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How to Verify a Peptide COA: HPLC, MS and Batch Records
A COA is only useful if you can read it and match it to the lot you received. What HPLC and MS should show, and the checks that catch a mismatch.
Most buyers receive a certificate of analysis and file it. Very few read it against the material in front of them, which is why a mismatched COA is one of the most common problems found after the fact.
What a usable COA contains
| Section | What to look for | Why it matters |
|---|---|---|
| Product identity | INCI name and/or chemical name, not only the trade name | Matches what you will declare |
| Lot / batch number | Same number as the vials you received | Links the paper to the goods |
| Appearance | Stated colour and form | First check against the physical sample |
| Purity | HPLC figure with the method described | The number you rely on |
| Identity | MS result with the expected mass | Confirms the molecule, not only its cleanliness |
| Date and signature | Test date and an authorised signatory | A document without a date is not a record |
Reading the HPLC section
Purity by HPLC is a percentage of peak area, which describes the chromatogram rather than the whole truth about the material. Three questions make the number meaningful:
- What method? Column, mobile phase and detection wavelength. A figure without a method cannot be reproduced or compared between suppliers.
- Peak purity or assay? Area percentage and content assay are different measurements. A 98% area figure does not mean 98% by mass.
- What is the rest? Water content, counter-ions and residual solvents do not appear as impurities on the chromatogram, but they are part of what you bought.
Reading the MS section
Mass spectrometry answers a different question from HPLC: is this the right molecule? Look for the observed m/z against the calculated mass, and the ionisation mode. A COA reporting “MS: conforms” without a number has given you a conclusion rather than a result.
The checks that catch a mismatched certificate
- Match the lot number on the vial label to the COA on arrival, before the vials go into stock.
- Match the stated appearance to the powder in front of you. Copper peptides are blue; a white powder against a COA describing blue is a stop-and-ask moment.
- Check the test date against the shipping date. A COA dated after dispatch is a reconstruction, not a record.
- Check the product name against your purchase order. This is where substitutions between similar peptides show up.
When to commission your own test
Third-party testing is worth the cost in three situations: a new supplier's first order, any lot that looks different from the last, and any lot going into a regulated market where you carry the file. For routine reorders from a supplier with a clean history, matching the documents is usually enough.
Keep the COA for every lot you hold. If a customer asks two years later what was in the batch, the certificate is the only answer you will have.
Frequently asked questions
What should a peptide COA contain?
Product identity with INCI or chemical name, lot number matching the goods, appearance, HPLC purity with method, MS identity with observed mass, test date and an authorised signature.
Is 98% HPLC purity the same as 98% content?
No. HPLC purity is usually peak area percentage; content assay is a mass measurement. They answer different questions.
What does 'MS: conforms' tell me?
Very little on its own. Ask for the observed m/z against the calculated mass and the ionisation mode used.
How often should I test independently?
At minimum on a new supplier's first lot, any lot that looks different, and any lot going into a regulated market where you carry the product file.
Do I need the COA for every lot?
Yes. The certificate for the specific lot is the record. A generic specification sheet is not a substitute.