Coulometry, determination cations

Control led-Potential Coulometry The majority of controlled-potential coulometric analyses involve the determination of inorganic cations and anions, including trace metals and halides. Table 11.8 provides a summary of several of these methods. 

Under conditions where the primary electrode product undergoes a slow chemical reaction, that is, ti/2 is of the order of seconds, the value of n determined by a relatively fast technique like LSV may differ from that obtained by a slow experiment like coulo-metry. This type of behavior was observed in the anodic oxidation of 2,3,5,6-tetraphenyl-1,4-dithiin in MeCN [278]. During CV the reversible oxidation to the radical cation is observed. However, when constant-current coulometry was carried out as described earlier, this time at i = 50 mA, 6.44 min was required to oxidize completely 0.1 mmol of the substrate to a product electroinactive in the potential region of interest, indicating an overall two-electron process (Fig. 43). Thus, apparently contradictory results may be obtained due to the difference in time scale between the two types of experiment. 

An electrochemical analyzer is used to perform polarography, voltammetry, and coulometry experiments using dropping mercury, noble metal, rotating disk, and carbon electrodes. These techniques are amenable to the trace analysis of electroactive anions, cations, metals, and organics. Applications include the determination of individual aldehydes in polymer solutions by voltammetry and the determination of stabilizers in polymer formulations. 

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