The Experts below are selected from a list of 273 Experts worldwide ranked by ideXlab platform
Eric Bakker - One of the best experts on this subject based on the ideXlab platform.
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effect of lipophilic ion exchanger leaching on the detection limit of carrier based ion selective electrodes
Analytical Chemistry, 2001Co-Authors: Eric BakkerAbstract:The equilibrium partitioning of lipophilic ion-exchanger salts from ion-selective polymeric membrane electrodes (ISEs) and its possible effect on the lower detection limit of these sensors is described. Predictions are made on the basis of various parameters, including the knowledge of tetraphenylborate potassium salt partitioning constants, the selectivity of ionophore-free ion-exchanger membranes, and ionophore stability constants in the membrane. Ion-exchanger lipophilicities are significantly increased if the membrane contains an ionophore that strongly binds the primary ion. Predicted detection limits are on the order of 10-5−10-8 M for ionophore-free membranes, and may reach levels as low as 10-18 M with adequate Ionophores in the membrane. Experiments are performed for well-described lead-selective membranes containing different tetraphenylborate derivatives, and detection limits appear to be independent of the ion-exchanger used. However, they are much higher if a more hydrophilic carborane cation...
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determination of complex formation constants of 18 neutral alkali and alkaline earth metal Ionophores in poly vinyl chloride sensing membranes plasticized with bis 2 ethylhexyl sebacate and o nitrophenyloctylether
Analytica Chimica Acta, 2000Co-Authors: Yanming Mi, Eric BakkerAbstract:A segmented sandwich membrane method is used to determine complex formation constants of 18 electrically neutral Ionophores in situ in solvent polymeric sensing membranes. These Ionophores are commonly used in potentiometric and optical sensors, and knowledge of such binding information is important for ionophore and sensor design. In this method, two membrane segments are fused together, with only one containing the ionophore, to give a concentration-polarized sandwich membrane. Unlike other approaches, this method does not require the use of a reference ion in the sample and/or a second ionophore in the membrane, and is typically pH insensitive. The following Ionophores responsive for the common cations lithium, sodium, potassium, magnesium and calcium are characterized and discussed: valinomycin, BME-44, bis[(benzo-15-crown-5)-4′-ylmethyl]pimelate, ETH 157, ETH 2120, bis[(12-crown-4)methyl]dodecylmethylmalonate], 4-tert-butylcalix [4] arene tetraacetic acid tetraethyl ester, ETH 149, ETH 1644, ETH 1810, 6,6-dibenzyl-14-crown-4, N,N,N′,N′,N″,N″-hexacyclohexyl-4,4′,4″-propylidyne tris(3-oxabutyramide), ETH 1117, ETH 4030, ETH 1001, ETH 129, ETH 5234, and A23187. The logarithmic complex formation constants range from 4.4 to 29 and compare well to published data for Ionophores that were characterized earlier. From the observed complex formation constants, maximum possible selectivities are calculated that would be expected if interfering ions show no binding affinity to the ionophore, and the values are compared with experimental findings. Each ionophore is characterized in poly(vinyl chloride) membranes plasticized either with a polar (NPOE) or a nonpolar plasticizer (DOS). Membranes based on NPOE always show larger complex formation constants of the embedded ionophore.
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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...
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carrier mechanism of acidic Ionophores in solvent polymeric membrane ion selective electrodes
Analytical Chemistry, 1995Co-Authors: Ulrich Schaller, Eric Bakker, E. PretschAbstract:The behavior of cation-selective solvent polymeric membrane electrodes based on acidic Ionophores is investigated by studying the selectivity coefficients as a function of cationic or anionic additive concentration. This technique allows discrimination between neutral and charged carrier-related mechanisms, resulting in the following findings. Ionophores with a carboxylic acid group act as neutral carriers and sulfonic acid derivatives behave as charged carriers irrespective of the plasticizer used. The Ca 2+ -selective organophosphate ionophore examined (bis-[4-(1,1,3,3-tetramethylbutyl)phenyl]phosphate) acts in low dielectric constant plasticizers in a mixed mode where the analyte ion forms two different complexes in the membrane phase-one with the charged form of the carrier and the other with the protonated form (neutral ionophore). From these results it can be seen that when developing novel ion-selective electrodes based on acidic Ionophores, both cationic and anionic additives as well as plasticizers of high and low dielectric constant should be tested since completely different selectivity behavior could be obtained due to the charged and neutral forms of the carrier in the organic phase. The addition of potassium tetrakis[3,5-bis(bifluoromethyl)phenyl]borate to the calcium-selective membrane phase based on the organophosphate ligand mentioned above, the plasticizer dioctyl phenylphosphonate, and poly(vinyl chloride) improves the potentiometric properties of the electrodes with respect to membrane resistance and anion interference
Philippe Buhlmann - One of the best experts on this subject based on the ideXlab platform.
