Identity testing answers “what is this compound?” — typically via mass spectrometry, comparing the observed mass to the theoretical mass of the expected sequence or structure. Purity testing answers “how clean is this sample?” — typically via HPLC, reported as a percentage of the detected material that matches the main compound.
Assay, or content, testing is a related but distinct question: “how much of the compound is actually present,” often expressed as a percentage of the labeled amount. Qualitative testing establishes whether something is present at all; quantitative testing measures how much. Not every certificate necessarily reports every one of these — what a given lot’s certificate actually states is the authoritative answer for that lot, not a general assumption.