Highly Selective and Sensitive Copper(II) Membrane Sensors Based on 6-Methyl-4-(1-phenylmethylidene)amino-3-thioxo-1,2,4-triazin-5-one as a New Neutral Ionophore

Ligands as copper and nickel ionophores: Applications and implications on wastewater treatment

Modern society depends on many finite natural resources, from which metals are of great importance. Copper and nickel's relevance is due to their vast applications, resulting in high market value and demand. As such, their polluting emissions are also significant and their removal from wastewaters is imperative. Moreover, effluent treatment techniques can be used to recover the metallic cations, via selective processes. In this review, copper and nickel selective ligands in the literature are surveyed. These are most commonly Schiff bases, along with crown ethers and porphyrins. They are usually employed in ion sensing (colorimetric chemosensors or electrodes) with great success - the disruption in response of colorimetric sensors is up to 7% and binding constants are usually at least one order of magnitude greater with the desired cation than with interferents. However, modified adsorbents are also reported. The possibilities of using ionophores in wastewater cleaning, allowing the treatment of effluents and the selective recovery of valuable materials, and their implications on new green policies is discussed.

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.

Potentiometric detection and removal of copper using porphyrins

Background

Copper is an essential trace element with a great importance in industry, environment and biological systems. The great advantage of ion-selective sensors in comparison with other proposed techniques is that they are measuring the free metal ion activity which is responsible for their toxicity. Porphyrins are known to be among the best ionophores in formulation of ion-selective sensors.

Results

A symmetrically substituted meso-porphyrin, namely: 5,10,15,20-tetrakis(4-allyloxyphenyl)porphyrin (TAPP) was used in the construction of a new copper selective-sensor and was also tested for the removal of copper from waste waters. The potentiometric response characteristics (slope and selectivity) of copper-selective electrodes based on TAPP in o-nitrophenyloctylether (o-NPOE), dioctyl phtalate (DOP) and dioctyl sebacate (DOS) plasticized with poly(vinyl chloride) membranes are compared.

Conclusions

The best results were obtained for the membrane plasticized with DOP. The sensor has linear response in the range 1x10^-7 – 1x10^-1 M with 28.4 ± 0.4 mV/decade near-Nernstian slope towards copper ions and presents good selectivity. Due to its chelating nature, the same porphyrin was also tested for the retention of copper from synthetic copper samples, showing a maximum adsorption capacity of 280 mg/g.

Electrochemical Analysis of Some Toxic Metals by Ion-Selective Electrodes

An overview of potentiometric sensors that are capable of detecting toxic heavy metal ions in environmental samples is presented and discussed. Notwithstanding the tremendous work performed so far, it is obvious that still several limitations do exist in terms of selectivity, limits of detection, dynamic ranges, applicability to specific problems, and reversibility. A survey on important advances in potentiometric sensors with regard to high selectivity, lower detection limit, fast response time, and on-line environmental analysis is presented in this review article. [Supplemental materials are available for this article. Go to the publisher's online edition of Critical Reviews in Analytical Chemistry to view the free supplemental file.].

Poly(vinyl) chloride membrane copper-selective electrode based on 1-phenyl-2-(2-hydroxyphenylhydrazo)butane-1,3-dione

1-Phenyl-2-(2-hydroxyphenylhydrazo)butane-1,3-dione (H(2)L) was used as an effective ionophore for copper-selective poly(vinyl) chloride (PVC) membrane electrodes. Optimization of the composition of the membrane and of the conditions of the analysis was performed, and under the optimized conditions the electrode has a detection limit of 6.30×10(-7) M Cu(II) at pH 4.0 with response time 10s and displays a linear EMF versus log[Cu(2+)] response over the concentration range 2.0×10(-6) to 5.0×10(-3) M Cu(II) with a Nernstian slope of 28.80±0.11 mV/decade over the pH range of 3.0-8.0. The sensor is stable for 9 weeks and exhibits good selectivity with respect to alkali, alkali earth and transition metal ions (e.g. Na(+), K(+), Ba(2+), Ca(2+), Zn(2+), Cd(2+), Co(2+), Mn(2+), Ni(2+), Fe(2+), Al(3+)) in the 3.0-8.0 pH range. It was successfully applied for the direct determination of copper(II) in zinc, aluminum and nickel based alloys, in soils polluted by oil, and as an indicator electrode for potentiometric titration of copper ions with EDTA.