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potentiometric selectivities of ionophore doped ion selective membranes concurrent presence of primary ion or interfering ion complexes of multiple stoichiometries
Analytical Chemistry, 2019Co-Authors: Ibrahim Yilmaz, Li D Chen, Xin V Chen, Evan L Anderson, John A. Gladysz, Rosenildo Correa Da Costa, Philippe BuhlmannAbstract:The selectivities of ionophore-doped ion-selective electrode (ISE) membranes are controlled by the stability and stoichiometry of the complexes between the ionophore, L, and the target and interfering ions (Izi and Jzj, respectively). Well-accepted models predict how these selectivities can be optimized by selection of ideal ionophore-to-ionic site ratios, considering complex stoichiometries and ion charges. These models were developed for systems in which the target and interfering ions each form complexes of only one stoichiometry. However, for a few ISEs, the concurrent presence of two primary ion complexes of different stoichiometries, such as ILzi and IL2zi, was reported. Indeed, similar systems were probably often overlooked and are, in fact, more common than the exclusive formation of complexes of higher stoichiometry unless the ionophore is used in excess. Importantly, misinterpreted stoichiometries misguide the design of new Ionophores and are likely to result in the formulation of ISE membranes ...
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fluorophilic Ionophores for potentiometric ph determinations with fluorous membranes of exceptional selectivity
Analytical Chemistry, 2008Co-Authors: Paul G Boswell, John A. Gladysz, Csongor Szijjarto, Markus Jurisch, Jozsef Rabai, Philippe BuhlmannAbstract:Ionophore-doped sensor membranes exhibit greater selectivities and wider measuring ranges when they are prepared with noncoordinating matrixes. Since fluorous phases are the least polar and least polarizable liquid phases known, a fluorous phase was used for this work as the membrane matrix for a series of ionophore-based sensors to explore the ultimate limit of selectivity. Fluorous pH electrode membranes, each comprised of perfluoroperhydrophenanthrene, sodium tetrakis[3,5-bis(perfluorohexyl)phenyl]borate, and one of four fluorophilic H+-selective Ionophores were prepared. All the Ionophores are highly fluorinated trialkylamines containing three electron withdrawing perfluoroalkyl groups shielded from the central nitrogen by alkyl spacers of varying lengths: [CF3(CF2)7(CH2)3]2[CF3(CF2)6CH2]N, [CF3(CF2)7(CH2)3]2(CF3CH2)N, [CF3(CF2)7(CH2)3]3N, and [CF3(CF2)7(CH2)5]3N. Their pKa values in the fluorous matrix are as high as 15.4 ± 0.3, and the corresponding electrodes exhibit logarithmic selectivity coeffi...
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response mechanism of ion selective electrodes based on a guanidine ionophore an apparently two thirds nernstian response slope
Electroanalysis, 2008Co-Authors: Secil Koseoglu, Chad Ferguson, Philippe BuhlmannAbstract:While ion-selective electrodes (ISEs) based on anion Ionophores with guanidine groups were reported in the past, their response mechanism was poorly understood. In this study, an ionophore with one guanidine group was prepared as a model compound, and the chloride and sulfate responses of ISE membranes containing this ionophore were investigated. The electrodes exhibit Nernstian responses resulting from a neutral or charged ionophore mode when added cationic or anionic sites are used, respectively. Based on this observation, it might be expected that membranes without added ionic sites exhibit Nernstian responses according to a charged carrier mechanism. However, experimental results show an apparently ‘two–thirds Nernstian’ equilibrium response, which can be explained on the basis of the phase boundary model.
