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

A method is described for near-quantitative extraction of micromolar concen trations of chlorinated aliphatic hydrocarbons (CAHs) from water for determ ination of chlorine (Cl) isotope ratios. A low pressure, carrier-gas proced ure of extraction was proven to be applicable to CH2Cl2, CCl4, C2H2Cl2, and C2HCl3. The pH of the water was adjusted with NaOH to prevent extraction o f CO2 from air and/or dissolved inorganic carbonate species. Recoveries of CAH samples (similar to 15 mu mol), added to and extracted from similar to 340 ml of water, averaged similar to 96%. Average changes in the delta Cl-3 7 values of the CAHs, attributable to the extraction process, were -0.01 +/ -0.06 parts per thousand. Significant isotopic fractionation of Cl was meas ured during partial extraction of C2CHCl3 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 measurem ents of hydrogen and carbon. (C) 2001 Elsevier Science Ltd. All rights rese rved.