Influence of decyl alcohol on the potentiometric behavior of three p-alkylbenzenesulfonate ion-selective electrodes

The influence of decyl alcohol on the potentiometric response of three para-alkylbenzenesulfonate (p-RBS) electrodes is analyzed. The results are clearly dependent on the membrane surface polarity due to the presence of the alcohol. The ionophore was the complex trioctylmethylammonium-p-RBS, (TOMA+)-p-RBS-, with R=H, CH3, and C2H5. The nature of the complex plays a fundamental role on the potentiometric behavior of the electrode showing that the more hydrophobic the complex, the better the potentiometric responses. Moreover, the electrodes selectivities for several hydrophilic and hydrophobic interfering anions were determined. The potentiometric results with interfering anions were coherent with the Pearson's hard and soft acid-base character of these anions.     

有机锡化合物结构与电极性能的构效关系研究

系统研究了三类有机锡化合物的阴离子响应行为。结果表明,有机锡化合物的结构与电极响应行为之间呈现出非常密切的构效关系。三类有机锡化合物对水杨酸根离子均呈现出选择性的电位响应性能,其中四配位有机锡化合物对水杨酸根离子呈现近nernst响应,而五、六配位有机锡化合物对水杨酸根离子均呈现超nernst响应。更重要的是,载体中心原子上正电荷密度对电极响应性能有很大影响。随着与锡原子相连的有机基团性质的变化,载体对水杨酸根离子的电位响应性能和选择性均发生规律性的变化,通过hammett常数定性地描述了载体结构与电极性能的构效关系。同时,通过交流阻抗、膜红外光谱等技术对电极响应机制作了初步探讨,并对超nernst现象和六配位有机锡化合物的响应行为进行了解释。     

Recent trends in potentiometric sensor arrays--a review

Nowadays there exists a large variety of ion sensors based on polymeric or solid-state membranes that can be used in a sensor array format in many analytical applications. This review aims at providing a critical overview of the distinct approaches that were developed to build and use potentiometric sensor arrays based on different transduction principles, such as classical ion-selective electrodes (ISEs) with polymer or solid-state membranes, solid-contact electrodes (SCE) including coated wire electrodes (CWE), ion-sensitive field-effect transistors (ISFETs) and light addressable potentiometric sensors (LAPS). Analysing latest publications on potentiometric sensor arrays development and applications certain problems are outlined and trends are discussed.     

Measurement of pork freshness using potentiometric sensor

This study evaluated pork freshness using potentiometric solid-state electrodes in order to detect chemical indices such as reduced compounds, organic compounds and sulfides, which are produced during the initial stage of putrefaction in meat. Pt, CuS and Ag₂S electrodes selected as solid-state electrodes have, respectively, been used to detect the organic compounds (regarded as chemical indices of deterioration in meat freshness). The outputs of these electrodes have been analyzed by principal component analysis (PCA) and multiple regression analysis (MRA) in order to find the correlation with the results of viable bacterial counts. By using the potentiometric sensor, the pork freshness was evaluated and the PCA and MRA corresponded to the degree of bacterial increases more simply and rapidly than other methods such as viable bacterial counts or a biosensor.     

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.     

Potentiometric carbon paste sensors for lead(II) based on dithiodibenzoic and mercaptobenzoic acids.

Dithiodibenzoic (DTB) acid and mercaptobenzoic (MB) acid were studied to characterize their abilities as modifier agents for lead(II) sensors. For both sensors, the best results were obtained with modified carbon paste electrodes with 24.1% of ligand. The pH influence on the potentiometric response was studied. The selectivity coefficients for both modified electrodes were tabulated. A potentiometric sensor based on DTB acid exhibited a more sensitive and selective response to lead ions than an MB electrode. The limits of detection for the DTB and MB electrodes were very similar, 5.01 x 10(-8) M and 3.98 x 10(-8) M, respectively, for lead(II) activity. The DTB sensor was applied to lead(II) ion determination in real samples and as an indicator electrode in potentiometric titrations. Natural and commercial humic acids were titrated using the DTB electrode to estimate the stability constant between these organic compounds and the lead(II) ions with successful results.     

