HIGHLY SENSITIVE ION MEASURING METHOD, USE OF MATERIAL SUITABLE FOR METHOD THEREOF AND CORRESPONDING REAGENT

PURPOSE: To increase the measuring sensitivity of ion in aqueous liquid by using substance selected from a group consisting of a plurality of specific compounds in phase immiscible with the liquid. CONSTITUTION: The method for measuring ion comprises the steps of transferring ion in aqueous liquid to a phase immiscible with the liquid, and receiving hue change capable of being used for ion measurement by an existing pH indicator to measure the ion in the liquid. To increase the measuring sensitivity, substance from a group consisting of compounds represented by formulae I, II and III is used in the phase immiscible with the liquid. In the formulae, one of R to R groups and R to R groups is a group from a group consisting of alkyl, alkoxy and aralkyl, the other group is the same or different, is nitro, halogen, cyano, alkylsulfonyl or alkyl group substituted for halogen or, in the case that R and R are nitor, R and R are hydrogen, R to R are the same or different, and means hydrogen, nitro, halogen, cyano, alkylsulfonyl or alkyl group substituted for halogen.