[Implementation of a pretreatment device for an electronic nose].

A pretreament device was implemented for removing the interference of humidity on the baseline signal response of sensors in an electronic nose, which was used for rapid detection and real-time monitoring of volatile chlorinated hydrocarbons (VCHs) pollution in soil. The desiccant material was optimized, and the humidity removal performance and adsorpiton of VCHs was studied. The pretreatment device was evaluated by both the electronic nose and gas chromatography (GC) for its applicability in monitoring the PCE concentration in the desorption gas during the soil ventilation process. The following results were obtained: 1) A desiccant tube with anhydrous calcium chloride followed by a halogenated hydrocarbon separation tube was the best device, with a humidity removal rate of over 99%, and the baseline values of each sensor in the electronic nose were close to that of the control. 2) The desiccant device described above could continuously remove almost all the humidity from air with 75% humidity within 90 min, and the humidity removal rate remained above 95% within 120 min, while little interference was observed on the baseline of each sensor. 3) Little adsorption was observed by the pretreatment device, the relative error being only 3% - 5% between the concentration of VCHs before and after the filtration by the pretreatment device. 4) When applied for monitoring the remediation progress in a soil ventilation process, 99% of humidity was removed within 120 min from air with humidity of over 98%, and the data determined with the electronic nose and GC fitted each other very well, with R2 > 0.99. From the above, the pretreatment device connected with the electronic nose was considered to be applicable for monitoring the soil remediation process.

[Applicability of an electronic nose for detection of volatile chlorinated hydrocarbons in soil].

An electronic nose principally composed of a photo ionization detector (PID) was developed for rapid detection of volatile chlorinated hydrocarbons (VCHs) in contaminated soil. Removal of interference gas such as benzene homologues with a pre-filtration tube was analyzed with gas chromatography (GC). A standard gas generator was applied to generate different concentrations of perchloroethylene (PCE) and trichloroethylene (TCE) gas, with which the determine precision and reproducibility of the electronic nose were evaluated by comparison with GC. Finally, simulated contamination soil with three typical paddy soils in Yangtze river delta region were used for ventilation purification experiments, the change of VCHs concentrations in the ventilation gas was monitored, based on which the applicability of the electronic nose was evaluated for on-line detection of the on-going of the ventilation purification process. Results showed that a halogenated hydrocarbon RAE-SEP tube was effective to remove interference gas, with 80%-97% of benzene homologues such as benzene and ethyl benzene being removed while more than 90% of VCHs passed through. With PCE or TCE gas, a linear dependence was derived between the data determined with the electronic nose and GC, the linear slope being 1.012 and R2 > 0.99. The electronic nose showed data consistent with GC (R2 > 0.99, n = 47) when applied for monitoring the remediation progress in a soil ventilation process. The electronic nose is therefore possibly applicable for rapid determination of soil pollution by VCHs, improving the efficiency of pollution diagnosis and remediation.