masking reagent

(analytical chemistry) A substance that decreases the concentration of a free metal ion or ligand by conversion into an essentially unreactive form, thus preventing undesirable chemical reactions that would interfere with the determination. Also known as masking agent.

An agent taken by an athlete to hide the use of a substance on the World Anti-Doping Agency's Prohibited list. Diuretic drugs have been abused to flush out drugs from, and reduce the concentration of, anabolic steroids in urine samples.