Potentiometric determination of mephedrone in oral fluids with ion-selective membranes

This work presents a potentiometric approach for the detection of two cathinone derivatives, namely mephedrone (4-MMC) and clephedrone (4-CMC). Contrary to neutral-carriers (dibenzo-18-crown-6-ether and calix[4]arene), cation-exchanger (tetraphenylborate sodium) as active component of ion-selective membrane showed near-Nernstian response (+47 mV/decade from 1.7 ⋅ 10⁻⁶ to 5.6 ⋅ 10⁻⁴ mol l⁻¹) and selectivity for 4-MMC in oral fluids (OF). The agreement between the quantitative results obtained with the potentiometric approach and the HPLC/MS-MS method determination of 4-MMC in OF shows the potential of the proposed potentiometric approach for forensic analysis.     

Potentiometric determination of boron in silicon with an ion-selective electrode

A potentiometric method is proposed for the determination or boron in silicon, based on dissolution of silicon by treatment with hydrofluoric acid and ammonium fluoride in the presence of hydrogen peroxide, and conversion of boron to fluoroborate ion. The fluoroborate activity is measured with the Orion fluoroborate-selective electrode. Some important points, such as the effect of various interfering ions and the hydrolysis of fluoroborate ion, are described in detail. The method is applied to the determination of boron in silicon containing at least 10 p.p.m. of boron, with a relative standard deviation of ±4%.     

Potentiometric ion-selective electrodes for determination of cyclopentolate hydrochloride and phenylephrine hydrochloride in their challenging ophthalmic formulation

Introduction of potentiometric ion-selective electrodes (ISEs) opened a new bright area in pharmaceutical analysis acknowledged as being an eco-friendly, simple, and energy-saving technique that is well-suited with microfabrication. In this contribution, potentiometric ISEs were employed as an alternative green analytical tool with the crucial goal of expanding the effective application of the potentiometric sensors in different disciplines of drug-stability studies and quality-control investigations. Four novel cyclopentolate hydrochloride and phenylephrine hydrochloride selective membrane sensors were constructed and evaluated. Sensors’ fabrication was achieved using potassium tetrakis (4-chlorophenyl) borate, a cationic exchanger, in a polyvinyl chloride polymeric matrix plasticized with 2-nitrophenyl octyl ether and using 2-hydroxy propyl-β-cyclodextrin as an ionophore. A comparative potentiometric study was implemented using two designs of ISEs; a conventional liquid inner contact and a glassy carbon solid-contact one. Using solid-contact ISEs, detection limit was substantially decreased and the discriminative ability in the presence of the most interfering substances was enhanced. This permits simultaneous estimation of both drugs, in spite of their similar ionic characteristics, abolishing the need for any pretreatment or separation steps in their challenging combined ophthalmic formulation as well as in rabbit aqueous humor and in the presence of their degradation products.     

Potentiometric determination of coextraction constants of potassium salts in ion-selective electrodes utilizing a nitrobenzene liquid membrane phase

A theoretical treatment of potentiometric data is applied to calculate coextraction constants (K_IA) for three potassium salts from water into a liquid nitrobenzene phase. The experiment involves treating nitrobenzene as a membrane and contacting it with two aqueous solutions of different ion activities. In the presence of either a cation or anion exchanger, the ratio of activities of ions in the two aqueous phases gives rise to a potential difference across the membrane that depends upon the nature and charge of the counter ion of the ion-exchanger in excess. Here, the cation exchanger was chosen to be potassium tetrakis(4-chlorophenyl)borate (KTpClPB) and the anion exchanger was tetradodecylammonium chloride (TDDACl). TDDACl was incrementally added to the nitrobenzene phase containing a fixed concentration of KTpClPB, and the corresponding emf was recorded as a function of concentration of TDDACl. The membrane changes from one with cation exchanger properties (excess KTpClPB) to one with anion exchanger properties (excess TDDACl). The potential difference and shape of the titration curve can be predicted by theory based on the phase boundary potential model. Log(K_IA) values calculated for KCl, KNO₃ and KClO₄ in nitrobenzene were found as: −10.53 (± 0.09), −8.16 (± 0.05) and −5.63 (± 0.03) respectively, in accordance with the Hofmeister series of lipophilicity, and similar to those observed in PVC membranes containing other plasticizers. The method presented here offers the advantage over other methods to calculate K_IA, in that it is relatively experimentally simple without compromising the accuracy of the calculated coextraction constants. The ability to titrate directly into the liquid membrane phase affords a higher precision compared to the preparation of a series of PVC/plasticizer membranes with different compositions.     

