Switching Ca2+/Ba2+ to Ba2+/Ca2+ Potentiometric Selectivities of Podands with Phosphoryl-containing Terminal Groups: A Molecular Modelling Study

It has been shown experimentally that theCa²⁺/Ba²⁺ potentiometric selectivity ofphosphoryl-containing podandR–-O–-(CH₂–-CH₂–-O)_nndash;-R,R = –-C₆H₄–-P(O)Ph₂, n = 3 (I),switches to Ba²⁺/Ca²⁺ when the ligand containsthe longer polyether chain, n = 5 (II). Here, we reportmolecular dynamics and free energy perturbation simulationsperformed using the amber 4.1 program on the complexesL ^.M²⁺ (M²⁺ = Ca²⁺, Sr²⁺ andBa²⁺, L = I and II) in the gas phase inorder to gain a microscopic insight into structural and energy bindingproperties of podands as a function of n. Mixed QM/MM (PM3/ amber) calculations were performed toanalyse the role of polarisation effects on the complexation selectivityof podands. It isshown that an increase of n does not affect the interactions ofM²⁺ with phosphine oxide groups,but leads to less efficient interactions of small cations with the polyether chain. Calculatedpotentiometric selectivities of I (Ca²⁺ > Ba²⁺)and II (Ba²⁺ > Ca²⁺) are in agreement with the experimental data.     

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.     

Combined Voltammetric‐Potentiometric Sensor with Silver Solid Amalgam Link for Electroanalytical Measurements

An arrangement of a combined voltammetric‐potentiometric sensor (CVPS) with a silver solid amalgam link (AgSAL) was designed, comprising a working electrode inserted into an internal solution of a proper depolarizer (e.g., 10 ppm Cu(II) in 0.2 M acetate buffer, 2% tartaric acid), which is separated from the analyzed solution by the AgSAL or other amalgam links. The preparation procedure of the AgSAL was described. The sensor has been successfully tested using solutions at various concentrations of Ag(I) and Hg(II) in various types of base electrolytes, exhibiting good selectivity with respect to Ag(I) or Hg(II) ions. The proportional voltammetric current concentration dependences i_p?ln c were obtained and interpreted.     

Structural Dependence of the Selectivity of Fluorescent Chemosensors to Mg2+ from Alkali Earth Metal Ions

A series of novel 2,2′‐bipyridylene‐containing conjugated polymers are synthesized through the Wittig reaction. Some of these polymers show a highly selective affinity toward Mg²⁺ in a mixture of alkaline earth metal ions, which is different from the 2,2′‐bipyridylene‐containing poly(phenylene vinylene) derivatives reported previously. This is the first case to demonstrate that some materials show a selectivity toward Mg²⁺. The structures of the polymers may play a crucial role for this selectivity.     

Molecularly Imprinted Potentiometric Sensor for Nanomolar Determination of Pioglitazone Hydrochloride in Pharmaceutical Formulations

Pioglitazone Hydrochloride (PG) is an insulin-sensitizing drug and is indicated for the treatment of type II diabetes. In this study, newly molecularly imprinted electrochemical sensors were constructed for the potentiometric determination of PG in the pharmaceutical formulations (Diabetonorm® 45 and 15 mg) with high accuracy and precision. The MIP particles (ionophore) were prepared by using the PG drug as a template, acrylamide (AC) or methacrylic acid (MAA) as a functional monomer, and ethylene glycol dimthacrylate (EGDMA) as a cross-linker. The best MIP was synthesized from AC as a functional monomer, AC-MIP. The best sensor (CPEs) was formulated from graphite (47 wt%) as a carbon source, AC-MIP (5 wt.%) as an ionophore, PMA (1 wt%) as an ion-exchanger, DNPOE (47 wt.%) as a conductive oil so-called plasticizer. The best CPE electrode exhibited response slope to the Nernstian slope of 63.0 mV Decade⁻¹, linear dynamic range of 10⁻⁸–10⁻⁴ M with the detection limit of 1.0×10⁻⁸ M, along with high reversibility, short response time 30 sec, and a long lifetime. The constructed biosensors showed high selectivity against similar interfering species (e. g. arabinose, galactose, lactose, maltose, glucose, Ba²⁺, Cu²⁺, Na⁺, Zn²⁺, Mg²⁺, Fe²⁺, Ca²⁺, NH₄⁺).     

pH电位滴定法测定溶液中钙、镁离子与聚天冬氨酸的生成稳定常数

pH电位滴定法测定溶液中钙、镁离子与聚天冬氨酸的生成稳定常数;pH电位滴定;聚天冬氨酸;配位化学;钙离子;镁离子     

Ion-selective electrode for measuring low Ca2+ concentrations in the presence of high K+, Na+ and Mg2+ background

