Polymer membrane electrodes, selectivity

An electrode in which an antibody or an antigen/hapten is incorporated in the sensing element is termed an immunoelectrode . The potential response of the immuno-electrode is based on an immunochemical reaction between the sensing element of the electrode and antibody or antigen/hapten in the sample solution. One example of such an electrode is the polymer membrane electrode shown in Fig. 7. The selective response of this electrode to specific immunoglobulins is based on the interaction between antibody in solution and an antigen-ionophore complex in the membrane ... 

E. Bakker, P. Buhlmann, and E. Pretsch, Polymer membrane ion-selective electrodes - what are the limits Electroanalysis 11, 915-933 (1999). 

T. Sokalski, A. Ceresa, T. Zwickl, and E. Pretsch, Large improvement of the lower detection limit of ion-selective polymer membrane electrodes. J. Am. Chem. Soc. 119, 11347-11348 (1997). 

E. Bakker, Determination of improved selectivity coefficients of polymer membrane ion-selective electrodes by conditioning with a discriminated ion. J. Electrochem. Soc. 43, L83—L85 (1996). 

Recent research in the field of polymer membrane ion-selective electrodes [389-391], has revealed that their se-lectivities [392-396] and limits of detections [394-397] could be improved by several orders of magnitude. The review of Bakker and Pretsch [398] summarized recent progress in the development and application of potentiometric sensors with low detection limit in the range 10-8-10-11 M. 

Shvedene, N.V., Chernyshov, D.V., Khrenova, M.G., Formanovsky, A.A., Baulin, V.E., and Pletnev, I.V., Ionic liquids plasticize and bring ion-sensing ability to polymer membranes of selective electrodes, Electroanal., 18,1416-1421, 2006. 

Redox potential pH Ionic activities Inert redox electrodes (Pt, Au, glassy carbon, etc.) pH-glass electrode pH-ISFET iridium oxide pH-sensor Electrodes of the first land and M" /M(Hg) electrodes) univalent cation-sensitive glass electrode (alkali metal ions, NHJ) solid membrane ion-selective electrodes (F, halide ions, heavy metal ions) polymer membrane electrodes (F, CN", alkali metal ions, alkaline earth metal ions)... 

By running a potentiometric precipitation titration, we can determine both the compositions of the precipitate and its solubility product. Various cation- and anion-selective electrodes as well as metal (or metal amalgam) electrodes work as indicator electrodes. For example, Coetzee and Martin [23] determined the solubility products of metal fluorides in AN, using a fluoride ion-selective LaF3 single-crystal membrane electrode. Nakamura et al. [2] also determined the solubility product of sodium fluoride in AN and PC, using a fluoride ion-sensitive polymer membrane electrode, which was prepared by chemically bonding the phthalocyanin cobalt complex to polyacrylamide (PAA). The polymer membrane electrode was durable and responded in Nernstian ways to F and CN in solvents like AN and PC. 

Figure 15-21 Response of Pb21 liquid-based ion-selective electrode with (black curve ) conventional filling solution containing 0.5 mM Pb2 or (colored curve) metal ion buffer filling solution in which [Pb2 ] =10 12 M. [From T. Sokalski, A. Ceresa. 1 Zw ickl, and E. Pretsch, "Large Improvement of the Lower Detection Limit of Ion-Selective Polymer Membrane Electrodes," J. Am. Chem. Soc. 1997, 119, 11347J...

Development of Polymer Membrane Anion-Selective Electrodes Based on Molecular Recognition Principles... 

Several of the polymer membrane anion-selective electrodes described in the literature use quaternary ammonium salts as ion carriers (ionophores) (7). These electrodes respond according to the Hofmeister series (CIO4 > SCN > I > NO3 > Br - N3 > NC>2 > Cl > HCO3 acetate) (2, 5), which is the order of relative lipophilicity of the anions. Therefore, in strict terms, electrodes that respond according to this series could be considered "nonselective". 

In this paper, we report the development of ISEs that have been designed by using molecular recognition principles. Specific examples include the development of polymer membrane anion-selective electrodes based on hydrophobic vitamin B12 derivatives and a cobalt porphyrin. The selectivity patterns observed with these electrodes can be related to differences in the structure of the various ionophores, and to properties of the polymer film. 

In summary, it has been demonstrated that ISEs can be designed by employing molecular recognition principles. In particular, the feasibility of using hydrophobic vitamin B12 derivatives and electropolymerized porphyrin films in the development of polymer membrane anion-selective electrodes has been demonstrated. The studies indicated that the changes in the selectivity of these ISEs can be explained by the difference in structure of the ionophores. In addition, it was shown that by electropolymerization of a cobalt porphyrin, anion-selective electrodes can be prepared that have extended lifetimes compared with PVC-based ISEs, which use a similar compound as the ionophore. 

One useful aspect of the ISE approach is the ease with which selectivity testing can be performed. Once the polymer is employed as the active ingredient in a polymer membrane electrode, the binding can be examined by measuring the potential of a cell as outlined below. We have seen that the selectivity obtained by batch extraction procedures gives the same affinity series as that measured by using the polymer in an electrode [11]. 

Polymer Membrane Ion-Selective Electrodes Similar to Liquid Membranes in Living Cells... 

In these devices polymer materials containing specific ingredients constitute the backbone of the film covering the electrochemical transducer. Here we deal with a liquid membrane, because the organic solvent provides the medium in which the ions permeate across the membrane. The polymer membrane ion-selective electrodes (ISE) and their ion transport across the membrane function similarly as the ion transport across the membranes of living cells (Figure 8.29). We follow the presentation given by Widmer (1993). 

Figure 8.29. Ion transport mechanisms through lipid membranes in living cells. There are principally two kinds of transport protein (a) channel proteins, that is, a channelforming ionophore, and (b) carrier proteins, that is, a mobile ion carrier ionophore. The phenomena observed in living cells have much in common with those in artificial polymer membrane ion-selective electrodes. (From Widmer, 1993.)...

As far as detection limits, selectivity, and Nemstian response ranges, the performance of CWEs is essentially analogous to that of conventional polymer membrane electrodes. However, one major drawback to their use appears to be the lack of reproducible potentials. Even within a single day, cell potentials can vary substantially for the same standard solution. As a result, CWEs must be recalibrated often, or better yet, standard addition or titration techniques must be utilized to ensure accurate results. Obviously, such analytical techniques could not be employed if in situ determinations are desired. 

B4. Baum, G., Lyim, M., and Ward, F. B., Polymer membrane electrodes. Part 1. A choline ester-selective electrode. Anal. Chim. Acta 65, 385-391 (1973). 

Greenburg, J. A., and Meyerhoff, M. E., Response properties, applications and limitations of carbonate-selective polymer membrane electrodes. Anal. Chim. Acta 141,57-64 (1982). 

M5. Meyerhoff, M. E., Preparation and response properties of selective bioelectrodes utilizing polymer membrane electrode-based ammonia gas sensors. Anal. Lett. 13,1345-1357 (1980). 

In practice, the selectivity of polymer membrane electrodes can be evaluated using the well known Nicolsky equation ... 

Such a differential gas sensing system is composed of two working gas sensors, each with a different inner ion-selective polymer membrane electrode as the transducer. For example, a differential ammonia sensing arrangement involves the use of two ammonia sensing probes whose... 

---