HR: 10:55h
AN: H22A-03    [Abstracts]
TI: A New, Rapid, Precise and Sensitive Method for Chlorine Stable Isotope Analysis of Chlorinated Aliphatic Hydrocarbons
AU: * Van Acker, M R
EM: m.r.m.d.vanacker@reading.ac.uk
AF: School of Human and Environmental Sciences, University of Reading, PO Box 227, Whiteknights, Reading, RG6 6AB United Kingdom
AU: Shahar, A
EM: ashahar@ess.ucla.edu
AF: UCLA, Department of Earth and Space Sciences and Institute of Geophysics, Los Angeles, CA 90095 United States
AU: Young, E D
EM: edyoung@ucla.edu
AF: UCLA, Department of Earth and Space Sciences and Institute of Geophysics, Los Angeles, CA 90095 United States
AU: Coleman, M L
EM: max.coleman@jpl.nasa.gov
AF: Jet Propulsion Laboratory, 4800 Oak drive, MS 183-301, Pasadena, CA 91109 United States
AB: Chlorinated aliphatic hydrocarbons (CAH) are recognized common groundwater contaminants. Because of their physico-chemical properties, their lifespan in groundwater is in the order of decades (Pankow and Cherry, 1996). Stable isotopes can play a role in determining the rate and extent of CAH attenuation (Slater, 2003). The use of chlorine has been hampered by the current time consuming and insensitive analytical methods. We present a new analytical procedure to measure chlorine stable isotope values using a gas chromatograph coupled to a multi-collector inductively coupled mass spectrometer (GC-MC-ICP-MS). The GC has a Porapack Q packed column. The carrier gas was helium and the temperature was constant at 160°C. The GC was coupled to the MC-ICP-MS by heated stainless steel tubing. Our high resolution spectra showed that ³⁷Cl is free of its main interference ³⁶Ar-H over a range of 0.004 amu. Two pure CAH, trichloroethene (TCE) and tetrachloroethene (PCE), were used for zero enrichment (sample relative to itself) and standard-sample difference measurements. Integrations and background corrections of transient signals were performed using Microsoft Excel after import of the raw data from the MC-ICPMS acquisition software. Zero enrichment tests with TCE and PCE yielded δ³⁷Cl of -0.04±0.16‰ and -0.03±0.17‰, respectively, results for sample injections of 0.12 to 0.02 microliters. Accuracy was tested by injecting 0.24 microliters of a 50/50 mixture of TCE and PCE of known isotopic compositions as the difference between the two solvents was of paramount interest. The δ³⁷Cl(TCE) value of PCE was -1.99±0.16‰. A highly satisfactory comparison with the conventional method is shown by published values for TCE and PCE, -2.04±0.12‰ and -0.30±0.14‰, respectively (Jendrzejewski et al., 2001), giving a δ³⁷Cl(TCE) value for PCE of -2.34±0.18‰. These tests of the GC-MC-ICP-MS method showed that we can obtain reproducible and accurate Cl isotope values using an internal standard. This method also offers increased sensitivity (down to 20 microgram chlorine) and a quicker and simpler procedure allowing its possible application to a wider range of CAH samples and other organic compounds. Jendrzejewski, N, Eggenkamp, HGM and Coleman ML (2001). Characterisation of chlorinated hydrocarbons from chlorine and carbon isotopic compositions: scope of application to environmental problems. Appl. Geochem. 16, 1021-1031. Pankow, JF and Cherry, JA (1996). Dense chlorinated solvents and other DNAPLs in groundwater: history, behavior, and remediation. Waterloo Press, Portland, Or. Slater, GF (2003). Stable isotope forensics - When isotopes work. Env. Forensics 4, 13-23.
DE: 1094 Instruments and techniques
DE: 1831 Groundwater quality
DE: 1895 Instruments and techniques: monitoring
SC: Hydrology [H]
MN: Fall Meeting 2005