Identity: is it the right compound?
Identity testing checks whether the material matches the compound on the label. A common approach is mass spectrometry, often paired with liquid chromatography (LC-MS or LC-MS/MS), which compares the measured mass of the molecule with the expected mass.
An identity result is usually reported as confirmed or not confirmed.
Purity: how much of the sample is that compound?
Purity testing estimates what share of the measured material is the target compound rather than related impurities. For peptides this is often done with reversed-phase high-performance liquid chromatography (RP-HPLC) and reported as a percentage of total peak area.
Area purity is an analytical measure. It is not the same as the amount of peptide in a vial, and it does not cover substances the method cannot detect.
Why both matter
A sample can show high purity for the wrong compound, or contain the right compound with significant impurities. Reading both results together gives a clearer picture of the sample tested.