A Certificate of Analysis (COA) is the most important document you'll receive alongside a research peptide. It's your evidence that the compound matches its claimed identity and purity. Knowing how to read it separates informed researchers from those flying blind.
What Is a COA?
A COA is a document issued by an analytical testing laboratory that certifies the results of testing performed on a specific batch of compound. For research peptides, a COA should include:
- Compound identity verification (typically by mass spectrometry)
- Purity analysis (typically by HPLC)
- Batch/lot number for traceability
- Testing laboratory name (should be a third-party lab, not the supplier's in-house lab)
- Date of analysis
A COA from the manufacturer's own lab is significantly less valuable than one from an independent third-party laboratory. Look for well-known peptide testing labs.
HPLC Purity: What the Number Means
High-Performance Liquid Chromatography (HPLC) separates a mixture into its components by pumping it through a column under high pressure. Different compounds elute at different times (retention times), and a UV detector measures the absorbance of each peak.
The purity % represents the area under the main compound peak divided by the total area under all peaks:
Purity % = (Target Peak Area / Total Peak Area) × 100
What the numbers mean: - >98%: Research-grade. This is the standard for high-quality peptide suppliers. - 95–98%: Acceptable for many research applications. Some impurities present. - <95%: Below research grade. Impurities could confound results. - <90%: Not suitable for serious research.
The HPLC chromatogram itself should also be included or available. Look for a clean main peak with minimal secondary peaks. Large secondary peaks near the main peak may indicate deletion sequences (synthesis byproducts).
Mass Spectrometry: Confirming Identity
Mass spectrometry (MS) confirms that the compound is actually what it claims to be — not just that it's pure. The technique measures the mass-to-charge ratio (m/z) of ions.
For peptides, the COA should show: - Expected molecular weight (calculated from the amino acid sequence) - Observed molecular weight (measured) - These should match within a small margin (typically ±1 Da for small peptides)
Common MS techniques on COAs include MALDI-TOF (Matrix-Assisted Laser Desorption/Ionization Time-Of-Flight) and ESI-MS (Electrospray Ionization). Both are acceptable. The key check is that expected and observed masses match.
A compound can be high-purity HPLC but still be the wrong molecule — which is why both tests matter together.
Red Flags to Watch For
- No third-party testing: The most important red flag. In-house COAs have obvious conflict of interest.
- Missing chromatogram: The number alone isn't sufficient. The chromatogram shows you the peak shape and any hidden impurities.
- No batch number: Without a lot number, you can't verify the COA matches your specific vial.
- Old test dates: Testing should be recent (within the past year for the batch you receive).
- HPLC method not specified: The purity result depends on the column, mobile phase, and gradient. Without these details, you can't evaluate the method's adequacy.
- Suspiciously round numbers: "99.9% purity" on every single product is a red flag — real testing shows variation.
Research Use Only. All content is for informational and educational purposes regarding preclinical research. None of the compounds discussed have been approved by the FDA for human therapeutic use. This information does not constitute medical advice.