A trimethoprim-selective membrane electrode

An electrode selective for trimethoprim is based on the ion-pair complex of trimethoprim with silicotungstate, and gives rapid response to change in trimethoprim concentration over the range 3 × 10⁻⁵−2 × 10⁻² M with a response slope of 51.0 ± 1.5 mV/decade. No significant interferences are caused by sulpha-drugs. The electrode can be used for the potentiometric determination of trimethoprim.     

New cocaine-selective membrane electrode

The sensitivity and selectivity of a cocaine-selective membrane electrode have been improved with the use of sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate as an ion-exchanger and tetrakis(2-ethylhexyl) pyromellitate (TEHPY) as a solvent mediator. The use of TEHPY suppressed the responses to lipophilic quaternary ammonium ions and strengthened the response to cocaine. The electrode exhibited a near-Nernstian response over a concentration range of 10⁻²to 10⁻⁶ M cocaine with a slope of 56 mV per decade. The lower limit of detection was 4 × 10⁻⁷ M cocaine. Interference by other drugs (morphine and codeine) and a stimulant (methamphetamine) was negligible. This electrode was applied for the determination of cocaine in a drug mixture containing cocaine and morphine, which is widely used to suppress acute pain in cancer patients. The concentration of cocaine, different in each patient, was measured precisely with an average recovery of 99.9% and a mean relative standard deviation of 0.56%.     

Bacterial membrane electrode for l-cysteine

Potentiometric response to L-cysteine is obtained by coupling bacteria of the type Proteus morganii to a modified version of a hydrogen sulfide gas-sensing membrane electrode. The resulting electrode system shows good response to cysteine in the millimolar concentration range with moderate selectivity over related sulfur-containing amino acids. The practical applicability of the electrode is limited by the poor discrimination of the internal gas sensor between hydrogen sulfide and carbon dioxide.     

The chalcocite copper membrane electrode

The membrane electrode based on a synthetic chalcocite (Cu(2)S) single crystal responds primarily to the activity of copper(I) ions in solution. The experimental selectivity coefficient with respect to copper(II) ions is in good agreement with the value calculated on the basis of solubility products of both sulphides. The electrode has been calibrated with metal-ion buffers containing a strongly complexing ligand. TETREN, and can be used as an indicator in titrations of copper with EDTA and TETREN. Comparison of an experimental titration curve with one calculated with the aid of the program HALTAFALL showed good agreement in the case of TETREN, but there were discrepancies for the EDTA titration, which are attributed to the presence and complexation of copper(I) ions. The electrode has also been applied in metal titrations with Cu(2+) as indicator ion, though the potential changes observed were smaller than predicted. All titrations showed errors less than 1%.     

Calcium ion selective membrane electrode

The calcium salts of the mono- and diesters of [4-(1,1,3,3-tetramethylbutyl)phenyl phosphoric acid] have been prepared, and the individual esters as well as mixtures of the esters have been used with several varieties of polyvinyl chloride to construct macro membrane electrodes selective to calcium ions. These electrodes have been calibrated by using solutions of CaCl₂ and Ca ion buffers. The mixed ester electrodes showed Nernstian response in the concentration range 10^-1 to 10^-7M; the diester electrodes showed Nernstian response down to 7.9 x 10^-8M. The detection limit of the mixed ester electrode was 10^-8M, whereas that of the diester electrode was 7.9 x 10^-9M. Contrary to these results, the monoester electrodes showed unsatisfactory behavior. The responses of both the mixed ester and diester electrodes to calcium ions were not affected by the presence of sodium, potassium, or other divalent ions. Only ferric and lanthanum ions showed interferences with the electrode response to calcium ions. p]The electrode response was independent of pH in the approximate range 5–8 at a CaCl₂ concentration of 10^-4M. As the Ca ion concentration was increased, the range of pH independence widened to approximately 4–8. The dynamic response time constant of the mixed ester electrode was in the range 0.7–1.5 sec, whereas that of the diester electrode was in the range 0.5–0.75 sec.     

Liquid ion-exchange membrane electrode for lithium

An electrode selective for lithium relative to other alkali metal ions is described. The sensor is based on n-decanol as both the liquid membrane and exchanger. The electrode exhibits more than 3 decades of linear near-Nernstian response and has selectivity comparable to the LAS 15-25 glass univalent-cation electrode.     

