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 0.1M 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 25mol% NaTFPB, where the electrode exhibits high selectivity towards phosphate anions with a slope of -60mV per decade. It was demonstrated that the interference from more lipophilic anions is drastically suppressed (logK_ij ^pot, i=H ₂PO₄ ^-: salicylate, 0.5; SCN^-, -0.8; ClO₄ ^-, -2.3) under this optimized measurement conditions.