Nernstian response, range

Sol-gel-derived membranes encapsulating a bis(crown ether) derivative [bis(12-crown-4-ylmethyl) 2-dodecyl-2-methylmalonate] [28] were also fabricated with an initial DEDMS/TEOS ratio of 3 for Na -ISFETs. The Na -ISFETs showed a Nernstian response to Na+ activity changes in the activity range of 1 x 10 " to 1 M and a short response time of 2 s. Employment of a polythiophene interlayer improved the potential instability and the lower detection limit in both of the K - and Na -ISFETs based on the sol-gel-derived membranes with the initial DEDMS/TEOS ratio of 3 (Fig. 8). 

Typical profiles for the potential response of Na -ISFETs based on the sol-gel-derived membranes modified chemically by alkoxysilylated 16-crown-5 (7) and bis(12-crown-4) (11), together with anion excluder (9) show that both of the Na -ISFETs have high sensitivity with a Nernstian response to Na activity changes in wide activity ranges of 3 x 10 to 1 M (Fig. 12). The potential response is quite fast in the Na -ISFETs in spite of the covalent bonding of the neutral carriers to the ion-sensing membranes, as exemplified in the membrane system of the bis(12-crown-4) (11). Some mobility of the chemically bonded neutral carriers can probably be maintained in the present sol-gel-derived membranes. The response time ( 9o) is several seconds for both of the Na -... 

Characteristics of the fluoride ion-selective electrode The LaFj ISE exhibits Nernstian response to the activity of fluoride ions in the concentration range 1 M to 10" M [31, 53,325]. When the solution is buffered for fluoride ions using ZiO and Th " salts, Baumann [28] has demonstrated that Nernstian response can be obtained down to a free fluoride ion concentration of 10" ° moldm". In solutions with an ionic strength of 2 moldm", the detection limit is 0.2 ppm, i.e. about 10" moldm", while in pure NaF solutions it may be as low as 10" moldm ... 

ISEs with both these groups of systems exhibit Nernstian response to the Ca activity in the range 10" to 10 M in metal buffers with a slope of d isE/d log flca = 0.029 V. They can be used in the presence of 50 mM Na" for down to micromolar concentrations of Ca. The potentials of these ISEs do not depend on the hydrogen ion activity in the pH range 5.5 to 9 [146]. 

A new solid state chemical sensor for sulfur dioxide utilizing a sodium sulfate/rare earth sulfates/silicon dioxide electrolyte has been developed. The addition of rare earth sulfates and silicon dioxide to the sodium sulfate electrolyte was found to enhance the durability and electrical conductivity of the electrolyte. The electrolyte exhibits a Nernstian response in the range of SC gas concentrations from 30 ppm to 1 %. 

Nernstian response) over a wide activity range. However, at very low MX activities, the pd becomes insensitive to decreasing M activities and levels off at a value... 

Cadogan et al. [73] deposited polypyrrole onto platinum from a variety of solutions and found the resultant films to be anion sensitive but very unselec-tive. When polypyrrole was deposited from NaN03 solution, however, the resultant electrode gave near-Nernstian responses to nitrate ion in the range 0.5-0.0005 M with selectivities of about 20 over other lipophilic ions such as iodide and perchlorate [74]. Similar electrodes could be fabricated via a screen-... 

The anions derived from 277-thiopyran 1,1-dioxides behave as ligands for various transition metal single site catalysts 591 that are employed for the polymerization of olefins <2002USP2002156211>. A nickel(ll) ion selective PVC-membrane electrode based on the 2,6-diphenyl-277-thiopyran 592 has been described. The electrode exhibits a Nernstian response over a wide concentration range of Niz+ with a lower detection limit of 9 X 10-6M and a response time of ca. 10 s <2000ELA1138>. 

Figure 6 shows the selectivity behavior of this NOx gas sensor. The sensor had a sub-Nernstian response toward nitrite, with slopes in the range of -45 to -50 mV/decade. Further, the response observed with salicylate and thiocyanate was diminished substantially, as compared to that obtained with the original nitrite-selective electrode (Figure 3). In addition, the gas sensor described here does not suffer interferences from nitrate, bicarbonate, acetate, benzoate, or chloride. These excellent selectivity properties of the sensor are a combination of the selectivity characteristics of the nitrite-selective electrode and the additional discrimination provided by the GPM.

A host of carriers, with a wide variety of ion selectivities, have been proposed for this task. Most of them have been used for the recognition of alkali and alkaline metal cations (e.g., clinically relevant electrolytes). A classical example is the cyclic depsipeptide valinomycin (Fig. 5.13), used as the basis for the widely used ISE for potassium ion (38). This doughnut-shaped molecule has an electron-rich pocket in the center into which potassium ions are selectively extracted. For example, the electrode exhibits a selectivity for K+ over Na+ of approximately 30,000. The basis for the selectivity seems to be the fit between the size of the potassium ion (radius 1.33 A) and the volume of the internal cavity of the macrocyclic molecule. The hydrophobic sidechains of valinomycin stretch into the lipophilic part of the membrane. In addition to its excellent selectivity, such an electrode is well behaved and has a wide working pH range. Strongly acidic media can be employed because the electrode is 18,000 times more responsive to K+ than to H+. A Nernstian response to potassium ion activities, with a slope of 59mV/pK+, is commonly observed... 

A polyvinyl chloride membrane electrode for heroin based on an ion-pair complex with tetraphenylborate is described (328). The sensor shows a near-Nernstian response over the heroin concentration range 0.01 M to 0.1 mM, with good selectivity for heroin in the presence of a number of adultercuits and base compounds present in illicit heroin powders. A cocaine sensor proposed by Zeng (329) uses a cocaine picrylaminate membrane. The calibration curve is linear in the range 0.01 M to 10 iM, with a coefficient of variation of less than... 

Extend the range of ferric species activities over which Pt electrode response is nernstian, and, provide evidence for the comparable behavior of another, physically and chemically distinct electrode material, wax-impregnated graphite. Experiments in laboratory and field situations indicate nernstian response of both Pt and WIG electrodes at pH s as high as 6.4, and thus total Fe(III) activities as low as 10 M. 

Tetrakis(4-A, A -dimethylaminobenzene)porphyrinato-manganese(III) acetate was used as a novel carrier for a selective iodide ion electrode (Farhadi et al, 2004). The sensor exhibited not only excellent selectivity to iodide ion compared to Cl and lipophilic anions such as CIO4 and salicylate, but also a Nernstian response for iodide ion over a wide concentration range from 1.0 X 10 to 7.5 X 10 mol-l h The potentiometric response was independent of the pH of the solution in the pH range 2-8. The electrode could be used for at least 2 months without any considerable divergence in the potential. The electrode was applied to the determination of iodide in seawater samples and drug formulations. 

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