Divalent/Monovalent Selectivities and Secondary Interactions of Multibasic Acids on Anion Exchange Resins

The ion exchange equilibria of Br^– on three strongly basic anion exchange resins of different exchange capacities and different cross-linking degrees by five alkanoates (MC_<i>m</i>), a phosphate, and eight alkanedioates (DC_<i>n</i>; <i>m</i>,<i>n</i> = number of carbon atoms) were analyzed, and the selectivity coefficients for their monoanion and dianion, <i>K</i>₁₁ and <i>K</i>₂₁ were evaluated as a function of percent exchange (%E). The decrease in the <i>K</i>₁₁ values of MC_<i>m</i> with an increase in %E was attributed to the interference with hydration of MC_<i>m</i> in the resin phase, while the increase in the <i>K</i>₁₁ values of DC_<i>n</i> to the intermolecular hydrogen bonding between exchanged acidic anions. The log <i>K</i>₂₁ values of DC_<i>n</i> at %<i>E</i> = 0 plotted against <i>n</i> showed the minimum rather than the maximum as described previously. The reason has been discussed in terms of the hydrophobic interaction of DC_<i>n</i> with the polymer matrix, intramolecular hydrogen bonding, and the charge density

Triphosphate Ion-Selective Electrode Based on Zr-Porphyrin Complex

Ion-selective electrode using zirconium­(IV) complex with octaethylporphin (H₂oep) as a carrier showed high selectivity to triphosphate (TP, H₅tp) against other hydrophilic anions including diphosphate and phosphate. The electroactive species was identified to be [(Zr₄(oep)₄(Htp)₂] (TP/Zr ratio of 0.5) of the unique structure; triphosphates are recognized by one Zr atom through three O atoms on three different P atoms and by another Zr atom through two O atoms on two terminal P atoms and are also involved in complementary intermolecular hydrogen bonding to be surrounded by four porphyrin complexes. In contrast, Zr­(IV) in the other complex with tetraphenylporphin has the higher Lewis acidity, due to the electron-withdrawing property of phenyl rings and, at the higher TP concentration, forms a species having a TP/Zr ratio of unity, which precipitates to lose the electroactivity. The electrode was successfully applied to monitor hydrolysis of TP that provides diphosphate and phosphate