Solvent Polymeric Membrane Research Articles

Detection of ultra-low activities of heavy metal ions by an array of potentiometric chemical sensors

A sensor array comprising potentiometric chemical sensors with solvent polymeric and chalcogenide glass membranes was developed and applied to the determination of copper, zinc, lead and cadmium ions’ activity at the nmol L−1 concentration levels. Sensors were able to detect copper down to the 0.2 nmol L−1, lead 0.4 nmol L−1, cadmium 0.06 nmol L−1 and zinc 30 nmol L−1 in individual buffer solutions. Collinearity of the sensors’ responses in the buffer and non buffer solutions confirms sensors’ sensitivity to these metals at the very low activity levels. Sensor array was capable to determine simultaneously these cations in the mixed buffer solutions at the background of 0.5 mol L−1 sodium chloride or artificial seawater with the accuracy of about 20%. Copper and zinc could be detected in the mixed solutions down to the concentration of 1 nmol L−1 and lead and cadmium at the concentration of 2 nmol L−1. Therefore, the sensor array is suitable for the detection of copper and zinc at the concentrations corresponding to the chronic seawater criteria, and lead and cadmium at the concentrations corresponding to the acute seawater criteria. The sensor array based on the potentiometric chemical sensors demonstrated a good promise as an instrument for rapid measurements of the ultra-low activities of copper, lead, zinc and cadmium in seawater.

Potentiometric measurement of ascorbate by using a solvent polymeric membrane electrode

A novel potentiometric method for the determination of ascorbate is described in this communication. It is based on ascorbate oxidation with permanganate which is continuously released from the inner reference solution of a ligand-free tridodecylmethylammonium chloride (TDMAC)-based polymeric membrane ion selective electrode (ISE). The ISE potential determined by the activity of permanganate ions released at the sample–membrane phase boundary is increased with the consumption of permanganate. The proposed membrane electrode is useful for continuous and reversible detection of ascorbate at concentrations in 0.1 M NaCl ranging from 1.0 × 10 −6 to 1.0 × 10 −3 M with a detection limit of 2.2 × 10 −7 M.

Potentiometric investigation of the thermodynamic properties of the ternary mixed (NH 4Cl + CaCl 2 + H 2O) electrolyte system

In this work, the results of a potentiometric investigation of the thermodynamic properties of the ternary NH 4Cl + CaCl 2 + H 2O mixed electrolyte system are presented. The reported results are based on the experimental data of a galvanic cell, combining a solvent polymeric ammonium ion-selective membrane electrode (NH 4 + ISE), and an Ag/AgCl electrode. The potentiometric measurements were performed at 298 K by using different series of mixed salt solutions, each characterized by a fixed salt molal ratio ( r = m N H 4 Cl / m CaC l 2 = 0.1 , 0.2 , 1 , and 5 ), but with similar ionic strengths within the series. The semi-empirical Pitzer ion-interaction theory for mixed salts was used for modeling this ternary electrolyte system over the ionic strength ranging from about 0.05 to 5.5 mol/kg. Besides the determination of the mixed θ N H 4 Ca and Ψ N H 4 CaCl ion-interaction parameters, the impact of the effect of the higher order electrostatic terms were also analyzed for this mixed ternary electrolyte system. Finally, based on the potentiometric experimental data and the determined mixing parameters, the calculated values of the osmotic coefficients, the excess Gibbs free energies and the water activities ( a w) were determined for the whole series of the studied ternary mixed electrolyte system.

TERNARY NaCl+LiCl+H2O MIXED ELECTROLYTE SYSTEM: DETERMINATION OF ACTIVITY COEFFICIENTS BASED ON POTENTIOMETRIC METHOD

The mean activity coefficients for NaCl in a ternary electrolyte system were determined by the potentiometric method, at 25°C, using a solvent polymeric (PVC) sodium-selective membrane electrode (Na+ ISE), containing N,N′-dibenzyl-N,N′-diphenyl-1,2-phenylenedioxydiacetamide as ionophore, and combined with an Ag/AgCl electrode. The potentiometric measurements were performed at the same ionic strengths in different series of mixed salt solutions, each characterized by a fixed salt molal ratio r (where r = m1/m2 = 1, 10, 50, 100). The nonideal behavior of the ternary NaCl(m1) + LiCl(m2) + H2O electrolyte system was described based on the Pitzer ion-interaction model for mixed salts over the ionic strength ranging from 0.01 up to about 4 mol/kg. Two- and three-particle Pitzer interaction parameters for a mixed electrolyte system were determined based on potentiometric data, and the critical role of potentiometric selectivity coefficient (K 12) of ISE as limiting factor in the potentiometric measurements was analyzed.

