An assay is a test of a substance to find out what chemicals it contains. It is usually carried out to find out how pure a substance is. The meaning of ASSAY is to analyze (something, such as an ore) for one or more specific components. How to use assay in a sentence. ASSAY definition: 1. to examine a substance to find out how pure it is or what its properties (= qualities) are: 2…. Learn more. An assay is a breakdown of a material, examining the individual parts that make up the whole. When you assay a situation, you look at all the elements that created the problem in order to come up with a solution. Define assay. assay synonyms, assay pronunciation, assay translation, English dictionary definition of assay. an analysis of a substance, esp. of an ore or drug: His find required an assay to determine its value. An assay is a laboratory procedure or test that is performed to determine the presence, concentration, quality, or biological activity of a specific substance or component within a sample. Assays are performed to establish the metal content in samples taken from the rock. About 24 hours before assay the sample was placed in 80% ethanol. As a noun, assay means a test or appraisal to determine the components of a substance or object. As a verb, it refers to the act of analyzing, or of conducting that test. It is usually used in chemistry-related fields like metallurgy and pharmaceuticals, but you can also assay a poem. An assay is a laboratory procedure that identifies or measures a specific substance in a sample. Whether it’s checking how much of a drug is in a tablet, detecting bacteria on a kitchen surface, or measuring hormone levels in your blood, the underlying process is an assay. An assay is an investigative (analytic) procedure in laboratory medicine, mining, pharmacology, environmental biology and molecular biology for qualitatively assessing or quantitatively measuring the presence, amount, or functional activity of a target entity.