A Certificate of Analysis (COA) is the lab report that tells you what is actually in a vial. For a clinic, it is the difference between trusting a supplier's word and verifying it. Yet most buyers glance at a single purity number and move on — which is exactly how low-quality product slips into the supply chain.
This guide walks through every section of a peptide COA, what each test proves, and the warning signs that a certificate is hiding more than it shows.
What a COA is — and what it is not
A COA documents the results of laboratory tests run on a specific batch (lot) of product. A trustworthy COA is tied to a lot number, dated, and issued by a qualified analytical lab. It is evidence, not marketing.
What a COA is not: a safety guarantee for human use. All products are supplied for physician use only. A COA verifies identity, purity, and contamination limits — it does not make a product an FDA-approved drug.
The fields that actually matter
A strong COA reports more than purity. Here is what to look for and why each one matters:
• • HPLC purity — High-performance liquid chromatography measures how much of the sample is the target peptide versus related impurities. Look for a stated percentage (e.g. ≥99%) and the method.
• • Identity (mass spectrometry) — Confirms the molecule's exact mass matches the intended peptide. Purity means nothing if the molecule is the wrong one.
• • Net peptide content — The true amount of peptide versus salts and water. Two vials labeled the same can differ significantly in real content; this is where buyers get quietly shorted.
• • Sterility / bioburden — Screens for microbial contamination, which matters for anything reconstituted and handled in a clinic.
• • Bacterial endotoxin (LAL) — Detects endotoxins that survive sterilization. Experienced buyers look for this first.
• • Heavy metals — Screens for lead, arsenic, cadmium, and mercury that can carry over from raw materials.
If you want the science behind why each of these tests exists and what risk it controls, read our companion guide below.
Read the dates before the results
A certificate carries a date the sample was received and a date the report was issued, and received must come first. The gap between them is informative: a sterility result needs incubation time, so a certificate reporting one with a two-day turnaround is reporting something other than a completed culture.
A single date with no receipt date removes that check entirely. Reading a certificate line by line goes through every field in the order worth reading them.
Content is the number to calculate with
The label is nominal and content is measured. A vial marked 10 mg whose certificate reports 10.4 mg contains 10.4 mg of peptide, and the powder weighs more than either figure because of counter-ion and residual water.
Using the label where the certificate gives content builds an error into everything downstream. Net peptide content covers why the two differ and reconstitution arithmetic covers what follows from it.
Red flags that should make you pause
• • No lot number, or a COA that does not match the lot on the vial in your hand.
• • Only one test (usually HPLC). A single purity number says nothing about contamination or identity.
• • An old certificate reused for many months — testing once and recycling the document for a year is common and misleading.
• • No issuing lab, no date, or an unverifiable source.
• • Vague language instead of numbers and methods.
Match the document to the lot
The single most useful habit: confirm the lot number on the COA matches the lot number on the vial. A supplier that re-tests each batch and publishes a fresh, lot-matched COA gives your providers a document that always reflects the product actually in hand.
Source from a supplier that tests every batch.
Seven-layer testing, a lot-matched COA with every order, made in the USA, white-label fulfillment. Verify your NPI for instant wholesale access.
This sits inside the wider picture of what gets tested and why, which why peptide testing matters sets out across the whole analytical panel.