How to Read a COA

A certificate of analysis is not a badge and not a marketing asset, though it gets used as both. It is a laboratory record: a statement that a specific sample was tested by a specific method on a specific date and produced specific results.

Everything useful about a COA follows from that sentence. Everything misleading about how they get used comes from forgetting it.

Section 1 — the header

The top of the document is the part people scroll past on the way to the purity figure. It is the part that determines whether the purity figure applies to you at all.

• Product name and identifier. The name should be unambiguous, ideally alongside a CAS number or sequence. A trade nickname alone is not an identifier.
• Lot / batch number. This is the single most important field on the page. Compare it against the number on the vial you actually hold. If they differ, stop — the document is describing a different batch.
• Date of analysis. Not the date the document was generated. Not the manufacturing date. The date the test was run.
• Testing laboratory. A named laboratory with an address. "In-house QC" is a legitimate thing to disclose, but it is not third-party testing and should not be presented as such.
• Analyst and signature. A real record is attributable to a person. Its absence is not proof of anything, but its presence is meaningful.

Section 2 — identity

Identity answers: is this the molecule the label claims? For peptides, the standard tool is mass spectrometry. The instrument measures the mass-to-charge ratio of the compound, which is compared against the theoretical mass calculated from the sequence.

On the document you are looking for two numbers side by side: expected mass and observed mass. They should agree closely. A mismatch is not a rounding issue — mass differences are informative, and a specific gap often points at a specific defect, like a missing residue.

If a COA contains no identity test at all, it has not established what the material is. It has only established that whatever it is, there is a lot of it. That distinction gets its own article.

Section 3 — purity and the chromatogram

The purity section is normally an HPLC result, reported as area percent. A complete entry names the method conditions: column, mobile phase or gradient, flow rate, run time, and detection wavelength.

A good COA includes the chromatogram image itself, not just the summary number. It is worth learning to glance at, because the picture carries information the number does not:

• A flat, stable baseline. Drift and noise make small peaks unresolvable.
• A main peak that returns to baseline on both sides. A peak with a shoulder, or one that never comes down, may be hiding a co-eluting impurity.
• A run long enough to matter. If the gradient ends shortly after the main peak elutes, late-eluting impurities were never given a chance to appear.
• Visible axis labels and scale. A cropped, unlabelled chromatogram is a picture of a chromatogram, not a result.

You do not need to be an analytical chemist to do this. You need to check that the document is showing you its work rather than showing you a conclusion.

Section 4 — the tests that are usually missing

Most peptide COAs cover identity and purity and stop. Depending on the material and its intended use, a fuller specification might also include:

None of these absences automatically means anything is wrong. But a specification is a claim about what was checked, and a short specification is a narrow claim. Knowing which boxes were never on the form is part of reading the form.

Red flags

In rough order of how much they should concern you:

1. No lot number, or a lot number that does not match your vial. Everything else on the page is unanchored.
2. A COA that is only ever shown as a low-resolution image. Ask for the source document from the laboratory.
3. No named laboratory. "Third-party tested" with no third party named is an adjective, not a fact.
4. Results with no method. A percentage with no conditions attached cannot be assessed or reproduced.
5. One COA used for every product, or every batch, forever. Certificates are batch documents. A single evergreen certificate is a category error.
6. Numbers that never vary. Real manufacturing has variance. A supplier whose every lot reports the identical figure is reporting a target, not a measurement.

A label is not a laboratory result.