| Soil heavy metal pollution is a global problem with great harm,and most of the existing soil heavy metal detection methods are based on large-scale instruments in the laboratory.This method needs a lot of pre-treatment,such as air drying,grinding,weighing,digestion,preparation of sample solution,etc.the preparation of each sample takes 1-2 hours,which is time-consuming and laborious.At present,laser-induced breakdown spectrum and X-ray atomic fluorescence spectrum are widely used in the field direct detection instruments.These two methods also have some defects.In the field application,they are generally only used for preliminary screening and semi quantitative detection of heavy metal content in polluted areas.Therefore,the development of a portable,low-cost heavy metal detector with low detection limit and quantitative accuracy,which can complete the soil direct injection detection,not only has great innovation,but also has high practical significance and commercial value.This paper mainly studies a kind of self-developed portable soil heavy metal detection device which can realize the direct injection of soil powder.In this study,electromagnetic heating was used innovatively as the atomization mode of heavy metals in soil,and dielectric barrier discharge micro plasma was used as the excitation mode of metal elements to be measured,combined the designed optical path system,realized rapid detection and analysis on site,thus eliminating the tedious sample pretreatment process.A W-boat was used as an electromagnetic heating medium and sample carrier,and copper coil spiraled around the tube was used as magnetic induction coil.The program compiled by Lab VIEW realizes the control of the instrument,and the designed software can complete the setting of key parameters such as monitoring wavelength,water removal time,atomization time,etc.The instrument consists of electromagnetic heating unit,dielectric barrier discharge excitation unit,gas path system,optical signal acquisition and processing unit,and corresponding circuit system.It is powered by portable battery and controlled by micro touch-screen computer and the total weight of the instrument is only about 7kg.It is easy to operate and small in size(40.5cm(L)× 30cm(W)× 15cm(H)),and can be carried to the field for direct detection of soil.The developed instrument has a long service life,low power consumption and fast detection speed(a soil sample can be detected within 5 minutes,and the average power does not exceed 118 W).Simultaneous detection of mercury,cadmium,lead,zinc,silver and other elements in the soil with the instrument.Optimized relevant experimental conditions such as carrier gas flow rate,sample injection volume,water removal voltage,and substrate removal voltage,under the optimal detection conditions,the detection limits(LODs)of the three important elements of mercury,cadmium,and lead are: 8.0 μg/kg,17.8 μg/kg and 3.5 mg/kg(Due to the higher background content in the soil,the calculation result of the detection limit of lead is higher than the actual result).Through testing and verification of soil samples,the stability,reliability and practicability of the developed device are proved.Its performance fully meets the requirements for the detection of heavy metal elements such as mercury,cadmium,and lead in the national first-level standard soil.At the same time,the instrument developed has the potential to detect other solid samples such as vegetables,which is an advancement in the research field of atomic emission spectroscopy and heavy metal detection. |
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