Stable isotope (C, Cl, and H) fractionation during vaporization of trichloroethylene

Stable isotope fractionation during vaporization of trichloroethylene has been measured, with possible application as a technique to investigate subsurface behavior. The equilibrium value of Delta(13)C(vapor-liquid) has been measured between 5 and 35 degrees C, and Delta(13)C(vapor-liquid), Delta(37)Cl(vapor-liquid), and Delta Dvapor-liquid have been measured during progressive evaporation of liquid trichloroethylene at 22 +/- 2 degrees C. Equilibrium values of Delta(13)C(vapor-liquid), show a total range of 0.07-0.82 parts per thousand, with a trend of decreasing Delta(13)C(vapor-liquid) with increasing temperature, from approximately +0.7 parts per thousand at 5-15 degrees C to approximately +0.1 parts per thousand at 35 degrees C. Progressive evaporation experiments yield values of Delta(13)C(vapor-liquid) = +0.35 parts per thousand and +0.24 parts per thousand, Delta(37)Cl(vapor-liquid) = -1.64 parts per thousand, and Delta Dvapor-liquid = +8.9 parts per thousand. The positive values for carbon and hydrogen isotope fractionation, while unexpected, are consistent with available quantitative and qualititative data for trichloroethylene and other contaminant hydrocarbons, but a satisfactory explanation for these observations, particularly in combination with the negative value for chlorine, remains elusive. Vapor-liquid fractionation factors have application to the investigation of the behavior of trichloroethylene at contaminated sites, particularly sites undergoing remediation by techniques such as soil vapor extraction and soil bioventing.