What is Certificate of analysis?
Also called: COA, CoA
A batch-specific document listing the tests performed on one lot of material, the specification for each test and the result obtained.
By the APL Research Team · Updated
A certificate of analysis (COA) records what was tested on a specific batch, against what limits, and with what result. For a research peptide it is the main evidence that a vial holds the right molecule at the stated purity, and it is only worth as much as its link to the batch actually in hand.
What a peptide COA usually contains
| Field | What to look for |
|---|---|
| Product and sequence | The full sequence with modifications (Ac-, -NH2, disulfides), not just a trade name |
| Batch or lot number | The same number as on the vial label |
| Test date and laboratory | Who ran the analysis, and when |
| Appearance | e.g. "white lyophilised powder" |
| Identity by MS | Theoretical and observed mass, with the convention (monoisotopic or average) stated |
| Purity by HPLC | The specification (e.g. ≥98%), the measured result, and the chromatogram |
| Optional tests | Net peptide content, water, counter-ion content, endotoxin |
| Release | Name or signature of the person approving the result |
Reading it critically
Specification versus result. "≥99%" is a limit; "99.4%" is a result. A COA that shows only the limit says the batch passed, not by how much.
The identity numbers. The observed mass spectrometry value should sit close to the theoretical one. Small differences come from calibration and from mixing monoisotopic and average conventions; a gap of 16 Da (an added oxygen) or of a whole residue points to a different species. The theoretical value can itself be checked against the stated sequence with the peptide molecular weight calculator.
The chromatogram. A purity figure without its chromatogram cannot be checked. Labelled axes, a peak table and a run long enough for late-eluting impurities are the minimum. The same trace, down to its baseline noise, on COAs for different lots suggests a reused document.
What is not there. A standard peptide COA says nothing about sterility, endotoxin or stability after reconstitution unless those tests are listed, and HPLC purity does not state how much of the powder is peptide (see peptide purity).
Worked example: reading two numbers together
Suppose a COA for a 10 mg vial reports HPLC purity of 99.2% and net peptide content of 81%. The vial then holds 10 × 0.81 = 8.1 mg of peptide material, of which 8.1 × 0.992 ≈ 8.04 mg is the target sequence and about 0.06 mg is related impurities. The remaining 1.9 mg is counter-ions, water and other non-peptide material. Neither number alone gives the 8.04 mg figure an experiment actually depends on.
Why the document matters more than the label
Label claims and measured values can diverge sharply. In a 2024 test-purchase study of semaglutide vials bought from illegal online pharmacies, laboratory analysis found semaglutide content 29–39% above the labelled amount, measured purity of 7.7–14.4% against the 99% printed on the labels, and endotoxin in every sample [1]. A purity claim on a label or web page is not a COA, and a COA that cannot be tied to a lot number is not much better.
APL batch documentation
Each APL batch is tested by HPLC against a ≥99% purity specification, with identity confirmed by mass spectrometry; batch documentation is available on request. The COA guide explains each section in more depth, and the supplier guide covers how documentation fits into judging a source.
References
- 1.Ashraf AR, Mackey TK, Vida RG, et al. Multifactor Quality and Safety Analysis of Semaglutide Products Sold by Online Sellers Without a Prescription: Market Surveillance, Content Analysis, and Product Purchase Evaluation Study. J Med Internet Res. 2024. PubMed 39509151