How to Read a Peptide Certificate of Analysis (COA)
A certificate of analysis (COA) is the document that tells you what is actually in a research vial. Knowing how to read one is the single most useful skill when evaluating a peptide supplier. This guide explains each field and the common red flags.
What a COA is
A certificate of analysis is a per-batch laboratory report recording the analytical tests run on that specific lot of material. A genuine COA is tied to a batch/lot number, names the methods used, and shows the actual results — not a generic statement that the product 'meets specification'.
Purity — usually by HPLC
Purity is typically measured by reversed-phase high-performance liquid chromatography (RP-HPLC). The result is a percentage (e.g. 99.2%) representing the proportion of the main peak relative to impurities. A strong COA shows the actual chromatogram, not just a number — the trace lets you see the main peak and any impurity peaks for yourself.
Identity — usually by mass spectrometry
Identity confirms the vial contains the molecule it claims to. This is usually done by liquid chromatography–mass spectrometry (LC-MS). The COA should give an expected mass and a detected mass; the two should match within the instrument's tolerance. A purity figure without an identity check is incomplete — a sample can be 99% pure and still be the wrong compound.
The fields to look for
Batch / lot number — ties the document to a specific production run. Compound name and claimed mass. HPLC purity (%) with a chromatogram. LC-MS identity with expected vs detected mass. Test date and testing party (ideally an independent third-party lab). Storage conditions. A COA missing the batch number, the chromatogram, or the identity result is a weaker document.
Red flags
The same COA reused across different batches; no batch/lot number; a purity figure with no chromatogram; no identity (MS) result at all; an image of a certificate with no way to verify it against the vial in your hand. The strongest setups let you check a batch independently by its lot number rather than relying on a forwarded image.
How Index Peptides documents this
Every released batch is HPLC purity tested and LC-MS identity confirmed (expected versus detected mass), the certificate is published on the product page, and any batch can be checked by its lot number on the verify page — no need to request a forwarded image.
Frequently asked questions
What is a good HPLC purity for a research peptide?
Research peptides are commonly supplied at 98%+ by RP-HPLC, but the figure is only meaningful alongside the chromatogram (so you can see the impurity peaks) and an identity confirmation.
Why does identity (MS) matter if purity is high?
Purity tells you how much of the main component is present; identity tells you whether that component is the right molecule. A sample can be highly pure and still be the wrong compound, so both checks are needed.
Can I verify a batch without contacting the seller?
On Index Peptides, yes — each released batch is checkable by its lot number on the verify page, which shows its COA, HPLC purity and identity status.
Research use only. Not for human or animal consumption.