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Abstract
A novel approach to compound-specific stable chlorine isotope analysis is presented to overcome many of the major drawbacks of existing methods. Contemporary methods often require either several laborious off-line procedures prior to isotope analysis or complicated mathematical data calculations and evaluation schemes to derive the chlorine isotope ratios from the mass spectra. In contrast to previous methods, our on-line setup was based on the use of gas chromatography-negative chemical ionization mass spectrometry. The ion traces of 35Cl−(m/z 35) and 37Cl−(m/z 37) were recorded to directly determine the isotopic ratios of chlorine. The chlorine fragments were obtained from each specific chlorinated compound using the appropriate energy and an optimized acquisition mode, and the method completely avoided isobaric interferences. The principle and the mechanism of this approach were presented and explained using trichloroethene. Optimization of the gas chromatography-negative chemical ionization mass spectrometry parameters and method validation were achieved using chlorinated alkenes, chlorinated benzenes, and organochlorine pesticides. The sensitivity of the method over previous methods was significantly improved, and the ultra-trace injection amounts of 0.4–473.5 pmol resulted in standard deviations (1σ) ranging from 0.55‰–2.15‰. The present study suggested that the gas chromatography-negative chemical ionization mass spectrometry method offered an innovative approach to compound-specific chlorine isotope analysis, and it could facilitate the application of compound-specific stable chlorine isotope analysis in environmental fields.
ACKNOWLEDGMENTS
The authors gratefully acknowledge Professor Jixiang Qi and Zhaoji Zhang for their support of this research.