An electronic tongue using potentiometric all-solid-state PVC-membrane sensors for the simultaneous quantification of ammonium and potassium ions in water

The simultaneous determination of NH₄⁺ and K⁺ in solution has been attempted using a potentiometric sensor array and multivariate calibration. The sensors used are rather non-specific and of all-solid-state type, employing polymeric (PVC) membranes. The subsequent data processing is based on the use of a multilayer artificial neural network (ANN). This approach is given the name "electronic tongue" because it mimics the sense of taste in animals. The sensors incorporate, as recognition elements, neutral carriers belonging to the family of the ionophoric antibiotics. In this work the ANN type is optimized by studying its topology, the training algorithm, and the transfer functions. Also, different pretreatments of the starting data are evaluated. The chosen ANN is formed by 8 input neurons, 20 neurons in the hidden layer and 2 neurons in the output layer. The transfer function selected for the hidden layer was sigmoidal and linear for the output layer. It is also recommended to scale the starting data before training. A correct fit for the test data set is obtained when it is trained with the Bayesian regularization algorithm. The viability for the determination of ammonium and potassium ions in synthetic samples was evaluated; cumulative prediction errors of approximately 1% (relative values) were obtained. These results were comparable with those obtained with a generalized regression ANN as a reference algorithm. In a final application, results close to the expected values were obtained for the two considered ions, with concentrations between 0 and 40 mmol L^–1.     

Back‐propagation artificial neural network and attenuated total reflectance‐Fourier transform infrared spectroscopy for diagnosis of basal cell carcinoma by blood sample analysis

A diagnostic method for the cancer, based on investigation of infrared spectra of blood samples, has been developed. The two‐layer modified principal component feed forward back‐propagation artificial neural network (BP‐ANN) was used to classify the attenuated total reflectance‐Fourier transform infrared (ATR‐FTIR) spectra of blood samples obtained from healthy people and those with basal cell carcinoma (BCC). Results showed 98.33% of accuracy, in comparison with the current clinical methods. In the first step, 20 blood samples (10 normal and 10 cancer cases) were applied to construct the calibration model. Spectroscopic studies were performed in 900–1800 cm⁻¹ spectral region with 3.85 cm⁻¹ data space. In order to modify the capability of ANN in prediction of test samples, two different algorithms were applied. The obtained results confirmed the compatibility of the proposed network with the architecture of 20‐8‐2 (input‐hidden‐output) with the pattern model. It was concluded that analysis of blood samples by ATR‐FTIR spectroscopy and ANN chemometric technique would be a reliable approach for detection of BCC. Copyright © 2009 John Wiley & Sons, Ltd.     

Paper‐Based Electronic Tongue

We present a low cost paper‐based electronic tongue capable of discriminating forged water samples. System comprises of 4 paper‐based potentiometric sensors (sensitive to Cl^?, Na⁺/K⁺, Ca²⁺/Mg²⁺, ) and a traditional Ag/AgCl reference electrode. Different electrode materials and methods of insulation were tested with best results obtained for pencil graphite and lamination. The presented electronic tongue was able to distinguish tap and lake water from mineral water samples (PCA – Principal Component Analysis and KNN ? K‐nearest neighbour). In total 14 different water samples were used in this study. Sensors presented good signal repeatability, selectivity and reasonable sensitivity.     

Detection of layer‐by‐layer self‐assembly multilayer films by low‐temperature plasma mass spectrometry

