Potentiometric Selectivity Research Articles

Copper (II) Ion Detection in Food and Water Harnessing Schiff Base-Enabled Electrochemical Sensor

A copper (II) ion-selective sensor was generated using a processed membrane that included 4-(2-(2,4-Dinitrophenylhydrazono) Methyl)Benzene-1,3-diol (L). The sensor’s efficacy was tested using a variety of plasticizers, comprising sodium tetraphenylborate (NaTPB), O-Nitrophenyloctyl ether (ONPOE), benzyl acetate (BA), dibutyl phthalate (DBP), and dibutyl sebacate (DBS). Membrane layers comprised of L:DBS:OA:PVC in a ratio of 5:55:10:30 (w/w,%) provided optimum sensing effectiveness. The detection system performed well in an average concentration that ranged from 5.3×10−8 to 1.0×10−1 mol L−1, with a Nernstian slope of 29.1±0.5 mV decade-1 for Cu(II) ions. The sensor’s minimal detection limit of 2.1×10−8 mol, broad pH range (3.1–8.2), quick reaction time (9 s), strong non-aqueous resistance (up to 25% v/v), and good retention time (2 months) demonstrates its value. Potentiometric selectivity coefficients revealed an exclusive exposure for Cu(II) ions under the influence of intervening ions, allowing for accurate identification of copper in a variety of materials such as food oils, tomato plant material, and river water. The proposed sensor is a promising means for accurately detecting Cu(II) ions in environmental and food specimens, with potential utilization in quality assurance and environmental surveillance.

Cheap and effective potentiometric PVC sensor for the determination of imidazolium based ionic liquids in aqueous and aqua-organic media

Owing to the extensive research on imidazolium based ionic liquids; the present study aims to design a potentiometric sensor for alkyl methylimidazolium ion. For this, poly(vinyl chloride) PVC membrane based on the neutral ion-pair complexes of cetylpyridinium chloride and sodium dodecyl sulfate (CPy+DS−) has been developed. The synthesized ion selective electrode (ISEs) have been found to show linear response with near-Nernstian slope for CnMeImCl (C10MeImCl, C12MeImCl and C14MeImCl). The proposed ISEs show quick response (5–6 s) and provide wide pH range for working. The influence of various ions on the performance of ion-selective electrode is investigated in terms of potentiometric selectivity coefficients, which were determined by separate solution method. The performance of synthesized ISE in examining the critical micellar concentration (cmc) of CnMeImCl in aqueous, aqua-organic media and in the presence of amino acids (glycine, L-glutamic acid and L-phenylalanine) has been found to be satisfactory and confirmed through conductivity and fluorescence measurements. This emphasizes its worth for in-situ analysis of alkyl methylimidazolium ions, during an organic reaction, and hence possible reaction mechanism evaluation. Different thermodynamic parameters such as Standard Gibbs energies of micellization (ΔGm∘), degree of counterion dissociation (α), amphiphile tail transfer Gibbs free energy (ΔGm,trans∘) have been evaluated. Further, the analytical application of synthesized electrode as end point indicator in the potentiometric titration of C14MeImCl with SDS has also been explored, which compared well with improved two-phase titration method. The current study is novel as it involves the use of a cheaper material (CPyCl) as ionophore and that the same electrode can be used for different chain alkyl methylimidazolium ions simply by changing the internal reference solutions.

Effect of the stability of 1,3-bis(diphenylphosphoryl)-2-oxapropane complexes on the separation of lanthanide ions and their detection.

