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Ion-selective Electrodes
Abstract
This review presents the significant developments in the field of ion-selective electrodes (ISE). Exciting advances in all areas of ISE methodology have been reported and are covered. Specifically, we review work that has been published between the Fall of 1983 and the Fall of 1985. A manual search of major analytical journals and a computer search of Chemical Abstracts have been employed to collect the presented information. We apologize in advance for any papers that are not included because they were inadvertently missed in our search.
... 1,2 It has been proven difficult to control selectivity among anions, due to low charge to radii ratios, sensitivities to pH and high solvation energies. 3,4 At first, anion selective membranes electrodes prepared with conventional ion exchangers such as quaternary ammonium or phosphonium salts, [5][6][7] which interact with the target anion through electrostatic attraction and induce a selectivity sequence governed by anion's enthalpy of hydration. ...
... BEHP, DBP, AP and BA), BEHP is a more effective solvent mediator than DBP, AP and BA in preparing the iodide ion-selective electrode (Nos. 5,[9][10][11]. It should be noted that the nature of the plasticizer influences both the dielectric constant of the membrane and the mobility of the ionophore and its complex. ...
Neste trabalho foi preparado um eletrodo altamente seletivo de membrana de PVC com o complexo cobalto-salofen. O sensor mostra uma seqüência seletiva anti-Hofmeister, com preferência por íons iodeto sobre vários anions comuns. O eletrodo apresentou uma dinâmica linear na faixa de 5,0×10-7 a 1,0×10-1 mol L-1, com uma inclinação Nernstiana de 58,9 mV com um limite de detecção de 3,0×10-7 mol L-1. A região de pH de trabalho do sensor é de 3,1 a 9,8. A leitura rápida é de 15 s, e tem uma vida útil de 2 meses. Os coeficientes de seletividade para o eletrodo proposto foram melhorados para alguns interferentes, se comparado com os eletrodos de membrana de iodeto disponíveis. O eletrodo proposto foi aplicado com sucesso na determinação direta de iodeto em sal comestível e como eletrodo indicador na titulação potenciométrica de I contra Ag+.
... Arnold & Solsky [12] and Buck & Lindner [13] have reviewed ion-selective electrodes (ISEs) employing inorganic ion-exchangers as sensory molecules. It has been recognized that anions such as vanadates, phosphates, molybdates combined with hydrous oxides produce better-quality ion exchangers [14][15][16][17]. ...
Zirconium phosphoborate based heterogeneous membrane electrode has been used as a chemical sensor in aqueous medium. The membrane demonstrates sub-Nernstian response in the concentration range of 10⁻⁵ to 10⁻¹ mol L⁻¹ Ba(II) ions, with a slope of 20.7 mV decade⁻¹. The designed sensor has a fast response time of 15 s and has a detection limit of 6.31 × 10⁻⁷ mol L⁻¹ for Ba(II) ions. Effect of internal solution concentration on the slope of calibration curve was studied. The electrode was successfully used in partially non-aqueous medium. The proposed sensor shows good selectivity for Ba(II) ions with respect to rare earth metal and alkaline earth metal ions. The electrode does not show any change in response within pH range 3.5 to 9. The system was used successfully as an indicator electrode in potentiometric titration of Ba(II) ions with EDTA.
... An ion-selective electrode (ISE) contains a high-selectivity sensor to convert chemical activity of a specific ion in solution to electrical potential. ISEs are widely used for quick and easy ion monitoring (Solsky, 1990). The most common ISE is the pH electrode, which is one of the most-common pieces of equipment in analytical laboratories. ...
The negative-ion mode of electrospray ionization mass spectrometry (ESI-MS) is intrinsically less sensitive than the positive-ion mode. The detection and quantitation of anions can be performed in positive-ion mode by forming specific ion-pairs during the electrospray process. The paired-ion electrospray ionization (PIESI) method uses specially synthesized multifunctional cations to form positively charged adducts with the anions to be analyzed. The adducts are detected in the positive-ion mode and at higher m/z ratios to produce excellent signal-to-noise ratios and limits of detection that often are orders of magnitude better than those obtained with native anions in the negative-ion mode. This review briefly summarizes the different analytical approaches to detect and separate anions. It focuses on the recently introduced PIESI method to present the most effective dicationic, tricationic, and tetracationic reagents for the detection of singly and multiply charged anions and some zwitterions. The mechanism by which specific structural molecular architectures can have profound effects on signal intensities is also addressed. © 2015 Wiley Periodicals, Inc. Mass Spec Rev
... Over the past decade, important advances in the disciplines of electrochemistry, solid-state chemistry, and membrane technology have led to the commercial production of a wide variety of ion-selective electrodes (ISEs). Many clinical laboratories now routinely use ISEs for measuring blood gases, electrolytes, metabolites, and some amino acids (37)(38)(39)(40). ...
Spectroelectrochemical techniques are becoming increasingly versatile tools to solve a diverse range of analytical problems. Herein, the use of in situ real-time luminescence spectroelectrochemistry to quantify chloride ions is demonstrated. Utilizing the bleaching effect of chlorine-based electrogenerated products after chloride oxidation, it is shown that the fluorescence of the Rhodamine 6G dye decrease proportionally to the initial chloride concentration in solution. A strong decrease of fluorescence is observed in acidic media compared to a lower decrease in alkaline media, which suggests that Cl2, favourably generated at low pH, could be the main species responsible of the fluorescence loss. This fact is corroborated with chronoamperometric measurements where the complete loss of fluorescence for the bulk solution is achieved. A fast mass transfer is needed to explain this behavior, in agreement with the generation of gaseous species such as Cl2. Chloride detection was performed in artificial sweat samples in less than 30 s with great accuracy. This electrochemical/optical combined approach allows to quantify species difficult to measure by electrochemistry due to the inadequate resolution of their redox processes or without significant optical properties.
IntroductionOn-Line and In Situ MonitoringTypes of Sensor SystemsSensors of the Physical EnvironmentSensors of the Chemical EnvironmentSensors of the Biological SystemConclusions
References
Now a days, more and more rare earth elements are being applied in agriculture as micro element fertilizer in China because of their ability to improve the yield and quality of crops. The concentration of the REEs has remarkably increased in soil eco system and becomes a serious environmental problem. Hence it is very important to devise techniques for selective determination of these metal ions. Praseodymium-selective electrodes have been prepared using PVC and polystyrene as binders with zirconium (IV) antimonotungstate as an electro-active material. Both membranes have been used for further studies. These membranes work well over a concentration range of 5×10-5 M to 1×10-1 M of Pr3+ ions with a near-Nernstian s. lope of 25.0 mV/decade. The polystyrene based membrane has a fast response time of 10 seconds as compared to a PVC based membrane that gives a response time of 15 seconds. The effect of internal solution has been studied for both membranes. The working pH range for both membranes is the same i.e., 4.5-9. 0. Selectivity coefficients are determined using the matched potential method (MPM) for a number of metal ions, normally present alongwith praseodymium in its ores. Finally, these electrodes are used as indicator electrodes for potentiometric titrations of Pr3+ ions against EDTA solution.
Membranes containing varying compositions of electroactive material and epoxy resin as binder were prepared and it is seen that the one having composition 60% ZrBP and 40% epoxy resin exhibits best performance. It shows excellent response in the concentration range of 10-4M to 10 -1 M Tb (III) ion with super-Nernstian slope of 45 mV/decade. It has fast response time of 15 seconds. Effect of internal solution was studied and the electrode was successfully used in partially non-aqueous medium. The proposed sensor revealed good selectivity with respect to alkali, alkaline earth, some transition and rare earth metal ions and can be used in the pH range of 2.0-10.0. It was used as an indicator electrode in the Potentiometrie titration of Tb (III) ion against EDTA.
Highly selective poly(vinyl chloride) (PVC) membrane electrode based on N,N'-1,1-isobutanebis-(salicylald- iminato)uranyl(II) complex as carrier for thiocyanate-selective electrode is reported. The electrode exhibited a good Nernstian slope of -55.5 ± 1.2 mV, over a wide pH range of 3.5-8.5 and a linear range of 1.0×10-6 - 1.0 M for thiocyanate. Detection limit of electrode was 8.0×10-7 M SCN. Selectivity coefficients determined with fixed interference method (FIM) indicate a good discriminating ability towards SCN ions in comparison to other anions. The proposed sensor had a fast response time of about 10-20 s and can be used for at least 2 months without any considerable divergence in potential. It was applied as an indicator electrode for the titration of thiocyanate with Ag+ and potentiometric determination of thiocyanate in saliva and urine samples.
