How to read a certificate of analysis (COA)
A COA is the lab report behind every vial. This guide walks through each part of a peptide COA, from identity and purity to content, endotoxin and heavy metals, so you can check a result yourself instead of taking a label at its word.
What a COA is
A certificate of analysis is a document issued by a testing laboratory that records what was found when a sample from one batch of a compound was analysed. It ties a set of results to a single batch number, a single sample and a test date.
A COA is only useful when it meets three conditions:
- Independent. Issued by a third-party lab, not written by the seller.
- Specific. Tied to the batch number printed on the vial you’re holding.
- Complete. It shows methods and supporting data, not just “pass”.
The parts of a COA
Layouts differ between labs, but most peptide reports contain the same blocks. Read them in this order.
- Lab and report numberWho did the testing. You should be able to find the lab and contact it.
- Sample detailsCompound, amount, batch number and test date. This is what links the report to a vial.
- IdentityConfirms the material is the compound on the label.
- PurityHow much of the detected material is the target compound, with the chromatogram behind the number.
- ContentHow much compound was measured in the vial.
- Contaminant testsEndotoxin and heavy metals, with units and limits.
- Sign-off and verificationAn authorised signature and a key or code you can check with the lab.
Identity: is it the right compound?
Identity is usually confirmed by mass spectrometry (MS, often listed as LC-MS or ESI-MS). The instrument measures the molecular weight of what’s in the sample. The report compares that observed mass with the expected mass for the compound’s sequence.
The two figures should agree closely. Small differences, often under 1 Da for a peptide, come down to instrument precision and rounding. A large gap means the material isn’t what the label says.
Some reports list values as m/z with a charge, for example [M+2H]²⁺. A doubly charged ion appears at roughly half the molecular weight. That’s normal, and the report should state which ion was measured.
If a COA shows purity but no identity test, it tells you the sample is pure, not what it is.
Purity: how much of it is the target?
Purity is measured by high-performance liquid chromatography (HPLC). The sample is pushed through a column that separates its components, and a detector records each one as a peak on a graph called a chromatogram.
What to check:
- One dominant peak, with the purity figure calculated from it.
- The method stated, for example HPLC-UV at 214 or 220 nm.
- The chromatogram included in the report, not just the percentage.
- A few small peaks, which are normal by-products of synthesis.
Purity tells you what share of the detected material is the target compound. It doesn’t tell you how much compound is in the vial. That’s the next section.
Every Omnix batch is third-party tested
Purity, endotoxin and heavy metals, with the report for each batch available to view.
Content: how much is in the vial?
A content or quantity assay reports the amount of compound measured in the vial, usually in milligrams. Compare it with the amount on the label. A small variance either way is normal. A result well below the label is not.
Some reports also show net peptide content as a percentage. Freeze-dried peptide powder includes counter-ions, such as acetate, and a little moisture alongside the peptide itself, so the net figure is lower than the gross weight of the powder. The report should make clear which figure it’s giving.
Endotoxin and heavy metals
Endotoxin is measured with the LAL (Limulus amebocyte lysate) test and reported in endotoxin units per milligram (EU/mg). Lower is better. Look for a numerical result alongside the limit it was tested against, not just “pass”.
Heavy metals such as lead, arsenic, cadmium and mercury are usually measured by ICP-MS and reported in ppm or µg/g. Results are often shown as “<LOQ”, meaning below the lowest level the method can measure. That’s a good result.
| Test | Usual method | What it answers | What a good result looks like |
|---|---|---|---|
| Identity | MS (LC-MS, ESI-MS) | Is this the compound on the label? | Observed mass close to expected mass, marked as conforming |
| Purity | HPLC-UV | What share of the material is the target? | High percentage, with the chromatogram attached |
| Content | HPLC assay | How much compound is in the vial? | Close to the labelled amount |
| Endotoxin | LAL | Is bacterial endotoxin present? | Low EU/mg figure, with the limit stated |
| Heavy metals | ICP-MS | Are metal contaminants present? | Below limits, or <LOQ |
Match the COA to your vial
A good report only counts if it belongs to the vial you have. Check it in this order:
- Find the batch number on your vial.It’s printed on the label, often next to a QR code.
- Find the same batch number on the COA.It must match exactly, character for character.
- Check the compound and amount.The sample details should name the same compound and amount as your label.
- Check the date.The test date should fall around the time that batch was produced.
- Confirm it with the source.Use the lab’s verification key if one is given, or look the batch up with the Omnix verification tool.
Red flags
Treat a report with caution if any of these apply:
- No lab name, address or contact details.
- The batch number is missing or doesn’t match the vial.
- A purity figure with no chromatogram.
- No identity test at all.
- Every result is a perfect 100.00%. Real data has small imperfections.
- Mismatched fonts, misaligned text, or a cropped screenshot instead of the full report.
- The same report reused across different compounds or batches.
- The lab can’t confirm the report exists when you ask.
Not sure about a report? Send us the batch number and we’ll walk you through it.
FAQ
Is a COA from the seller enough?
A report produced in-house is a starting point, but a result from an independent third-party laboratory carries more weight because the lab has no stake in the outcome. Look for the lab’s name, address and a way to confirm the report with them directly.
What does “99%+ purity” on a label mean?
It means the HPLC result for that batch met or exceeded 99%. The COA shows the exact figure, for example 99.3%, along with the chromatogram it was calculated from.
What does “<LOQ” or “ND” mean on a COA?
LOQ is the limit of quantitation: the lowest amount the method can measure reliably. “<LOQ” means the result was below that level. “ND” means not detected. For contaminants such as heavy metals, both are good results.
How long is a COA valid for?
A COA describes a specific batch at the time it was tested. It doesn’t expire, but it only applies to that batch. Correct storage, cold, dry and away from light, keeps the material close to what was tested.
Can I see the COA for my exact vial?
Yes. Enter the batch number printed on your vial in the Verify Your Vial tool to pull up the report for that batch.
Check the report for your vial
Enter the batch number from your label to see the COA for that exact batch.
This guide is for educational purposes. All Omnix Research products are sold strictly for laboratory research use only and are not intended for human or veterinary use.
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