Phosphoryl podands of neutral type with a flexible ethylene glycol chain and diphenylphosphorylmethyl end groups are known for their complexation properties towards various cations. In this work, the complexation process between 1,3-bis(diphenylphosphoryl)-2-oxapropane (L) and lanthanide ions was studied. Namely, the stability constants of lanthanide complexes with L in acetonitrile were estimated by the method of spectrophotometric titration. It was found that the stability constants of Ln3+ complexes with L increase in the lanthanide series, which is consistent with the extraction and ion-selective properties of L. The extraction ability of L and this ligand in the presence of ionic liquids (ILs) such as methyltrioctylammonium nitrate (MTOAN) and bis[(trifluoromethyl)sulfonyl]imide 1-butyl-3-methylimidazolium (C4mimTf2N) was studied. It was found that in the presence of ILs, L extracts the elements of the yttrium subgroup of lanthanides much better than those of the cerium subgroup: SFLu/Ce(L-MTOAN) = 2.29; SFLu/Ce(L-C4mimTf2N) = 110.38. The use of the L-C4mimTf2N mixture in the processes of lanthanide separation into subgroups is much more efficient than the use of L without the addition of ILs or the use of the L-MTOAN mixture. The ion-selective properties of L towards Ln3+ ions were studied. Podand L exhibits potentiometric selectivity to Lu3+ ions.

Prediction of Carbonate Selectivity of PVC-Plasticized Sensor Membranes with Newly Synthesized Ionophores through QSPR Modeling

Developing a potentiometric sensor with required target properties is a challenging task. This work explores the potential of quantitative structure-property relationship (QSPR) modeling in the prediction of potentiometric selectivity for plasticized polymeric membrane sensors based on newly synthesized ligands. As a case study, we have addressed sensors with selectivity towards carbonate—an important topic for environmental and biomedical studies. Using the logKsel(HCO3−/Cl−) selectivity data on 40 ionophores available in literature and their substructural molecular fragments as descriptors, we have constructed a QSPR model, which has demonstrated reasonable precision in predicting selectivities for newly synthesized ligands sharing similar molecular fragments with those employed for modeling.

Development of Chromium(III) Selective Potentiometric Sensors for Its Determination in Petroleum Water Samples Using Synthesized Nano Schiff Base Complex as an Ionophore.

Many analytical techniques, such as X-ray fluorescence spectrometry, inductively coupled plasma-atomic emission spectrometry, and even traditional spectroscopic and fluorimetric methods, are used for the measurement of Cr(III) ions. These methods are sophisticated and very expensive, so thecheapest and low-cost ion selective electrodes were used. The quantification of Cr(III) ions in various samples of petroleum water using ion selective electrodes was suggested. Nano chromium modified carbon paste sensor (MCPE) and nano chromium modified screen printed sensor (MSPE) based on Schiff base Cr(III) complex are developed. The developed nano Cr(III) Schiff base chelate was characterized using elemental, spectroscopic, and thermal analysis techniques. The proposed nano Cr(III) has good properties for antibacterial and antifungal activity. The modified carbon paste and screen-printed sensors were fabricated for determination of Cr(III) ion. The proposed MCPE (sensor I) and MSPE (sensor II) obeys Nernstian equation upon incorporating nano Cr(III) ionophore in the paste at 25°C with a trivalent cationic slope of 18.8 ± 0.2 and 20.0 ± 0.4 mV/decade. They have showed fast response time around 8 and 5 s, and they may be used for at least 98 and 240 days without significant changes in MCPE and MSPE potential, respectively. The sensors I and II showed good selectivity for Cr(III) ion toward a wide variety of metal ions or anions as confirmed by potentiometric selectivity coefficients values. The detection and quantification limits were defined alongside the other process validation parameters. The results have been compared well to those obtained by atomic absorption spectrometry (AAS), and the data of F- and t-test indicated no significant difference between the proposed and AAS methods. These sensors have been used to determine Cr(III) ions in genuine spiked different petroleum well water samples with satisfactory percentage recoveries, low standard, and relative standard deviation values using direct potentiometric and standard addition methods. The proposed method of producing nano Cr(III) complex as a sensor material possesses the distinct advantages of being simple, easily reproducible, appropriate for operation, and highly selective and sensitive. Modified carbon paste and screen-printed electrodes were fabricated based on nano Cr(III) complex as ionophore. The electrodes follow Nernstian behavior, and they optimized according to IUPAC recommendation. They showed a high selectivity for Cr(III) ion over many bi- or trivalent metal ions and anions. The results obtained compared well with those obtained using AAS. They successfully applied for determination of Cr(III) in petroleum water samples.

