How to Read a Certificate of Analysis (COA): A Plain-English Guide

The short version: A Certificate of Analysis (COA) is the lab report that documents what a compound actually is and how pure it is. Knowing how to read one turns a label claim into something that can be independently verified.

What a COA actually is

A COA is a third-party laboratory report tied to one specific batch of a compound. It answers the two questions that matter most in research: is this the molecule it claims to be (identity), and how much of the sample is that molecule versus everything else (purity).

Think of it like a nutrition label that an independent lab filled in after testing the actual material in front of them, rather than the manufacturer printing whatever they like on the box. A real COA names the testing lab, the test methods used, the batch or lot number, and the date of analysis. If those details are missing, the document is decoration, not evidence.

HPLC: how pure is it?

The purity figure on a COA almost always comes from HPLC, which stands for High-Performance Liquid Chromatography. In plain terms, HPLC pushes a dissolved sample through a long, tightly packed column. Different molecules travel through that column at different speeds, so they come out separated, one after another, like runners finishing a race at different times.

A detector counts each component as it exits and draws a chart of peaks. A clean sample shows one tall, dominant peak. Impurities show up as smaller peaks alongside it. The purity percentage is simply that main peak measured against the total of everything detected.

So when a COA states a purity such as >99%, it means the main peak accounted for more than 99% of the detected material in that run, with under 1% attributable to other components. That figure is only meaningful when the document also states the method (HPLC) and the conditions, because a number with no method behind it cannot be checked.

Mass spectrometry: is it the right molecule?

HPLC tells you how much of one thing is present, but not what that thing is. That is the job of mass spectrometry (MS). MS weighs molecules with extreme precision by measuring their mass-to-charge ratio.

Every compound has an expected molecular weight, like a fingerprint expressed as a number. MS measures the actual mass of the sample and confirms it matches the expected value for the named molecule. If a COA lists a measured mass that lines up with the theoretical mass for the compound, that is identity confirmation. Purity without identity is half a story: you would know the sample is clean, but not clean of what.

A trustworthy COA does two things at once: it confirms identity (mass spectrometry) and quantifies purity (HPLC), both tied to the exact batch in front of you.

The two pillars, side by side

Red flags: when to walk away

A few warning signs separate a real document from a reassuring-looking image:

• No COA at all. If a supplier cannot produce one, there is nothing to verify. This is the loudest signal of them all.
• Batch-number mismatch. The lot number on the COA should match the lot number on the vial it documents. A generic COA reused across every batch tells you nothing about the specific item it claims to cover.
• No test method stated. A purity figure with no mention of HPLC, or an identity claim with no MS data, is an unsupported number. Method and result belong together.
• No lab named, no date. An anonymous, undated report cannot be traced back to anyone accountable.
• Image-only “certificates.” A screenshot with a logo and a percentage, but no peaks, no masses, and no methodology, is marketing dressed up as analysis.

The habit worth building is simple: cross-check the batch number on the COA against the batch number on the vial it documents, then confirm the document names a method for every claim it makes.

Why this matters for research

In any research setting, the integrity of results depends on the integrity of the inputs. A compound that is mislabelled, or that carries a meaningful fraction of unknown impurities, quietly undermines everything downstream. Reading a COA is not box-ticking; it is the first control in good laboratory practice. The purity percentage and the molecular weight are how researchers confirm that a starting material is what the literature assumes it is.

Where JP fits

We would rather you check the work than take our word for it, so the independent Janoshik reports we hold are published in full and can be read before you order — methods and results on the document, exactly as described above. Being straight about the limits: we do not commission a report for every batch, and not every compound in the range has one. Where a report exists it is linked on that product’s page, and where it does not, the page says nothing. Compounds with a report on file today include Retatrutide, GHK-Cu, Semax, NAD+ and Cagrilintide. You can also browse the catalogue to see the rest of what we stock.