How to Read a Certificate of Analysis (COA): A Line by Line Guide

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Offline Receipts Team

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A certificate of analysis, or COA, is the receipt for a research compound. It is the document that says an independent lab tested a specific batch and found it to be what the label claims. A good one answers three questions: is it the right compound, how pure is it, and how much is in the vial. A bad one answers none of them while looking official.

This guide walks through a COA line by line, so you can tell the difference in under two minutes.

What a COA actually is

A COA is a lab report tied to one batch. It is not a product description and it is not a marketing sheet. Because it covers one batch only, a COA from last year, or from a different batch, tells you nothing about the vial in front of you.

Most COAs have four parts: the header, an identity result, a purity result, and a quantity result. Here is what to look for in each.

1. The header: who tested it, and when

The top of the report should name the testing lab, give a report date, and list a sample or batch number. Check each one:

  • Lab name and contact details. A real lab can be looked up. If the report has no lab name, or only a logo, treat it as unverified.
  • Accreditation. Many labs hold ISO/IEC 17025 accreditation, the international standard for testing laboratory competence. It is a strong signal, though not every good lab lists it.
  • Report date. It should be recent enough to match the batch being sold.
  • Batch number. This is the link between the paper and the product. If it does not match the batch you have, the COA is not your receipt.

2. Identity: is it the right compound?

Identity is usually confirmed with mass spectrometry, often shortened to MS. The instrument measures the mass of the molecules in the sample. The report compares the expected molecular weight, calculated from the compound’s known structure, with the observed molecular weight the instrument found.

What you want to see: the observed value sits very close to the expected value, usually within a fraction of a dalton for small molecules and within the instrument’s stated tolerance for larger ones. A report that lists a purity number but no identity result has skipped the most basic question.

3. Purity: how much of the sample is the target?

Purity is usually measured with high performance liquid chromatography, or HPLC. The sample is pushed through a column that separates its components, and a detector records each one as a peak on a chart called a chromatogram.

  • The main peak is the target compound. Its share of the total peak area is the purity figure, often written as area percent.
  • Smaller peaks are impurities or related substances. A few small peaks are normal.
  • The chromatogram itself should be shown. A purity number with no chart behind it is a claim, not a result.

Research grade material commonly reports purity at or above 98 percent. Treat a flat 100 percent with suspicion: real instruments almost always detect something.

4. Quantity: is the amount in the vial right?

A vial labeled 10 mg should contain about 10 mg of the target compound. Some COAs report this as net content or quantity, measured against a reference standard. Purity and quantity are different: a sample can be 99 percent pure and still be underfilled. If a supplier only reports purity, you only know half the story.

5. Matching the COA to your vial

The final check connects the paper to the product. Look for the batch number, and on some reports a photo of the tested vial, including the cap color and label. If the photo, batch or label does not match what you have, ask the supplier before using the material in any research.

Five red flags

  1. No lab name, or a lab you cannot find anywhere.
  2. A purity figure with no chromatogram and no identity result.
  3. A perfect 100 percent purity score.
  4. A batch number or date that does not match the product.
  5. Signs of editing: mismatched fonts, blurred numbers, or a lab that will not confirm the report when you ask.

The bottom line

A COA is only as good as the three answers it gives: identity, purity and quantity, all tied to one batch. If any of the three is missing, you do not have a receipt. You have a flyer.

Want to see real receipts? Offline Peptides publishes an independent COA for every batch it sells. See the COAs

Sources

For educational purposes only. Compounds discussed on this site are for laboratory research use only and are not for human or animal use. Nothing here is medical advice.

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