Design and synthesis of highly selective ionophores for lithium ion based on 14-crown-4 derivatives for an ion-selective electrode
摘要:
Highly Li+-selective ionophores based on 14-crown-4 derivatives were designed and synthesized, and the relationship of their molecular structures and ion selectivities was investigated in order to obtain a highly Li+-selective electrode. The ion selectivities were examined with 11 kinds of 14-crown-4 derivatives, which were prepared according to the proposed two types of Li+ ionophore models. Excellent Li+-selective ionophores were obtained by introducing a bulky ''block'' subunit into the ethano-bridge section of the base crown ring, which effectively prevents the formation of a 2:1 or 3:1 sandwich-type complex consisting of the crown ether and cations larger than Li+. The best Li+/Na+ selectivity (more than 1000) was obtained for the electrode using the 14-crown-4 derivative with a bulky decalin subunit. These results offer the general ion selectivity features of 14-crown-4-based compounds.
Flow-through type fiber-optic silver ion selective optodes based on novel cyclic and noncyclic thia crown ether compounds and a Lipophilic anionic indicator dye have been developed. Pellicular octadecylsilica beads were coated with a lipophilic organic liquid containing the thia ether compound as the silver ion selective ionophore and LAD-3 as the color changeable indicator dye, The optode system was constructed by packing these color changeable ion sensing beads ina now-through optical cell (cell volume, 7 mu L) having a quartz window attached directly to the distal end of a bifurcated optical fiber. The optode based on a lipophilic thia crown ether that has two sulfur atoms (tetradecyl-14-dithiacrown-4) exhibited the most sensitive response to silver ion of all the optodes investigated. This optode could detect silver ion in concentrations ranging from 10(-6) to 10(-2) M at pH 7.0 with 0.05 M Tris-H2SO4 buffer as the flowing solution by measuring the absorbance change in the sensing beads at 516 mm. This optode showed a higher selective response to Ag+ without any interference from other transition metal ions, except for Hg2+, up to 10(-3) M, as well as alkali metal and alkaline earth metal ions up to 1 M. Optodes employing highly lipophilic ionophores showed good reproducible response to Ag+ for at least 2 weeks.