A Certificate of Analysis (COA) is the single most important document in research compound procurement. It is also the most misunderstood. Most buyers glance at one number — the purity percentage — and move on. But a COA is a multi-part analytical record, and learning to read the whole thing is what separates a confident purchasing decision from a hopeful one.
Here is how to read a peptide COA, section by section, and the one question a COA must be able to answer before you trust it.
What a COA Is Supposed to Prove
A Certificate of Analysis exists to answer a single question: is the material in this vial actually what the label claims, at the purity stated?
A well-constructed COA answers that question with data from several independent analytical methods. Each method confirms a different property of the compound, and no single method is sufficient on its own. When you understand what each section is testing, the document stops being a marketing artifact and becomes what it was meant to be — evidence.
The Core Sections of a Peptide COA
Identity — Mass Spectrometry
Identity confirms that the compound is the molecule it claims to be. The standard method is mass spectrometry (ESI-MS), which measures the molecular mass of the peptide and compares it to the theoretical mass calculated from the sequence.
What to look for: the observed mass should match the theoretical mass within a small tolerance. A mismatch — even by a few mass units — can indicate a wrong sequence, a missing or extra amino acid, or an unexpected modification. Higher-rigor COAs also include tandem MS/MS sequencing, which confirms the actual order of amino acids rather than just the total mass.
Purity — Reversed-Phase HPLC
Purity tells you how much of the sample is the target compound versus everything else. The standard method is reversed-phase high-performance liquid chromatography (RP-HPLC), usually monitored at 215–220 nm, where peptide bonds absorb strongly.
What to look for: a purity figure (e.g. 98%+), but more importantly, the chromatogram itself. A single dominant peak with a clean baseline is what you want. Multiple significant peaks, a noisy baseline, or shoulders on the main peak suggest impurities — truncated sequences, deletion products, or side-reaction byproducts. The number means little without the trace behind it.
Mass Balance and Net Peptide Content
This is the section most buyers skip, and it is where “99% purity” can quietly mislead. HPLC purity measures the peptide relative to other peptide-related material — it does not account for water, residual salts, and counterions (commonly TFA) that make up part of the vial’s weight.
What to look for: net peptide content (or peptide content by mass balance) tells you how much of the vial’s mass is actually peptide. A compound can be 99% pure by HPLC and still be a meaningfully smaller fraction of the total weight once water and counterions are accounted for. A thorough COA reports both.
Additional Safety Assays
Chemical purity does not capture everything. Two contaminants are invisible to HPLC and mass spectrometry:
- Endotoxin (LAL assay, USP <85>) — bacterial lipopolysaccharide, reported in endotoxin units per milligram. A compound can be 99%+ chemically pure and still carry an endotoxin load that confounds any work involving cellular or live-system research models.
- Sterility (USP <71>) — confirms no viable microbial growth in the finished product.
These assays elevate a COA from chemical characterization to full biosafety profiling. Beginning with all batches produced from June 2026 onward, Sirius Molecules includes both endotoxin and sterility testing on every forward batch.
Red Flags on a COA
Once you know what belongs on a COA, the warning signs become easy to spot:
- A purity number with no chromatogram. The trace is the evidence; a bare percentage is a claim.
- No identity confirmation. Purity without an identity test tells you the sample is clean — not what it is.
- A stale or missing test date, or a date that predates the batch.
- The same COA across multiple batch numbers or multiple storefronts — a hallmark of recycled documents.
- No counterion or net peptide content, leaving the real peptide mass unstated.
The Question a PDF Cannot Answer
Here is the uncomfortable part: every red flag above assumes the document in front of you is genuine. A PDF cannot prove that. A Certificate of Analysis is just a file, and any file can be edited — a purity figure changed, a logo swapped, a date updated, a single legitimate report copied across an entire catalog.
This is the gap verification closes. A cryptographically verified COA ties the certificate to the actual testing record for the specific batch you are receiving. Instead of a static file you are asked to trust, the document is a live record you can independently confirm — and if a single value is altered after the fact, verification fails.
Sirius Molecules partners with Accumark Labs for exactly this. Every batch carries a COA you can verify yourself at the source, rather than a PDF you are asked to believe.
Three Questions to Ask Before You Trust Any COA
You can apply this standard to any supplier, not just Sirius Molecules. Before placing an order, ask:
- Can I verify this COA independently, or is it only a PDF?
- Is the certificate tied to the specific batch I am receiving?
- Who performed the testing, and can I confirm the results directly from the source?
If a supplier cannot answer those questions clearly, you are no longer comparing products. You are comparing certainty against uncertainty.
The Bottom Line
A Certificate of Analysis should be read in full — identity, purity, mass balance, and safety — not reduced to a single number. And it should be something you can verify, not merely believe. That is the difference between documentation and evidence, and it is the standard research procurement deserves.
Research Use Disclaimer. Sirius Molecules supplies research-use-only reference compounds. Products are not intended for human or animal consumption, diagnostic use, or therapeutic application. These statements have not been evaluated by the FDA.
