Use of carbon stable isotope to investigate chloromethane formation in the electrolytic dechlorination of trichloroethylene

Carbon stable isotope trichloroethylene ((13)C TCE) was used to investigate the formation of chloromethane (CM) during the electrolytic dechlorination of trichloroethylene (TCE) at a granular-graphite packed cathode. A method was developed to use a conventional GC/MS to analyze and quantify regular and (13)C TCE and their dechlorination products. The concentration of a (13)C compound can be calculated, based on the concentration of its regular counterpart, from the response ratio of two fragments of different mass per charge values from the compounds in a sample and two characteristic MS spectrum ratios: one is the response ratio of the two fragments of the regular compound, and the other is the response ratio of the corresponding fragments of the regular and (13)C compounds at the same concentrations. The method was used to analyze the regular and (13)C compounds observed in an experiment of dechlorination in an ammonium acetate solution that contained both regular TCE and (13)C TCE. Results of analysis confirmed that CM was not a direct product of TCE dechlorination at the granular graphite cathode that cis-DCE was an intermediate product of TCE dechlorination, and that 1,1-DCE was not a dechlorination product.