Lipophilic long-chain tetraalkyltin compounds as neutral carriers for nitrite-selective PVC membrane electrodes show selectivity patterns radically different from those obtained with classical anion-exchangers. The potentiometric selectivity coefficient for NO2- with respect to NO3- was improved by ~4 orders of magnitude. The linear response range of the electrode based on tetralauryltin (TLT) is from 0.1 mol/dm3 down to 2 ?10-5 mol/dm3 with a detection limit of 5 ?10-6 mol/dm3. The Nernstian response of the electrode in medium of pH ? gradually changes to a double super-Nernstian response when the solution turns slightly acidic. The change of the response slope has a close relation with the stepwise complex formation equilibrium of the carrier with the anion involved, which was experimental studied with UV spectroscopy. An explanation of the anomalous response behavior as well as the curve form of the mV-pH plot is given.

Key words: CARRIERS, POLYVINYL CHLORIDE, SELECTIVITY, MEMBRANE ELECTRODES, ALKANE P, TIN COMPOUND, LONG CHAIN COMPOUND, NITROUS ACID P