Tetrabenzyl pyrophosphate as a new class of neutral carrier responsive to lead ion

Tetrabenzyl pyrophosphate and diphenylphosphinic anhydride, with two phosphoryl groups (PO) as ligating sites, can be used as novel ionophores to make Pb(2+)-selective membrane electrodes. A good result was obtained with tetrabenzyl pyrophosphate, and the electrode based on this ionophore and bis(1-butylpentyl) adipate as a solvent mediator in a poly(vinyl chloride) membrane matrix exhibited a near-Nernstian response to Pb(2+) in the concentration range of 1x10(-5)-1x10(-2) M with a slope of 28.7 mV per concentration decade in a solution containing 0.1 M Mg(NO(3))(2). The limit of detection was 3x10(-6) M. The selectivity of this electrode to other metal cations was comparable to the best case in many Pb(2+)-selective electrodes so far developed. Addition of potassium tetrakis(p-chlorophenyl)borate (40 mol% relative to tetrabenzyl pyrophosphate) caused a drastic change in the response slope (53.3 mV per concentration decade), probably due to the formation of PbA(+), where A stands for anions present in the sample solution, and decreased significantly the electrode selectivity to other metal cations.