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At least 91 records · Page 5Linked to original sources
PubMed1984

[Demonstration of hormonal actions on Escherichia coli K 12 by potentiometry in the presence of lipoic acid; correlation with measurements of microbial growth and glucose consumption].

The action of hormones on Escherichia coli K 12 was followed by potential-time measurements in the presence of lipoic acid (LA), photometric determinations of growth and glucose titrations. Bovine growth hormone (5 to 60 IU/1) increased O2 consumption. The (10 IU/1) insulin-facilitated transport of LA was stimulated by glucose. Adrenaline (0.5 to 15 mg/l) increased more glucose and O2 consumption than growth.

Epinephrine↗
PubMed1984

Interferences with potentiometry of CO2 in the Ektachem 400 Analyzer.

We have investigated the Kodak Ektachem 400 Analyzer procedure for CO2 for interferences from benzyl alcohol, benzoic acid, and several compounds structurally similar to benzoic acid. Benzoic acid in plasma, at concentrations found in neonates intoxicated with benzyl alcohol, caused a large increase in the results for CO2, as did substantially above-normal concentrations of certain fatty acids and keto-acids, and toxic concentrations of aspirin. We observed a correlation between increasing benzoic acid concentrations (up to 17 mmol/L) and falsely increasing CO2 values (greater than 47 mmol/L) obtained with the Ektachem Analyzer for samples from a neonate in the intensive-care unit, who was receiving benzyl alcohol-preserved saline solutions. Although the Ektachem CO2 procedure is simple and rapid, and in most cases accurate, questionable results are occasionally encountered, as indicated by a low anion gap or a measured CO2 exceeding that calculated from blood gas measurements. Such results require the use of another method for verification.

Benzoates↗
PubMed1982

The room temperature potentiometry of xanthine oxidase. pH-dependent redox behavior of the flavin, molybdenum, and iron-sulfur centers.

A series of potentiometric titrations of xanthine oxidase have been performed at room temperature in the pH range 6.1-9.9. Reduction of the two Fe/S centers was monitored by CD, and that of the FAD and Mo center by EPR. The Fe/S centers behave as centers having a protonable group whose pKa changes with reduction state (E = -344 mV, pKo = 6.4, and pKr = 8.1 for Fe/S I; E = -249 mV, pKo = 6.4, and pKr = 8.0 for Fe/S II). The flavin and the two types of molybdenum centers show varying behavior, but, in all cases, electron addition is accompanied by protonation. The sequence for FAD is reduction, protonation, reduction, protonation with E1 = -398 mV, E2 = -240 mV, pK1 = 9.5, pK2 = 7.4. For "rapid" molybdenum, the sequence is protonation, reduction, protonation, reduction with E1 = -369 mV, E2 = -301 mV, pK1 = 7.9, pK2 = 8.4; and for slow molybdenum, protonation, reduction, protonation with E1 = 320 mV, E2 = -477 mV, pK1 = 7.5, pK2 = 9.5. Comparison to data obtained previously at cryogenic temperatures (Cammack, R., Barber, M. J., and Bray, R. C. (1976) Biochem. J. 157, 469-468 and Barber, M. J., and Seigel, L. M. (1982) in Flavins and Flavoproteins (Massey, V., and Williams, C. H., eds) pp. 796-804, Elsevier/North-Holland, New York) showed the centers to have significant temperature dependence, which calls for a re-evaluation of conclusions reached using cryogenic techniques (e.g. rapid-freeze). The optical absorbance characteristics of the enzyme were also investigated and a possible absorbance for molybdenum was suggested.

Animals↗
PubMed1982

Iontophoresis: mechanism of action studied by potentiometry and x-ray fluorescence.

Physiotherapists often apply electrotherapeutic treatments to the knees with sponges impregnated with potassium iodide (KI). To study the fate of iodine applied in this way, the amount of iodide (I-) that penetrates the skin was determined using an iodide-selective electrode. The I- uptake was shown to take place only when galvanic current was applied. Iontophoresis did not result in superficial migration of the applied ions on the skin from one pole to the other, but led to penetration into the skin. The hyperemia, which occurs at the zone of application during iontophoresis, did not affect the uptake of subsequent treatments. Only very slight differences in uptake were observed for each patient with sequential application, whereas the interindividual differences were more pronounced. Combined evidence from all experiments suggested that about 10% of the applied KI had penetrated the skin. X-ray fluorescence scans of the volunteers' thyroid gland, before and after a series of 10 iontophoretic treatments, to establish whether I- was taken up by the thyroid, showed that the average iodine content of the gland was increased by more than 30%.

Humans↗
PubMed1981

Sodium and potassium measurements: direct potentiometry and flame photometry.

Data from the 1979 and part of the 1980 College of American Pathologists (CAP) Chemistry Survey Program have been reviewed in order to compare the direct potentiometric measurement of sodium and potassium with flame-emission photometric measurements. As may have been predicted from earlier intralaboratory evaluations, the results of the CAP interlaboratory comparison confirm that flame-emission photometry of the two electrolytes yields lower mean concentrations. Reasons for this difference lie in the physicochemical aspects of the sample and methods. In Survey specimens, the magnitude of difference was rarely one of clinical significance, but the documented increase in the use of direct electrode measurements in laboratories warrants informing clinicians of potentially significant differences in selected patients.

Chemical Phenomena↗
PubMed1999

Competitive Metal Ion Adsorption in Goethite Systems Using In Situ Voltammetric Methods and Potentiometry.

