Characteristics of lariat crown ether-copper(II) ion-selective electrodes

An ion-selective electrode using ionophore 2'.-picolyl sym-dibenzo-16-crown -5 ether as membrane carrier, sodium tetraphenylborate (NaTPB) as an anion excluder, and 2-nitrophenyl-octyl ether (NOPE) as the plasticing solvent me diator has been successfully developed. This electrode exhibits a linear re sponse with a slope of 42 mV/decade in concentration ranging from 10(-5) mo lL(-1) to 10(-1) molL(-1), slightly larger than the 30 mV expected from the one-to-one complex. The reason for the super-Nernstain slope is the partia l dimmer formation inside the membrane of the electrode, because this dimme r [Cu(C25H27NO6)(2)(H2O)(2)] 2ClO(4), has been isolated and confirmed by si ngle crystal X-ray crystallography. The detection limit for the copper(II) ion was estimated to be 1 x 10(-6) molL(-1). Electrodes composed of other p lasticing solvent mediators such as tris(2-ethylhexyl) phosphate (TOP), his (2-ethylhexyl) sebacate (DOS) and dibutyl phthalate (DBP) were also invest igated. Stability constants (logKs) of the two to one and the one to one 2- picolyl sym-dibenzo-16-crown-5 ether-Cu (II) complexes have been determined by potentiometric titration in methanol.