How to Request a COA From a Peptide Supplier
One email, sent before ordering, tells you more than the entire website did. What to ask for, and how to read what comes back.
Asking a supplier for a certificate of analysis before ordering is the single most informative thing a buyer can do, and it costs one email. What comes back — and how fast — tells you more than the entire website did.
Why ask before ordering rather than after
A supplier who tests every batch has the document already. Producing it takes minutes. A supplier who does not will need time, will send a certificate for a different batch, will send a manufacturer’s datasheet instead, or will explain why it is not necessary.
All four of those responses are answers to your question. None of them require you to have spent money first.
What to ask for
Be specific. A vague request gets a vague reply.
- The compound, by name and quantity
- The certificate for the batch currently in stock, with its batch number
- The HPLC chromatogram, not just the purity figure — with axis labels and integration
- The mass spectrometry result, showing theoretical and observed mass
- The name of the testing laboratory
- Endotoxin and heavy metals, if the work is cell-based
- The counter-ion or peptide content, if the work is quantitative
A template
Subject: COA request — [compound], current batch
Hello,
Before ordering I would like to review the certificate of analysis for
the batch of [compound] currently in stock.
Could you send:
• the COA for the current batch, including the batch number
• the HPLC chromatogram with the integration table
• the mass spectrometry result (theoretical vs observed mass)
• the name of the laboratory that performed the analysis
[If cell work:] I also need the endotoxin figure in EU/mg.
[If quantitative:] And the peptide content or counter-ion, if available.
Thank you,
[Name]Reading the reply
| What comes back | What it means |
|---|---|
| Full COA within a day, named lab, batch number matching current stock | Per-batch testing is real and records exist |
| COA with no batch number, or a batch that will not be the one shipped | Testing may be occasional rather than per-batch |
| A purity figure typed into an email, no document | No verifiable analysis |
| A manufacturer’s specification sheet | A claim about what the product should be, not a measurement of what it is |
| “All our products are 99% pure” without a document | The question was not answered |
| Silence, or a delay of a week | The document did not exist when you asked |
Checking what you receive
Once the document arrives:
- Does the batch number appear on the certificate? Without it the document is not about any particular material.
- Is a laboratory named? “Third-party tested” without a name is not a claim.
- Is there a chromatogram with axes and an integration table, or only an image?
- Does the observed mass match the theoretical mass for the stated sequence?
- Is the date recent relative to the batch?
Some laboratories will verify a report they issued if you contact them with the report identifier — a step worth taking for a first order from an unfamiliar supplier.
After the order
Check that the batch number on the vial matches the certificate. If it does not, ask for the correct one. A supplier with proper records can supply it; one who cannot has told you what you needed to know, slightly later than ideal.
Our certificate guide covers reading the document line by line, and the vendor red flags article covers what else is checkable before ordering.
Every batch we supply is analysed by Janoshik Analytical, an independent laboratory. Batch-matched certificates are available on request at support@onyxpeptides.com, and we will send one before you order.
All products and information referenced are for in-vitro research and laboratory use only. Nothing here is medical advice, and no therapeutic claim is made or implied.