In this work, ion-selective electrodes for calcium ion were investigated. Two ionophores were used in the membranes: ETH 1001 and ETH 129. An internal filling solution buffered for primary ion was used that allowed the lower detection limit to be decreased down to 10^−8.8 M. Theoretical and experimental electrode characteristics pertaining to both primary and interfering ions are discussed. Better behavior was obtained with the electrode prepared with ETH 129 in the membrane. This electrode would be the most likely candidate for obtaining a low Ca²⁺ detection limit in measurements performed with high K⁺, Na⁺, Mg²⁺ background, which is found inside the cells of living organisms, for example. The potentiometric response of the electrode in solutions containing main and interfering ions is in good agreement with simulated curves obtained using the Nernst–Planck–Poisson (NPP) model.     

Synthesis of a Tweezer—like Bis（Phenylthiapropoxy）calix[4]—arene as a Cation／π Enhanced Sensor for Ion—Selective Electrodes

Two novel 25,27-dihydroxy-26,28-bis(3-phenylthiapropxy)-calix[4]arene(3) and 25,27-dihydroxy-26,28-bis(3-phenylthiapropoxy)-5,11,17,23-tetra-tert-butylcalix[4] arene (4) were synthesized for the evaluation of their ion-selectivity in ion-selective electrodes(ISEs).ISEs based on 3 and 4 as neutral ionophores were prepared,and their selectivity coefficients for Ag^ (lg KAg,M^pot)were investigated against other alkali metal,alkaline-earth metal,aluminum,thallium(Ⅰ）,Lead and some transition metal ions using the separate solution method (SSM).These ISEs showed excellent Ag^ seletivity over most of the interfering cations examined,except for Hg^2 and Fe^2 having relative smaller interference(lg KAg,M^pot≤-2.1).     

Thin‐film Potentiometric Sensor to Detect CO2 Concentrations Ranging Between 2 % and 100 %

A potentiometric thin‐film sensor to detect CO₂ in a wide range (2–100 %) has been developed. The system has been fabricated depositing a reference electrode of Pt, a solid electrolyte of YSZ (Yttria‐stabilized Zirconia), a sensing phase made of Li₂CO₃ and a working electrode of Au via Physical Vapor Deposition (PVD). Characterization of the different elements has provided the optimal fabrication parameters and the system response for CO₂ concentrations can be measured from 2 to 100 % at 450 °C. The sensor behaves as a non‐Nerstian system and slightly deviates from a linear response with the logarithm of CO₂ until the CO₂ concentration reaches the 30 %. Higher CO₂ amounts make the response divert more from the Nernst law but give a stable and reproducible response to CO₂ in a wide range of concentrations. Based on these promising results the recovery time, stability, repeatability and selectivity of the sensor have been measured. The performance showed by the thin film sensor proves the feasibility of the use of this system for biogas and natural gas applications owing to its very good consistency at low temperature in a wide concentration range.     

Selective and Sensitive Fluorescent Chemosensors for Cu2+ Ion Based upon Bis‐1,8‐naphthalimide Dyads

A series of new fluorescent chemosensors 5a – 5e , composed of two aminonaphthalimide fluorophores and 2,6‐bis((N‐aminoalkyl)aminocarboxy)pyridines, were prepared, characterized, and their fluorescent properties towards heavy and transition metal (HTM) ions were investigated. Chemosensors 5c – 5e exhibited high selectivity and sensitivity for Cu²⁺ ion over other HTM ions with fluorescent quenching (green to colourless). It clearly demonstrated that the length of the linkers (diamines) between the aminonaphthalimides and 2,6‐dicarboxypyridine of 5a – 5e was very important for their sensitivity and selectivity for Cu²⁺ ion over other HTM ions.     

An All‐solid‐state Polymeric Membrane Ca2+‐selective Electrode Based on Hydrophobic Alkyl‐chain‐functionalized Graphene Oxide

An all‐solid‐state polymeric membrane Ca²⁺‐selective electrode based on hydrophobic octadecylamine‐functionalized graphene oxide has been developed. The hydrophobic composite in the ion‐selective membrane not only acts as a transduction element to improve the potential stability for the all‐solid‐state Ca²⁺‐selective electrode, but also is used to immobilize Ca²⁺ ionophore with lipophilic side chains through hydrophobic interactions. The developed all‐solid‐state Ca²⁺‐selective electrode shows a stable potential response in the linear range of 3.0×10⁻⁷–1.0×10⁻³ M with a slope of 24.7±0.3 mV/dec, and the detection limit is (1.6±0.2 )×10⁻⁷ M (n =3). Additionally, due to the hydrophobicity and electrical conductivity of the composite, the proposed all‐solid‐state ion‐selective electrode exhibits an improved stability with the absence of water layer between the ion‐selective membrane and the underlying glassy carbon electrode. This work provides a simple, efficient and low‐cost methodology for developing stable and robust all‐solid‐state ion‐selective electrode with ionophore immobilization.     