A completely spray-coated membrane electrode assembly

We present a proton exchange membrane fuel cell (PEMFC) manufacturing route, in which a thin layer of polymer electrolyte solution is spray-coated on top of gas diffusion electrodes (GDEs) to work as a proton exchange membrane. Without the need for a pre-made membrane foil, this allows inexpensive, fast, large-scale fabrication of membrane-electrode assemblies (MEAs), with a spray-coater comprising the sole manufacturing device. In this work, a catalyst layer and a membrane layer are consecutively sprayed onto a fibrous gas diffusion layer with applied microporous layer as substrate. A fuel cell is then assembled by stacking anode and cathode half-cells with the membrane layers facing each other. The resultant fuel cell with a low catalyst loading of 0.1 mg Pt/cm² on each anode and cathode side is tested with pure H₂ and O₂ supply at 80 °C cell temperature and 92% relative humidity at atmospheric pressure. The obtained peak power density is 1.29 W/cm² at a current density of 3.25 A/cm². By comparison, a lower peak power density of 0.93 W/cm² at 2.2 A/cm² is found for a Nafion NR211 catalyst coated membrane (CCM) reference, although equally thick membrane layers (approx. 25 μm), and identical catalyst layers and gas diffusion media were used. The superior performance of the fuel cell with spray-coated membrane can be explained by a decreased low frequency (mass transport) resistance, especially at high current densities, as determined by electrochemical impedance spectroscopy.     

Effect of electrode membrane surface ratio and thickness on lead electrode potential

Summary The lead ion selective electrode (ISE) consisting of PbS-Ag₂S is normally used with a membrane surface of outer layer areaA _o) and inner layer area (A _i) at unity (A _o=A _i). Partial covering of one surface area with an insulating material and keeping the other surface layer intact resulted in different ratios of membrane surface areas exposed to lead solutions. The potential linearly increased with increasing theA _o/A _i ratio and decreased with decreasing theA _o/A _i ratio. The lead ISE potential increased linearly with increasing the membrane thickness, but which required much longer time for a stable potential.

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Wirkung von Oberflächenverhältnis und Dicke der Elektrodenmembran auf das Potential einer Bleielektrode

Zusammenfassung Die aus PbS-Ag₂S bestehende spezifische Bleiionen-Elektrode wird üblicherweise mit einem Oberflächenverhältnis der Außenfläche (A _o) und der Innenfläche (A _i) mitA _o=A _i verwendet. Durch teilweise Abdeckung einer Oberfläche mit isolierendem Material, ohne daß die andere Oberfläche verändert wird, ergaben sich verschiedene Verhältnisse der mit der Bleilösung in Berührung stehenden Oberflächen. Mit dem VerhältnisA _o/A _i stieg das Potential linear an bzw. es fiel mit diesem Verhältnis ab. Das Potential der spezifischen Bleielektrode stieg mit der Dicke der Membran, stabilisierte sich aber wesentlich langsamer.

     

Composite liquid membrane for enzyme electrode construction

Microporous polycarbonate membranes were treated with a lipid, isopropyl myristate. The resulting composites were used as external membranes for the construction of hydrogen peroxide-based glucose-detecting enzyme electrodes. The linearity of glucose electrodes was increased to well above the substrate physiological range; for treated membranes of pore size 0.015 μm, linearity was up to 100 mM of glucose. The electrode system had a greatly decreased dependence on temperature, solution pH and background oxygen levels. It also showed reduced interference from electrochemically active species in blood and eliminated the need for sample stirring. Use with whole blood indicated that the treated membrane also had good haemocompatibility, and blood measurements showed an acceptable correlation with a routine spectrophotometric method (y = 0.739x + 1.153; r = 0.969).     

Optimization of a bicarbonate-selective liquid membrane electrode

Summary Based on a theoretical analysis, the response characteristics of a gas permeable/hydrogen ion carrier membrane exhibiting selectivity for bicarbonate have been improved. Novel minielectrodes show a linear response to HCO₃ ^– in the range 10^–3 M to 10^–1 M (slope:-54 mV) and a 95%-response time of 94 s (10^–1 M solution).

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Optimierung einer bicarbonatselektiven Flüssigmembranelektrode

Zusammenfassung Auf der Grundlage einer theoretischen Analyse wurden die Elektrodeneigenschaften eines Bicarbonatsensors, beruhend auf einer gasdurchlässigen und gleichzeitig Wasserstoffionencarrier enthaltenden Membran, optimiert. Neuartige Minielektroden weisen eine lineare Elektrodenfunktion im Bereich 10^–3 M bis 10^–1 M HCC₃ ^– auf (Steilheit:-54 mV); die 95%-Ansprechzeit in 0,1M Lösungen beträgt 94 s.

