Research And Application Of Dielectric Barrier Discharge Combined With Atomic Fluorescence Spectrometer In Heavy Metal Detection

Dielectric barrier discharge（DBD）,also known as silent discharge,is an effective way to generate micro-plasma at room temperature and pressure.DBD shows broad prospects of applications with good compatibility,including assist chemical vapor generation,solid ablation sampling,mass spectrometry ion sources,spectral excitation sources or atomizers.DBD has its unique advantages,especially for concentrate elements,and can combine with various types of detectors（AES,AAS,AFS）to detect trace or ultratrace elements,so as to help law enforcement personnel related to food security,public security,and market supervision to quickly,effectively and accurately screen for toxic and harmful elements in food and the environment.When DBD is used in atomic spectroscopy,it possess many unique features,for instance,instrument miniaturization,low consumption,and green development.The prospect of DBD is promising,and it is more awaiting its further commercialization.However,DBD suffers from various drawbacks,including narrow range of concentrate elements,little combination with other sampling techniques,and insufficient development of actual sample application methods.Meanwhile,it is still challenging to develop novel analytical model and explore the detection mechanism in depth.In this thesis,we are committed to develop the enrichment method of DBD,explore the combination strategy with other sampling methods,explore its mechanism,and establish the high-sensitivity detection of metal ions in food and environmental samples.In preface part,we provide a brief introduction to the concept and technology combination of DBD,as well as their recent progress in atomic spectrum analysis.Then,we conduct our research from the following four aspects:1.With lead as the model element,the HG-DBD-AFS system was established and evaluated by combining with the hydride generation（HG）sampling method,and the compatibility and robustness of DBD as an AFS atomizer and enrichment device were proved.A novel DBD reactor was utilized to in situ enrich and atomize lead in gas phase.The structure of DBD reactor was optimized to broaden the acidity window of plumbane generation from 1%to 3.5%,bringing better analytical stability and practicability deriving from hydride generation process.For the first time DBD proved effective in lead preconcentration and broadening the acidity window of plumbane generation.Pb can be trapped quantitatively（～100%）on the quartz surface of DBD tube under O₂-containing atmosphere and released（～100%）under H₂-containing atmosphere.The absolute detection limit（LOD）for Pb was 5 pg（injection volume=1.2 mL）,and the linear（R²>0.999）range was 0.05-100μg/L.The results were in good agreement with those of certified reference materials（CRMs）,and spiked recoveries for surface water samples were 99-104%with 2-8%RSD.By gas phase analyte enrichment,the proposed method reduced absolute LOD by 10 times.It was deduced that plumbane was changed to lead oxide species trapped on the quartz tube surface and then released,and transported in form of atoms to the detection zone.2.With selenium as the model element,the UVG-DBD-AFS system is established by combining with the ultraviolet vapor generation（UVG）sampling method,which expands the application of DBD and provides auxiliary material support for its subsequent development,application and mechanism research.UVG,as an environmental/user-friendly and effiffifficient sampling approach,was first combined with the gas phase enrichment of Se by DBD microplasma.Volatile Se species from UVG,being much more complicated than conventional hydrides,can be trapped quantitatively（～100%）on the quartz surface of DBD tube under O₂-containing atmosphere and released（～100%）under H₂-containing atmosphere.The absolute detection limit（LOD）for Se was 4 pg（injection volume=1.2 mL）,and the linear（R²>0.995）range was 0.05-50μg/L.The results were in good agreement with those of CRMs of water and soil samples,and spiked recoveries for real samples were 90-102%with 1-10%relative standard deviations（RSDs）.By gas phase analyte enrichment,the proposed method improved analytical sensitivity（peak height）by 16times.The mechanism was deduced that dominating Se CO species besides H₂Se generating from UVG were all trapped on the DBD quartz tube surface as Se O₂or selenite and then released/transported as atoms to the detection zone.The combination of UVG and DBD can facilitate the green uses,miniaturization,and portability revealing its promising