Ion-Selective Electrodes with Three-Dimensionally Ordered Macroporous Carbon as the Solid Contact

Electrodes with three-dimensionally ordered macroporous (3DOM) carbon as the intermediate layer between an ionophore-doped solvent polymeric membrane and a metal contact are presented as a novel approach to solid-contact ion-selective electrodes (SC-ISEs). Due to the well-interconnected pore and wall structure of 3DOM carbon, filling of the 3DOM pores with an electrolyte solution results in a nanostructured material that exhibits high ionic and electric conductivity. The long-term drift of freshly prepared SC-ISEs with 3DOM carbon contacts is only 11.7 microV/h, and does not increase when in contact with solution for 1 month, making this the most stable SC-ISE reported so far. The electrodes show good resistance to the interference from oxygen. Moreover, in contrast to previously reported SC-ISEs with conducting polymers as the intermediate layer, 3DOM carbon is an electron conductor rather than a semiconductor, eliminating any light interference.

Thermodynamic investigation of KCl in the ternary KCl/LiCl/ H 2 O mixed electrolyte system based on potentiometric method

The results of a thermodynamic investigation of KCl salt in the ternary KCl+LiCl+H 2O electrolyte system by potentiometric method are reported in this work. The experimental potentiometric data were obtained from a galvanic cell by combining a solvent polymeric (PVC) potassium-selective membrane electrode (K + ISE), containing Valinomycin as ionophore, and an Ag/AgCl electrode. The measurements were performed, at similar constant ionic strengths, in different series of mixed salt solutions, each characterized by a fixed salt molal ratio r (where r = m 1 / m 2 = 0.1 , 0.2 , 1 , 5 , 10 , and m 1 , m 2 are the molalities of KCl and LiCl, respectively). The non-ideal behaviour of the system was described on the base of the Pitzer ion-interaction model for mixed salts, over the ionic strength ranging from 0.01 up to about 5 mol/kg, at 298.15 K. Based on the obtained Pitzer ion-interaction parameters, the osmotic coefficients, solvent activities, and excess Gibbs free energies were determined for these investigated ternary electrolyte systems.

Amide and Acyl‐Hydrazine Functionalized Calix[4]arenes as Carriers for Hydrogen Phosphate Selective Electrodes

AbstractAnion‐selective solvent polymeric membrane based on hydrogen bond‐forming, neutral ionophores with amide or acyl‐hydrazine groups are described. The use of the two calix[4]arenes results in anion‐selective electrodes with a selectivity for phosphate. The electrodes of the optimum characteristic have the composition of 1 wt% ionophore, 66 wt% o‐NPOE, 33 wt% poly (vinyl chloride) (PVC) and TDMACl (15 or 30 mol% relative to the ionophore 1 and 2, respectively). The optimized membrane electrodes show Nernstian responses towards monohydrogen phosphate (−29.1 and −29.3 mV/decade) based on ionophore 1 and 2, respectively, in a wide concentration range (1.0×10−5 to 1.0×10−2 or 1.0×10−5 to 1.0×10−1 M). The selectivity coefficients are determined with the fixed interference method and the activity ratio method. The electrodes display an anti‐Hofmeister series selectivity pattern and highly selective for HPO42− over Cl−, Br−, CH3COO−, NO3− and SO42−. The lifetime of the electrodes is at least 1 month and their response time is found to be 25 s. The proposed sensors could be put to analytical use both by direct potentiometry as well as potentiometric titration.

Voltammetry of some catamphiphilic drugs with solvent polymeric membrane ion sensors

The transfer of some catamphiphilic drugs across a water–solvent polymeric membrane interface is researched using differential voltammetric techniques with a solvent polymeric membrane ion-sensor and a four-electrode potentiostat. The standard ion transfer potentials of the antiarrhythmic drugs procainamide and quinidine, the antimalarial quinine and the anesthetics bupivacaine, lidocaine, procaine and tetracaine have been determined. In addition to their main pharmacological action, these drugs are of interest as multidrug resistance reversers in the chemotherapy treatment for cancer. The relationship between the pharmacological potency of the different drugs and the corresponding standard ion transfer potentials obtained in the present work has been studied. The relationship between the sensitivity of an amperometric sensor based on the ion transfer across the water–solvent polymeric membrane interface towards the different catamphiphilic drugs and the standard ion transfer potentials has also been studied. A dependence between them was obtained when the applied potential of the sensor was set at a value previous to the diffusion controlled zone.

