Types Of Ion-selective Electrodes Research Articles

Self-Calibrated Ion-Selective Electrodes.

Ion-selective electrode (ISE) potentiometry is reliable only if on-site calibration using a standard solution is performed before ion measurements. The complex device and operation required for calibration hinder the implementation of ISEs in decentralized sensing. Reported herein is a new type of ISE that is calibrated by a built-in component of the sensor without requiring any fluid handling processes. The indicator and reference electrodes are connected by a thin ionic conductor such as an aqueous phase containing the measuring ions in a capillary tube. This connection establishes a baseline electromotive force (EMF) that incorporates phase boundary potentials across multiple interfaces of the electrochemical cell and serves as a one-point calibration. Unlike conventional ISEs that rely on one EMF reading for each measurement, the proposed sensor utilizes a sample-induced EMF change relative to the baseline for each ion measurement. The variability in relative EMF is found to be <2.0 mV for multiple full potentiometric sensors consisting of plasticizer-based K+ ISEs and hydrogel-based Ag/AgCl reference electrodes. This value is significantly smaller than the variability of absolute EMF readouts in similar sensors without the self-calibration design. Moreover, when the ion-conducting calibration bridge has a low concentration of primary ions, low ion mobility, and/or a small contact area with the indicator and reference phases, it does not compromise the Nernstian response slope toward the analyte ions in the sample and therefore does not need to be removed for sample testing. The accuracy of the single-use self-calibrated K+ sensor in testing undiluted human blood samples is validated using a commercial blood gas analyzer as the reference method. Although this study focuses on disposable sensors consisting of tubes, the fluidics-free self-calibration strategy may be adapted to other sensor configurations such as planar sensors.

Ion-Selective Electrodes for Detection of Lead (II) in Drinking Water: A Mini-Review

Despite the fact that the adverse health effects due to the intake of lead have been well studied and widely recognized, lead contamination in drinking water has been reoccurring worldwide, with some incidents escalating into a public drinking water crisis. As lead contamination is often related to lead-based pipes close to or inside homes, it is not realistic, at least in the near term, to remove and replace all lead connection pipes and lead-based plumbing. Effective monitoring of lead concentration at consumers’ water taps remains critical for providing consumers with first-hand information and preventing potential wide-spread lead contamination in drinking water. This review paper examines the existing common technologies for laboratory testing and on-site measuring of lead concentrations. As the conventional analytical techniques for lead detection require using expensive instruments, as well as a high time for sample preparation and a skilled operator, an emphasis is placed on reviewing ion-selective electrode (ISE) technology due to its superior performance, low cost, ease of use, and its promising potential to be miniaturized and integrated into standalone sensing units. In a holistic way, this paper reviews and discusses the background, different types of ISEs are reviewed and discussed, namely liquid-contact ISEs and solid-contact ISEs. Along with the potential opportunities for further research, the limitations and unique challenges of ISEs for lead detection are also discussed in detail.

PVC membrane, coated-wire, and carbon-paste ion-selective electrodes for potentiometric determination of galantamine hydrobromide in physiological fluids

We report on highly-sensitive ion-selective electrodes (ISEs) for potentiometric determining of galantamine hydrobromide (GB) in physiological fluids. Galantamine hydrobromide (GB) was selected for this study due to its previous medical importance for treating Alzheimer's disease. Three different types of ISEs were investigated: PVC membrane electrode (PVCE), carbon-paste electrode (CPE), and coated-wire electrode (CWE). In the construction of these electrodes, galantaminium–reineckate (GR) ion-pair was used as a sensing species for GB in solutions. The modified carbon-paste electrode (MCPE) was prepared using graphene oxide (MCPE-GO) and sodium tetrakis (trifluoromethyl) phenyl borate (MCPE-STFPB) as ion-exchanger. The potentiometric modified CPEs (MCPE-GO and MCPE-STFPB) show an improved performance in term of Nernstian slope, selectivity, response time, and response stability compared to the unmodified CPE. The prepared electrodes PVCE, CWE, CPE, MCPE-GO and MCPE-STFPB show Nernstian slopes of 59.9, 59.5, 58.1, 58.3 and 57.0 mV/conc. decade, and detection limits of 5.0 × 10−6, 6.3 × 10−6, 8.0 × 10−6, 6.0 × 10−6 and 8.0 × 10−6 mol L−1, respectively. The prepared ISEs also show high selectivity against cations (i.e. Na+, K+, NH4+, Ca2+, Al3+, Fe3+), amino acids (i.e. glycine, L-alanine alanine), and sugars (i.e. fructose, glucose, maltose, lactose). The prepared ISEs are applicable for determining GB in spiked serums, urines, and pharmaceutical preparations, using a standard addition and a direct potentiometric method. The fast response time (<10 s), long lifetime (1–5 weeks), reversibility and stability of the measured signals facilitate the application of these sensors for routine analysis of the real samples.

