Key takeaway
A certificate of analysis (COA) reports identity and purity from an independent lab. This guide explains what HPLC and mass spectrometry actually measure and how to read a COA critically.
What is a certificate of analysis?
A certificate of analysis (COA) is a document from an analytical laboratory reporting the identity and purity of a sample. For peptides, the two most common techniques are high-performance liquid chromatography (HPLC), which estimates purity as a percentage of the main peak, and mass spectrometry (MS), which confirms molecular weight and therefore identity.
A COA is only meaningful if it is recent, traceable to a specific batch, and issued by an independent lab rather than the seller.
How do you read an HPLC purity figure critically?
An HPLC trace shows peaks; purity is typically reported as the area of the main peak relative to total peak area. A high number does not guarantee the peptide is the correct one — that is what mass spectrometry verifies. Always check that both identity (MS) and purity (HPLC) are present.
Be cautious of COAs without batch numbers, dates, or the testing lab’s name, and of images that cannot be cross-checked with the issuing laboratory.
Frequently asked questions
It estimates purity as the percentage area of the main chromatographic peak relative to total peaks — but it does not by itself confirm identity.