Hexadentate Macrocyclic ligand (3,5,13,15-tetramethyl 2,6,12,16,21-22-hexaazatricyclo[15.3.1.(1-17) 1(7-11)]cosa-1(21),2,5,7,9,11(22),12,15,17,19-decane) (L) was explored as an ionophore in determination of Samarium ion. Interaction study revealed that metal coordinated as a hexa-dentate ligand to the metal through four nitrogen atoms of azomethine groups and two of pyridine ring, characterized by FTIR spectrometry. Membrane composition of 3:30:65:2 (L: PVC: DBP: NaTPB) (wt%), worked best in the linear range of 1 x 10(-1) -1 x 10(-8) M. The lower limit of detection was found to be 1.58 x 10(-7) M with a response time of 10 s. The proposed electrode shows the super Nernstian slope of 20.7 mV decade(-1) with reasonably comparable selectivity to other transition metal and heavy metal ions. The selectivity coefficient was calculated using matched potential method. The lifetime of the electrode was found to be nearly 9 weeks. The response mechanism and the interaction of Sm(III) ion with the complexes have been discussed by FTIR and UV-Visible spectroscopic techniques and conductometrically. The electrode was further applied in the recovery of fluoride content in mouthwash samples.
A solvent polymeric plasticized membrane electrode based on Bis-(o-phenylenediamine)Cu(II) (Cu(II)BOPD) complex has been investigated as iodide selective electrode exhibiting anti-Hofmeister selectivity pattern. The membrane electrode exhibits a near Nernstian slope of –60.3 mV/decade in the linear range of 1.0 × 10–2–1.0 × 10–6 M with the detection limit of 3.2 × 10–7 in the pH range of 3–6. The response mechanism is discussed by UV-visible spectroscopic technique. The best membrane composition for the sensor is ionophore 3%, PVC 33%, Plasticizer 63%, cation excluder 1%. The proposed electrode was applied for the direct determination of iodide as an indicator electrode in potentiometric titration of I– against Ag+ and in the determination of iodide in pharmaceutical drugs.
The effect of temperature changes on the potential response of hexadecylpyridinium (HDP) and cetyltri-methylammonium (CTA) plastic-membrane, cation-selective electrodes was studied. These electrodes were found to be thermally stable up to 60 and 70°C, respectively. The isothermal temperature coefficients of the electrodes calculated from the standard electrode potentials at different temperatures were 0.00222 and 0.00097 V/°C. A method for regenerating such electrodes was applied successfully in case of the HDP electrodes.
A new salicylate-selective electrode based on the complex N,N'-1,4-butylene bis(3-methyl salicylidene iminato) copper(II) as the membrane carrier was developed. The electrode exhibits a good Nernstian slope of 59.1 1.0 mV/decade and a linear range of -1.0 M for salicylate. The limit of detection was M. It has a fast response time 10 s and can be used for more than three months. The selective coefficients were determined by the fixed interference method (FIM) and could be used in the pH range 4.5-10.5. It was employed as an indicator electrode for direct determination of salicylate in pharmaceutical samples.
A method is presented that allows one to calculate changes in ion concentration from the response of an ion sensitive electrode, under conditions where the response of the electrode is nonlinear. In the calculations the response curve of the electrode is fitted with a polynomial function of the fourth power. Changes in the concentration of the probe-ion can be calculated with this polynomial. The calculation is based on a converging iteration procedure in which the concentration to be calculated is the zero value of the polynomial. The iteration procedure is run in Basic on a personal computer. This method extends the useful range of ion concentrations by more than one order of magnitude.
N, N'-Ethylene bis (salicylideneimine) was found to have a very sensitive and selective behavior towards Dysprosium (III) ions. The sensor was prepared comprising of varying compositions of electro-active material using epoxy resin as binder. It was found that the electrode with 60% Schiff base exhibits best performance. The electrode exhibited a linear response with a near Nernstian slope of 20 mV/decade in the concentration range of 10 -6 M to 10 -1M. It shows a working pH range of 2.3-10.8 and response lime of 10 s presenting satisfactory reproducibility. The results show that this can be used in partially non-aqueous medium without interference. Effect of internal solution was studied and the electrode gave satisfactory results. Selectivity coefficients for Dy (III) with respect to many cations were studied. The electrode shows high selectivity over various monovalent, bivalent and trivalent cations. The electrode was successfully used as an indicator electrode in potentiometric determination of Dy (III) ions with oxalic acid.
A two-step potential waveform is demonstrated for the detection of carbohydrates at a Au electrode in alkaline solutions for application in flow injection and liquid chromatography systems. Pulsed amperometric detection of carbohydrates previously based on a three-step waveform is now extended to potentiostats capable of programming an asymmetric square waveform (e.g., normal-pulse voltammetric waveforms). Detection limits for glucose, sorbitol, and sucrose are approximately 1 nmol in a 50-..mu..L sample (i.e., ca. 200 ng of glucose and 360 ng of sucrose) in a flow injection system.
The potentiometric method based on surfactantion-selective electrodes (SISEs) was broadly applied to ionic surfactants in solution due to the change in their activities, i.e., concentration in dilute solution, of both the counterions and ionic surfactants at the point of aggregation. The monomeric surfactant concentration can be determined by SISEs with almost no pretreatment, even if the sample solutions were colored or viscous. Ion-sensitive electrodes are usually used to investigate the dimerization, aggregation, and micelle formation of ionic surfactants in aqueous solution. By using SISEs, the binding isotherm of ionic surfactants bound to other materials such as polymers and biomolecules (DNA and proteins) can be calculated easily. According to the binding isotherms, the different binding and aggregation processes between ionic surfactants and other materials can be identified and characterized, which is important for understanding the interaction between ionic surfactants and polymers and/or biomolecules. Herein we present a comprehensive review of the literature devoted to SISEs used in the aggregation of surfactants in solution over the last two decades, looking back the developmental history of SISEs, reviewing the applications of SISEs in the studies of surfactant/surfactant mixtures, the adsorption of surfactants on polymers, including neutral polymers, polyelectrolytes, and biopolymers and the interactions between surfactants and lipidvesicles, etc., prospecting the new wave of SISEs.
A coated graphite-epoxy iron(III) ion-selective electrode, based on the ion-pair between [Fe(oxalate)3] anion and tricaprylylmethylammonium cation (Aliquat 336) in a poly(vinylchloride) (PVC) matrix is constructed. A thin membrane film of this ion-pair, dibutylphthalate (DBPh) in PVC was deposited directly onto a Perspex tube containing a graphite-epoxy conductor substrate attached to the end of a glass tube. The effect of membrane composition (ion pair, DBPh and PVC), oxalate concentration, pH and some cations and anions upon the electrode response is investigated. The electrode shows a linear anionic response to E vs. log[Fe] in the iron(III) concentration range from 2.9×10 to 10 mol/L, and a slope of −18.7±0.5 mV/dec, at pH working range 2-8 and 0.3 mol/L oxalate concentration. Variation in the potential of about ±2 mV was observed during a working day of 7-8 h. The response time was less than 5 sec and the lifetime of this electrode was superior to one year (over 1500 determinations by each polymeric membrane), with a practical detection limit of 2.1×10 mol/L. Application of this electrode for iron(III) determination in biotônico sample (Brazilian tonic formula) is described.
The ability of flowers and blossoms to convert biochemical substrates into volatile products is utilized for the development of biosensors using such plant tissues as catalytic components. It is shown that both minced and intact tissue portions from carnation and chrysanthemum flowers can be coupled with potentiometric ammonia gas sensing electrodes to prepare sensors for urea and some amino acids with good response properties. Surprisingly different response and selectivity patterns are found among species of flowers and for the structural subelements of a single type of flower.
