Application of a coated-wire electrode to an acetylcholine sensor

An acetylcholine sensor was constructed with acetylcholinesterase which was immobilized on a hydrogen ion-selective coated-wire electrode and fundamental properties of this sensor were investigated. Acetylcholine could be determined in the range 0.1–10 rum with response times of 3–10 min. The effects of pH and concentration of buffer solution on the determination and fluctuations in the data obtained with this sensor were also investigated. Possibilities for the practical use of this acetylcholine micro-sensor are suggested.     

A photo-cured coated-wire calcium ion selective electrode for use in flow injection potentiometry

A multi-sensor cell containing a new photo-cured calcium ion selective electrode sensor is reported. Four membranes containing different components are prepared to determine the one with optimum selectivity and sensitivity. This is shown to consist of the N,N,N',N'-tetracyclohexyl-3-oxapentanediamide ligand (ETH 129) as the ionophore, 2-nitrophenyl octyl ether as the plasticiser and tetradodecyl ammonium tetrakis(4-chlorophenyl) borate as the lipophilic additive. The photo-curing process is applied after coating a thin membrane on a silver wire as substrate transducer to produce the calcium sensor. The curing process is demonstrated to be faster (1 min) than previous methods and does not require a nitrogen atmosphere for reproducible production of membrane response characteristics. Four sensors constructed with the identical optimum membrane are shown to function reproducibly in a multi-sensor flow-through cell using the steady-state mode of flow measurement, and an average calibration slope of 28.5+/-0.4 mV change per activity decade is observed over a log-linear concentration range between 0.01 and 10 mM. The sensor is also shown to respond to changes in pH. Hence, in the flow injection potentiometric mode, a constant carrier buffer composition of pH 8.3 is required for accurate potentiometric calcium determinations. The sensor is used to determine calcium in water samples by flow injection potentiometry. The accuracy of the electrode determination relative to atomic absorption spectroscopy was in the range 5-9% for three different water samples.     

Selective potentiometric determination of Bi(III) with a coated-wire electrode

A bismuth-selective electrode based on the chlorobismuthate(III) salt of Aliquat 336 is described. The electrode gives nearly linear response in the bismuth concentration range 10⁻¹–10⁻⁴M. The optimum solution conditions for operation of the electrode have been determined together with possible interference effects. The application of the electrode to analysis of samples containing large amounts of other metals is illustrated by the determination of bismuth in pharmaceuticals. The electrode is shown to give results by direct potentiometry and the standard-addition method which differ from atomic-absorption results by not more than 2%.     

Investigation of methods of enzyme immobilization on a coated-wire electrode for the development of micro-biosensors

Tridodecylamine- and carboxyl-substituted poly(vinyl chloride)-based hydrogen ion-selective coated-wire electrodes are investigated as transducers for micro-biosensors. Various methods for immobilization of enzyme on the electrode were evaluated by using penicillinase as a model enzyme. The best method was immobilization with glutaraldehyde on the electrode previously modified with bovine serum albumin in the presence of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide to increase the amount of immobilized enzyme. A stable, large potential change is obtainable even in salt-containing samples with this sensor. The possibility of the practical use of such a micro-biosensor is suggested.     

A new coated-wire cobalt(II)-selective electrode based on the benzalkonium tetrathiocyanatocobaltate(II) ion pair

A cobalt-selective electrode based on the benzalkonium tetrathiocyanatocobaltate(II) ion pair is described. The response is Nemstian (slope 29.3 $\text{mV}\text{pCo}$) in the cobalt concentration range 10^-1–10^-4 M in solutions with a constant ionic strength of 3.0 M made up with KSCN at 25°C. The electrode is suitable for end-point detection in titrations of cobalt(II) with EDTA as well as for direct potentiometric determinations of cobalt(II), even in the presence of large amounts of several metal ions (Ni²⁺, Fe²⁺, Mn²⁺, Mg²⁺, Ca²⁺, Ba²⁺) and anions (HCO₃^-, Br^-, I^-, NO₃^-, SO₄^2-).     

Silver(I)-selective coated-wire electrode based on an octahydroxycalix[4]arene derivative.

The performance of octahydroxycalix[4]arene derivative used as a neutral carrier for silver polymeric membrane electrode was studied. The sensor gave a good Nernstian response of 58 +/- 1 mV per decade for silver ion in the activity range 3.3 x 10(-6) to 3.3 x 10(-2) M Ag+. The limit of detection reached 2.1 x 10(-6) M Ag+ and exhibited high selectivity for silver ion against the alkali, alkaline earth and transition metal ions. The sensor can be used in wide pH range from 1.5 to 6.5. The response time of the sensor is less than 20 s. The potentiometric sensor was used as the indicator electrode in the titration of Ag+ ions by sodium chloride solution.     

Phosphate ion-sensitive coated-wire/field-effect transistor electrode based on cobalt phthalocyanine with poly(vinyl chloride) as the membrane matrix

An ion-selective coated-wire/field-effect transistor electrode responding to dihydrogenphosphate is described. The device consists of a coated-platinum wire electrode connected to the gate of a conventional field-effect transistor. Cobalt phthalocyanine is used as ion-exchange electroactive substance and poly(vinyl chloride) as the membrane matrix. The characteristics of the device are investigated and its response is studied by two methods, the linear dependence of the square root of the drain current in the saturated region on the logarithm of ion activity for sodium dihydrogenphosphate, and the dependence of the gate-source potential on the logarithm of ion activity of the same ion. A linear response is obtained in the range of ion activity 10^?5-10^?1 mol dm^?3 and the response slope is 45 mV per decade change of H₂PO₄^? ion activity; the selectivity coefficients are discussed.     

