Understanding Certificates of Analysis

Research note · 4 June 2026 · ~4 min read

A Certificate of Analysis (COA) is the document that tells you what is actually in a vial. For laboratory work, the COA is the difference between a labelled compound and a verified one. This note explains the core analytical methods behind a COA and what to look for when you read one.

What a COA reports

A per-batch COA links a specific production lot to its test results. A complete COA typically lists the compound name and batch number, the test date, the analytical methods used, the measured purity, and the identity confirmation. Because results are tied to a single batch, a COA from one lot does not certify another — reputable suppliers issue a fresh COA per batch.

HPLC: measuring purity

High-Performance Liquid Chromatography (HPLC) separates the components of a sample as they pass through a column at different rates. The result is a chromatogram with peaks; the main peak corresponds to the target compound, and smaller peaks represent impurities. Purity is reported as the percentage of the total peak area attributable to the target — for example, “≥99% by HPLC”. A clean chromatogram with a dominant single peak indicates a well-purified preparation.

Mass spectrometry: confirming identity

HPLC tells you how pure a sample is, but not definitively what it is. Mass spectrometry (MS) fills that gap by measuring the molecular mass of the compound. When the observed mass matches the theoretical mass of the target peptide, identity is confirmed. Used together, HPLC and MS answer the two questions that matter most: is this the right molecule, and how pure is it?

How to read a COA critically

• Batch-specific: confirm the batch number on the COA matches the vial you received.
• Methods stated: look for both a purity method (HPLC) and an identity method (MS).
• Purity threshold: note the reported figure and the method it was measured by.
• Third-party testing: independent verification adds confidence beyond in-house claims.

Why it matters for research

In the lab, unverified material undermines reproducibility: an impurity or a mis-identified compound can confound an assay long before anyone suspects the reagent. Per-batch COAs make a result traceable back to a characterised input — which is exactly what good research practice requires.