Glass Nanopore-Based Ion-Selective Electrodes

Glass nanopore-based all-solid-state ion-selective electrodes (ISEs) have been developed to probe the distribution of ionic species at micro- or submicrometer-length scales, e.g., mapping of ion flux through micrometer-sized pores. The all-solid-state ISE was fabricated by sealing a conically etched platinum wire (d = 25-microm; radius of etched tip <10 nm) into a soda lime glass capillary. A Pt disk was exposed by gentle polishing the glass and the disk etched to form a conical pore of submicrometer dimension (radius < approximately 500 nm; depth < approximately 30 microm). Ag was electroplated on the Pt electrode in the pore and gently chloridated to obtain a AgCl/Ag layer within the pore. The AgCl/Ag layer-coated ISE was used as a highly selective Cl- probe in scanning electrochemical microscope experiments to map the ion flux through a micropore. The same ISE was also used as the base transducer of the neutral carrier-doped solvent polymeric membrane. The optimized polymer membranes used for the glass nanopore-based all-solid-state ISE require a higher ratio of plasticizer/polymer (9/1) compared to those for conventional ISE (2/1). An ISE based on deposition of an IrO2 layer at the base of a glass nanopore electrode exhibited a highly sensitive response (79.7 +/- 2.3 mV/pH) to variations in pH and could be used for approximately 3 weeks.

Potentiometric liquid membrane pH sensors based on calix[4]-aza-crowns

The calix[4]-aza-crown derivatives have been used in polymeric ion selective electrodes (ISEs) for pH sensing. The membranes containing ionophores and cation exchangers showed near Nernstian response to hydrogen ions and wide dynamic range. New carrier based electrodes exhibited high selectivity over alkali metal ions. The binding properties of ionophores with hydrogen ions (acidity constants pKa) in solvent polymeric membranes were characterized in situ by the so-called sandwich membrane method. The influence of membrane solvents (plasticizers) and the types of the ion exchangers were studied.

Thermodynamic investigation of a ternary mixed electrolyte (NaCl/MgCl 2/H 2O) system using Na + solvent polymeric membrane ion-selective electrode

This work reports the results of a thermodynamic investigation of the ternary NaCl–MgCl 2–H 2O mixed electrolyte system. The potentiometric measurements were performed at 298 K, using a galvanic cell by combining a solvent polymeric sodium ion-selective membrane electrode (Na + ISE), containing a mixture of N, N′-dibenzyl- N, N′-diphenyl-1,2-phenylene-dioxydiacetamide as ionophore, and an Ag/AgCl electrode. Different series of mixed salt solutions, each characterized by a fixed salt molal ratio r ( r = m NaCl / m MgC l 2 = 0.100 , 0.199, 0.995, 4.990 and 10.364) but with similar ionic strengths, were used in this investigation. The modeling of the ternary electrolyte system was based on the Pitzer ion-interaction semi-empirical theory for mixed salts, over the ionic strength ranging from 0.05 to 4.3 mol/kg. Pitzer ion-interaction parameters for mixed salts including the effect of the higher-order electrostatic terms were determined for this system. Moreover, based on the potentiometric experimental data and the determined mixing parameters, the values of the mean activity coefficients, the osmotic coefficients, the excess Gibbs free energies and the water activities ( a w) were reported for the whole series of the studied ternary mixed electrolyte systems. Finally, the impact of the magnitude of the potentiometric selectivity coefficient of this Na + ISE on the quality of the potentiometric data revealed that Nernst equation could suitably be used for the evaluation of mean activity coefficients (with at least 3 decimal numbers), for the ionic strength beyond 0.25 mol/kg and for mixed electrolyte systems with molal salt ratio higher than r = m NaCl / m MgC l 2 ≥ 5 .