The detection of layer‐by‐layer self‐assembly multilayer films was carried out using low‐temperature plasma (LTP) mass spectrometry (MS) under ambient conditions. These multilayer films have been prepared on quartz plates through the alternate assembling of oppositely charged 4‐aminothiophenol (4‐ATP) capped Au particles and thioglycolic acid (TGA) capped Ag particles. An LTP probe was used for direct desorption and ionization of chemical components on the films. Without the complicated sample preparation, the structure information of 4‐ATP and TGA on films was studied by LTP‐MS. Characteristic ions of 4‐ATP (M) and TGA (F), including [M]^+?, [M‐NH₂]⁺, [M‐HCN‐H]⁺, and [F + H]⁺, [F‐H]⁺, [F‐OH]⁺, [F‐COOH]⁺ were recorded by LTP‐MS on the films. However, [M‐CS‐H]⁺ and [F‐SH]⁺ could not be observed on the film, which were detected in the neat sample. In addition, the semi‐quantitative analysis of chemical components on monolayer film was carried out, and the amounts of 4‐ATP and TGA on monolayer surface were 45 ng/mm² and 54 ng/mm², respectively. This resulted the ionization efficiencies of 72% for 4‐ATP and 54% for TGA. In order to evaluate the reliability of present LTP‐MS, the correlations between this approach and some traditional methods, such as UV–vis spectroscopy, atomic force microscope and X‐ray photoelectron spectroscopy were studied, which resulted the correlation coefficients of higher than 0.9776. The results indicated that this technique can be used for analyzing the films without any pretreatment, which possesses great potential in the studies of self‐assembly multilayer films. Copyright © 2013 John Wiley & Sons, Ltd.     

Void‐Assisted Ion‐Paired Proton Transfer at Water–Ionic Liquid Interfaces

At the water–trihexyl(tetradecyl)phosphonium tris(pentafluoroethyl)trifluorophosphate ([P_14,6,6,6][FAP]) ionic liquid interface, the unusual electrochemical transfer behavior of protons (H⁺) and deuterium ions (D⁺) was identified. Alkali metal cations (such as Li⁺, Na⁺, K⁺) did not undergo this transfer. H⁺/D⁺ transfers were assisted by the hydrophobic counter anion of the ionic liquid, [FAP]^?, resulting in the formation of a mixed capacitive layer from the filling of the latent voids within the anisotropic ionic liquid structure. This phenomenon could impact areas such as proton‐coupled electron transfers, fuel cells, and hydrogen storage where ionic liquids are used as aprotic solvents.     

Subnanometre depth resolution in sputter depth profiling of Si layers using grazing‐incident low‐energy O2+ and Ar+ ions

The sputter damage profiles of Si(100) by low‐energy O₂⁺ and Ar⁺ ion bombardment at various angles of incidence were measured using medium‐energy ion scattering spectroscopy. It was observed that the damaged Si surface layer can be minimized down to 0.5–0.6 nm with grazing‐incident 500 eV Ar⁺ and O₂⁺ ions at 80°. To illustrate how the damaged layer thickness can be decreased down to 0.5 nm, molecular dynamics simulations were used. The SIMS depth resolution estimated with trailing‐edge decay length for a Ga delta‐layer in Si with grazing‐incident 650 eV O₂⁺ was 0.9 nm, which is in good agreement with the measured damaged layer thickness. Copyright © 2004 John Wiley & Sons, Ltd.     

Determination of Some Heavy Metal Ions with a Carbon Paste Electrode Modified by Poly(glycidylmethacrylate‐methylmethacrylate‐divinylbenzene) Microspheres Functionalized by 2‐Aminothiazole

A carbon paste electrode modified with 2‐aminothiazole functionalized poly(glycidylmethacrylate‐methylmethacrylate‐divinylbenzene) microspheres was used for trace determination of mercury, copper and lead ions. After the open‐circuit accumulation of the heavy metal ions onto the electrode, the sensitive anodic stripping peaks were obtained by square wave anodic stripping voltammetry (SWASV)). Many parameters such as the composition of the paste, pH, preconcentration time, effective potential scan rate and stirring rate influence the response of the measurement. The procedures were optimized for most sensitive and reliable determinations of the desired species. For a 10‐min preconcentration time in synthetic solutions at optimum instrumental and experimental conditions, the detection limit (LOD) was 12.3, 2.8 and 4.5 μg L^?1 for mercury, copper and lead, respectively. The limits of detection may be enhanced by increasing the preconcentration time. For example, LOD of mercury and copper was 4.9 and 1.0 μg L^?1 for fifteen minutes preconcentration time. The sensitivity may also considered to be increased by using a more suitable electrode composition targeting the more conductive electrode with lesser amount of modified polymer for sub‐μg L^?1 levels of heavy metal ions. The optimized method was successfully applied to the determination of copper in tap water and waste water samples by means of standard addition procedure. The copper content found was comparable with the certified concentration of the waste water sample. The calibration plots for mercury and lead spiked real samples were also drawn.     

