How to read a Certificate of Analysis

A Certificate of Analysis (CoA) is the document a manufacturer provides to confirm that a specific lot of material matches its label. For a research peptide, a complete CoA should let you answer three questions: Is this the right molecule? Is it pure enough to use? And is it free of contaminants that would confound a study?

The first section to check is mass spectrometry. The instrument ionizes the peptide and measures its mass-to-charge ratio with high accuracy. The reported observed mass should match the theoretical mass of the sequence within a few daltons — typically well under 0.1% deviation for modern instruments.

If the observed mass is off by 18 daltons, that often means a water loss during synthesis. If it is off by larger, irregular amounts, the peptide may not be what the label says. A clean, sharp peak at the expected mass is the single strongest piece of identity evidence on a CoA.

High-performance liquid chromatography (HPLC) separates the peptide from related impurities — incomplete sequences, oxidized variants, and synthesis byproducts — and reports the result as a percentage of the total area under the curve. For research peptides, 98% or higher is typical for a premium product; 95% is a common floor.

Look at the actual chromatogram, not just the headline number. A clean profile shows one dominant peak with a few small satellite peaks. A profile with multiple large peaks of similar size suggests a mixture, even if the math still adds up to a high purity number.

Peptides intended for any in-vivo research need an endotoxin test, almost always the Limulus Amebocyte Lysate (LAL) assay. Endotoxins are fragments of bacterial cell walls that survive sterilization and trigger immune responses. Results are reported in endotoxin units per milligram (EU/mg). For most research applications, under 1 EU/mg is the working benchmark; for parenteral pharmaceutical use, the FDA's USP <85> standard is much stricter.

Bioburden — the count of viable bacteria in the powder — should be reported separately. A sterile-filtered, lyophilized peptide should show no growth.

Water content (Karl Fischer titration) tells you how much of the powder is actually peptide versus residual moisture. Acetate or trifluoroacetate (TFA) counterion content matters when calculating dose, because the salt form adds mass that is not the active peptide.

Finally, the CoA should list the lot number, manufacture date, and storage conditions. A lot number that ties back to the vial in your hand is the audit trail that makes the rest of the document meaningful.

Generic CoAs that do not name a lot, missing or blank chromatograms, purity reported without a method, and absent endotoxin data are all reasons to ask the supplier for clarification. A reputable manufacturer will provide the underlying instrument files on request.