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A new solid-contact ion-selective electrode (ISE) sensitive to lead (II) ions, obtained by modifying a polymer membrane with a nanocomposite of carbon nanofibers and an ionic liquid 1-hexyl-3-methylimidazolium hexafluorophosphate, is presented. Electrodes with a different amount of nanocomposite in the membrane (0–9% w/w), in which a platinum wire or a glassy carbon electrode was used as an internal electrode, were tested. Potentiometric and electrochemical impedance spectroscopy measurements were carried out to determine the effect of the ion-sensitive membrane modification on the analytical and electrical parameters of the ion-selective electrode. It was found that the addition of the nanocomposite causes beneficial changes in the properties of the membrane, i.e., a decrease in resistance and an increase in capacitance and hydrophobicity. As a result, the electrodes with the modified membrane were characterized by a lower limit of detection, a wider measuring range and better selectivity compared to the unmodified electrode. Moreover, a significant improvement in the stability and reversibility of the electrode potential was observed, and additionally, they were resistant to changes in the redox potential of the sample. The best parameters were shown by the electrode obtained with the use of a platinum wire as the inner electrode with a membrane containing 6% of the nanocomposite. The electrode exhibited a Nernstian response to lead ions over a wide concentration range, 1.0 × 10−8–1.0 × 10−2 mol L−1, with a slope of 31.5 mV/decade and detection limit of 6.0 × 10−9 mol L−1. In addition, the proposed sensor showed very good long term stability and worked properly 4 months after its preparation without essential changes in the E0 or slope values. It was used to analyze a real sample and correct results of lead content determination were obtained. [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 magnetic field-directed self-assembly solid contact has been proposed for developing an all-solid-state polymeric membrane Ca 2+ -selective electrode. The solid contact is prepared by physically adsorbing magnetic graphene powder on a magnetic gold electrode under the direction of the magnetic field. The proposed method for preparing solid contact avoids using the aqueous solutions and is simple, fast and general as compared to the multilayer drop-casting and electrodeposition methods. The all-solid-state Ca 2+ -selective electrode based on magnetic graphene as solid contact shows a stable potential response in the linear range of 1.0 × 10 −6 -1.0 × 10 −3 M with a slope of 28.2 mV/decade, and the detection limit is about 4.0 × 10 −7 M. Additionally, the magnetic graphene-based electrode shows a comparable potential stability performance to other graphene-based all-solid-state ion-selective electrodes, such as reduced undesirable water layer and insensitive to the interferences of O 2 , CO 2 and light. This work provides a favorable way to prepare solid contact for use in the field of all-solid-state ion-selective electrodes. [ABSTRACT FROM AUTHOR]

An all-solid-state polymeric membrane Ca2+-selective electrode based on hydrophobic octadecylamine-functionalized graphene oxide has been developed. The hydrophobic composite in the ion-selective membrane not only acts as a transduction element to improve the potential stability for the all-solid-state Ca2+-selective electrode, but also is used to immobilize Ca2+ ionophore with lipophilic side chains through hydrophobic interactions. The developed all-solid-state Ca2+-selective electrode shows a stable potential response in the linear range of 3.0×10−7-1.0×10−3 M with a slope of 24.7±0.3 mV/dec, and the detection limit is (1.6±0.2 )×10−7 M ( n=3). Additionally, due to the hydrophobicity and electrical conductivity of the composite, the proposed all-solid-state ion-selective electrode exhibits an improved stability with the absence of water layer between the ion-selective membrane and the underlying glassy carbon electrode. This work provides a simple, efficient and low-cost methodology for developing stable and robust all-solid-state ion-selective electrode with ionophore immobilization. [ABSTRACT FROM AUTHOR]

The three-dimensional porous graphene-mesoporous platinum nanoparticle (3D PGR-MPN) composite is used as solid contact for developing an all-solid-state polymeric membrane Cd 2+ ion-selective electrode (Cd 2+ -ISE). The 3D PGR with MPNs as cross-linking sites can be synthesized by a facile hydrothermal co-assembly method. The obtained 3D PGR-MPN composite is promising for acting as solid contact due to its unique characteristics such as high interfacial area, superior double layer capacitance, excellent conductivity and high hydrophobicity. The ISE exhibits a stable Nernstian response in the range of 10 −8 –10 −4 M and the detection limit is 10 −8.8 M. The 3D PGR-MPN-based Cd 2+ -ISE shows good potential response and no water layer exists between the polymeric membrane and the 3D PGR-MPN layer. Additionally, the proposed Cd 2+ -ISE is robust to O 2 , CO 2 and light interferences. This work provides a versatile method for preparing an effective solid contact to develop a stable and reliable all-solid-state ISE. [ABSTRACT FROM AUTHOR]

• An integrated potentiometric sensor includes a Cu2+-ISE as an indicator electrode and an Ag/AgCl electrode with a PVB reference membrane is developed. • Self-assembled porous graphene aerogels (PGAs) used as solid contact were prepared through an electrodeposition method. • The potentiometric sensor shows a stable potential response with a small potential drift. An integrated all-solid-state screen-printed ion-selective potentiometric sensor for the determination of Cu2+ is proposed. The whole-cell potentiometric sensor incorporates a polymeric membrane copper ion-selective electrode (Cu2+-ISE) as an indicator electrode and an Ag/AgCl reference electrode with a polyvinyl butyral reference membrane. The three-dimensional (3D) self-assembled porous graphene aerogel (PGA) can be conveniently and rapidly electrodeposited on the electrode substrate surface. Due to its interior 3D interconnected porous structures, the PGA has a large electrical double layer capacitance and fast charge transfer capability, which make it promising to be used as solid contact for the fabrication of the Cu2+-ISE. The developed potentiometric sensor shows a good Nernstian response over a range from 10−6 to 10−3 M with a detection limit of 10−6.5 M. In addition, the sensor exhibits a stable potential response with the absence of an undesirable water layer at the ion-selective membrane/PGA interface. [ABSTRACT FROM AUTHOR]