A certificate of analysis (COA) is the lab report that shows what is actually inside a vial of research peptide. It is the only document that separates a product that has been tested from one that is simply labelled. But COAs are easy to misread, and some are not worth the paper they are printed on.
This guide explains each line on a typical peptide COA, what the numbers mean, what they do not tell you, and how to spot a report that does not hold up.
- A useful COA names the exact batch that matches your vial, the testing lab and the test date.
- Purity (HPLC) and identity (mass spectrometry) answer different questions. You need both.
- Purity is not content. A 99% pure peptide can still contain much less than the labelled amount of peptide.
- Endotoxin results matter for cell-based and other sensitive research.
- A report you cannot verify with the lab is only a claim.
What a certificate of analysis is
A COA is a document that reports the results of analytical tests run on one specific production batch. For peptides, the core tests are HPLC for purity and mass spectrometry for identity, often joined by tests for peptide content, endotoxin and sometimes residual solvents or water.
A COA can come from the manufacturer (in-house), or from an independent third-party laboratory. Third-party reports are generally more persuasive because the lab has no stake in the result, but only if you can confirm the lab actually issued them.
Step 1: Check the batch number, lab and date
Before reading any result, look at the header. Every COA should show:
- Product name and sequence or CAS number, so you know which compound was tested.
- Batch or lot number, which must match the number on your vial label.
- Testing laboratory name and contact details.
- Test date, so you can tell how old the data is.
If the batch number is missing or does not match your vial, the results describe some other material. Everything below is then irrelevant.
Step 2: Understand HPLC purity
High-performance liquid chromatography (HPLC) separates the components of a sample as it flows through a column. A detector draws each component as a peak. The purity percentage is the area of the main peak divided by the total area of all peaks.
What a good chromatogram looks like
One tall, sharp main peak with small, well-separated minor peaks. Research-grade peptides are commonly reported at 98% purity or above.
What to watch for
- Only a number, no chromatogram. A purity percentage with no trace cannot be checked.
- A wide, shouldered or split main peak, which can indicate related impurities.
- Method details. A credible report lists the column, mobile phase and detection wavelength (often 214 or 220 nm).
HPLC purity tells you how much of the peptide-like material is the target compound. It does not tell you how much peptide is in the vial.
Step 3: Confirm identity with mass spectrometry
Mass spectrometry (MS) measures the molecular weight of the compound. The result should match the theoretical mass for that peptide within a small tolerance. HPLC can show a clean peak for the wrong molecule, so purity without identity is incomplete. Look for the measured and theoretical masses side by side, and a spectrum image.
Step 4: Know the difference between purity and content
Lyophilized peptides are not pure peptide powder. They also contain counter-ions from purification (commonly trifluoroacetate or acetate) and residual water. As a result, net peptide content is typically somewhere around 70 to 90 percent of the powder weight, depending on the sequence and process.
This is why a vial labelled 10 mg can reasonably contain a little less than 10 mg of free peptide, and why reputable COAs sometimes report content separately. If a report claims both 99+% purity and 100% content with no explanation, ask how content was determined (for example, by amino acid analysis or quantitative HPLC against a reference standard).
Step 5: Look for endotoxin and sterility results
Endotoxins are fragments from bacterial cell walls. They are measured with the limulus amebocyte lysate (LAL) assay and reported in endotoxin units (EU) per mg or per vial. Low endotoxin matters most when a peptide will be used in cell culture or other sensitive biological systems. A COA that includes endotoxin data, with the method named, is more complete than one that stops at purity.
Red flags that a COA is not reliable
- No batch number, or a number that differs from your vial.
- No lab name, no date, or no way to contact the lab.
- A cropped screenshot instead of the full report.
- The same report shown for every product or every batch.
- Round numbers with no raw data, such as exactly 99.00% and no chromatogram.
- Purity quoted, but no mass spectrometry.
- Fonts, logos or layouts that look edited or inconsistent.
How to verify that a COA is genuine
- Match the batch on the report to the label on your vial.
- Contact the lab and ask them to confirm they issued the report. Many labs offer a verification code or portal.
- Compare reports across batches. Real data varies slightly from batch to batch. Identical numbers every time are suspicious.
- Ask for the raw files (chromatogram, spectrum). A real supplier can provide them.
At Lodge, every report in our COA library lists its batch number and a verification key so you can confirm it is genuine.
Quick COA checklist
| Check | What you want to see |
|---|---|
| Batch number | Matches your vial label exactly |
| Laboratory | Named, with contact details and date |
| HPLC purity | Chromatogram with a clean main peak, typically 98% or higher |
| Mass spectrometry | Measured mass matches theoretical mass |
| Peptide content | Reported with a stated method, or explained |
| Endotoxin | Reported in EU with the LAL method named |
| Verification | Code, portal or lab contact you can check |
Frequently asked questions
What is a good purity for a research peptide?
Research-grade peptides are commonly sold at 98% HPLC purity or above. The purity figure only means something if you can see the chromatogram and the batch matches your vial.
Is a third-party COA better than an in-house COA?
Generally, yes. An independent lab has no stake in the result. The report should still carry a batch number and a way to verify it with the lab.
Why is my peptide content lower than the vial label?
Lyophilized peptides contain counter-ions and residual water, so net peptide content is usually below the total powder weight. A reputable supplier explains how content was measured.
Do I need an endotoxin test?
It is most important for cell culture and other sensitive systems. It is a good sign when a supplier includes it, because it shows testing goes beyond purity.
How can I tell if a COA is fake?
Check that the batch number matches your vial, that the lab is named and contactable, and that a chromatogram and mass spectrum are included. Then ask the lab to confirm the report or use its verification code.
Sources and further reading
- High-performance liquid chromatography (overview)
- Mass spectrometry (overview)
- Limulus amebocyte lysate (LAL) endotoxin assay
- Certificate of analysis (overview)
Products sold by Lodge are intended for laboratory research use only and are not for human or animal consumption. This article is general educational information, not medical or legal advice.
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