Thin layer coulometric determination of nitrate in fresh waters

A nitrate ion-selective electrode (ISE) employing a permeable tubular membrane impregnated with a conventional ISE cocktail has been used successfully in the coulometric analysis of nitrate in fresh waters. The liquid ISE membrane comprising a nitrate ionophore [tridodecylmethylammonium nitrate (TDMAN)], lipophilic electrolyte [tetradodecyl-ammoniumtetrakis(4-chlorophenyl)borate (ETH 500)] and plasticizer [bis(3-ethyl-hexyl)sebacate (DOS)] was supported on a porous polypropylene tube. Coulometric analysis with the tubular membrane ISE showed that nitrate could be detected in the range 10–100 μM with a precision of 2.3% relative standard deviation (RSD), limit of detection of 1.1 μM and relative accuracy of 4.4% compared to a certified reference material (CRM) Lake sample.     

Construction and evaluation of ion-selective electrodes for potassium and calcium with a summing operational amplifier. Application to wine analysis

Electrodes selective to potassium and calcium with improved senstivity were constructed like conventional electrode (ISEs), but used an operational amplifier to sum the potentials supplied by the four membranes (ESOAs). The results obtained during the evaluation of their working characteristics were compared to those obtained by conventional ISEs and were found to be similar, but with higher precision. The electrodes were used in the potentiometric determination of potassium, calcium and magnesium in wines. The results given by ESOAs were more precise than those from ISEs. The results obtained by potentiometry were in good agreement with those from AES for potassium and AAS for calcium and magnesium.     

Construction and evaluation of ion-selective electrodes for potassium and calcium with a summing operational amplifier. Application to wine analysis

Electrodes selective to potassium and calcium with improved senstivity were constructed like conventional electrode (ISEs), but used an operational amplifier to sum the potentials supplied by the four membranes (ESOAs). The results obtained during the evaluation of their working characteristics were compared to those obtained by conventional ISEs and were found to be similar, but with higher precision. The electrodes were used in the potentiometric determination of potassium, calcium and magnesium in wines. The results given by ESOAs were more precise than those from ISEs. The results obtained by potentiometry were in good agreement with those from AES for potassium and AAS for calcium and magnesium. Received: 27 June 1997 / Revised: 29 September 1997 / Accepted: 3 October 1997     

叠层型串联ISE的电分析化学性能与Nernst倍增效应

设计了多元叠层型串联ISE,结构紧凑,组装简便,适用于微体积样液分析。对四元叠层型串联ISE的试验表明:与现行ISE比较,其线性响应斜率、测定精密度与灵敏度均增大4倍,但响应速度、选择性系数与检测下限不变。     

An accurate and stable nitrate-selective electrode for the in situ determination of nitrate in agricultural drainage waters

A field evaluation of a novel nitrate-ion selective electrode (ISE) was undertaken by continuous immersion over a period of 5 months in agricultural drainage weirs. The nitrate sensor N,N,N-triallyl leucine betaine was covalently attached to polystyrene-block-polybutadiene-block-polystyrene (SBS) using a free radical initiated co-polymerisation, to produce a rubbery membrane which was incorporated into a commercially available electrode body. A measurement unit was constructed comprising the nitrate-ISEs, a reference electrode and a temperature probe connected through a pre-amplifier to a data-logger and battery supply. A temperature correction algorithm was developed to accomodate the temperature changes encountered in the drainage weirs. The nitrate results obtained with the ISEs at hourly intervals compared very favourably (R2 = 0.99) with those obtained with laboratory automated chemical determinations made on contemporaneous samples of drainage in a concentration range 0.47-16 ppm nitrate-N. The ISEs did not require re-calibration and no deterioration in performance or fouling of the membrane surface was observed over four months of deployment.     

Development of miniaturized potentiometric nitrate- and ammonium selective electrodes for applications in water monitoring

Mobile analysis with potentiometric sensors is well suited for field measurements. Ion-selective electrodes (ISE) based on polymeric membranes for in-situ determination of nitrate and ammonium contents in ground water, drinking water and surface water have been developed. The ISE are integrated in a multisensor module (MSM) for monitoring these ions over longer time intervals. The receptor is a PVC-membrane with tridodecylammonium nitrate (TDDA) for nitrate- and nonactine for ammonium-electrodes as ionophores. As plasticizer dibutylphthalate (DBT) was used. The main parameters for assessing the efficiency of these ISE are presented.     

Development of miniaturized potentiometric nitrate- and ammonium selective electrodes for applications in water monitoring

Mobile analysis with potentiometric sensors is well suited for field measurements. Ion-selective electrodes (ISE) based on polymeric membranes for in-situ determination of nitrate and ammonium contents in ground water, drinking water and surface water have been developed. The ISE are integrated in a multisensor module (MSM) for monitoring these ions over longer time intervals. The receptor is a PVC-membrane with tridodecylammonium nitrate (TDDA) for nitrate- and nonactine for ammonium-electrodes as ionophores. As plasticizer dibutylphthalate (DBT) was used. The main parameters for assessing the efficiency of these ISE are presented.     

