Abstract
Solid-contact ion-selective electrodes with carbazole-derived ionophores were prepared. They were characterized as acetate sensors, but can be used to determine a number of carboxylates. The potentiometric response characteristics (slope, detection limit, selectivity, and pH sensitivity) of sensors prepared with different membrane compositions (ionophore, ionophore concentration, anion exchanger concentration, and plasticizer) were evaluated. The results show that for the macrocyclic ionophores, a larger cavity provided better selectivity. The sensors exhibited modest selectivity for acetate but good selectivity for benzoate. The carbazole-derived ionophores effectively decreased the interference from lipophilic anions, such as bromide, nitrate, iodide, and thiocyanate. The selectivity, detection limit, and linear range were improved by choosing a suitable plasticizer and by reducing the ionophore and anion exchanger concentrations. The influence of the electrode body’s material upon the composition of the plasticized poly(vinyl chloride) membrane, and thus also upon the sensor characteristics, was also studied. The choice of materials for the electrode body significantly affected the characteristics of the sensors.
Highlights
Ion-selective electrodes (ISEs) were invented over a hundred years ago [1] and they have become routinely used instruments in analytical laboratories, clinical laboratories, industrial quality control, etc
A previous study [30] showed that the binding constants of the macrocyclic receptors, which were determined in 99.5 %:0.5 % (w/w) dimethyl sulfoxide (DMSO)-d6:H2O, were not indicative of the selectivity of the membranes that incorporated those receptors when used for measurements in aqueous solutions
Acetate was chosen as the primary analyte for this study, since it was the target analyte in the two previous studies [30,31], which made the comparison of results easier
Summary
Ion-selective electrodes (ISEs) were invented over a hundred years ago [1] and they have become routinely used instruments in analytical laboratories, clinical laboratories, industrial quality control, etc. A key advantage that ISEs possess in comparison to many other analytical techniques is portability, which stems from the form factor of the equipment needed to perform the measurements combined with the minimal sample pretreatment needed in many cases. The conventional liquid-contact ISEs are still used to manufacture commercial ISEs and to conduct research, but solid-contact ISEs (SC-ISEs) quickly gained traction for several reasons. Those reasons include a rugged construction that is often based around polymeric materials, the lack of need for filling solutions that evaporate and require refilling, and the ease of manufacturing different form factors using, e.g., Chemosensors 2021, 9, 4.
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