A certificate of analysis (COA) packs a lot of technical vocabulary onto one page. This COA glossary defines the 30 terms that appear most often on peptide certificates, grouped by what they tell you: what the material is, how it was tested, what the powder contains, what safety checks were run, and how the results are judged. Bookmark it next to your procurement records.
Quick answer
What terms matter most on a peptide certificate of analysis? Start with the lot number, which ties the document to your vial. Then check purity by HPLC, identity by mass spectrometry, and the method behind each. Net peptide content, counter-ion and water content describe what the powder contains. Endotoxin, retest date and storage condition complete the picture when they are reported.
Identity and documentation
| Term | Meaning |
|---|---|
| 1. Certificate of analysis (COA) | A document reporting the test results for one specific lot against its specification. How to read one is covered in how to read a certificate of analysis. |
| 2. Lot number | The identifier for one production batch. The lot on the certificate must match the lot on the vial, or the results do not apply to it. |
| 3. Sequence | The order of amino acids from N-terminus to C-terminus, written in one- or three-letter codes; see how to read a peptide sequence. |
| 4. CAS number | A Chemical Abstracts Service registry number, a unique identifier for a defined chemical substance. |
| 5. Molecular formula | The count of each element in one molecule, for example C, H, N, O and S atoms. |
| 6. Molecular weight | The mass of one molecule, given as average or monoisotopic mass. Check whether it refers to the free peptide or includes counter-ions. |
| 7. Appearance | A visual description, typically “white to off-white lyophilized powder”, compared against the expected form. |
| 8. Testing laboratory | The laboratory that performed the analysis. An independent third-party laboratory adds a check that in-house testing cannot. |
Analytical methods
| Term | Meaning |
|---|---|
| 9. HPLC / UPLC | High-performance (or ultra-high-performance) liquid chromatography: separates the components of a sample so each can be measured. UPLC-type systems use smaller particles and higher pressure for faster, sharper separations. |
| 10. Reversed-phase (RP) | The HPLC mode most used for peptides, separating molecules by hydrophobicity on a C18 or similar column. |
| 11. Retention time | When a component reaches the detector, in minutes. The main peak’s retention time helps identify it within a method. |
| 12. Area percent | Each peak’s share of the total integrated peak area. The main peak’s area percent is usually reported as purity; see how to read an HPLC chromatogram. |
| 13. Detection wavelength | The UV wavelength monitored, typically 214–220 nm for peptides, where the peptide bond absorbs strongly. |
| 14. Mass spectrometry (MS) | Measures molecules by mass-to-charge ratio to provide identity evidence. Electrospray (ESI) is the usual ionization method for peptides. |
| 15. LC-MS and LC-MS/MS | Chromatography coupled directly to mass spectrometry. MS/MS fragments the molecule for more detailed sequence confirmation. |
| 16. Observed vs theoretical mass | The measured mass compared with the mass calculated from the sequence. Close agreement supports identity; see HPLC vs mass spectrometry. |
Composition
| Term | Meaning |
|---|---|
| 17. Purity | The share of the peptide material that is the correct sequence, usually by HPLC area percent. See what 99% purity actually means. |
| 18. Net peptide content | The share of the powder’s total weight that is peptide, as distinct from counter-ions, water and solvent; see net peptide content vs purity. |
| 19. Counter-ion (salt form) | The negative ion paired with the peptide’s positive charges, usually trifluoroacetate, acetate or chloride; see TFA vs acetate. |
| 20. Water content | Residual moisture in the powder, commonly measured by Karl Fischer titration. |
| 21. Residual solvents | Traces of solvents left from synthesis and purification. |
| 22. Amino acid analysis (AAA) | Hydrolysis of the peptide into amino acids that are then quantified; a common route to net peptide content and composition checks. |
Quality and safety checks
| Term | Meaning |
|---|---|
| 23. Related impurities | Near-miss molecules such as deletion or truncated sequences; see peptide impurities. |
| 24. Endotoxin | Bacterial lipopolysaccharide, reported in endotoxin units per milligram (EU/mg); see endotoxin testing. |
| 25. LAL test | The limulus amebocyte lysate assay used to measure endotoxin, in gel-clot, turbidimetric or chromogenic formats. |
| 26. Sterility | A test for living microorganisms. It is separate from endotoxin testing and is not implied by a purity result. |
Specifications, dates and storage
| Term | Meaning |
|---|---|
| 27. Specification | The acceptance criterion set before testing, for example a minimum purity. Results are judged against it. |
| 28. Result, pass/fail and “conforms” | The measured value and whether it meets the specification. “Conforms” means the result matches the expected outcome, often used for identity and appearance. |
| 29. Retest date and expiry date | A retest date is when material should be re-examined against its specification; an expiry date is when it should no longer be used. See how long lyophilized peptides last. |
| 30. Storage condition | The temperature and handling the lot requires, such as −20 °C, dry and protected from light; see peptide storage temperature. |
Using the glossary with real documents
A strong certificate names the method behind every number, shows the chromatogram and mass spectrum rather than only summarizing them, and carries a lot number and date that match the vial. When a term is missing, the test was not reported for that lot. Revoryn Labs publishes available batch documentation in its public COA ledger, and how to evaluate a research peptide supplier turns these terms into a checklist.
Key takeaways
- The lot number is the first thing to check; it ties every result to a specific vial.
- Purity (HPLC) and identity (MS) answer different questions, and both need a named method.
- Net peptide content, counter-ion and water content describe what the powder actually contains.
- Endotoxin and sterility are separate tests that a purity figure does not cover.
- A term missing from a certificate means that result was not reported for that lot.
Frequently asked questions
What is a certificate of analysis for a peptide?
A lot-specific document reporting test results, such as purity by HPLC and identity by mass spectrometry, against the specification for that material.
What is the most important number on a peptide COA?
No single number stands alone. Purity, identity and a matching lot number together carry most of the weight, and each is only as meaningful as the method behind it.
What does “conforms” mean on a certificate?
That the result matches the expected outcome or specification. It is common for identity and appearance tests, where the outcome is a match rather than a percentage.
How do I know a COA belongs to my vial?
Compare the lot number on the certificate with the lot number printed on the vial. If they differ, the certificate describes a different batch.
Sources
- Mant CT, Chen Y, Yan Z, et al. HPLC analysis and purification of peptides. Methods Mol Biol. 2007;386:3-55. doi:10.1007/978-1-59745-430-8_1
- D’Hondt M, Bracke N, Taevernier L, et al. Related impurities in peptide medicines. J Pharm Biomed Anal. 2014;101:2-30. doi:10.1016/j.jpba.2014.06.012
- Bachem. Quality Control of Amino Acids & Peptides: A Guide. bachem.com
For laboratory and in-vitro research use only. Not for human or veterinary use.
For laboratory and in-vitro research use only. Not for human or veterinary use. See our research-use disclaimer.