Electrochemical Study of the Chelation of Cu2+ Cation by 18-Crown-6-Ether and Hydroxybenzoic Acids in Aqueous Solution

The chelation of Cu²⁺ cation by salicylic acid, sodium salicylate, m- and p-hydroxybenzoic acids, and a macrocyclic receptor, such as 18-crown-6-ether, have been studied by means of pH and emf measurements with a Cu²⁺/Cu ion-selective electrode (ISE). The latest permit the determination of thermodynamic stability constants based on activity quotients, which is unusual in potentiometric studies. An experimental procedure has been set up to measure simultaneously both properties by using the combined glass electrode as the reference electrode of the ISE, with clear advantages with respect to the conventional double-junction electrodes with sleeve diaphragms. The studies have been carried out at 25°C as a function of ligand concentration at constant [Cu²⁺], and as a function of [Cu²⁺] at constant ligand concentration. Several models have been proposed to determine the stability constants of the chelates, proving different stoichiometries.     

Solid-state reference electrodes based on carbon nanotubes and polyacrylate membranes

A novel potentiometric solid-state reference electrode containing single-walled carbon nanotubes as the transducer layer between a polyacrylate membrane and the conductor is reported here. Single-walled carbon nanotubes act as an efficient transducer of the constant potentiometric signal originating from the reference membrane containing the Ag/AgCl/Cl⁻ ions system, and they are needed to obtain a stable reference potentiometric signal. Furthermore, we have taken advantage of the light insensitivity of single-walled carbon nanotubes to improve the analytical performance characteristics of previously reported solid-state reference electrodes. Four different polyacrylate polymers have been selected in order to identify the most efficient reservoir for the Ag/AgCl system. Finally, two different arrangements have been assessed: (1) a solid-state reference electrode using photo-polymerised n-butyl acrylate polymer and (2) a thermo-polymerised methyl methacrylate:n-butyl acrylate (1:10) polymer. The sensitivity to various salts, pH and light, as well as time of response and stability, has been tested: the best results were obtained using single-walled carbon nanotubes and photo-polymerised n-butyl acrylate polymer. Water transport plays an important role in the potentiometric performance of acrylate membranes, so a new screening test method has been developed to qualitatively assess the difference in water percolation between the polyacrylic membranes studied. The results presented here open the way for the true miniaturisation of potentiometric systems using the excellent properties of single-walled carbon nanotubes.     

Potentiometric measurement of ascorbate by using a solvent polymeric membrane electrode

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

Flow-Through Sandwich PVC Matrix Membrane Electrode for Flow Injection Analysis

Abstract

A flow-through sandwich potentiometric detector for FIA in which a PVC membrane sensor is applied on a conductive epoxy support is described. It allows simple replacement of the membrane when exhausted or substituition of the sensor system and shows good mechanical and electric stability. The device can be easily included in a block with a location for the reference electrode. The detector was activated with a commercial sensor selective to nitrate and its behaviour in FIA was studied. A comparison of its perfomance with that of a nitrate selective electrode of classic shape constructed by the same technique is presented.     

Simultaneous Determination of Na+, K+, Ca2+, Mg2+ and Cl− in Unstimulated and Stimulated Human Saliva Using All Solid State Multisensor Platform

Human saliva is one of the body fluids which collection method is relatively simple and non‐invasive. The article is dedicated to assess concentration (activity) of Na⁺, K⁺, Ca²⁺, Mg²⁺ and Cl⁻ in fresh, unstimulated or stimulated human saliva samples using single solid contact ion‐selective electrodes with conventional reference electrode and self‐made multisensor platform (MP) equipped with ion‐selective membranes for Na⁺, K⁺, Ca²⁺, Mg²⁺ and Cl⁻ and reference electrode made in solid state technology, based on dispersed KCl in the polymer. Both kind of electrodes, single ISE and miniaturized electrodes in multisensor platform (ISE‐MP) were made of glassy carbon. The electrode surfaces have been modified by conductive polymer (PEDOT) layer deposition; with the exception of Cl⁻ electrode, in which conducting polymer was not applied. Potentiometric measurements were used to compare the changes of the ionic composition in various samples of saliva.     

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.     

New titrants for perchlorate and fluoroborate

Three new titrants have been evaluated for the precipitation titration of perchlorate: cetylpyridinum chloride (CPC), cetyltrimethylammonium chloride (CETAC), and benzyldimethyltetradecylammonium chloride (BDTAC). CETAC yielded the highest precision and largest potentiometric break, closely followed by CPC. BDTAC produced considerably lower precision and smaller breaks. Fluoroborate was similarly determined with CPC and CETAC. Again CETAC yielded the highest precision and largest potentiometric break. Titrations were monitored with a fluoroborate ion-selective indicator electrode and a double-junction reference electrode. The perchlorate and nitrate ISEs may also be used for monitoring the emf. Both titrants are considerably less expensive than equivalent amounts of the commonly used tetraphenylarsonium chloride titrant.     

