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Eric Bakker - One of the best experts on this subject based on the ideXlab platform.
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polyurethane Ionophore based thin layer membranes for voltammetric Ion Activity sensing
Analytical Chemistry, 2016Co-Authors: Maria Cuartero, Gaston A Crespo, Eric BakkerAbstract:We report on a plasticized polyurethane Ionophore-based thin film material (of hundreds of nanometer thickness) for simultaneous voltammetric multianalyte Ion Activity detectIon triggered by the oxidatIon/reductIon of an underlying poly(3-octylthiophene) film. This material provides excellent mechanical, physical, and chemical robustness compared to other polymers. Polyurethane films did not exhibit leaching of lipophilic additives after rinsing with a direct water jet and exhibited resistance to detachment from the underlying electrode surface, resulting in a voltammetric current response with less than <1.5% RSD variatIon (n = 50). In contrast, plasticized poly(vinyl chloride), polystyrene, and poly(acrylate) Ionophore-based membranes of the same thickness and compositIon exhibited a significant deterioratIon of the signal after identical treatment. While previously reported works emphasized fundamental advancement of multi-Ion detectIon with multi-Ionophore-based thin films, polyurethane thin membranes...
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Ionophore based voltammetric Ion Activity sensing with thin layer membranes
Analytical Chemistry, 2016Co-Authors: Maria Cuartero, Gaston A Crespo, Eric BakkerAbstract:As shown in recent work, thin layer Ion-selective multi-Ionophore membranes can be interrogated by cyclic voltammetry to detect the Ion Activity of multiple species simultaneously and selectively. AdditIonal fundamental evidence is put forward on Ion discriminatIon with thin multi-Ionophore-based membranes with thicknesses of 200 ± 25 nm and backside contacted with poly-3-octylthiophene (POT). An anodic potential scan partially oxidizes the POT film (to POT+), thereby initiating the release of hydrophilic catIons from the membrane phase to the sample solutIon at a characteristic potential. Varying concentratIon of added catIon-exhanger demonstrates that it limits the Ion transfer charge and not the deposited POT film. Voltammograms with multiple peaks are observed with each associated with the transfer of one type of Ion (lithium, potassium, and sodium). Experimental conditIons (thickness and compositIon of the membrane and concentratIon of the sample) are chosen that allow one to describe the system by a...
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thin layer Ionophore based membrane for multianalyte Ion Activity detectIon
Analytical Chemistry, 2015Co-Authors: Gaston A Crespo, Maria Cuartero, Eric BakkerAbstract:A concept is introduced that allows one to detect the Activity of multiple Ions simultaneously and selectively with a single Ion-selective membrane. This is demonstrated with ∼300 nm thin plasticized PVC membranes containing up to two Ionophores in additIon to a lipophilic catIon-exchanger, overlaid on an electropolymerized poly-3-octylthiophene (POT) film as the electron to Ion transducer. The Ion-selective membranes are formulated under Ionophore depleted conditIons (avoiding excess of Ionophore over Ion-exchanger), which is purposely different from common practice with Ion-selective electrodes. Cyclic voltammetry is used to interrogate the films. An anodic scan partially oxidizes the POT underlayer, which results in the expulsIon of catIons from the membrane at an appropriate potential. During the scan of a membrane containing multiple Ionophores, the least bound Ion is expelled first, giving distinct Gaussian peak shaped Ion transfer voltammetric waves that are analyzed in terms of their peak potential. These potentials are found to change with the logarithm of the Ion Activity, in complete analogy to Ion-selective electrodes, and multiple such waves are observed with multiple Ionophores that exhibit no obvious interference from the other Ionophores present in the membrane. The concept is established with lithium and calcium Ionophores and accompanied by a response model that assumes complete equilibratIon of the membrane at every applied potential. On the basis of the model, diffusIon coefficients in the membrane or aqueous phase bear no influence on the peak potentials as long as thin layer behavior is observed, further confirming the analogy to a potentiometric experiment. Idealized Ion transfer waves are narrower than experimental findings, which is explained by a broader than expected anodic peak for the oxidatIon of conducting polymer. The correspondence between experiment and theory is otherwise excellent in terms of thin layer behavior and Nernstian shift of the peaks with analyte concentratIon.
