Cyanide electrochemical data

Table 7.6. Electrochemical Data for the Electrocatalytic Detection of nitrites, Cyanides and Thiocyanades using M — N4 Complexes ... 

An alternative approach, adopted by Albery et al. [59-61], is to determine the mechanism giving rise to the sensor response and to use this information together with the measured data at short times to calculate the final response. This was used for an electrochemical sensor system incorporating cytochrome oxidase where the steady-state responses of the measurement system were insufficiently fast for useful measurement of respiratory inhibitors such as cyanide, hydrogen sulphide, etc. By using mechanistic information, it was possible to successfully calculate the concentration in a test sample by real-time analysis of the sensor signals at short times after exposure to the test sample. The analysis could cope with the gradual loss of enzyme activity commonly found in these biosensor devices. 

Our results indicate that the autoreduction cannot occur by a conventional outer sphere mechanism because of the gross mismatch of the electrochemical potentials. Experimental data available at this time are consistent with homolytic iron-carbon bond cleavage which may or may not involve a simultaneous nucleophilic attack on the coordinated cyanide. The homolytic metal-carbon bond cleavage may serve as a model for similar processes reported for vitamin Bi2 (26). 

According to Gerischer [136], Zn(OH)2 is the electrochemically active complex that takes place in the charge transfer processes occurring in sufficiently alkaline solutions. This EAC can be formed not only in zincate solutions but in cyanide solutions as well. Similar mechanism was also postulated for Zn(II) reduction in alkaline D-mannitol solutions [134] however, this view seems to be unacceptable for acidic media. It follows from the data obtained at 3.7 < pH < 5 [127] that both Zn " " and ZnE" " might be electrically active. This leaves the question of the EAC structure open. 

FIGURE 11.4 Hardness versus earbon content in gold films plated from additive free phosphate and citrate buffered Au(l)-cyanide solutions, either at 65°C (hot bath) or 25°C (cold bath). (Data from Carbon in Gold Electrodeposits, H. A. Reinheimer, J. Electrochem. Soc., 1974,121,490.)... 

Since they operate in the same fashion, the electric and electrochemical properties of the heterogeneous solid-state membrane electrodes on the market today resemble those of the homogeneous precipitate membrane electrodes in many ways. The most important data are summarized in Table 3. By the same principles outlined in the previous chapter, the heterogeneous iodide electrode can also detect cyanide. In contrast to the homogeneous membranes, those which include silicone rubber as a support ma-... 

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