Potentiometry with ion-selective electrodes

Sodium, Na(I) has a normal concentration in human serum of 136-145 mmol/L (Tohda 1994) and makes up about 90 % of the cations present. (Many extracellular body fluids possess ranges from 7 mmol/L [mature milk] via 33 [saliva] to 145 mmol/ L [bile]). The reference method for determination is potentiometry with ion-selective electrodes (PISE). 

The ion-selective field-effect transistor (ISFET) represents a remarkable new construction principle [7, 63], Inverse potentiometry with ion-selective electrodes is the electrolysis at the interface between two immiscible electrolyte solutions (ITIES) [28, 55],... 

In potentiometry with ion-selective electrodes (ISE), as a rule, it is the electromotive force of a cell such as the following that is measured. 

The most common analytical methods used were gas chromatography, HPLC, AA spectrophotometry, polarography, colorimetry, and potentiometry with ion-selective electrodes. In this study GC/MS and other more expensive instrumentation were avoided. If sorbent tubes could not be used for gaseous substances, then the less desirable miniature bubblers or impingers were considered. Although these devices are inconvenient they were often used because no better alternatives were available. Bags were used in a few cases where the analyte could not be retained on a sorbent because of volatility and a small tendency to sorb. Filters were used for particulates. Combinations of collection devices were used if we felt that both particulates and vapor might be present in the analyte. 

Vesely, J. andStulik, K. (1987) Potentiometry with ion-selective electrodes. In R. Kalveda (Ed.) Electroanalytical Methods in Chemical and Environmental Analysis. Plenum, Prague. 

Any type of detector with a flow-through cell can be used for FIA. Photometric detectors are most often used in FIA (15-18, 25). However, many other analyses using fluorimeters (28, 29), refractometers (24), atomic absorption (30, 31), and inductively coupled plasma emission spectrometers (32) have been described. Electrochemical detectors based on potentiometry with ion-selective electrodes (15, 33), anodic stripping voltammetry (15, 34), potentiometric stripping (35), and amperometry (36) have also been used. 

Analytical Chemistry the group of Prof Vasil D. Simeonov is performing research in analytical chemistry, chemometrics, environmetrics, multivariate calibration classification, interpretation and modelling of environmental data sets evaluation and optimization of analytical procedures potentiometry with ion selective electrodes atmospheric and marine chemistry. A very wide network of international collaboration is associated with the group. 

The order of presentation of the electroanalytical methods will be direct potentiometry with ion-selective electrodes, potentiometric titrations, voltammetry/polarography, polarisation titrations (amperometric and potentiometric), conductometry/coulometry and electrochemical detectors. 

Definite Method. No definitive method exists for ionized calcium. To date there is no international consensus agreement on a reference method and no certified reference materials available for standardization. Potentiometry with ion-selective electrodes has been selected as the method to be used. The International Federation of Clinical Chemists (IFCC) Working Group on Selective Electrodes is currently preparing a draft document on the reference method and testing a prototype reference cell [20]. 

The detection methods used include spectrophotometry, chemiluminescence, fluorescence, amperometry, conductometry, thermometry and potentiometry with ion-selective electrodes or gas sensors. We have focused our attention only on the electrochemical detectors. Some examples of applications of reactor biosensors with the specification of enzyme used, reactor type and detection system are summarized in Table 5. 

Brand, M.J.D. and Rechnitz, G.A. (1970) Differential potentiometry with ion-selective electrodes. New instrumental approach. Anal. Chem., 42 (6), 616-622. 

Fig. 9.2 Two-electrode electrochemical cell used for potentiometry with ion-selective electrodes...

In this category, direct potentiometry with ion-selective electrodes (ISEs) has to be mentioned. Unfortunately, traditional ISEs can be operated at the trace concentration level only scarcely and, therefore, their employment for real samples containing heavy metals is limited. 

Buck, R. P. Potentiometry pH Measurements and Ion Selective Electrodes. In Weissberger, A., ed.. Physical Methods of Organic Chemistry, Vol. 1, Part IIA. Wiley New York, 1971, pp. 61-162. Cammann, K. Working with Ion-Selective Electrodes. Springer-Verlag Berlin, 1977. 

Electrochemical methods such as potentiometry allow analyses up to p,gL quantities, or, with methods such as voltammetry, they extend into the micro-trace range. Table 8.74 compares potentiometry to other electroanalytical techniques. Potentiometry and ion-selective electrodes are described in various books [476-480],... 

The simplest method of measurement with ion-selective electrodes is direct potentiometry by use of the Nemst equation. However, this makes extreme demands on the reproducibility of the junction potential, and there is the problem of variation of activity with ionic strength. Concentration-cell techniques have proved to be very precise, especially in terms of null-point potentiometi... 

A thin-layer electrophoretic method for separation of pilocarpine from drug sources has been developed. Other recent analytical methods used for the determination of pilocarpine include t.l.c., potentiometry with ion-selective membrane electrodes,and photodensitometry. Histamine (7) has been found not to be active at the water-air interface by electric-potential and surface-tension measurements of aqueous solutions of the alkaloid. ... 

You are reminded that other Units in the ACOL scheme are devoted to other electro-analytical techniques. Those available at the moment are Principles of Electroanalytical Methods (some of the material overlaps with this Unit) Potentiometry and Ion-selective Electrodes. 

Contents Introduction. - Fundamentals of Potentiometry. -Electrode Potential Measurements. - Ion-Selective Electrodes. - Measuring Techniques with Ion-Selective Electrodes. - Analysis Techniques Using Ion-Selective Electrodes. - implications of Ion-Selective Electrodes. - Outlook. - Appendix. - Literature. - Subject Index. - Index of Symbols Used. 

As noted above, voltage is developed between two electrodes in an electrochemical cell. The voltage depends upon the kinds and concentrations of dissolved chemicals in the solutions contacted by the electrodes. In some cases this voltage can be used to measure concentrations of some substances in solution. This gives rise to the branch of analytical chemistry known as potentiometry. Potentiometry uses ion-selective electrodes or measuring electrodes whose potentials relative to a reference electrode vary with the concentrations of particular ions in solution. The reference electrode that serves as the ultimate standard for potentiometry is the standard hydrogen electrode shown in Figure 8.13. In practice, other electrodes, such as the silver/silver chloride or calomel (mercury metal in contact with are... 

When first developed, potentiometry was restricted to redox equilibria at metallic electrodes, limiting its application to a few ions. In 1906, Cremer discovered that a potential difference exists between the two sides of a thin glass membrane when opposite sides of the membrane are in contact with solutions containing different concentrations of H3O+. This discovery led to the development of the glass pH electrode in 1909. Other types of membranes also yield useful potentials. Kolthoff and Sanders, for example, showed in 1937 that pellets made from AgCl could be used to determine the concentration of Ag+. Electrodes based on membrane potentials are called ion-selective electrodes, and their continued development has extended potentiometry to a diverse array of analytes. 

If metallic electrodes were the only useful class of indicator electrodes, potentiometry would be of limited applicability. The discovery, in 1906, that a thin glass membrane develops a potential, called a membrane potential, when opposite sides of the membrane are in contact with solutions of different pH led to the eventual development of a whole new class of indicator electrodes called ion-selective electrodes (ISEs). following the discovery of the glass pH electrode, ion-selective electrodes have been developed for a wide range of ions. Membrane electrodes also have been developed that respond to the concentration of molecular analytes by using a chemical reaction to generate an ion that can be monitored with an ion-selective electrode. The development of new membrane electrodes continues to be an active area of research. 

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