Pentacoordinate organotin complexes as neutral carriers for salicylate-selective PVC membrane electrodes

Selectivity properties are established for three new electrodes prepared by incorporating three pentacoordinate organotin(IV) complexes, mono(2,4-pentanedionato-o,o') tri(phenylmethyl)tin (DMTBS), mono(benzoylacetonato-o,o') tri(phenylmethyl)tin (MPTBS) and mono(dibenzoylmethanato-o,o') tri(phenylmethyl)tin (DPTBS) into plasticized PVC membranes. These electrodes exhibit linear response to salicylate and an anti-Hofmeister selectivity pattern with high specificity for salicylate over many common anions. The results show that the potentiometric response characteristics are related to the structure of organic ligands. The detection limit and the slope of the electrodes based on these pentacoordinate organotin complexes exhibit a tendency to decrease as the substituent in organic ligands changes from a methyl group to a phenyl group. Electrodes prepared with DMTBS have the best detection limit and the highest degree of selectivity and sensitivity for salicylate. The response mechanism is also investigated by use of a.c. impedance and i.r. spectroscopic techniques.