All Solid State Nickel(II)‐Selective Potentiometric Sensor Based on an Upper Rim Substituted Calixarene

A new ionophore, i.e. p‐(2‐thiazolazo)calix[4]arene ( I ) has been explored for its selective behavior towards Ni(II) ions. A poly(vinyl chloride) based membrane containing ( I ) as an electroactive material along with sodiumtetraphenylborate (NaTPB), and nitrophenyloctyl ether in the ratio 10 : 100 : 3 : 150 (I:PVC:NaTPB:NPOE) (w/w) was used to fabricate an all solid state nickel(II)‐selective sensor. The developed sensor exhibited a working concentration range of 1.0×10^?6–1.0×10^?1 M, with a Nernstian slope of 28.9±1.0 mV/decade of activity and a response time of 10–15 s. This sensor shows a detection limit of 9.0×10^?7 M. Its potential response remains unaffected of pH in the range 3.0–7.6, and the cell assembly could be used successfully in partially nonaqueous medium (up to 10 % v/v) without any significant change in the slope value or the working concentration range. The sensor worked satisfactorily for about ten weeks and exhibited excellent selectivity over a number of mono‐, bi‐, and tri‐valent cations including alkali, alkaline earth metal, and transition metal ions. It could be used as an indicator electrode for the end point determination in the potentiometric titration of nickel ions against ethylenediaminetetraacetic acid (EDTA) as well as for the determination of nickel ion concentration in real samples.     

New Macrocyclic Diamides as Neutral Ionophores for Highly Selective and Sensitive PVC‐Membrane Electrodes for Be2+ Ion

Five recently synthesized macrocyclic diamides were investigated to characterize their ability as beryllium ion carriers in potentiometric PVC‐membrane electrodes. The electrodes based on 1,15‐diaza‐3,4;12,13‐dibenzo‐5,8,11‐trioxabicyclo[13,2,2] heptadecane‐2,14‐dione exhibited a Nernstian response for Be²⁺ ion over wide concentration ranges (from 3.0×10^?6 to 3.0×10^?2 M for polymeric membrane electrode, PME, and from 5.0×10^?7 to 2.0×10^?2 M for coated glassy carbon electrode, CGCE) and very low detection limits (2.0 ×10^?6 M for PME and 4.0×10^?7 M for (CGCE). The electrodes possess low resistances, fast responses, satisfactory reproducibilities and, most importantly, good selectivities relative to a variety of other common cations. The potentiometric response of the electrodes is independent of pH of test solution in the pH range of 4.0–7.5. The proposed sensors were used to determine beryllium ion in water samples.     

A Novel Molecularly Imprinted Potentiometric Sensor for the Fast Determination of Bisoprolol Fumarate in Biological Samples

In this study, molecularly imprinted polymer (MIP) was prepared and used in the preparation of carbon paste electrode (CPE) for the quantification of bisoprolol fumarate (BF) in pure, pharmaceutical formulation and biological fluids. The selective MIP for BF was synthesized from methacrylic acid as the functional monomer, ethylene glycol dimethacrylate as the cross-linker in dimethyl sulfoxide solution, BF as the template molecule and 2, 2-azobisisobutyronitrile (AIBN) as the initiator. The non-imprinted polymer (NIP) was synthesized by the same procedure, but in the absence of the template molecule then incorporated in the paste of the carbon paste electrodes (CPEs). The prepared MIP for BF and its corresponding NIP were well characterized using scanning electron microscopy (SEM), Fourier transform infrared spectrometer, and thermal gravimetric analysis (TGA). The MIP and NIP based CPEs were further used for the determination of BF and the obtained results indicated that the sensor modified by the MIP have much higher recognition power for the BF molecules than the NIP based sensor where the MIP based CPE exhibited a Nernstian response 29.50±0.55 mV decade⁻¹ within a concentration range of 1.0×10⁻⁷–1.0×10⁻² mol L⁻¹and pH independence in the range 3.50–7.15. The proposed sensor has high selectivity over several possible interfering compounds. The obtained results by the proposed sensor were satisfactory with excellent percentage recovery and relative standard deviation and were comparable with those obtained from HPLC reported method.     

