Nikolskii-Eisenman equation

Equation (5-3) has been written on the assumption that the electrode responds only to the ion of interest, i. hi practice, no electrode responds exclusively to the ion specified. The actual response of the electrode in a binary mixture of the primary and interfering ions (z and j, respectively) is given by the Nikolskii-Eisenman equation (9) ... 

Use the Nikolskii-Eisenman equation to explain why lowering of the detection limits requires careful attention to the selectivity of the resulting ISE. 

Nikolskii-Eisenman equation, 143 Nitric oxide, 121 Nonactin, 157 Nonfaradaic processes, 21 Normal pulse voltammetry, 67 Nucleic acids, 82, 185... 

Ion-selective electrodes in trace level analysis of heavy metals Nikolskii-Eisenman equation ... 

Fig. 2.1. Zero-current ion fluxes in the ion-selective membrane. Left (A) Concentrated inner solution induces coextraction of electrolyte into the membrane increasing the primary ion-ionophore concentration within the membrane. Consequently, primary ions leach into the sample increasing the activity of primary ions at the membrane/sample phase boundary. (B) Diluted inner solution and ion exchange at the inner solution side decreases the concentration of the complex within the membrane. Primary ions are siphoned-off from the sample, and their activity at the membrane/sample phase boundary is significantly decreased. (C) Ideal case of perfectly symmetric sample and inner solution resulting in no membrane fluxes. Note that fluxes of other species (counterions or interfering ions) are not shown for clarity. Right potential responses for each case. Ideal LOD is defined by the Nikolskii-Eisenman equation (Y Kj°jaj) and is obtained only in the ideal case (C). Fluxes in either direction significantly affect the LOD.

Figure 2.3 depicts comparison of the theoretical predictions and experimental observations of the potential response of a silver-selective electrode based on o-xylylenebis(/V,/V-diisobutyldithiocarbamate. Figure 2.3A demonstrates the potential response of an electrode that utilizes a classical experimental setup, i.e. concentrated inner solution (open circles) compared with theoretical prediction based on Eq. (2.2) (full line). The experimentally observed LOD of 10 7M corresponds poorly with the optimistic theoretical prediction of 4 x 10 15M. On the other hand, after optimization of the inner solution [19], the potential response is extended (Fig. 2.3B closed circles) and the detection limit is improved by almost three orders of magnitude to 3 x 10 10M. At the same time, an excellent correspondence between experimental observation and theoretical prediction was achieved by employing the extended Nikolskii-Eisenman equation (Eq. (2.4)—full line). This demonstrates the essential role of membrane fluxes in the potential response of ion-selective electrodes. (For all experimental and calculations parameters see the figure caption.)... 

The ultimate detection limit as described by the Nikolskii-Eisenman equation (Eq. (2.2)) is defined by the displacement of a fraction of the primary ions with interfering ions at the sample/membrane phase boundary, which amounts to 50% in the case of monovalent primary and interfering ions. Equation (2.8) (the part in parenthesis) implies two obvious solutions (1) avoiding the bias introduced by the inner solution and (2) reducing the amount of the primary ion-ionophore complex at the sample/membrane phase boundary and hence reducing the absolute amount of released primary ions due to the ion exchange. 

Nanodes (nanoelectrodes) 771 Nanoparticles 802, 809, 817, 943 Nanotubes 802 Native peroxidase 373 Natural water samples el4 Negative feedback 912 Neisseria meningitidis 102 Neomycin 817 Nernst equation 26, 359 Nernstian function 12 Neuronal cell 105 Neurotoxins 311 Neutravidin 808, 817 Newcastle disease virus 107 Nikolskii-Eisenman 31 expression 727 Nitrate reductase 917 sensor 79 Nitric oxide 428... 

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