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direct optical carbon dioxide sensing based on a polymeric film doped with a selective molecular tweezer type Ionophore
Analytical Chemistry, 2012Co-Authors: Xiaojiang Xie, Marcin Pawlak, Marylou Tercierwaeber, Eric BakkerAbstract:A novel optical method for the determinatIon of CO2 concentratIon in aqueous and gaseous samples of plasticized PVC film is presented. The detectIon principle makes use of a direct molecular recognitIon of the carbonate Ion by a molecular tweezer-type Ionophore, which has previously been demonstrated to exhibit excellent carbonate selectivity. The carbonate Ion is extracted together with hydrogen Ions into a polymeric film that contains the anIon exchanger tridodecylmethylammonium chloride, a lipophilic, electrically charged, and highly basic pH indicator, which is used for the readout in absorbance mode, in additIon to the lipophilic carbonate Ionophore. According to known bulk optode principles, such an optical sensor responds to the product of the carbonate Ion Activity and the square of hydrogen Ion Activity. This quantity is thermodynamically linked to the Activity of carbon dioxide. This allows one to realize a direct carbon dioxide sensor that does not make use of the traditIonal Severinghaus sensi...
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determinatIon of complex formatIon constants of lipophilic neutral Ionophores in solvent polymeric membranes with segmented sandwich membranes
Analytical Chemistry, 1999Co-Authors: Yanming Mi, Eric BakkerAbstract:A potentiometric method to determine Ionophore complex formatIon constants in solvent polymeric membrane phases, proposed originally by Russian researchers, is critically evaluated and compared to other established methods. It requires membrane potential measurements on two-layer sandwich membranes, where only one side contains the Ionophore. The resulting initial membrane potential reflects the Ion Activity ratio at both aqueous phase−membrane interfaces and can be conveniently used to calculate complex formatIon constants in situ. This method is potentially useful, since it does not require the use of a reference Ion or second Ionophore in the measurement. In this paper, the five Ionophores valinomycin, BME-44, ETH 2120, tert-butylcalix[4]arene tetraethyl ester, and S,S‘-methylenebis(diisobutyldithiocarbamate) are characterized in poly(vinyl chloride) (PVC) plasticized with dioctyl sebacate (DOS) and compared with other established methods. The resulting formatIon constants correspond well to literature...
Esther De Kort - One of the best experts on this subject based on the ideXlab platform.
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effect of calcium chelators on heat coagulatIon and heat induced changes of concentrated micellar casein solutIons the role of calcium Ion Activity and micellar integrity
International Dairy Journal, 2012Co-Authors: Esther De Kort, Thom Snoeren, Marcel Minor, Toon Van Hooijdonk, Erik Van Der LindenAbstract:There is general consensus that calcium chelators enhance heat stability in milk. However, they increase the heat stability to considerably different extents. For this reason, the effect of various calcium chelators on heat coagulatIon and heat-induced changes of concentrated micellar casein solutIons was investigated by measuring the heat coagulatIon time (HCT), together with changes in calcium-Ion Activity, viscosity, turbidity, and zeta potential before and after heating. Surprisingly, the weakest chelator, disodium uridine monophosphate (Na2UMP), gave the most pronounced increase in HCT. Stronger chelators, i.e., disodium hydrogen phosphate, trisodium citrate and sodium phytate, gave a lower HCT than Na2UMP. Sodium hexametaphosphate (SHMP) was the least effective heat stabilizer. Heat-induced changes in SHMP were the major cause for this reduced heat stability effect. Differences in HCT caused by the additIon of the various calcium chelators could be attributed to the calcium-Ion Activity and state of the micellar structure before and during heating.
