Compound-Specific Chlorine Isotope Analysis of Organochlorines Using Gas Chromatography-Double Focus Magnetic-Sector High Resolution Mass Spectrometry

TL;DR

This paper presents a highly precise method for compound-specific chlorine isotope analysis of PCE and TCE using advanced mass spectrometry, enabling better pollution source identification and process understanding.

Contribution

Developed a novel CSIA-Cl method with high precision for PCE and TCE using GC-DFS-HRMS, improving detection limits and isotope ratio accuracy.

Findings

Achieved precision of 0.021% for PCE and 0.025% for TCE.

Lower detection limits of 0.1 ng for PCE and 1.0 ng for TCE.

Complete molecular-ion isotopologue scheme outperforms isotopologue-pair scheme.

Abstract

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.