Simultaneous observation of concurrent two-dimensional carbon and chlorine/bromine isotope fractionations of halogenated organic compounds on gas chromatography

TL;DR

This study investigates simultaneous two-dimensional isotope fractionations of carbon and halogen elements in halogenated organic compounds during gas chromatography, providing insights crucial for improving compound-specific isotope analysis.

Contribution

It presents the first detailed measurement and analysis of concurrent C and Cl/Br isotope fractionations on GC using high-resolution mass spectrometry, revealing significant inverse fractionations and their correlations.

Findings

Significant inverse isotope fractionations observed for C and Cl/Br.

Correlations between C and Cl/Br isotope fractionations identified.

Mechanistic insights based on a modified two-film model and zero point energy theories.

Abstract

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.