Electroanalysis with potentiometric sensors

Owing to their specificity, sensitivity, and range of measurable concentrations, potentiometric sensors based on ionic or enzymatic selectivity have wide application in analytical determinations. Other potentiometric sensors using electrodes of the first kind (Mn+ M), used in precipation titrations, are not easy to manipulate and redox electrodes have a reduced application owing to their lack of selectivity, reacting to any oxidizable or reducible species. 

Since ISEs can be used in continuous flow systems or in flow systems with sample injection (flow injection analysis, FIA)21 their application is wide, not limited to discrete samples. Analysis time becomes shorter, with faster recycling. Additionally, in flow systems the experimental assembly and data analysis can be controlled automatically by microcomputer, including periodic calibration. Another development is the use of sensors for the detection of eluents of chromatographic columns in high-pressure liquid chromatography (HPLC). Miniaturization has permitted an increase in the use of sensors in foods, biological tissues, and clinical analyses in general. 

It remains an objective to develop potentiometric sensors with longer lifetimes, greater reproducibility and greater stability. The importance of an appropriate statistical treatment of the results in order to determine their precision is stressed. Frequent calibration is necessary, at least at the beginning of each measurement session and in a medium as similar as possible to that where the sensors are to be employed, in order to ensure the accuracy of the analytical determinations. 

Sawyer and J. L. Roberts, Experimental electrochemistry for chemists, Wiley, New York, 1974, Chapter 9. 

Bailey, Analysis with ion selective electrodes, Heyden, London, 1976. 

---

The key component of a potentiometric sensor is the ion-selective electrode (ISE), an electrode or electrode assembly with a potential that is dependent on the concentration of an ionic species in the test solution and is used for electroanalysis. This interfacial potential at the electrode surface is caused by the selective ion exchange reaction. Ion-selective electrodes are often membrane type electrodes. The well-known glass pH electrode, which is selectively sensitive to hydrogen ions, is a typical ISE and has been used for years for the measurement of acidity or basicity of aqueous solutions in... 

Fig. 1 Typical potentiometric sensor setup incorporating an ion-selective membrane electrode [1] (Reprinted from Electroanalysis, 1999. 11(13) p. 915-933 with permission from John Wiley Sons)...

L. Liu, X.C. Tan, X.X. Fang, Y.X. Sun, F.H. Lei and Z.Y. Huang, Electrochemical sensor based on molecularly imprinted polymer film prepared with functional abietic-type acids as cross-linker for the determination of quinine. Electroanalysis, 24 (7) 1647-1654,2012. R.N. Liang, Q. Gao and W. Qin, Potentiometric sensor based on molecularly imprinted polymers for rapid determination of clenbuterol in pig urine, Chinese J. Anal. Chem., 40 (3) 354-358, 2012. 

Teixeira MFS, CavaUieiro ETG, Bergamini ME, Mmaes PC, Bocchi N (2004) Use of carbon paste electrode modified with spinel-type manganese oxide as potentiometric sensor for lithium ions in flow injection analysis. Electroanalysis 16 633-639... 

Recently, a novel two electrode differential potentiometric cell for enzyme electrode systems has been described that provides enhanced substrate sensitivities compared to conventional cells composed of a single enzyme electrode and reference (Cha, G.S. Meyerhoff, M.E. Electroanalysis, in press). The cell employs two working enzyme electrodes, one which responds to the analyte in the positive potential direction via detection of cations, and one which responds to the same analyte but in a negative direction owing to anion detection. A similar approach can be applied in the design of new two electrode gas-selective sensors with enhanced gas sensitivity. 

This chapter describes progress in the application of polymer-modified electrodes (PMEs) to voltammetric chemical sensing. Several excellent reviews on the general preparation, properties, theory, and applications of modified electrodes have appeared over the past decade. Literature surveys and reviews of advances in the field of chemical sensors and electroanalysis " are also available. The area of polymeric potentiometric electrodes and the vast research field of biosensors are not dealt with in this chapter, which introduces the reader to selected representative examples of the diverse modification strategies available for prepar-... 

Reprinted with permission from Bobacka J, Ivsaka A, and Lewenstam A (2003) Potentiometric ion sensors based on conducting polymers. Electroanalysis 15 366-374 Wiley-VCH. 

Mousavi Z, Bobacka J, Ivaska A. Potentiometric Ag sensors based on conducting pol3Tners a comparison between poly(3,4-ethylenedioxythiophene) and polypyrrole doped with sufibnated caUxarenes. Electroanalysis 2005 17(18) 1609—15. 

---