Cation-selective electrodes

Often, however, the PBP model can be used to describe the influence of key membrane parameters on the selectivity with a simplified equation after making certain assumptions. It is here given for cation-selective electrodes based on neutral carriers [30] ... 

Y. Tani, H. Eun, and Y. Umezawa, A cation selective electrode based on copper(II) and nickel(II) hexacyanoferrates dual response mechanisms, selective uptake or adsorption of analyte cations. Electrochim, Acta 43, 3431-3441 (1998). 

M. Giorgetti, E. Scavetta, M. Berrettoni, and D. Tonelli, Nickel hexacyanoferrate membrane as a coated wire cation-selective electrode. Analyst 126, 2168—2171 (2001). 

Neutral Carrier-Based Cation-Selective Electrodes... 

A number of methods have been used for determining Kg values cation selective electrodes, pH-metric methods, conductimetry, calorimetry, temperature-jump relaxation measurements, membrane conductance measurements, nuclear magnetic resonance, optical rotatory dispersion. The results listed in Tables 7—10 have been obtained by various methods and at different ionic strengths so they may not always be strictly comparable. However, the corrections are probably small and the experimental accuracy is generally the same or very similar within a certain ligand type. 

Baum reported a potentiometric determination of acetylcholine activity using an organic-cation-selective electrode [15], The performance of a liquid membrane electrode selective for acetylcholine (Corning No. 476.200) was investigated. Measurements of the potential difference at various concentration of acetylcholine were made against a calomel reference-electrode. 

The enzymes are rather nonspecific, so most amines in solution will be determined. The reaction can be monitored by oxygen uptake, aldehyde production, ammonia production, or hydrogen peroxide. By coupling the reaction to peroxidase-p-hydroxyphenylacetic acid the reaction can be followed fiuorimetrically (37). The formation rate of ammonia can be determined conveniently by use of a Beckman 39137 cation selective electrode which permits the determination of 1-100 /xg/ml of amine (19). 

B6. Baum, G., Organic cation-selective electrode Potentiometric determination of acetylcholine activity. Anal. Lett. 3, 105-111 (1970). 

The sign will be + for cation-selective electrodes and - for those that are anion-selective. To be predominantly responsive to the concentration Ci, the factor Kij must be small. Where liquid membrane ion-selective electrodes responsive primarily to double-charge ions are concerned, and for interference by single-charge ions, equation (1) modifies to ... 

POT-CSE Potentiometry with cation-selective electrodes. OD Optical density. 

The selectivity coefficient for a cation-selective electrode for with respect... 

E. Bakker, Determination of Unbiased Selectivity Coefficients of Neutral Carrier-Based Cation-Selective Electrodes, Anal. Chem., 69 (1997) 1061. 

Liquid crystals representing an intermediate state between the liquid and crystalline states can also be used to prepare ISEs. A liquid-crystal-type ionophore is dissolved in a liquid crystal solvent to obtain a cation-selective electrode, the selectivity of which is highly temperature dependent. 

The first urea electrode was prepared in 1969 by immobilizing urease in a polyacrylamide matrix on nylon or Dacron nets. These nets were then placed onto a glass cation-selective electrode. To improve the selectivity, an ammonium-ion selective electrode with... 

Importantly, the unbiased selectivity coefficients are thermodynamically meaningful. When an interfering ion, such as tetraethylammonium ion for cation-selective electrodes, does not bind to an ionophore, the selectivity coefficient for an ion of interest against such an interfering ion can be used to determine the formation constant of the ion-ionophore complexes (9). For example, when a neutral ionophore forms complexes with an ion, i, and does not bind to an interfering ion, j, the formation constant is given as... 

Cationic-selective electrodes generally respond to hydrogen ions as well as the ion of interest. Thus one must adjust a test solution to suppress the influence of the hydrogen ions. This is achieved by adjusting the hydrogen-ion concentration so that it is at least four orders of magnitude lower than the lowest ion concentration to be measured. 

Guilbault and Hrabankova (1970, 1971) have described electrodes that are specific for L-amino acids and D-amino acids. Enzymes were immobilized by gel techniques (using acrylamide gel) on the tips of commercial cation-selective electrodes. L-Amino acid oxidase (l-AAO) was used for L-amino-acid-selective electrodes with the reaction... 

Ion-selective electrodes. Podands have proved useful in the preparation of cation-selective electrodes (Morf et cd., 1979), and a system working for 5f cations has been designed (Bertrand et al., 1983). There is, however, only one report mentioning an eventual application to 4f elements (Shono and Kimura, 1977). 

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