“…The fundamental features of the conventional IXRs based on polystyrene-divinylbenzene (PS-DVB) copolymer once settled have been spotlighted by modern instrumental analyses and by in-depth studies, as summarized in a recent review. 1 One of the topics is the size of quantitatively exchangeable ions. It has been recognized that the saturated exchange capacity of tetraalkylammonium (TAA + ) ion on a cation exchange resin (CXR, -R -,M + ) decreases with an increase in size of the alkyl (R) group of TAA + (R, abbreviation, volume: methyl, TMA + , 140 Å 3 ; ethyl, TEA + , 250 Å 3 ; propyl, TPA + , 360 Å 3 ) and with an increase in cross-linking (CL) degree (CL degree, saturated % exchange for TMA + and TEA + : 2, 100, 100; 5, 90, 87; 10, 69, 63; 15, 63, 48).…”