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effect of calcium chelators on physical changes in casein micelles in concentrated micellar casein solutIons
International Dairy Journal, 2011Co-Authors: Esther De Kort, Thom Snoeren, Marcel Minor, Toon Van Hooijdonk, Erik Van Der LindenAbstract:Abstract The effect of calcium chelators on physical changes of casein micelles in concentrated micellar casein solutIons was investigated by measuring calcium-Ion Activity, viscosity and turbidity, and performing ultracentrifugatIon. The highest viscosities were measured on additIon of sodium hexametaphosphate (SHMP), because it cross-linked the caseins. For the weak calcium chelator disodium uridine monophosphate (Na 2 UMP), physical changes in the solutIons were negligible. Disodium hydrogen phosphate (Na 2 HPO 4 ), trisodium citrate (TSC), and sodium phytate (SP) caused similar increases in viscosity, but had different effects on turbidity. The increase in viscosity was attributed to swelling of the casein micelles (i.e., increased voluminosity) at decreasing calcium-Ion Activity. The major decrease in turbidity was due to dissociatIon of the casein micelles. The extent of micellar dissociatIon was dependent on the type and concentratIon of calcium chelator. It seems that the micelles were dissociated in the order of SHMP ≥ SP > TSC > Na 2 HPO 4 > Na 2 UMP.
Alan L Rockwood - One of the best experts on this subject based on the ideXlab platform.
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meaning and measurability of single Ion activities the thermodynamic foundatIons of ph and the gibbs free energy for the transfer of Ions between dissimilar materials
ChemPhysChem, 2015Co-Authors: Alan L RockwoodAbstract:Considering the relatIonship between concentratIon and vapor pressure (or the relatIonship between concentratIon and fugacity) single-Ion Activity coefficients are definable in purely thermodynamic terms. The measurement process involves measuring a contact potential between a solutIon and an external electrode. Contact potentials are measurable by using thermodynamically reversible processes. ExtrapolatIon of an equatIon to zero concentratIon and Ionic strength enables determinatIon of single-Ion Activity coefficients. Single-Ion activities can be defined and measured without using any extra-thermodynamic assumptIons, concepts, or measurements. This method could serve as a gold standard for the validatIon of extra-thermodynamic methods for determining single-Ion activities. Furthermore, it places the concept of pH on a thermodynamically solid foundatIon. Contact potential measurements can also be used to determine the Gibbs free energy for the transfer of Ions between dissimilar materials.
Arthur K Covington - One of the best experts on this subject based on the ideXlab platform.
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re evaluatIon of the first and second stoichiometric dissociatIon constants of phthalic acid at temperatures from 0 to 60 c in aqueous phthalate buffer solutIons with or without potassium chloride 2 estimatIon of parameters for the model for the firs
Journal of Chemical & Engineering Data, 2006Co-Authors: Jaakko I Partanen, Arthur K CovingtonAbstract:Previously (in Part 1, J. Chem. Eng. Data 2006, 51, 777−784), equatIons were determined for the calculatIon of the second stoichiometric (molality scale) dissociatIon constant (Km2) of phthalic acid in buffer solutIons containing potassium hydrogen phthalate (KHPh), dipotassium phthalate, and potassium chloride from the determined thermodynamic values of this dissociatIon constant (Ka2) and the molalities of the components in the solutIons. These equatIons apply at temperatures from (0 to 60) °C up to Ionic strengths of about 0.5 mol·kg-1, and they were based on the single-Ion Activity coefficient equatIons of the Huckel type. The parameters of phthalate species for these equatIons and the second thermodynamic dissociatIon constant of this acid at various temperatures were determined from Harned cell data of Hamer and Acree (J. Res. Natl. Bur. Stand. 1945, 35, 381−416), and the resulting parameter values were also tested with these data. In the present study, the corresponding equatIons were determined fr...
