A New Method for the Determination of Polybrominated Diphenyl Ethers by Gas Chromatography-Isotope Dilution Inductively Coupled Plasma Mass Spectrometry

Author:Zhang Chi

Supervisor:chen yan ling zhang qing he


Degree Year:2019





Polybrominated diphenyl ethers(PBDEs)are a common class of brominated flame retardants that were promoted in the late 1970s by replacing more toxic polychlorinated biphenyls(PCBs)and polybrominated biphenyls(PBB).Currently,such compounds have become a class of persistent organic pollutants(POPs)that are ubiquitous in the global environment.Studies have shown that PBDEs have the potential toxicity of interfering with thyroxine,affecting endocrine,causing neurobehavioral defects.In addition,since PBDEs are lipophilic,they are easily enriched in foods with high lipid content through food chains to achieve higher levels.A large number of statistics show that food is the main way for humans to consume PBDEs,so the analytical techniques of PBDEs in foods have attracted widespread attention.Due to the complex composition of the food matrix,the concentration levels of PBDEs in food cover 9 orders of magnitude,in addition,there are 209 congeners of PBDEs,the analysis of PBDEs often requires high selectivity and high sensitivity detection techniques.At present,the analytical techniques of PBDEs are mainly GC-MS and HPLC-MS.Considering the vapor pressure and polarity of PBDEs,gas chromatography-mass spectrometry is a detection technique that is more commonly used to analyze PBDEs.Despite extensive research on methods for the detection of PBDEs by GC-MS at home and abroad,there are still some difficulties in the analysis of PBDEs in foods:conventional electro-collision(EI)ionization mass spectrometry or electron capture detectors have poor sensitivity to meet the demand for ultra-trace PBDEs in foods;the mass spectrometry of most ion sources requires additional optimization for the fragmentation of each analyte.For a wide variety of PBDEs(there are 209 congeners in theory),it takes a lot of time to optimize the corresponding fragment ions for each type of instrument.;Because of the differences in the response of different PBDEs congeners in conventional thermo-ionization mass spectrometry,it is necessary to quantify each congener using the corresponding specificity standard,resulting in the analysis cost is too high or impossible.In this context,inductively coupled plasma mass spectrometry(ICP-MS)combine with gas chromatography has been developed in recent years.Although ICP-MS is generally used for inorganic analysis,it has good sensitivity and selectivity for bromine in PBDEs.Therefore,it can be used for the detection of organic PBDEs by combining with GC.The ICP ionization source is more sensitive to PBDEs than the EI source and CI source.Moreover,there is no need to additionally optimize the ion fragments of different types of PBDEs when detecting,which greatly improves the analysis efficiency.Finally,since the response of the analytes have compound-independent properties when analyzed using ICP-MS,multiple types of PBDEs can be quantified using fewer types of standards,this is very significant for PBDE analysis where the specificity standards are expensive and difficult to obtain.Although many studies have been carried out internationally for the analysis of PBDEs by GC-ICP-MS,there are still some problems and gaps:1)Although the response of ICP-MS has characteristics unrelated to the structure of the compound,after the combination with gas chromatography,the difference in chromatographic conditions,matrix components,etc.may affect the response,resulting in the response of the compound related to the structure,which requires the compound independent calibration technique to be quantitative evaluation,and the mechanism of the influence of gas chromatography conditions on the analyte response has not been studied.2)Decabromodiphenyl ether is the highest concentration of PBDEs in the environment,but its sensitivity to the determination of decabromodiphenyl ether by GC-MS is generally low due to its ease of decomposition at high temperatures.Conventional EI or CI source mass spectrometry detectors are difficult to quantify the rate of decomposition of decabromodiphenyl ether because the response of the decomposition products is related to the structure of the compound.Therefore,the existing research lacks the decomposition of decabromodiphenyl ether in gas chromatography.3)GC-Isotope Dilution-ICP-MS method is a quantitative method that can effectively overcome the matrix effect on the analysis results,but the spectral interference of ICP-MS may cause the bromide ions and polyatomic ions to overlap,resulting in the determination of the isotope ratio is deviation from the actual value,which affects the accuracy of the isotope dilution measurement.However,the source of spectral interference in GC-ICP-MS and the possible impact on the determination of isotope ratios lack systematic research.In this paper,the above problems are studied:A rapid and efficient QuEChERS pretreatment method for fish samples was established.The PBDEs in the samples were detected by GC-Isotopic dilution-ICP-MS.The analytical