How to Read a Certificate of Analysis

A COA tells you what’s actually in the vial. If you don’t know how to read one, the number “≥98% pure” is just a marketing line — and you’re back to trusting a logo. This is the short version of how to read a peptide COA, written by people who handle them daily.

What a COA is (and isn’t)

A Certificate of Analysis is a lab report. It records what an independent analytical lab found when they tested a specific batch of material — usually identity (is it really the peptide on the label?), purity (how much of the sample is the target compound versus everything else?), and the analytical methods used to determine both.

A COA is not:

A regulatory approval of any kind
A safety document for human or animal use
A guarantee about anything other than what the lab measured, on the date they measured it, on the sample they were given

For research-supply work, a COA is the single most useful document a vendor can give you. It’s the only thing on the page that an outside party — a chemist with instruments — has put their name on.

If a vendor doesn’t publish COAs, that’s a hard pass. If a vendor publishes a “COA” that’s actually a one-page in-house spec sheet with no lab name or signature, same deal — skip it. Both are common.

Anatomy of a real COA

A useful COA has roughly these elements. They won’t always be in the same order or labeled identically, but they should all be there.

1. Product name and CAS number. The compound’s chemical name (not just the trade name) and its registry number where one exists. The CAS lets you confirm the lab tested the same molecule the label claims.

2. Lot or batch number. The unique identifier for this production run. Different lots can have different test results. A COA dated 2024 for “BPC-157” tells you nothing about the vial in front of you unless the lot number on the COA matches the lot number on your vial.

3. Manufacture date and test date. When the material was made and when it was tested. Some peptides have shelf-life implications you’ll want to read against.

4. Test methods. Which analytical techniques were used — typically HPLC for purity, MS (mass spectrometry) for identity confirmation. More on each below.

5. Results. The numbers. Purity %, identity match (mass observed vs. calculated), any impurity profile.

6. Lab identification. The name and signature (or stamp) of the analytical lab. A COA without a named lab isn’t a COA. It’s a printout.

7. Specifications and pass/fail. What the spec is (e.g., “≥98.0% by HPLC”) and whether this lot passed it.

HPLC purity: what ≥98% actually means

HPLC stands for High-Performance Liquid Chromatography. In one line: it separates a sample into its components, measures the relative amount of each, and reports the target compound as a percentage of the total.

When you see “≥98% purity by HPLC” on a COA, the lab is reporting that at least 98% of the area under the chromatogram corresponds to the target peptide. The remaining ≤2% is everything else — typically truncated sequences, deletion peptides, or trace solvents from synthesis.

How to think about the number:

<95% — flag it. For most research peptides, sub-95% purity means the synthesis didn’t go cleanly or wasn’t cleaned up properly. Some specialized compounds have lower achievable purity limits — but the COA should say so, with context. If it doesn’t, treat it as a quality issue.
95–97% — acceptable for some applications, not others. Depends entirely on what the research is studying. A binding-assay reagent has lower purity tolerance than a kinetics study.
≥98% — the modern research-supply baseline. This is the floor most reputable vendors hold to. It’s what CoMo holds to.
≥99% — published, but read carefully. Some labs report >99% as a marketing number when the integration is rounded aggressively. The honest difference between 98.2% and 99.1% in real-world peptide work is usually negligible. Don’t pay a premium based on a fraction of a percent unless your assay needs it.

The chromatogram itself — the actual graph with peaks on it — is the real data. A vendor who publishes the chromatogram (not just the summary number) is showing their work.

Identity: mass spectrometry

Purity tells you how much of the sample is one compound. Identity tells you whether that one compound is the right compound.

Mass spectrometry (MS) measures the molecular weight of the target peak. Every peptide has a calculated theoretical mass based on its amino-acid sequence. A clean COA reports the calculated mass and the observed mass — the two should match to within a small tolerance (typically <1 Da for small peptides, slightly more for larger ones).

If the COA reports HPLC purity but no identity confirmation, you have a number for “how clean is this thing” but no confirmation that “this thing” is actually what’s on the label. Both pieces matter.

Lot numbers, and why they’re not decorative

A peptide vendor’s catalog SKU is the same across years. The lot is the specific batch that came off a specific synthesis run. Two lots of the same SKU can — and sometimes do — differ slightly in measured purity, in impurity profile, or in stability characteristics.

That’s why:

Your COA should match your vial. The lot number on the COA the vendor publishes should match the lot number printed on the vial you received. If you can’t match them, you have a generic document, not a certificate for the material in front of you.
A vendor should be able to look up old lots. If you receive a vial six months from now and want to verify its COA, the vendor should still be able to retrieve it by lot number. That’s a basic operational requirement.

CoMo publishes COAs by SKU at /certificates-of-analysis/. The lot number on the COA matches what ships. If you ever can’t match them, email us — that’s a corrections-process problem on our side and we want to know.

Red flags when evaluating any vendor

A short checklist. Run it against any peptide vendor before you order, not just CoMo:

No COAs at all. Common at the bottom of the market. Skip.
COAs published, but no named third-party lab. “Internally tested” is a marketing line, not an independent measurement. The whole point of a COA is that a different organization with instruments and a reputation puts their name on the result.
COA dates older than the batch. A COA from 2022 for a lot manufactured in 2024 is either the wrong document or a careless one. Either way it tells you something about operations.
Purity numbers without methodology. “98% pure” with no mention of HPLC, no method, no chromatogram is a claim, not a result.
A pinned generic COA used for every SKU. Some vendors publish one COA and link to it from every product page. The COA should be per-SKU, per-lot, ideally with the lot directly retrievable.
No mass spec. Purity-only COAs cut the data in half. You want both identity and purity.
Inconsistent lot numbering across documents. If the COA, the invoice, and the vial all show different lot numbers, the chain of custody isn’t traceable.

None of this is exotic — it’s the same kind of due diligence a research lab would run on any reagent supplier. The point is that the same standards should apply to research peptides as to anything else you’d buy for a lab.

How CoMo handles this

We were a customer of the research-peptide market before we built CoMo, and most of what’s above is a list of frustrations we had ourselves. So here’s what we do:

Every batch is tested at ≥98% purity by HPLC. That’s the spec.
Every batch gets a per-lot COA from a third-party lab, retrievable by SKU at /certificates-of-analysis/.
Lot numbers on the COA match what ships. If they don’t, that’s a problem we want to hear about — email us.
If a vial fails purity testing, we don’t sell the batch.

We’re not the only vendor doing this. We don’t claim to be. But it’s the floor we hold to, and we want you to be able to verify it for yourself rather than take our word for it.

Quick reference

A one-screen cheat sheet for the next time you’re reading a COA:

What to look for	What it tells you	Red flag if missing
Product name + CAS number	The molecule being tested	“Generic peptide” — no specifics
Lot / batch number matching your vial	This document describes your material	Lot mismatch or no lot at all
Manufacture + test date	Document is current to the material	Stale COA, undated lot
HPLC method + chromatogram	The actual purity measurement	“98% pure” with no method
Mass spec identity confirmation	The molecule is what the label claims	Purity reported with no identity
Named third-party lab	An independent organization stands behind the result	“Internal QC” only
Specification + pass/fail	A standard was set and met	A number with no spec to compare against

If a COA you’re looking at — from any vendor, not just us — checks all seven, you’re reading a real document. If it doesn’t, that’s information too.