Potentiometric selectivity coefficients

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-... 

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

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. 

Potentiometric selectivity coefficient Standard rate constant... 

In this equation, E is the potentiometric response, is the standard potential, and is the potentiometric selectivity coefficient [23]. The Nickolsky Eisenman equation is only valid if ions of the same valency are compared [24]. If that is not the case, if a divalent cation is interfering the measurement of a monovalent ion or vice versa, a new selectivity factor AT is recommended [24,25] which more accurately describes the degree of interference log/Tfj is derived graphically from the horizontal distance of the separately measured calibration curves towards the two ions, i and j, of interest (Figure 5) and is formulated as follows ... 

Ion-selective membrane electrodes have as a main characteristic their selectivity. They are constructed to be utilized to determine an analyte directly in the solution without any prior separation from the matrix. This is achieved assuming a high selectivity of the electrode vs. the possible interfering ions. The selectivity is characterized through the potentiometric selectivity coefficient. The values of the coefficients that can be taken into account for validation are those obtained through the mixed solutions method at a ratio between analyte and interferent of 1 10. The method is... 

We have formulated this problem in a manner that considers only Na and as active species. Glass membranes also respond to other ions, such as Li, K", Ag, and NH4. The relative responses can be expressed through the corresponding potentiometric selectivity coefficients (see Problem 2.16 for some typical numbers), which are influenced to a great extent by the composition of the glass. Different types of electrodes, based on different types of glass, are marketed. They are broadly classified as (a) pH electrodes with a selectivity order >>> Na" > K, Rb", Cs >> Ca , (b) sodium-sensitive electrodes with the order Ag > > Na >> K, Li >> Ca ", and (c) a more... 

H potentiometric selectivity coefficient of interferent j toward a measurement of species i none 2.4... 

The same host was also used as a base component of a polyvinyl chloride (PVC)-plasticized membrane electrode selective to (protonated) OctNH2. The electrode operates in the pH range 5—8, the detection limit being equal to 2 x 10 M, and the response time being as short as 5—10 s. Potentiometric selectivity coefficients are 0.005 (Na), 0.004 (K), 0.006 (NH3 and MeNH2), and 0.003 (t-BuNHa). 

The same group most recently reported the use of neutral lanthanide(III) tris-diketonates of type 121 for the determination of chloride [84]. The response in luminescence of the Eu(III) complex for chloride in acetonitrile solution was large enough to be seen by the naked eye. Incorporation of the complexes in PVC membrane electrodes allowed measvuement of potentiometric selectivity coefficients. These showed the Eu(III) complex to be the more selective for chloride than the Pr(III), Dy(III) or Yb(III) analogues. 

Umezawa, Y. Biihlmann, P. Umezawa. K. Tohda, K. Amemiya, S. Potentiometric selectivity coefficients of ion-selective electrodes. Part I. Inorganic cations. Pure Appl. Chem. 2000. 72. 1852-2082. 

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