Membrane-based ion-selective electrodes

E. Bakker, R.K. Meruva, E. Pretsch, and M.E. Meyerhoff, Selectivity of polymer membrane-based ion-selective electrodes — self-consistent model describing the potentiometric response in mixed ion solutions of different charge. Anal. Chem. 66, 3021—3030 (1994). 

In considering the differential or selective binding of one anion or another, the intrinsic properties of anions mean that we are not on a level playing field it is considerably easier to bind some anions than others. In general, in the absence of specific chemical recognition between anion and host, anion binding selectivity, particularly in solvent extraction experiments or in the detection of anions by membrane-based ion selective electrodes, follows the order of anion hydrophobicity. This order is termed the Hofmeister series, or lyotropic series and was first outlined in 1888 from experiments based on the... 

Most of the analytes (pC02, Na , K, Ca , and pH) are determined by potentiometric measurements using membrane-based ion-selective electrode technology. The hematocrit is measured by electrolytic conductivity detection, and p02 is determined with a Clark voltammetric sensor (see Section 23B-4). Other results are calculated from these data. 

E. Bakker, R. K. Meruwa, E. Pretsch, and M. E. Meyerhoff Selectivity of Polymer Membrane-Based Ion-Selective Electrodes Self-Consistent Model Describing the Potentiometric Response in Mixed Ion Solutions of Different Charge, Ana/. Chem., 66 (1994) 3021. 

The solid-contact reference systems used in all-solid-state membrane based ion selective electrodes are discussed in Sect. II.9.3.4.3. 

For the establishment of the receptor selectivity, different chemical interactions can be used. For example, the output of potentiometric sensors is strongly influenced by the equilibrium of the analyte with the sensitive layer of the chemosensor. Polymeric matrix membrane-based ion-selective electrodes are utilizing the concentration-dependent extraction of the analyte in the organic layer, while the analyte-dependent shift of potential of ion-selective sensors based on electrodes of the second kind can be described by the solubility product of the hardly soluble salt and the resulting Nemst equation of the electrochemical base reaction. Further equilibria can be predicated on ion exchanges, complexation, or adsorption effects. The interplay of analyte and receptor is determined by... 

Radu A, Anastasova-Ivanova S, Paczosa-Bator B, Danielewski M, Bobacka J, Lewenstam A, Diamond D (2010) Diagnostic of functionality of polymer membrane - based ion selective electrodes by impedance spectroscopy. Anal Methods 2 1490-1498... 

Gavach et al. were probably the first to apply liquid membrane-based ion-selective electrodes (ISEs) for the titration of long chain alkyl methyl ammonium salts with sodium tetraphenyl borate. Birch et al." were also among the first researchers to use liquid ion-exchange electrodes responsive to ionic surfactants in 1972. 

One example of a liquid-based ion-selective electrode is that for Ca +, which uses a porous plastic membrane saturated with di-(n-decyl) phosphate (Figure 11.13). As shown in Figure 11.14, the membrane is placed at the end of a nonconducting cylindrical tube and is in contact with two reservoirs. The outer reservoir contains di-(n-decyl) phosphate in di- -octylphenylphosphonate, which soaks into the porous membrane. The inner reservoir contains a standard aqueous solution of Ca + and a Ag/AgCl reference electrode. Calcium ion-selective electrodes are also available in which the di-(n-decyl) phosphate is immobilized in a polyvinyl chloride... 

The properties of several representative liquid-based ion-selective electrodes are presented in Table 11.3. An electrode using a liquid reservoir can be stored in a dilute solution of analyte and needs no additional conditioning before use. The lifetime of an electrode with a PVC membrane, however, is proportional to its exposure to aqueous solutions. For this reason these electrodes are best stored by covering the membrane with a cap containing a small amount of wetted gauze to... 

Faraday s law (p. 496) galvanostat (p. 464) glass electrode (p. 477) hanging mercury drop electrode (p. 509) hydrodynamic voltammetry (p. 513) indicator electrode (p. 462) ionophore (p. 482) ion-selective electrode (p. 475) liquid-based ion-selective electrode (p. 482) liquid junction potential (p. 470) mass transport (p. 511) mediator (p. 500) membrane potential (p. 475) migration (p. 512) nonfaradaic current (p. 512)... 

