How to Read a Peptide Certificate of Analysis (COA)

What a COA is

A Certificate of Analysis is a laboratory document reporting the analytical results obtained for one specific production batch. That scope is the whole point: a COA is not a statement about a compound in general, or about a supplier, or about a product line. It is a statement about one lot, tested on one date, by one laboratory. Every field on it exists to make that statement checkable.

Header — who issued it

A credible COA names the laboratory that performed the analysis, with an address and, where applicable, an accreditation reference. Independence is the property that gives the document its weight: analysis performed by a laboratory unconnected to the seller is third-party testing, and a certificate produced by the supplier's own laboratory is materially weaker evidence of the same numbers.

The phrase "third-party tested" with no laboratory named is not third-party testing. It is a claim about testing, and it is the single most common substitution for the document itself.

Sample identification

The compound name, the lot or batch number, and the analysis date should all be unambiguous. The lot number is the load-bearing field: it is what ties this document to the vial in hand. A COA whose lot number does not appear on the physical label documents a different batch, however genuine the document is.

Check that the compound name matches the listing exactly, including any salt form or modification. An analog and its parent compound are different substances with different masses, and a name that is close but not identical is worth resolving before anything else on the page is read.

Methods and results

• HPLC purity — a numeric result with its basis stated, accompanied by the chromatogram itself. The trace should be legible, with visible axes and a full baseline. See HPLC purity for what to look for in the plot.
• Mass spectrometry — theoretical and measured mass with a stated tolerance, and ideally the convention used for the theoretical value. See mass spectrometry.
• Net peptide content — the proportion of the vial's mass that is peptide, as distinct from purity. Reported separately when reported at all.
• Water content — residual moisture from lyophilisation, where determined.
• Counterion or salt content — synthesis and purification leave a counterion associated with the peptide, contributing mass that is not peptide.
• Appearance — typically a description such as "white lyophilised powder". A colour deviation in the vial received is a reason to look again at the document.

Purity, content and potency are three different things

These are routinely conflated, and the distinction changes how a result should be read. Purity is the proportion of the detected material that is the target compound, determined chromatographically. Net peptide content is the proportion of the vial's total mass that is peptide, with counterions, water and excipients making up the remainder. Potency is the amount required to produce a given effect, and it is not established by either of the other two: chemically pure material that has aggregated or partially degraded can be correspondingly less active.

A vial can therefore be 99% pure by HPLC and still contain considerably less peptide by mass than its label weight suggests, without anything on the certificate being false.

Excipients

Lyophilised vials often contain a bulking or stabilising agent — mannitol and buffering salts are common — added to protect the peptide during freeze-drying and to help it redissolve. Excipients are a normal part of a well-made preparation, not a contaminant, and a thorough COA lists them. Their presence is also part of why net peptide content and label weight are not the same number.

Dates, and the gap between them

Two dates matter and they are not interchangeable. The lot or manufacturing date says when the material was made; the analysis date says when it was characterised. A long gap between them means the certificate describes the batch at a point that may be well after production. Neither date says anything about what happened to a specific vial during shipping and storage afterwards — stability is a property of handling, and no certificate can certify it retrospectively.

The storage and stability statement

Most COAs close with a recommended storage condition, typically along the lines of storing cold and protected from light. This statement is generic to the material class rather than specific to the lot, and it describes the conditions under which the reported results are expected to hold. Handling detail belongs elsewhere — see the storage, reconstitution and handling guide.

Red flags

• A purity percentage with no chromatogram attached.
• A chromatogram with no lot number, or one that appears on multiple different products.
• No issuing laboratory named, or only the wording "third-party tested".
• A lot number that does not match the vial label.
• A cropped or unlabelled trace, or an image at a resolution that cannot be read.
• Identical results across many lots — real analytical results vary slightly.
• Any therapeutic or human-use language on the document, which has no place on an analytical certificate.

What a COA never certifies

A Certificate of Analysis reports chemistry. It does not establish safety, efficacy, or fitness for any use, and it is unrelated to regulatory status — see research grade versus pharmaceutical grade. A complete, credible COA on a research compound describes a research compound. PeptiDex documents these methods for research and educational purposes only.