A Potentiometric Sensor for Cd2+ Based on Carbon Nanotube Paste Electrode Constructed from Room Temperature Ionic Liquid,Ionophore and Silica Nanoparticles

A novel and effective potentiometric sensor for the rapid determination of Cd²⁺ based on carbon paste electrode consisting of the room temperature ionic liquid 1‐butyl‐3‐methylimidazolium hexafluorophosphate, multiwalled carbon nanotubes, silica nanoparticles and ionophore was constructed. The prepared composite has a low potential drift, high selectivity and fast response time, which leads to a more stable potential signal. A linear dynamic range of 4.50×10^?9–1.00×10^?1 mol L^?1 with a detection limit of 2.00×10^?9 mol L^?1 was obtained. The modified electrode was successfully applied to the accurate determination of trace amounts of Cd²⁺ in environmental and biological samples.     

Evaluation of a PVC‐Based Thionine‐Zeolite and Zeolite Free Membranes as Sensing Elements in Ion Selective Electrode

The construction and performance characteristics of thionine electrodes based on the ion‐pair complex thionine‐tungstophosphate and thionine‐mordenite zeolite embedded in a polyvinyl chloride (PVC) matrix is described. Thionine electrode based on the ion‐pair is used for the indirect determination of ascorbic acid by standard addition method.     

New Ion‐Pair Based All‐Solid‐State Surfactant Sensitive Sensor for Potentiometric Determination of Cationic Surfactants

Cationic surfactants of different types were determined using a few potentiometric sensors based on ion‐pair complexes (dodecyldimethylbenzylammonium dodecylsulfate, dodecylmethylbenzylammonium dodecylbenzensulfonate, tetrahexadecylammonium dodecylsulfate and Hyamine (benzethonium dodecylsulfate)) as sensing materials. The response of the all‐solid state surfactant sensitive electrode based on a Teflonized graphite conducting substrate, coated with a PVC membrane containing sensing material, was investigated in the solutions of Hyamine and hexadecyltrimethylammonium ion in the concentration range from 1 μM to 10 mM. Potentiometric surfactant cation titration has been performed using sodium dodecylsulfate as titrant and an ion‐pair‐based surfactant sensitive electrode as a potentiometric indicator. Several commercial surfactant products have also been titrated and the results were compared with those obtained with two‐phase standard titration method.     

Characterization of a Silver Modified PVCAc Electrode and Its Application as a Ag(I)‐Selective Potentiometric Sensor

An all solid‐state Ag(I) ion‐selective electrode has been prepared by simply immersing a glassy carbon rod coated with PVCAc, which contained plasticizer and additive but no ionophore, into the AgNO₃ solution. The response of the electrode was linear with a Nernstian slope of 60.25 mV/decade within the concentration range from 1×10^?1 to 1×10^?5 M and with a detection limit of 4.25×10^?6 M. The stability as an effect of various cations was defined. The electrode is suitable for use in high acidic solutions (pH<1 to 7) and has successfully been applied for the determination of silver(I) concentrations in different samples.     

Benzothiazole‐Pyimidine‐Based BF2 Complex for Selective Detection of Cysteine

Due to the similar structure and reactivity of cysteine (Cys), homocysteine (Hcy) and glutathione (GSH), the simultaneous discrimination of Cys over Hcy and GSH by a single fluorescent sensor is still a great challenge. In this work, a benzothiazole‐pyimidine‐based boron difluoride complex ( BPB ) was developed as a new fluorescent sensor for Cys. The sensor exhibits a highly selective “turn‐on” response to cysteine over Hcy, GSH and other amino acids in aqueous solution at physiological pH. The observed pseudo‐first‐order rate constant for the reaction of BPB with Cys was calculated to be about 0.062 min⁻¹. The detection limit of this sensor for Cys was determined to be 332 nm, and bioimaging of exogenous Cys by this sensor was successfully applied in living cells, thus indicating that this sensor holds great potential for biological applications.     

Potentiometric Iodide Selectivity of Polymer‐Membrane Sensors Based on Co(II) Triazole Derivative

The 3‐amion‐5‐mercapto‐1,2,4‐triazole cobalt(II) [Co(II)AMETR] was used as a new carrier for preparing polymeric membrane selective sensor which exhibited high affinity for iodide ion. The effects of membrane composition, pH, the influence of lipophilic ion additives and plasticizer on the response characteristics of the sensor were investigated. The sensor showed a near Nernstian slope of ?56.6 mV/decade for I^? ion over a wide concentration range from 8.5×10^?7 to 1.0×10^?1 M with a low detection limit of 5.1×10^?7 M. The sensor has a fast response time and could be used over a wide pH range of 2–8. The response mechanism is discussed in view of the AC impedance technique. The sensor was successfully applied to direct determination of iodide content in environmental water samples and mouth wash samples.