Uniformity recognition sites for water-soluble ionic compounds were constructed onto the pores of porous polymer particles. This concept is based on a modified interval immobilization technique, which was used for the selective recognition of paralytic shellfish poison, saxitoxins (STXs). The results of batch adsorption and solid-phase extraction for one of the STX analogues, a prepared polymer that had special sites for the recognition of STXs, showed that the analogue could selectively recognize and concentrate STXs. Selective recognition was facilitated by interval-immobilized functional groups.