Paper-Based Potentiometric Device for Rapid and Selective Determination of Salicylhydroxamate as a Urinary Struvite Stone Inhibitor.

Novel paper-based potentiometric platforms for rapid, cost-effective, and simple determination of the salicylhydroxamic acid (SHAM) drug are presented. Both the SHAM sensor and the reference Ag/AgCl electrode were integrated together on the miniaturized paper platforms. The ion-sensing membrane for the presented sensor is based on the use of SnIV-tetraphenylporphyrin (SnIVTPP) as a charged carrier within a plasticized poly(vinyl chloride) (PVC) matrix. Multiwalled carbon nanotubes (MWCNTs) were used as an ion-to-electron transducer. The resulting sensor revealed a rapid and stable response with a Nernstian slope of −59.3 ± 0.7 mV/decade over the linear range of 1.0 × 10–6 to 1.0 × 10–3 M and a detection limit of 0.7 μM. All measurements were carried out in 30 mM phosphate-buffered solution (PBS) at pH 7.2. Intra- and interday precision were measured and found to be 1.7%. The relative standard deviation (RSD%) ( = 5) was calculated as 2.43% after utilizing five different electrodes (n = 5). The selectivity behavior of the prepared electrodes in the absence and presence of ionic additives was evaluated. The selectivity pattern showed a non-Hofmeister selectivity pattern in the existence of anionic additives with enhanced potentiometric selectivity for SHAM over different lipophilic anions (e.g., ClO4–, SCN–, and I–). The presented device was successfully applied for SHAM determination in pharmaceutical preparations. This paper-based analytical device can be potentially manufactured at large scales and provides a portable, rapid, disposable, and cost-effective analytical tool for measuring the SHAM drug.

Prospective of modified polymeric MgO/ZnO nanocomposite sensor for potentiometric determination of chronic myelogenous leukemia medication

Recent attention has been developed towards the use of metal oxide nanocomposites as significant and electroactive nanomaterials in potentiometric and sensing applications. Two potentiometric cytarabine (CTB) coated wire sensors were fabricated using cytarabine-tetraphenyl borate (CTB-TPB), a modified cytarabine-tetraphenyl borate decorated with MgO/ZnO nanocomposite (CTB-TPB-MgO/ZnO) ion associates, polyvinyl chloride (PVC) and o-nitrophenyloctyl ether (o-NPOE) as electroactive materials for conventional and modified sensors, polymeric matrix and fluidizer agent, respectively. The functionalized CTB-TPB-MgO/ZnO polymeric sensor displayed Ultra potentiometric selectivity and high sensitivity for the determination of CTB within 1.0 × 10−10-1.0 × 10−2 mol L−1 solutions, correlation coefficient (r2 = 0.9999), lower detection limit 4.9 × 10-11 mol L−1 and least regression equation EmV = (57.433 ± 0.2) log [CTB] + 673.16 mV. The obtained results were compared to the conventional CTB-TPB type of 1.0 × 10-6-1.0 × 10−2 mol L−1 linear concentration range, correlation coefficient (r2 = 0.9995), lower detection limit 5.0 × 10−7 mol L−1 and least regression equation EmV = (52.633 ± 0.6) log [CTB] + 432.52 mV. It was potentially applied for the quantification of CTB in its commercial injections and spiked serum samples with mean recoveries % 99.85 ± 0.3, 99.87 ± 0.4 and 99.78 ± 0.4 %, respectively. The outcomes were compared with those obtained from various addressed analytical techniques and showed high selectivity and sensitivity for CTB determination rather than other reported analytical techniques. The rationality of the demonstrated potentiometric probe was ensured and assessed with respect to international conference harmonization recommendations. The outcomes proved that the method was accurate and precise for the determination of the investigated drug.

