Compound-Specific Chlorine Isotope Analysis of Organochlorine Pesticides by Gas Chromatography-Negative Chemical Ionization Mass Spectrometry

Abstract

Compound-specific stable chlorine isotope analysis (CSIA-Cl) is an important method for identifying sources of organochlorine contaminants and helping assess their quantification of transformation processes. However, the present CSIA-Cl is challenged by either redundant conversion pretreatment or complicated mathematical correction. To overcome the mentioned problems, a novel method has been developed for the CSIA-Cl of eight organochlorine pesticides using gas chromatography-negative chemical ionization mass spectrometry (GC-NCI-qMS) in this study. The instrument parameters, acquisition mode, and required injection amounts were optimized in terms of the precision of GC-NCI-qMS. An ionization energy of 90 eV and emission current of 90 μA were selected, and the precisions for eight organochlorine pesticides were in the range of 0.37‰–2.15‰ in single ion monitoring (SIM) mode when the injected amount was 0.50 mg L−1 (viz. 0.5 ng on column). Furthermore, when standards from Supelco and O2si were calibrated using standards from AccuStandard regarded as external isotope standard, chlorine isotope composition of α-hexachlorocyclohexane (α-HCH) and 2, 2-dichloro−1, 1-bis (4-chlorophenyl) ethylene (p, p′-DDE) in Supelco and O2si was confidently differentiated. The provenance identification method was validated by three organochlorine contaminated groundwater samples and showed a prospect in identifying the source of organochlorine pesticides.

Improving Separation Efficiency for Compound Specific Stable Chlorine Isotopic Analysis of Perchloroethylene

“…Nevertheless, the actual concentration was slightly lower than the theoretical value (Guo, 2020). The decrease in isotope ratios with different relative standard deviations at different concentrations veri ed that the highest precision for the chlorine isotope ratio could be achieved only for solutions of equal concentrations because of its concentration-dependent effect (Zhang, 2021). The optimal concentration used in this experiment was 0.002 µg/mL.…”

Stable Carbon Isotope Analysis of Hexachlorocyclohexanes by Liquid–Liquid Extraction Gas Chromatography Isotope Ratio Mass Spectrometry: Method Evaluation and Applications

“…In this study, the liquid-liquid extraction method was selected, which is an effective approach for simple experimental procedures, has good flexibility and is free of cross contamination. Until now, some studies have used CSIA and ESIA to study the degradation mechanism, source identification, and field analyses of HCHs (Table 1) [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26]. Ivdra et al [1] developed an extraction procedure and a clean-up method for measuring carbon isotope ratios for HCHs, DDT, and chlorinated metabolites in soil samples.…”