Differential Pulse Voltammetry and Additive Differential Pulse Voltammetry with Solvent Polymeric Membrane Ion Sensors

The ion transfer across the water-solvent polymeric membrane interface is investigated by using a new device based on a modification of a commercial ion-selective electrode body that permits the accommodation of a platinum counter electrode inside the inner filling solution compartment and, therefore, use of a four-electrode potentiostat with ohmic drop compensation. This device is used here to apply two different double potential pulse techniques--differential pulse voltammetry and additive differential pulse voltammetry--which are more advantageous than other voltammetric techniques, such as normal pulse voltammetry or cyclic voltammetry, for the determination of the characteristic electrochemical parameters of the system. This is due to the concurrence of two factors in these double potential pulse techniques, the peak-shaped response together with a considerable reduction of undesirable current contributions.

Pyrrole Azocrown Ethers. Synthesis, Complexation, Selective Lead Transport and Ion-Selective Membrane Electrode Studies

New 21-membered lipophilic crown ethers, each incorporating a pyrrole unit and two azo groups as macrocyclic ring components, have been synthesized. The complexation behavior of these and two further macrocycles has been investigated in acetonitrile. These ligand systems have been employed as ionophores in transport experiments involving the competitive transport behavior of an equimolar mixture of Co2 + , Ni2 + , Cu2 + , Zn2 + , Cd2 + , Ag+ and Pb2 + across a water (pH 4.9)/chloroform/water (pH 3) bulk membrane system. In each case transport selectivity for lead(II) was obtained. The macrocycles have been incorporated in solvent polymeric membrane electrodes and their behavior towards a selection of metal ions, including those mentioned above, is reported.

Highly Selective Recognition of Adenine Nucleobases by Synthetic Hosts with a Linked Five‐Six‐Five‐Membered Triheteroaromatic Structure and the Application to Potentiometric Sensing of the Adenine Nucleotide

A new structure for an adenine-selective host molecule, featuring the pertinent link of five-six-five-membered heteroaromatic rings and two carbamoyl NH sites, was developed. This structure provides a correctly oriented array of complementary hydrogen bonding sites for the adenine nucleobase, which exploits both Watson-Crick and Hoogsteen-type interactions. The complexation with adenine nucleobases by multiple hydrogen bonding was supported by (1)H NMR spectroscopy. This type of host displayed high selectivity in complexation, with an accompanying fluorescent response to lipophilized adenosine in CHCl(3). Furthermore, a remarkably selective potentiometric response was attained for adenosine 5'-monophosphate over 5'-GMP, 5'-CMP, and 5'-UMP by using an ion-selective electrode with a PVC-supported solvent polymeric membrane. This indicates recognition of water-soluble nucleotide guests through the membrane-water interface. These findings are expected to form a reliable basis for the development of artificial sensing systems for mononucleotides in biological systems.

Detection of alcohols in beverages: An application of porphyrin-based Electronic tongue

According to the World Drink Trends data monitor, a stable growth of alcohol consumption across most of the countries has been registered in the last years. Quality evaluation of alcoholic beverages becomes, hence an important industrial task and fast and inexpensive analyzers are the targets of interest. In a present study we aimed to develop an analytical instrument which may permit a rapid, online control of ethanol content in beverages of various sources in a wide range of concentrations. Potentiometric responses of porphyrin-based solvent polymeric membranes towards several aliphatic monatomic alcohols in single-, two- and four-component solutions were evaluated. Sensitivity of membranes in single-component alcohol solutions decreased in the following order: ethanol > methanol > isobutyl alcohol. A performance of potentiometric porphyrin-based Electronic tongue (ET) for analysis of alcoholic beverages is described. The utility of ET system for an identification of beverages made of two different source materials: grape and barley has been shown. Simultaneously a scale of beverages’ ‘alcoholic degree’ in ethanol concentration units was evolved. The alcoholic strength of several commercial sorts of wine, beers, grappa and whiskey was successfully evaluated according to the evolved scale.

Novel potentiometric and optical silver ion-selective sensors with subnanomolar detection limits

Ten Ag +-selective ionophores have been characterized in terms of their potentiometric selectivities and complex formation constants in solvent polymeric membranes. The compounds with π-coordination show much weaker interactions than those with thioether or thiocarbamate groups as the coordinating sites. Long-term studies with the best ionophores show that the lower detection limit of the best Ag + sensors can be maintained in the subnanomolar range for at least 1 month. The best ionophores have also been characterized in fluorescent microspheres. The so far best lower detection limits of 3 × 10 −11 M (potentiometrically) and 2 × 10 −11 M Ag + (optically) are found with bridged thiacalixarenes.

