PURPOSE: To detect and determine a member of a specific coupled pair by decomposing a stable 1,2-dioxetane, which can emit an optically detectable energy, with a phosphatase in the presence of an enhancer.

CONSTITUTION: A dioxetane compound, which is expressed by formula I (R is a 14C alkyl; M is an alkali metal or ammonium) and can emit an optically detectable energy by the reaction with a phosphatase, is decomposed with the phosphatase in the presence of an enhancer to emit light. Preferable examples of the phosphatase include an alkali phosphatase. Further, concrete examples of the enhancer include a protein such as bovine serum albumin, a fluorescent agent such as fluorescein, a vinylbenzyl qualernary ammonium salt polymer, etc.