Use Of Ion-selective Electrodes Research Articles

Selectivity coefficient for Ca/Na ion exchange in highly compacted bentonite

Bentonite clay is proposed as buffer material around the waste canisters and as tunnel backfill material in several concepts for disposal of radioactive waste. The distribution of charge compensating cations in the bentonite is of interest for several reasons, one being possible release of colloid particles from the bentonite to groundwater with very low ionic strength. The cation distribution at equilibrium may be calculated for various relevant groundwater compositions by use of selectivity coefficients. However, present literature data generally concerns coefficients measured in batch experiments with high water-to-solid ratios. The basic aim with the present work was therefore to determine selectivity coefficients for sodium/calcium exchange in bentonite with low water-to-solid ratios, and thereby give a reliable base for calculating the cation distribution in a confined bentonite buffer with a relatively high density. In total, six tests with homo-ionic Na- and Ca-montmorillonite, prepared to three material densities, were equilibrated with test solutions of successively increasing concentration. The distribution of cations at equilibrium was measured by use of ion selective electrodes and ICP/AES, and selectivity coefficients were calculated according to the Gaines–Thomas convention. The obtained selectivity coefficient was found to be in the range of 3.8–7.8, which is similar to those previously reported for high water-to-solid ratios.

Studies on the Preparation and Analytical Applications of Various Metal Ion-Selective Membrane Electrodes Based on Polymeric, Inorganic and Composite Materials—A Review

Ion-selective membrane electrodes commonly known as electrochemical sensors are important in view of the ability to make direct or indirect measurement of various metal ions. The fact is that the use of ion-selective electrodes for such type of measurements requires relatively inexpensive equipment, which makes ion-selective electrodes attractive to scientists in many disciplines. Thus, potentometric sensors can offer an inexpensive and convenient method for the analysis of heavy metal ions in solutions providing acceptable sensitivity and selectivity. For this purpose, many organic, inorganic, chelating, intercalating and composite materials were studied as electroactive materials for the preparation of ion-selective membrane electrodes. The present study provides a detailed review of literature for the fabrication, characterization and analytical applications of ion-selective membrane electrode based on different electro active components.

Investigation of Silver(I) Ion Sensing Property of Ruthenium(II) Thiosemicarbazone Complex Using Coated Graphite and Polymeric Membrane Electrodes

AbstractA ruthenium(II) complex [Ru(PPh3)2(pytsc)2] {Hpytsc = pyridine‐2‐carbaldehydethiosemicarbazone, (C5H5N)C2(H)=N3‐N2(H)‐C1(=S)N1H} has been used as an ion carrier for the selective determination of silver(I) ions in solution. Silver(I) ion‐selective coated graphite based (CGE) and PVC polymeric membrane based (PME) electrodes exhibit Nernstian slope for silver(I) ions over a wide concentration range from 1.0 × 10−1 M to 5.0 × 10−6 M (with CGE) and 1.0 × 10−1 M to 2.0 × 10−5 M (with PME). The working pH range of these electrodes has been found to be from 1.2 to 7.2 for CGE and 2.2 to 6.5 for PME. The proposed CGE sensor exhibits better analytical features like sensitivity and selectivity towards different secondary ions in comparison to the corresponding PME with no interference from mercury(II) ions $({\rm log} K ^{Pot}_{AG{\rm ^{+}}, \textrm{ } Hg{\rm ^{2+}}}=-3.30)$. These electrodes also act as indicator electrodes in potentiometric titration and have been successfully used for the determination of silver content in solution of real samples (1 gm dissolved in 100 mL of dilute nitric acid) such as silver ornaments and thin silver foils. Silver content determined by the use of ion selective electrode was found to vary in the concentration range from 1.20 x 10−2 M to 7.45 x 10−2 M and results were found to be comparable with those obtained from the traditional volumetric method of analysis. It is the first report of a metal‐ligand complex used as an ion carrier in ion selective electrode, which is selective for a metal ion other than the one used in the complex.

