Chlorine Isotope Analysis For Organochloro Pesticides And The Environmental Significance

Organochloro Pesticides (OCPs)-a class of chlorinated organic compounds, once were used in agriculture and disease control. On May23,2001, more120countries and regions including China signed the Stockholm Convention on Persistent Organic Pollutants (POPs) to ban12sorts of POPs. In the notorious list of dirty dozen there were9OCPs or herbicides, i.e. DDT, Chlordane, mirex, aldrin, dieldrin, endrin, heptachlor, toxaphane; and the other3are technique chemicals (hexachlorobenzene, and PCBs) and dioxin and Furan as the by-products in industry or from combustion. In2009, α-,β-and γ-(Lindane) HCH were supplemented to the banning list; and Endosulfan too in2011. POPs are toxic to the ecology, long half-live in the environment, and stay as residues in the nature for long time and can be transported far away from sources. China has a long history of producing OCPs. Though the produce and use of OCPs were banned since1982, the heavy residues of the OCPs still in lots of the territory.The studies on the OCPs are still going on on the distribution, contamination, environmental behaviors, and fate of OCPs. And the molecular can be a a unit of environmental science studies. However, the environmental pollutions are from always multi-sources, the pollution pathway and the transform of the pollutants are complex. The traditional environmental chemical methods could hardly completely retrieve the chemical sources and environmental behaviors. Recently, the stable isotope analysis were more and more introduced into the field of environmental sciences, i.e. the apportionment, attenuation, and degradation efficiency of the pollutants. Especially the Compound Specific Isotope Analysis expanded the applications of traditional environmental organic chemistry.Chlorine, with an atomic number of17, has two stable isotopes,35Cl and37Cl. The abundance of these two isotopes vary between phases or compounds, and the variation is unique as fingerprints-isotope fingerprints. The chlorine is one of the most widely presented elements which are studied widely. Compared to carbon and hydrogen, the stable isotope analysis are lately applied into the environmental organic pollutions. Various pollutants and the studies purpose call for more powerful chlorine analysis techniques. To date, related isotope researches on organochloro pesticides were rarely reported, and there are many technical difficulties for the the stable chlorine isotope analysis for organochloro pesticides. The enrichment, separation, purification, chromatographic extraction may be required by the traditional chlorine isotope analysis method. The inconveniences of the pretreatment of the chlorine isotope methods make chlorine isotope analysis a difficult art. The recent online approach has been applied in a volatile chlorinated hydrocarbon, reducing the analysis of pre-treatment difficulties, to improve the method sensitive. Online methods such as GC-qMS analysis may be applied to the chlorine isotope analysis of organochloro pesticides. But there are still some technique problems to be solved and then the online CSIA-Cl (compound specific isotope analysis) could be a unique tool.This thesis mainly analyzed the feasibility for online instrument chlorine isotope analysis for organochloro pesticides, and tried analyzing chlorine isotopes of OCPs in environmental samples. The innovations of this study are systematical analysis of the possibility of chlorine isotope analysis of OCPs using GC-qMS; novel test of the feasibility of GC-MS/MS method for chlorine isotope analysis; and initial application of the GC-qMS method in chlorine isotope analysis of the OCPs in actual soil samples.This thesis based on the theoretical and experimental researches mainly focuses on the following issues:I. GC-qMS method for chlorine isotope analysis of OCPs and relevant structures in the congener molecules.The instrumental analysis of chlorine isotope may require different mass spectrometry signals based on specific apparatus or the targets. Different target ions with different mass to charge ratios may be required for further detection in the mass spectrometry. IRMS (stable isotope ratio mass spectrometry) method counts the CH3Cl+ions and the TIMS (thermal ionization mass spectrometry) method the CS2Cl-. Due to the differences of the instruments and analytes, the chlorine isotope signal expression is different for different mass spectrometry methods, and the calculation strategy of mass spectrometry may vary.37Cl/35Cl ratios are calculated from ions carrying37Cl and35Cl. Polychlorinated ions calculation should be corrected to the number of the chlorine nucleus of the target ion. And also the multi-fragment ion calculation may be performed after relevant ion masses are scanned in the mass spectrometer.To date, the online chlorine isotope analysis using GC-qMS is mainly dealing with light weighted volatile chlorinated hydrocarbons. There was only one case till now analyzed the Cl isotopes in DDT using GC-qMS, but only use one certain ion and large sample amount. The reason why it is hard to apply GC-qMS method for Cl isotope in DDTs is that the DDT fragments in the El source are much more complex than those of light weighted chlorinated hydrocarbons. The fragmentation pattern of OCPs in the ion source can be sorted from the spectral library where the composition and structure of the mass peak can be paired using a mass interpreter tool. Suitable ions for the GC-qMS isotope analysis method should be ions with cleared structure, with enough abundance, and also isotopologues.1. With mass spectral library tools including mass information of a number of indexed compounds and mass interpreter tool, OCPs compounds in the ion source fragmentation regularity are analyzed. For the El source mass spectrometry, Chlorine isotope analysis may be easily setup using the molecular ions of HCB and p, p’-DDE; the chlorinated aromatic fragments ions of p,p’-DDT, o,p’-DDT, p,p’-DDD (m/z235,237), and the unique structure of the chlorinated cyclopentene structures of chlordane, heptachlor, and endosulfan (m/z270,272).2. The results of chlorine isotope analysis for OCPs using GC-qMS can be affected by the following factors:the dwell time of the mass scan; and the concentrations of target compounds. Too low or too high amount of injection of the target compounds may yield unstable37Cl/35Cl ratio. The results shown that for certain ion from target compound, appropriate injection volume should be set to ensure reproducibility of the measured values chlorine isotope.3. An