  Compound-specific chlorine isotope analysis (CSIA-Cl) is a practicable and
high-performance approach for quantification of transformation processes and
pollution source apportionment of chlorinated organic compounds. This study
developed a CSIA-Cl method for perchlorethylene (PCE) and trichloroethylene
(TCE) using gas chromatography-double focus magnetic-sector high resolution
mass spectrometry (GC-DFS-HRMS) with a bracketing injection mode. The achieved
highest precision for PCE was 0.021% (standard deviation of isotope ratios),
and that for TCE was 0.025%. When one standard was used as the external
isotopic standard for another of the same analyte, the lowest standard
deviations of relative isotope-ratio variations ({\delta}37Cl') between the two
corresponding standards were 0.064% and 0.080% for PCE and TCE, respectively.
As a result, the critical {\delta}37Cl' for differentiating two isotope ratios
are 0.26% and 0.32% for PCE and TCE, respectively, which are comparable with
those in some reported studies using GC-quadrupole MS (GC-qMS). The lower limit
of detection for CSIA-Cl of PCE was 0.1 ug/mL (0.1 ng on column), and that for
TCE was determined to be 1.0 ug/mL (1.0 ng on column). Two isotope ratio
calculation schemes, i.e., a scheme using complete molecular-ion isotopologues
and another one using a pair of neighboring isotopologues, were evaluated in
terms of precision and accuracy. The complete-isotopologue scheme showed
evidently higher precision and was deduced to be more competent to reflect
trueness in comparison with the isotopologue-pair scheme. The CSIA-Cl method
developed in this study will be conducive to future studies concerning
transformation processes and source apportionment of PCE and TCE, and light the
ways to method development of CSIA-Cl for more organochlorines.