Developments in the Field of Conducting and Non-conducting Polymer Based Potentiometric Membrane Sensors for Ions Over the Past Decade

Many research studies have been conducted on the use of conjugated polymers in the construction of chemical sensors including potentiometric, conductometric and amperometric sensors or biosensors over the last decade. The induction of conductivity on conjugated polymers by treating them with suitable oxidizing agents won Heeger, MacDiarmid and Shirakawa the 2000 Nobel Prize in Chemistry. Common conjugated polymers are poly(acetylene)s, poly(pyrrole)s, poly(thiophene)s, poly(terthiophene)s, poly(aniline)s, poly(fluorine)s, poly(3-alkylthiophene)s, polytetrathiafulvalenes, polynapthalenes, poly(p-phenylene sulfide), poly(p-phenylenevinylene)s, poly(3,4-ethylenedioxythiophene), polyparaphenylene, polyazulene, polyparaphenylene sulfide, polycarbazole and polydiaminonaphthalene. More than 60 sensors for inorganic cations and anions with different characteristics based on conducting polymers have been reported. There have also been reports on the application of non-conducting polymers (nCPs), i.e. PVC, in the construction of potentiometric membrane sensors for determination of more than 60 inorganic cations and anions. However, the leakage of ionophores from the membranes based on these polymers leads to relatively lower life times. In this article, we try to give an overview of Solid-Contact ISE (SCISE), Single-Piece ISE (SPISE), Conducting Polymer (CP)-Based, and also non-conducting polymer PVC-based ISEs for various ions which their difference is in the way of the polymer used with selective membrane. In SCISEs and SPISEs, the plasticized PVC containing the ionophore and ionic additives govern the selectivity behavior of the electrode and the conducting polymer is responsible of ion-to-electron transducer. However, in CPISEs, the conducting polymer layer is doped with a suitable ionophore which enhances the ion selectivity of the CP while its redox response has to be suppressed.

Schiff's Bases and Crown Ethers as Supramolecular Sensing Materials in the Construction of Potentiometric Membrane Sensors

Ionophore incorporated PVC membrane sensors are well-established analyticaltools routinely used for the selective and direct measurement of a wide variety of differentions in complex biological and environmental samples. Potentiometric sensors have someoutstanding advantages including simple design and operation, wide linear dynamic range,relatively fast response and rational selectivity. The vital component of such plasticizedPVC members is the ionophore involved, defining the selectivity of the electrodes' complexformation. Molecular recognition causes the formation of many different supramolecules.Different types of supramolecules, like calixarenes, cyclodextrins and podands, have beenused as a sensing material in the construction of ion selective sensors. Schiff's bases andcrown ethers, which feature prominently in supramolecular chemistry, can be used assensing materials in the construction of potentiometric ion selective electrodes. Up to now,more than 200 potentiometric membrane sensors for cations and anions based on Schiff's bases and crown ethers have been reported. In this review cation binding and anioncomplexes will be described. Liquid membrane sensors based on Schiff's bases and crownethers will then be discussed.

Determination of gadolinium(III) ions in soil and sediment samples by a novel gadolinium membrane sensor based on 6-methyl-4-{[1-(2-thienyl)methylidene]amino}3-thioxo-3,4-dihydro-1,2,4-triazin-5-(2H)-one

