Research On Optical Emission Spectrometry Coupled With Dielectric Barrier Discharge Reactor Based On Gas Phase Enrichment And Its Application

Over the years,with the rapid development of industry,agriculture and other social economy in China,environment pollution is increasingly aggravated.Among various environment pollution problems,heavy metals/metalloids pollution has been regarded as one of the most serious problems.Heavy metals/metalloids can accumulate in the food chain and thereby cause a potential risk for human health.Hence,it is crucial to monitor levels of heavy metals/metalloids in environmental samples.However,conventional atomic spectrometric methods such as atomic fluorescence spectrometry(AFS),atomic absorption spectrometry(AAS),inductively coupled plasma optical emission spectrometry(ICP-OES),microwave induced plasma optical emission spectrometry(MIP-OES)etc.,are not suitable for field analysis of heavy metals/metalloids due to their large size,high power consumption and high cost.Miniature microplasma-based OES offers low power consumption,small size and low cost,while its detection limit is poorer than that of conventional atomic spectrometry.Preconcentration methods have been proved to be an effective and available method to improve detection limits.Especially,dielectric barrier discharge reactor(DBDR)developed in recent years can preconcentrate elements with low power consumption,and do not need any regents,thus demonstrating great potential to be utilized as preconcentration device in field analysis.In addition,the core component of DBDR is dielectric barrier discharge(DBD)which is a kind of microplasma.Hence,DBDR has the potential not only as preconcentration device but also as excitation source of OES.In this work,a portable DBDR-OES is firstly developed by utilizing DBDR as an excitation source and a preconcentration device of OES simultaneously,which has advantages of small size,low power consumption,low cost and low detection limit.The research work is carried out from the following four aspects:1.Research and development of DBDR-OES instrumentIn this work,DBDR-OES instrument is developed by utilizing DBDR as preconcentration device and excitation source simultaneously.According to the principles of OES,sample introduction and DBDR preconcentration,the whole system structure of DBDR-OES is divided into four parts:sample introduction system,DBDR system,spectrum detection system,and measurement and control system.The four subsystems are designed and developed,respectively.The sample introduction system consists of liquid sample introduction system,hydride generation(HG)system and solid reagent automatic placement system.The sample can be introduced into DBDR-OES by combining liquid sample introduction system with HG system.Solid reagent automatic placement system can automatically mix the solid reagent used for HG with sample solution,so as to automate the sample analytical process;DBDR system consists of a gas line system for switching the gas type entering DBD and a DBD excitation source system for preconcentration and excitation of analytes;A USB2000+fiber spectrometer(Ocean Optics)with small size and low cost advantages is selected as the spectrum detection system of DBDR-OES.Moreover,the preconcentration of DBDR can compensate for the inferior sensitivity of USB2000+.Finally,the whole DBDR-OES instrument is obtained by integrating all subsystem.The whole volume of the integrated instrument is 0.6 m×0.5 m×0.3 m,weight is 15 kg and power consumption is less than 60 W,which meet the demands of field analysis including small size,light weight,and low power consumption.2.Analytical method research and software development of DBDR-OESTo improve the analytical performance,data processing algorithms of DBDR-OES are studied.In analyte release and excitation procedure,mixture gas of H₂/Ar is used as discharge gas,which will cause a higher baseline due to H₂ excitation.Since the fluctuation of baseline will severely compromise reproducibility of measurement,an iteratively modified moving average algorithm is employed for the background correction.In addition,since the release of the trapped analyte takes a certain amount of time,the spectrum of DBDR-OES is a group of 3-dimensional data involving time,wavelength and intensity.Based on this characteristic,a time window adaptive peak volume algorithm in which signals are calculated based on time,wavelength and intensity is proposed for quantitative