Boronic esters as ionophores for potentiometric discrimination of the cis-trans isomeric dicarboxylic acids

Boronic esters incorporated into a poly(vinyl chloride) (PVC)-supported liquid membrane electrodes have displayed an anionic ionophore properties enabling their use in the potentiometric high-throughput screening procedures. These compounds belong to the class of ligands in which the anion recognition process can be explained on the concept of Lewis type acid-base interactions. Membranes containing boronic esters showed fairly good sensitivity for maleate (cis-isomer) in comparison to fumarate anions (trans-isomer). The potentiometric selectivity coefficients of proposed electrodes proved that common anions did not interfered with the maleate anion determination. The influence of structure of the three boronic esters ionophores on generation of potentiometric signal by developed liquid membrane electrodes was shortly discussed.     

Coated wire ion-selective electrode for palladium(II) and its application to catalyst analysis

The construction, performance and application of polymeric membrane (PME) and coated wire (CWE) palladium(II)-selective electrodes based on the ion pair between tetra bromopalladate(II) and hexadecylpyridinium cation (HDP⁺) in a poly(vinyl chloride) matrix, plasticized with o-NPOE are described. The influence of membrane composition, bromide ion concentration and pH on the potentiometric responses of electrodes were investigated. Nernstian responses were obtained for the two type of electrodes with low limits of detection (1.0×10⁻⁶ M for PME and 5.0×10⁻⁸ M for CWE). The potentiometric responses are independent of the pH of test solution in the range 3–8. The response time of electrodes are fast (30 s for PME and 10 s for CWE), and they can be used for at least 3 months without any considerable divergence in potentials. The proposed electrodes revealed good selectivity for palladium(II) respect to different cations and anions. They were used to the direct potentiometric determination of palladium(II) in silicon-alumina catalysts.     

Maltodextrins as new chiral selectors in the design of potentiometric, enantioselective membrane electrodes

Maltodextrins (dextrose equivalent (DE) 4.0-7.0, 13.0-17.0, and 16.5-19.5) are proposed as novel chiral selectors for the construction of potentiometric, enantioselective membrane electrodes. The potentiometric, enantioselective membrane electrodes can be used reliably for the assay of S-captopril as raw material and in pharmaceutical formulations such as Novocaptopril tablets, by use of direct potentiometry. The best response was obtained when maltodextrin with higher DE was used for construction of the electrode. The best enantioselectivity and time-stability was achieved for the lower DE maltodextrin. L-proline was found to be the main interferent for all the proposed electrodes. The surface of the electrodes can be regenerated by simply polishing; this furnishes a fresh surface ready for use in a new assay.     

Effect of the association of azo compounds on the results of the potentiometric determination of copper(II) in process solutions

The direct potentiometric determination of copper(II) using chalcogenide glass electrodes was studied in solutions containing azo dyes. The association of azo dyes, most pronounced in aqueous solutions of acid Blue 2K, was demonstrated by spectrophotometry. The interfering effect of reagent association on the results of the potentiometric determination of copper(II) was found.     

Validity of polarographic theory at short controlled drop times

Our studies are extended to investigate conventient baths for the anodic deposition of managanese and cobalt oxides, and to check the utility of these oxides as indicator electrodes in potentiometric titrations. The results showed new baths for the deposition of these oxides from their metal salt solutions in presence of complexing agents. The results of electron microscopic investigation confirmed by data given in the A.S.T.M. cards for all the oxides coincided with those given by the chemical analysis. The migration mechanisms were proposed and discussed in the light of different factors affecting the anodic deposition of the oxides. The oxide electrodes showed sensitive variation with pH and were successfully used as indicator electrodes in potentiometric titrations. Sharp inflections were generally observed in the vicinity of the end points.     

PVC Membrane electrodes for manual and flow-injection determination of tetraphenylborate: Applications to separate and sequential titrations of some metal ions

Three novel poly (vinyl chloride) matrix membrane electrodes, highly sensitive and selective for tetraphenylborate anion (TPB), are developed and electrochemically evaluated. They are based on the use of iron(II) bathophenanthroline, nickel(II) bathophenanthroline-and nitron-TPB ion-pair complexes as electroactive materials with dioctylphthalate (DOP) and 2-nitrophenyl phenyl ether (NPPE) as plasticizing solvent mediators. The electrodes exhibit stable and rapid near-Nernstian response for 10(-2)-10(-6)M TPB over the pH range 4-10. Use of these electrodes for direct potentiometric determination and potentiometric titration of as low as 1 mug of TPB/ml and 0.6 mg of TPB/ml give results with average recoveries of 99.3% (mean standard deviation 0.5%) and 99.4% (mean standard deviation 0.2%), respectively. Incorporation of nitron-TPB PVC sensor in a flow-through sandwich cell provides an efficient flow-injection detector for determining TPB with an input rate of at least 60 samples/hr. The limit of detection is 1.6 mug TPB/ml in a 20-mul sample. The electrodes are also used to monitor separate and sequential titrations of some metal ions with TPB. Alkaline earth and transition-metal ions upon reaction with polyethylene glycol and ethylenediamine, respectively, form cationic complexes readily titrated with TPB. Optimum conditions are outlined for sequential titrations of various combinations of metallic species.     

