  It has been reported that isotope fractionation can occur on gas
chromatography (GC), yet little is known about concurrent dual-elements isotope
fractionations on GC. Revelation of concurrent two-dimensional carbon and
chlorine/bromine isotope fractionations of halogenated organic compounds (HOCs)
on GC may be of important significance for compound-specific isotope analysis
(CSIA). This study presents an in-depth investigation of the two-dimensional C
and Cl/Br isotope fractionations of HOCs on GC using GC-double focus
magnetic-sector high resolution mass spectrometry (GC-DFS-HRMS). The
two-dimensional C and Cl/Br isotope fractionations of four organochlorines and
four bromobenzenes on GC were simultaneously measured by GC-DFS-HRMS. The
isotope fractionations were evaluated with isotope ratios, relative variations
of isotope ratios and isotope fractionation extents. All the HOCs exhibited
significant inverse C and Cl/Br isotope fractionations. The isotope
fractionations were significant in both ends of chromatographic peaks, while
the isotope ratios in center retention-time segments were the closest to
comprehensive isotope ratios in the whole peaks. Significant correlations
between C isotope fractionation and Cl/Br isotope fractionation were observed,
indicating that the isotope fractionations might have strong relationships
and/or be dominated by similar factors. Relevant mechanisms for the
two-dimensional C and Cl/Br isotope fractionations were tentatively proposed on
basis of a modified two-film model and the theories related to zero point
energy. The results of this study gains new insights into concurrent
two-dimensional isotope fractionation behaviors of HOCs during physical
processes, and are conducive to CSIA studies involving C, Cl and Br for
obtaining high-quality data, particularly to dual-elements CSIA of C and Cl/Br.