Arrays of solid contact potentiometric sensors for separate determination of some cephalosporin antibiotics

Arrays of potentiometric sensors including developed solid-contact unmodified and modified sensors based on tetradecylammonium associates with complex compounds of silver (1) and some β-lactam antibiotics (cefazoline, cefuroxime, cefotaxime (n = 3 – 6)) are proposed; polyaniline and copper oxide being modifiers. The main electroanalytic properties of the sensors are determined (the range of the determined concentrations in antibiotic solutions 1 × 10–4 – 0.1 M, 46.3 < S < 48, Cmin = n × 10–5 М, response time 4 – 10 sec, potential drift 4 – 6 mV/day, service life — 2 months). It is shown that modification of the membrane surfaces brings the steepness of the electrode functions to Nernst-values for single-charged ions of the antibiotics under study; reduces the response time and the detection limits, the linearity intervals of the electrode functions being the same. The potentiometric selectivity coefficients of unmodified and modified sensors based on different electrode active components (EAC) to the studied cephalosporins in the presence of interfering antibiotics are close to unity; cross sensitivity parameters for the considered sensors (the average slope of the electrode function of the sensor Sav, the unselectivity factor F, and the reproducibility factor K) are 46.3 < S (mV/pC) < 48; 0.85 < F < 0.90; 144 < K < 170, respectively. Application of sensors in the multisensory analysis of model mixtures of cephalosporin antibiotics is shown. Method of artificial neural networks (ANN) is used for processing of analytical signals. The correctness of the determination is carried out using «spike tests» on the reference model mixtures (the relative error of the determination does not exceed 12 %).

Anion-Selective Electrodes Based On a CH-Hydrogen Bonding Bis-macrocyclic Ionophore with a Clamshell Architecture.

CH-hydrogen bonding provides access to new building blocks for making macrocyclic ionophores with high degrees of preorganization and selective anion recognition. In this study, an anion-binding ionophore in the shape of a clamshell (ClS) was employed that is composed of two cyanostar (CNstar) macrocycles with preorganized cavities linked with a 12-carbon chain. This ionophore allows for anion complexation by CH-hydrogen bonding. The potentiometric performance of membrane-based ion-selective electrodes incorporating this ionophore was evaluated. Different membrane compositions were prepared to determine the optimum concentrations of the ionophore and lipophilic additive in the membrane. The optimized electrode had a slope of -58.2 mV/decade and demonstrated an anti-Hofmeister selectivity pattern toward iodide with a nanomolar detection limit. Electrospray ionization mass spectrometry was employed to study the relative association strengths of ClS with various anions. The observed mass peaks of the ion-ionophore complexes were found to be consistent with the potentiometric selectivity pattern of the corresponding electrodes. Overall, the selectivity of the electrode could be altered by using an ionophore in which the two CNstar macrocycles are linked together with a flexible 12-carbon chain to control the molecularity of the binding event.

Determination of levamisole using ion-selective electrode

Current development of applied ionometry requires focusing of theoretical studies both on revealing the nature of the selectivity of electrode membranes and on the developing the new methods of membrane synthesis and their modification with the goal of obtaining more perfect structural units with improved functional properties. Elucidation of the relationship between the structural characteristics of the membranes and their effect on the electro-analytical properties is a rather important task. The interaction of organic cation levamisole with bromophenol blue was studied to meet the goals. Levamisole-selective sensor with a plasticized polyvinyl chloride (PVC) membrane has been developed. The electrode contains an ionic associate of levamisole with bromophenol blue. PVC was used as a matrix to model the membrane composition. Membranes plasticized with dibutyl phthalate (DBP), diethyl phthalate (DEP), dioctyl phthalate (DOP), dinonyl phthalate (DNP), dibutyl sebacate (DBP), tricresyl phosphate (TCP) were studied. It was shown that the nature of the plasticizer insignificantly affected the analytical characteristics of the electrode. The response is linear within the concentration range of 1 × 10–5 – 1 ×10–1 mole/liter with the slope of the electrode function 52.1 ± 1.0 mV/pC. The sensor has a quick response (10 sec) and can be used for at least 8 weeks without any divergence in the long run. The operation life of the membranes with a high plasticizer content is much longer. The electrode can be used within pH range of 3.0 – 8.0. Potentiometric selectivity coefficients of the electrode relative to a number of potentially interfering ions were determined. The developed electrode was tested in determination of levamisole in model solutions and pharmaceuticals («Decaris» and «Levamisole-Zdorovye»).

