GlossaryVendor & SourcingCOA (Certificate of Analysis)
Vendor & Sourcing

COA (Certificate of Analysis)

Also known as: certificate of analysis · lab report

A certificate of analysis (COA) is a lab report showing test results, such as purity and identity, for one specific production batch of a product.

A certificate of analysis (COA) is a document that reports the results of analytical tests run on a particular lot of a product. For a peptide, a useful COA names the compound, gives a batch or lot number, states who did the testing and when, names the test methods, and lists each result next to the specification it was meant to meet. The two results most peptide buyers look for are purity, usually measured by high-performance liquid chromatography (HPLC), and identity, usually confirmed by mass spectrometry (MS).

A COA describes only the material that was actually tested. It says nothing about a different batch, and it says nothing about what happened to a vial after the test, such as heat exposure in shipping. A COA written by the seller is a claim; a COA from an independent lab that you can confirm with that lab is stronger evidence, though it still covers only one sample.

Why it matters

Labels on peptides sold outside regulated pharmacies can be badly wrong. In one test-purchase study, three semaglutide vials bought from illegal online pharmacies were analyzed by liquid chromatography with mass spectrometry: the labels claimed 99% purity, but measured purity ranged from 7.7% to 14.37%, the semaglutide content was 28.56% to 38.69% above the labeled amount, and endotoxin was found in every sample. A COA is how you check whether a seller has measured any of this for the batch you hold.

Peptide impurities are not just filler. Reviews of peptide medicines describe deletion and insertion sequences, oxidized residues, leftover synthesis reagents and contamination with unrelated peptides, which can change what a product does. A batch-specific COA with named methods is the minimum record that someone looked.

How to read a COA

  1. Match the batch or lot number on the COA to the number printed on your vial. No match means the report is not about your product.
  2. Check the test date. An old report on a product that is sold continuously probably describes an earlier batch.
  3. Find the lab name and contact details, and check whether the lab is independent of the seller.
  4. Look for both a purity result (HPLC, given as a percentage) and an identity result (MS, given as a measured mass compared with the expected mass).
  5. Check whether sterility or endotoxin testing is reported. If it is not listed, assume it was not done; purity results do not cover it.
  6. If anything is unclear, email the lab with the report number and ask it to confirm the document is genuine.
Worked example

A COA reads: Lot 2409-B, HPLC purity 98.6%, MS observed mass matches expected mass, tested by an outside lab three weeks ago. Your vial says Lot 2411-A. The report describes a different batch, so it tells you nothing direct about your vial.

Common mistakes

  • Accepting a COA whose lot number does not match the vial in your hand.
  • Treating an HPLC purity number as proof of identity; purity alone does not show the main peak is the right molecule.
  • Assuming a high purity figure means the vial contains the labeled amount; purity and content are different measurements.
  • Assuming a COA covers sterility or endotoxin when those tests are not listed on it.
  • Trusting a COA hosted only on the seller's site without checking that the named lab issued it.

Sources

  1. ReferenceMultifactor Quality and Safety Analysis of Semaglutide Products Sold by Online Sellers Without a Prescription: Market Surveillance, Content Analysis, and Product Purchase Evaluation Study. J Med Internet Res, 2024. PMID 39509151.
  2. ReviewRelated impurities in peptide medicines. J Pharm Biomed Anal, 2014. PMID 25044089.
  3. ReferenceAnalysis of illegal peptide drugs via HILIC-DAD-MS. Talanta, 2017. PMID 28738623.

Page updated . How we grade evidence: methodology.

Related Terms

HPLC (High-Performance Liquid Chromatography)

HPLC (high-performance liquid chromatography) is a lab method that separates a sample into its components so the main compound's purity can be measured.

Mass Spectrometry

Mass spectrometry (MS) is a lab method that measures the mass of molecules, used to confirm a peptide is the molecule it is supposed to be.

Vendor Trust Score

DoseCraft's vendor trust score is an editorial rating of a peptide seller's documentation, testing claims, reputation and business details, not a lab result.

Batch Variance

Batch variance is the difference in purity, content or impurity profile between separate production lots of the same product.

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