Crown bridged thiacalix[4]arenes as cesium-selective ionophores in solvent polymeric membrane electrodes

Novel 1,3-alternate thiacalix[4]mono- and biscrown-6 ethers were studied as ionophores in poly(vinyl chloride) membrane electrodes. Their selectivity behavior was characterized with respect to large number of cations, including potential interferents in environmental samples, and the membrane composition was optimized for cesium ion response. Among the ionophores, 1,3-alternate thiacalix[4]mono(crown-6) ether showed, especially high selectivity for cesium over other alkali-metal ions. Transition and heavy metal ions did not interfere seriously with the electrode response, which indicates that the bridging sulfur atoms do not take part in the ion recognition process. The potentiometric cesium responses of all electrodes involved in this study were found close to Nernstian and the detection limits were lower than 10 −7 M. The Cs +/Na + selectivity of the different ionophore-based sensors and the solvent extraction ability of the ligands were interpreted based on the respective constants of complex formation.

Quantitative determination of heparin levels in serum with microtiter plate-format optode

A new assay method has been developed for the quantitative determination of heparin in serum using a microtiter plate-format optode (MPO). Heparin and proton in physiological sample are favorably co-extracted into the solvent polymeric optode membrane containing both cationic lipophilic additive, tridodecylmethyl ammonium chloride (TDMAC), and proton-selective ionophore, 3-hydroxy-4-(4-nitrophenylazo)-phenyloctadecanoate (ETH 2412), resulting in the absorbance change of the membrane to varying heparin levels. The optimized MPO composition contains low polymer-to-plasticizer ratio compared to those of conventional ion-selective optodes or electrodes, i.e., poly(vinyl chloride) (20.0)/dioctylsebacate (76.3)/ETH 2412 (1.7)/TDMAC (1.0) (wt.%): it resulted in a quantitative response to heparin from 0 to 15 unit/mL in serum with high sensitivity. The heparin–protamine titration on the MPO could provide rapid and precise determination of heparin. It was shown that the heparin levels in serum sample could be determined from the rate of absorbance change over time (Δ A/Δ t); this method was more effective than the direct absorbance measurement in minimizing the interferences from color and turbidity of serum samples. MPO has been developed as a high throughput and convenient disposable sensing device, and may find a wide application in the determination of polyions and charged macromolecules.

Nano-level monitoring of ytterbium(III) by a novel ytterbium(III) membrane sensor based on 3-hydroxy- N′-[(2-hydroxyphenyl) methylene]-2-naphthohydrazide

In this work, a highly sensitive ytterbium(III)-selective solvent polymeric membrane sensor based on 3-hydroxy- N′-[(2-hydroxyphenyl)methylene]-2-naphthohydrazide (HPMN), poly(vinyl chloride) (PVC), the plasticizer dibutyl phthalate (DBP), and sodium tetraphenyl borate (NaTPB) anionic site is described. This sensor responds to Yb(III) activity in a linear range from 1.0 × 10 −7 to 1.0 × 10 −2 M, with a slope of 19.2 ± 0.2 mV per decade and a detection limit of 4.0 × 10 −8 M at a pH range of 3.0–8.5. It has a very fast response time of <6 s in the whole concentration range, and can be used for at least 6 weeks without any considerable divergences in its potentials. The proposed sensor revealed comparatively good selectivity with respect to common alkali, alkaline earth, transition and heavy metal ions, and especially lanthanide ions. It was used as an indicator electrode in the potentiometric titration of Yb(III) ions with EDTA and in determination of concentration of Yb 3+ ions in binary mixtures.

Potentiometric determination of activity coefficients for NH 4Cl in the ternary NH 4Cl/LiCl/H 2O mixed electrolyte system

This work reports the results of the determination of mean activity coefficients for NH 4Cl in ternary (NH 4Cl( m 1) + LiCl( m 2) + H 2O) electrolyte system by potentiometric method at 25 °C. The experimental potentiometric data were obtained by combining a solvent polymeric (PVC) ammonium-selective membrane electrode ( NH 4 + ISE), containing a mixture of nonactin/monactin as ionophore, and an Ag|AgCl electrode. The measurements were performed, at constant ionic strength, in different series of mixed salt solutions characterized by a fixed salt mole ratio r (where r = m 1/ m 2 = 25, 50, 75, 100). The non-ideal behavior of the system was described on the base of the Pitzer ion-interaction model for mixed salts, over the molality ranging from 0.01 to 3 mol/kg.