Phenothiazine Drug Poly(vinyl chloride) Matrix Membrane Electrodes and Their Use in Pharmaceutical Analysis

The construction and performance characteristics of ion-selective membrane electrodes for phenothiazine drugs based on their ion-pair complexes with tetraphenylborate and dinonylnaphthalenesulfonate in a poly(vinyl chloride) matrix are described. The electrodes show a near-Nernstian response over various ranges depending on the nature of the phenothiazine drug. The selectivity of these electrodes to a number of amino acids, alkaloids, neurotransmitters, quaternary ammonium compounds, and other drugs or pharmaceutical excipients is reported. The standard additions method and potentiometric titrations are used to determine the phenothiazine drugs in pharmaceutical preparations with satisfactory results.     

Cation selectivity of ionophores based on tripodal thiazole derivatives on benzene scaffold

The synthesis and potentiometric evaluation of new 1,3,5-tris(thiazolylcarbethoxy)-2,4,6-trimethylbenzene (3), 1,3,5-tris(thiazolylhydroxy)-2,4,6-trimethylbenzene (4), 1,3,5-tris(thiazolylmethyl)-2,4,6-trimethylbenzene (5), and 1,3,5-tris(thiazolylphenyl)-2,4,6-trimethylbenzene (6), toward mono and divalent cations under various pH conditions are outlined. The ion-selective properties of the newly synthesized compounds were studied by measuring the potentiometric responses of the 3-, 4-, 5-, and 6-based membrane electrodes to alkali metal, alkaline earth metal, ammonium, and transition metal ions, under various pH conditions. The 3-based electrode exhibited a Nernstian response to ammonium and potassium under alkaline pH conditions, while the other three electrodes showed a poor potentiometric performance. All electrodes showed substantial responses to silver ion under acidic condition, but there was almost nil response to other transition metal ions (Fe²⁺, Co²⁺, Zn²⁺, Ni²⁺, Pb²⁺, Cd²⁺, Cu²⁺ and Hg²⁺). The 3- and 5-based electrodes resulted in near Nernstian responses (51.3 mV and 59.5 mV/pAg⁺, respectively) with low detection limits (100 ppt), while the 4- and 6-based ones showed sub-Nernstian below 40 mV/pAg⁺. The results were interpreted with semi-empirically modeled structures.     

Antibody response of polymer membrane electrodes incorporating antigenic ionophores

An investigation of the antibody sensing properties of potentiometric polymer membrane electrodes incorporating antigens shows that at least two categories of such electrodes are possible. When the immobilized antigen has no ionophoric character of its own, antibody response can be obtained only upon conjugation of the antigen to an ionophore. The second category, corresponding to a new class of electrodes, yields potentiometric antibody response in the absence of a conjugated ionphore. These effects are illustrated with electrodes for antidigoxin, anti-DNP, and antiquinidine, respectively.     

Ti/TiO2 indicator electrodes formed by plasma electrolytic oxidation for potentiometric analysis

Ti/TiO₂ indicator electrodes were prepared by plasma electrolytic oxidation (PEO) method in the tetraborate electrolyte and were used for potentiometric indication of chemical reactions of different types and for analysis of surface and industrial wastewaters on the example of potentiometric determination of alkalinity and chloride. The electrodes formed at current densities of 0.05, 0.1, 0.15 and 0.2 A/cm² are different in composition, surface morphology and electroanalytical properties. The electrodes formed at a current density of 0.05 A/cm² exhibit the highest pH-sensitivity and generate the highest analytical signal at the equivalence point in the acid–base and precipitation titrations. The maximum analytical signal at the equivalence point, exceeding in magnitude the analytical signal, obtained by classical Pt electrode in oxidation–reduction and complexometric titrations generates PEO layers formed at a current density of 0.05 A/cm² and a platinum-modified nanoparticles. The results of the potentiometric titration of the surface and technogenic waters using as indicator Ti/TiO₂ electrodes are comparable with the conventionally used glass electrode (to determine alkalinity) and Ag electrode (to the determine chloride) and the results of visual titration. The advantage of the obtained metal oxide systems is the ability to determine two hydrochemical parameters due to their multifunctionality and opportunity to work with a single electrode. In addition, these sensors offer some analytical characteristics such as sensitivity, good reproducibility, high mechanical stability and a simple preparation procedure.     

