Electrochemical cells, vapor detection

The gas phase detection of iodine vapor with an electrochemical probe has been investigated [195]. The Ag AgI Au electrochemical cell was observed to be sensitive to interference from both oxygen and humidity. A sensor based on a Ag Ag(Cs)I graphite electrode system has been reported by Sola etal. [196]. Temperature effects were studied and the effect of Csl doping of the Agl explored to widen the working temperature range. 

There are two methods that are predominantly used to analyze CO these are based on infrared (IR) absorption and electrochemistry. The IR technique is based on the fact that CO will absorb light at 4.67 pm (2165 cm ). The CO concentration is then determined from the extent of absorption of the sample. There are two types of analyzer design, known as nondispersive and gas filter correlation analyzers. Interferences from CO2 and water vapor can be overcome by instrumental design and are generally not significant. Reported detection limits are <0.5mgm for this technique. The electrochemical cell technique is based on the electrochemical detection of CO as it is oxidized to CO2. Interferences from other oxidizable gases can be minimized by the use of special inlet filters and the detection limits obtained are comparable to the IR technique described earlier. 

It was in 1990 that Kratschmer et al. [217,218] reported the first macroscopic preparation of in gram quantities by contact-arc vaporization of a graphite rod in a 100 Torr atmosphere of helium, followed by extraction of the resultant soot with toluene. Fullerene ions could also be detected by mass spectrometry in low-pressure hydrocarbon flames [219]. The door was opened by, Kratschmer and co-workers preparative success to extensive studies of the electrochemical behavior of the new materials. Cyclic voltammetry of molecular solutions of Ceo in aprotic electrolytes, e.g., methylene chloride/quatemary ammonium salts, revealed the reversible cathodic formation of anionic species, the radical anion, the dianion, etc. (cf. [220,221]). Finally, an uptake of six electrons in the potential range of 1-3.3 V vs. SHE in MeCN/toluene at — 10°C to form the hexavalent anion was reported by Xie et al. [222]. This was in full accordance with MO calculations. A parametric study of the electroreduction of Cgo in aprotic solvents was performed [223]. No reversible oxidation of C o was possible, not even to the radical cation. However, the stability of di- and trications with special counterions, in the Li/PEO/C 3 MoFf cell, was claimed later [224]. 

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