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We propose here a pulsed galvanostatic control of a solid-contact ion-selective electrode coupled with a thin-layer ion-exchanger free membrane, which allows chronopotentiometric trace-level ion detection with a high-interfering background in a rapid and reversible way. [ABSTRACT FROM AUTHOR]

A novel freestanding all-solid-state polymeric membrane Cu2+-selective electrode (Cu2+-ISE) is proposed based on three-dimensional graphene sponge (3D GS). The 3D GS electrode has been characterized by cyclic voltammetry, electrochemical impedance spectroscopy, and contact angle measurements. Experiments show that 3D GS possesses a large electrical double layer capacitance, good conductivity, and high hydrophobicity. Based on these superior properties, 3D GS has been applied as both electrode substrate and solid contact for construction of a freestanding all-solid-state polymeric membrane Cu2+-ISE. The 3D GS-based Cu2+-ISE shows a good Nernstian response ranging from 1.0 × 10−8 to 7.9 × 10−4 M with a low detection limit of 2.5 × 10−9 M. Moreover, the proposed Cu2+-ISE exhibits a stable potential response with a reduced water layer at the sensing membrane/3D GS interface and is not affected by interferences from light, O 2 and CO 2. A freestanding all-solid-state polymeric membrane Cu2+ -selective electrode based on three-dimensional graphene sponge was fabricated. Image 1 • A freestanding all-solid-state polymeric membrane Cu2+-ISE based on three-dimensional graphene sponge (3D GS) is developed. • The 3D GS can be used as both electrode substrate and solid contact for construction of Cu2+-ISE. • The electrode shows a stable potential response with a LOD of 2.5 × 10−9 M. [ABSTRACT FROM AUTHOR]

A solid-contact ion-selective electrode (SC-ISE) based on a covalent organic framework@reduced graphene oxide (rGO) composite is proposed. The composite can be synthesized through the polycondensation of 1,3,5-triformylphloroglucinol (TFP) and 2,6-diaminoanthraquinone (DAAQ) on the rGO nanosheets, which shows high capacitance and good redox-active properties. By applying Cd2+-ISE as a model, the electrode exhibits a Nernstian slope of 29.7 ± 0.4 mV/decade in the activity range of 1.0 × 10−7 - 7.9 × 10−4 M and the limit of detection is 6.8 × 10−8 M. Particularly, the electrode based on DAAQ-TFP@rGO exhibits a low potential drift of 1.2 ± 0.2 μV/h over 70 h due to the large capacitance of 2.0 mF. Moreover, the DAAQ-TFP@rGO-based Cd2+-ISE shows good reproducibility and the standard deviations of the standard potentials for single batch and batch-to-batch are 0.28 (n = 4) and 0.30 mV (n = 4), respectively. The developed SC-Cd2+-ISE is not disturbed by light or gas and no aqueous layer occurs between the sensing membrane and DAAQ-TFP@rGO layer. The DAAQ-TFP@rGO composite is highly promising for construction of calibration-free SC-ISEs. [Display omitted] • DAAQ-TFP@rGO combining the benefits of large capacitance and good redox-active properties is used as solid contact. • The DAAQ-TFP@rGO-based Cd2+-ISE exhibits a low potential drift of 1.2 μV/h over 70 h and a large capacitance of 2 mF. • E° standard deviations of the single batch and batch-to-batch electrodes are 0.28 (n = 4) and 0.30 mV (n = 4), respectively. [ABSTRACT FROM AUTHOR]

In situ growth of quasi-superhydrophobic porous NiCo 2 S 4 nanosheet arrays with a one-step electrodeposition method was provided. A calcium ion-selective electrodes (Ca2+-ISE) was subsequently constructed by using the prepared NiCo 2 S 4 as a solid contact layer. The proposed Ca2+-ISE exhibits a good Nernstian slope of 30.7 ± 0.3 mV/dec and a detection limit of 1.6 × 10−7 M. Due to the large redox capacitance of 1.8 mF, the Ca2+-ISE based on NiCo 2 S 4 nanosheet arrays shows a high potential stability of 1.9 ± 0.5 μV/h over 90 h. Excellent reproducibilities for the NiCo 2 S 4 -based Ca2+-ISEs can be obtained with the single batch and batch-to-batch E° standard deviations of 0.3 (n = 6) and 0.7 mV (n = 5), respectively. The NiCo 2 S 4 nanosheet arrays have a large contact angle of 148 ± 1.4°, which effectively suppresses the formation of a water layer at the sensing membrane/NiCo 2 S 4 interface. [Display omitted] • Quasi-superhydrophobic NiCo 2 S 4 nanosheets arrays has been synthetized by a one-step electrodeposition method. • Good reproducibilities for the NiCo 2 S 4 -based Ca2+-ISEs are obtained with the single batch and batch-to-batch E° standard deviations of 0.3 (n = 6) and 0.7 mV (n = 5), respectively. • The developed Ca2+-ISE shows a low potential drift of 1.9 ± 0.5 μV/h over 90 h and a large redox capacitance of 1.8 mF. [ABSTRACT FROM AUTHOR]

The developments of alternative signal readout strategies for the ion-selective electrodes (ISEs) are necessary in order to break through the limitation of the Nernst equation. In this work, a simple, convenient and easily operated strategy based on the non-enzymatic amperometric measurement of H 2 O 2 is proposed to read out the potentiometric responses for the ISEs. The proposed amperometric signal readout based on H 2 O 2 is carried out in a two compartment electrochemical cell configuration containing a detection cell and a sample cell, physically connected by a salt bridge. A glassy carbon (GC) electrode is placed in the detection cell to monitor the oxidation current of H 2 O 2 , and an ISE is placed in the sample cell to act as both the reference electrode and the potentiometric sensor for obtaining the ion activities. The oxidation of H 2 O 2 is induced by a constant potential applied between the GC electrode and the ISE, and subsequently modulated by the potential change of the ISE in the presence of the primary ion. The proposed amperometric signal readout based on H 2 O 2 shows the satisfied slope sensitivity and detection limit, which are better than or compared to those for the potentiometric responses for the ISEs. This work provides a general strategy for transforming the potential response of the ISEs into the amperometric readout, and is promising for detection of cations (eg., Ca2+) and anions (eg., NO 3 −) with high sensitivity and excellent selectivity. [Display omitted] • The transformation from the potential to the amperometric signal is proposed. • The amperometric readout for ISEs is obtained based on the oxidation of H 2 O 2. • The amperometric readout strategy is simple, convenient, and easy operated. • The amperometric readout for ISEs shows high sensitivity and high selectivity. [ABSTRACT FROM AUTHOR]