performance of the method was evaluated and verified using standard reference materials.The response of the series of PBDEs on GC-ICP-MS under various conditions was investigated.It was confirmed the feasibility of the Compound Independent Calibration(CIC)method for the measurement of PBDEs.The method is very good for improving the detection efficiency and reducing the detection cost.An innovative analytical method is proposed,which uses gas chromatography inductively coupled plasma triple quadrupole mass spectrometry(GC-ICP-MS/MS).The effect of spectral interference on the determination of PBDEs was determined by measuring BrO+in mass-shift mode.The research content can be divided into the following aspects:1.Aiming at the problems of the existing pretreatment methods for processing high lipid content samples which is too complicated,the purification effect is not ideal,and the flux is low,a method based on QuEChERs(Quick,Easy,Cheap,Effective,Rugged,Safe)is established to pretreatment of PBDEs in fish samples effectively.Combined with the improved secondary dispersion solid-phase microextraction purification method,macromolecular co-elution interferences in most complex samples can be removed.The results showed that the matrix effects of the seven analytes decreased significantly,ranging from-29.4-0.8%,which was better than the literature range(-62%-52%).A GC-isotope dilution-ICP-MS method was established to determine six priority PBDEs in NIST fish matrix reference material(SRM 1947).The recoveries range were 85.9%-118.0%.The detection limits and quantitation limits of the method were respectively 0.03-0.56 ng g-1 and 0.10-1.86 ng g-1.2.The effects of chromatographic conditions on the elemental response of GC-ICP-MS were investigated in depth,and the feasibility of using CIC method for the determination of polybrominated diphenyl ethers(PBDEs)by GC-ICP-MS was evaluated.The effects of sample introduction conditions,the flow rate of the carrier gas,splitless delay time and the matrix of the complex sample on the response of 11 PBDEs compounds were explored.When pulsed splitless injection was used,the transmission efficiency of analytes from the inlet to the column can speed up with increasing injection temperature and pulse pressure,the elemental response of bromine of each analyte becomes closer.Under optimized chromatographic conditions,the response is independent of the compound can be found from the slope of the pure solution standard from tri-to hepta-brominated compounds(BDE 28 as reference)ranged from 0.968 to1.001(R2>0.998).The degradation of BDE 209 in the GC-ICP/MS system was estimated by the CIC method to be 18.7%.During the determination of fish tissue sample,big difference of the elemental response ratio(BDE 28 as reference)was obtained a range from 0.678 to 0.976.However,a similar elemental response was observed among isomers range from 0.990 to 1.056.This may mean that the isomers can be calibrated to each other in a complex matrix sample.The CIC method was validated by determination 3 PBDEs in NIST SRM 1947 frozen fish tissue certified reference materials using isomers as reference compounds.The recoveries of BDE 49and BDE 66 were 105.7%and 88.1%by using BDE 47 as calibrants,and that of BDE155 was 108.8%by using BDE 154 as calibrant.The results of the determination confirm the accuracy of the proposed method.3.Gas chromatography-inductively coupled plasma triple quadrupole mass spectrometry(GC-ICP-MS/MS)operated in N2O reaction mode(Mass-Shift Mode)was established for the analysis of six priority PBDEs(BDE 28,BDE 47,BDE 99,BDE100,BDE 153 and BDE 154)in fish samples.The spectral interference on the determination of PBDEs was eliminated by measuring the product ion(BrO+)instead of traditional method measuring of Br+.Comparing the signal intensities of the three reaction gases(O2,H2,N2O),the highest sensitivity was found using N2O as the reaction gas.The results showed that the bromine is an element suffers from strong spectral overlap in ICP,mainly from Ar-based polyatomic interferences.Spectral interference was assessed by measuring the bromine isotope ratio of 81Br+and 79Br+of the six priority PBDEs in the He collision mode and N2O reaction mode,respectively.In the conventional He collision mode,the relative isotope ratio(the measured isotope ratio to the natural isotope ratio)of analytes was range from 0.955 to 0.965,which proves that the collision gas cannot completely eliminate the spectral interference,resulting in a low isotope ratio of all analytes.In the N2O reaction mode,the relative isotope ratio was range from 0.991 to 1.004,demonstrating that spectral interference can be fully eliminated.To verify this conclusion,six priority PBDEs were determined in the NIST reference materials SRM 1947(frozen fish tissue homogenate)was analyzed by species-specific isotope dilution.There was no significant statistical difference between the measured value and the certified value with recoveries ranged from 95%to 114%.The detection limits ranged from 0.03 to 0.09 ng g-1 with a relative standard deviation lower than 3%.The analytical method was successfully used to determine the content of PBDE in marine fish samples.