Organotin compounds: an ionophore system for fluoride ion recognition.

Ion-selective properties were established for membrane electrodes prepared by using organotin compounds of type (L(CN)RSnF2)n, (R=n-Bu (I),=Ph (II)) and (L(CN)SnF3)n (III) (L(CN)=C(6)H4(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(-1) 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- approximately 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.