Competitive complexation with respect to the binary-metal ion combinations Cu(II)-Zn(II), Cu(II)-Pb(II), and Pb(II)-Zn(II) were studied at the goethite (alpha-FeOOH)-water interface (25 degrees C, I = 0.1 M NaNO(3)). In addition to potentiometric titrations and batch adsorption experiments, an in situ voltammetric technique was utilized. Sorption studies were performed within the ranges 3.5 </= pH </= 8.5, 10(-6) </= [M(II)](tot) </= 10(-3 )M, and with solid concentrations between 0.09 and 9 g dm(-3). The results obtained (metal uptake and proton release curves) were compared with corresponding predicted values, based upon previously determined thermodynamic surface complexation models for the different single-metal ion goethite systems. The surface complexation modeling was based upon the constant capacitance concept. The results showed that the Cu(II) and Zn(II) surface complexation submodels were combinatory in all two-metal systems studied, both at 10(-3) M and at 10(-6 )M concentrations of the metals. For Pb(II) a somewhat stronger adsorption to goethite than predicted by the previously determined submodel was observed in all two-metal systems studied. These deviations could be corrected for by a moderate adjustment of the equilibrium constant for the most acidic surface complex &tbond;FeOHPb(2+). It can also be concluded that the in situ voltammetric technique can be applied to measure trace concentrations of at least two metal ions simultaneously occurring in goethite suspensions under varying experimental conditions with good accuracy. Copyright 1999 Academic Press.

Journal Article↗
PubMed2000

Sorption Studies of Cobalt(II) on Colloidal Hematite Using Potentiometry and Radioactive Tracer Technique.

The sorption of Co(II) on colloidal hematite was studied as a function of pH, ionic strength, and Co(II) concentration. Two different techniques were used, yielding two different sets of information: (i) potentiometric titrations that provide information on the number of protons released as a function of pH owing to the sorption of Co(II) and (ii) measurement of the amount of cobalt sorbed on the surface as a function of pH using a radioactive tracer, (60)Co. At low Co(II) concentrations (10(-8) M), the sorption was found to be independent of ionic strength but there seems to be a weak ionic strength dependence at higher Co(II) concentrations (10(-4) M). The adsorption edge moved to higher pH with increasing Co(II) concentration. For the high Co(II) concentration, the number of protons released per cobalt sorbed increased from zero to approximately 1.5. The basic charging properties of hematite were modeled with four different surface complexation models. The 1-pK Basic Stern Model (BSM), with binding of electrolyte ions to the Stern plane, seems to be the most reasonable model if the ambition is to describe experimental data at different ionic strengths. The sorption of cobalt was modeled with the 1-pK BSM. By introducing a low concentration of high affinity surface sites for cobalt sorption it was possible to model the sorption in very wide cobalt concentrations, ranging from 10(-8) M to 10(-4) M. Copyright 2000 Academic Press.

Journal Article↗
PubMed1996

On the analysis of CO(2), H(2)- and CO, H(2)-mixtures by water-gas potentiometry with solid electrolyte cells.

The potentiometric analysis of CO(2), H(2) and CO, H(2)O-mixtures using oxide ion-conducting solid electrolytes requires the adjustment of the water-gas equilibrium without side reactions in the high-temperature galvanic cell. Conventional cell designs suitable for the analysis of H(2), H(2)O and CO, CO(2)-mixtures are not applicable due to the insufficient gas residence times in the cells and the insufficient catalytical activity of the platinum electrodes. Solid electrolyte cells have to be modified by integrating of suitable catalysts. Under optimized conditions of gas velocity and cell temperature both gas systems can be analyzed only by measuring the cell tension U (=-emf) and temperature in the favorized temperature range around 813 degrees C. Here systematical errors of the component ratio or the mole fraction were smaller than 6%. Several fundamental requirements for the application of catalysts in solid electrolyte cells for the analysis of reactive water-gas mixtures are pointed out.

Journal Article↗
PubMed1996

Complexation of Ln(III) and Ca(II) Cations with 3,4-Dicarboxyinulin and Model Compounds: Methyl 3,4-Dicarboxy-alpha-D-fructofuranoside and 3,4-Dicarboxynystose, As Studied by Multinuclear Magnetic Resonance Spectroscopy and Potentiometry.

Complexes of Ln(III) and Ca(II) cations with 3,4-dicarboxyinulin (DCI) and model compounds, methyl 3,4-dicarboxy-alpha-D-fructofuranoside (DCF) and 3,4-dicarboxynystose (DCN) were studied using multinuclear magnetic resonance spectroscopy and potentiometric methods. Complexes of the model compounds with Ln(III) ions provided a feasible way in which to study complexation phenomena of the dicarboxyinulin/Ca(II) system using NMR techniques. Information on complex geometry was derived from the effect of Ln(III) ions on chemical shifts and longitudinal relaxation rates. Metal-ligand stoichiometries of 1:2 and 1:1, in which the ligand coordination was tridentate as well as tetradentate, were found. Potentiometric measurements carried out with Ca(II) yielded information on the stoichiometry as well as the cooperativity of metal ion binding by the ligands.

Journal Article↗
PubMed2001

Non-aqueous potentiometry using zeolites.

Potentiometric investigations using pressed zeolite discs are reported. Potential measurements have been performed in non-aqueous solutions--this is the first report, to our knowledge, of potentiometric detection of ions in non-aqueous media with zeolite materials. Nernstian behaviour is also displayed in aqueous solutions for ions that are only able to penetrate a fraction of the internal volume of the zeolite employed.

Journal Article↗