potential in field elemental analysis.3.A sequential gas phase separation and enrichment technique for heavy metal was developed for precise and accurate determination of elemental concentration by DBD integrated hydride generation atomic fluorescence spectrometry（HG-in-situ DBD-AFS）.The technology is proposed as a novel and powerful analytical technique for the separation of arsenic and tin.The analytes were transformed into the volatile hydride form（Sn H₄,and As H₃）by on-line reaction with potassium tetrahydroborate（10 g/L KBH₄in 1.5 g/L KOH）in acidic medium（2%HCl）.The in-situ DBD apparatus was first employed to separate arsenic and tin by concentrating them due to different character and function for each element and different conditions of releasing,as well to enhance the analytical sensitivity of HG-AFS.And from the perspective of principle,the reason for the separation of elements in DBD is explained.Followed by trapping with 1.8 A at 45 mL/min of air carrier gas,and 190 s Ar gas sweeping,As was released with 1.4 A at 120 mL/min H₂,Sn was released with 1.8 A at 180 mL/min H₂to the AFS for measurement.The effect of the main experimental variables,such as acidic media,potassium tetraborohydrate concentration,Ar/Air/H₂flow rate on the analytical signals of the arsenic were studied.Under the optimal conditions,a good linearity R²=0.995 ranging from 0.5 to 50μg/L.The spiked recoveries for real aqueous samples were in ranged from 98%to 104%,with the detection limits（3σ）of7 ng/L,9 ng/L for arsenic and tin,and the measurements were in accordance with the CRMs value.Further,the potential of the proposed technique is extremely suitable to separation of arsenic and tin and ultratrace arsenic determination.4.To develop the application method of DBD enrichment technology in actual samples,three application systems were established to detect toxic and harmful elements in actual samples.（1）SLS-HG-in-situ DBD-AFS system.The slurry sampling hydride generation（SLS-HG）system was first coupled with in situ dielectric barrier discharge atomic fluorescence spectrometry（DBD-AFS）for arsenic analysis in biological samples based on the gas phase enrichment（GPE）principle.The prepared sample suspension is introduced into the HG-DBD-AFS,and the discharge and working gas conditions of the in-situ DBD are optimized at the same time.Under optimal conditions,8 pg or14 pg detection limits（2 mL sampling）for the microbiological or hair samples were achieved without extra pre-concentration,respectively.Compared with the traditional digestion pretreatment combined with atomic spectroscopy,this method has advantages in simplicity,speed,low cost,greenness and safety.The proposed SLS-HG-in-situ DBD-AFS method is extremely suitable for ultratrace arsenic determination in biological samples to protect human health and environmental safety.（2）DL-HG-in-situ DBD-AFS system.A novel direct sampling（DS-HG）system consisting of an enlarged gas liquid separator（GLS）coupled with a foam breaker was firstly utilized for the in-situ DBD-AFS.After direct dilution using 5%HCl（v:v）,a prepared blood sample was introduced into the DS-HG with a UV digestion unit.Herein,the newly designed DS-HG is capable of effectively eliminating foam generation deriving from protein in blood sample.Under the optimized conditions,the method detection limit（LOD）was 7 pg arsenic（0.14 ng/mL）and 8 pg lead（4 ng/L）.Furthermore,the whole analytical time can be controlled within 15 min including sample dilution.As a matter of fact,this method has excellent sensitivity,digestion-free,fast and simple operation.Thus,the recommended DS-HG-in-situ DBD-AFS are suitable to the fast analysis of ultratrace arsenic and lead in blood samples to protect human’s health.（3）HG-in-situ DBD-AFS system.An in-situ DBD employed as a concentration device was coupled with HG-AFS for the determination of antimony（Sb）that migrated from plastic to bottle water.The relevant parameters of DBD trap and release of antimony were studied in detail,the detection of limit（LOD）was 9 pg or 5pg/mL,which has good detection ability.In comparison,the HG-in-situ DBD-AFS method is capable to increase the analytical sensitivity using the peak height by 7-fold compared to standard HG-AFS.In addition,the influence of storage temperature and time on the migration of Sb in plastic bottles was also studied.The results show that the established method is suitable for the detection of ultra-trace Sb that has migrated to bottled water,and based on this,it proves that long-term high temperature storage will increase the migration of Sb in plastic bottles to protect human health.