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re evaluatIon of the first and second stoichiometric dissociatIon constants of phthalic acid at temperatures from 0 to 60 c in aqueous phthalate buffer solutIons with or without potassium chloride 1 estimatIon of the parameters for the huckel model a
Journal of Chemical & Engineering Data, 2006Co-Authors: Jaakko I Partanen, Arthur K CovingtonAbstract:EquatIons were developed for the calculatIon of the second stoichiometric (molality scale) dissociatIon constant (Km2) of phthalic acid in buffer solutIons containing potassium dihydrogen phthalate, hydrogen phthalate, and chloride from the determined thermodynamic values of this dissociatIon constant (Ka2) and the molalities of the components in the solutIons. These equatIons apply at temperatures from (0 to 60) °C up to Ionic strengths of about 0.5 mol·kg-1, and they are based on the single-Ion Activity coefficient equatIons of the Huckel type. The parameters of phthalate Ions for these equatIons and the thermodynamic values of the second dissociatIon constant of this acid at various temperatures were determined from the Harned cell data measured by Hamer and Acree (J. Res. Natl. Bur. Stand. 1945, 35, 381−416). In these parameter estimatIons, the stoichiometric values of the first dissociatIon constant of phthalic acid were needed, and these values were obtained from the Harned cell results of Hamer et ...
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re evaluatIon of stoichiometric dissociatIon constants from electrochemical cell data for formic acid at temperatures from 0 to 60 c and for some other aliphatic carboxylic acids at 18 or 25 c in aqueous potassium chloride solutIons
Journal of Chemical & Engineering Data, 2005Co-Authors: Jaakko I Partanen, Arthur K CovingtonAbstract:EquatIons were determined for the calculatIon of stoichiometric (molality-scale) dissociatIon constants, Km, of monoprotic aliphatic carboxylic acids in buffer solutIons containing formic acid, acetic acid, or some other weak acids of this kind and potassium chloride from the thermodynamic dissociatIon constants, Ka, of the acids and the molalities of the components in the solutIons. These equatIons apply for formic acid to temperatures from (0 to 60) °C and were based on the single-Ion Activity-coefficient equatIons of the Huckel type. The parameters of formic acid species for these equatIons and the thermodynamic dissociatIon constants of this acid at various temperatures were determined from the Harned cell data of Harned and Embree (1934). All calculatIons from these data were revised, and the final parameter values obtained are independent of the temperature. The interactIon parameters between hydrogen and chloride Ions were taken from the results of a previous HCl paper (2002). The parameters that r...
Jaakko I Partanen - One of the best experts on this subject based on the ideXlab platform.
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re evaluatIon of the first and second stoichiometric dissociatIon constants of phthalic acid at temperatures from 0 to 60 c in aqueous phthalate buffer solutIons with or without potassium chloride 2 estimatIon of parameters for the model for the firs
Journal of Chemical & Engineering Data, 2006Co-Authors: Jaakko I Partanen, Arthur K CovingtonAbstract:Previously (in Part 1, J. Chem. Eng. Data 2006, 51, 777−784), equatIons were determined for the calculatIon of the second stoichiometric (molality scale) dissociatIon constant (Km2) of phthalic acid in buffer solutIons containing potassium hydrogen phthalate (KHPh), dipotassium phthalate, and potassium chloride from the determined thermodynamic values of this dissociatIon constant (Ka2) and the molalities of the components in the solutIons. These equatIons apply at temperatures from (0 to 60) °C up to Ionic strengths of about 0.5 mol·kg-1, and they were based on the single-Ion Activity coefficient equatIons of the Huckel type. The parameters of phthalate species for these equatIons and the second thermodynamic dissociatIon constant of this acid at various temperatures were determined from Harned cell data of Hamer and Acree (J. Res. Natl. Bur. Stand. 1945, 35, 381−416), and the resulting parameter values were also tested with these data. In the present study, the corresponding equatIons were determined fr...