On the potentiometric investigation of the thermodynamic properties of mixed electrolyte systems: a new mixed solution method for the determination of potentiometric selectivity coefficients of ion-selective electrodes

With the aim of extending the use of ion-selective electrodes (ISEs) for the thermodynamic investigation of concentrated mixed electrolyte systems based on potentiometry, a mixed solution method (MSM) is reported for the determination of potentiometric selectivity coefficients () of ISEs. In this new method, the measurements are performed simultaneously in the presence of all relevant interfering ions in mixed electrolyte systems. As a result, the determination of is carried out in a realistic matrix environment with composition and ionic strength close to that of real mixed electrolyte samples and under experimental conditions where the ISE reveals its real practical mixed ion response behaviour.

Polymerized Nile Blue derivatives for plasticizer-free fluorescent ion optode microsphere sensors

Lipophilic H +-selective fluorophores such as Nile Blue derivatives are widely used in ISE-based pH sensors and bulk optodes, and are commonly dissolved in a plasticized matrix such as PVC. Unfortunately, leaching of the active sensing ingredients and plasticizer from the matrix dictates the lifetime of the sensors and hampers their applications in vivo, especially with miniaturized particle based sensors. We find that classical copolymerization of Nile Blue derivatives containing an acrylic side group gives rise to multiple reaction products with different spectral and H +-binding properties, making this approach unsuitable for the development of reliable sensor materials. This limitation was overcome by grafting Nile Blue to a self-plasticized poly( n-butyl acrylate) matrix via an urea or amide linkage between the Nile Blue base structure and the polymer. Optode leaching experiments into methanol confirmed the successful covalent attachment of the two chromoionophores to the polymer matrix. Both polymerized Nile Blue derivatives have satisfactory pH response and appropriate optical properties that are suitable for use in ion-selective electrodes and optodes. Plasticizer-free Na +-selective microsphere sensors using the polymerized chromoionophores were fabricated under mild conditions with an in-house sonic microparticle generator for the measurement of sodium activities at physiological pH. The measuring range for sodium was found as 10 −1–10 −4 M and 1–10 −3 M, for Nile Blue derivatives linked via urea and amide functionalities, respectively, at physiological pH. The observed ion-exchange constants of the plasticizer-free microsphere were log K exch = −5.6 and log K exch = −6.5 for the same two systems, respectively. Compared with earlier Na +-selective bulk optodes, the fabricated optical sensing microbeads reported here have agreeable selectivity patterns, reasonably fast response times, and more appropriate measuring ranges for determination of Na + activity at physiological pH in undiluted blood samples.

Use of ion-selective electrodes for determination of content of potassium in Egner-Rhiem soil extracts

Potassium is one of the most important nutrients for plants and its content in the soil should be monitored. In the precision agriculture, which is recommended now, the ion selective electrodes are tested to determine chemical properties of the soil. The objective of this work was an evaluation of use of the valinomycin-based ion selective sensors for determination of assimilated potassium in Egner-Rhiem soil extracts. Flame photometry was used as a reference method. Results obtained from potentiometric and photometric methods in soil extracts correlated linearly (<i>R</i><sup>2</sup> = 0.84). Analysis of soil extracts by the ion selective electrodes is simple and there is not a need for calcium ions precipitation.

