Understanding Certificates of Analysis

A Certificate of Analysis (COA) is the analytical passport of a specific peptide batch. It reports every quality-relevant result generated during release testing and is signed off by the testing laboratory before the batch is cleared for dispatch.

A COA is always batch-specific. Two batches of the same product will have two separate COAs, each keyed to its own batch number, its own manufacture date and its own analytical fingerprint. If a supplier provides only a generic product COA that does not reference a batch number, that is a red flag — the document has no traceability.

A well-formed peptide COA has five core sections: identity, purity, appearance, water / solvent residuals and endotoxin. The exact wording varies by laboratory but the underlying data does not.

Identity is confirmed by mass spectrometry — the observed molecular mass is compared to the theoretical mass of the target peptide. Purity is quantified by reverse-phase HPLC-UV as the percentage of total integrated peak area assigned to the peptide of interest. Appearance describes the physical state of the lyophilised vial contents. Water content records residual moisture from the lyophilisation cycle. Endotoxin is measured by the LAL assay and reports the bacterial-contamination floor of the batch.

HPLC-UV purity is expressed as a percentage — the sum of the peptide's peak area divided by the total peak area, times one hundred. A ≥99% result means less than one percent of the integrated signal is attributable to related impurities, truncated sequences or process residues.

Reputable COAs include the chromatogram alongside the numeric result. The chromatogram is what you actually verify: a single dominant peak with a clean baseline is what ≥99% purity should look like. If the numeric result claims high purity but the chromatogram shows several unlabelled peaks of similar magnitude, treat the batch with scepticism.

Mass spectrometry confirms the batch is the peptide it claims to be. The COA reports both the theoretical monoisotopic mass and the observed mass — the two should match within the instrument's tolerance (typically a few atomic mass units for peptides in this size range).

A batch that hits its purity target but misses its identity target is not the compound on the label. Always confirm both sections agree.

Endotoxin testing via the LAL assay quantifies bacterial cell-wall fragments in the finished vial. For research peptides the acceptable limit depends on the intended downstream assay — cell-culture and in-vitro work is typically the most sensitive.

Appearance is a simple visual specification: a white to off-white lyophilised cake, no discolouration, no visible foreign matter. A discoloured or partially collapsed cake is a hard reject on any well-run release process.

Cross-reference the batch number printed on your vial label with the batch number at the top of the COA. The two must match exactly. If they don't, the COA does not describe the vial in your hand — stop and contact the supplier.

Every BuyRetaUK batch is published in our verification library. Enter the batch number from your vial and pull the matching COA directly. This is the last, quick check before starting laboratory work.