditions, what degrades a peptide, and how to specify storage in a supply agreement.