Recent progress of all solid state ion selective electrode

All solid state ion selective electrodes (ISE) is a significant research orientation in the study of potentiometric sensors. With the development of science, traditional liquid junction ISEs exhibit many disadvantages. The study of all solid state ISE has been attracted more and more attention in recent decade. They have been applied in so many fields, such as clinical test, environment monitoring and industry analysis. According to the different ion electron transfer principle of all solid state transducer, all solid state ISEs are classified into three types: double layer capacitance all solid state ISE, redox capacitance all solid state ISE, and double layer and redox mixed capacitance all solid state ISE. In this mini-review, the progress of the above three types of all solid state ISE were introduced and summarized. Meanwhile, the responding mechanism of every type all solid state ISE was discussed. The development tendency of all solid state ISE was also predicted.

Validated electrochemical and chromatographic quantifications of some antibiotic residues in pharmaceutical industrial waste water.

Realistic implementation of ion selective electrodes (ISEs) into environmental monitoring programs has always been a challenging task. This could be largely attributed to difficulties in validation of ISE assay results. In this study, the electrochemical response of amoxicillin trihydrate (AMX), ciprofloxacin hydrochloride (CPLX), trimethoprim (TMP), and norfloxacin (NFLX) was studied by the fabrication of sensitive membrane electrodes belonging to two types of ISEs, which are polyvinyl chloride (PVC) membrane electrodes and glassy carbon (GC) electrodes. Linear response for the membrane electrodes was in the concentration range of 10-5-10-2mol/L. For the PVC membrane electrodes, Nernstian slopes of 55.1, 56.5, 56.5, and 54.0mV/decade were achieved over a pH 4-8 for AMX, CPLX, and NFLX, respectively, and pH 3-6 for TMP. On the other hand, for GC electrodes, Nernstian slopes of 59.1, 58.2, 57.0, and 58.2mV/decade were achieved over pH 4-8 for AMX, CPLX, and NFLX, respectively, and pH 3-6 for TMP. In addition to assay validation to international industry standards, the fabricated electrodes were also cross-validated relative to conventional separation techniques; high performance liquid chromatography (HPLC), and thin layer chromatography (TLC)-densitometry. The HPLC assay was applied in concentration range of 0.5-10.0μg/mL, for all target analytes. The TLC-densitometry was adopted over a concentration range of 0.3-1.0μg/band, for AMX, and 0.1-0.9μg/band, for CPLX, NFLX, and TMP. The proposed techniques were successfully applied for quantification of the selected drugs either in pure form or waste water samples obtained from pharmaceutical plants. The actual waste water samples were subjected to solid phase extraction (SPE) for pretreatment prior to the application of chromatographic techniques (HPLC and TLC-densitometry). On the other hand, the fabricated electrodes were successfully applied for quantification of the antibiotic residues in actual waste water samples without any pretreatment. This finding assures the suitability of the fabricated ISEs for environmental analysis.

Construction of Different Types of Ion-Selective Electrodes. Characteristic Performances and Validation for Direct Potentiometric Determination of Orphenadrine Citrate.

Construction of Different Types of Ion-Selective Electrodes. Characteristic Performances and Validation for Direct Potentiometric Determination of Orphenadrine Citrate.

Electronic tongue for the detection of taste-masking microencapsulation of active pharmaceutical substances

Electronic tongues can produce chemical images of samples, whose changes can be correlated with general properties, e.g. taste sensations. In this work, a sensor array equipped with eight types of ion-selective electrodes was coupled with Principal Components Analysis in order to detect microencapsulation effect of two Active Pharmaceutical Ingredients (APIs), which influences their taste properties. The character of change of sensor array responses in samples modified by microencapsulation was the same in two investigated APIs (Ibuprofen and Rixithromycin), proving, that the “sensed taste” becomes similar in both formulations after Eudragit modification. The obtained results show, that the presented electronic tongue can be used for analysis of masking effects in drugs and detection of microencapsulation effect.

