Ananlytical Method Development And Application Of Carbon And Hydrogen Isotope For Typical Volatile Organic Compounds In Groundwater

In recent decade, compound-specific stable isotope analysis(CSIA) using gas chromatography-isotope ratio mass spectrometry(GC/IRMS) has been widely applied in many areas. In this paper, an analytical method of carbon and hydrogen isotope for typical volatile organic compounds in groundwater was established for laboratory simulated experiments and field monitoring. The batch experiments showed the carbon isotope fractionation happened during toluene degradation process. In a contamination site, degradation of aromatic hydrocarbons and chlorinated hydrocarbons was also observed. The detailed results are following:(1) There is no isotope fractionation when target compounds were fully purged and trapped. Purge & trap can be used as the pre-treatment mode for CSIA of volatile organic compounds(VOCs).(2) Inlet mode has some effects on analyzing results. The target’s peak shape is sharp for split mode. There is isotope fractionation of hydrogen, and the value of hydrogen isotope is significantly reduced. The peak shape of target gets worse for splitless mode(the chromatographic peak is wide and has acceptable tailing), though the signal is stronger. There was no hydrogen isotope fractionation, and the value of hydrogen isotope was as same as the value obtained by direct injection into gas chromatography. So splitless mode is selected.(3) The biodegradation experiments of toluene showed that pollutant concentration, COD, DO, NO3--N, ORP, CON and p H have obviously declined and reached steady state after 10 days. The ratio value of carbon isotope was increased from-26.378 ‰ to about-24 ‰, Microorganism is main factor to cause the biodegradation of toluene because the control set without microorganism has no any change. The enrichment factor is-3.4 for selected microorganism, while-0.7 for local microorganism.(4) Based on the monitoring data of the field, the plume of organic contamination was depicted. The direction of the plume was similar as that of the groundwater flow. Therefore, the flow of groundwater was the major factor for the organic pollutants distribution.(5) The relationships between the concentration and the carbon isotope value for 1,2,3-trichloropropane and toluene showed that they were degraded. The changes of inorganic ions showed that the degradation was the denitrification type.