Spontaneous Monolayer Dispersion Theory For Determination Of Cadmium By Solid Sampling Electrothermal Vaporization

Cadmium（Cd）is a recognized hazardous heavy metal element that poses a serious hazard to human health,and it is also a heavy metal element that has attracted much attention in current food and environmental safety.At present,the detection of Cd mainly adopts the liquid sampling method and combines the spectrometric methods.Other liquid sampling methods require complicated and time-consuming sample pretreatment,mostly microwave digestion and wet digestion,etc.The purpose is to remove the sample organics,etc.to eliminate the interference of the matrix on the detection process,and it is difficult to achieve rapid detection of heavy metals.The use of solid sampling technology,there is no digestion process,with simple environmental protection,high efficiency,etc.,can achieve rapid detection of samples.However,the matrix interference problem has limited the rapid development of solid sampling techniques.In this work,on the basis of the previous studies,the spontaneous monolayer dispersion theory which was widely used in the catalyst field to study the Cd in the SS-EVT-AFS method,and established the spontaneous monolayer dispersion theory for SS-ETV-AFS determination Cd.The method realizes the elimination of the interference of the rice matrix on the detection and solid dilution of the Cd high concentration samples.This thesis mainly achieved the following research progress:1.Spontaneous monolayer dispersion theory was used to determine the cadmium by solid sampling atomic fluorescence spectrometry.The preliminary mechanism study was carried out.The Cd standard solution and the dispersion carrier were pretreated,and the Cd was uniformly dispersed on the surface of the dispersion carrier by high temperature conditions,and the Cd was measured by the SS-ETV-AFS method.The effects of experimental conditions such as carrier gas flow rate,dispersion thermodynamics（ashing temperature）,dispersion kinetics（ashing time）,and evaporation power on the detection of Cd by this method were investigated.The interference factors of some common inorganic elements were investigated and the existence of spontaneous monolayer dispersion of Cd on the surface of Al₂O₃ was verified by secondary ion mass spectrometry（SIMS）test.It was verified that Cd can disperse on the surface of the carrier by the method originally developed in this study.2.A method for the determination of Cd in rice by solid sample sampling atomic fluorescence spectrometry was established.Combining spontaneous monolayer dispersion theory with SS-ETV-AFS method,the detection and analysis of Cd in rice was realized.The experimental conditions were optimized.The optimized experimental conditions were:carrier gas flow rate,600 m L/min;thermodynamic conditions（ashing temperature）,700°C;kinetic conditions（ashing time）,40 min;evaporation power,120 W.The detection limit of the method was 0.3 pg,and the recovery was in the range of 88%¹10.3%（n=3）.RSD was 2.9%for multiple determinations and the stability was good.The method realizes matrix replacement and adopts solution matching,eliminates the influence of complex matrix interference in rice on the detection of Cd elements,and the results of the detection of Cd in rice samples were satisfactory.3.A method for the determination of Cd in plastic by solid sample injection atomic fluorescence spectrometry was established.Taking the analysis of reference materials for cadmium,chromium,mercury,and lead in polypropylene as an example,the spontaneous single-layer theory combined with SS-ETV-AFS method has enabled the detection of high concentrations of Cd in plastic samples,realizing solid dilution for high-concentration solid samples.The experimental conditions were optimized.The optimized experimental conditions were:carrier gas flow rate,600 m L/min;thermodynamic conditions（ashing temperature）,600°C;kinetic conditions（ashing time）,30 min;evaporation power,100 W.The detection limit of the method was 0.8pg.The recoveries were in the range of 85.7%to 110%（n=3）.RSD was 6.6%for multiple determinations with good stability.The method was applied to the determination of Cd in plastic samples with high Cd concentration,and the results were satisfactory.