A double-membrane nitrate-selective electrode [as a modified coated wire electrode (CWE)] was prepared with an internal conductor membrane made of tetrabutylammonium bromide (BrTBA) in naphthalene, and an external active membrane (Aliquat-NO
3−in paraffin), on an Agamalgamated electrode. The nitrate-electrode exhibits linear Nernstian response over the range 1 to 10−4.5 mol/l of nitrate, with a slope of 56.01 ± 0.9 mV decade−1. The selectivity coefficients \(K_{{\text{NO}}_{\text{3}}^ - }^{{\text{Pot}}}\) for 17 ions were calculated. The effects of pH, membrane composition and thickness were also studied. The life-time of the electrode is 15 days and the stability of its potential is 0.6 mV/12 h. The electrode was preserved dry because of the better sensitivity, range of linear response and detection limit attained. The determination of nitrates in waters and fertilizers was also attemped with this electrode, using the interpolation and standard-addition methods.
Potentiometric sensors (ion-selective electrodes [ISEs]) are able to directly determine the activity of the ion of interest in the sample. ISEs are the method of choice for clinical analysis of ions of clinical relevance such as K+, Na+, Ca2+, Mg2+, and Cl–. In recent years, the field has undergone a renaissance when determination of selectivity coefficients and Pb2+-selective electrode with limit of detection in picomolar range are reported. A very important direction in the development of ISEs is their miniaturization. While microelectrodes have been known for a long time, there is only one report so far describing miniature ISEs with low limit of detection. Because of the relative simplicity of construction and optimization, solid-contact polymer-based membrane ISEs are very promising platforms for this research direction. Low-cost construction and simple data acquisition facilitate the integration of such platforms into sensor arrays and further into sensor communities based on networks of simple and accurate devices for widely distributed monitoring of—for example, water quality. In addition, microelectrodes can be used for spatial mapping of low chemical concentrations (e.g., in chemical microscopy or the study of ion uptake by the plant roots. Moreover, in contrast to most other analytical techniques, potentiometric sensors ideally do not perturb the sample, and such microelectrodes can therefore be used in very small sample volumes allowing determination of extremely small total quantities.
A glucose electrode was fabricated by immobilizing glucose oxidase covalently onto a platinized platinum electrode. The sensor
showed rapid response with response time of 2—4 s, and also the linear response to the glucose concentration, ranging from
2 x 10-3 to 5 mM. The sensitivity was found to be correlated with the surface area of a base electrode used.
A PVC phenoxyacetate selective electrode has been developed for the indirect sensing of phenol, after in situ derivatization with chloroacetic acid. The electrode exhibits a Nernst response in the range 10−1 − 3.2 × 10−4M phenoxyacetate with a slope of 68.9 mV per concentration decade. The electrode has a wide working pH range (7.5–11.0), a fast response time (less than l min), and is stable for at least months.
Thiocyanate selective electrodes were prepared by incorporating cobalt and manganese phthalocyanines into plasticized ploy(vinyl chloride) membranes which were directly coated on the surface of graphite electrodes. A calibration plot with Nernstian slope for thiocyanate was observed over a linear range of five decades of concentration (1x10-1x10 M). The electrode has a fast response time, very low detection limit (5x10 M thiocyanate), is easy to prepare, and could be used for over a month. The proposed sensor revealed good selectivity for thiocyanate over several anions and could be used over a wide pH range. Applications of the electrode to the potentiometric titration of silver ion with thiocyanate and determination of thiocyanate in urine samples are reported.
A choline-sensitive membrane electrode made with potassium tetrakis(p-chlorophenyl) borate as the exchanger and o-nitrophenyl phenyl ether as membrane solvent in poly (vinyl chloride) was almost insensitive to the surfactant sodium deoxycholate. By using this electrode, choline ( 10−5 M) formed by the enzymatic hydrolysis of phosphatidylcholine with phospholipase D in the presence of sodium deoxycholate as activator was successfully measured. The method was applied to the determination of phosphatidylcholine in serum.
A new inorganic ion exchanger, zirconium (IV) antimonoarsenate has been synthesized at different pH values. An amorphous sample prepared at pH 1 having an ion-exchange capacity of 0.40 meq/g was selected for further studies. The material is characterized using various analytical techniques, like XRD, IR, TGA and SEM, in addition to the ion-exchange capacity and distribution coefficient (Kd) studies. Further the exchanger has been used as an electro-active material for the determination of Cerium (III) ions with epoxy resin, PVC and polystyrene as binding materials. A membrane having a composition: ZrSbAs (50%) and polystyrene (50%) gives the best performance. It works well over a wide Ce (III) ion-concentration range of 5×10−5–1×10−1M with a super-Nernstian slope of 52.0mV/decade. It has a fast response time of 10s and has an average lifetime of four months. The proposed sensor shows a good selectivity for cerium (III) ions with respect to alkali, alkaline earth, some transition and rare earth metal ions that are normally present along with cerium in its ores. The electrode has also been used as an indicator electrode in potentiometric titrations of Ce (III) ions against oxalic acid.
Recently, potentiometric sensors have found numerous applications involving on-line monitoring in flow systems [1–4]. With trends toward the use of multielectrode arrays and electrode miniaturization, simple diagnostic tests for the routine assessment of device performance will become increasingly important. In this work, we present the possibility of using dc resistance measurements for this purpose. Mini-sodium-selective electrodes with polyvinyl chloride (PVC) membranes incorporating the ionophore methyl p-t-butylcalixaryl acetate [4, 5] were constructed, and a gradual increase in resistance with lifetime was observed. A lifetime mimicking study was set up in which leaching of the active components from the membrane was simulated by a series of dilutions, and the effect on overall electrode performance was monitored at each stage. Complete electrode malfunction has been shown to occur abruptly when the active membrane component concentration falls below a critical level. Electrode failure is accompanied by a sharp increase in membrane resistance.
An ion-selective electrode based on a naturally ocurring carboxylic polyether antibiotic salinomycin is described which exhibits high Ba selectivity. The selectivity coefficients of the electrode based on salinomycin, log K BaCa, log K BaK and log K BaNa are −2.65, −2.86 and −3.55, respectively.
Membrane electrodes are relatively simple electrochemical devices that can be used for the direct measurement of ions, gases, and biomolecules in complex samples. Selectivity for one species over another is determined by the nature and chemical composition of the membranes and associated reaction layers used to fabricate the devices. All membrane electrode probes employ at least one ion-selective membrane as the ultimate transduction element. This indicator membrane serves as an additional component of a classic two-electrode galvanic cell. The potential developed at the membrane/sample interface is directly or indirectly related to the activity or concentration of analyte in the sample. Because cell potentials are detected under essentially zero-current conditions, analytical measurements with these probes are generally not subject to the mass transfer and electron transfer kinetic limitations that often plague voltammetric or amperometric techniques.In this report, we review the current state of the art with respect to development and application of potentiometric membrane electrode probes. As a starting point, we provide a brief introduction to the fundamentals of membrane-based galvanic cell potentials and their measurement. Subsequent sections summarize the various membranes now in use for direct ion sensing, the approaches taken to miniaturize these same ion-selective systems, and the use of such membranes in conjunction with secondary membranes to devise a variety of potentiometric gas sensing systems. Finally, we conclude with an overview of the approaches being employed presently to devise potentiometric bioprobes suitable for the selective, in situ detection of biologically important molecules.
Potentiometric discrimination of series of linear homologs (4-7), geometrical isomers (8,9), and positional isomers (10-12) of dicarboxylate guests by a liquid membrane sensor containing Iipophiiic macrocyclic polyamine 1 as a sensory element is described. the pH conditions were carefully set so that the potentiometric response to the dianionic forms of the guests could be specifically observed. Whereas only small discrimination was observed for the flexible linear homologs (4-7), marked discrimination was observed, for the geometrical isomers (8,9) and positional isomers (10-12) having rigid structures. the selectivities of the potentiometric response were found to correlate well with the reported selectivities of host-guest complexation in water displayed by macrocyclic polyamines having the structures related to 1.
