How to Read a Peptide Certificate of Analysis (COA)

A Certificate of Analysis (COA) is a batch-specific lab report that documents a peptide’s measured purity, confirmed identity, and physical characteristics for one production lot — most commonly through HPLC purity testing and mass spectrometry. Reading one means matching each result to its analytical method and checking that the COA corresponds to the lot you received. All products and information here are intended strictly for in-vitro research and laboratory use only (RUO).

What is a Certificate of Analysis?

A Certificate of Analysis is generated when a specific batch (lot) of material is tested in an analytical laboratory. Rather than describing a compound in general, a COA reports what was actually measured for that one lot — the numbers, methods, and dates behind them. Because peptide synthesis can vary between runs, results for one lot do not automatically apply to another, which is why each COA is tied to a batch identifier.

What’s on a peptide COA?

• HPLC purity (%) — the main peak relative to total detected peaks, typically by reverse-phase HPLC.
• Mass spectrometry identity — observed molecular weight compared against the theoretical (expected) mass.
• Appearance — a physical description, such as a white lyophilized powder.
• Net peptide content — the fraction of dry mass that is actual peptide (the rest is water, counter-ions, salts).
• Batch / lot number — the identifier linking the report to a production run.
• Test date — when the analyses were performed.

How to interpret HPLC purity

Reverse-phase HPLC separates a sample as it passes through a column, producing a chromatogram (detector signal versus time). Each compound elutes at a characteristic retention time and appears as a peak; the peptide of interest is normally the largest peak, and smaller peaks are related impurities. Purity is usually the main-peak area as a percentage of total peak area — so ≥99% means that, under that method, at least 99% of the detected material corresponds to the main peak. Published peptide methods commonly use a C18 column with a TFA/acetonitrile/water mobile phase and UV detection, validated under ICH guidelines [1]. Purity is method-dependent: the column, wavelength, and gradient all influence what is detected.

How identity is confirmed (mass spectrometry)

HPLC shows how much main peak is present, but not what it is. Mass spectrometry (MS) addresses identity. Because the intended sequence of a synthetic peptide is known, its theoretical molecular weight can be calculated; MS measures the observed mass, and a close match supports that the correct peptide was made. MS is well suited to analyzing the identity and purity of synthetic peptides, with MALDI-TOF-MS and LC-MS being standard approaches [2]. On a COA, look for both expected and found masses.

Why third-party COAs matter

A COA produced solely by the manufacturer reflects that manufacturer’s own testing. An independent, third-party COA provides separate verification of the same lot. Quality frameworks for peptide reference materials lean on multiple orthogonal methods (RP-HPLC for content/impurities plus MS for identity) because no single test captures everything [3]. When evaluating a report, confirm the lot number on the COA matches the vial, check the test date, and look for named methods rather than a bare percentage.

Related

• COA Library — browse batch-specific certificates of analysis.
• Peptides catalog — view available research peptides.

FAQ

Does a higher HPLC purity number always mean a better COA? Not on its own. A purity percentage is only meaningful alongside the method used and a matching identity confirmation by MS.

What is the difference between HPLC purity and net peptide content? HPLC purity describes the main peak relative to other detected peaks; net peptide content describes how much of the dry mass is peptide versus water and salts. Both can appear on one COA.

Should the lot number on the COA match the vial? Yes. A COA documents one specific batch; if the lot numbers do not match, the report does not describe your material.

References

1. Bavand Savadkouhi M, et al. RP-HPLC method development and validation for a peptide. Iran J Pharm Res. 2017.
2. Prabhala BK, et al. Characterization of Synthetic Peptides by Mass Spectrometry. Methods Mol Biol. 2015.
3. McCarthy D, et al. Reference Standards to Support Quality of Synthetic Peptide Therapeutics. Pharm Res. 2023.

For research use only. Not for human or veterinary use. Statements have not been evaluated by the FDA.