Construction of a new Cu2+ coated wire ion selective electrode based on 2-((2-(2-(2-(2-hydroxy-5-methoxybenzylidene amino)phenyl)disufanyl)phenylimino)methyl)-4-methoxyphenol Schiff base

S-S bridged Schiff bases as versatile ionophores: Synthesis and application for electrochemical sensing of Copper(II) and Mercury(II)

Schiff base derivates (3, 4 and 5) comprising pseudo cavity with different heteroatoms (O, N and S) were designed, synthesized and explored for their detection behaviour towards diverse metal ions. In UV and fluorescence studies, all three receptors exhibited sensitive response towards Cu2+ while 5 showed sensitivity for Hg2+ also. To explore the synthesized receptors for electrochemical behaviour, voltammetric studies were conducted where 3, 4 and 5 exhibited sensitive response towards Cu2+ with detection limits of 9.8 × 10-7 M, 9.0 × 10-7 M and 1.41 × 10-7 M, respectively. The receptor 5 also showed response towards Hg2+ with detection limit of 5.61 × 10-8 M. The formation of complexes, 3/4+Cu2+ and 5+Cu2+/Hg2+ was supported by large values of binding constant and associated negative free energy change. The binding mechanism of 3, 4 and 5 towards respective metal ions was confirmed using 1H-NMR and HR-MS studies. Further, to utilize the proposed sensors for on-site monitoring of analyte metal ions, carbon paste electrodes (CPEs) were constructed by incorporating 3, 4 and 5. All CPEs showed Nernstian response with lower detection limits and excellent selectivity and successfully utilized for the determination of Cu2+ and Hg2+ in groundwater samples.

Chromium measurement in pharmaceutical samples: a comparative study of three new membrane electrodes with different electron-ion exchangers

The present study deals with synthesis of N-(thiazol-2-ylcarbamothioyl) benzamide. It was utilized as a neutral ionophore for designing three types of chromium(III) sensors including coated wire ion selective electrodes (CW-ISEs), ion selective electrodes with liquid internal electrolyte (LIE-ISEs), and solid-state ion selective electrodes (SS-ISEs). UV-visible spectrophotometry was used to confirm the affinity of N-(thiazol-2-ylcarbamothioyl) benzamide to chromium(III). It was found that a membrane with a composition of 2% NaTPB, 8% ionophore, 60% DBP, and 30% PVC showed the best performance and a Nernstian slope of 21.6 mV per decade. Scanning electron microscopy was used to assess the PVC membrane morphology. The existence of chromium(III) in the liquid membrane matrix was proved by energy-dispersive X-ray spectroscopy. Detection limits for SS-ISE (1 × 10^-6 M) and CW-ISE (1 × 10^-6 M) were enhanced relative to LIE-ISE (1 × 10^-5 M). All three electrodes showed a response time of about 5 s. The sensors' applicable pH range was 4.0-6.0. Fourier transform infrared spectra recorded through the electrode membrane showed that chromium(III) ion can interact with sulfur, nitrogen and oxygen atoms of N-(thiazol-2-ylcarbamothioyl) benzamide. The sensors were utilized as indicator electrodes in chromium(III) potentiometric titration with ethylenediaminetetraacetic acid and for directly measuring chromium(III) in some pharmaceutical samples.

All-solid-state potentiometric salicylic acid sensor for in-situ measurement of plant

Using PEDOT as the conductive polymer, an innovative small-scale sensor for directly measuring salicylate ions in plants was developed, which avoided the complicated sample pretreatment of traditional analytical methods and realized the rapid detection of salicylic acid. The results demonstrate that this all-solid-state potentiometric salicylic acid sensor is easy to miniaturize, has a longer lifetime (≥1 month), is more robust, and can be directly used for the detection of salicylate ions in real samples without any additional pretreatment. The developed sensor has a good Nernst slope (63.6 ± 0.7 mV/decade), the linear range is 10^-2 ~ 10^-6 M, and the detection limit can reach (2.8 × 10^-7 M). The selectivity, reproducibility, and stability of the sensor were evaluated. The sensor can perform stable, sensitive, and accurate in situ measurement of salicylic acid in plants, and it is an excellent tool for determining salicylic acid ions in plants in vivo.

