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The potentiometric anion selectivity of polymer membrane-based electrodes formulated with a palladium organophosphine complex (benzylbis(triphenylphosphine)palladium(II) chloride) as the membrane active component is examined. The electrode is shown to exhibit a non-Hofmeister selectivity pattern with a significantly enhanced response toward nitrite over the concentration range of 10 microM-10 mM (log-linear range) and a detection limit 5.0 microM. The effect of lipophilic anionic (tetraphenylborate derivatives) and cationic (tetraalkylammonium) site additives within the membrane on the anion selectivity is examined in detail. Addition of both cationic and anionic sites is shown to improve potentiometric anion selectivity, suggesting that the palladium complex may operate simultaneously as a neutral and charged carrier-type ionophore within the polymer membrane phase. Using optimal membrane formulations (with added 20-30 mol % cationic sites), the sensors prepared with the palladium complex do not exhibit proton/hydroxide response in the range of pH 3.5-12, a potential advantage over previously reported nitrite electrodes prepared with Co(III) corrins and porphyrin complexes.

A novel potentiometric assay method for arylsulfatase enzyme is described based on measuring the initial reaction rate of hydrolysis of 4-nitrocatechol sulfate (4-NCS) substrate under optimized conditions. A monitoring sensor incorporating a PVC membrane with a nickel(II) bathophenanthroline-4-NCS ion-pair complex as electroactive material and 2-nitrophenyl phenyl ether as solvent mediator is developed and characterized. the sensor exhibits fast and stable linear response for 8×10 -3 -7.5×10 -6 M 4-NCS with an anionic slope of 58.5±0.2 mV/decade over the pH range 3-6. The sensor is used to follow up the decrease in a fixed concentration of 4-NCS (2×10 -4 M) as a function of arylsulfatase activity at pH 5.6 and 37 o C. A linear relationship between the initial rate of substrate hydrolysis and enzyme activity holds for 0.2-2.4 IU/mL (SD 2%). Activity measurement of arylsulfatase enzyme isolated from camel liver gives results that compare favorably well with data obtained using the standard spectrophotometric assay method. Significant advantages over many of the previously described spectroscopic methods are offered by the proposed potentiometric technique

A novel potentiometric sensor for simple, sensitive, and selective determination of acetate ion is developed and electrochemically evaluated. This assembly is based on the use of a flat-bottom combination glass pH electrode behind a Teflon membrane and in contact with a thin film of sodium acetate-sodium chloride internal electrolyte solution. Acidifying the analyte acetate solution to pH

In this paper, fabrication, characterization, and physiological application of a miniaturized amperometric lactate biosensor are described. The sensor is based on cross-linked lactate oxidase and tetrathiafulvalene-tetracyano-quinodimethane (TTF-TCNQ) charge transfer complex. The sensor was developed for continuous quantitative measurement of the lactate accumulation in ischemic myocardium under severe depletion of oxygen. The sensor was evaluated in vitro at an applied potential of 0.15 V vs Ag/AgCl; it proved to combine all the performance characteristics desired for the present application, such as proper response in absence of oxygen, good operational stability, good accuracy and precision (103.5 +/- 1.2%), adequate response time (t95% = 80 s), and wide linear dynamic range up to 27 mM (r = 0.9998) in N2-saturated solutions and at 37 degrees C. The prepared sensors (n = 12) showed sensitivity of 380 +/- 90 nA/mM, and a background current of 240 +/- 50 nA. The lower limit of detection is 0.4 +/- 0.15 mM with a S/N ratio equal to 3. Results obtained for direct lactate monitoring in ischemic rabbit papillary muscle under no-flow conditions and PO26 mm Hg are presented.

The performance characteristics of nitrogen oxide gas sensor with regard to the origin of response, limit of detection, response time, influence of the membrane type, and selectivity have been systematically examined. Optimum conditions for direct potentiometric determination of as low as 0.1 ..mu..mol mL/sup -1/ nitrite are described and results with an average recovery of 98.2% (standard deviation +/- 0.3%) are obtained. The sensor is also used to monitor direct titration of micromole per liter quantities of primary aryl amines, hydrazines, and azide with sodium nitrite or sodium cobaltinitrite. Results with an average recovery of 98.3% (standard deviation +/- 1.3%) are obtainable without any significant interference from 1000-fold molar excess of amides, imides, anilides, tertiary amines, and quaternary ammonium salts. 24 references, 2 figures, 4 tables.

Two novel membrane electrodes highly sensitive and selective for amphetaminium cation are developed and electro-chemically evaluated according to IUPAC recommendations. These electrodes incorporate amphetamine-dibenzo-18-crown-6 (DB18C6) and amphetamine-dibenzo-24-crown-8 (DB24C8) as the active components in 1,2-dichloroethane solvent. Both electrode systems exhibit stable near-Nernstian response over the range 10 −2 −10 −5 M amphetaminium cation with a slope in the range of 55-58 mV/decade of concentration. The working pH range is 3-7, the response time varies from 30 to 50 s and the lower limit of detection is ∼3 ppm. The selectivity toward amphetaminium cation is reasonably high relative to many common inorganic cations and alkaloids as well as some amines structurally related to amphetamine

Sensitive and reasonably selective methods are described for the spectrophotometric, potentiometric, and gravimetric determination of lanthanides using peri-dihydroxynaphthindenone as a novel chromogenic and precipitating reagent. The reagent forms a stable 1:2 (metal:reagent) type of complex with light lanthanides at pH 2-7 in 1:1 ethanol-water mixture. Low metal concentrations ( 100 ..mu..g/mL permits both gravimetric quantitation by igniting the precipitates to the metal oxides and potentiometric titration of the excess reagent. Results with an average recovery of 98% (standard deviation 0.7%) are obtainable for 0.1 ..mu..g to 200 mg of all light lanthanides. Many foreign ions naturally occurring or frequently associated with lanthanides do not interfere or can be tolerated.

An electrode sensitive for diethyldithiocarbamate ions (DDC) down to 10/sup -5/ M is prepared by precipitation of copper diethyldithiocarbamate and silver sulfide within a graphite rod. The electrode is used as a monitor for simultaneous titration of binary, tertiary, and quaternary metallic mixtures of Cu, Cd, Ni, Pb, V, Th, and Zn in 50 to 75% ethanol at pH 4 to 6 using NaDDC as a titrant. Stepwise titration curves with sharp end point breaks and results with an average recovery of 98.5% (mean standard deviation +- 0.4%) are obtained with as little as 50 ..mu..g/mL of all these metal ions. Application of the method to simultaneous determination of some major elements in five different copper-base alloys gives results which compare favorably with certified values.