Construction of different types of ion-selective electrodes and validation of direct potentiometric determination of phenytoin sodium

Abstract The construction and performance characteristics of phenytoin sodium selective electrodes are detailed. Two types of electrodes: plastic membrane I and coated wire II, were constructed based on the incorporation of phenytoin sodium with tungstosilicic acid. The influence of membrane composition, kind of plasticizer, pH of the test solution, soaking time and the electrodes’ foreign ions were investigated. The electrodes showed a Nernstian response with a mean calibration graph slope of 30.9±0.1 and 28.9±0.1 mV decade−1 at 25°C for electrode I and II respectively, over a phenytoin sodium concentration range of 5×10−3−5×10−6 M and 1×10−3−1×10−6 M with a detection limit 1.3×10−6 M and 2.5×10−7 M for electrode I and II, respectively. The electrodes gave average selective precision and were usable within the pH range 6–10. Interference studies from common cations, alkaloids, sugars, amino acids and drug excipients are reported. The results obtained by the proposed electrodes were also applied successfully for the determination of the drug in pharmaceutical preparations and biological fluids.

In-situ measurement of the dissolved S2− in seafloor diffuse flow system: sensor preparation and calibration

The preparation approach and calibration result of an improved type of ion selective electrode (ISE), which is used to measure the total dissolved S2−, are introduced in this paper. The improved Ag/Ag2S electrode uses silver wire as the substrate, which is surrounded by electric polymer containing superfine silver powder. After the stabilization of the epoxy-resin, Ag2S layer was formed by chemical reaction with 0.2 mol/L (NH4)2S solution for 5 min. With Ag/AgCl as reference electrode, the Ag/Ag2S electrode can be used to measure dissolved S2−. The correlation between the measured potentials and the logarithm of dissolved S2− is found to be linear, within range of the concentration of dissolved S2− from 10−2∼10−7 mol/L. The slope of the regression line between measured potential and logarithm of dissolved S2− is about −27.7, which agrees well with the theoretical Nernst value −29.6. Furthermore, the performance of the improved Ag/Ag2S electrode, such as the response time, sensitivity and stability, greatly outweighs the conventional Ag/Ag2S electrode.

Functional layers for chemical sensors based on conducting polypyrrole

Functional thin layers based on polypyrrole were used in electrochemical sensors as mixed conducting interfaces between ion-selective membranes and the wiring. In particular, new types of ion-selective electrodes for potentiometric measurement of pH value and concentration of sulfate ions in solutions were developed. The resulting electrodes do not need any inner liquid junction. First determinations of the sensor parameters sensitivity, selectivity and long term stability indicate a good performance of the prepared sensors. The results imply that interfaces, containing polypyrrole, could be an interesting basis for the construction of a new type of all-solid-state ion-selective electrodes.

Potential Stability of All-Solid-State Ion-Selective Electrodes Using Conducting Polymers as Ion-to-Electron Transducers

Demanding analytical applications such as on-line process analysis and clinical analysis require robust, reliable, and maintenance-free ion sensors of high potential stability. In this work the stability of the electrode potential of all-solid-state ion-selective electrodes using conducting polymers as ion-to-electron transducers is critically evaluated by using chronopotentiometry and electrochemical impedance spectroscopy. This study is focused on the relationship between the potential stability of the electrode and the capacitance of the solid contact where ion-to-electron transduction takes place. The influence of this capacitance on the potential stability of all-solid-state ion-selective electrodes is studied experimentally by using conducting polymer layers of different thickness as solid contacts in potassium ion-selective electrodes based on a solvent polymeric membrane. Because of its excellent environmental stability, the conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) is used as a model compound for the solid contact material. Chronopotentiometry is found to be a convenient and fast experimental method to critically evaluate the potential stability of different types of ion-selective electrodes.

Co-Ion Interference for Ion-Selective Electrodes Based on Charged and Neutral Ionophores: A Comparison

Interferences from co-ions, i.e., ions with a charge sign opposite to that of the measured ion, limit the upper detection limit of ion-selective electrodes (ISEs) based on electrically neutral or charged ionophores. A theoretical description based on phase boundary equilibria is used here to predict the co-ion interference (Donnan failure) of both types of ISEs quantitatively and to compare the extent of co-ion interference in these two cases. It is shown that, for practically relevant ionophore−site ratios, Donnan failure for ISEs based on electrically charged and neutral ionophore occurs at very similar co-ion concentrations if the charged and the neutral ionophores form complexes of equal stabilities and stoichiometries. With the exception of the selective complexation of the primary ion and charged ionophores, association of two or more ions such as between ionic sites and complexes has only a limited effect on co-ion interference. If relevant at all, ion pairing is predicted to affect upper detection...