Exploitation of o-benzoyl benzoic acid as an efficient electroactive material for selective determination of Cr (III) ions in pharmaceutical samples and industrial waste water using carbon sensor

Herein, for the first time, o-benzoyl benzoic acid has been explored as a promising electroactive material for the fabrication of sensitive, precise and accurate carbon paste electrode (CPE) for selective detection of Cr (III) ion. o-benzoyl benzoic acid (o-BBA) as a sensing material and tricresylphosphate (TCP) as a solvent mediator improved the developed sensor performance to get the Nernstian cationic slope of 20.03 ± 0.11 mV decade−1 within the concentration range of 5.0 × 10−7-1.0 × 10−1 mol L−1. The sensor displayed a fast response time of 12 s reflecting a pH independency over the pH range of 3.1–4.7. Moreover, the reaction between the sensing material and Cr (III) ion on the developed sensor surface was elucidated using the microscopic technique such as scanning electron microscope (SEM) in addition to the energy dispersive X-ray analyzer (EDX). The proposed sensor showed an adequate shelf lifetime (∼33 days). The values of potentiometric selectivity coefficient were obtained by fixed interference and separate solution methods affirming a high distinguishing power of the fabricated sensor toward Cr (III) ions over the other interfering ions. The established sensor could be utilized with a promising success for the Cr (III) ion estimation in the industrial waste water and in the pharmaceutical forms. Additionally, it has been employed as a promising indicator sensor with a superior performance for potentiometric titration of Cr (III) ion against EDTA.

Мультисенсорные системы типа «электронный язык» для раздельного определения цефотаксима и цефазолина

Electroanalytical properties of unmodified and modified by polyaniline and by CuO nanoparticles solid-contact potentiometric sensors which are based on associates of tetradecylammonium with complex compounds of silver (I) with cephuroxime, cephotaxime and cephazoline Ag(β-lac)2TDA in solutions of corresponding antibiotics were studied. It was revealed that Ag(β-lac)2TDA –based sensors had no specificity to the basic ion but showed sensitivity to other cephalosporins. Taking into account the potentiometric selectivity coefficients and cross-sensitivity parameters of sensors based on different electrode-active components, their use for creating «electronic tongue» multi-sensor systems was shown. Arrays of low-selective potentiometric sensors were created for separate determination of cephazoline and cephotaxime in two-component model mixtures at concentration intervals of 2,5·10-4 – 0,01 М. The method of artificial neural networks was used for processing analytical signals (the relative error of determination not exceeding 13%).

Fluorous-Phase Ion-Selective pH Electrodes: Electrode Body and Ionophore Optimization for Measurements in the Physiological pH Range.

Because of their low polarity and polarizability, fluorous sensing membranes are both hydrophobic and lipophobic and exhibit very high ion selectivities. Here, we report on a new fluorous-membrane ion-selective electrode (ISE) with a wide sensing range centered around physiologically relevant pH values. The fluorophilic tris[perfluoro(octyl)butyl]amine (N[(CH2)4Rf8]3) was synthesized and tested as a new H+ ionophore using a redesigned electrode body that provides excellent mechanical sealing and much improved measurement reliability. In a challenging 1 M KCl background, these fluorous-phase ISEs exhibit a sensing range from pH 2.2 to 11.2, which is one of the widest working ranges reported to date for ionophore-based H+ ISEs. High selectivities against common interfering ions such as K+, Na+, and Ca2+ were determined (selectivity coefficients: logKH, Kpot = – 11.6; logKH, Napot = – 12.4; logKH, Capot < – 10.2). The use of the N[(CH2)4Rf8]3 ionophore with its −(CH2)4– spacers separating the amino group from the strongly electron-withdrawing perfluorooctyl groups improved the potentiometric selectivity as compared to the less basic tris[perfluoro(octyl)propyl]amine ionophore. The use of N[(CH2)4Rf8]3 also made the ISE less prone to counter anion failure (i.e., Donnan failure) at low pH than the use of tris[perfluoro(octyl)pentyl]amine with its longer −(CH2)5– spacers, which more effectively shield the amino center from the perfluorooctyl groups. In addition, we exposed both conventional plasticized PVC-phase pH ISEs and fluorous-phase pH ISEs to 10% serum for 5 days. Results show that the PVC-phase ISEs lost selectivity while their fluorous-phase counterparts did not.

