Extraction of chlorinated aliphatic hydrocarbons from groundwater at micromolar concentrations for isotopic analysis of chlorine

Chlorine isotopic ratio techniques are used to characterize low molecular weight (solvent) hydrocarbons in groundwaters. A method is described for near-quantitative extraction of micromolar concentrations of chlorinated aliphatic hydrocarbons (CAHs) from water for determination of chlorine (Cl) isotope ratios. A low pressure, carrier-gas procedure of extraction was proven to be applicable to CH 2Cl 2, CCl 4, C 2H 2Cl 2, and C 2HCl 3. The pH of the water was adjusted with NaOH to prevent extraction of CO 2 from air and/or dissolved inorganic carbonate species. Recoveries of CAH samples (∼15 μmol), added to and extracted from ∼340 ml of water, averaged ∼96%. Average changes in the δ 37Cl values of the CAHs, attributable to the extraction process, were −0.01±0.06‰. Significant isotopic fractionation of Cl was measured during partial extraction of C 2CHCl 3 from water, indicating that near-quantitative extraction is required for reliable stable Cl isotope analysis of CAHs. This method is also suitable for the extraction of dissolved CAH for gas chromatography-combustion-isotope ratio mass spectrometric measurements of hydrogen and carbon.