New salicylate-selective electrodes based on aluminum(III) and tin(IV) salophens are described. The electrodes were prepared by incorporating the ionophores into plasticized poly(vinyl chloride) (PVC) membranes, which were directly coated on the surface of graphite electrodes. These novel electrodes display high selectivity for salicylate with respect to many common inorganic and organic anions. The influence of membrane composition and pH and the effect of lipophilic cationic and anionic additives on the response properties of the electrodes were investigated. The electrode based on aluminum salophen, with 32% PVC, 65.8% plasticizer, and 2.2% ionophore, shows the best potentiometric response characteristics and displays a linear log [Sal-] vs EMF response over the concentration range 1 × 10-6−1 × 10-1 M in phosphate buffer solutions of pH 7.0, with a Nernstian slope of −59.2 mV/decade of salicylate concentration. Highest selectivity was observed for the membrane incorporating 38.8% PVC, 57.3% plasticizer, 2.6% Sn(salophen), and 1.3% sodium tetraphenylborate. The electrodes exhibit fast response times and micromolar detection limits ( 1 × 10-6 M salicylate) and could be used over a wide pH range of 3−8. Applications of the electrodes for determination of salicylate in pharmaceutical preparations and biological samples are reported.
Copper phthalocyanine was used as ion carrier for preparing polymeric membrane selective sensor for detection of iodide. The electrode was prepared by incorporating the ionophore into plasticized poly(vinyl chloride) (PVC) membrane, coated on the surface of graphite electrode. This novel electrode shows high selectivity for iodide with respect to many common inorganic and organic anions. The effects of membrane composition, pH and the influence of lipophilic cationic and anionic additives and also nature of plasticizer on the response characteristics of the electrode were investigated. A calibration plot with near-Nernestian slope for iodide was observed over a wide linear range of five decades of concentration (5×10−6−1×10−1 M). The electrode has a fast response time, and micro-molar detection limit (ca. 1×10−6 M iodide) and could be used over a wide pH range of 3.0–8.0. Application of the electrode to the potentiometric titration of iodide ion with silver nitrate is reported. This sensor is used for determination of the minute amounts of iodide in lake water samples.
This article begins with an introduction to ion-selective electrodes (ISEs). The classification protocol based on the most recent International Union of Pure and Applied Chemistry (IUPAC) recommendations is given. The historical development of ISEs is summarized, starting with the pH electrode. For the inorganic cations and anions, a periodic table “time-line” is given. Recent history has seen the rise of polymer membrane ISEs, which are important in clinical analysis. The historical section concludes with a brief look at these ISEs. The general theory of the potential generation process is explained, and then aspects of the potential generation process that are specific for the different classes of ISEs. A short review of the instrumentation needed to make the measurements is given, followed by an overview of the latest commercially available instrumentation. One aspect of ISE research is the development of selective probes for determining the analyte content of individual cells. This requires miniaturization, and this has been achieved by the development of microelectrode ISEs. An overview of this area is given. Finally, some recent developments that represent the directions of research in the ISE field are given. Included are the development of sensors for patient monitoring, the development of ISE sensor arrays, and the development of more sophisticated electronic and mathematical methods of data analysis.
Tin(IV) porphyrins derivatives were used as ionophores for phthalate selective electrodes preparation. The influence of ionophore structure and membrane composition (amount of incorporated ionic sites) on the electrode response, selectivity and long-term stability were studied. Poly(vinyl chloride) polymeric membranes plasticized with o-NPOE (o-nitrophenyloctylether) and containing Sn(IV)-tetraphenylporphyrin (TPP) dichloride (Sn(IV)[TPP]Cl2) or Sn(IV)-octaethylporphyrin (OEP) dichloride (Sn(IV)[OEP]Cl2), and in some cases incorporating lipophilic cationic (tetraocthylammonium bromide - TOABr) and anionic (sodium tetraphenylborate – NaTPB and potassium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate-KTFPB) additives, were prepared and their potentiometric characteristics compared. Both ionophores are shown to operate via a neutral mechanism, and the addition of 10 mol % of lipophilic quaternary ammonium salt derivative to the membrane is required to achieve optimal electrode performance. The potentiometric units prepared, with Sn(IV)[TPP]Cl2 (Type A) or Sn(IV)[OEP]Cl2 (Type B) without additives, presented a slope of −52.8 mV dec−1 and −58.8 mV dec−1 and LLLR of 9.9×10−5 mol L−1 and 9.9×10−6 mol L−1, respectively. The units prepared using the same metalloporphyrins and incorporating 10% mol TOABr presented a slope of −55.0 mV dec−1 and −57.8 mV dec−1 and LLLR of 5.0×10−7 mol L−1 and 3.0×10−7 mol L−1. Their analytical usefulness was assessed by potentiometric determinations of phthalate in water and industrial products providing results that presented recoveries of about 100%.
Selective transport of given substrates through artificial membranes can be achieved by incorporation of electrically neutral or charged carriers. Such mediated transport described for alkali and alkaline-earth metal cations is reported here for the first time for certain anions using cobyrinate-type ionophores, and it is also conceivable to be realized for nonionic substrates (e.g. glucose). The fundamental requirements for corresponding co-transport and counter-transport membrane systems are set forth in view of a design of novel substrate-selective sensors for analytical-chemical applications.
IntroductionOn-Line and In Situ MonitoringTypes of Sensor SystemsSensors of the Physical EnvironmentSensors of the Chemical EnvironmentSensors of the Biological SystemConclusions
References
Discrepancies of one pH unit and more have been observed after a few days, between continuous on-line in situ pH measurements and instant off-line pH measurements during anaerobic digestion of an agroindustrial wastewater. Concomitantly, the electrical resistance across the porous diaphragm of the on-line electrode increased, and a black clogging developed on its diaphragm. Measurements of the relative liquid junction potential in KCl or Na2S solutions excluded that high concentrations of ions such as, K+, Na+, Cl−, HS−, or S2− were the major cause of the drifts in pH values. It has been possible to limit the rapid increase of the liquid junction potential and the black clogging formation on the porous diaphragm either by acidification and/or by overpressurization of the electrode-filling liquid. Continuous on-line in situ pH values consistent with instant off-line pH values over long periods of time have been obtained with a newly designed pH sensor in which a special jellied electrode filling replaced the porous diaphragm.
The applications of chemically modified electrodes to analytical chemistry have been reviewed. Five aspects, including electrocatalysis, selective preconcentration, permselectivity, specific recognization, and potentiometric responses are covered with 77 references.
Podand- and crown-types of new chiral receptors, characterized by a chiral polyether skeleton and an amide junction, were derived from naturally occurring monensin ionophore. Their chiral recognition ability was investigated by ion-selective electrode and 1H-NMR spectroscopic methods. Several podand-type monensin amides formed 1:1 complexes with chiral amine salts and exhibited excellent enantiomer selectivity. Since biological monensin and its macrocyclic derivatives were less effective for chiral recognition, a molecular combination of pseudo-cyclic monensin cavity, chiral polyether skeleton and neutral amide moiety offered high enantiomer selectivity. Chemical modification of biological monensin allowed remarkable development of new ionophoric-functions and provided an effective synthetic strategy for chiral receptors.
A potassium ion-selective electrode based on a cobalt(II)-hexacyanoferrate(III) (CHCF) film-modified glassy carbon electrode is proposed. The electroactive film is introduced onto the glassy carbon electrode surface by electrodeposition of cobalt, which forms a thin CHCF film on subsequent anodic scanning in KClHCl solution (pH 5.0–5.5) containing K3Fe(CN)6. The thickness of the film on the electrode surface can be controlled by changing the electrodeposition time and the concentrations of cobalt(II) and Fe(CN)3−6 ions. The modified electrode exhibits a linear response in the concentration range 1 × 10−1 −3 × 10−5 M potassium ion activity, with a near-Nernstian slope (48–54 mV per decade) at 25 ± 1°C. The detection limit is 1 × 10−5 M. The stability, response time and selectivity were investigated. The electrode exhibits good selectivity for potassium ion with the twelve cations investigated. The relative standard deviation is 1.5% (n=10). The effects of the thickness of the electroactive film and the pH of the solution on the electrode response were also investigated.
Electroanalytical techniques are currently gaining popularity in the area of biochemical analysis. There are several reasons for this growth. Electrochemical techniques provide both excellent detection limits with wide dynamic range. These methods are typically readily amenable to miniaturization. This leads to being able to use very small sample volumes. In vivo analysis is also possible. Finally, electrochemical techniques are generally very selective and when not selective enough can easily be coupled to even more selective techniques such as liquid chromatography or immunoassay. In this chapter, the basic concepts underlying electroanalytical methods of bioanalysis will be described. How these techniques can be used in bioanalytical chemistry will be illustrated. In addition, the interrelationship of the various electroanalytical techniques will be discussed.
