A certificate, line by line
| Field | What it tells you | What to check |
|---|---|---|
| Product name and sequence | Which peptide was tested | The sequence matches the product you ordered, including any modifications (for example an acetylated N-terminus, Ac-, or an amidated C-terminus, -NH₂) |
| Batch or lot number | Which production run the results belong to | It matches the number on your vial, box, packing list and delivery note |
| Manufacture date, test date | When the batch was made and tested | Testing comes after manufacture, and the dates fit the batch you received |
| Retest or expiry date | How long the manufacturer stands behind the results | Your batch is within it |
| Appearance | What the material looked like (for example, white lyophilised powder) | Your material looks the same |
| Molecular formula and weight | The theoretical values for the sequence | They match the sequence; you can check with our peptide mass calculator |
| Mass spectrometry (MS) | The measured mass | It matches the theoretical mass (see below) |
| HPLC purity | The share of the target peptide among UV-absorbing material, usually measured at 220 nm | The value, the method and, ideally, the chromatogram itself |
| Net peptide content | The share of the powder's weight that is peptide | Needed to calculate real concentrations; often reported as "assay" or "peptide content" |
| Water content | Moisture in the powder | Part of the mass balance |
| Counter-ion content | Acetate or trifluoroacetate (TFA) bound to the peptide | Tells you the salt form, which affects weight calculations |
| Endotoxin, if tested | Bacterial endotoxin level | Present only if the batch was tested; absence of a result means it wasn't |
| Storage | Recommended storage condition | Matches the label and how the product was shipped |
| Laboratory and approval | Who tested it, and who signed it off | A named laboratory you can contact, and a named or signed approval |
Identity: does the mass match the sequence?
Mass spectrometry measures the mass of the molecules in the sample. For a peptide, the main signal should match the mass expected from its sequence (if sequence notation is new to you, see what is a peptide). Two things trip people up:
- Charge states. Instruments report mass-to-charge ratios. A peptide carrying one extra proton appears at its mass plus about 1; carrying two, at roughly half that plus 1; and so on. A good certificate states which ion it is reporting, for example [M+H]⁺.
- Average versus monoisotopic mass. Small peptides are often reported by monoisotopic mass, larger ones by average mass. They differ slightly, so compare like with like. Our mass calculator gives both.
What mass spectrometry does not tell you is purity. A sample can contain the right molecule and a lot of other material besides.
Purity: reading the HPLC result
High-performance liquid chromatography separates the components of a sample, and a UV detector records them as peaks. Bachem describes the result like this: HPLC purity "corresponds to the percentage of requested peptide in relation to the total amount of material absorbing at 220 nm."
In practice:
- The main peak is the target peptide; its share of the total peak area is the purity figure.
- Smaller peaks are mostly related peptides made during synthesis, such as chains missing an amino acid.
- A certificate that shows the chromatogram as well as the number lets you see how clean the separation was. Ask for it if it isn't attached.
What HPLC does not tell you on its own is identity: a peak shows that something is there, not what it is. That is why a sound certificate reports both HPLC and mass spectrometry.
Content: how much of the powder is peptide
A peptide powder is never 100% peptide by weight. It also holds water and counter-ions, the acetate or trifluoroacetate bound to the peptide during purification. Net peptide content measures the peptide fraction. Bachem determines it by elemental analysis, because counter-ions and water contain no nitrogen, or by amino acid analysis.
Purity and net peptide content answer different questions, and you need both to know how much target peptide you really have. GenScript's formula: "The amount of the target peptide is calculated by the multiplication of gross weight x net peptide content x HPLC purity." A full set of results should also balance: target peptide, peptide impurities, counter-ion and water should add up to 100%. There is a fuller explanation in peptide purity and net peptide content.
What a certificate does not tell you
- Sterility. Unless the certificate reports a sterility test, it says nothing about it.
- Endotoxin. Only if an endotoxin result is printed.
- How the product has been stored since testing. That depends on the supplier's handling and yours; see peptide storage and handling.
- Suitability for any use in people or animals. A certificate describes a batch of material. It doesn't make a research material suitable for use in a body, and no honest supplier will suggest that it does.
Manufacturer's certificate or independent test?
Most certificates come from the manufacturer, which tests each batch before release. Some suppliers also send samples to an independent laboratory and publish those reports as well. Both are useful, and they are different things:
- A manufacturer's certificate tells you what the producer found when it released the batch.
- An independent report tells you what a third party found in a sample, often taken from the supplier's own stock.
Whichever you are looking at, check that it names the laboratory and carries a reference number you can quote back to that laboratory. Many testing laboratories will confirm whether a report with that number is genuine.
Seven signs a certificate may not be genuine
- No batch number, or one that doesn't match your vial and delivery note.
- The same certificate for every batch or every strength. Results belong to one batch.
- Dates that don't fit: a test date before the manufacture date, or a certificate years older than the batch.
- No named laboratory, or a laboratory you can't find or contact.
- A measured mass that doesn't match the sequence. Work out the expected mass and compare.
- Numbers that are too perfect: purity printed as exactly 100%, or identical results across different batches.
- Only a cropped image, with no full document, chromatogram or mass spectrum available on request.
None of these proves fraud on its own, but any one of them is a reason to ask questions before you buy.
How we handle certificates
We ship a batch only with the manufacturer's certificate of analysis, and the batch number and expiry are recorded on every packing list and delivery note. Ask for the certificate of the current batch before you order. How we test explains the rest.
Questions people ask
- What is a certificate of analysis?
A document reporting test results for one batch of a product: typically identity, purity and content, with the methods used, the dates, and who tested and approved it.
- What does HPLC purity mean on a CoA?
The share of the target peptide among all the material the detector sees, usually at 220 nm. It is not the same as the share of the powder's weight that is peptide; that is net peptide content.
- Is a certificate of analysis proof that a peptide is safe?
No. It describes the composition of a batch. It says nothing about sterility unless that was tested, and nothing about suitability for use in people or animals.
- How can I tell if a peptide CoA is fake?
Check that the batch number matches your product, that the dates fit, that the laboratory is named and can confirm the report, and that the measured mass matches the sequence. The seven signs above are a good checklist.
- Can I ask for the chromatogram and mass spectrum?
Yes. A supplier that tests properly should be able to send them.
- What is the difference between a certificate of analysis and a specification?
A specification sets the limits a product must meet (for example, purity of at least a stated percentage). A certificate of analysis reports the actual results for one batch against those limits.
Sources
- Bachem, FAQ: analysis of peptides
- GenScript, AccuPep QC testing