Organic tin compounds combined with anionic additives—an ionophore system leading to a phosphate ion-selective electrode?

The potentiometric response characteristics of electrodes based on organic trialkyl/aryl-tin compounds combined with various amounts of anionic additive (NaTFPB) were investigated in 0.1 M bis-Tris–H2SO4 buffer solution at pH 7.0. The best result for phosphate sensing was obtained for the electrode membrane containing tributyltin chloride and 25 mol% NaTFPB, where the electrode exhibits high selectivity towards phosphate anions with a slope of −60 mV per decade. It was demonstrated that the interference from more lipophilic anions is drastically suppressed (log Kijpot, i=H2PO4−: salicylate, 0.5; SCN−, −0.8; ClO4−, −2.3) under this optimized measurement conditions.