An Ion Selective Electrode for the Determination of Pertechnetate Ions

The electroanalytical characteristics of an ion-selective electrode (ISE) with a membrane based on a supramolecular polymer composition containing polyvinyl chloride, o-nitrophenyl octyl ether plasticizer, tetradecyphosphonium pertechnetate ionophore, and a lipophilic additive of tetradecylphosphonium tetraphenyborate are studied. The limit of detection for the ISE in aqueous solutions containing KTcO4 was 2 × 10–7 M and the slope of the electrode function at 20°C was 58 ± 1 mV/pTc $${\text{O}}_{4}^{ - }$$ . Potentiometric selectivity coefficients were determined for various anions. A correlation between the hydration energy ΔGhydr and selectivity coefficients calculated by the method of mixed solutions is observed. It was found that a change in the pH of the solution in the range 2–12 slightly affects the electrode potential when the concentration of Tc $${\text{O}}_{4}^{ - }$$ in the analyzed solution is 1 × 10–6–0.001 M. The behavior of the electrodes in strongly acidic solutions was studied.

Potentiometric Solid-Contact Ion-Selective Electrode for Determination of Thiocyanate in Human Saliva.

A new solid-contact potentiometric ion-selective electrode for the determination of SCN− (SCN-ISE) has been described. Synthesized phosphonium derivative of calix[4]arene was used as a charged ionophore. The research included selection of the ion-selective membrane composition, determination of the ISEs metrological parameters and SCN-ISE application for thiocyanate determination in human saliva. Preparation of the ISEs included selection of a plasticizer for the ion-selective membrane composition and type of the electrode material. The study was carried out using ISE with liquid internal electrolyte (LE-ISE) and solid-contact electrodes made of glassy carbon (GC-ISE) and gold rods (Au-ISE). The best parameters were found for GC sensors for which the ion-selective membrane contained chloroparaffin as a plasticizer (S = 59.9 mV/dec, LOD = 1.6 × 10−6 M). The study of potentiometric selectivity coefficients has shown that the thiocyanate-selective sensor could be applied in biomedical research for determination of SCN− concentration in human saliva. The accuracy of the SCN− determination was verified by testing 59 samples of volunteers’ saliva by potentiometric sensors and UV-Vis spectrophotometry as a reference technique. Moreover, SCN− concentrations in the smokers’ and non-smokers’ saliva were compared. In order to investigate the influence of various factors (sex, health status, taken medications) on the thiocyanate level in the saliva, more extensive studies on a group of 100 volunteers were carried out. Additionally, for a group of 18 volunteers, individual profiles of SCN− concentration in saliva measured on a daily basis for over a month were collected.

A tetradecylphosphonium compounds–based membrane sensor for potentiometric quantitation of pertechnetate-ions in cementitious radioactive waste

A novel potentiometric sensor has been developed for the determination of pertechnetate ions (TсO4‾) by using on two synthesized tetradecylphosphonium salts, tetradecylphosphonium pertechnetate and tetradecylphosphonium tetraphenylborate, as sensing components of a poly (vinyl chloride) matrix membrane. Potentiometric studies have confirmed the improvement in response characteristics of the sensor based on the membrane system containing a mixture of both tetradecylphosphonium salts. Such sensor exhibits a stable Nernstian response over a wide concentration range of pertechnetate ions (10−2 – 5 × 10-7 M) in aqueous solutions with the acidity from 3 M HCl to pH 12. The lower limit of detection is 0.15 μM. The calculated potentiometric selectivity coefficients moderate selectivity for TсO4‾ ions over the interfering anions and these values are clearly in agreement with the standard Gibbs energies of the ions transfer between water and NPOE. The reported sensor was successfully employed for the pertechnetate quantitation in the radioactive waste disposal products (cement cubes).

