3 research outputs found
Determination of p<i>K</i><sub>a</sub> 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><sub>a</sub> values of chromogenic hydrophobic
pH sensitive probes directly in nanospheres. p<i>K</i><sub>a</sub> 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<sup>+</sup> responses of the nanospheres (containing
solvatochromic dyes and ion exchanger). The p<i>K</i><sub>a</sub> 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<sup>–6</sup> cm<sup>2</sup> s<sup>–1</sup>, 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