Mercury‐modified Lignosulfonate‐stabilized Gold Nanoparticles as an Alternative Material for Anodic Stripping Voltammetry of Thallium

Lignosulfonate‐stabilized gold nanoparticles (AuNPs‐LS) were synthesized and subsequently used as a complexing agent for mercury ions. The obtained AuNPs‐LS/Hg²⁺ complex was characterized by means of various physicochemical techniques such as UV‐vis spectroscopy, transmission electron microscopy and cyclic voltammetry. Furthermore, the resulting complex was evaluated as an electrode modifier for the development of amperometric sensors. Upon sufficient negative potential, the bound mercury ions are reduced to form an amalgam with AuNPs‐LS. Thus, the performance of glassy carbon electrode (GCE) modified by AuNPs‐LS/Hg film was investigated as an electrochemical sensor in the determination of Tl⁺ ions in a 0.05 M EDTA at pH 4.5. The presence of the mercury containing film improves the analyte accumulation due to its ability to form a fused amalgam with thallium. The presented data indicate that the GCE/AuNPs‐LS/Hg modified electrode shows better performance toward Tl⁺ determination in comparison to bare GCE. The stripping anodic peak current of thallium was linear over its concentration range from 1.7⋅10⁻⁷ to 5.0⋅10⁻⁶ M. The detection limit (3σ) was estimated to be 1.4⋅10⁻⁷ M. The proposed method was successfully applied for the determination of thallium ions in real samples of soil derived from the area of the copper smelter near Głogów (Poland).     

An experimental and computational approach to pH‐dependent self‐aggregation of poly(2‐isopropyl‐2‐oxazoline)

Besides temperature, self‐aggregation of poly(2‐isopropyl‐2‐oxazoline) (PIPOX) can also be triggered via pH in aqueous solution (25 °C, pH > 5). Lowest energy structures and interaction energies of PIPOX with H₃O⁺, OH^?, and H₂O were calculated by DFT methods showed that, in addition to their ability to protonate PIPOX, H₃O⁺ ions had strong interaction with both water and PIPOX in acidic conditions. H₃O⁺ ions acted as compatibilizer between PIPOX and water and increased the solubility of PIPOX. OH^? ions were found to have stronger interaction with water compared to PIPOX resulting in desorption of water molecules from PIPOX phase and decreased solubility, leading to enhanced hydrophobic interactions among isopropyl groups of PIPOX and formation of aggregates at high pH. Results concerning the effect of end‐groups on aggregate size were in good agreement with statistical mechanics calculations. Moreover, the effect of polymer concentration on the aggregate size was examined. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 210–221     

Potentiometric Ag+ Sensors Based on Conducting Polymers: A Comparison between Poly(3,4‐ethylenedioxythiophene) and Polypyrrole Doped with Sulfonated Calixarenes

Potentiometric Ag⁺ sensors were prepared by galvanostatic electropolymerization of 3,4‐ethylenedioxythiophene (EDOT) and pyrrole (Py) on glassy carbon electrodes by using sulfonated calixarenes as doping ions. Poly(3,4‐ethylenedioxythiophene) (PEDOT) and polypyrrole (PPy) doped with p‐sulfonic calix[4]arene (C4S), p‐sulfonic calix[6]arene (C6S) and p‐sulfonic calix[8]arene (C8S) were compared. PEDOT and PPy doped with poly(styrene sulfonate) (PSS) were also included for comparison. The analytical performance of the conducting polymer‐based Ag⁺ sensors was studied by potentiometric measurements. All conducting polymer and dopant combinations showed sensitivity and selectivity to Ag⁺ compared to several alkali, alkaline‐earth, and transition‐metal cations. The type of the conducting polymer used for the fabrication of the electrodes was found to have a more significant effect on the selectivity of the electrodes to Ag⁺ than the ring size of the sulfonated calixarenes used as dopants. Selected conducting polymer‐based sensors were studied by cyclic voltammetry (CV) and energy dispersive analysis of X‐rays (EDAX) measurements. Results from the EDAX measurements show that both PEDOT‐ and PPy‐based membranes accumulate silver.     