High selective potentiometric sensor for determination of nanomolar con-centration of Cu(II) using a polymeric electrode modified by a graphene/7,7,8,8-tetracyanoquinodimethane nanoparticles

In this paper we present several possibilities for modification of the all-solid-state copper(II)-selective electrodes in order to obtain high stability and selectivity potentiometric sensor signal. The copper(II)-selective electrodes were modified in a simple way by introducing solid contact layer based on graphene or graphene oxide, 7,7,8,8-tetracyanoquinodimethane or its copper salt. Each of electrodes shown a Nernstian response, wide linear range of Cu²⁺ concentration and a low detection limit. Nevertheless, some differences between the groups of electrodes have been noticed and resulted from application of intermediate layers of various compositions. The electrode modified with graphene and 7,7,8,8-tetracyanoquinodimethane nanocomposite exhibited the best potential reproducibility and detection limit. Moreover, prepared sensors were characterized by an improved selectivity for copper(II) in relation to non-modified electrodes. The developed electrodes were successfully used for the Cu²⁺ determination in different samples and results were comparable with those obtained using voltammetry.

Rapid determination of trace level copper in tea infusion samples by solid contact ion selective electrode

A new solid contact copper selective electrode with a poly (vinyl chloride) (PVC) membrane consisting of o-xylylenebis(N,N-diisobutyldithiocarbamate) as ionophore has been prepared. The main novelties of constructed ion selective electrode concept are the enhanced robustness, cheapness, and fastness due to the use of solid contacts. The electrode exhibits a rapid (< 10 seconds) and near-Nernstian response to Cu²⁺ activity from 10^-1 to 10^-6 mol/L at the pH range of 4.0-6.0. No serious interference from common ions was found. The electrode characterizes by high potential stability, reproducibility, and full repeatability. The electrode was used as an indicator electrode in potentiometric titration of Cu(II) ions with EDTA and for the direct assay of tea infusion samples by means of the calibration graph technique. The results compared favorably with those obtained by the atomic absorption spectroscopy (AAS).

Supramolecular based-ligandless ultrasonic assisted-dispersion solidification liquid–liquid microextraction of uranyl ion prior to spectrophotometric determination with dibenzoylmethane

A simple and environmentally friendly method has been developed for preconcentration of uranyl ion by supramolecular based-ligandless ultrasonic assisted-dispersion solidification liquid–liquid microextraction before spectrophotometric detection.

Membrane sensors based on Schiff bases as chelating ionophores--a review

The development of chemical sensors has received widespread attention during the past two decades because of their extensive use in environmental monitoring and clinical analysis via rapid, accurate, reproducible, and low-cost methods. Chemically modified CPEs have frequently been employed as potentiometric sensors in trace analysis for metal ions, organic pollutants and biological substances. Most of these electrodes are operated via the ion-exchange process of the active component incorporated into the carbon paste matrix. This review article concentrates on such achievements in the context of the general development across the field. An overview of potentiometric sensors that are capable of detecting metal ions in environmental samples is presented and discussed. A survey on important advances in potentiometric sensors with regard to high selectivity, lower detection limit, and fast response time is presented in this review article.

Solid-contact polyvinyl chloride membrane electrode based on the bis[(2-(hydroxyethylimino)phenolato]copper(II) complex for trace level determination of copper ions in wastewater

A miniaturized solid-contact polyvinyl chloride membrane electrode based on the bis[(2-(hydroxyethylimino)phenolato]copper(II) complex has been prepared for the determination of Cu(II) ion in real samples. The influence of coating membrane composition, pH, and possible interfering cations on the response of the ion-selective electrode was investigated. A number of membranes at different compositions were prepared and their Cu2+ sensing capabilities were investigated. The best results for Cu2+ sensing was obtained for the electrode membrane containing ionophore − 2-nitrophenyloctyl ether – polyvinyl chloride and potassium tetrakis(p-chlorophenyl)borate in a ratio of 4:65:30:1 (w/w, mg), respectively. The prepared electrode exhibited a near-Nernstian response (28.3 mV/decade) to Cu2+ in the concentration range from 1.0 × 10−6 to 1.0 × 10−1 mol/L with a limit of detection of 8.3 × 10−7 mol/L. The potentiometric response of the electrode was independent from the pH of the test solution in the pH range of 3.0–6.0. The electrode has a very short response time, about 15 s, and it can be used over a period of 3 months without any divergence in potential. The electrode has been successfully applied as an indicator electrode in potentiometric titration of Cu(II) ions with ethylenediaminetetraacetic acid and in the determination of Cu(II) in wastewater of the copper processing industry.

Chronopotentiometric synthesis of quantum dots with efficient surface-derived near-infrared electrochemiluminescence for ultrasensitive microchip-based ion-selective sensing

Metalantidote-stabilized QDs were synthesized via hydrodynamic chronopotentiometry with efficient NIR-ECL derived from the unique surface states for ultrasensitive microchip-based ion-selective sensing.