Anodic surfactants

To improve the long-term stability of the common nickel oxide anodes, surfactants, such as substituted polyglycol ethers, are added to the electrolyte 291). Merck has proposed a combined process (in which about 80 % of the diacetonesorbose are oxidized electrochemically, and the remainder conventionally 292)) and a special procedure for the work-up procedure by electrodialysis (removal of the unconverted diacetonesorbose 293)). It is said that Merck is using the electrosynthesis of diacetoneketogulonic acid for the industrial production of vitamin C. 

Both anodic and general inhibitors are nonpassivating and are suitable for use with hydrochloric acid-based cleaners. Other inhibitor groups include filming amines such as polymethylimine and diamines, the rosin-amine ketones, and also some of the imidazoline surfactants. The imidazolines provide increased protection at levels up to their critical miscelle concentration (CMC), above which there is a leveling off as a thick, adherent diffusion barrier is formed. 

An electric field-induced bending of gel makes a worm-like motion feasible [18]. A weakly crosslinked PAMPS gel in a surfactant solution bends toward the anode under dc electric fields. Both ends of the gel are placed on front and rear hooks and are then hung on a plastic ratchet bar. When a varying electric field of 10 V/cm and 0.5 Hz is applied, the gel moves forward in the solution with a bending motion at a velocity of 25 cm/min. 

Fig. 3.14 Anodic stripping square-wave voltammetry (ASSWV) of 1 X 10- M Dependence of peak currents on the accumulation time, itacc = —0.8 V, tacc = 5 s. (1) organic carbon-free water and (2) double-distilled water contaminated by unknown surfactant. Additions of Triton X-100 to (2) inmg/1 (3) 0.1, (4) 0.3, (5) 0.5, (6) 0.8 and (7) 1. Esv/ = 30 mV, / = 100 Hz and AE = 2.4 mV (reprinted from [247] with permission)...

In MEKC, mainly anionic surface-active compounds, in particular SDS, are used. SDS and all other anionic surfactants have a net negative charge over a wide range of pH values, and therefore the micelles have a corresponding electrophoretic mobility toward the anode (opposite the direction of electro-osmotic flow). Anionic species do not interact with the negatively charged surface of the capillary, which is favorable in common CZE but especially in ACE. Therefore, SDS is the best-studied tenside in MEKC. Long-chain cationic ammonium species have also been employed for mainly anionic and neutral solutes (16). Bile salts as representatives of anionic surfactants have been used for the analysis of ionic and nonionic compounds and also for the separation of optical isomers (17-19). 

Oily emulsions containing surfactants and/or stabilizers Anodization rinse water... 

Figure 8.6—Effect of a cationic surfactant reversing the polarity of the capillary inner wall. Because the migration of analytes must always be in the direction of the detector, the voltage polarity of the instrument must be reversed in order for anionic species to move towards the anode, thus towards the detector.

Another model compound, the tris(2,2 -bipyridine)ruthenium(II) complex, has prompted considerable interest because its water-splitting photoreactivity has been demonstrated in various types of photochemical systems (77,99,100,101). Memming and Schroppel (102) have attempted to deposit a monolayer of a surfactant Ru(II) complex on a Sn02 OTE. In aqueous solution, an anodic photocurrent attributable to water oxidation by the excited triplet Ru complex was observed. A maximum quantum efficiency of 15% was obtained in alkaline solution. 

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