ion with specific structure or position in the molecule may be used for position-specific chlorine isotope analysis. The37Cl/35Cl ratio of fragments ions with m/z of235and237in DDT may stand for the chlorine isotope ratio of the chlorinated aromatic part of the DDT. The mass abundance of237/235can be high enough at a low sample amount and the results may be more stable than that calculated from the molecular ions.4. The abundance of main fragment ions containing chlorine from OCP molecule may vary in the El source, and thus the stability in chlorine isotope analysis for different fragment may be different at a set amount of OCPs sample. The equation using different fragment ions for chlorinated VOCs can hardly adapted for OCPs.5. Continuous days of multi-batch of sample analysis of the instrument were tested.4concentrations of standard material solution with5ng～100ng were injected at each batch and" repeated in3days. The experiment results show that the data of the chlorine isotope ratios of certain fragments in DDT were stable during the3days (Standard deviation of RCl:0.00042～0.00071, n=3; sample amount10ng～50ng).6. A DDT standard material, with its δ37Cl measured by IRMS, was tested in the GC-qMS method validation. For measuring the chlorine isotope ratios of the double benzene structures of DDT by scanning the m/z237/235ions, the best injection amount of DDT is tested. With50ng of DDT injected into the GC, the method accuracy is±.51‰; in a scale of50～100,±1.59‰. For measuring the chlorine isotope ratios of DDT by scanning the m/z354/352ions,300ng is a valid injection amount for DDT whiles the accuracy stay within±2.24%oⅡ. The feasibility study of GC-MS/MS with triple-quadrupole mass analyzer in the chlorine isotope analysis for OCPs.Gas chromatography-tandem mass spectrometry with the core part tandem mass spectrometry (or marked as MS/MS) is developed in the late1970s. Tandem mass spectrometry with triple quadrupole mass analyzer has two mass analyzers tracing the mass ions (i.e. precursor ions or product ions) and an part of collision-induced dissociation (CID) for yielding product ion. By pairing the precursor ion and the specific product, the structure information of the molecular ions is given and thus expand the detection mass range. To explore more possibilities of chlorine isotope analysis method of OCPs, in this thesis the feasibility of chlorine isotope analyzing using gas chromatography-triple quadrupole tandem mass spectrometer was discussed. 1. Standard solution with gradient concentrations of DDT’s two isomers was analyzed. In each single injection, the second-stage quadrupole (Q2) was set to pathway mode, the first quadrupole (Q1) and third quadrupole (Q3) were set SIM mode with the same MS settings. Experimental results show that under50ng-250ng injection volume, the abundance of each ion in the respective pole quadrupole analysis have a good linear relationship versus the injection volume, indicating sample amount in the range of50ng-250ng is still in the linearity scale of each mass analyzer.2. Two pairs of ions with m/z237/235and354/352of two isomers of DDT were analyzed for chlorine isotope calculation. In the range of50ng-250ng the mass abundance responded in a good linearity against the sample amount. However, in Q1and Q3there is a big difference in chlorine isotope calculation results, indicating chlorine isotope fractionation may occur. Therefore, if a mode with tandem mass spectrometry working, the chlorine isotope of a certain compound may be fractionated from Q1to Q3, and thus affect the accuracy of further measurement. Tandem Mass Spectrometry with triple-quadruple mass analyzer may be not so suitable for chlorine isotope analysis like GC-qMS for OCPs, whereas further study is needed.Ⅲ. The chlorine isotope analysis of OCPs in the environmental samples are of unique signification in environmental studies.In this thesis, chlorine isotope analysis of several environmental samples were carried out using GC-qMS method. Combined with the chlorine isotope analysis, the source apportionment and environmental behaviors of the pollutants in the study area were analyzed. The environmental meanings of the chlorine isotope was discussed.1. The position specific chlorine isotope information of DDT in several soil sample were analyzed using GC-qMS. Compared with the traditional chlorine isotope method, the GC-qMS method need only the pretreatment like that for environmental chemistry analysis. And this method requires sample2. To date, the mechanism study shows the chlorine isotopes on aromatic position of the DDT molecular are not effected in the main degradation routine of DDT, and therefore may be a chlorine isotope indictor in pollutant apportionment.3. The variation of chlorine isotope in different compound is mainly caused by the chlorine isotope fractionation during the producing process. The semi-volatile chlorinated organic compounds have a narrower range of chlorine and carbon isotope ratios than the volatile ones, and the chlorine isotope ratios of semi-volatile chlorinated compounds range wider than its carbon isotope ratios. These characteristics may be an unique indication in the source apportionment of the semi-volatile chlorinated compounds.4. The source information may be still blurred when applied an chlorine isotope apportionment. Therefore, the chlorine isotope analysis should be combined with the environmental analysis.More expectations than OCPs, the prospects of chlorine isotope analysis can be expected for the following aspects:1. OCPs were once long-time used, and different residues were found in farmland. In different locations, there were differences in content. In different depths of soil, the content of OCPs was also distinctive. In the environmental chemical analysis, the analysis of organic pollution often require "trace analysis". For the techniques of chlorine isotope analysis, the sensitivity and accuracy of the instruments and methods needs to be improved;2. The new online application isotope mass spectrometry method has expanded to other mass spectrometer, such as quadrupole mass spectrometry, mcICP-MS. It also broaden the object of the compounds of the chlorine isotope analysis, and reduced the difficulty of the analysis. However, the method accuracy was less than that of the traditional method, therefore more efforts should be input to improve the accuracy.3. The chlorine isotope ratios in different product batch or kinds of compounds can be isotopic fingerprints for pollution apportionments. And the multi-isotope analysis with chlorine isotope may be a trend in future studies.