In-Line and In Situ Monitoring of Ionic Surfactant Dynamics in Latex Reactors Using Conductivity Measurements and Ion-Selective Electrodes

In an emulsion polymerization process, surfactant type and concentration play an important role in the stability, appearance, reaction kinetics, and particle size distribution of latexes. The possibility of carrying out in-line evaluation of the distribution of free surfactant molecules in the media is of interest in polymer reaction engineering, because this would provide information about the rates of nucleation and particle stabilization. Both ion-selective electrodes and conductimetry seem to be very promising techniques for this objective. Ion-specific electrodes are able to determine the concentration of several substances, in a quantitative and specific manner, and may also be a good way of monitoring ionic surfactant. Conductivity measurements offer a means of monitoring the evolution of concentrations of different species in the latex. The objective of this work is to evaluate the use of ion-selective electrodes as a tool for the on-line monitoring of an emulsion polymerization reaction and to compare this method to conductivity. Ion-selective electrodes were prepared for two ionic surfactant species: dodecyl sulfate and dodecyltrimethylammonium, coming from SDS (sodium dodecyl sulfate) and DTAB (dodecyl trimethylammonium bromide), respectively. To do so, a glass electrode was coated with polymeric membranes specific for each surfactant. It is demonstrated that ion-selective electrodes can provide insight into the evolution of the colloidal surface in the latex, even when temperature and composition drifts are present.

Kinetic properties of wild-type and altered recombinant amidases by the use of ion-selective electrode assay method

A novel assay method was investigated for wild-type and recombinant mutant amidases (EC 3.5.1.4) from Pseudomonas aeruginosa by ammonium ion-selective electrode (ISE). The initial velocity is proportional to the enzyme concentration by using the wild-type enzyme. The specific activities of the purified amidase were found to be 88.2 and 104.2 U mg protein −1 for the linked assay and ISE methods, respectively. The kinetic constants— V max, K m, and K cat—determined by Michaelis–Menten plot were 101.13 U mg protein −1, 1.12 × 10 −2 M, and 64.04 s −1, respectively, for acrylamide as the substrate. On the other hand, the lower limit of detection and range of linearity of enzyme concentration were found to be 10.8 and 10.8 to 500 ng, respectively, for the linked assay method and 15.0 and 15.0 to 15,000 ng, respectively, for the ISE method. Hydroxylamine was found to act as an uncompetitive activator of hydrolysis reaction catalyzed by amidase given that there is an increase in V max and K m when acetamide was used as the substrate. However, the effect of hydroxylamine on the hydrolysis reaction was dependent on the type of amidase and substrate involved in the reaction mixture. The degrees of activation ( ε a) of the wild-type and mutant (T103I and C91A) enzymes were found to be 2.54, 12.63, and 4.33, respectively, for acetamide as the substrate. However, hydroxylamine did not activate the reaction catalyzed by wild-type and altered (C91A and W138G) amidases by using acrylamide and acetamide, respectively, as the substrate. The activating effect of hydroxylamine on the hydrolysis of acetamide, acrylamide, and p-nitrophenylacetamide can be explained by the fact that additional formation of ammonium ions occurred due to the transferase activity of amidases. However, the activating effect of hydroxylamine on the hydrolysis of p-nitroacetanilide may be due to a change in conformation of enzyme molecule. Therefore, the use of ISE permitted the study of the kinetic properties of wild-type and mutant amidases because it was possible to measure initial velocity of the enzyme-catalyzed reaction in real time.

Determination of Antiseptic Dyes with Ion-Selective Electrodes

The possibility of determining Methylene Blue and Brilliant Green antiseptic dyes in solutions with the use of ion-selective electrodes based on trioctyl oxybenzosulfonic acid was examined. Data on application of the electrodes fabricated to analysis of powdered dyes are presented. A gravimetric method for analysis for Brilliant Green was suggested and used as a comparative technique.

Binding of fluoride, bromide and iodide to bovine serum albumin, studied with ion-selective electrodes

The interactions of halide ions, F −, Br − and I −, with bovine serum albumin (BSA) in neutral aqueous solutions (pH=7.1) were investigated by the use of ion selective electrodes. The number of ions bound to BSA was determined from the difference in the amount of ion added to BSA solution and the amount of ion remaining free after equilibration. These data were treated according to the Klotz equation to find the number of binding sites, their equivalency and the binding constants. It was found that BSA has one binding site each for Br − and I −, and two equivalent binding sites for F − in neutral solutions. The rather small number of binding sites for the halides studied was attributed to a net charge of −18 reported in the literature for BSA. The binding constants for Br − and I − and the two stepwise binding constants for F − were also determined.

