Sensors proton

The coordination chemistry of the trichalcogenophosphonates is very undeveloped when compared to the analogous metal organophosphonates (RP032), which have been extensively studied owing to their potential and practical applications as ion exchangers, sorbents, sensors, proton conductors, nonlinear optical materials, photochemically active materials, catalysts and hosts for the intercalation of a broad spectrum of guests.145... 

Fig. 3. Working principle of sensor proton-transfer coupling reverse PET, on-off.

The sensor is an ammonium ion-selective electrode surrounded by a gel impregnated with the enzyme mease (Figme 6-11) (22). The generated ammonium ions are detected after 30-60 s to reach a steady-state potential. Alternately, the changes in the proton concentration can be probed with glass pH or other pH-sensitive electrodes. As expected for potentiometric probes, the potential is a linear function of the logarithm of the urea concentration in the sample solution. 

Today, the term solid electrolyte or fast ionic conductor or, sometimes, superionic conductor is used to describe solid materials whose conductivity is wholly due to ionic displacement. Mixed conductors exhibit both ionic and electronic conductivity. Solid electrolytes range from hard, refractory materials, such as 8 mol% Y2C>3-stabilized Zr02(YSZ) or sodium fT-AbCb (NaAluOn), to soft proton-exchange polymeric membranes such as Du Pont s Nafion and include compounds that are stoichiometric (Agl), non-stoichiometric (sodium J3"-A12C>3) or doped (YSZ). The preparation, properties, and some applications of solid electrolytes have been discussed in a number of books2 5 and reviews.6,7 The main commercial application of solid electrolytes is in gas sensors.8,9 Another emerging application is in solid oxide fuel cells.4,5,1, n... 

We outline experimental results and provide theoretical interpretation of effect of adsorption of molecular oxygen and alkyl radicals in condensed media (water, proton-donor and aproton solvents) having different values of dielectric constant on electric conductivity of sensors. We have established that above parameter substantially affects the reversible changes of electric conductivity of a sensor in above media which are rigorously dependent on concentration of dissolved oxygen. 

Klymchenko AS, Demchenko AP (2002) Electrochromic modulation of excited-state intramolecular proton transfer the new principle in design of fluorescence sensors. J Am Chem Soc 124 12372-12379... 

Tan S.S.S., Hauser P.C., Chaniotakis N.A., Suter G., Simon W., Anion-selective optical sensors based on a coextraction of anion-proton pairs into a solvent-polymeric membrane, Chimia 1989 43 257. 

The optical sensors are composed of ion-selective carriers (ionophores), pH indicator dyes (chromoionophores), and lipophilic ionic additives dissolved in thin layers of plasticized PVC. Ionophores extract the analyte from the sample solution into the polymer membrane. The extraction process is combined with co-extraction or exchange of a proton in order to maintain electroneutrality within the unpolar polymer membrane. This is optically transduced by a pH indicator dye (chromoionophore)10. 

Figure 5. Mechanism of ion-exchange of an analyte ion (E) and a proton (H+) between the sensor membrane and the aqueous phase.

In the case of co-extraction, a selective anion-carrier (ionophore) extracts the analyte anion into the lipophilic sensor membrane. In order to maintain electroneutrality, a proton is co-extracted into the membrane where it protonates a pH indicator dye contained in the polymer membrane. Due to protonation, the dye undergoes a change in either absorption or fluorescence. (Figure 6 and Tables 13 and 14). 

Figure 6. Mechanism of co-extraction of the analyte anion (X ) together with a proton (H+) into the sensor layer.

The use of this approach can be illustrated by the perovskite structure proton conductor BaYo.2Zro.gO3 g- This material has been investigated for possible use in solid oxide fuel cells, hydrogen sensors and pumps, and as catalysts. It is similar to the BaPr03 oxide described above. The parent phase is Ba2+Zr4+03, and doping with... 

---