The coupling of intact natural chemoreceptor structures to potentiometric electrodes results in a new class of electrochemical biosensors with exceptionally fast dynamic response properties and attractive analytical limits. The use of intact sensing structures is advantageous in that both the transduction and conduction functions are contained in the native environment of the neural element. This novel approach is illustrated with antennule structures of the blue crab and characterized in terms of analytical responses to some amino acids.
Membranes containing varying compositions of electroactive material and epoxy resin as binder have been prepared and it has
been shown that the one having composition 60% ZrSbMo and 40% epoxy resin exhibits best performance. The membrane demonstrates
excellent response in the concentration range of 10−4 to 10−1 M Dy(III) ion with super-Nernstian slope of 44.0 mV/decade and fast response time of less than 10 s. Effect of internal solution
was studied and the electrode was successfully used in partially non-aqueous medium. The proposed sensor revealed good selectivity
with respect to alkali, alkaline earth, some transition and rare earth metal ions. It can be used in the pH range of 2.10–9.80.
The sensor was used as an indicator electrode in the potentiometric titration of Dy(III) ion against EDTA.
Key wordspotentiometry-determination of disprosium-zirconium(IV) antimonomolybdate-electroactive materials
A samarium(III) selective potentiometric sensor has been prepared on the basis of polyvinyl chloride (PVC) membranes containing
an ion exchanger (zirconium boratophosphate) as an electro-active material. The best performance was exhibited by a membrane
having the following composition: zirconium boratophosphate (10%) and poly vinylchloride (90%). This membrane works well over
a wide concentration range (from 1 × 10−5 to 1 − 10−1 M) of Sm(III) ions with a Nernstian slope of 20.2 mV/decade. The response time of the sensor is 15 s, and the membrane can
be used for more than six months with good reproducibility. Selectivity coefficients determined by the fixed interference
method for a number of mono-, di-, and trivalent cations are reported. The sensor has also been used as an indicator electrode
in the potentiometric titrations of samarium (III) ions with EDTA solution.
Four major areas of electrochemistry related to medical diagnostics have been reviewed. Blood pH and gas measurements as well as ISE's represent relatively mature areas which enjoy widespread commercialization. New approaches should yield devices which have superior performance and which are less expensive to produce. Enzyme electrodes and electrochemical immunoassay are still largely experimental, but the intense level of current research effort coupled with some interesting recent developments should lead to commercial success over the next decade.
Ion-selective electrodes are widely used for non-destructive, rapid, sensitive and precise determination of many ions in a great variety of media and therefore, provide a powerful analytic tool. Since the appearance of the first edition of Professor Koryta's book in 1975 progress in the whole field of ion-selective electrodes has been rapid and a vast amount of diverse data has appeared. In this edition, based on the literature to mid-1981, a compact and unified treatment of the theory of ion-selective electrodes is presented along with an updated account of their analytical, biomedical and physicochemical applications. The book will be of interest to advanced undergraduate and graduate chemists, biophysicists, physiologists, biochemists and environmental scientists, as well as research workers in both universities and industry.
A simple and rapid method of pre-treatment was established for applying ion selective electrode of silver chloride membrane to the determination of chloride ion in environmental samples. The proposed methods enabled to avoid the interference from sulfide, cyanide, and iodide ion. The addition of potassium permanganate to the sample solution adjusted to pH 4 (TISAB) brought the more rapid and complete oxidation of sulfide than that of hydrogen peroxide and an aeration, and also was effective for iodide. The addition of excess potassium permanganate had not a bad effect upon the response and membrane. Though it eliminated to a certain extent the interference of cyanide it didn�t bring the complete oxidation of cyanide. Therefore, nickel nitrate which formed nickel cyanide was added to the sample previously adjusted to the pH of about 11. The analytical procedures are as follows: Add successively a drop of 0.5 M potassium hydroxide and 0.2 ml of 1 M nickel nitrate to 20 ml of sample solution with stirring. After 3 min, add 2 ml of TISAB (5 % potassium nitrate, pH 4) and 0.2ml of 0.5M potassium permanganate. Measure potential response after it has stabilized (after a lapse of time over 3 min). The maximum concentrations of interfering ions permitted for 10 -3M chloride ion are as follows: sulfide (10 -3 M); cyanide (5x10~ -5M); iodide (3 X 10 -5 M). Add merely TISAB and potassium permanganate to the sample containing cyanide smaller than one fiftieth of chloride. © 1984, The Japan Society for Analytical Chemistry. All rights reserved.
An application of a fluoride ion-selective electrode after coprecipitation of fluoride with aluminum phosphate to the determination of fluoride ion in various water samples has been studied. Analytical procedure is as follows. To sample solution of 250 cm3, 4 cm3 of potassium aluminum sulfate solution (5 mg Al/cm3) and 10 cm3 of 0.5 mol dm~3 potassium dihydrogenphosphate solution are added and then pH is adjusted to 4.7 with dilute ammonia solution. After heating for about 5 min, the precipitate is separated and dissolved in about 6 cm3 of 2 mol dm-3 hydrochloric acid. To this solution, 4 cm3 of the complexing buffer solution (mixture of citrate, CyDTA, and sodium chloride: CBS) for masking of aluminum is added and pH is adjusted to about 6 with ammonia solution, moreover, 4 cm3 of CBS is added. The potential is measured with an ion-selective electrode after the total volume is adjusted to 50 cm3 with water. Fluoride ion of 5~100 jig was quantitatively coprecipitated with adding 20 mg of aluminum at pH 4.4~5.0. The relative standard deviation was 1.8% in the six analytical results of 0.04 ppm fluoride ion. Large amounts of sodium ion and chloride ion do not interfere with the determination of fluoride ion. The proposed method was applied to the determination of fluoride ion in natural water such as river-, well-, and sea-water. The values determined by the proposed method agreed well with those obtained by the other method. This method is simple and rapid, and suitable for the determination of fluoride ion at the concentration of ppb level in water. © 1984, The Japan Society for Analytical Chemistry. All rights reserved.
Hydrogen sulfide permeation-membrane and absorption solution were used in the continuous determination of hydrogen sulfide with sulfide ion-selective electrode. Fluorophore (Sumitomo Electric Ind., Tokyo; Pore size 0.22µm, diameter 7.0 mm) was used as hydrogen sulfide permeation-membrane. A 0.5 N NaOH-8 wt% sodium salicylate-1.8 wt% L-ascorbic acid-2X 10-7M sulfide ion; mixed solution was used as a absorption solution for hydrogen sulfide (This solution inhibits the air oxidation and produce a stable electrode potential). Hydrogen sulfide impinge onto the permeation-membrane, through which the hydrogen sulfide is absorbed into absorption solution. The volume of absorption solution in the absorption pass cell is about 0.15 ml. The response time of this system for hydrogen sulfide was about 50 s. The absorption efficiency of hydrogen sulfide was constant, that is 88 %, at constant flow rate of both sample gas (40 ml min-1) and absorption solution (7.4 ml h -1) between 200 ppm and 0.1 ppm. In this range Nernst equation was valid with a coefficient of variation of less than 1 %. Lower determination limit of hydrogen sulfide was as low as 0.05 ppm. The coexistence of various gases such as carbon dioxide, sulfur dioxide, and hydrogen chloride had no influence on this method. © 1983, The Japan Society for Analytical Chemistry. All rights reserved.
Kinetic method for the determination of trace amount of tungsten (VI) by the use of an iodide ion-selective electrode is described. Indicator reaction on which the method is based is the oxidation of iodide to iodine by hydrogen peroxide in acidic medium. Trace amount of tungstate ion works as a catalyst. Ascorbic acid was added to the reaction mixture to achieve the Landolt effect. The iodine produced by the indicator reaction is reduced rapidly until all the ascorbic acid is consumed. Incubation period is measured by tracing the concentration of iodide ion by iodide ion-selective electrode. Concentration of iodide ion begins to decrease just after all the ascorbic acid is consumed. The reciprocal value of incubation period is linear to the concentration of tungsten (IV). The appropriate reaction conditions were decided graphically. The most suitable pH and concentrations of hydrogen peroxide, potassium iodide, and ascorbic acid are found to be 2.5, 10 mM, 10 mM, and 0.8 mM, respectively. The calibration curve for tungsten shows a good linearity in the concentration range from 0.1µM to 1.2µM. Interference of diverse ions were tested and Fe(III), Zr(IV), V(IV), and Mo (VI) showed interference. Iron (III) can be masked by the addition of almost equal amount of Na2H2edta. Present method was applied to the determination of tungsten in tool steel. © 1983, The Japan Society for Analytical Chemistry. All rights reserved.
