How to Read a Certificate of Analysis (COA)

A certificate of analysis (COA) is the document a lab issues to report what a material actually is and how pure it is. For anyone sourcing research peptides, the COA is the primary evidence that a specific lot matches its label — everything else is marketing. This guide explains what a legitimate COA contains, how to read the two tests that matter most, and the warning signs that a document (or a supplier) isn't what it claims to be.

What a certificate of analysis is for

A COA is a lab report tied to one specific production lot of a material. It answers two narrow questions: is this the compound it's labeled as, and how much of the sample is that compound versus everything else (residual solvents, byproducts, degradation, or unrelated substances). A COA is not a safety certification, a regulatory approval, or a claim about what a compound does — it's a snapshot of a lot's chemical composition at the time of testing.

Because peptide synthesis is a multi-step chemical process, no two production runs are chemically identical. Purity and identity can vary lot to lot even under a well-controlled process. That's why a COA is issued per lot, not once per product line — a report from an earlier batch tells you nothing about the material currently in stock.

The two tests that matter: HPLC purity vs. mass-spec identity

Most legitimate COAs report results from two distinct analytical methods, and it's worth understanding what each one is actually measuring.

HPLC — how pure

High-performance liquid chromatography (HPLC) separates a sample into its individual components based on how they interact with a column as they're pushed through it under pressure. Each component elutes (comes off the column) at a different time, producing a chromatogram — a series of peaks plotted against time. The lab's software integrates the area under each peak to calculate what percentage of the total sample each component represents.

The number typically labeled "purity" on a COA is the area of the main peak — presumed to be the target peptide — as a percentage of total peak area. This is relative purity by peak area, not an absolute measure of chemical mass, and it says nothing on its own about what the main peak actually is. A clean, single dominant peak with minimal shoulder peaks or baseline noise is what you're looking for; multiple significant peaks, broad or split peaks, or a low main-peak percentage all indicate impurities, incomplete synthesis, or degradation.

Mass spectrometry — what it is

HPLC tells you how much of one thing is present relative to everything else, but it doesn't confirm identity. Mass spectrometry (MS) does that job. MS ionizes the sample and measures the mass-to-charge ratio of the resulting ions, producing a molecular weight, which is compared against the expected theoretical weight for the target peptide's amino acid sequence.

A COA reporting MS results should show an observed mass close to the expected mass, within a small stated tolerance. This is the step that actually verifies identity — that the isolated peak from the HPLC run is the intended peptide sequence, not a truncated, modified, or entirely different molecule eluting at a similar time.

Purity without identity confirmation is close to meaningless. A high HPLC percentage only tells you the sample is homogeneous — not that the dominant substance is the peptide it's labeled as. A legitimate COA reports both.

What a legitimate COA should contain

At minimum, a complete and useful COA includes:

• Product name and lot/batch number — tying the document to a specific production run,

matching what's printed on the vial or package.

• Test date and report date.
• Identity of the testing laboratory. Independent, third-party testing (a lab with no

ownership stake in the supplier) is the standard that gives a COA credibility; an in-house report with no independent verification carries far less weight.

• HPLC chromatogram and purity result — ideally with the chromatogram image, not just a number.
• Mass spectrometry result — observed vs. expected molecular weight.
• Method or instrument reference — so results are reproducible and auditable.
• Appearance and storage-relevant notes — physical description (e.g., lyophilized powder) and

any material-specific handling notes relevant to laboratory storage and stability.

Why lot traceability and third-party testing matter

Traceability is what turns a COA from a static PDF into something you can actually verify. A COA should reference a lot number physically printed on the vial or packaging you receive, so you can confirm the document in hand corresponds to the material in hand — not a different batch, and not a generic template reused across every shipment. A COA with no lot number, or one that doesn't match anything on the product, isn't traceable to anything.

Independence is what gives the underlying numbers weight. Third-party testing means the entity measuring the material and the entity selling it are not the same organization, removing an obvious incentive to round up — the same reason financial audits are performed by outside firms rather than a company's own accounting department. When evaluating a supplier, check whether the testing lab is named and identifiable, and whether the COA is described as third-party rather than internal.

Red flags to watch for

• No lot or batch number on the document. If the COA can't be tied to a specific production

run, it can't be verified against what you received.

• No named analyzing lab. A report with no lab identity — or one that only says "independent

laboratory" without naming it — cannot be checked or held accountable.

• HPLC only, no mass spec. A high purity percentage with no identity confirmation tells you the

sample is consistent, not that it's the correct compound.

• A single generic COA used across every order. If the same document appears regardless of

lot, it isn't a per-lot report — it's a template.

• Outdated or undated reports. A COA with no test date, or one issued long before the current

inventory was produced, doesn't reflect what's actually on the shelf now.

• No chromatogram or raw data, only a summary number. A bare percentage with no supporting

chromatogram is harder to evaluate and easier to fabricate.

• Unwillingness to provide a COA on request. A supplier that treats testing documentation as

optional is asking you to take composition on faith.

A COA is one input into evaluating a supplier, not a substitute for the rest of the picture: consistent lot-level documentation, a named third-party lab, and a willingness to produce current paperwork on request are all part of the same pattern. Materials on this site are supplied for laboratory research use only — not for human or veterinary use — and a certificate of analysis, requested by lot, is a standard part of evaluating any research reference material before it enters a laboratory workflow.

Frequently asked questions

Does a high HPLC purity percentage guarantee the material is what it's labeled as? No. HPLC purity measures homogeneity — how much of the sample is one dominant component relative to everything else. It does not confirm identity. That requires mass spectrometry, ideally reported alongside the HPLC result on the same COA.

Should a COA be specific to the exact lot I receive? Yes. A document not tied to a lot number matching the product in hand — or one reused across multiple shipments — doesn't tell you anything verifiable about the material you actually received.

Is an in-house lab report as reliable as third-party testing? Independent, third-party testing is the stronger standard, since the testing lab has no financial stake in the result. An in-house report from the selling organization carries an inherent conflict of interest, even if the instrumentation itself is sound.

What should I do if a supplier can't produce a COA for a specific lot? Treat it as a significant gap in traceability. A supplier engaged in third-party testing should be able to provide a current, lot-specific certificate on request.