A Certificate of Analysis (COA) is the document that connects a specific vial to specific test results. For research peptides it is the single most important piece of quality documentation. This guide walks through each section of a typical peptide COA and explains what it tells you, and what it does not.
1. Header and traceability information
The top of a COA should identify exactly what was tested:
- Product name and sequence: the compound and, ideally, its full amino acid sequence or structure.
- Lot or batch number: the most important field. It must match the lot number on the vial. A COA without a lot number cannot be tied to any particular material.
- Dates: manufacture, test, and release dates. Some COAs also list a retest date.
- Testing laboratory: the name of the lab that performed the analysis, and whether it is independent of the seller.
2. Identity: mass spectrometry
Identity testing confirms the material is the peptide it claims to be. The standard method is mass spectrometry (MS), usually electrospray ionization (ESI-MS) or MALDI-TOF. The COA should report the theoretical (expected) mass calculated from the sequence and the observed mass measured by the instrument. The two should agree within the instrument’s tolerance. Peptides often appear as multiply charged ions in ESI-MS, so you may see several peaks that all correspond to the same molecule.
3. Purity: HPLC
Purity is almost always measured by reversed-phase high-performance liquid chromatography (RP-HPLC) with UV detection, typically at 214 or 220 nm, where the peptide bond absorbs. A good COA includes the chromatogram itself, not just a number. The reported purity is the area of the main peak as a percentage of the total peak area.
Two things to keep in mind:
- HPLC purity only counts substances that absorb UV light and elute from the column. Water and salts are invisible to it.
- A single sharp peak is good, but two compounds with very similar properties can co-elute. That is why identity testing by MS is reported alongside purity.
For a deeper explanation, see our guide on what “≥99% purity by HPLC” actually means.
4. Other tests you may see
- Net peptide content: the percentage of the powder’s weight that is actually peptide, often measured by amino acid analysis or nitrogen analysis. It is normally well below 100% because lyophilized peptides contain bound water and counter-ions.
- Water content: commonly measured by Karl Fischer titration.
- Counter-ion content: peptides are usually supplied as acetate or trifluoroacetate (TFA) salts.
- Appearance: for example, “white to off-white lyophilized powder.”
- Endotoxin, residual solvents, or bioburden: reported for some materials, depending on the intended research application.
5. Red flags
- No lot number, or a lot number that doesn’t match the vial.
- A purity figure with no chromatogram.
- No mass spectrometry data, or an observed mass that doesn’t match the theoretical mass.
- No identifiable testing laboratory, or test dates that predate the stated manufacture date.
- Identical COAs reused across different products or lots.
Where to find our COAs
Lot-specific certificates for The Pure Vial Co. materials are published in our COA Library, searchable by product name or lot number. If you can’t find the certificate for your lot, contact us.
The Pure Vial Co. supplies research materials for laboratory, analytical, and scientific research use only. Nothing in this guide is medical advice or an indication that any material is suitable for human or veterinary use. See our Research Disclaimer.
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