As proteins react with heavy metal ions, concentrations of protein could be determined by measuring the concentrations of residual heavy metal ions in the presence of albumin using ion-selective electrode. In the present work, egg albumin (ovalbumin) was chosen as protein and the silver sulfide membrane electrode was used as ion-selective electrode as well as silver nitrate solution as metal ions resources. Electode response time increased linearly as the albumin concentration increased. © 1983, The Japan Society for Analytical Chemistry. All rights reserved.
It is well known that ion-specific electrodo method to determine fluoride in many kinds of samples such as water, industrial drainage, hot spring water and air is rapid, simple and accurate. However, an application of this method to determination of fluoride in foods is not investigated in detail yet. The results of reexamination which involve the analytical procedures of this method (i. e., digestion, distillation and determination) were described. By using the condition established here, it was found that fluoride in some kinds of foods could be conveniently determined with recovery 98.5-105.0% and coefficient of variation about 0.7%. Furthermore, fluoride contents in twenty six kinds of foods were satisfactorily determined by this method. © 1983, The Pharmaceutical Society of Japan. All rights reserved.
This chapter reviews the information available from magnetic resonance measurements. These come into two categories: nuclear magnetic resonance (NMR) and electron spin resonance (ESR). Nuclear magnetic resonance gives insights on the environment near a given atom (H or D) because it senses how the nuclear field is distorted by that of neighboring atoms. Two types of configuration are found: isolated SiH that gives a narrow resonance line riding on top of a broad resonance due to clusters of hydrogen atoms, probably in microvoids. Nuclear magnetic resonance data of boron suggest that B is mostly threefold coordinated, thus explaining the low doping efficiency of B in a-Si:H. There is also evidence that B is bonded to at least one H and that 1% of the hydrogen is in the molecular H2 form. Electron spin resonance probes the resonance of unpaired electrons. Silicon dangling bonds have a characteristic resonance corresponding to a gyromagnetic ratio g = 2.0055. There are about 1019 cm–3 dangling bonds in a-Si; their concentration drops by several orders of magnitude in a-Si:H, becoming as low as 1015cm–3. The evolution of H and the restructuring of bonds can be followed by ESR. Phosphorus doping yields a resonance at g = 2.004, whereas that of B occurs at g = 2.013. Optical excitation produces a light-induced ESR that decays in time. High-intensity optical excitation creates metastable states owing to dangling bonds that can be annealed thermally.
The spectroscopic techniques of nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR or ESR) have been known for more than 30 years. Only in the past 15 years, however, have they been widely applied in the field of surface science. In principle EPR spectroscopy is limited to observation of surface species containing unpaired electrons. These may include adsorbed radicals, molecules containing unpaired electrons (e.g., NO), transitional metal ions and surface defects of various types. Furthermore, EPR is a highly sensitive technique, able to detect (in favourable cases) as few as 1011 spins. NMR spectroscopy, on the other hand, is much broader in scope, since there are many different nuclei possessing non-zero nuclear spins. As a surface technique however, NMR suffers the disadvantage of having a relatively low sensitivity. Both EPR and NMR provide information about the structure and environment of the species being observed, in a completely nondestructive manner.
Studies of biological materials by pulsed EPR techniques are generally regarded as exotic. Up to the present time, all pulsed EPR spectrometers have been homemade and represent an investment of $100,000 to $200,000. The demands upon time and financial resources have kept the total number of operating systems to less than thirty worldwide.* Moreover, to this point in time, the signal-to-noise obtainable with pulsed EPR techniques has been significantly less than that obtainable by conventional continuous wave (cw) EPR and is often marginal for the study of biological materials.
The past dozen years or so have witnessed the application of a new spectroscopic method to the investigation of biological molecules. Optical detection of triplet-state magnetic resonance (ODMR) represents in the broadest sense a combination of optical measurement (phosphorescence, fluorescence, absorption) with electron spin resonance (ESR) spectroscopy. In ODMR, microwave-induced transitions between magnetic sublevels of the lowest triplet state are detected by their effect on some optical property of the sample which is monitored simultaneously. Historically, the field may be traced back to early work on optical detection of magnetic resonance transitions of atoms and ions in the gas phase by Fermi and Rasetti (1925), Breit and Ellet (1925), and by Brossel and Bitter (1952). The first optically detected magnetic resonance experiment in the solid state was reported by Geschwind et al. (1959) on the 2E excited state of Cr3+ in ruby at 1.6 K. This early work has been reviewed by Bernheim (1965). At about the time of Geschwind’s experiment, Hutchinson and Mangum (1958; 1961) made the first ESR measurements on a photoexcited triplet state in the solid state—the phosphorescent (T
1) state of naphthalene substitutionally incorporated in a single crystal of durene.
The history of EPR applications to the study of manganese dates to the very first successful resonance experiments by Zavoisky (1945). Since then there have been numerous EPR studies of Mn(II) in diverse materials. The reader may find references to many of these studies in review articles and monographs on EPR (Abragam and Bleaney, 1970; Goodman and Raynor, 1970; König, 1968; Kaiser and Kevan, 1968). Applications of EPR to studies of Mn(II) complexes with proteins began with studies by Malmström et al. (1958) wherein the strong isotropic EPR signal for “unbound” Mn(H2O)
62+was used to determine dissociation constants for Mn(II)-protein complexes. Such analytical applications of the EPR signal for Mn(H2O)
62+(Cohn and Townsend, 1954) for measuring dissociation constants have continued. However, during the last decade the EPR signals for the protein-bound Mn(II) have been measured for enzymes and other proteins, and this latter application is the basis for the present chapter.
In this summary of the Holweck prize lecture, given at the Collège de France, Paris, on 22 June 1984, Professor Bleaney shows how the investigation of electron magnetic resonance was preceded by that of microwave gas spectroscopy, and how it contributed to other important developments such as nuclear alignment
The potential response of ion-selective electrodes generally shows a slow drift as immersion of the electrode is repeated even in the same solution. Such a drift can cause a large error in the determination if the concentration vs. potential calibration curve method is used. To minimize the error due to this type of drift, the following procedure was applied to the determination of bromide, iodide, and fluoride ions by ion-selective electrodes: The total ionic strength and the pH of the reference and the sample solutions are adjusted at 0.66 M and 5.2, respectively, throughout the measurements. The solutions are stirred at a nearly constant rate with a magnetic stirrer at 25.6±0.1 °C. A bromide, iodide, or fluoride ion-selective electrode is first immersed in the reference solution, and the potential is read as a concentration-proportional scale (S1) by use of an ion meter after 5 min. After the surface of the electrode is wiped with a sheet of filter paper, the electrode is immersed in the sample solution and the concentration-proportional scale (U2) is measured after 5 min. © 1984, The Japan Society for Analytical Chemistry. All rights reserved.
Electron spin resonance (ESR) is a spectroscopic technique that is specific for paramagnetic material. Various books and articles deal with the theory and experimental techniques of the method; a selection of three monographs may be cited here.(1–3) ESR furnishes valuable and detailed information about free radicals and radical ions. These species play an important role in various electrode processes, because electrons are in general transferred singly, particularly in organic electrode processes. (Under suitable conditions, inorganic substrates exhibit similar behavior, e.g., in the reduction processes 02 + ℯ- →O2-or S02 + ℯ- SO2-.) Since 1957 excessive use has been made of ESR spectroscopy in electrochemical investigations as well as of electrochemical radical generation for ESR investigations of such species. Some early papers(4–7) and some reviews on the application of ESR to electrochemistry(8–12) may be mentioned.
