Organotin compounds: An ionophore system for fluoride ion recognition

Ion-selective properties were established for membrane electrodes prepared by using organotin compounds of type ((LRSnF2)-R-CN), (R=n-Bu (I),=Ph (II)) and ((LSnF3)-Sn-CN) (III) (L-CN=C6H4(CH2NMe2)-2). Electrodes formulated with the optimized membranes containing the organotin compounds I-III as ionophores and sodium tetraphenylborate (10-30%) exhibited high selectivity for fluoride over other anions. An electrode prepared with ionophore II using dibutyl phthalate as the plasticizer and 15% sodium tetraphenylborate (NaTPB) as anion additive, possesses the best potentiometric response characteristics. It shows a detection limit of 7.9 x 10(-7) M with a slope of 62.7 mV decade I of activity in buffer solutions of pH 5.5. The interference from other anions is suppressed under this optimized measurement conditions. An entirely non-Hofmeister selectivity sequence (F- > CH3COO- > Cl- > I- similar to Br > ClO4- > NO2- > NO3- > SCN-) with remarkable preference towards fluoride is obtained. The influence on the electrode performances by anion additive was studied, and the possible response mechanism was investigated by UV-vis spectra. The electrode has been used for direct determination of fluoride in drinking mineral water with satisfactory results. (c) 2006 Elsevier B.V. All rights reserved.