Liquid-based ion-selective electrode

Schematic diagram of a Ca + liquid-based ion-selective electrode.

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... 

Representative Examples of Liquid-Based Ion-Selective Electrodes... 

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)... 

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...

The black curve in Figure 15-21 is typical of many liquid-based ion-selective electrodes. The response of this Pb2+ electrode levels off at an analyte concentration around 10 6M. The electrode detects changes in concentration above 10 (> M, but not below 10-6 M. The solution in the internal electrode compartment contains 0.5 mM PbCl2. 

Carbonate liquid-based ion-selective electrodes also are available ... 

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. 

Why is measuring [H ] with a pH electrode somewhat inaccurate, whereas locating the end point in an acid-base titration with a pH electrode can be very accurate 15-12. Explain the principle of operation of a liquid-based ion-selective electrode. 

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