Ion-selective Electrode Membranes Responsive to Maleic and Phthalic Acids

Abstract

Ion-selective electrodes responsive to maleic and phthalic acids were prepared. The organic solvent solution of the ion-pair of the objective monovalent acid anion with a Crystal Violet or a tris(bathophenanthroline)-iron(II) ion was used as the electrode membrane. The responses of both electrodes were linear down to 10−4–10−4.5 M, with an ideal Nernstian slope of 57–58 mV per activity decade at 20 °C. Together with the potential slope, the pH dependence of the potential showed that the electrode responded to the monovalent anion of maleic or phthalic acid. The interferences of acetate, benzoate, and chloride were extremely low, whereas iodide and perchlorate interfered greatly. The maleic acid electrode works well without the interference of fumaric aicd. The phthalic acid electrode also functions without any interferences by isophthalic or terephthalic acid.

Carrier-Based Ion-Selective Electrodes and Bulk Optodes. 2. Ionophores for Potentiometric and Optical Sensors

“…Other Carboxylates. Discrimination between the ortho, meta, and para isomers of phthalate is possible even with ionophore-free ion-exchanger electrodes (log (FIM): m -phthalate, <−2; p -phthalate, <−2; nitrobenzene, pH 4). , Because of the fairly large differences in the p K values of the three isomers, the selectivities depend strongly on the pH, which also determines whether mono- or dianions are detected. Also the choice of the membrane solvent seems to have a notable influence on selectivities.…”

“…At neutral or acidic pH, ionophore-free anion-exchanger electrodes respond more strongly to maleate than to fumarate (log (FIM): <−3; nitrobenzene, pH 4) . While the maleate selectivity of these ISEs is nearly completely lost at pH 8.22, where both isomers occur almost exclusively in their dianionic form, an ISE based on the macrocyclic polyamine CA-7 discriminates fumarate even at this high pH and has a much lower detection limit than the ionophore-free anion-exchanger ISE …”

“…969 At neutral or acidic pH, ionophore-free anionexchanger electrodes respond more strongly to maleate than to fumarate (log K mal,fum pot (FIM): <-3; nitrobenzene, pH 4). 966 While the maleate selectivity of these ISEs is nearly completely lost at pH 8.22, where both isomers occur almost exclusively in their dianionic form, an ISE based on the macrocyclic polyamine CA-7 discriminates fumarate even at this high pH and has a much lower detection limit than the ionophore-free anion-exchanger ISE. 895 Membranes containing a classical ion exchanger, a cyclic polyamine, or a macrocycle with either a diaminopyridine or a diaminopyrimidine unit were used for the potentiometric detection of carboxylates in liquid chromatography.…”