Chemical sensors are primarily needed to control the concentration of specified components within gases and liquids. In electrolytes, ion-selective electrodes (ISE's) - especially glass electrodes - are being used today in a wide range of applications. In comparison to these ISE's this paper presents the operation principle, design, technology, and field of application of ion-sensitive field-effect transistor (ISFET) devices.
The developments and various applications of new electrochemical sensors continues to be a rapidly growing area of analytical chemistry. For analytical control of pharmaceuticals, most of the pharmacopoeias describe accurate methods, but in some cases these are lengthy and difficult. The ion-selective electrode techniques offer several advantages in terms of simplicity, rapidity and accuracy over many of known official methods. This review is intended to discuss the recent aspects in the field of pharmaceutical analysis with membrane electrodes.
Work [1] published recently in Germany describes a method for nitrate analysis in which nitrate is reduced, using a solution of titanous chloride, to ammonia. An ammonia gas-sensing electrode is used to make the measurement, so interferences usually associated with nitrate determination are minimized. A decrease in the time required for analysis is also reported. We have evaluated the method in an attempt to simplify it, and we have compared it with techniques which utilize a liquid membrane, nitrate-selective electrode, both with and without chemical suppression of interferences. The methods were developed with particular regard for the chloride interference to the nitrate electrode and for temperature effects in the ammonia measurement. Samples tested using these methods included drinking water, river and lake waters, and seawater. This paper tabulates the comparative test results and reports on reproducibility at low concentrations, spike recoveries, and calibration stability. The advantages and limitations of the methods are discussed.
This chapter describes those aspects of electron pragmatic resonance (EPR) that are of particular importance. Iron-sulfur (Fe–S) clusters are relatively well-characterized class of prosthetic groups in proteins and enzymes occurring in almost all living organisms. Energy-transducing membranes, in particular those containing quinones or dehydrogenases, invariably possess one or more Fe–S clusters, all of which apparently function as electron-transferring redox groups. In energy-transducing membranes or in isolated enzyme complexes derived from them, however, an Fe–S cluster is always accompanied by other paramagnetic and chromophoric prosthetic groups, frequently even by other Fe–S clusters. At present, this limits their specific detection to only one technique: EPR spectroscopy. The chapter also explains the symbols that are used to refer to the several microwave frequency bands: L-band, around 1 GHz; S-band, around 3 GHz; X-band, around 9 GHz; K-band, around 24 GHz; and Q-band, around 35 GHz
The clinical laboratory use of ion-selective electrodes for measurements of K** plus , Na** plus and Ca**2** plus in blood serum, plasma, whole blood and urine is an important and growing application. The use of ion-selective electrodes involves two reference electrodes. In this article, the authors are concerned with the external reference electrode, which except for a few commercially available combination, or dual electrodes, remains the choice of the user. Alternative procedures are also considered but, in view of the extensive use of reference electrodes with liquid junction, most of the article is devoted to the discussion of liquid junction potentials.
Carbon-substrate electrodes are reviewed across the whole field of potentiometry. This review shows that carbon-based electrodes can operate according to various mechanisms, depending on the properties of the materials which confer selectivity towards any particular species. The most striking feature that emerges is the versatility of the carbon-substrate type of construction and the comparative ease with which new types of electrode can be prepared.
A flow injection method for determining cyanide was applied to the screening of waste water samples from metal plating processes. A sample flowing at 1.2 ml/min was mixed with a sulfuric acid solution stream [2% (v/v), 0.4 ml/min] to adjust its pH to below 2. The acidified solution (200 μl) was introduced into a carrier stream [10% (w/v) NaCl, 2.0 ml/min] via an injector valve. Hydrogen cyanide liberated was diffused into a collector stream (0.1 N NaOH, 1.2 ml/min) through a Teflon membrane in a gas diffusion cell at 40°C. The collector solution was monitored with a flow-through cyanide ion selective electrode. The apparent permeability of cyanide was calculated as 34% at the 1 μg/ml level. A linear relationship was observed between the peak height and logarithmic concentration of cyanide in the range of 0.3-100μg/ml. The values determined by the present method (x) were in fair agreement with those obtained by the official method (y) for cyanide liberated at pH5. The following correlation was obtained between the two methods ; y=0.957 x+0.013 (r=0.946, n=50). By this method, 40 samples can be analyzed in one hour.
The last two decades have seen increasing interest in methods of analysis and production control based on the application of ion-selective electrodes (ISEs). This branch of chemistry may be given the title of 'ionometry'. The great practical significance of ionometry provides the initiative for various ISE improvements. This article deals with one such improvement, namely, substitution of the liquid internal contact by solid contact (SC) between the metal conductor and the ion-selective membrane. Several advantages of ISEs with the correctly arranged solid contact if compared with the usual ones (with liquid filling) show the importance of this improvement.
There has been considerable innovation in the field of ion-selective electrodes almost since the invention of the glass electrode but particularly so in the last one and a half decades. Much of this work has been directed toward the way in which electrodes are constructed. The desire to miniaturize, simplify and to produce cheaper ion-selective electrodes has engrossed workers in a number of laboratories. The main feature of the coated-wire electrode is the elimination of the conventional aqueous reference system found in normal polymer membrane electrodes. Thus, coated-wire electrodes are those types in which an electroactive reagent is incorporated into a polymeric film, most commonly polyvinyl chloride, coated directly on to a metallic substrate. Recent developments in the field are reviewed with emphasis on constructional details, theory and thermodynamics of coated-wire electrodes selective for inorganic cations, organic ions and simple anions.
This chapter discusses the variation of electron spin resonance (ESR) that is optically detected magnetic resonance (ODMR). In ODMR the ESR is tuned to a known resonance, thus homogenizing the population of the split levels; then one compares the luminescence spectrum with and without the microwaves. Generally, if the luminescence signal increases in the presence of the microwaves, the resonance involves a radiative center. If the luminescence decreases, the center is a nonradiative recombination center. Since the various states (dangling bonds, donors, acceptors) have been identified, one can assess their role in the luminescence process. Thus, dangling bonds are nonradiative recombination centers. Their concentration increases when light-induced metastable states are formed. A center identified with trapped holes is radiative at −0.8 eV; it also can be a light-induced metastable state. A refinement of the ODMR technique consists in adding to the microwave a tunable rf pump that accesses the nuclear fine splitting. This technique is called electron nuclear double resonance.
A simple and sensitive micro method for chloral hydrate determination based on oxidation with iodine in chloroform solution is described. The produced iodide ion in the extract is determined using the iodide ion-selective electrode by either a direct measurement, standard addition technique or potentiometric titration with standard silver nitrate solution. Samples containing 0.1 - 4.0 mg chloral hydrate are analyzed with an average recovery of 99-9% and standard deviation of 0.1%.
The method of detecting reactive short-lived free radicals by the spin-trapping technique was first demonstrated in the late 1960s. At this time, the spin-trapping method involves the addition of an organic compound (spin trap) to the solution under investigation. The spin trap is capable of rapidly trapping free radicals to form more persistent radicals (spin adducts) detectable by electron spin resonance (ESR). The most commonly used spin traps are nitrones and nitroso compounds that usually give nitroxide spin adducts. An immediate requirement of the technique is that the spin trap and spin adducts are soluble in the medium of interest and that free diffusion of the spin trap to the location of the free radical event is allowed. The environment should permit high mobility of the spin adduct so that the ESR spectrum consists of a pattern of sharp lines. The detection of the ESR spectrum of a nitroxide spin adduct is proof that a radical has been trapped in the solution under investigation. Spin trapping is a kinetic method––that is, the success of the spin trapping experiment depends critically on the rate conditions that exist in the system.
Some possibilities have been studied of application of the Crytur 20-15 Ca ²⁺ -selective electrode in volumetric analysis especially for determination of the compounds which react with calcium(II) salts to form precipitates or complexes. Titrations with standard calcium(II) nitrate solution have particularly proved useful for determination of aminocarboxylic acids, but sufficiently developed potentiometric titration curves have also been obtained in titrations of fluoride, oxalate and higher carboxylic acid anions (soaps). Also reliable results have been obtained in titrations of Ca ²⁺ besides Mg ²⁺ with standard EGTA solution.
Preparation of some new macrocyclic polyetherdiamides and their complexes with calcium and tetra(4-chlorophenyl) borate is described. The selectivities of these compounds for calcium with respect to ions of the other alkaline earth and alkali metals in poly(vinyl chloride) membranes plasticized with 2-nitro-1-octyloxybenzene are compared.