Potentiometric PVC-Membrane-Based Sensor for Dimethylamine Assessment Using A Molecularly Imprinted Polymer as A Sensory Recognition Element.

A new simple potentiometric sensor is developed and presented for sensitive and selective monitoring of dimethylamine (DMA). The sensor incorporates a molecularly imprinted polymer, with a pre-defined specific cavity suitable to accommodate DMA. The molecularly imprinted polymer (MIP) particles were dispersed in an aplasticized poly(vinyl chloride) matrix. The MIP is synthesized by using a template molecule (DMA), a functional monomer (acrylamide, AM), cross-linker (ethylene glycol dimethacrylate, EGDMA) and initiating reagent (benzoylperoxide, BPO). Using Trizma buffer solution (5 mmol L−1, pH 7.1), the sensor exhibits a rapid, stable and linear response for 1.0 × 10−5 to 1.0 × 10−2 mol L−1 DMA+ with a calibration slope of 51.3 ± 0.3 mV decade−1, and a detection limit of 4.6 × 10−6 mol L−1 (0.37 µg mL−1). The electrode exhibited a short response time (10 s) and stable potential readings (± 0.5 mV) for more than 2 months. Potentiometric selectivity measurements of the sensor reveal negligible interferences from most common aliphatic and aromatic amines. High concentration levels (100-fold excess) of many inorganic cations do not interfere. The sensor is successfully used for quantification of low levels of DMA down to 0.5 µg mL–1. Verification of the presented method was carried out after measuring the detection limit, working linearity range, ruggedness of the method, accuracy, precision, repeatability and reproducibility. Under flow-through conditions, the proposed sensor in its tubular form is prepared and introduced in a two-channel flow injection setup for hydrodynamic determination of DMA. The sampling rate is 50–55 samples h–1. The sensor is used to determine DMA in different soil samples with an accuracy range of 97.0–102.8%.

A novel porous silicon multi-ions selective electrode based extended gate field effect transistor for sodium, potassium, calcium, and magnesium sensor

One of the most informative parameters of the bio-chemical sensors is the multi-ions selectivity. Characterizing the biocompatible materials with high sensitivity and efficiency for the immobilization and detection of bio-signals and conversion of biochemical signal into quantifiable electronic signal is very important in biosensor research. Extended gate field-effect transistor (EGFET) based on porous silicon (PS) n-type (111) was characterized as sodium, potassium, calcium, and magnesium sensor over the concentration ranges 10−4 to 1 M of the four cations at room temperature. This study extracted the sensitivity of Na+, K+, Ca2+, and Mg2+ in terms of current/voltage sensitivity. Separate Solution Method was used to concept of PS response which suggest a single constant value of the potentiometric selectivity coefficient ($$K_{A,B}^{\text{pot}}$$). Regarding EGFET operation, PS manifested significantly enhanced Na+, K+, Ca2+, and Mg2+ voltage sensitivity of 58.76, 57.91, 34.90, and 31.75 mV/dec, respectively, and they are very close to the theoretical value of Nernst. Moreover, the Na+, K+, Ca2+, and Mg2+ current sensitivity was of 1.09, 1.04, 0.54, and 0.52 (µA)1/2/dec. PS showed high Na+ selectivity towards K+, Ca2+, and Mg2+. The results showed the values of the current/voltage sensitivity have high linearity. Using of PS n-type (111) as multi-ions sensor, and extracting the sensitivity of Na+, K+, Ca2+, and Mg2+ in terms of IDS were not reported in the literature.