Trifluoroacetophenone derivatives as amino acid selective ionophores for the potentiometric determination of phenylalanine.

Selective sensors: Trifluoroacetophenone derivatives were synthesized with a hexasubstituted benzene ring as a preorganized spacer (see scheme) and their characteristics as ionophores were examined for use in ion-selective electrodes. The electrode membranes based on these neutral carriers combined with a cationic additive showed a monoanionic Nernstian response to underivatized phenylalanine, with excellent selectivity towards other essential amino acids and inorganic anions. Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2002/2002/z18872_s.pdf or from the author. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Detection of myocardial ischemia by epicardial detection of potassium ion activity

Early detection of myocardial ischaemia is a central problem in cardiological and cardiosurgical intensive care. A new approach is the use of ion-selective electrodes implanted directly on the myocardium, enabling detection of increased potassium activity as an indication of general hypoxia. After a comprehensive study of the electrode parameters, an animal experiment was carried out, in which it was found that respiration-induced hypoxia resulted in an increase in epicardial potassium activity (p < 0.01). Blood gas analysis performed simultaneously revealed reduced arterial pO2, but no acidosis. Haemodynamic data evidenced hypoxic depression of circulatory parameters. Histological examinations of the myocardium beneath the electrodes revealed typical lymphocytic infiltration. Electron microscopy demonstrated crystolysis in the mitochondria as an early sign of hypoxia, thus confirming the sensitivity of these electrodes. This underscores the potential of ion-selective electrodes for the detection of myocardial ischaemia, and they should now be investigated in the clinical setting.

Ionophores Based on Cationic Dye-Containing Ion Pairs and Their Use in Ion-Selective Electrodes

The use of ion-selective electrodes (ISEs) based on cationic dye-containing ion pairs in analytical chemistry was considered. The most important chemical analytical characteristics of the developed liquid and plasticized ISEs are presented. These electrodes offer promise for the creation of sensors for many inorganic and organic substances.

The use of ion-selective electrodes for evaluating residence time distributions in expanded bed adsorption systems.

The suitability of ion-selective electrodes (ISE) for the determination of residence time distribution (RTD) in turbid, cell-containing fluids was examined. The electrodes were found to give reproducible signals in biomass-containing feedstock with up to 20% wet weight of solids. The enhanced feedstock compatibility of IES, when compared to other tracer sensing devices, allows the study of expanded bed system hydrodynamics under relevant operating conditions. Within the linear range of the corresponding ISE-tracer pair, both examined ISE (Li(+)- or Br(-)-selective) showed to be insensitive against the range of flow rate and pH normally employed during expanded bed adsorption (EBA) of proteins. Analyzing the RTD obtained after a perfect ion tracer pulse in terms of the PDE model (PDE, axially dispersed plug-flow exchanging mass with stagnant zones) gave a quantitative description of the underlying hydrodynamic situation during EBA processing. These data provided a powerful tool to make predictions on the adsorptive global process performance with a defined feedstock type and composition. The link between the hydrodynamic events during feedstock application and the actual process performance was shown when applying intact yeast cell suspensions at different biomass content (up to 7.5% wet weight) and buffer conductivity (5-12 mS) onto an EBA column filled with the adsorbent Streamline Q XL as fluidized phase. On the basis of our experimental results, a guideline for the successful application of the ISE/RTD method to EBA process design is presented.

