SEQUENTIAL DETERMINATION OF CHLORINE AND CARBON ISOTOPIC COMPOSITION IN SINGLE MICROLITER SAMPLES OF CHLORINATED SOLVENT

Chlorinated hydrocarbons, significant environmental pollutants, may be characterized by stable isotopic compositions of carbon and chlorine. Previously published analytical methods needed separate preparations for carbon and chlorine and were not ideal for environmental studies b ecause of low sensitivity and precision. This method quantitatively ex tracts both carbon and chlorine from a single aliquot of chlorinated s olvent of a size practical applicable to natural systems, Samples of 1 -2 mu L of chlorinated solvent are combusted in sealed tubes with cupr ic oxide at 620-820 degrees C. After separation of CO2 for isotopic an alysis of carbon, the residue contains all the chloride in water-solub le form. It is then processed by conventional methods for chlorine iso topic analysis and gives a yield of 97 +/- 27% (SD) on standard trichl oroethylene (TCE) and 97 +/- 4% on standard perchloroetlhylene (PCE) f or the whole of the Cl preparation process. TCE and PCE laboratory sta ndards show reproducibilities (SD) for both products of 0.08 parts per thousand for delta(13)C and 0.15 and 0.10 parts per thousand, respect ively, for delta(37)Cl. The technique is applicable to all five types of chlorinated solvents investigated (TCE, PCE, dichloromethane, 1,1,1 -trichloroethane, and chloroform) and was tested by application to apr environmental sample of a vacuum-extracted mixture of chlorinated sol vents from a polluted site, giving excellent reproducibilities for bot h carbon and chlorine isotopic compositions (respectively +/-0.05 acid +/-0.08 parts per thousand).