Assay

A laboratory measurement of the concentration or activity of a specific substance in a sample. On a Certificate of Analysis, the assay value confirms the actual percentage of the active ingredient in a batch — typically expressed as a percentage of the theoretical or labelled amount (e.g. "Assay (as L-Carnitine): 99.2%"). The assay result is one of the most important values to verify on a COA before accepting a shipment.