How to read a Certificate of Analysis (COA)

A Certificate of Analysis (COA) is the document that turns “trust us” into “check for yourself”. Every batch-verified compound should come with one. If you’ve never read a peptide COA before, here’s what each part means — and which lines actually matter.

The header: what and which batch

Start at the top. A COA identifies the compound name, the SKU / product code, and — crucially — the batch (or lot) number. That batch number is the thread that ties the paperwork to the vial in your hand. If a certificate doesn’t name a specific batch, it isn’t evidence about your material.

The purity line (HPLC)

This is the number most people look for: a percentage from HPLC analysis, e.g. 99.2%. It’s the area of the main peak as a fraction of all peaks. Look for the accompanying chromatogram — a single, tall, symmetrical peak is what you want. Several large peaks, or a broad shoulder, suggest impurities regardless of the headline figure.

The identity line (Mass Spec)

Purity is meaningless if the compound is the wrong one. The identity section reports the observed mass from mass spectrometry against the theoretical mass for that sequence. A match — often shown as “identity confirmed” — means the big, pure peak really is the compound you ordered.

The endotoxin line

An endotoxin (LAL) result appears as a quantitative value in EU/mL with a pass/fail. It’s a contamination screen; a “pass” indicates endotoxins are below the stated threshold.

Dates and signatures

Finally, check the analysis date and any release / re-test date, plus the issuing laboratory. An independent lab that doesn’t sell peptides carries more weight than an in-house claim.

Read it in this order: batch number → purity (with chromatogram) → identity → endotoxin → date & lab. If any of those is missing, the certificate is incomplete.

A quick reference