Anion selective polymeric membrane electrodes based on cyclopalladated amine complexes

The potentiometric anion selectivity of two polymer membrane based electrodes (I and II) formulated with two new cyclopalladated amine complexes as the active components are examined. The electrodes exhibit a non-Hofmeister selectivity pattern with a significantly enhanced response towards thiocyanate, iodide and nitrite. The graph potential versus log c is linear over the concentration range 10(-6)-6x10(-2) M thiocyanate with electrode I and 10(-6)-10(-3) M with electrode II; 10(-5)-10(-2) M iodide with electrode I and 10(-3)-6x10(-2) M with electrode II; and 10(-3)-6x10(-2) M nitrite with both electrodes. The influence of the plasticizer and pH are studied. The potentiometric selectivity coefficients for I, II and blank membrane electrodes are reported. The selective interaction between Pd(II) thiocyanate, iodide and nitrite is postulated to be the reason for its higher response.     

溶剂聚合膜pH电极作内电极的气敏电极的研究

研究了以中性载体为活性物的石墨内导平头溶剂聚合膜(SPM)pH电极作内电极的二氧化碳和氨气敏电极。电极的性能取决于中性载体的特性,其中以菸酸十八酯为内电极膜活性物的二氧化碳气敏电极和以二辛基十八胺为活性物的氨气敏电极性能较佳。二氧化碳气敏电极用作丙酮酸脱羧酶酶电极的原电极,其性能院于传统的以玻璃pH电极作内电极的二氧化碳气敏电极。     

Ionic Liquids Modify the Performance of Carbon Based Potentiometric Sensors

A new type of potentiometric sensor based on a recently constructed carbon ionic liquid electrode (CILE) is described. Two kinds of ionic liquids, i.e., N‐octylpyridinium hexafluorophosphate (OPFP) and 1‐butyl‐3‐methylimidazoluim hexafluorophosphate (BMFP) were tested as binder for construction of the carbon composite electrode. The characteristics of these electrodes as potentiometric sensors were evaluated and compared with those of the traditional carbon paste electrode (CPE). The results indicate that potentiometric sensors constructed with ionic liquid show an increase in performance in terms of Nernstian slope, selectivity, response time, and response stability compared to CPE.     

Potentiometric membrane sensors for the selective determination of pyridoxine hydrochloride (vitamin B6) in some pharmaceutical formulations

The construction and general performance characteristics of two novel potentiometric PVC membrane sensors responsive to the pyridoxine hydrochloride known as vitamin B6 (VB6) are described. These sensors are based on the use of the ion-association complexes of the pyridoxine cation with phosphomolybdate, and phosphotungstate counter anions as ion pair in a plasticized PVC matrix. The electrodes show a stable, near-Nernstian response for 6x10(-5)-1x10(-2) M VB6 at 25 degrees C over the pH range 2-4 with a cationic slope of 54.0+/-0.5 and 54.5+/-0.4 per concentration decade for pyridoxine-phosphomolybdate and pyridoxine-phosphotungstate respectively. The two electrodes have the same lower detection limit (4x10(-5) M) and the response times are 45-60 and 30-45 s in the same order for both. Selectivity coefficients for VB6 relative to a number of interfering substances were investigated. There is negligible interference from many cations, some vitamins and pharmaceutical excipients. Direct potentiometric determination of 15-2000 microg/ml pyridoxine shows an average recovery of 98.0% and 99.0% with relative standard deviation 1.5% and 1.2% at 100.0 microg/ml for pyridoxine-phosphomolybdate and pyridoxine-phosphotungstate electrodes, respectively. The determination of VB6 in some pharmaceutical preparations using the proposed electrodes gave an average recovery of 98.0 and 99.0% of the nominal value and a mean standard deviation of 1.1% and 0.9% (n=10) for pyridoxine-phosphomolybdate and pyridoxine-phosphotungstate electrodes, respectively. The results compare favorably with data obtained by the British Pharmacopoeia method.