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Lifetime of Ion-Selective Electrodes Based on Charged Ionophores
Analytical Chemistry, 2000Co-Authors: Philippe Buhlmann, Yoshio Umezawa, Sandra Rondinini, Alberto Vertova, Anatolio Pigliucci, Luisella BertesagoAbstract:The lifetime of solvent polymeric ion-selective electrodes (ISEs) is limited by leaching of the membrane components into the sample solutions. In this article, leaching of charged Ionophores is discussed. Because of the electroneutrality principle, the loss of the charged ionophore into the sample must be accompanied by parallel transport of an ion of the opposite charge sign into the sample or by ion exchange with a sample ion of the same charge sign. Because ionic sites of high lipophilicity are available, the loss of ionic sites is, in general, not a concern. Therefore, it is assumed here that the cotransported or ion-exchanging ions are primary or interfering ions forming complexes with the ionophore. A general theory that allows quantification of ionophore lipophilicities and a discussion of changes in the membrane composition and selectivity with time is presented. A high complex stability and high analyte concentrations diminish the rate of ionophore loss into the sample if a charged ionophore is c...
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cationic or anionic sites selectivity optimization of ion selective electrodes based on charged Ionophores
Analytical Chemistry, 2000Co-Authors: Shigeru Amemiya, Philippe Buhlmann, E. Pretsch, Bruno Rusterholz, Yoshio UmezawaAbstract:The influence of ionic sites on the selectivities of ionophore-based ion-selective electrodes (ISEs) is described on the basis of a phase boundary potential model. The discussion presented here is significantly more general than previous ones. It is formulated for primary and interfering ions of any charges and it is valid for ISEs based on electrically charged or neutral Ionophores. Furthermore, it also applies to membranes that contain more than one type of complex of the primary or interfering ion. It has been believed thus far that only ionic sites of the same charge sign as the primary ion improve the selectivities of ISEs based on charged Ionophores. However, it is shown here that the charge sign of the ionic sites that give the highest potentiometric selectivities depends on the charge number of the primary and interfering ions and on the stoichiometry of their complexes with the ionophore. The validity of our model was confirmed experimentally with three ISEs based on different charged Ionophores....
E. Pretsch - One of the best experts on this subject based on the ideXlab platform.
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cationic or anionic sites selectivity optimization of ion selective electrodes based on charged Ionophores
Analytical Chemistry, 2000Co-Authors: Shigeru Amemiya, Philippe Buhlmann, E. Pretsch, Bruno Rusterholz, Yoshio UmezawaAbstract:The influence of ionic sites on the selectivities of ionophore-based ion-selective electrodes (ISEs) is described on the basis of a phase boundary potential model. The discussion presented here is significantly more general than previous ones. It is formulated for primary and interfering ions of any charges and it is valid for ISEs based on electrically charged or neutral Ionophores. Furthermore, it also applies to membranes that contain more than one type of complex of the primary or interfering ion. It has been believed thus far that only ionic sites of the same charge sign as the primary ion improve the selectivities of ISEs based on charged Ionophores. However, it is shown here that the charge sign of the ionic sites that give the highest potentiometric selectivities depends on the charge number of the primary and interfering ions and on the stoichiometry of their complexes with the ionophore. The validity of our model was confirmed experimentally with three ISEs based on different charged Ionophores....
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determination of formal complex formation constants of various pb2 Ionophores in the sensor membrane phase
Analytica Chimica Acta, 1999Co-Authors: Alan Ceresa, E. PretschAbstract:Abstract Formal complex formation constants of seven Ionophores with Pb 2+ and a series of interfering cations have been determined in the organic membrane phase. To this purpose, potentiometric selectivities of the target ions relative to tetramethylammonium are compared for ion-exchanger- and ionophore-based ion-selective electrode membranes. Furthermore, information on the stoichiometry of the complexes formed is obtained from measurements with two membranes of different ionophore concentrations. Surprisingly, the results show that Ionophores having thioamide are less efficient in coordinating Pb 2+ than corresponding ones with oxamide. The formal complex formation constants found are in excellent agreement with those determined by bulk optode measurements. A generally applicable method is proposed to gain more insight with a view to designing ligands and optimizing sensor membrane compositions.
