How to Read a Peptide Certificate of Analysis
A field guide to the numbers that actually matter on a COA — and the ones that don't.
A Certificate of Analysis, or COA, is the single most important document attached to any research compound. It is the record of what an independent laboratory measured when it examined a specific batch — not a marketing claim, not a target, but a measurement. Yet many COAs are read at a glance: purity number, pass, done. The document contains far more, and knowing how to read it is a core research-documentation skill.
This guide walks through each section of a typical peptide COA and explains what the value represents, why it is measured, and what a researcher should note when logging batch provenance.
Purity by HPLC
High-performance liquid chromatography separates the compounds in a sample by how they travel through a column. The resulting chromatogram shows a series of peaks; the main peak represents the target compound, and the area under it, expressed as a percentage of total peak area, is the reported purity. A value of ≥99% indicates that the overwhelming majority of the measured material corresponds to the intended sequence.
When reviewing a chromatogram, note the baseline and the presence of smaller secondary peaks. These represent process-related impurities. A clean baseline with a single dominant peak is the visual signature behind a high purity value.
Identity by Mass Spectrometry
Purity tells you how much of the sample is one thing; mass spectrometry tells you what that thing is. By measuring the molecular weight of the compound, the laboratory confirms that the material matches the expected mass of the target sequence. A purity figure without an identity confirmation is incomplete — a sample can be 99% one compound that is not the compound you intended to study.
Endotoxin and Heavy Metals
Endotoxin screening measures bacterial contamination, reported in endotoxin units per milligram. Heavy-metal screening checks for elemental contaminants introduced during synthesis or handling. Both are safety-adjacent quality markers that speak to how carefully a batch was produced and handled, and both belong in a complete batch record.
Batch and Date
Finally, every COA is tied to a specific batch identifier and a test date. This is what makes the document traceable. When a compound is logged in a research record, the batch ID links the physical vial back to the exact analytical data that describes it. Klinity Labs publishes a COA for every released batch in a searchable archive for exactly this reason.
This article is educational and informational only. It does not constitute guidance for the use of any compound. All Klinity Labs compounds are supplied for laboratory research use only.
