Alcohol sensors, general

Adsorption temperature, effect on TPD spectra of oxygen on Pd-doped tin(IV) oxide, 74,75 Airborne chemicals, detection and identification, 299-307 Alcohol sensors, general discussion, 333... 

In general, EC reactions are typically observed according to the following general rank order (by relative ease of oxidation) o,p-quinol and o,p-aminophenol > tertiary amine > m-quinol rv phenol rv arylamine > secondary amine thiol > thioether primary amines, aliphatic alcohols. (HDVs) each redox active metabolite are obtained from the response across adjacent EC-Array sensors. These data are a reflection of the kinetic and thermodynamic components of electron transfer reactions. Since chemical structure is a critical determinant of an analyte s redox behavior, the intrinsic generation of an HDV with EC-Array provides qualitative information for each species. 

The entanglement generally reduces the leaching of active components from the matrix and so extends the operational lifetime of the ISE. However, PTC can also be blended with different amounts of vinyl chloride/vinyl acetate/vinyl alcohol copolymer (VAGH) which permits grafting of alkyl phosphate sensors and phosphonate mediators and 90 further reduces leaching effects. 

Fig. 4 shows the adsorption isotherm of n-propanol on the QCM sensor at room temperature. The observed trend of the n-propanol film thickness as a function of partial pressure is consistent with the general characteristic of the alcohol adsorption isotherm observed for other systems. The inset in Fig. 4 gives the approximate thickness of the adsorbed alcohol layer on the QCM sensor measured at a partial pressure of 90 10% to the saturation pressure of each alcohol. The actual alcohol thickness on the clean, hydrophilic silicon oxide surface would be slightly larger than that on gold. 

However, several problems still exist. These include sensor drift, which leads to the inability to provide proper calibration. This is of special concern to quality control laboratories and is one of the reasons for the general absence of these instruments in these laboratories [3]. Limitations to the use of the electronic nose include loss of sensitivity in the presence of water vapor and high concentrations of individual components such as alcohol, relatively short life of some sensors, and the inability to obtain quantitative data for aroma differences [72]. Each device also still needs considerable method development, but progress is being made at a rapid rate. Einally, sensor arrays and PR tend to predict the quality of a sample without providing hard data with respect to composition and concentration [74]. 

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