Assay and purity are two types of measurements used to determine the components of a sample. serve different purposes.

Assay

• Assay experimentally determines the presence, amount, or functional activity of a target entity (the analyte)
• It aims to measure the analyte or main target component present in the sample.
• The measurement may be quantitative, semi-quantitative, qualitative or functional.
• Endpoint assays and kinetic assays are the two types of assays used, based on type and number of measurements taken. Endpoint assays measure signals after a specific incubation period. Kinetic assays take multiple measurements over fixed intervals.
• Assays may also be single target or multiplex. Single target essays measure one component at a time in a sample. Multiplex essays measure several components simultaneously during the same essay.

 Purity

• Purity is an analysis of the impurities present in a sample.
• It aims to accurately reflect the purity characteristics of the sample.
• It is a quantitative measurement and is indicated as a percentage.
• Chromatography is the primary analytical method used to determine the purity of a sample. Both, liquid chromatography and gas chromatography are equally capable of measuring the purity of a sample.