Bis(2-hydroxyacetophenone)ethylenediimine as a neutral carrier in a coated-wire membrane electrode for lead(II).

A coated-wire ion-selective electrode (CWISE), based on a Schiff base as a neutral carrier, was successfully developed for the detection of Pb(II) in aqueous solution. CWISE exhibited a linear response with a Nernstian slope of 29.4 +/- 0.5 mV/decade within the concentration range of 1.0 x 10(-5) - 1.0 x 10(-1) M lead ion. CWISE has shown detection limits of 5.0 x 10(-6) M. The electrode exhibited good selectivity over a number of alkali, alkaline earth, transition and heavy metal ions. This sensor yielded a steady potential within 10 to 20 s at a linear dynamic range. The electrode was suitable for use in aqueous solutions in a pH range of 2.0 to 5.0. Applications of this electrode for the determination of lead in real samples and as indicator electrode for potentiometric titration of Pb2+ ion using K2CrO4 are reported.     

A study of coated-wire potassium-valinomycin and sodium-monensin ion-sensing systems by use of a conventional field-effect transistor

Polymer films containing a sodium or potassium ion-selective exchanger were coated onto platinum wire and incorporated into a potentiometric arrangement. Comparative results obtained by utilizing different measuring devices, one a conventional pH-meter and the other a field-effect transistor (FET) in series with an electrometer, are discussed. The linear range of either system is comparable with that of other electrochemical techniques. Possible applications of such a device are described.     

Determination of some pharmaceuticals using simple potentiometric sensors of coated-wire type

Summary The preparation of simple potentiometric sensors of the coated-wire type is described and working instructions for their use are given. The sensors prepared from an ordinary aluminium conductor, being simple and cheap, can well serve to monitore the titrations based on ion-pair formation. The application possibilities are discussed and shown as practical examples on analyses of nasal and eye drops containing cationic surfactants or salts of alkaloids.

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Bestimmung einiger Arzneimittel mit Hilfe einfacher potentiometrischer Sensoren

Zusammenfassung Die Herstellung einfacher potentiometrischer Sensoren mit isoliertem Draht und deren Verwendung wurde beschrieben. Aus einfachem Aluminiumdraht sind sie billig und können für Titrationen auf der Grundlage von Ionenpaar-Bildung dienen. Die Möglichkeiten ihrer Anwendung wurden erörtert und praktiziert für die Untersuchung von Nasen- und Augentropfen mit kationischen Schaumbildnern oder von Alkaloidsalzen.

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According to the Poster XII-23 presented at Euroanalysis V, Cracow, August 1984; the comments inserted into the text are a consequence of the discussion.     

Biosensor for peptide determination constructed by immobilizing proteolytic enzymes on coated-wire electrodes

A biosensor for peptide determination was constructed with trypsin or α-chymotrypsin immobilized on hydrogen ion-selective coated-wire electrode and its fundamental properties were investigated with two artificial peptides. The substrates could be determined in the range 0.1–40 mM with response times of 5–10 min. The effects of pH and concentration of buffer solution on the determination were investigated.     

New conventional coated-wire ion-selective electrodes for flow-injection potentiometric determination of chlordiazepoxide.

New chlordiazepoxide hydrochloride (Ch-Cl) ion-selective electrodes (conventional type) based on ion associates, chlordiazepoxidium-phosphomolybdate (I) and chlordiazepoxidium-phosphotungstate (II), were prepared. The electrodes exhibited mean slopes of calibration graphs of 59.4 mV and 60.8 mV per decade of (Ch-Cl) concentration at 25 degrees C for electrodes (I) and (II), respectively. Both electrodes could be used within the concentration range 3.16 x 10(-6)-1 x 10(-2) M (Ch-Cl) within the pH range 2.0-4.5. The standard electrode potentials were determined at different temperatures and used to calculate the isothermal coefficients of the electrodes, which were 0.00139 and 0.00093 V degrees C(-1) for electrodes (I) and (II), respectively. The electrodes showed a very good selectivity for Ch-Cl with respect to the number of inorganic cations, amino acids and sugars. The electrodes were applied to the potentiometric determination of the chlordiazepoxide ion and its pharmaceutical preparation under batch and flow injection conditions. Also, chlordiazepoxide was determined by conductimetric titrations. Graphite, copper and silver coated wires were prepared and characterized as sensors for the drug under investigation.     

A lithium-selective glass electrode

We pioneered the study of the electrode properties of glasses containing 80 and 85 wt % LiF and 20 and 15 wt % A1(PO₃)₃. LiF-80-based glass electrodes functioned as lithium-selective electrodes in 1-0.0001 M LiCl solutions. Contrary to aliminosilicate glasses, these glasses responded to the Li⁺ ion better than to the Na⁺ ion and were nonselective to the Hi⁺ ion. This made them promising for the development of sensors for Li⁺ ions in different solutions. Forward and reverse transitions of these glasses from the hydrogen to the lithium function and from the lithium to the sodium function are described by the equation of the simple Nikol’skii theory. Presented at the V All-Russian Conference with the Participation of CIS Countries on Electrochemical Methods of Analysis (EMA-99), Moscow, December 6–8, 1999.