Highly selective and sensitive poly(vinyl chloride) (PVC) membrane electrodes based on 6-methyl-4-{[1-(2-thienyl)methylidene]amino}3-thioxo-3,4-dihydro-1,2,4-triazin-5-(2H)-one (MATDTO) as new carriers for gadolinium ion-selective electrode was reported. The membrane solutions containing PVC, o-nitrophenyl octyl ether (NPOE) as plasticizer, sodium tetraphenyl borate (NaTPB) as lipophilic ionic additive, and MATDTO, displays a calibration response for Gd3+ ions over a wide concentration range of 1.0x10(-6)-1.0x10(-1) M with Nernstian slopes of 19.8+/-0.2 mV per decade and a detection limit as 5.8x10(-7) M. The sensor has a relatively fast response time of <10 s and can be used in the pH range 3.2-8.7 for at least 2 months without any significant divergence in potentials. The selectivity coefficients for mono-, di-, and trivalent cations indicate good selectivity for Gd(III) ions over a large number of interfering cations. The membrane sensor was used as an indicator electrode in the potentiometric titration of Gd(III) ions with EDTA. The proposed electrode was also applied to the determination of concentration of Gd(III) ions in soil and sediment samples and validation with CRMs.

Synthesis of N'-(1-pyridin-2-ylmethylene)-2-furohydrazide and its application in construction of a highly selective PVC-based membrane sensor for La(III) ions

A highly La(III) ion-selective PVC membrane sensor based on N'-(1-pyridin-2-ylmethylene)-2-furohydrazide (NPYFH) as an excellent sensing material was successfully developed. The electrode shows a good selectivity for La(III) ion with respect to most common cations including alkali, alkaline earth, transition and heavy metal ions. The proposed sensor exhibits a wide linear response with slope of 19.2 +/- 0.6 mV per decade over the concentration range of 1.0 x 10(-6) - 1.0 x 10(-1) M, and a detection limit of 7.0 x 10(-7) M of La(III) ions. The sensor response is independent of pH in the range of 3.5-10.0. The proposed electrode was applied as an indicator electrode in potentiometric titration of La(III) ion with EDTA.

Dysprosium(III) Ion-Selective Electrochemical Sensor Based on 6-Hydrazino-1,5-diphenyl-6,7-dihydropyrazolo[3,4-d]pyrimidine-4(5H)-imine

A Dy(III) ion-selective electrode based on 6-hydrazino-1,5-diphenyl-6,7-dihydropyrazolo[3,4-d]pyrimidine-4(5H)-imine (HDDPI) as an excellent sensing material was developed. The sensor exhibits a Nernstian behavior (a slope of 19.6 ± 0.3 mV per decade) over a wide concentration range (from 1.0 × 10-1 to 8.0 × 10-7 M Dy) with a detection limit of 4.2 × 10-7 M. The sensor response is independent of pH of the solution in the pH range 3.5-8.3. The sensor possesses the advantages of short conditioning time, fast response time (<10 s) and in particular, good selectivity and sensitivity to the dysprosium ion in the presence of a variety of cations, including alkali, alkaline earth, transition and heavy metal ions. The sensor also showed a great enhancement in selectivity coefficients for dysprosium ions, in comparison with the formerly mentioned dysprosium sensors. The electrode can be used for at least 10 weeks without any considerable divergence in the potentials. The proposed electrode was successfully used as an indicator electrode in potentiometric titration of Dy(III) ions with EDTA. The membrane sensor was also used in the determination of concentration of F- ions in some mouth washing solutions and in the Dy3+ recovery from solution.

A Copper(II)-selective PVC Membrane Electrode Based on a Macrocyclic Ligand, 1,2,5,6,8,11-Hexaazacyclododeca-7,12-dione-2,4,8,10-tetraene

An attempt has been made to develop a highly selective Cu2+-ion selective electrode based on a poly(vinyl chloride) based sensor using 1,2,5,6,8,11-hexaazacyclododeca-7,12-dione-2,4,8,10-tetraene as ionophore with 61.5% DBP in the presence of 29% PVC, 4.5% ionophore and 5% NaTBP as an anion excluder. The sensor exhibits a near Nernstian potential response of 29.5 +/- 0.3 mV per decade over a wide concentration range (2.0 x 10(-7) - 1 x 10(-1) M) with a detection limit of 8.1 x 10(-8) M between pH 3 - 11 with a fast response time of < 5 s. The selectivity coefficient values, as determined by the matched potential method (MPM), indicate excellent selectivity for Cu(II) ions over a large number of ions. The proposed sensor exhibits an adequate shelf life (4 - 5 months) with good reproducibility. The quantification of Cu(II) in electroplating wastewater and various brands of Indian tea was successfully achieved using the proposed sensor.