How To Read a Certificate of Analysis
The four numbers on every COA that separate a real supplier from a fake one.
A Certificate of Analysis (COA) is the primary quality document that accompanies a research chemical. For synthetic peptides, a well-formed COA reports the identity, purity, and physical properties of a specific manufactured lot and links those results to defined analytical methods. Reading a COA critically is a core competency for any laboratory that purchases peptide reference materials for in-vitro research.
The first section to examine is identity confirmation, most often demonstrated by mass spectrometry. Electrospray ionization (ESI-MS) or MALDI-TOF results should show an observed monoisotopic or average mass that matches the theoretical mass of the target sequence within the instrument's stated tolerance. A COA that lists a molecular weight without an accompanying spectrum or a stated instrument tolerance provides weaker evidence of identity than one that documents both.
Purity is typically reported by reverse-phase HPLC at a defined wavelength, most commonly 214 nm for the peptide bond or 280 nm when aromatic residues are present. The COA should state the column, mobile phase gradient, and detection wavelength alongside the numeric purity value. A purity claim expressed only as a single percentage — with no chromatogram and no method description — should be treated as unverified.
Beyond identity and purity, a complete COA reports water content (often by Karl Fischer titration), residual solvent content (by gas chromatography), acetate or trifluoroacetate counterion content when relevant, and appearance. For peptides intended for cell-culture research, endotoxin testing by the LAL method may also appear. Each of these values has an accepted method described in the United States Pharmacopeia or the ICH Q6A specification framework, and a credible COA cites the method it followed.
Lot traceability is the final piece. The COA should carry a unique lot number that matches the label on the physical vial, a manufacture date, a retest or expiration date, and the signature or electronic approval of a quality-control reviewer. Retain the COA alongside your inventory record; when an experimental anomaly arises months later, the ability to trace a result back to a specific lot and its release data is often what separates a resolvable question from an unresolvable one.
All materials described are for in-vitro laboratory research only and are not for human or veterinary use.
Sources & Citations
External research links open in a new tab. ENOS Lab Notes are research-education summaries — always review the primary literature before designing bench work.