Peptide Certificates of Analysis (COA): How to Read Them and Why They Matter

A Certificate of Analysis (COA) is a third-party laboratory report that verifies a peptide’s identity, purity, and quantity against its labeled specification. For anyone sourcing research peptides, the COA is the single document that turns “trust the label” into “verify the label” — and reading one correctly is a basic research-quality skill.

What a COA Actually Certifies

A properly issued COA is produced by an independent lab, not the manufacturer, and typically reports on three separate questions:

Identity — is this actually the peptide it claims to be? Confirmed via mass spectrometry (MS), which matches the molecular weight of the sample against the expected peptide sequence.
Purity — what percentage of the sample is the target peptide versus degradation products, truncated sequences, or synthesis byproducts? Confirmed via High-Performance Liquid Chromatography (HPLC), reported as a percentage (for example, “98.2% purity”).
Quantity — does the vial contain the labeled amount (e.g., 5mg, 10mg)? Confirmed via HPLC peak-area quantification against a reference standard.

A COA missing any one of these three is an incomplete verification. A document that only states “tested” without HPLC/MS data attached is not a functional COA.

Reading an HPLC Chromatogram

The HPLC trace is the part of a COA most researchers skip past, but it is the most informative section. Look for:

A single dominant peak — this represents the target peptide. Its area relative to the total area under all peaks is the purity percentage.
Retention time — the time at which the peak elutes should be consistent across batches for the same peptide; large shifts can indicate a different compound or degraded sample.
Secondary peaks — smaller peaks represent impurities, incomplete synthesis fragments, or degradation products. Multiple significant secondary peaks alongside a stated high purity percentage is worth scrutinizing.

Reading a Mass Spectrometry (MS) Result

The MS section confirms molecular identity by reporting an observed mass. This observed mass should match the theoretical molecular weight of the peptide’s amino acid sequence within a small tolerance. A mismatch here means the vial does not contain what the label says, regardless of what the HPLC purity number shows — HPLC alone cannot confirm identity, only relative purity of whatever compound is present.

Batch Numbers and Traceability

A COA should be tied to a specific batch or lot number, not issued generically for a product line. This matters because:

Peptide synthesis is a batch process; purity and yield can vary between runs
A batch-specific COA lets a researcher verify that the document corresponds to the exact vial in hand, not a different production run
Reputable suppliers keep batch-level COAs on file and make them available per lot, not just per product

If a COA has no batch identifier, or the same COA is presented for every batch of a given product indefinitely, that is a signal the document is not doing its job as a verification tool.

Why “Lab Tested” Claims Need the Underlying Document

“Lab tested” as a marketing phrase is not equivalent to a published COA. The phrase alone tells you nothing about which lab, which method, which batch, or what the actual purity and identity results were. A credible research supplier makes the underlying HPLC/MS documentation available, not just the summary claim.

A Practical Checklist

When reviewing a COA before using a peptide in research, confirm:

Independent (third-party) testing lab named
HPLC purity percentage stated with visible chromatogram
MS identity confirmation with observed vs. theoretical mass
Batch or lot number matching the vial received
Test date recent enough to be relevant to the current stock

Where to Verify This in Practice

Every peptide in our catalog is documented with its own study references and specification data on its product page — see, for example, BPC-157, retatrutide, or ipamorelin for how mechanism and sourcing information is presented per compound. For questions about our own testing and sourcing practices, see About Milo-Lab.

Research Use Only

This article is an educational guide to interpreting laboratory documentation and does not constitute a guarantee of any specific product’s testing status. All peptides referenced are sold for research use only, not for human or veterinary consumption, and nothing here is medical advice.