ACE applied to the quantitative characterization of benzo‐18‐crown‐6‐ether binding with alkali metal ions in a methanol–water solvent system

ACE was applied to the quantitative evaluation of noncovalent binding interactions between benzo‐18‐crown‐6‐ether (B18C6) and several alkali metal ions, Li⁺, Na⁺, K⁺, Rb⁺ and Cs⁺, in a mixed binary solvent system, methanol–water (50/50 v/v). The apparent binding (stability) constants (K_b) of B18C6–alkali metal ion complexes in the hydro‐organic medium above were determined from the dependence of the effective electrophoretic mobility of B18C6 on the concentration of alkali metal ions in the BGE using a nonlinear regression analysis. Before regression analysis, the mobilities measured by ACE at ambient temperature and variable ionic strength of the BGE were corrected by a new procedure to the reference temperature, 25°C, and the constant ionic strength, 10 mM . In the 50% v/v methanol–water solvent system, like in pure methanol, B18C6 formed the strongest complex with potassium ion (log K_b=2.89±0.17), the weakest complex with cesium ion (log K_b=2.04±0.20), and no complexation was observed between B18C6 and the lithium ion. In the mixed methanol–water solvent system, the binding constants of the complexes above were found to be about two orders lower than in methanol and about one order higher than in water.     

Preparation of novel organic‐inorganic nanoporous membranes

In this study, the water permeability, the rejection property of sucrose and glucose, the fouling property of humic acid as the foulant for a novel porous fluorinated polyimide membrane made by combining the ion irradiation and plasma treatment have been reported. First, an asymmetric polyimide membrane with a defect‐free and thin skin layer was prepared, then ions on the skin layer were irradiated and the ion‐irradiated layer was treated by plasma to form nanopores in the layer. The asymmetric polyimide membranes with a defect‐free skin layer were irradiated with 50 keV He⁺ at 1 × 10¹⁵ ions/cm², and the irradiated polyimide surfaces were treated by Ar glow discharge. The porous polyimide membrane showed a high water flux and excellent rejection properties and fouling resistance when compared with NTR‐7250, which is commercially available. These findings indicated that the pore size formed on the porous polyimide membrane was effectively controlled by the plasma treatment time and the skin layer thickness. Copyright © 2005 John Wiley & Sons, Ltd.     

A 16‐connected three‐dimensional hydrogen‐bonding network in tetrakis(4‐aminopyridinium) perylene‐3,4,9,10‐tetracarboxylate octahydrate

The novel title organic salt, 4C₅H₇N₂⁺·C₂₄H₈O₈⁴⁻·8H₂O, was obtained from the reaction of perylene‐3,4,9,10‐tetracarboxylic acid (H₄ptca) with 4‐aminopyridine (4‐ap). The asymmetric unit contains half a perylene‐3,4,9,10‐tetracarboxylate (ptca⁴⁻) anion with twofold symmetry, two 4‐aminopyridinium (4‐Hap⁺) cations and four water molecules. Strong N—H...O hydrogen bonds connect each ptca⁴⁻ anion with four 4‐Hap⁺ cations to form a one‐dimensional linear chain along the [010] direction, decorated by additional 4‐Hap⁺ cations attached by weak N—H...O hydrogen bonds to the ptca⁴⁻ anions. Intermolecular O—H...O interactions of water molecules with ptca⁴⁻ and 4‐Hap⁺ ions complete the three‐dimensional hydrogen‐bonding network. From the viewpoint of topology, each ptca⁴⁻ anion acts as a 16‐connected node by hydrogen bonding to six 4‐Hap⁺ cations and ten water molecules to yield a highly connected hydrogen‐bonding framework. π–π interactions between 4‐Hap⁺ cations, and between 4‐Hap⁺ cations and ptca⁴⁻ anions, further stabilize the three‐dimensional hydrogen‐bonding network.     

