What is a certificate of analysis?
A certificate of analysis, usually shortened to COA, is a document produced by a laboratory recording what it found when it tested a specific lot of material. A complete one states the substance tested, the method used, the results, the date, the lot identifier and the laboratory responsible.
The important word is specific. A certificate is evidence about one batch on one date. It is not a statement about a vendor, a product line, or anything that has been manufactured since. Vendors sometimes present a single strong certificate as though it characterised everything they sell; it does not.
Why certificates matter in this market
Research-grade peptides are sold outside the regulatory framework that governs medicines. There is no pre-market approval, no mandatory batch release testing, and no authority checking that what is on the label is in the vial. The certificate is frequently the only evidence that exists.
That makes the document’s checkability more important than its numbers. A certificate that cannot be traced to a named laboratory, matched to a lot, and read without an account is not evidence — it is a picture of evidence.
The seven things to check on every certificate
- 01Purity percentage, and the method that produced itA purity figure means nothing without the method beside it. High-performance liquid chromatography (HPLC) is the usual method for peptide purity. A bare "99% pure" with no named method is a marketing claim, not a result.
- 02The chromatogram itself, not just the numberA real certificate reproduces the HPLC trace. The trace shows the main peak and everything else in the sample. A certificate that states a purity figure but omits the chromatogram has removed the only part a reader could check.
- 03Mass spectrometry confirming identityPurity says how much of the sample is one substance. Mass spectrometry says whether that substance is the one on the label, by matching the observed mass against the expected molecular weight. Purity without identity confirmation tells you the vial contains a lot of something.
- 04Quantity: labeled mass versus assayed massThe most useful number on a certificate, and the most often absent. A vial labeled 5 mg that assays at 4.4 mg is 12 percent short. Purity can be excellent while quantity is not, and a certificate reporting only purity cannot tell you the difference.
- 05Microbial and endotoxin testingSterility and endotoxin results appear on more complete certificates. Their absence is not automatically a failure — it depends what the material is sold for — but their presence tells you the laboratory scope was broader than an identity check.
- 06The laboratory name, and whether it is independentA named laboratory can be looked up; "third-party tested" cannot. Check whether the laboratory is accredited to ISO/IEC 17025 for the relevant scope, and whether it is independent of the vendor. In-house quality control is a legitimate activity, but it is not third-party testing and should not be described as such.
- 07The lot number and the date, matched to what you holdA certificate applies to one lot, tested on one date. If the lot identifier on the certificate does not appear on the vial — or on the vendor’s own published lot list — the certificate is evidence about a different batch of material.
Red flags checklist
Any one of these is a reason to stop and ask a question
- A purity figure with no named analytical method.
- No chromatogram reproduced anywhere on the document.
- No mass spectrometry result, so identity is never confirmed.
- Purity reported but labeled-versus-assayed mass omitted entirely.
- "Third-party tested" with no laboratory named.
- A laboratory that cannot be found, or has no verifiable accreditation.
- A test date far older than the lot you are being offered.
- A lot identifier that does not match the vial or the vendor’s lot list.
- A certificate supplied as a flat image with no document metadata, where numbers cannot be checked against a source.
- Certificates available only after creating an account, so nobody can audit them.
A worked example
Here is what the checks look like applied to a single record in this index. The figures come from a certificate we read and indexed; the reasoning is the same one you can apply to any document a vendor sends you.
| Check | What the certificate showed | Reading |
|---|---|---|
| Laboratory named | Janoshik Analytical | Traceable, and can be looked up |
| Accreditation | ISO/IEC 17025 stated on the certificate header | Checkable on the document itself |
| Purity | 99.1% by HPLC | Method named alongside the figure |
| Labeled vs. assayed mass | 5 mg labeled, 5.06 mg assayed | 1.2% deviation — quantity confirmed |
| Lot identifier | ARC-2411, matching the vendor’s published lot list | Applies to the material offered |
| Who commissioned it | The vendor | A claim, not corroboration — scored accordingly |
Note the last row. Every check passes, and the record is still recorded as a vendor claim, because the vendor paid for the test. That is not an accusation; it is a statement about who the evidence comes from.
How PepIndex uses certificate data
Certificate handling drives the two heaviest criteria in our rubric: testing transparency at 26 percent and documentation depth at 22 percent. Within those, we score whether the laboratory is named, whether it is accredited, whether certificates are lot-specific, whether anyone can read them without an account, whether labeled-versus-assayed mass is published, whether superseded certificates are retained, and how large the deviations are across every lot we have indexed.
Of the vendors currently indexed, 34 publish certificates that can be read without an account, and 0 of the certificate records we hold come from independently commissioned assays rather than vendor-published documents. Only the latter are scored as corroborated.
The full rubric is published, and every vendor profile prints the arithmetic behind its score.