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re evaluatIon of the first and second stoichiometric dissociatIon constants of phthalic acid at temperatures from 0 to 60 c in aqueous phthalate buffer solutIons with or without potassium chloride 1 estimatIon of the parameters for the huckel model a
Journal of Chemical & Engineering Data, 2006Co-Authors: Jaakko I Partanen, Arthur K CovingtonAbstract:EquatIons were developed for the calculatIon of the second stoichiometric (molality scale) dissociatIon constant (Km2) of phthalic acid in buffer solutIons containing potassium dihydrogen phthalate, hydrogen phthalate, and chloride from the determined thermodynamic values of this dissociatIon constant (Ka2) and the molalities of the components in the solutIons. These equatIons apply at temperatures from (0 to 60) °C up to Ionic strengths of about 0.5 mol·kg-1, and they are based on the single-Ion Activity coefficient equatIons of the Huckel type. The parameters of phthalate Ions for these equatIons and the thermodynamic values of the second dissociatIon constant of this acid at various temperatures were determined from the Harned cell data measured by Hamer and Acree (J. Res. Natl. Bur. Stand. 1945, 35, 381−416). In these parameter estimatIons, the stoichiometric values of the first dissociatIon constant of phthalic acid were needed, and these values were obtained from the Harned cell results of Hamer et ...
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re evaluatIon of stoichiometric dissociatIon constants from electrochemical cell data for formic acid at temperatures from 0 to 60 c and for some other aliphatic carboxylic acids at 18 or 25 c in aqueous potassium chloride solutIons
Journal of Chemical & Engineering Data, 2005Co-Authors: Jaakko I Partanen, Arthur K CovingtonAbstract:EquatIons were determined for the calculatIon of stoichiometric (molality-scale) dissociatIon constants, Km, of monoprotic aliphatic carboxylic acids in buffer solutIons containing formic acid, acetic acid, or some other weak acids of this kind and potassium chloride from the thermodynamic dissociatIon constants, Ka, of the acids and the molalities of the components in the solutIons. These equatIons apply for formic acid to temperatures from (0 to 60) °C and were based on the single-Ion Activity-coefficient equatIons of the Huckel type. The parameters of formic acid species for these equatIons and the thermodynamic dissociatIon constants of this acid at various temperatures were determined from the Harned cell data of Harned and Embree (1934). All calculatIons from these data were revised, and the final parameter values obtained are independent of the temperature. The interactIon parameters between hydrogen and chloride Ions were taken from the results of a previous HCl paper (2002). The parameters that r...
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comparison of different methods for calculatIon of the stoichiometric dissociatIon constant of acetic acid from results of potentiometric titratIons at 298 15 k in aqueous sodium or potassium chloride solutIons
Fluid Phase Equilibria, 2000Co-Authors: Jaakko I Partanen, Pekka M JuusolaAbstract:Abstract Single-Ion Activity coefficient equatIons were determined for the calculatIon of the molality-scale dissociatIon constants, Km, for acetic acid in aqueous NaCl or KCl solutIons at 298.15 K. The salt alone determines the Ionic strength, Im, of the solutIons considered in this study. The Activity coefficient equatIons are of the Huckel type, and Km can be calculated by those for a certain Ionic strength from the thermodynamic dissociatIon constant. The data used for the estimatIon of the parameters for these equatIons were measured by potentiometric titratIons in a glass electrode cell. Three different methods to calculate the experimental Km values from the titratIon data were considered. The Activity parameters for the Huckel equatIon were determined from the Km values calculated by all of these methods. The parameters obtained by these methods are very consistent with each other and also with the Huckel parameters obtained previously for acetic acid from the literature data measured on Harned cells. The final Activity parameters recommended in this study seem to be reliable. Despite the theoretical difficulties associated with the single-Ion Activity coefficients and the simplicity of the calculatIon method based on Huckel equatIons, Km can be obtained by this method almost within experimental error for acetic acid in NaCl and KCl solutIons up to Im of about 1 mol kg−1. It was shown in this study, in additIon, that the Km values obtained by the Huckel equatIons agree well also with those calculated by the Pitzer equatIons.