Automated SIA System Using an Array of Potentiometric Sensors for Determining Alkaline‐Earth Ions in Water

This work deals with the simultaneous determination of Mg²⁺, Ca²⁺, and Ba²⁺ in water using a PVC‐membrane potentiometric sensor array and multivariate calibration, in what is known as electronic tongue. The subsequent processing of the data was based on the use of a multilayer artificial neural network (ANN). The information needed for training or generation of the model was obtained with the aid of an automated analytical system based on the Sequential Injection Analysis (SIA) technique. The modeling ability was verified with an external set of standards, and next the determinations were performed in real samples of mineral waters, where close results for Mg²⁺ and Ca²⁺ were obtained to those obtained with reference methods. The determination of Ba²⁺ can be considered as semi‐quantitative for synthetic samples – due to the absence of Ba²⁺ in mineral waters, its concentration in real samples was not measured.     

Simultaneous Quantification of Heavy Metals Using a Solid State Potentiometric Sensor Array

A potentiometric sensor array of four nonspecific electrodes with solid‐state membranes is developed and tested for simultaneous analysis of copper(II), mercury(II), and silver(I) ions. The cross‐sensitivity responses of the sensors for these ions are evaluated. The array potentiometric signals are processed by partial least‐squares regression (PLS) and back propagation artificial neural networks (ANN) to determinate analyte concentrations. The ANN configuration is optimized and two different training algorithms of the ANN are also evaluated. Best results are obtained when the potentiometric sensors are activated and the data are processed using ANN and the gradient descent adaptive algorithm. The system is used to quantify these heavy metals in synthetic samples and in dental amalgams with successful results.     

A Disposable Planar Paper‐Based Potentiometric Ion‐Sensing Platform

Ion‐selective electrodes (ISEs) are widely used tools for fast and accurate ion sensing. Herein their design is simplified by embedding a potentiometric cell into paper, complete with an ISE, a reference electrode, and a paper‐based microfluidic sample zone that offer the full function of a conventional ISE setup. The disposable planar paper‐based ion‐sensing platform is suitable for low‐cost point‐of‐care and in‐field testing applications. The design is symmetrical and each interfacial potential within the cell is well defined and reproducible, so that the response of the device can be theoretically predicted. For a demonstration of clinical applications, paper‐based Cl^? and K⁺ sensors are fabricated with highly reproducible and linear responses towards different concentrations of analyte ions in aqueous and biological samples. The single‐use devices can be fabricated by a scalable method, do not need any pretreatment prior to use, and only require a sample volume of 20 μL.     

Ammonium 1‐hydroxy‐2‐(2‐pyridinio)ethane‐1,1‐diyldiphosphonate dihydrate and potassium 1‐hydroxy‐2‐(2‐pyridinio)ethane‐1,1‐diyldiphosphonate dihydrate

The crystal structures of the title compounds, ammonium risedronate dihydrate, NH₄⁺·C₇H₁₀NO₇P₂⁻·2H₂O, (I), and potassium risedronate dihydrate, K⁺·C₇H₁₀NO₇P₂⁻·2H₂O, (II), have been determined from single‐crystal X‐ray data collected at 120 K. Compound (I) forms a three‐dimensional hydrogen‐bonded network which connects the ammonium and risedronate ions and the water mol­ecules. In compound (II), the K⁺ ions are seven‐coordinated in a capped distorted trigonal prism. The coordination polyhedra form chains by corner‐sharing, and these chains are connected by phosphon­ate groups into layers in the ac plane. The layers are stacked and connected by hydrogen bonds in the b direction. The risedronate conformation is determined by intra­molecular inter­actions fine‐tuned by crystal packing effects. All H‐atom donors in both structures are involved in hydrogen bonding, with D⋯A distances between 2.510 (2) and 3.009 (2) Å.     