A rapid analytical method utilizing the difference of formation constants of the complexes has been established for the determination of mixtures of cadmium, calcium, and magnesium ions by potentiometric titration using a cadmium ion-selective electrode. In a typical example, 5 ml each of sample containing O.l~10mM cadmium, calcium, and magnesium ions were taken into two titration cells and a buffer solution (pH 10) was added to each cell. After the solutions were made up to 100 ml with redistilled water, one of the two solutions was titrated potentiometrically with a 1~100 mM standard disodium ethylenediaminetetraacetate solution (The amount of Cd(II) and that of solution Ca(II) +Mg(II) were obtained). Similarly the other was titrated with a 1~100 mM standard glycolether-diaminetetraacetic acid solution (The amounts of Cd (II) and Ca(II) were obtained). By the difference of the two titration values, three of the constituents were able to be determined. The procedures were completed within 15 min. Cadmium, calcium, and magnesium ions in mixtures were determined in the concentration range of 0.005~5 mM. The best results with relative error and relative standard deviation, both of less than 0.9%, were obtained on 0.5 mM cadmium, calcium, and magnesium ions. Cadmium, calcium, and magnesium ions in synthetic samples (cadmium ion was added in river water, sea water or waste water) were determined by this method. The reconamended procedures are proposed. © 1984, The Japan Society for Analytical Chemistry. All rights reserved.
The gate of ion sensitive field effect transistor (ISFET) was coated with urease-albumin membrane to fabricate a micro urea sensor. Potentiometric response of the sensor is markedly dependent on the nature of the membranes. Using the sensor with a thiner membrane (ca. 2μm), linear response with a slope of -44 mV/decade has been obtained over the range of 1×10-4-5×10-3mole/dm3 (M) urea concentration, response time being 2 min. In contrast, for the thicker membrane (ca. 10 μm), Nernstian response with 30 min of the response time has been obtained. The diffusion rate of H+ or OH- in the membranes has been estimated to be a main factor governing the response time of the sensor. Some operating variables such as the buffer concentration and the life time of the sensor have been also examined.
Crown ethers can selectively form complexes with alkali and alkaline earth metal ions, and sometimes other cations by ion-dipole interaction. Taking advantage of the cation binding selectivity, they have been widely used in analytical chemistry in the separation and the analyses of metal ions. In this review, general features of crown ethers and their analytical applications are described.
Etude des deplacements du potentiel d'une electrode specifique des ions calcium, a base du complexe dibenzyl-7,19 tetramethyl-2,2,3,3-diaza-7,19 pentaoxacycloheneicosane-1,4,10,13,16dione-6,20 et du tetra(chlorophenyl) borate de calcium; dans divers solvants de membrane, dus a des variations des conditions hydrodynamiques. L'utilisation de l'ether fluoro-2 nitro-2' diphenylique en tant que solvant de membrane, combine au remplacement des groupes benzyle par des groupes octyle dans l'entraineur neutre, elimine ce phenomene defavorable et preserve la selectivite de l'electrode
The construction of a perchlorate ion-selective electrode and its application to potentiometric titration of perchlorate ion in the explosives with Zephiramine was described. The PVG matrix membrane containing 7.7 (w/w)% of tris-(bathophenanthroline)iron (II) perchlorate ion-associate was used as an ion-sensing membrane. The disk membrane was affixed to a PVG tube (I.D. 7 mm) and silver-silver chloride electrode was used as the internal reference electrode. The composition of the cell including the present ion-selective electrode is as follows. Ag-AgCl electrode/reference solution, 50mMNaC104 in 50 mM NaCl/PVG ion-exchange membrane//sample solution/SGE The present ion-selective electrode exhibited a Nernstian response to perchlorate ion in the concentration range from 10 -6 to 10 -1 M. The potential of the electrode was constant over the pH range from 1 to 13. Selectivity coefficients were evaluated and the electrode exhibited a good selectivity with respect to most common anions, while it showed some interferences with respect to periodate, iodide, and thiocyanate ion. The present ion-selective electrode was successfully adopted to the potentiometric precipitation titration of perchlorate ion with Zephiramine. It was revealed that the presence of equal or excess amounts of nitrate ion in the sample solution lowered the potential break at the end-point. However, the interference can be eliminated by the reduction of nitrate ion by heating with acetic acid and zinc powder. © 1984, The Japan Society for Analytical Chemistry. All rights reserved.
A method for the successive determination of sulfide and hydrogen sulfide ions in a mixed solution in the absence of buffer substance such as sulfite was studied by argentimetric potentiometric titration using a sulfide ion-selective electrode as the indicator electrode and a silver-silver chloride electrode (the reference electrode). Sulfide, hydrogen sulfide, and the total sulfide ions could be rapidly titrated with silver nitrate standard solution or hydrochloric acid standard solution at room temperature. The mixtures(total sulfide concentration of about 2.5×10-3 M) of sulfide ion [(3×10-42×10-3)M] and hydrogen sulfide ion [(2×10-42.5×10-3)M] were determined with a relative standard deviation less than 0.3 %. Halide, thiosulfate, and sulfate ions did not interfere with the titration. The recommended procedure is as follows : Place 10 ml of the sample solution (mixed solution containing sulfide and hydrogen sulfide ions) in a titration cell containing 1-cm-thich liquid-paraffin layer. Add water 80 ml, which should be gently poured along the wall of the titration cell so that air bubbles are not entrained. Titrate the resultant solution with 0.1 M silver nitrate standard solution or 0.1 M hydrochloric acid standard solution potentiometrically. The titration times needed is less than 10 min.
In the introduction, the necessity of the employment of ionselective electrodes in the water-control practice and for process control in water treatment processes is explained. After the description of the general construction principle of measuring chains for recording potential differences, special data and details are presented concerning the composition of the ion-selective electrodes. The principle of operation and the dependence on special conditions are described by the example of theoretical considerations. The following detection sensitivities with ISE (solid membranes) are stated: iodide 10−2… 10−7; sulphide 10−2… 10−6; cyanide 10−2… 10−5 mol/1. The communication is concluded by suggestions concerning the possibility to detect also chloride concentrations lower than 10−5 mol/1, e.g., with the aid of ISE on a solid membrane basis.
Poly(methacrylic acid) (PMA) forms complexes with divalent metal ions in aqueous solution. Spectrophotometric, potentiometric, titration, and equilibrium dialysis methods have been used to study the complexes. Complex formation in aqueous solution can be evaluated from the amount of free metal ions not bound to the polymer. However, this amount is not easy to be estimated, and several methods have been proposed. In this paper, electron spin resonance (ESR) was applied to estimate the amount of free Mn(II) ions in aqueous PMA containing Mn(II).
An araldite-based titanium tungstoarsenate solid membrane electrode has been developed to estimate rubidium ion concentration in the range 10−1 to 4×10−5M. The electrode shows considerable selectivity for rubidium ions over other cations. Treatment with a 10−4M solution of the anionic surfactant, sodium dodecyl sulphate, not only makes the membrane immune to detergent effects but the selectivity and validity range of the electrode assembly are also improved.
Sodium chloride in Blue, Camembert, Cheddar, Gouda, Muenster, part-skim Mozzarella, Ricotta, Swiss, and whole-milk Mozzarella cheeses in duplicate was measured with a specific ion meter (Orion – Model 407) and pH meter with expanded millivolt scale (Fisher – Accumet Model 230) with a sodium ion electrode. In preparation of samples, 1 g of cheese was blended in an ionic strength adjustment buffer, filtered through cheese-cloth to disperse foam, and tempered to 21 ± 1°C. Sodium was measured directly on filtrates with the specific ion meter. Millivolt potential was measured on filtrates with the pH meter, and a calibration curve was used to convert millivolts to percentage sodium. Percentage salt was calculated by multiplying percentage sodium by 2.54. Cheeses ranged from .22 to 4.76% salt by Volhard titration. Correlations of the sodium ion electrode method with Volhard titration were .999 both for specific ion meter and for pH meter. Comparative results of sodium ion electrode and Volhard titration methods differed by an average of .04 ± .03% salt with specific ion meter and .05 ± .05% salt with pH meter.