Guide · 8 min read
How to read a peptide COA
A Certificate of Analysis (COA) is the only objective evidence you usually get about what's inside a research peptide vial. This guide walks through a typical peptide COA section by section, so you know what each line means, what good looks like, and what should make you stop and ask questions.
On this page
The header: product, batch and date
The top of the COA identifies what was tested and when. Look for:
- Product name: it should match exactly what you bought. "CJC-1295" alone is ambiguous, because the with-DAC and no-DAC versions are different molecules. "TB-500" is used for two very different compounds.
- Batch / lot number: this ties the report to a specific production run. It should match the lot printed on your vial. No batch number means the COA can't be linked to anything.
- Test date: when the analysis was performed. A report from two years ago describes a batch that has probably sold out.
- Sample or report ID: many independent labs give each report a unique ID, sometimes with a QR code, so anyone can confirm the document is genuine.
HPLC purity: how clean is it?
High-performance liquid chromatography (HPLC) separates the components of a sample and measures how much of the total signal comes from the main peak. The result is reported as a percentage, such as "Purity (HPLC): 99.2%", usually with a chromatogram, a graph with one tall peak and a few small ones.
- ≥99%: excellent for a research peptide.
- 98–99%: meets the benchmark most reputable suppliers use.
- 95–98%: acceptable for some uses, but 2–5% of the material is something else.
- <95%: a meaningful quality problem.
HPLC purity has one big limitation: it tells you a sample is pure, not that it is the right substance. A vial of the wrong peptide can still be 99% pure. That's why mass spectrometry matters. Read more in What HPLC Purity Means.
Mass spectrometry: is it the right molecule?
Mass spectrometry (MS) weighs the molecules in the sample. Every peptide has a theoretical molecular weight calculated from its formula; for example, BPC-157 is about 1419.5 Da. The COA should report an observed mass that matches within about ±1 Da (a little more for very large peptides).
Two things often confuse people:
- Average vs monoisotopic mass. Labs may report either. For small peptides they differ by less than 1 Da; for 4–5 kDa peptides like semaglutide or tirzepatide the gap is 2–3 Da.
- m/z values. Electrospray MS measures mass-to-charge. A peptide carrying 3 extra protons shows up at roughly one-third of its mass. A COA listing "1123.6" for Mod GRF (1-29) is showing the 3+ ion of a 3367.9 Da molecule.
The COA checker handles both automatically. For a deeper explanation, see Mass Spectrometry Explained.
Content, endotoxin and heavy metals
Better COAs go beyond purity and identity:
- Net peptide content or quantity: how many milligrams of actual peptide are in the vial. Lyophilized peptides contain counter-ions (such as acetate or TFA) and water, so a "10 mg" vial might contain 8–9 mg of peptide. A quantity test shows whether the vial is underfilled.
- Endotoxin (LAL test): measures bacterial endotoxin, a common contaminant in biologically sourced or poorly handled materials.
- Heavy metals / residual solvents: less common for peptides, but a sign of a thorough supplier.
Who did the testing
A COA is only as trustworthy as the lab behind it. An independent, named third-party laboratory with a verifiable report ID is strong evidence. A COA produced in-house by the seller is weaker, since the seller is grading their own homework, and an anonymous COA with no lab name is close to worthless. See COA Red Flags for the warning signs of an edited or recycled report, third-party testing labs explained for how to judge the lab, and how to tell if a COA is fake for confirming a report with the lab. If your vendor sent a "certificate of purity" instead, read COA vs certificate of purity.
A worked example
Imagine a COA for an Ipamorelin vial reading: Lot IP-0425 · Tested 2026-04-18 by an independent lab · HPLC 99.1% · ESI-MS m/z 712.4 [M+H]+.
- Product and lot are stated, and the lot matches the vial. Pass
- Tested within the last 12 months by a named independent lab. Pass
- HPLC 99.1% clears the 98% benchmark. Pass
- 712.4 m/z minus one proton (1.007) is 711.4 Da, which matches Ipamorelin's monoisotopic mass of 711.39 Da. Pass
That's a consistent COA. If the same report showed 818 Da, it would match GHRP-2 instead, which is a different product entirely.
Have a COA in front of you? Enter the numbers and get an instant verdict.
Open the free COA checker →Sources
- PubChem (U.S. National Library of Medicine): Reference formulas and masses.
- CIAAW: Standard atomic weights: Basis for average molecular weights.
- NIST CODATA: proton mass: Used to convert m/z charge states to neutral mass.
- Janoshik help center: how reports can be verified: Example of how a lab confirms a report is genuine.
- PeptideCOACheck methodology: The exact rules the checker applies.
Last updated . Written and maintained under our editorial policy. Found an error? See corrections.
Frequently asked questions
What is a peptide COA?
A Certificate of Analysis (COA) is a lab report for one specific production batch. For peptides, it normally shows HPLC purity (how much of the sample is the target peptide) and a mass spectrometry result (confirming the molecule's identity), plus the batch number, test date and testing laboratory.
What are the two most important numbers on a peptide COA?
The HPLC purity percentage and the mass spectrometry (MS) molecular weight. Purity tells you how clean the sample is. MS tells you whether it's the right molecule at all. You need both.
Should the batch number on the COA match my vial?
Yes. A COA only describes the batch that was tested. If the lot number on your vial is different, the COA doesn't apply to your product.
How old can a peptide COA be?
As a rule of thumb, look for a test date within the last 12 months for the batch currently being sold. Older reports may not reflect the material you receive.
Educational content only. Not medical advice. Research peptides are sold for laboratory research purposes only.