Potentiometric selectivity

The sufficient selectivity to a principal component is the most important condition determining the possibility of ion-selective electrodes (ISEs) practical appliances. In this work, the relationship between the potentiometric selectivity of alkylammonium-selective electrodes and factors such as the nature of plasticizer, ion-exchanger and substitution degree of cationic nitrogen atoms of the principal and foreign ions, is discussed. 

ION-SELECTIVE ELECTRODES REVERSIBLE TO PHYSIOLOGICALLY ACTIVE AMINE CATIONS THE MAIN WAYS FOR CONTROLLING POTENTIOMETRIC SELECTIVITY... 

The potentiometric selectivity coefficients (Kj ° ) of ISEs with polyfvinyl... 

The so-called potentiometric selectivity coefficient K " reflects the non-ideal behavior of ion-selective membranes and determines the specificity of this electro-... 

V.V. Egorov, E.M. Rakhman ko, E.B. Okaev, E.V. Pomelenok, and V.A. Nazarov, Effects of ion association of lipophilic quaternary ammonium salts in ion-exchange and potentiometric selectivity. Talanta 63,119-130 (2004). 

Possible measures that are expected to improve the potentiometric selectivity are (1) use of hosts that form stronger complexes, (2) modification of the host to avoid ionophore self-association, and (3) an improved choice of the membrane solvent to avoid strong solvation of the hosts in the membrane. Evidence for the importance of (2) and (3) has been obtained from C NMR spectra of 12. While the properties of 1 1 host-guest complexes are very often of primary interest in supramolecular chemistry, the above results show that use of receptors for sensing purposes must be based on a receptor design that goes beyond this viewpoint. 

Table 3. Potentiometric Selectivity Coefficients for PVC Matrix Liquid Membranes Based on Calixl6)arene Hexaester or Dibenzo-18-crown-6 ...

This view is consistent with the fact that host 29 displays potentiometric selectivities for guests 33,34, and 38. For these guests, the formation of strong tripodal hydrogen bonds will not be interfered because there is no substituent around the NHj group. Complexation with geometry A is supported by the H NMR results. 

Thus, the characteristic potentiometric selectivity of calix[6]arene hexaester 29 for primary amine guests can be reasonably interpreted on the basis of the structural factors relevant to the nonpolar moieties of guests. Such a mode of discrimination can also be achieved by a calix[6]arene hexaester with short alkyl chains [28 (R = H)]. In addition, the selectivity was found to be essentially the same in the presence or absence of lipophilic anionic site HFPB added in the membrane (Table 3). Potentiometric discrimination of protonated amines by host 28 (R = H, Bu ) as well as of aldehydes (as the protonated hydrazones generated in situ) by hosts 26 (R = Bu ) and 28 (R = H) was also reported. Recently, quantitative estimation of optical selectivities for alkali metal ions or protonated amines were made with liquid membranes containing chromogenic derivatives of calixarenes. ... 

Fig. 4. Transport selectivity Kjj and potentiometric selectivity Kj j of a Na+-selective neutral carrier membrane using ligand 11. Experimental coefficients fCNaM obtained with (2) and (11) respectively given for different cations M. Membrane composition 32wt.% polyvinyl chloride, 65 wt.% dibutyl sebacate, 3wt.% carrier //. Thickness of membrane = 100 p.m. Current density approx. 0.1 p.Amm 2.

Fig. 6. Transport selectivity and potentiometric selectivity of a Ca2 selective neutral carrier membrane (3 wt.% carrier 10, 65 wt.% o-nitrophenyl-octyl ether, 32wt.% polyvinyl chloride). Experimental selectivity coefficients KCaNa obtained with (16) and (18), respectively, as a function of the cationic concentration m (in moles/liter).

Stem-Volmer constant for quenching inside MIP cavities Potentiometric selectivity coefficients... 

Here, the potentiometric selectivity coefficient is given with respect to the hydroxyl ion. Single-crystal lanthanum fluoride is a wide bandgap semiconductor in which the electrical conductivity is due only to the hopping mobility of fluoride ions through the defects in the crystal. It does not respond to the La3+ ion because of the slow ion exchange of that ion. Hydroxyl ion is the only other ion that has appreciable mobility, and is the only known interference. For this reason, the measurements with a fluoride electrode are always done below pH 7, which circumvents this interference. As shown later, the consideration of ionic and/or electronic conductivity of the membrane plays a critical role also in the design of the internal contact in nonsymmetric potentiometric sensors. 

S-enalapril assay can be done using the potentiometric electrode based on impregnation of 2-hydroxy-3-trimethylammoniopropyl-/i-cyclodextrin (as chloride salt) solution in a carbon paste, in the 3.6 x 10 5-6.4 x 10-2 mol/L (pH between 3.0 and 6.0) concentration range with a detection limit of 1.0 x 10 5 mol/L [25]. The slope is near-Nernstian 55.00 mV/decade of concentration. The average recovery of S-enalapril raw material is 99.96% (RSD — 0.098%). The potentiometric selectivity coefficient over D-proline (6.5 x 10 4) proved the sensor s enantioselectivity. S-enalapril was determined from pharmaceutical tablets with an average recovery of 99.59% (RSD — 0.20%). 

The EPME based on impregnation of 2-hydroxy-3-trimethylammoniop-ropyl-//-cyclodextrin (as chloride salt) solution in a carbon paste can be reliably used for S-trandolapril assay with an average recovery of 99.77% (RSD — 0.22%) [24]. The linear concentration range is 10 4-10 2 mol/L on the 2.5-5.5 pH range. The detection limit is of 10 5 mol/L magnitude order. The slope is near-Nernstian 52.45 mV/decade. The sensor enantioselectivity was determined over D-proline, when a 10 4 magnitude order was obtained for potentiometric selectivity coefficient. 

Unbiased potentiometric selectivity coefficients, log obtained for a PVC-DOS membrane containing Cs I and UIC... 

PVC membrane electrodes allowed measurement of potentiometric selectivity coefficients. These showed the Eu(III) complex to be more selective for chloride than the Pr(III), Dy(III) or Yb(III) analogues. 

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