Reference ranges of electrolyte and anion gap on the Beckman E4A, Beckman Synchron CX5, Nova CRT, and Nova Stat Profile Ultra

The widespread use of ion-selective electrode causes the reference range of the anion gap (AG) to be lowered from 8–16 to 3–11 mmol/l. The use of the outdated reference range (8–16 mmol/l) leads to the misinterpretation of the value of the anion gap. To interpret the anion gap accurately, one must use an analyzer-specific reference range. This study established the reference ranges of the electrolyte and anion gap in four ion-selective electrode analyzers. We collected clotted and lithium-heparinized blood from 124 healthy volunteers. We determined the electrolyte in the Beckman E4A (serum), Beckman Synchron CX5 (serum), and Nova CRT (serum and plasma). The anion gap was calculated from the formula: [Na+−(Cl−+HCO3−)]. Blood sodium, potassium and bicarbonate were determined using the Nova Stat Profile Ultra. We used the plasma chloride from the Nova CRT to calculate the value of the anion gap in the Nova Stat Profile Ultra. We established the reference ranges using the non-parametric percentile estimation method. Accuracy and precision of the electrolyte performances obtained from all analyzers were acceptable. Reference values of serum and plasma sodium, potassium, and chloride were similar in all analyzers. The value of blood sodium obtained from the Nova Stat Profile Ultra was slightly higher than the values for the serum and plasma sodium obtained from the other analyzers. The bicarbonate ranges obtained from the Nova analyzers were higher than the values obtained from the Beckman analyzers. For the anion gap, the reference ranges in this study were low but similar to other studies (3–11 mmol/l) using ion-selective electrode. However, our reference ranges were lower than the previous reference ranges obtained from the continuous-flow analyzer (8–16 or 9–18 mmol/l) incorporated with flame photometry and colorimetry techniques.

Ionometric Study of the Kinetics of Acid Decomposition of Fluorapatite

A procedure is proposed for studying acid decomposition of solid materials with the use of ion-selective electrodes, with the experimental data recorded and processed with a personal computer. Variation of the H3O+, F-, and Ca2 + concentrations in reaction of fluorapatite concentrate with nitric, sulfuric, and orthophosphoric acids and also the effect of particle size on the rate of solid phase decomposition were studied.

The use of a phenylpyrazine liquid crystalline material with a liquid crystalline solvent mediator as an ion-selective electrode

Liquid crystalline 2-n-hexyloxy-5-(4-bromophenyl)pyrazine was investigated as a novel neutral ionophore for use in ion selective electrodes. Two membrane compositions were studied. The first membrane included o-nitrophenyl octyl ether as a plasticising solvent mediator, and in the second membrane the plasticising mediator was replaced with a commercial non-ionophoric liquid crystal material (E7 Merck). The inclusion of E7, which exhibits solvent mediator properties, ensured the ionophore was present in a room temperature liquid crystalline phase. For membranes containing the E7, improved Nernstian response was observed for ammonium ions over the same concentration range, together with improved selectivity when used as ammonium and caesium selective electrodes. This is believed to be the first calamitic liquid crystalline ionophore polymer system described and may have potential in direct manipulation of ionophores in polymer membrane electrodes, using established liquid crystal switching technology.

Ion-Selective Electrodes, Misinterpretation of Functional Mechanism, and New Results

This publication describes how the use of ion-selective electrodes (and also glass electrodes) has given rise to misinterpretation of the emergence of electrode potential over the years. It has been assumed that electrode potential is connected with ion transport through a membrane. It is now shown that the potential is established on the surface of the electrode by the energy giving the charge separation with the chemical potential of the salt, a component of which establishes chemisorption with a component of the membrane.

