B Reference Electrodes

The ideal reference electrode has a potential that is accurately known, constant, and completely insensitive to the composition of the analyte solution. In addition, this electrode should be rugged and easy to assemble and should maintain a constant potential while passing minimal currents. 

The crystal structure of calomel, Hg2Cl2, which has limited solubility in water (A jp = 1.8 X 10 at 25°C). Notice the Hg-Hg bond in the structure. There is considerable evidence that a similar type of bonding occurs in aqueous solution, and so mercury(I) is represented as Hg.  

Formal Electrode Potentials for Reference Electrodes as a Function of Composition and Temperature  

A system analogous to the use of a saturated calomel electrode employs a silver electrode immersed in a solution that is saturated in both potassium chloride and silver chloride  

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Y for a definite electrode or object X (B, reference electrode Me, metal E, ground M, mast R, pipe S, rail T, tunnel)... 

Figure 9.6. A—temperature electrode B—reference electrode suitable for ISE measurements C—nitrate ISE electrode D—combination electrode E—conductivity electrode.

B, reference electrode with Luggin capillary C, auxiliary electrode ... 

Fig. 7. Typical rotating ring—disc electrode cell. A, rotating ring—disc electrode B, reference electrode with Luggin capillary C, counter electrode D, teflon lid E, porous frit F, thermostatted water jacket.

Figure 9.3 Stationary solution voltammetry cells, (a) Platinum wire loop auxiliary electrode, (b) reference electrode or reference electrode probe tip, (c) carbon paste working electrode, (d) graphite auxiliary electrode, (e) dropping mercury electrode, (0 platinum wire contact to mercury pool working electrode, (g) nitrogen gas inlet tube, (h) magnetic stirrer, (i) mercury pool working electrode, (j) glass frit isolation barrier.

Figure 9.4 Reference electrodes and reference electrode probe. (A) Silver-silver chloride reference electrode, (B) calomel reference electrode, (C) reference electrode probe, a, Silver wire, ca. 22 gauge b, reference electrode filling solution, saturated or known concentration of KC1 c, silver chloride electrochemically precipitated on silver wire by anodization d, reference electrode junction e, Pt/glass seal f, mercury g, calomel h, electrochemical cell body wall i, working electrode surface.

Figure 17.10 Gas-tight transmission cell for IR spectroelectrochemistry in moderate-melting salts (A) optically transparent electrode (OTE) port, (B) reference electrode and auxiliary electrode ports, (C) Si windows, (D) vacuum valve, (E) light path. [From P. A. Flowers and G. Mamantov, J. Electrochem. Soc. 136 2944 (1989), with permission.]...

Figure 5.41 Selective-ion electrodes (a) glass membrane (b) liquid ion exchange (c) homogeneous solid membrane (d) heterogeneous solid membrane (e) solid membrane without reference electrode (/) gas-permeable membrane 1, sensing electrode 2, electrolyte, 2(e) ohmic contact, 2(f) gas-permeable membrane 3, membrane sur-port 4, reference electrode, 4(f) outer electrode body, 5(b) liquid ion exchanger 5(f) electrode body 6(b) reference electrode body, 6(f) electrolyte 7, liquid junction.

Figure 5.42 Flow cell for a selective-ion electrode A, sensor electrode B, reference electrode C, solution ground D, sensing membrane E, Teflon sleeve F, Plexiglas cap G, washer H, sample inlet flow /, sample outlet flow J, magnetic stirring bar K, potentiometer L, solution outlet.

Fig. 7.17. High-pressure flow-cells. (A) Cell for voltammetric measurements in water-in-CO, microemulsions a working electrode, b reference electrode, c supercritical fluid inlet, d supercritical fluid outlet, e sample port, f Teflon O-ring. (B) Fibre optic-assisted cell for fluorimetric measurements. (Reproduced with permission of the American Chemical Society.)...

Fig. 9.18. Typical plasma emission spectra obtained in different zones of a screen-printed electrode (A) working electrode, (B) reference electrode, (C) electrical contacts and (D) polymeric coating used as insulator. Atomic emission lines used in the LIBS-PCA analysis are indicated. (Reproduced with permission of Elsevier.)...

Fig.l View of a glass cell (capacity 5 to 7 ml of solution) connected to a power source (potentiostat). Case of a reduction at a copper cathode. A inlet for inert gas, B reference electrode like a saturated calomel electrode, C anodic compartment (a glass tube ended by a glass frit), D platinum grid as anode, E working electrode copper grid (area about 4 cm2), F inert gas outlet. The solution is stirred with a magnetic bar. Thus for an amount of electroactive compound (one-electron reduction) of 10 3 mol, electrolysis current could be of the order of 0.1 A and the reaction completed (until nil current) in much less than 1 hour. 

Fig. 5.119. Schematic drawing of an electrochemical cell for in situ NMR spectroscopy [649]. A counter electrode connection B reference electrode joint C counter electrode D platinum black working electrode E working electrode connection F purge connection...

Fig. 5.8 SFG cell for electrochemistry and spectroscopy. (A) Pt working electrode, (B) reference electrode, (C) vacuum stopcock, (D) connection for working electrode, (E) counter electrode, (F) Cap2 window.

Figure 5.6. Hydrogen electrodes (a) dipping electrode (b) reference electrode.

Fig. 12.31 Cell for electrochemical radiotracer experiments with a thin-foil electrode constructed by Horanyi in 1971 [94], Central compartment (A), auxiliary electrode (B), reference electrode (C), working electrode (D), and scintillation counter (E)...

A Control electrode B Reference electrode C Supercritical fluid inlet D Supercritical fluid outlet E Sample port F Teflon 0-rtng. 

Basic circuit for classical potentiometry a = indicator electrode b = reference electrode. 

Figure A.4 Amperometric titration R, rheostat A, micro- or milliammeter C, reaction vessel B, reference electrode...

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