analysis.Comparing to the commonly used calculation methods such as peak height and peak area in OES,the proposed peak volume algorithm extends the linear range from 1-20?g L^-1 to 1-200?g L^-1,and improves the sensitivity from 502 L?g^-1 to 32786 L?g^-1,and improves the precision from 4.5%to 2.8%.In addition,to process,store and display the spectral data,an analytical testing software was developed.Taking arsenic as an example,the analytical performance of DBDR-OES is evaluated.The detection limit(LOD)of As is 0.2?g L^-1,and the relative standard deviation(RSD)is 2.8%.The linear correlation coefficient(R²)of calibration curve is better than 0.995 in the concentration range of1-200?g L^-1.By an application to seaweed samples,the instruments is proved to have good accuracy.3.Application of DBDR-OES in analysis of environmental water samplesIn this work,field analytical methods of solid acid HG-DBDR-OES were developed for determination of As,Sb,and Pb in environmental water.HG is utilized for sample introduction,in which acid and reductant play crucial roles.The most frequently used acid in HG is HCl.However,the portability of HCl is an obstacle for field analysis due to the transportation and security.To solve this problem,solid acid is selected to replace HCl.The hydride formation of As and Sb belongs to strong acid system in HG.Therefore,solid sulfamic acid is firstly selected for co-generation of As and Sb hydrides in this work.In addition,multi-elemental preconcentration of As and Sb is achieved for the first time by DBDR.Under optimal conditions,the LODs are0.5?g L^-1 for As and 0.2?g L^-1for Sb,respectively,which are improved by about 1order of magnitude comparing with those obtained by other microplasma-based OES techniques.The linear concentration ranges are 2-200?g L^-1 for As and 1-200?g L^-1for Sb.The RSDs are 2.8%for As and 2.9%for Sb,respectively.The determined concentrations of certified reference materials(CRMs)by solid sulfamic acid HG-DBDR-OES are in good agreement with their certified values and the recoveries for As and Sb are 87-97%for real environmental water samples,demonstrating the good accuracy of the solid acid HG-DBDR-OES.Since the hydride formation of Pb belongs to weak acid system in HG,solid citric acid is utilized to replace HCl for the generation of PH₄ in this work.Under optimal conditions,the LOD is 0.12?g L^-1 for Pb,which is improved by about 1order of magnitude comparing with those obtained by other microplasma-based OES techniques.The linear concentration range is 1-100?g L^-1 and RSD is 3%.The determined concentrations of CRMs by solid acid HG-DBDR-OES are in good agreement with their certified values and the recoveries for Pb are 94-111%for real environmental water samples,demonstrating the good accuracy of the solid citric acid HG-DBDR-OES.4.To develop application methods of DBDR-OES in sample containing complex matrix,two application systems are established for the determination of As in soil and olive oil,respectively.(1)Ultrasonic assisted slurry sampling(SLS)DBDR-OES method.The ultrasonic assisted SLS procedure is first coupled with DBDR-OES to provide a simple and fast method for the determination of arsenic in soil.Under optimal conditions,a method detection limit of 0.18 mg kg^-1 is achieved for As in soil(250times dilution).The RSD for the soil slurries is 3.4%(n=11).Three soil CRMs and two real soil samples are analyzed to validate the method's accuracy.Comparing with conventional microwave digestion,wet digestion etc.,ultrasonic assisted SLS has advantages of simpler procedure and lower power consumption.DBDR-OES provides advantages of small size and low power consumption.Therefore,the combination of ultrasonic SLS procedure and DBDR-OES shows great potential in field analysis of soil.(2)Ultraviolet digestion-extraction induced by emulsion-breaking(EIEB)-DBDR-OES method.In this work,ultraviolet digestion-EIEB is coupled with DBDR-OES to determine the total arsenic level in olive oil.Under optimal condition,a method detection limit of 2?g L^-1 is achieved for As in olive oil(10 times dilution).The RSD for the olive oil is 4.3%(n=11).The accuracy of ultraviolet digestion EIEB-DBDR-OES method for the determination of total arsenic contents are verified by adding inorganic and organic arsenic to olive oil samples,respectively.The ultraviolet digestion EIEB-DBDR-OES provides advantages of simple procedure and low power consumption,thus showing great potential in field analysis of olive oil.