Compound‐specific hydrogen isotope analysis of 1,2‐dichloroethane: potential for delineating source and fate of chlorinated hydrocarbon contaminants in groundwater

A Delta Plus XL continuous flow gas chromatography/high‐temperature conversion‐isotope ratio mass spectrometer system (GC‐TC‐IRMS) with a liquid nitrogen trap installed at the end of the micropyrolysis oven was used to measure hydrogen isotope ( δ 2 H) values of 1,2‐dichloroethane (1,2‐DCA). The 1,2‐DCA δ 2 H values were within uncertainty of the δ 2 H value for the same 1,2‐DCA analyzed using off‐line sample preparation and conventional dual inlet mass spectrometry, verifying that this system can accurately measure 1,2‐DCA δ 2 H values. After 71 reproducible and accurate 1,2‐DCA δ 2 H measurements had been obtained, the standard deviation on the mean of the cumulative 1,2‐DCA δ 2 H measurements was greater than ±5‰. The cumulative load of chlorine at this point was ∼5.5 × 10 −6 moles, which may be the limit to the quantity of chlorine that can be input before the reproducibility of 1,2‐DCA δ 2 H measurements is compromised. This study is the first to our knowledge to demonstrate a method for obtaining accurate and reproducible compound‐specific δ 2 H values for chlorinated hydrocarbons at dissolved concentrations typical of field conditions. Paired δ 2 H and δ 13 C values suggest that dual parameter isotopic measurements can distinguish between different contaminant sources, as well as providing additional constraints on degradation pathways and contaminant remediation.