Peptide Academy · Research use only
The receipt that matters: how to read a peptide COA
Peptide Academy · Chapter 4 of 7
When you buy a laptop, the receipt says which laptop, which serial number and what you paid. A certificate of analysis (COA) does a similar job for one batch of a research material: it's the document that links the label on a vial to measured data about what's inside.
This chapter is the quick version: a checklist you can run in about 30 seconds, plus the red flags worth a second look. If you want the full background, we have two deeper pages:
- What is a certificate of analysis? covers what a COA is, who issues it, and what international manufacturing guidance says it should contain.
- How to read lot documents walks through a peptide COA field by field.
One certificate, one lot
The single most important idea: a COA belongs to one lot (also called a batch). It's not a general description of a product. Guidance for pharmaceutical ingredients, ICH Q7, says authentic certificates of analysis should be issued for each batch, and lists what they should carry, including the batch number, the tests performed with their limits, and the numerical results [1].
Research materials aren't made under that guidance, and we don't claim ours are. But it's a widely used public description of what a good certificate looks like, which makes it a handy yardstick [1].
The 30-second check
Grab the vial and the certificate and tick these off:
✅ Lot number matches. The lot number on the COA is the same as the one printed on the vial label. If they don't match, the certificate tells you nothing about that vial.
✅ Compound name and identity. The COA names the compound and, for a peptide, ideally shows its sequence or expected molecular weight.
✅ Purity result, with the method. Peptide purity is usually reported by HPLC as the main peak's share of the total peak area, under a stated method [2]. A number without the method is half an answer.
✅ Identity result. Mass spectrometry (MS) measures the molecule's mass, which should match the expected mass for that sequence [2]. Purity and identity are different questions (Chapter 5 explains why you want both).
✅ The actual data. The chromatogram and mass spectrum themselves, not just a summary line.
✅ Who tested it, and when. A named laboratory, a test date, and a sign-off.
If every box is ticked, you have a document you can actually use.
🚩 Red flags worth a second look
None of these prove anything is wrong. They're reasons to ask questions:
- No lot number, or a lot number that doesn't appear on the vial.
- The same certificate used for different batches. Different lots should have their own results.
- Every product showing the identical purity figure. Real measurements vary from lot to lot and from compound to compound.
- A percentage with no chromatogram and no method details.
- Only purity, no identity (or the reverse).
- A testing lab you can't identify, with no name, address or way to contact it.
- Missing dates or an unsigned document.
Purity vs. net peptide content: don't mix them up
Two numbers can look similar but mean different things:
- Purity (HPLC) tells you what share of the peptide material is the right peptide, compared with peptide-related impurities.
- Net peptide content describes what share of the powder's total weight is peptide at all. The rest can include water and counter-ions such as trifluoroacetate, a common leftover from synthesis and purification [3].
A high purity figure does not mean the powder is 100% peptide by weight. If a certificate reports one, don't read it as the other.
Where a COA fits with other documents
A COA isn't the only paper that matters. For laboratory material you'll usually also want the safety data sheet (SDS), which covers hazards, handling and storage. Ours are in the SDS library. Storage conditions and any retest or expiry date on the lot documents are the ones to follow (Chapter 3).
Keep the lot COA and the SDS on file, and record the lot number, date received and storage location for every vial.
Three questions to ask when something's missing
If a certificate leaves you unsure, a serious supplier should be able to answer these without fuss:
- "Can I have the COA for lot number ___?" Quote the exact lot number from your vial label.
- "Which method was used for the purity result?" You're looking for the technique (for peptides, usually HPLC) and enough detail to understand the number.
- "Where is the identity result?" A mass spectrometry result that shows the measured mass next to the expected mass.
Clear, specific answers are a good sign. Vague answers, or a generic certificate with no lot number, are a reason to keep asking.
Our policy
Batch-specific certificates of analysis are available on request. Ask for the COA that matches the lot number on your vial.
Frequently asked questions
What does COA stand for? Certificate of analysis: a document reporting the tests and results for one specific lot of a material.
What should a peptide COA include? At minimum: the lot number, the compound name, a purity result by HPLC with its method, an identity result by mass spectrometry, the actual data, the testing lab, and a date.
Is HPLC purity the same as net peptide content? No. Purity compares the right peptide with peptide-related impurities. Net peptide content is the share of the powder's weight that is peptide at all.
How do I get the COA for my vial? Lot COAs are available on request. Ask for the certificate that matches the lot number on your vial label.
Series navigation: ← Chapter 3: Storage and stability · Hub · Next: Chapter 5: HPLC and mass spec explained →
For laboratory research use only. Not for human or veterinary use. Not a drug, food, cosmetic or dietary supplement.
References
- ICH Q7, Good Manufacturing Practice Guide for Active Pharmaceutical Ingredients, Step 4, 10 Nov 2000, section 11.4 (certificates of analysis). database.ich.org/sites/default/files/Q7%20Guideline.pdf
- Esposito S, et al. Synthesis and characterization of the N-terminal acetylated 17-23 fragment of thymosin beta 4 identified in TB-500. Drug Test Anal. 2012;4(9):733–738. PMID 22962027 (LC-MS characterisation of a peptide)
- D'Hondt M, et al. Related impurities in peptide medicines. J Pharm Biomed Anal. 2014;101:2–30. PMID 25044089 (counter-ions such as trifluoroacetate)