Evaluation of a new wall‐jet flow‐through cell for commercial ion‐selective electrodes in flow injection potentiometry

AbstractAn improved wall‐jet configuration type flow‐through cell has been developed for use with commercial ion‐selective electrodes (ISEs) and has been evaluated in the flow injection potentiometric (FIP) mode. The flow‐through cell was designed to accommodate commercial ISEs that employ a range of sensing surfaces, including gas‐sensing, liquid polymer membrane and solid‐state based ISEs. Commercial ISEs employed for the evaluation of the flow‐through cell were ammonia, calcium and iodide ion‐selective electrodes. The observed electrode slopes were −58.8 ± 0.9, 25.2 ± 0.5 and −58.3 ± 0.9, mV change / activity decade, respectively, over a wide log‐linear range using a 100 μL sample volume in the FIP mode. Sample throughput rates as fast as 240 injections/h and analytically useful peak height responses can be achieved using injected sample volumes as low as 25 μL with all three types of ISEs.

Coated-wire and composite ion-selective electrodes based on doped poly(pyrrole)

Chemically and electrochemically prepared doped poly(pyrrole) has been evaluated as a membrane component for ion-selective electrodes (ISEs). Two types of ISE were prepared: coated-wire electrodes (CWEs) and classical ISEs with heterogeneous membranes. The classical ISE membranes investigated consisted of poly(pyrrole) particles dispersed in a polymer binder; the CWEs were doped poly(pyrrole) films produced by electropolymerization onto platinum wire or glassy carbon rods. Polymerization was carried out in aqueous electrolytes containing chloride, fluoride or nitrate counter anions. The characteristics of the electrodes varied with the electrode type and the conditioning procedure. The CWEs generally exhibited a sub-Nernstian response to the corresponding dopant anion, the actual response depending on polymerization conditions and subsequent conditioning of the electrode. In comparison, the classical ISEs with a heterogeneous membrane of electrochemically prepared poly(pyrrole) showed either reduced sub-Nernstian responses or cationic responses. The classical ISEs with membranes containing chemically polymerized pyrrole exhibited a sub-Nernstian response to the corresponding dopant anion. Electrode failure and poor electrode response appears to be related to the incorporation of cationic sites into the membrane.

Coated wire ion-selective electrodes and their application to environmental problems

Abstract

30] Ion selective electrode measurements

This chapter discusses selective electrodes that are used to measure the activities of ions in solution, primarily aqueous solutions. The measurement is potentiometric and requires a pair of electrodes—the ion selective electrode (ISE) and a reference electrode—and a high input impedance electrometer. The data obtained provides information concerning ionic activity. Except for very dilute solutions, ionic activity is proportional to ionic concentration. The proportionality factor relating activity to concentration is the activity coefficient. It highlights the activities and activity coefficients that can be measured, so that the measurement is made with a pair of ion selective electrodes, one of the electrodes being selective for each of the two ions involved. One ISE is used with a reference electrode having a liquid junction. The potential measured with the electrode pair then becomes primarily a function of the activity of the ion for which the ISE is selective. The activities and activity coefficients measured in this way are referred to as single ion activities and activity coefficients. The chapter also presents three types of ISE's: glass, liquid membrane, and solid state. Although the ion sensitive element is different in each of the three types, the principle of operation is the same for all—that is, the potential at the interface between the ion sensitive element and the solution in which it is immersed is proportional to the activity of the ions in the solution.

Ion-selective polymeric-membrane electrodes with immobilised ion-exchange sites. Part I. Development of a calcium electrode

A new type of ion-selective electrode is described in which ion-exchange sites are immobilised in a polymeric membrane by covalent bonding. Membranes were prepared by cross-linking a styrene-butadiene-styrene triblock copolymer with triallyl phosphate. After subsequent hydrolysis these membranes were evaluated as Ca2+ sensors. The electrodes formed exhibited an extended Nernstian response to Ca2+(10–1– 10–6M) and good selectivity over other alkaline earth and alkali metals. Such electrodes offer very fast response times, extended lifetimes and a wide pH working range. The possibilities of this new class of ion-selective electrode are also discussed.

Solid-state ion-selective electrodes based on thin ion-selective layers deposited on ionic conductors

A new type of ion-selective electrode has been developed. The electrode consists of a supporting material that is a good ionic conductor, covered with a thin ion-selective layer. The electrode response is fast and reproducible. Electrodes for measuring chloride, bromide, iodide and hydrogen orthophosphate ions are described.