How to Read a Peptide Certificate of Analysis (COA)
A Certificate of Analysis (COA) is the primary document a laboratory uses to verify that a research compound is what it claims to be, before it's used in any experimental protocol. For anyone sourcing peptides for research, knowing how to actually read one — not just check that one exists — is the difference between verifying a compound and just trusting a label.
This guide walks through the sections that matter on a typical peptide COA, what each one is actually telling you, and the signs that a document isn't doing its job.
1. Identity Confirmation (Mass Spectrometry)
The first thing a COA needs to establish is that the vial contains the compound it's labeled as — not a purity result for the wrong molecule. This is typically done via mass spectrometry (MS), which measures the mass-to-charge ratio of the sample and compares it against the expected molecular weight of the target peptide.
Look for a reported molecular weight that matches the published value for that compound, along with the specific MS method used (e.g., MALDI-TOF, LC-MS). A COA that only reports a purity percentage with no identity confirmation hasn't actually established what's in the vial — only how "clean" whatever it is appears to be.
2. Purity (HPLC)
Purity is most commonly reported via High-Performance Liquid Chromatography (HPLC), which separates the sample into its component peaks and measures what percentage of the total peak area corresponds to the target compound. This is usually expressed as a single percentage (e.g., ">99% purity").
3. Batch / Lot Number
Every COA should be tied to a specific batch or lot number that matches the number printed on the vial or label. This is what allows a specific result to be traced back to a specific production run — without it, there's no way to confirm the COA you're looking at actually corresponds to the vial in front of you.
4. Testing Laboratory and Date
A COA should identify which laboratory performed the testing (ideally third-party, independent of the seller) and the date testing was completed. Third-party testing matters here specifically because it removes the seller from the position of grading their own product.
Red Flags
- No batch/lot number, or a batch number that doesn't match the product label.
- Purity reported with no identity confirmation — a high purity number is meaningless if the compound's identity was never actually verified.
- No testing lab named, or the "lab" is the seller itself with no independent verification.
- Undated results, or a COA reused across multiple, unrelated batches.
- No raw data available on request — a legitimate lab can typically provide the underlying chromatogram or spectrum if asked.