Assay

A quantitative test that the active ingredient is present in the stated amount, within the specified range. In Japanese Pharmacopoeia monographs the corresponding section is headed with a different word (定量法), rendered in the English JP as Assay; specifications and certificates use both. For biologics, content usually means protein concentration, often by UV absorbance, while biological activity is measured separately by a potency assay, and a Japanese specification may list both. Because other results are often expressed per unit of content, a content result that is wrong distorts the rest of the certificate.