Modified solid-contact sensors for determination of cefuroxime and cefalexin in medicines and oral fluid

Cefuroxime, cefuroxime axetil and cefalexin are broad-spectrum pluripotential cephalosporin antibiotics. Their determination in various objects suggests using expensive spectroscopic, chromatographic, electrochemical equipment and organic solvents. Potentiometric sensors can provide rapid detection of cephalosporin antibiotics in a small sample volume without a preliminary sample preparation. The study is aimed at the developing of modified solid-contact potentiometric sensors for determination of cefuroxime and cefalexin in aqueous, biological media, and pharmaceuticals. The electroanalytical characteristics of unmodified and modified polyaniline and copper oxide nanoparticle sensors are evaluated. Tetradecylammonium(TDA) with a silver (I) – cefuroxime complex are used as the active membrane components, whereas polyaniline and copper oxide nanoparticles are used as modifiers. The main electroanalytic and operational characteristics of the studied sensors in aqueous solutions of antibiotics and against the background of oral fluid (LRP) are determined. The results of comparative evaluation of the electroanalytical properties of unmodified and modified solid-contact sensors in aqueous media of some â-lactam antibiotics and against the background of oral fluid are presented. The sensors based on Ag (Cefur)2TDA are characterized by a short response time: for modified polyaniline (PAN) and copper oxide nanoparticles within 5 – 10 sec, for unmodified — 10 – 20 sec. The linear range of the electrode functions for unmodified and modified sensors is 1 × 10–4 – 1 × 10–1 M, the detection limit is 7.4 × 10–5 M for unmodified and 6.3 × 10–5 M for modified sensors, respectively. The potential drift is 6 – 12 and 4 – 6 mV/day, service life is 1.5 and 2 months for unmodified and modified sensors, respectively. The modifiers stabilize the electrode potential, perform the function of the electron transfer mediator thus enhancing the electroanalytical characteristics of the sensors. The effect of the redox agents on the sensor properties is revealed: 1 × 10–3 – 1 × 10–4 MK 2Cr2O7 and FeCl3 solutions reduce the linearity intervals of the electrode functions, KI and Mohr’s salt do not affect the characteristics of the sensors in cefuroxime and cephalexin solutions. The coefficients of potentiometric selectivity of cefuroxime-selective sensors (modified with CuO nanoparticles) with respect to cefazolin, cefotaxime, and cefalexin are close to unity; Kijpot with respect to inorganic anions being part of the oral fluid (, Cl Br,I,HCO3 ,H PO 24 ,HPO4 2) are n × 10–2 – n × 10–3. This indicates the possibility of using sensors for detecting individual cephalosporin antibiotics or their total content in the presence of 100 – 1000 fold excesses of inorganic ions in medicinal and biological environments, small sample volumes, which is important when studying the pharmacokinetics of antibiotics and in determination of the maximum therapeutic dose when adjusting the treatment process.

Electrochemically controlled transport of anions across polypyrrole-based membranes

Electrosynthesized polypyrrole (PPy) films on PVDF/Pt support membranes were used to study electrochemically controlled transport of monovalent and divalent anions across the PPy-based membranes. The PVDF/Pt/PPy membrane separated two compartments in a transport cell and served simultaneously as the working electrode allowing electrochemical switching of PPy between its oxidized and reduced forms during the transport experiments. PPy was electrosynthesized in presence of p-toluene sulfonate, camphorsulfonate and hexafluorofosfate (doping ions) and the ion transport properties of the resulting PPy-based membranes were investigated. The morphology and elemental composition of PPy before and after the anion transport studies were studied by SEM and EDXA. The anion fluxes obtained during transport of a mixture of Cl−, NO3−, SO42− and HAsO42− across the PPy-based membranes were found to decrease in the following order: NO3− > Cl− » SO42− > HAsO42−. PPy films with the same composition as for the transport studies were also electrodeposited on glassy carbon electrodes (GC/PPy) and studied by potentiometry. The potentiometric selectivity of the GC/PPy electrodes towards Cl−, NO3− and SO42− was found to correlate with the ion transport characteristics of the corresponding PPy membranes used in the transport cell. The PPy-based membranes allowed separation of monovalent from divalent anions.