Based On Solid Sampling Gas Phase Enrichment Of Heavy Metal Determination Research And Application

In recent years,with the rapid industrialization,urbanization and intensified agriculture in China,heavy metals have been the main contaminant in the environment and agri-foods.Heavy metals have threatened food safety and may lead to human health risks including neurotoxicity,teratogenicity,cancers.Hence,to protect grain safety and human health,fast and precise monitoring heavy metal is of great significance.However,conventional atomic spectrometric techniques typically require complex sample digestion,which are time-consuming,costly,use toxic reagents and suffer possible contamination,resulting in failure in fast and field detection.In addition,X-ray fluorescence（XRF）spectrometry and laser-induced breakdown spectroscopy（LIBS）are suitable for portable,rapid and multi-element analysis,but are limited by their inadequate limits of detection（LODs）at the mg/kg level and difficulty in accurate detection of trace Hg and Cd for agricultural products.In this study,the different instruments with gas phase enrichment（GPE）devices based on the direct solid sampling electrothermal vaporization（ETV）were constructed for the rapid determination of Hg and Cd in soils and grain;otherwise,a trapping elution system was designed,which combined colorimetric sensor to detect Cd.The main research contents and results of this work are as follows.A novel enrichment material and device based on the thermal principle was explored,and an MCH-Pt/Ni-AFS device was constructed.A novel Pt/Ni trap based on platinizing the foamed nickel was firstly fabricated to trap Hg and Cd simultaneously,and combined with a metal-ceramic heater（MCH）and an atomic fluorescence spectrometry（AFS）for the MCH-Pt/Ni-AFS system.Thus,an MCH-Pt/Ni-AFS method was established and applied for the fast detection of Hg and Cd in soils.Under the optimal conditions,the limits of detection（LODs）of Hg and Cd were 8 pg and 0.7 pg,and the RSDs of repeated measurements of soil were 12%and 8%,respectively.The results for real samples were consistent with the standard method（p>0.05）and the analysis time was<5 min,indicating favorable analytical sensitivity,precision and accuracy.It was proved that trapped and released Hg and Cd by Pt/Ni trap are atomic species using X-ray photoelectron spectroscopy（XPS）and other approaches;specially,the effective co-trapping of Hg and Cd might be due to forming alloys of Hg+Pt and Cd+Ni on the Pt/Ni trap.A portable Hg-Cd analyzer was constructed with an on-line catalytic pyrolysis furnace（CPF）,a composite Pt/Ni trap and a miniature atomic absorption spectrometry（AAS）.The CPF and composite Pt/Ni trap were combined to eliminate grain matrix interference.A miniature AAS with a folded light path to enhance the sensitivity was newly designed.And an MCH-CPF-Pt/Ni-AAS method was proposed for Hg and Cd analysis in solid grains.Under optimal conditions,the LODs of Hg and Cd were 21 pg and 6pg;the RSDs were less than 12%using grain,respectively.The results for real samples were consistent with the standard method（p>0.05）and the analysis time was<5 min,demonstrating the favorable analytical accuracy and precision.this newly designed Hg-Cd analyzer size and power consumption are<14 kg and 270 W,proved to be simplicity,portability,and robustness,is thus suitable to fast monitor the Hg and Cd contamination in the field and to protect grain and food safety.A dielectric barrier discharge（DBD）trap based on the microplasma principle to trap Cd was developed,which followed the ETV,and an ETV-DBD-AFS method was established to directly detect Cd in soils.The DBD enrichment system was explored,using ETV and AFS as the sample introduction and detector.To eliminate the grain matrix interference,the on-line DBD digestion was utilized to couple with the sample ashing.Under the optimal conditions,the LOD of Cd was 16 pg,and the RSD of multiple determinations for soil was less than 8%,and the analysis time was less than 7 min.The detection results of soil samples were consistent with standard methods（p>0.05）,demonstrating that the established ETV-DBD-AFS method can be applied for accurately determine Cd in soil sensitively and accurately.An ETV-DBD-TMT-Au NPs colorimetric detection system was constructed to visualize the detection of Cd²⁺after the solid sampling for soils.The transport efficiency of Cd after electrothermal vaporization were investigated,and the ETV-DBD trapping and elution system for Cd was established.The effect of transport conditions on the transport efficiency of Cd after electrothermal evaporation was investigated;the structure of ETV-DBD was optimized to integrate solid sampling,heated transportation,gas phase enrichment and on-line elution,achieving 95%absolute Cd trapping and elution efficiency.A TMT-Au NPs colorimetric system for Cd was explored to achieve the rapid determination of Cd²⁺,the LOD was2.5μg/L,the RSD was less than 5%.The ETV-DBD-TMT-Au NPs colorimetric detection system for the determination of Cd in solid soil was developed coupled with the ETV-DBD elution device and TMT-Au NPs colorimetric system.Under the optimal conditions,the LOD of ETV-DBD-TMT-Au NPs was 0.14mg/kg,the detection results of soil samples were consistent with standard methods（p>0.05）,indicating that the proposed method has a good analytical performance and stability,which could be used for the colorimetric detection of Cd in soil.