Chlorine stable isotope measurements of chlorinated aliphatic hydrocarbons by thermal ionization mass spectrometry Original Research Article

An improved method for chlorine isotopic analysis using thermal ionization mass spectrometry (TIMS) of Cs2Cl+ has been investigated. The δ 37Cl values (parts per mil deviations from the standard seawater 37Cl/35Cl ratio) for 10 commercial chlorinated aliphatic hydrocarbons (CAHs), provided by six suppliers are presented. The CAHs were treated with a sodiumbiphenyl reagent. The liberated chloride ions were converted to CsCl and their isotopic compositions were determined by TIMS. Replicate analysis of the CAHs gave an external precision of 0.1–0.4‰ (1σS.D.). As each compound and each supplier has a distinctive δ 37Cl value (δ 37Cl values: −5.0 to +2.9‰), Cl isotope data can be used to trace a specific source of pollutants in the subsurface environment. Trichloroethene (TCE) and tetrachloroethene (PCE) were extracted from aqueous solutions with toluene and their chlorine isotope compositions were analyzed. The solvent extraction method presented here may be applicable to the analysis of actual contaminated water samples. Chlorine atoms were recovered as inorganic chloride from unsaturated chlorinated aliphatic compounds (TCE and PCE) by KMnO4 oxidation. However, the saturated compounds were resistant to KMnO4 oxidation. The isotopic compositions of the recovered chloride ion were then determined by TIMS. It is suggested that such compound-specific isotopic analyses may give information about the past record of each contaminant.