Measurement of Serum Ionized Magnesium in Capd Patients

To evaluate the magnesium status of continuous ambulatory peritoneal dialysis (CAPD) patients using a new method for assessing the level of the ionized fraction of serum magnesium. Serum ionized magnesium was measured in CAPD patients using the ion-selective electrode for Mg2+. The Dialysis Unit of Tampere University Hospital. Twenty-six patients on CAPD (age: 21-81 years, mean 54 +/- 16 years; duration of CAPD: 3-52 months, mean 13 months), and 26 sex- and age-matched healthy controls. Both serum ionized magnesium (0.73 +/- 0.11 mmol/L vs 0.56 +/- 0.07 mmol/L, p < 0.001) and total magnesium (1.11 +/- 0.22 vs 0.81 +/- 0.08 mmol/L, p < 0.01) were higher in CAPD patients than in sex- and age-matched controls. The ionized magnesium fraction of total magnesium was slightly lower in dialysis patients in spite of the fact that 16/26 patients had serum albumin less than 36 g/L. Hypermagnesemia (mean serum ionized magnesium 0.78 +/- 0.10 mmol/L) was observed in the 13 of 26 patients with 0.75 mmol/L Mg2+ dialysate; those with lower magnesium dialysate (Mg2+ 0.50 mmol/L in 10/26 and Mg2+ 0.25 mmol/L in 3/26) had mean serum ionized magnesium at the upper normal margin (0.69 +/- 0.10 mmol/L). In CAPD patients with Mg2+ 0.5-0.75 mmol/L in their dialysis fluid, both serum ionized and total magnesium concentrations were higher but the ionized/total magnesium ratio was lower than in healthy control subjects. Use of ion-selective electrodes to measure ionized magnesium may be a more useful methodology than measuring total magnesium in the evaluation of magnesium status of CAPD patients, because it is not influenced by hypoalbuminemia or increased complexed fraction of magnesium often present in dialysis patients.

Serum anion gap: reevaluation of normal values

As it is well known, the serum anion gap (SAG) equals the difference between the serum concentrations of the major cation (sodium) and the major measured anions (chloride + bicarbonate), and it is a useful tool for identifying the cause of a metabolic acidosis.1,2 Additionally, a low SAG has been found to be of value when evaluating a variety of conditions, such as multiple myeloma, hypoalbuminaemia, po1yc1onal hypergammaglobu1inaemia and bromism.3 The normal values of SAG are considered to be 12 ± 4 mmol/l (range 8-16 mmol/l). However, it has repeatedly been reported that because of the widespread use of ion-selective electrodes, the range for the SAG should be significantly lowered.4,5 We have prospectively studied 92 individuals (46 male, 46 female) with a mean age of 41 years (range. 18-64 years) admitted to our hospital for elective procedures. Subjects with diabetes mellitus. liver or renal failure, hypoalbuminaemia (serum albumin <40 g/l), as well as subjects receiving drugs affecting acid-base and electrolyte parameters were excluded. In all individuals the SAG was calculated. Serum sodium and chloride levels were determined by ion-selective electrodes, while serum bicarbonate levels were calculated from arterial blood pH and arterial blood carbon dioxide tension according to the Henderson-Hasselbalch equation. The results of our study are as follows: serum sodium level, 139 ± 3 mmol/l (range 136-143 mmol/l); serum chloride level, 104.5 ±4 mmol/l (range 99-110 mmol/l); serum bicarbonate level, 24.5 ± 2 mmol/l (range 21-26 mmol/l); and SAG, 8 ± 2 mmol/l (range 5-11 mmol/l). The SAG level measured was slightly higher than that recently reported.4,5 but significantly lower than the previously regarded normal value. In 36 cases, serum chloride levels were also measured by the mercuric nitrate-thiocyanate colorimetric reaction. By this method, the mean (SD) value of serum chloride levels was significantly lower than that obtained by ion-selective electrode (100.8 ± 3 vs 104 ± 3.5 mmol/l, respectively), while the mean (SD) value of SAG was 12 ± 3 mmol/l, almost identical to the traditionally normal value. We suggest that with ion-selective electrode technology, values of SAG should be re-evaluated. Additionally, the normal values of the serum sodium/chloride concentration ratio, commonly used for the assessment of mixed acid-base disorders, should be modified, as a previously normal value of 1.4 seems to be inappropriately high in the light of the higher serum chloride concentration measured by the newer autoanalysers.