The effect of the ion exchanger site-counterion complex formation on the selectivities of ISEs

Егоров, В. В.; Borisenko, N. D.; Рахманько, Е. М.; Lushchik, Ya. F.; Kacharsky, S.S.

doi:10.1016/s0039-9140(97)00042-8

Cited by 19 publications

(10 citation statements)

References 31 publications

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“…18 Instead, the membranes with Teflon AF2400 give a Nernstian pH response in the range of pH 1.6 to 4.2 (for a graph, see Figure S1 in Supporting Information). This is the well-known behavior of potentiometric membranes that contain cationic sites and functional groups acting as negatively charged ionophores 37,42,43 for H + , as it is expected for carboxylate groups. To confirm that carboxyl groups can indeed be deprotonated in a fluorous phase and act as electrically charged ionophores, experiments were also performed with the same cationic sites ( 5 , 2.0 mM) and the perfluorooligoether Krytox®157FS-H, which has terminal carboxyl groups.…”

Section: Resultsmentioning

confidence: 66%

Fluorous Polymeric Membranes for Ionophore-Based Ion-Selective Potentiometry: How Inert Is Teflon AF?

et al. 2009

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Fluorous media are the least polar and polarizable condensed phases known. Their use as membrane materials considerably increases the selectivity and robustness of ion-selective electrodes (ISEs). In this research, a fluorous amorphous perfluoropolymer was used for the first time as a matrix for an ISE membrane. Electrodes for pH measurements with membranes composed of poly[4,5-difluoro-2,2-bis(trifluoromethyl)-1,3-dioxole]-co-poly(tetrafluoroethylene) (87% dioxole monomer content; known as Teflon AF2400) as polymer matrix, a linear perfluorooligoether as plasticizer, sodium tetrakis[3,5-bis(perfluorohexyl)phenyl]borate providing for ionic sites, and bis[(perfluorooctyl)propyl]-2,2,2-trifluoroethylamine as H+-ionophore were investigated. All electrodes had excellent potentiometric selectivities, showed Nernstian responses to H+ over a wide pH range, exhibited enhanced mechanical stability and maintained their selectivity over at least four weeks. For membranes of low ionophore concentration, the polymer affected the sensor selectivity noticeably at polymer concentrations exceeding 15%. Also, the membrane resistance increased quite strongly at high polymer concentrations, which cannot be explained by the Mackie–Meares obstruction model. The selectivities and resistances depend on the polymer concentration because of a functional group associated with Teflon AF2400, with a concentration of one functional group per 854 monomer units of the polymer. In the fluorous environment of these membranes, this functional group binds to Na+, K+, Ca2+, and the unprotonated ionophore with binding constants of 103.5, 101.8, 106.8 and 104.4 M−1, respectively. Potentiometric and spectroscopic evidence indicates that these functional groups are COOH groups formed by the hydrolysis of carboxylic acid fluoride (COF) groups originally present in Teflon AF2400. The use of higher ionophore concentrations removes the undesirable effect of these COOH groups almost completely. Alternatively, the C(=O)F groups can be eliminated chemically, or they can be used to readily introduce new functionalities.

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Section: Resultsmentioning

confidence: 66%

Fluorous Polymeric Membranes for Ionophore-Based Ion-Selective Potentiometry: How Inert Is Teflon AF?

et al. 2009

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“…It is interesting that for all membranes studied potentials in sulfate solutions are almost independent on site concentration. According to [35,45] in the case of strong ionic association the concentration of free double-charged ions does not depend on the total site concentration. So the obtained results provide the evidence that sulfate is strongly associated even with such QAS cation as TNODA.…”

Section: Ion-pairing Of Anions With Quaternary Alkylammonium Sitesmentioning

confidence: 99%

Estimation of Ion‐Pairing Constants in Plasticized Poly(vinyl chloride) Membranes Using Segmented Sandwich Membranes Technique

et al. 2009

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Segmented sandwich membrane method was used to determine ion-pairing constants for four cationic sites: tris-(2,3,4-dodecyloxy)benzenetrimethylammonium, tris-(2,3,4-dodecyloxy)benzenedimethyloctylammonium, tris-(2,3,4-dodecyloxy)benzenemethyldioctylammonium, and dimethyldioctadecylammonium with chloride, bromide, nitrate, benzene sulfonate, trichloroacetate, thiocyanate, perchlorate and picrate, as well as ion-pairing constants for two anionic sites: tetraphenylborate and tris-(2,3,4-octyloxy)benzenesulfonate with dimedrol, quinine, anapriline, and amantadine cations in poly(vinyl chloride) membranes plasticized with 2-nitrophenyl octyl ether. Ion association constants of anions with quaternary ammonium sites regularly increase from picrate to chloride along with reduction of the anion radius and with improvement of site exchanger center steric accessibility. Ion association constants of amine cations with tris-(2,3,4-octyloxy)benzenesulfonate are several orders higher than those with tetraphenylborate and regularly increase from tertiary amine to primary one.

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“…Perhaps the most disputable point of the proposed approach is the assumption of equality of K A,B pot MSSM value to the ion‐exchange constant K A B . It is well‐known that for the membranes with low dielectric constant, where strong ion association takes place, these values do not coincide 15, 18, 30. It turned out however that good agreement between the estimated improved values of the selectivity coefficients and unbiased ones is observed not only for the membranes plasticized with NPhOE ( ε =21 31) but for the membranes plasticized with TEHP ( ε =4.8 32) and BEHS ( ε =4.2 32) as well, in spite of these membranes hardly can be considered as completely dissociated ones.…”

Section: Resultsmentioning

confidence: 99%

Generalized Diffusion Parameter: Main Factors of Influence and Application for Estimation of Selectivity Coefficients for Highly Selective Electrodes

2015

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The influence of membrane composition, ion nature, measuring time and stirring mode on the generalized diffusion parameter q was investigated. It was found that the main factors of influence are PVC to plasticizer ratio and measuring time, which obey rigid regularities and can be estimated. It makes possible to evaluate the role of the diffusion factor for other systems and measuring conditions using some averaged q value determined for a limited set of systems. It was shown that averaged q value allowed reliable estimating of low selectivity coefficients (down to 10−8) from strongly biased values determined by separate solution method.

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The effect of the ion exchanger site-counterion complex formation on the selectivities of ISEs

Cited by 19 publications

References 31 publications

Fluorous Polymeric Membranes for Ionophore-Based Ion-Selective Potentiometry: How Inert Is Teflon AF?

Fluorous Polymeric Membranes for Ionophore-Based Ion-Selective Potentiometry: How Inert Is Teflon AF?

Estimation of Ion‐Pairing Constants in Plasticized Poly(vinyl chloride) Membranes Using Segmented Sandwich Membranes Technique

Generalized Diffusion Parameter: Main Factors of Influence and Application for Estimation of Selectivity Coefficients for Highly Selective Electrodes

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