Potentiometric responses of ion-selective electrodes after galvanostatically controlled incorporation of primary ions

A new method of quantitative incorporation of primary cations into ion-selective membrane by means of galvanostatic cathodic polarization/conditioning, before measurement step, was proposed and tested on the example of potassium-selective electrode with ionophore - valinomycin in poly(vinyl chloride) based membrane and with polypyrrole solid contact. Open circuit potential values recorded after polarization can be quantitatively explained by changes of primary cations and ionophore concentration in the surface part of the membrane. The influence of potassium ions concentration in the membrane (in relation to ion exchange sites amount) on the shape of potentiometric calibration plots was also observed. Improved characteristics, with extended linear range, can be obtained for membrane of minor loading with primary cations (around 25%), the responses are relatively stable in course of following calibrations.     

Properties of ion-selective electrodes with polymeric membranes for ketoprofen determination

The aim of the research was to create electrodes based on PVC membrane with solid contact. The membranes were plasticized with bis(2-ethylhexyl)sebacate, (DOS), dibutylphthalate (DBP) diisobutylphthalate (DIBP), tris(2-ethylhexyl) phosphate (TEHP), and 2-nitrophenyloctyl ether (o-NPOE) in which the active substance tetraoctylammonium 3-benzoyl-??-methylbenzeneacetate (KET-TOA) was dissolved. The basic analytical parameters of the ketoprofen electrode such as measuring range, detection limit, response time, lifetime, and selectivity coefficients for some organic and inorganic anions were determined. For all electrodes similar potentiometric responses were obtained: measuring range 1 × 10^?4 ?1 × 10^?1 M, and Nernstian slope of characteristics of about 55?C60 mV/decade. The electrode was used to determine ketoprofen in the synthetic sample and pharmaceutical preparations, in injections, tablets and capsules in the concentration range of 0.025?C25 mg/mL in aqueous solution at pH 5.5?C8.5.     

Potentiometric performance of silver ion-selective electrodes based on tridentate Schiff base derivatives.

To examine the directivity for improving the silver ion discrimination ability of a Schiff base, three kinds of tridentate ligands were synthesized and compared with the similar quadridentate ligand as the silver ionophore. Among the Schiff base derivatives tested, 3-(2-pyridylethylimino)-2-butanoneoxime, having one oxime and a pyridine substituent, was found to be the best ionophore for a silver-ion electrode. The electrode based on this derivative exhibited good silver-ion selectivity, -log Kpot(Ag+,K+) = 3.8, comparable to that of a quadridentate Schiff base, N,N'-bis(2'-hydroxyimino-1'-phenylpropyleden)-1,3-propanediamine, reported previously, except for a pseudo Nernstian response (35.6 mV decade(-1)) with a wide silver-ion activity change in the activity change from 5.0 x 10(-7) to 7.9 x 10(-2) mol dm(-3).     

Potentiometric behavior of N,N,N',N'-tetrabenzylmethylenediamine-based hydrogen ion-selective electrodes

H(+)-ion selective electrodes (H(+)-ISE) based on N,N,N',N'-tetrabenzylalkylenediamine (alkylene: methylene, ethylene, propylene, hexylene) are prepared. We are compared with their response potentials to carbon numbers between diamino groups. They were showed linear selective to hydrogen ion in the range of pH 1.5-9.0, 2.5-9.0, 3.5-9.0 and 4.0-9.0, and their Nernstian slopes were 57.3, 53.5, 57.4 and 56.1 mV pH(-1) at 20+/-0.2 degrees C (theoretical value: 58.2 mV pH(-1)), respectively. The interference effect on the cations were measured to alkali metal ions, alkaline earth metals ions. Selectivity coefficients were measured by the mixed-solution method. Among all electrodes the N,N,N',N'-tetrabenzylmethylenediamine (TBMDA)-based electrode has shown the best selectivity in acidic solution.     

Direct potentiometric water hardness determination using ion-selective electrodes

Summary The use of ion-selective electrodes for direct potentiometric water hardness determinations is restricted to relatively soft waters if they are to be competitive with other techniques in terms of uncertainty on the water hardness scale. The selectivity factorK _MgCa ^Pot must be within 1.1% of unity if a hardness of 10 degrees on the German scale is to be measured to within 0.1 degrees in the composition rangec _Mg:c _Ca=0.25 to 25. The expressionK _MgNa ^Pot ·a _Na ² / (a _Mg+a _Ca) must be less than 0.001 if freedom from sodium interference is to be achieved. Under these conditions a 1% relative standard deviation can be obtained for an uncertainty of the EMF100V.

