in radioanalytical chemistry
A substance in appreciable amount which, when associated with a @T06422@ of a specified substance, will carry the @T06422@ with it through a chemical or physical process, or prevent the @T06422@ from undergoing nonspecific processes due to its low concentration.
PAC, 1994, 66, 2513. (Nomenclature for radioanalytical chemistry (IUPAC Recommendations 1994)) on page 2516 [Terms] [Paper]