Reading a Certificate of Analysis: a worked example

A Certificate of Analysis is the closest thing the research-chem peptide market has to a quality stamp. But most users glance at the headline purity number, see "99%," and stop reading. That's not how a COA is meant to work. This is a worked example — a line-by-line walkthrough of what a real COA contains, what each section actually means, and what should make you put the vial back in the box and email the vendor.

What a Certificate of Analysis is

A Certificate of Analysis (COA) is a third-party laboratory report documenting the contents of a specific peptide batch. A complete COA covers four kinds of testing: identity (mass spectrometry), purity (HPLC), endotoxin (LAL), and sometimes sterility. It carries a batch number that links the document to the actual vial in your hand, plus a test date and the laboratory's name.

The single most important word in that sentence is "third-party." A COA from the vendor's in-house lab is a marketing document. A COA from an independent ISO-17025-accredited lab is the real thing. For the legal and regulatory backdrop on why COAs matter, see the sourcing pillar.

The header — what should be on every COA

Every legitimate COA has a header that identifies five things:

If any of those is missing, the COA is incomplete. If the batch number on the COA does not match the batch number on your vial, the COA is for a different batch — which means it tells you nothing about the vial in your hand.

Section 1: Identity (mass spectrometry)

Mass spectrometry confirms the molecular identity of the peptide. The COA should report:

• Theoretical molecular weight — what the peptide should weigh
• Observed molecular weight — what the lab actually measured
• A statement that the two match within instrument tolerance

A worked example for BPC-157:

The two numbers should match to within roughly 1 Da. Mismatches of 5+ Da mean the molecule is not what's on the label — possibly a related peptide, possibly something else entirely. This is how identity-substitution counterfeits get caught (or not caught — many never do).

For more on the substitution problem, see counterfeit peptide red flags.

Section 2: Purity (HPLC)

High-performance liquid chromatography (HPLC) measures what percentage of the vial is the labeled peptide versus impurities. A COA should show:

• Purity percentage (the headline number)
• The chromatogram itself — a graph with peaks
• Method details — column type, mobile phase, detection wavelength

A worked example:

Two things to actually check:

1. The main peak should be sharp and well-resolved. A wide, smeared peak means the compound isn't homogeneous.
2. The "other peaks" matter. If the document shows 99% purity but the chromatogram has a 0.8% peak right next to the main peak, that impurity is likely a related peptide — possibly bioactive — and the practical purity is closer to 98%.

How to interpret the headline number:

For more on what purity actually predicts, see peptide purity explained.

Section 3: Endotoxin (LAL assay)

Endotoxin is the bacterial-cell-wall fragment that survives sterile filtration. It's the most common cause of "this peptide gave me flu-like side effects." Endotoxin testing uses a Limulus Amebocyte Lysate (LAL) assay and reports results in EU/mg (endotoxin units per milligram).

A worked example:

How to read the number:

If the COA shows a purity number but no endotoxin number, the testing is incomplete for an injectable product. A 99% pure peptide that's loaded with endotoxin will still make you feel terrible. For more, see endotoxin testing explained.

Section 4: Sterility (when applicable)

Some COAs include a sterility test — confirming the vial is free of viable bacteria. This is more common for compounded products than research-chem peptides. The test typically reports:

Lyophilized peptide is generally not a hospitable environment for bacterial growth, but sterility matters for the moment of injection. If the COA omits sterility, the practical question is whether your reconstitution and storage practices keep things clean.

What's not on the COA — and what should be

A COA tells you about the batch as tested. It doesn't tell you about:

• Stability — how long the peptide stays at this purity in storage
• Bioactivity — whether the peptide actually does what it's supposed to in cells
• Vial-to-vial consistency — only the tested aliquot is on the COA
• Reconstituted concentration accuracy — depends on your math, not the vial

Some vendors publish stability data separately. Bioactivity testing is rare in the research-chem market. Vial-to-vial consistency is generally good when the source manufacturer is reputable.

Comparing two COAs side by side

Here's the same hypothetical batch as it might appear from two vendors:

Vendor A (full COA):

Vendor B (incomplete COA):

Vendor A's COA tells you what's in the vial. Vendor B's COA is decorative — it tells you nothing useful. If Vendor B is dramatically cheaper, the price difference is what you're paying for in side-effect risk.

Red flags on a COA

What to do if the COA is incomplete

A polite, direct email to the vendor:

Hi — I'm preparing to order from your shop. Could you send the full COA for the current batch of [peptide name], including identity (mass spec), HPLC purity with chromatogram, and endotoxin (LAL) results? I'd also like the batch number and test date so I can verify it matches the vial when it arrives.

A reputable vendor sends the COA. A vendor that pushes back, evades, or claims COAs are proprietary is telling you something — and it's not flattering.

For the broader vendor evaluation framework, see vendor due diligence and choosing a vendor.

The bottom line

A COA is not a marketing document. It's a record of what was actually in the vial when an independent lab tested it. Reading it line by line — header, identity, purity, endotoxin, sterility — takes about three minutes once you know what you're looking at. Doing that for every batch is the difference between knowing what you're injecting and guessing.

Related reading

• COA reading guide
• Vendor due diligence checklist
• Endotoxin testing explained
• Vendor quality checks
• Counterfeit peptide red flags