Wilhelm Simon

CARRIER ANTIBIOTICS AND MODEL COMPOUNDS AS COMPONENTS OF SELECTIVE ION-SENSITIVE ELECTRODES

ABSTRACT The ion selectivity exhibited by different types of membrane electrodes is rationalized by a theoretical treatment of the membrane potential. An equation, which is admirably suited for the interpolation of e.m.f.-values, is derived for the electrode response of membrane electrodes of the electrically neutral ligand type (antibiotics, model compounds) to mixed solutions of monovalent and divalent cations. In contrast to the classical Nicolsky equation it describes the contribution of interfering ions to the e.m.f. by an activity-independent selectivity term. Electrically neutral ligands selective for calcium ions to be used as components for liquid membrane electrodes were designed and prepared. The corresponding electrodes are in all respects superior to the calcium ion liquid membrane electrodes described so far.

Anion selectivities of trifluoroacetophenone derivatives as neutral ionophores in solvent-polymeric membranes

Abstract Trifluoroacetophenones with different substituents in the para -position are studied in order to examine their anion selectivities in solvent-polymeric membranes. The selectivities of the corresponding ion-selective electrodes and the hydration of the ligands in membranes depend on the Hammett constants σ of the substituents. Better selectivities for carbonate over chloride were reached throughout for ligands with substituents of high σ values.

Extra- and intracellular hydrogen ion-selective microelectrode based on neutral carriers with extended pH response range in acid media

A series of new neutral hydrogen ion carriers suitable for application in H+-selective microelectrodes is presented. One carrier (ETH 1907) proves to be superior to tridodecylamine currently very much in use. Microelectrodes based on ETH 1907 in an optimized membrane composition exhibit a linear dynamic response function from pH 2 to 9 extended into the acidic range, a response time ≤ 5 s, and a resistance of about 35 GΩ for a tip diameter of about 1 μm. This makes the electrode suitable for measurements at normal physiological intracellular pH as well as in acid physiological media. Measurements using this microelectrode in proximal tubule cells of isolated perfused frog kidney are presented.

A new double-barrelled, ionophore-based microelectrode for chloride ions

A new Cl− selective microelectrode based on the ionophore 5,10,15,20-tetraphenyl-21H,23H-porphin manganese(III) chloride is presented which discriminates better against HCO3− and several organic anions than electrodes containing the Corning 477913 ion-eschanger. Using a redesigned construction procedure, fine-tip double-barrelled microelectrodes were produced which had slopes of −52.4±0.6 mV (SE,n=24), resistances of about 7·1011 Ω and a selectivity coefficient logKCl, HCO3pot of −1.40±0.03. Some electrodes showed a small unexplained sensitivity to pH>7.6. When used to puncture cells of isolated S3 segments of rabbit renal proximal tubule during perfusion with HCO3− Ringer solution, the electrodes gave a membrane potential of −69.8±1.5 mV and an intracellular Cl− activity, [Cl−]i, of 35.3±2.6 mmol/l. Upon switching bath and lumen perfusions to Cl−-free solutions the “residual” [Cl−]i dropped to 1.20±0.03 mmol/l, while in similar measurements with ion-exchanger electrodes the “residual” [Cl−]i dropped only to 10.9±0.5 mmol/l. These observations demonstrate the superiority of the new electrode and prove that previously determined high [Cl−]i values in Cl−-free ambient solutions reflect interference problems rather than non-exchangeable intracellular chloride.