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Direkte potentiometrische Bestimmung der Wasserhärte mit ionen-selektiven Elektroden

Zusammenfassung Die direkte potentiometrische Bestimmung der Wasserhärte mit ionenselektiven Elektroden kann nur für relativ weiches Wasser verwendet werden, sofern sie mit anderen Methoden konkurrenzfähig sein soll. Der SelektivitätsfaktorK _MgCa ^Pot sollte nicht mehr als 1,1% von 1 abweichen, um eine Messung von 10 deutschen Härtegraden auf 0,1 Grad genau zu ermöglichen, wenn gleichzeitig das Mischungsverhältnisc _Mg:c _Ca im Bereich 0,25 bis 25 schwankt. Der AusdruckK _MgNa ^Pot ·a _Na ² /(a _Mg +a _Ca) sollte 0,001 nicht überschreiten, wenn eine Störung durch Natrium vermieden werden soll. Unter den obigen Bedingungen läßt sich eine Wasserhärte auf 1% genau bestimmen, wenn die Unsicherheit der gemessenen EMK100V.

     

Potentiometric behavior of ion-selective electrodes to large cationic species modulated by decyl alcohol

The effect of 1-decanol on the potentiometric response of three ion-selective electrodes to large cationic species is analyzed. The electrodes were constructed with plasticized PVC membranes. The results suggest that 1-decanol alters the ionic transport through the membrane/water interface to an extent that depends on the strength of the active ion pair. The water solubility of the cation, its molecular weight, and the size of the ion pair seem to be relevant factors in this type of behavior. The potentiometric selectivity coefficients are also dependent on the presence of 1-decanol in the membrane. These results are similar to those already described in ion-selective electrodes with membranes capable of sensing anionic benzene sulfonate-type systems. Thus, the effect of the alcohol appears to be general by affecting mainly the membrane surface polarity.     

Solid-state ion-selective electrodes for the potentiometric determination of phosphate

A number of solid-state ion-selective electrodes for the potentiometric determination of phosphate have been made and their properties investigated. The most successful of these electrodes, which had a membrane comprising silver sulphide, lead sulphide and lead hydrogen phosphate, had a theoretical Nernstian response to orthophosphate ion at concentrations down to 5 mug/ml total phosphate at pH 8.3. The electrode had a slow response and its standard potential changed with time. Anions such as sulphate, bicarbonate and nitrate did not interfere; chloride had a transient effect, but even at its worst the interference was less serious than with other phosphate electrodes. The electrode was used as an indicator in the potentiometric precipitation titration of phosphate and lanthanum.     

Micro and semimicro determination of arsenate using ion-selective electrodes

Summary An indirect method for the microestimation of 0.75 to 15 ppm (1–10^–5 to 2·10^–4 M) of As(V) has been described: Arsenate is precipitated with lanthanum nitrate at a pH of 8.65. The excess of lanthanum is titrated with standard fluoride, using a fluoride ion-selective electrode. Equivalence points are located on volume-corrected Gran's plot paper. This method can also be used to estimate the sum of arsenate and phosphate. For larger amounts of arsenate and for increased precision and accuracy, potentiometric titration with lead perchlorate, using a lead ion-selective electrode, is recommended. Other possibilities for determining arsenate and a method for estimating tungstate are suggested.

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Zusammenfassung Eine indirekte Methode zur Mikrobestimmung von 0,75 bis 15 ppm (10^–5 bis 2·10^–4-m) As(V) wurde beschrieben. Arsenat wird bei pH 8,65 mit Lanthannitrat gefällt, dessen Überschuß man mit einer Fluoridstandardlösung unter Verwendung einer fluoridspezifischen Elektrode titriert. Die Äquivalenzpunkte trägt man auf einem volumenkorrigierten Millimeterpapier nach Gran auf. Nach diesem Verfahren kann auch die Summe von Arsenat und Phosphat bestimmt werden. Für größere Arsenatmengen und für erhöhte Anforderungen an Genauigkeit wird die potentiometrische Titration mit Bleiperchlorat gegen eine bleispezifische Elektrode empfohlen. Andere Möglichkeiten der Arsenbestimmung sowie eine Methode zur Wolframbestimmung werden vorgeschlagen.