     

Moclobemide-selective membrane electrode and its pharmaceutical applications

A liquid membrane electrode prepared with moclobemide-dipicrylamine ion-pair complex, dissolved in nitrobenzene as solvent, was studied for analytical performance. The linear response covers the range 10(-3)-10(-6) M moclobemide solution, with a slope of 50.7 mV decade(-1) (pH range 3.5-8). The detection limit is 3 x 10(-7) M. The electrode shows stability, good reproducibility and fast response. The selectivity of the electrode is good. There are two important interfering ions: mianserin and thiamine (Vitamin B(1)). The compression excipients (such as Mg(2+), starch, talcum powder) do not interfere. These characteristics of the electrode enabled it to be used for the determination of moclobemide in drugs and as an active substance, via indirect and direct potentiometric methods. Via an indirect potentiometric method moclobemide, as an active substance, can be determined with an average recovery of 99.96% and a relative standard deviation of 0.85%, and this method can also be used for its determination in drugs with a relative standard deviation of < 2%. The electrode is useful for the determination of the dissolution rate of moclobemide tablets. The physical processes are numerically simulated by typical equations. The apparent first-order rate constants for disintegration and dissolution were calculated.     

Plant tissue-based bioselective membrane electrode for glutamate

A novel potentiometric membrane electrode with selective response to L-glutamate over the 2 × 10^-4–1.3 × 10^-2 M concentration range is constructed by immobilizing slices of yellow squash tissue at a CO₂ gas sensor. This system represents the first successful use of intact plant materials as biocatalysts in the construction of bioselective potentiometric membrane electrodes; as a result, the range of future possibilities may be greatly extended. The glutamate-sensing electrode combines excellent selectivity characteristics over some 25 possible interferences tested, good reproducibility, and a useful lifetime of 7 days in aqueous samples.     

Chloride estimation by a solid membrane electrode

Summary A solid membrane electrode based on Cr-Zr mixed hydrous oxide gel doped with Sn(II) ion has been proposed for the estimation of chloride ions. The electrode can be used in the concentration range 0.1 to 5×10^–5 M. The selectivity of the electrode system is much better as compared to other electrodes reported for the same ion.

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Chloridbestimmung mit Hilfe einer festen Membran-Elektrode

Zusammenfassung Eine feste Membran-Elektrode auf der Basis einer mit Sn(II)-Ionen gedopten Mischung aus Chrom- und Zirkon-Oxidhydratgel wurde für die Bestimmung von Chloridionen vorgeschlagen. Diese Elektrode läßt sich im Konzentrationsgebiet 0,1 bis 5×10^–5 M verwenden. Die Selektivität ist erheblich besser als diejenige anderer Elektroden.

     

Urea sensors based on PVC membrane pH electrode

Several procedures of urease immobilization on the surface of the polymeric membrane pH electrode with tri-n-dodecylamine as a neutral carrier were compared. The best results were obtained for the urea sensor with covalently bound urease. The sensor characteristics including the effect of buffer, pH and concentration and the effect of stirring rate are presented. These effects are in good agreement with theoretical expectations.     

Streaming potential in a liquid ion-exchange membrane electrode

A streaming potential in a liquid membrane electrode sensitive to nicotinate ion (3-pyridinemonocarboxylate), has been observed during dynamic electrode response measurements carried out by sodium nicotinate step-wise concentration increases. It was possible to separate the streaming potential from the dynamic electrode response and to study it as a function of the flow-rate in the cell and of the nature of the liquid membrane support.A streaming potential was observed with Millipore MF-PH supports (mixed esters of cellulose) but not with Fluoropore (polytetrafluoroethylene bonded to polyethylene net) supports.     

Improved membrane electrode using plant tissue as biocatalyst

A newly developed pyruvate selective membrane electrode using plant tissue as biocatalyst is described. Comparison studies of electrodes which employ corn kernel portions as biocatalyst with similar electrodes based on isolated enzyme show that the former achieve longer lifetimes and enhanced activities with no loss of selectivity. This improvement is attributed to stabilization of the biocatalytic activity by the plant tissue matrix.     

A chloroquine membrane electrode with low detection limit

A PVC membrane electrode for chloroquine [7-chloro-4-(4-diethylamine-1-methylbutylamino)-quinoline] based on a chloroquine/dinonylnaphthalene sulphonic acid ion-pair is described. The electrode shows near-Nernstian response in the 10^?2–10^?6 M range and a detection limit of 2 × 10^?7 M. Its selectivity relative to various inorganic ions, amino acids, neurotransmitters, drugs, and some excipients is reported. Direct potentiometry is used to determine chloroquine in pharmaceutical preparations with good results.