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carrier mechanism of acidic Ionophores in solvent polymeric membrane ion selective electrodes
Analytical Chemistry, 1995Co-Authors: Ulrich Schaller, Eric Bakker, E. PretschAbstract:The behavior of cation-selective solvent polymeric membrane electrodes based on acidic Ionophores is investigated by studying the selectivity coefficients as a function of cationic or anionic additive concentration. This technique allows discrimination between neutral and charged carrier-related mechanisms, resulting in the following findings. Ionophores with a carboxylic acid group act as neutral carriers and sulfonic acid derivatives behave as charged carriers irrespective of the plasticizer used. The Ca 2+ -selective organophosphate ionophore examined (bis-[4-(1,1,3,3-tetramethylbutyl)phenyl]phosphate) acts in low dielectric constant plasticizers in a mixed mode where the analyte ion forms two different complexes in the membrane phase-one with the charged form of the carrier and the other with the protonated form (neutral ionophore). From these results it can be seen that when developing novel ion-selective electrodes based on acidic Ionophores, both cationic and anionic additives as well as plasticizers of high and low dielectric constant should be tested since completely different selectivity behavior could be obtained due to the charged and neutral forms of the carrier in the organic phase. The addition of potassium tetrakis[3,5-bis(bifluoromethyl)phenyl]borate to the calcium-selective membrane phase based on the organophosphate ligand mentioned above, the plasticizer dioctyl phenylphosphonate, and poly(vinyl chloride) improves the potentiometric properties of the electrodes with respect to membrane resistance and anion interference
Dechen Jiang - One of the best experts on this subject based on the ideXlab platform.
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squaramide based tripodal Ionophores for potentiometric sulfate selective sensors with high selectivity
Analyst, 2015Co-Authors: Dechen JiangAbstract:A class of squaramide-based tripodal molecules was employed as new Ionophores for highly sensitive and selective sulfate-selective sensors. Compared with the reported tripodal ionophore with urea, squaramide groups as superior hydrogen bonding donor were introduced into the tripodal structure to obtain new Ionophores leading to better electrode performance. Three derivatives with unsubstituted (I), p-carbon trifluoride (II), and p-nitro (III) phenyl groups were attached to squaramide groups for the optimization of ionophore based sensors. Electron withdrawing p-nitrophenyl groups gave a greater enhancement of the hydrogen bond donor ability of squaramide so that Ionophore III was chosen as the best candidate for sulfate ion recognition. Such a membrane with 30 mol% TDMACl exhibited a Nernstian slope of −30.2 mV per decade to sulfate ions with a linear range from 1 μM to 100 mM in potentiometric measurement. The selectivity coefficients of the proposed sensor over H2PO4−, Cl−, Br−, NO3−, SCN−, I− and ClO4− were −4.3, −3.4, −2.5, −0.6, +3.1, +3.4 and +5.9, respectively, which were much better than the existing sulfate-selective sensors. The new sensors with high selectivity were successfully applied for the quantification of sulfate in cell lysates and drinking water with good recoveries.
Yanming Mi - One of the best experts on this subject based on the ideXlab platform.
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determination of complex formation constants of 18 neutral alkali and alkaline earth metal Ionophores in poly vinyl chloride sensing membranes plasticized with bis 2 ethylhexyl sebacate and o nitrophenyloctylether
Analytica Chimica Acta, 2000Co-Authors: Yanming Mi, Eric BakkerAbstract:A segmented sandwich membrane method is used to determine complex formation constants of 18 electrically neutral Ionophores in situ in solvent polymeric sensing membranes. These Ionophores are commonly used in potentiometric and optical sensors, and knowledge of such binding information is important for ionophore and sensor design. In this method, two membrane segments are fused together, with only one containing the ionophore, to give a concentration-polarized sandwich membrane. Unlike other approaches, this method does not require the use of a reference ion in the sample and/or a second ionophore in the membrane, and is typically pH insensitive. The following Ionophores responsive for the common cations lithium, sodium, potassium, magnesium and calcium are characterized and discussed: valinomycin, BME-44, bis[(benzo-15-crown-5)-4′-ylmethyl]pimelate, ETH 157, ETH 2120, bis[(12-crown-4)methyl]dodecylmethylmalonate], 4-tert-butylcalix [4] arene tetraacetic acid tetraethyl ester, ETH 149, ETH 1644, ETH 1810, 6,6-dibenzyl-14-crown-4, N,N,N′,N′,N″,N″-hexacyclohexyl-4,4′,4″-propylidyne tris(3-oxabutyramide), ETH 1117, ETH 4030, ETH 1001, ETH 129, ETH 5234, and A23187. The logarithmic complex formation constants range from 4.4 to 29 and compare well to published data for Ionophores that were characterized earlier. From the observed complex formation constants, maximum possible selectivities are calculated that would be expected if interfering ions show no binding affinity to the ionophore, and the values are compared with experimental findings. Each ionophore is characterized in poly(vinyl chloride) membranes plasticized either with a polar (NPOE) or a nonpolar plasticizer (DOS). Membranes based on NPOE always show larger complex formation constants of the embedded ionophore.
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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...
