What does peptide purity really mean?

A clear-eyed introduction to the science and the questions worth asking.

Purity is one part of the picture

An analytical purity percentage generally describes the relative signal attributed to a target compound under a particular method. The result depends on the technique and how it is reported.

Identity is a separate question

Mass spectrometry can help evaluate whether a detected mass matches the expected compound. Chromatography may help distinguish a target from certain impurities. These methods answer related but different questions.

What purity cannot tell you

A purity percentage alone does not verify exact content, establish sterility, exclude every contaminant or establish suitability for human use.

Reading a certificate of analysis

Look for the sample and lot, testing method, date, identity evidence, and the report’s limitations. Documentation is more useful when its claims can be traced to specific tests.

Editorial note: This article is a baseline educational draft. Add verified primary-source citations and complete editorial review before public publication. It is not medical advice.