Fourier transform infrared/attenuated total reflectance analysis of water diffusion in poly[styrene‐b‐isobutylene‐ b‐styrene] block copolymer membranes

A Fourier transform infrared/attenuated total reflectance technique was used to study the diffusion of water through poly(styrene‐b‐isobutylene‐b‐styrene) block copolymers (BCPs), as well as sulfonated (H⁺) and Na⁺‐sulfonated ionomer versions. Diffusion data were collected and interpreted for these membranes versus polystyrene block composition, degree of sulfonation, Na⁺ ion content in the ionomers, and the effect of initially dry versus prehydrated conditions. An “early time” diffusion coefficient, D, decreased with increasing percent polystyrene for a series of unmodified BCPs. D decreased with increasing degree of sulfonation, and with increasing ion content for the Na⁺‐exchanged samples and this was interpreted in terms of diffusion limitations caused by a strong tendency for ion hydration. The method also yielded information relating to the time evolution of water structure from the standpoint of degree of intermolecular hydrogen bonding. Membrane prehydration causes profound increases in D for both the unmodified BCP and sulfonated samples, as in plasticization. The simultaneous acquisition of information relating to interactions between water molecules and interactions of water molecules with functional groups on the host polymer matrix offers more information than conventional diffusion measurement techniques that simply count transported molecules. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 764–776, 2005     

Synthesis and optical properties of cis‐dibenzothiazolyldibenzo‐24‐crown‐8

New crown ether carrying two fluorionophores of cis‐dibenzothiazolyldibenzo‐24‐crown‐8 was synthesized from cis‐diformyldibenzo‐24‐crown‐8 and 2‐aminobenzenethiol. The binding behavior and the optical properties of the crown ether were examined through UV‐visible spectroscopy and fluorescence spectroscopy. When complexed with Na⁺, K⁺, Rb⁺, and Cs⁺ ions, it led to intramolecular charge transfer and caused the changes of the fluorescence spectra. The protonation of the crown ether was also studied. With protonation using CF₃COOH, the absorption bands and the fluorescence spectroscopy changed, the maximal fluorescence wavelengths red shifted and the fluorescence intensity with the maximum at 433 nm enhanced strongly. J. Heterocyclic Chem., (2011).     

Preparation and Application of Cholesteryl‐Benzo‐15‐Crown‐5/Cholesteryl Mixed Liquid Crystals

Various mixed liquid crystals containing crown ether‐cholesteryl liquid crystal, benzo‐15‐crown‐5‐COO‐C₂₇H₄₅ (B15C5‐COOCh), with various common cholesteric liquid crystals, e.g., cholesteryl chloride, cholesteryl benzoate and cholesteryl palmitate, were prepared and studied using polarizing microscopy and differential scanning calorimetry. Investigating the concentration effect of B15C5‐COOCh in mixed liquid crystals revealed that the addition of B15C5‐COOCh resulted in wider phase transition temperature ranges of these cholesteryl liquid crystals. The stability of these B15C5‐COOCh/cholesteryl mixed liquid crystals was studied using comprehensive graphic molecular modeling computer programs (Insight II and Discover) to calculate their molecular energy and stability energy. The effect of salts, e.g. Na⁺, Co³⁺, Y³⁺ and La³⁺, on the transition temperature range of the mixed liquid crystals was also investigated. The crown ether cholesteric liquid crystal B15C5‐COOCh was applied both as a surfactant and an ion transport carrier to transport metal ions through liquid membranes. Cholesteryl benzo‐15‐crown‐5 exhibited distinctive characteristics of a surfactant and the critical micellar concentration (CMC) of the surfactant was investigated by the pyrene fluorescence probe method. Cholesteryl benzo‐15‐crown‐5 was successfully applied as a good ion transport carrier (Ionophore) to transport various metal ions, e.g. Li⁺, Na⁺, La³⁺, Fe³⁺ and Co³⁺, through organic liquid membranes. The transport ability of the cholesteryl benzo‐15‐crown‐5 surfactant for these metal ions was in the order: Co³⁺ ≥ Li⁺ > Fe³⁺ > Na⁺ > La³⁺.