Determination of p<i>K</i>_a Values of Hydrophobic Colorimetric pH Sensitive Probes in Nanospheres

A simple and novel method is proposed here for the first time to determine p<i>K</i>_a values of chromogenic hydrophobic pH sensitive probes directly in nanospheres. p<i>K</i>_a values can be obtained by measuring the pH response of the nanospheres (containing the probes and ion exchanger) followed by measuring the pH and Na⁺ responses of the nanospheres (containing solvatochromic dyes and ion exchanger). The p<i>K</i>_a values of four chromoionophores were successfully determined. This method is in principle also applicable to characterize colorimetric probes in other water immiscible nanomaterials

Capacitive Model for Coulometric Readout of Ion-Selective Electrodes

We present here a capacitive model for the coulometric signal transduction readout of solid-contact ion-selective membrane electrodes (SC-ISE) with a conducting polymer (CP) as an intermediate layer for the detection of anions. The capacitive model correlates well with experimental data obtained for chloride-selective SC-ISEs utilizing poly­(3,4-ethylenedioxythiophene) (PEDOT) doped with chloride as the ion-to-electron transducer. Additionally, Prussian blue is used as a simple sodium capacitor to further demonstrate the role of the transduction layer. The influence of different thicknesses of PEDOT as a conducting polymer transducer, different thicknesses of the overlaying ion-selective membranes deposited by drop casting and spin coating, and different compositions of the chloride-selective membrane are explored. The responses are evaluated in terms of current–time, charge–time, and charge–chloride activity relationships. The utility of the sensor with coulometric readout is illustrated by the monitoring of very small concentration changes in solution

Chronopotentiometric Carbonate Detection with All-Solid-State Ionophore-Based Electrodes

We present here for the first time an all-solid-state chronopotentiometric ion sensing system based on selective ionophores, specifically for the carbonate anion. A chronopotentiometric readout is attractive because it may allow one to obtain complementary information on the sample speciation compared to zero-current potentiometry and detect the sum of labile carbonate species instead of only ion activity. Ferrocene covalently attached to the PVC polymeric chain acts as an ion-to-electron transducer and provides the driving force to initiate the sensing process at the membrane–sample interface. The incorporation of a selective ionophore for carbonate allows one to determine this anion in a background electrolyte. Various inner electrolyte and all-solid-state-membrane configurations are explored, and localized carbonate depletion is only observed for systems that do not contain ion-exchanger additives. The square root of the transition times extracted from the inflection point of the chronopotentiograms as a function of carbonate specie concentration follows a linear relationship. The observed linear range is 0.03–0.35 mM in a pH range of 9.50–10.05. By applying the Sand equation, the diffusion coefficient of carbonate is calculated as (9.03 ± 0.91) 10^–6 cm² s^–1, which corresponds to the established value. The reproducibility of assessed carbonate is better than 1%. Additionally, carbonate is monitored during titrimetric analysis as a precursor to an in situ environmental determination. Based on these results, Fc-PVC membranes doped with ionophores may form the basis of a new family of passive/active all-solid-state ion selective electrodes interrogated by a current pulse