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

Tetrabenzyl pyrophosphate and diphenylphosphinic anhydride, with two phosphoryl groups (PO) as ligating sites, can be used as novel ionophores to make Pb2+-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 Pb2+ in the concentration range of 1×10−5–1×10−2 M with a slope of 28.7 mV per concentration decade in a solution containing 0.1 M Mg(NO3)2. The limit of detection was 3×10−6 M. The selectivity of this electrode to other metal cations was comparable to the best case in many Pb2+-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.