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

Jing Zhang,Jianye Gui,Xiaoya Li,Guochen Qi,Shenghua Liu,Ricardo Jorgensen Cassella

doi:10.1155/2021/8874679

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.

Highlights

Various chlorinated organic compounds are widely used in many industries, while most of them have shown strong toxicity and persistence [1], and are found throughout the environment [2, 3]
Shouakar-Stash et al [18] first established an online method without a conversion process for the compound-specific stable chlorine isotope analysis (CSIA-Cl) of chlorinated alkene using gas chromatography coupled with continuous flow isotope ratio mass spectrometry (GC-CFIRMS), determining the lower limits of quantification (LOQ) and eliminating offline separation
Using electron ionization (EI), α-HCH produced weak molecular ion peaks and common fragments comprising a series of ions losing Cl and HCl (Figure 2(a))

Summary

Introduction

Various chlorinated organic compounds are widely used in many industries, while most of them have shown strong toxicity and persistence [1], and are found throughout the environment [2, 3]. Compound-specific stable chlorine isotope analysis (CSIA-Cl) has been developed as an effective tool to identify sources of chlorinated organic compounds and assess their biodegradation processes and abiotic transformation [4,5,6,7,8,9,10,11,12]. Shouakar-Stash et al [18] first established an online method without a conversion process for the CSIA-Cl of chlorinated alkene using gas chromatography coupled with continuous flow isotope ratio mass spectrometry (GC-CFIRMS), determining the lower limits of quantification (LOQ) and eliminating offline separation. Journal of Analytical Methods in Chemistry method for the CSIA-Cl of tetrachloroethene (PCE) and trichloroethene (TCE) by direct injection using a standard GC-qMS system This method did not involve offline sample preparation, a set of mathematical equations were still required to calculate the chlorine isotope ratios. Organochlorine-contaminated groundwater samples were analyzed by this novel CSIA-Cl method to validate the provenance identification by δ37Cl′ values

Experimental

Results and Discussion

Conclusions