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Work performed under the auspices of the U.S. Atomic Energy Commission.     

Joint determination of fluorine and chlorine in granitic rocks with ion-selective electrodes

This enables both fluorine and chlorine in granitic rocks to be determined with a single sample. A rapid technique, using fusions in culture tubes, and a slower technique, employing fusions in platinum crucibles are described. The culture-tube technique is suitable for geochemical exploration and employs an oxidizing flux so that sulphide-bearing rocks can be analysed. The platinum-crucible technique yields fluorine and chlorine results for the standard rocks G-2 and GSP-1 that are comparable in value and precision to those obtained by other analytical methods. It is faster, easier to manipulate and yields higher fluorine values than the existing joint spectrophotometric method.     

The determination of microgram amounts of orthophosphate using ion-selective electrodes

Summary The potentiometric titration ofg amounts of orthophosphate with lead perchlorate using a lead ISE, and with silver nitrate using a silver sulfide ISE, was investigated. With 0.001N lead perchlorate the practical limit of the determination is approximately 10g (0.3mol) of phosphorus. Microgram amounts of phosphate require the application of a small polarizing current to the lead ISE to enhance the potential breaks near the endpoint.Previously reported titrimetric methods for orthophosphate with silver nitrate were reinvestigated using a silver sulfide ISE. The borate-buffered system proved superior to the sodium acetate-methanol system when a partially non-aqueous medium of 60–70% methanol was used. With the borate-buffered system, 0.005N silver nitrate can be used, while it cannot be used in the sodium acetate-methanol system. Also, considerably larger amounts of sulfate and fluoride can be tolerated in the borate-buffered system. The sequential determination of halides and phosphate is feasible in this system.

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Zusammenfassung Die potentiometrische Titration von Mikrogrammengen Orthophosphat mit Bleiperchlorat und einer bleispezifischen Elektrode bzw. mit Silbernitrat und einer silberspezifischen Elektrode wurde untersucht. Mit 0,001-n Bleiperchlorat liegt die praktische Grenze der Bestimmbarkeit bei etwa 10g (0,3Mol) Phosphor. Bei Mikrogrammengen Phosphat muß man an die bleispezifische Elektrode einen schwachen Polarisationsstrom anlegen, um den Potential-Knick nahe dem Endpunkt zu verstärken.Früher veröffentlichte Titrationsmethoden für Orthophosphat mit Hilfe von Silbernitrat wurden neuerlich mit einer Silbersulfidelektrode bearbeitet. Ein Boratpuffersystem erwies sich der Pufferung mit Natriumacetat-Methanol überlegen, wenn in 60–70%igem Methanol gearbeitet wird. In boratgepufferter Lösung kann man mit 0,005-n Silbernitrat titrieren im Gegensatz zu acetat-methanolischer Lösung. Auch können wesentlich größere Mengen Sulfat und Fluorid im boratgepufferten System toleriert werden. Halogenide und Phosphat können in diesem Milieu nacheinander bestimmt werden.

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This work was performed under the auspices of the U. S. Atomic Energy Commission.     

Coated-wire ion-selective electrodes

Coated-wire ion-selective electrodes were first developed in 1971, and comprise a film of polyvinyl chloride or other suitable polymeric matrix substrate containing a dissolved electroactive species, coated on a conducting substrate (generally a metal, although any material with conductivity substantially higher than that of the film can be used). Electrodes of this sort are simple, inexpensive, durable and capable of reliable response in the concentration range of 10^?1 to 10^?6 M for a wide variety of both organic and inorganic cations and anions. The principles on which these electrodes are based, as well as their application to a variety of analytical problems, will be discussed.     

Neutral-carrier-based ion-selective electrodes

Neutral-carrier-based ion-selective electrodes for the assay of alkali and alkaline earth metal cations have advanced to become the most frequently used potentiometric sensors in clinical chemistry. The major developments since the realization of the first potentiometric cell assemblies utilizing electrically neutral complexing agents (valinomycin and the macrotetrolides) in 1966 are presented.     

Linear titration plots with ion-selective electrodes

A computational method for simultaneous determination of the equivalence volume and the Nernstian slope of an ion-selective electrode is described. Treatment of data from linear titration and standard addition procedures is simplified by the use of equal additions of standard solution. Equivalence volumes and concentrations were determined with errors of 0.5-2% by the proposed method.