Platinum wire electrodes coated with

The development of the reductive mode LCEC technique has been slow because of difficulties in preparing convenient and reliable working electrodes for use with a high efficiency chromatographic separation. In addition, problems are encountered with dissolved oxygen and heavy metals. Solid electrodes have been used with limited success for reductive LCEC. Mercury pool electrodes (44-47), the DME (48-53), and platinum wire electrodes coated with mercury (49) are generally not satis-... 

Kappes et al. evaluated the potentiometric detection of acetylcholine and other neurotransmitters through capillary electrophoresis [209]. Experiments were performed on an in-house capillary electrophoresis instrument that made use of detection at a platinum wire, dip-coated in 3.4% potassium tetrakis (4-chlorophenyl) borate/64.4% o-nitrohenyl octyl ether/32.2% PVC in THF. The results were compared to those obtained using capillary electrophoresis with amperometric detection at a graphite electrode. Samples prepared in the capillary electrophoresis buffer were electrokinetically injected (7 s at 5 kV) into an untreated fused silica capillary (88 cm x 25 pm i.d.) and separated with 20mM tartaric acid adjusted to pH 3 with MgO as the running buffer. The system used an applied potential of 30 kV, and detection versus the capillary electrophoresis ground electrode. 

Several methods have been described for the preparation of silver-silver chloride electrodes a small sheet or short coil of platinum is first coated with silver by electrolysis of an argentocyanide solution, and this is partly converted into silver chloride by using it as an anode in a chloride solution. Alternatively, a spiral of platinum wire may be covered with a paste of silver oxide which is reduced to finely divided silver by heating... 

Consider Figure 14-9 in which the left half-cell contains a silver electrode coated with solid AgCl and dipped into saturated aqueous KCl. The right half-cell has a platinum wire dipped into a solution containing Fe and Fe. ... 

Anodic stripping voltammetry was in use already in 1972 to determine Bi in plasma [120]. Bismuth is one of the elements most easily determined with this method. It can be deposited on electrodes at potentials at which most other elements ate in solution. Glassy carbon electrodes coated with films of mercury [100,121-124], but also of gold [101,125], are used. As reference served calomel or silver/silver chloride electrodes [121]. Platinum foils or wires were used as counterelectrodes. At -0.7 V carbon electrodes are precoated with mercury from acid Hg(II) or gold from acid Au(III) solutions. To deposit Bi on the electrode -0.2 to -0.3 V is a sufficient potential for preelectrolysis, but mostly higher voltages are chosen to determine other metals as well. Bi is stripped fiom the electrode at potentials of about -0.10 to -0.16 V. Only some elements interfere with Bi, such as arsenic, mercury, copper, and antimony. Copper interferes at high concentrations and is separated by extraction [101]. Arsenic or antimony in urine are oxidized to their pentavalent states [125]. 

The most recent version of the cell (Ho et al., 1994) consists of two coaxial 75% platinum-25% iridium electrodes coated with platinum black. As can be seen in Figure 4.1, one electrode is external platinum-iridium lined high-pressure vessel (6.35 cm long and 1 cm volume) and the other, a thin platinum wire, insulated by a non-porous sintered AI2O3 or Al203/Zr02 tube (for alkaline media), welded to a platinum-iridium cylinder located in the center. 

This electrode is perhaps next in importance to the calomel electrode as a reference electrode. It consists of a silver wire or a silver-plated platinum wire, coated electrolytically with a thin layer of silver chloride, dipping into a potassium chloride solution of known concentration which is saturated with silver chloride this is achieved by the addition of two or three drops of 0.1M silver nitrate solution. Saturated potassium chloride solution is most commonly employed in the electrode, but 1M or 0.1 M solutions can equally well be used as explained in Section 15.1, the potential of the electrode is governed by the activity of the chloride ions in the potassium chloride solution. 

By setting the ratio of the oxidized and reduced forms of a redox couple in an electrode coating film to unity, the potential of this electrode in an inert electrolyte is poised at the half-wave potential of the couple. This has indeed been shown for platinum wires coated with polyvinylferrocene or ferrocene modified polypyrrole But the long term stability of these electrodes during cell connection... 

The Electrodes. In most commercial and homemade apparatus the electrodes are of platinum wire or platinum-coated silver. Carbon electrodes are just as satisfactory as long as the same buffer continues to be used, but washing out carbon electrodes when changing to new buffers is difficult. Silver electrodes connected with AgCl/KCl bridges give excellent results (F7), as they do in free electrophoresis. 

Note that the metal does not dissolve in the solution. An electrode of this type, which is often used because of its stability, is the calomel electrode shown in Fig. 4. This consists of a platinum wire inserted into liquid mercury, which is coated with mercurous chloride. The electrode reaction is... 

In the thermal-electrolytic-type AgCl electrode, silver is formed by heating a paste of silver oxide coated on a spiral of platinum wire. Part of the spongy silver mass in converted to AgCl by the electrolysis process described above. Because the silver is porous, the electrodes tend to be rather sluggish, but they can be prepared with very small bias potentials ( 20 jtV). 

The conductance cells different in shape which are illustrated in Fig. 4. are of glass or quartz two exactly parallel electrodes made of thick platinum sheet (in order to keep Constant their mutual position) are dipped into the cells. To suppress the polarization phenomena the electrodes are coated with platinum black. The current is fed through glass tubes filled with mercury the connections of the electrodes are sealed in the glass at the bottom of the tubes while at the top lead-in wires are immersed in the mercury for connection with the terminals of the measuring instruments. 

The silver-silver chloride electrode is made of silver or silver plated platinum wire, coated with a thin layer of silver chloride, immersed into... 

The right-hand electrode consisted of a tantalum foil (attached to a Pt wire) coated with a platinum-iridium alloy. This alloy, containing 45% iridium, is used as a CI2 electrode because Pt is not fully appropriate since it is subject to corrosive attack by CI2 in the presence of HCl. Their results for the cell i are as follows 25°C eeiKO = 1.13596 V 30°C = 1.13309 V 40 C ... 

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