How to Read a Certificate of Analysis

A Certificate of Analysis (COA) is a document from an independent testing laboratory confirming what’s actually in a given batch of material, and how pure it is. If you’re ordering research peptides, the COA is the single most important document to check before you rely on that batch for anything — it’s the difference between trusting a label and having independent proof behind it.

Here’s what you’ll typically find on one, and what each field actually means.

The key fields on a COA #

Field	What it means
Batch / Lot Number	Identifies the specific production batch tested — matches the number on your product label
Purity (%)	The percentage of the sample confirmed to be the intended compound, as opposed to impurities or byproducts
Test Method	The analytical technique used, most commonly HPLC (High-Performance Liquid Chromatography) or Mass Spectrometry
Molecular Weight	Confirms the compound’s identity matches the expected molecular structure
Testing Date	When the analysis was carried out

When checking a COA, the two things worth confirming first are that the batch number matches your product, and that the purity percentage is clearly stated and from a named, independent lab rather than self-reported.

Interpreting the purity percentage #

Purity is usually the number people look at first, but it’s easy to misread in isolation. A purity figure on its own doesn’t tell you much without context on how it was measured.

A few things worth knowing:

• Purity is almost always reported alongside the test method (HPLC, MS, or both) — a percentage without a stated method is far less meaningful, since different methods can produce different readings.
• Higher purity generally means fewer synthesis byproducts or degradation products remain in the sample, but “high” is relative — always compare against the specific figure stated, not a general assumption.
• A COA reflects the batch it was tested on, not necessarily every unit ever produced under that product name. This is exactly why the batch number matters — it ties the certificate to the specific material you actually received.

Why independent testing matters #

Not all purity claims carry the same weight. There’s a meaningful difference between:

• Self-reported results — figures generated in-house by the seller or manufacturer, with no outside verification
• Independent third-party testing — analysis carried out by a separate laboratory with no commercial stake in the result

Independent testing is the standard most researchers look for, because it removes the incentive problem — a lab with no financial interest in the outcome has no reason to inflate a purity figure. When reviewing a COA, it’s worth checking whether the testing lab is named and appears to operate independently of the seller.

What to do if a COA looks wrong or inconsistent #

Occasionally a COA might raise a question — a batch number that doesn’t match, a purity figure that seems unusually low, or a testing date far removed from when the product was sold. If that happens:

• Double-check the batch number against your product label first — this is the most common source of confusion, not usually a sign of a genuine problem.
• Get in touch with the seller directly and ask for clarification before drawing conclusions.
• Keep a copy of the COA alongside your own records for that batch, so you can refer back to it later if needed.

A seller who can quickly produce a clear, matching COA on request is generally a good sign of a well-run process — it should never feel like a difficult or evasive conversation to have.

The short version #

A COA exists to answer one question: does this batch actually contain what the label says, at the stated purity, verified by someone other than the seller? Checking the batch number, the purity percentage, and whether testing was independent covers the essentials in under a minute, and is worth doing as a habit every time you receive a new batch.