| In recent years,under the trend of miniaturization and multiple functions,the application research of microplasma technology in analytical science has become a hot topic.Atmospheric Pressure Glow Discharge（APGD）is a microplasma technology that develops rapidly.Compared with conventional elemental analysis methods such as Inductively Coupled Plasma-Optical Emission Spectrometry（ICP-OES）/Inductively Coupled Plasma-Mass Spectrometry（ICP-MS）,it has the advantages of simple structure,low power consumption,low cost,etc.Therefore,it has received more and more attention in the field of atomic spectroscopy.When APGD is used as a spectral excitation source and introduced samples by pneumatic nebulization,the microplasma is susceptible to water vapor,resulting in a decrease in stability and excitation capability,and caused a weak detection limit for certain elements with higher excitation energies.Based on the APGD deficiency mentioned above,this paper introduces electrothermal vaporization sampling technology（ETV）.ETV is a method in which a sample is loaded in an evaporator made of a high temperature resistant material such as metal or graphite,and the solvent and the substrate are removed by current heating and turn into dry aerosol,which subsequently is transferred into the plasma by the carrier gas.By this way,ETV can solve a series of interference problems caused by moisture in APGD.This topic has carried out the following work around ETV injection technology and APGD-AES instrument:Using tungsten coil as electrothermal vaporization material,a tungsten coil electrothermal vaporization-atmospheric glow discharge atomic emission spectrometry（W-coil ETV-APGD-AES）analyzer was designed.It mainly consists four parts:ETV sampling system,APGD excitation system,the detection system and the power control system.The whole device has a simple structure,high integration and good stability.Pipette 10μL of the solution sample on the W-coil,control the ETV to complete the drying,matrix removal,vaporization process of the sample by heating program.The resulting analyte-containing dry aerosol is introduced into the APGD by a carrier gas to further excite the characteristic atomic emission spectrum,which is collected by the detection system and analyzed.Studying the discharge situation when using different medium gases（carrier gas）.By incorporating 3%concentration of hydrogen（H2）in helium（He）to eliminate the spectral interference caused by air impurities,and ensure the instrument can be used in real sample analysis and the stability was well.The main experimental parameters of the analyzer were optimized,including discharge current,discharge spacing,heating program,and carrier gas flow rate.Under the optimal conditions,the detection limit of Cd was 0.7μg·L-1,and the absolute detection limit was0.007 ng.The correlation coefficient was 0.9969 which was within the linear range of 5-100μg·L-1,and the relative standard deviation（RSD）of 5μg·L-1 Cd was 1.65%（n=11）.The standard addition method is used to compensate the matrix interference caused by alkali metal and alkaline earth metal in the sample,and is applied to the analysis of environmental standard materials and water samples.The results agree well with the reference values of standard materials and ICP-OES.The analyzer couples the APGD microplasma as a spectral excitation source and ETV sampling technology,which fully exploits the advantages of APGD and ETV,such as stability,high elemental selectivity,high injection efficiency,and can improve the excitation ability of the excitation source.Improves the detection ability and stability of APGD for heavy metal element Cd.The detection limit was improved by about an order of magnitude compared to the analytical method of introducing liquid samples directly into APGD.Compared with mature laboratory instruments such as ICP-OES or ICP-MS,it has its unique advantages in cost price. |
