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How to Read a Certificate of Analysis (CoA)

Educational only — not a buying guide

Many peptides are research-only or regulated; “research use only” labeling is NOT a legal shield. No vendors are endorsed here. See the Disclaimer and Terms & Conditions.

A Certificate of Analysis (CoA) is a document that reports the results of analytical testing on a specific batch of material. It is not proof of quality by itself — a CoA is only as trustworthy as the lab that produced it and the chain of custody behind it. This page explains what each field means, what a “good” CoA looks like, and how to read one critically.

A CoA tells you two fundamentally different things: how pure the material is (mostly via HPLC) and whether it is the right molecule (via mass spectrometry). Those are separate questions — see HPLC vs Mass Spec. A CoA from the seller’s own bench is weaker evidence than one from an independent lab — see Third-Party Testing.

Field-by-field walkthrough

Product / compound name and sequence

The CoA should name the compound and, ideally, give its amino-acid sequence and molecular formula. The sequence is what the mass-spec result is checked against. A CoA that names a compound but gives no sequence or theoretical mass leaves you unable to verify identity independently.

Batch / lot number

A unique identifier for the specific manufactured batch. This is the single most important traceability field. The batch number printed on the CoA must match the batch number on the physical vial or label. If they don’t match — or the vial has no batch number at all — the CoA does not describe what you are holding, no matter how good the numbers look.

A single CoA cannot legitimately cover “all batches.” Each batch is a separate manufacturing run and should have its own test.

Test date (and manufacture date)

When the analysis was performed. Two checks:

  • The test date should be on or after the manufacture date. A test dated before the material existed is impossible and signals fabrication.
  • A very old test date on a freshly sold batch suggests the document is being reused across batches.

HPLC purity (%)

The percentage of the sample that is the target peptide, as measured by High-Performance Liquid Chromatography. This is a relative measure: it compares the main peak’s area to all other peptide-related peaks (deletion sequences, oxidized forms, synthesis by-products). For many research peptides, ≥98% is a commonly cited threshold, though what counts as “good” depends on the compound. A good CoA includes the chromatogram (the actual trace) — not just a bare number — so you can see the main peak and any impurity peaks. See HPLC vs Mass Spec for how to read the trace.

Mass spectrometry (identity)

The CoA should state both the theoretical molecular weight and the observed (found) mass from mass spec. These should agree within instrument tolerance. HPLC purity alone does not confirm identity — a sample can be 99% pure and still be the wrong molecule. Mass spec is what rules that out. A CoA with HPLC but no MS answers “how pure?” but never answers “pure what?”

Net peptide content (peptide content / mass balance)

HPLC purity and net peptide content are different numbers, and conflating them is a common trap. Net peptide content is the fraction of the dry powder that is actually peptide — versus water, residual salts, and counterions (e.g. trifluoroacetate or acetate). A sample can read 99% pure by HPLC but only ~80% net peptide content, because the “other 20%” is salt and bound water, not impurity peptide. This matters for Reconstitution & Dosing Math: purity ≠ how much peptide is in the vial.

Other assays (where applicable)

Depending on intended use, a CoA may also report water content (Karl Fischer), endotoxin (e.g. in EU/mg), acetate/TFA content, or appearance. Be skeptical of impossibly clean values — see “what good looks like” below.

Issuing laboratory and signature

A named, identifiable lab — with contact details you can independently verify — should issue and sign the document. “Issued by the seller’s in-house QC” is weaker than an independent lab. If the lab cannot be found by an independent search, treat the CoA with caution. See Third-Party Testing.

What “good” looks like

  • Batch number on the CoA matches the vial, and the batch appears in an independent lab’s verifiable records.
  • Both HPLC and MS are present: purity and identity.
  • A real chromatogram / spectrum is attached, not just summary numbers.
  • Net peptide content is reported separately from HPLC purity.
  • Realistic, non-round numbers. Genuine instrument output has decimal precision and small imperfections. Values like exactly 99.0%, exactly 0.0 impurities, and a perfectly round molecular weight across every product are a fabrication signal.
  • Internally consistent dates (test date on/after manufacture date).
  • A named third-party lab you can verify.

Worked example (illustrative)

Imagine a CoA for a batch labeled Lot 2406-A, tested 2026-05-12:

  • HPLC purity: 98.7% — a main peak at a stated retention time, with two small impurity peaks visible on the attached chromatogram (realistic, not a flat 99.0%).
  • Mass spec: theoretical mass 1234.5 Da; observed 1234.6 Da — agreement within tolerance, so identity is supported.
  • Net peptide content: 82% — clearly distinct from the HPLC number, accounting for salt/water.
  • Issuing lab: a named independent laboratory whose batch record matches Lot 2406-A.

You would then confirm Lot 2406-A is printed on the actual vial, and (if the lab offers it) look the batch up in the lab’s public verification portal. A mismatch anywhere breaks the chain.

The chain-of-trust checklist

  1. Does the vial batch number match the CoA?
  2. Does the CoA show both HPLC purity and MS identity?
  3. Is there a real chromatogram / spectrum, not just numbers?
  4. Is net peptide content reported separately from purity?
  5. Are the numbers realistic (not suspiciously round, not identical across products)?
  6. Is the test date on/after the manufacture date?
  7. Is the issuing lab independent and verifiable? (see Third-Party Testing)

If any answer is “no,” the CoA is weaker evidence than it appears. For the patterns that indicate outright fabrication, see Red Flags & Scams.

See also

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Educational information only — not medical advice. See Disclaimer.

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