All ion-exchanger membranes with fixed ion-exchanger sites are porous to a certain degree (in contrast to liquid membranes and to membranes of ion-selective electrodes based on solid or glassy electrolytes, such as a single crystal of lanthanum fluoride). 

Potentiometric measurements are based on the determination of a voltage difference between two electrodes plunged into a sample solution under null current conditions. Each of these electrodes constitutes a half-cell. The external reference electrode (ERE) is the electrochemical reference half-cell, which has a constant potential relative to that of the solution. The other electrode is the ion selective electrode (ISE) which is used for measurement (Fig. 18.1). The ISE is composed of an internal reference electrode (IRE) bathed in a reference solution that is physically separated from the sample by a membrane. The ion selective electrode can be represented in the following way ... 

A liquid-based ion-selective electrode is similar to the solid-state electrode in Figure 15-16, except that the liquid-based electrode has a hydrophobic membrane impregnated with... 

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...

H. Yanagi, T. Sakaki and T. Ogata, Development of high-performance ion sensors based on the functions of crown ethers and synthetic bilayer membranes, Nippon Kagaku Kaishi, 1999, 1999, 629 P. Izatt, E. Pretsch and E. Bakker, Carrier-based ion-selective electrodes and bulk optodes. 2. Ionophores for potentiometric and optical sensors, Chem. Rev., 1998, 98, 1593 S. Yajima and K. Kimura, Recent trends in ionsensing research, Bunseki Kagaku Anal. Chem.), 2000, 49, 279 etc. 

Ionophore-based solvent polymeric membranes are widely used as sensing membranes in ion-selective electrodes (ISEs) [24,25]. This type of potentiometric sensor has attracted great interest in the last decade due to the extraordinary improvement in the detection limit down to picomolar (10-12 M) levels [26,27], Furthermore, solid-contact ISEs have been developed by using various conducting polymers, including PEDOT, as the ion-to-electron transducer [28-31],... 

Polymer-based LMs have been known for over 40 years and have been used as the sensing membranes of ion-selective electrodes (ISEs) and optodes where they have been usually referred to as plasticized membranes. However, separation... 

Svancara, I. and Vytfas, K, (1993) Voltammetry with carbon paste electrodes containing membrane plasticizers used for PVC-based ion-selective electrodes. Anal Chim. Acta, 273, 195-204. 

The principle of a liquid-based ion-selective electrode was described in Figure 15-6. Figure 15-13 shows a Ca ion-selective electrode, featuring a hydrophobic poly(vinyl chloride) membrane saturated with a neutral Ca -binding ligand (L) and a salt of a hydrophobic anion (Na R ) dissolved in a hydrophobic liquid (Figure 15-14). The response is... 

It is possible to reduce interference by ions from the filling solution of a liquid-based ion-selective electrode (Figures 15-13 and 15-15) by replacing the filling solution with an electrically conductive polymer. The filling solution or the conductive polymer translates an electric potential difference at the Ag ion-exchange membrane into an electric potential at the metallic inner electrode. 

Ion-selective electrodes are widely used in pharmaceutical analysis. Numerous ion-selective electrodes based on poly(vinyl)chloride (PVC) have been constructed in order to determine various pharmacologically active substances in pharmaceutical preparations. The inherent advantages of ISE-s are simple design, construction and manipulation, reasonable selectivity, fast response time, low cost, adequate detection limit and adequate precision and accuracy. Therefore, the ISE potentiometric method is very attractive for pharmaceutical analysis. The first part of this chapter describes the properties and uses of PVC, as well as the general characteristics and preparation of the polymer membranes of ion-selective electrodes. The second part deals with the development of solid contact electrodes formed on non-crystal electrodes with a microporous matrix (e.g., vinyl polychloride dissolved in an appropriate modifier) selective for various nonsteroidal anti-inflammatory drugs (NSAlD-s) and their applications in pharmaceutical research. 

A.D.C. Han, X. Li., D. Harrison, Evidence for a water-rich surface region in poly(vinyl chloride)-based ion-selective electrode membranes. Ana/ Chem, 64, 2512-2517,1992. 

Pechenkina I, Mikhelson K. Materials for the ionophore-based membranes for ion-selective electrodes problems and achievements (review paper). Russian Journal of Electrochemistry 2015 51(2) 93-102. 

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