PURPOSE: To obtain a new coupler compound by oxidatively condensing a hydrogen donor, coloring in a higher wavelength and in absorbance than 4- aminopyrine, having high absorbance, suitable for microanalysis of hydrogen peroxide useful in clinical chemical test, etc.
CONSTITUTION: This new coupler compound comprises and aminodiphenyl-based compound of formula I (R1 to R9 are each an alkyl, sulfo group, an alkoxy, a halogen, carboxyl, etc.; R2 and R5 may be bonded as they are or through a methylene chain; R10 is a 1-5C alkyl which may contain sulfo group, carboxyl group, hydroxyl group, etc.). A compound of formula II among the compound of formula I is treated with a compound of formula III as a hydrogen donor in the presence of a peroxidase by hydrogen peroxide to form an oxidative condensate of formula IV and colored. The colored substance has the maximum absorption wavelength in the vicinity of 750nm.