New Ag~+-and Pb~(2+)-selective electrodes with lariat crown ethers as ionophores

摘要

Two sym-dibenzo-16-crown-5 ethers with sidearms were synthesized and fabricated as ion selective (PVC) membrane electrodes. Among these two ion selective electrodes (ISEs), 3-butenyl sym-dibenzo-16-crown-5 ether I gives the best Ag+ selectivity and 2'-methoxyethoxyl sym-dibenzo-16-crown-5 ether 2 the best selectivity for Pb2+. These electrodes are com- posed of the respective lariat crown ether (LCE) as ionophore, sodium tetraphenylborate (NaTPB) as anion excluder, and 2-nitrophenyl-octyl ether (NPOE) as plasticizer. Electrodes composed of other plasticizer including tris(2-ethylhexyl) phos- phate (TOP), bis(2-ethylhexyl) sebacate (DOS) and dibutyl phthalate (DBP) were also investigated. The best performance observed include the two membrane electrodes with the following composition: (1) 3-butenyl sym-dibenzo-16-crown-5 ether-PVC-NaTPB-NPOE, and (2) 2'-methoxyethoxyl sym-dibenzo-16-crown-5 ether-PVC-NaTPB-NPOE, at a ratio of 5:50+-100. These two membrane electrodes show Nemstain response toward silver and lead (55.4 and 28.9mV per decade, respectively) over a wide concentration range from 5 x 10~(-5) to 5 x 10~(-1) M. The detection limit for silver(I) and lead(II) ions were estimated as 1 x 10-6 M. The response time was less than 30 sand a good reproducibility over a period of 3 months was observed. The newly designed Ag~+ -I and Pb2~+ -2 ISEs appear more reliable than the corresponding commercial Ag~+ - and Pb2+ -ISEsdue to a greater resistance to the interference of Hg~(2+) or to Cd_2~+ .Stability constants (log Ks) of 3-butenyl sym-dibenzo-16-crown-5 ether (for Ag~+) and 2'-methoxyethoxyl sym-dibenzo-16-crown-5 ether (for Pb~(2+)) weredeterrnined as 3.11 and 3.23, respectively, by potentiometric titration in methanol.