Novel Anion Exchangers for Electrodes with Improved Selectivity to Divalent Anions

It has been found that replacing of several long‐chain alkyl substituents at the nitrogen atom of lipophilic quaternary ammonium salts (QAS) by methyls results in a dramatic increase of the potentiometric selectivity of ion‐selective electrodes (ISE) with QAS‐based plasticized PVC membranes to some divalent anions against the monovalent ones. The discussed effect of QAS cation nature on the potentiometric selectivity is also partly retained for ISE with neutral carrier‐based membranes doped with QAS to provide anion permselectivity. This opens up new possibilities to control the potentiometric selectivity of ISE for divalent anions by the appropriate selection of the anion exchanger.     

Development of a Poly(vinyl chloride)-based Nitrate Ion-selective Electrode

The authors developed a nitrate ion-selective electrode(ISE) based on poly(vinyl chloride)(PVC) membrane with methyltrioctylammonium nitrate as a carrier and 1-decanol as a plasticizer. The performance of the nitrate-sensitive membranes was optimized by tuning the composition of components. The electrode exhibits a linear response with a Nernstian slope of (52±1.0) mV per decade for the nitrate ion concentration ranging from 5.8×10^-5 mol/L to 1.0 mol/L. The electrode can be used to detect a low concentration of nitrate ions down to 3×10^-5 mol/L in a pH range of 2.1-11.5 without any compensation. The advantage of the electrode includes simple preparation, short response time and good repeatability. The detection performance of the novel electrode on nitrate ions has been tested for water samples.     

Continuous flow analysis of iron in zinc electrowinning electrolyte using an iron chalcogenide glass ion-selective electrode Part I. Synthetic media

It is shown that the iron(III) chalcogenide glass membrane ion-selective electrode (ISE) can be calibrated in continuous flow analysis (CFA) using acidified iron(III) nitrate standards, yielding a 60+/-3 mV per decade change in activity of Fe(3+) response in the range 10(-7)-10(-2) M total iron(III). Extended ageing of the iron(III) ISE in 2 M zinc(II) sulphate did not alter the potentiometric response characteristics of the electrode. Furthermore, electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy in the presence and absence of zinc(II) sulphate failed to detect a zinc(II) interference on the iron(III) ISE. CFA/ISE determined activities of Fe(3+) in synthetic zinc electrolyte containing 2x10(-3)-2x10(-1) M total iron(III) yielded results falling within +/-0.2logaFe(3+) unit of the corresponding iron speciation data calculated using the minteqa2 program.     

Biparametric Potentiometric Analytical Microsystem Based on the Green Tape Technology

The construction and evaluation of a Low Temperature Co‐fired Ceramics (LTCC)‐based microsystem prototype as a possible on‐site microanalyzer to monitor the presence of two ions in water simultaneously is presented. The approach has been assayed to detect nitrate and chloride ions as model analytes by means of integrating in the same single substrate an ion selective polymeric membrane to nitrate and two screen‐printed Ag/AgCl electrodes. One supplies the chloride ion concentration and the other is to complete the potentiometric detection system as the reference electrode. The results obtained by the full characterization of the microanalyzer prove the relevance of the proposal and the possibility to be transferred to real‐world samples and environmental monitoring.     

A Solid-State Reference Electrode Based on a Self-Referencing Pulstrode

The design of solid-state reference electrodes without a liquid junction is important to allow miniature and cost-effective electrochemical sensors. To address this, a pulse control is proposed using an Ag/AgI element as reliable solid-state reference electrode. It involves the local release of iodide by a cathodic current that is immediately followed by an electromotive force (EMF) measurement that serves as the reference potential. The recapture of iodide ions is achieved by potentiostatic control. This results in intermittent potential values that are reproducible to less than one millivolt (SD=0.27 mV, n=50). The ionic strength is shown to influence the activity coefficient of released iodide in accordance with the extended Debye–Hückel equation, resulting in a predictable change of the potential reading. The principle is applied to potentiometric potassium detection with a valinomycin-based ion-selective electrode (ISE), demonstrating a completely solid-state sensor configuration.     

New polyacrylate-based lead(II) ion-selective electrodes

A novel polyacrylate-based matrix for potentiometric ion-selective electrodes has been developed. Isododecyl acrylate, acrylonitrile and hexanedioldiacrylate co-monomers along with the thermo-initiator 2,2-dimethoxy-2-phenylacetophenone were used as polymeric matrix components. A lead(II)-selective electrode (Pb-ISE) was constructed using the above matrix. The electrode showed comparable analytical performance in the micromolar range to Pb-ISEs with conventional poly(vinyl chloride)-based membranes containing neutral ionophore and with solid-state membranes containing a mixture of lead sulphide and silver sulphide. Electrochemical impedance spectroscopy studies revealed much lower ion mobility in the polyacrylate membrane than in plasticized poly(vinyl chloride) membranes. This result additionally indicates the possibility of obtaining a lower detection limit for ISEs using the new acrylate matrix.