Study On Fast Detection Of Mercury And Cadmium By Solid Sampling Electromagnetic Induction Electrothermal Vaporization Atomic Spectrometry

At present,with the rapid development of industry and agriculture in China,industrial pollutant emission and unreasonable use of agricultural inputs further aggravate heavy metal pollution.Among them,mercury(Hg)and cadmium(Cd)in agro-products and soils are harmful to consumers’ health.The verification analysis methods frequently used for Hg and Cd detection require complicated sample pretreatments,which are thereby not suitable to on-field analysis.In comparison,solid sampling(SS)atomic spectrometric methods are able to direct introduce sample without acid digestion process,and thereby fulfil the feasibility of rapid detection of heavy metals in soil and agri-food.In this study,electromagnetic induction electrothermal evaporation(IETV)was first used to introduce Hg and Cd in soil and agri-food sample;dielectric barrier discharge(DBD)on-line digestion and gas phase enrichment(GPE)devices were combined to construct the solid sampling unit coupled with atomic fluorescence spectrometer(AFS).The main contents and related research results of this paper are as follows:1.Fabrication of the IETV-AFS instruments.The vaporizer based on electromagnetic induction was first designed,in which Tantalum foil was used to generate induced current under the electromagnetic environment for rapid heating via joule heat.The IETV-AFS instrument system was preliminarily constructed,and then the vaporization performances for Hg and Cd by IETV were evaluated.The solid sampling DBD-GPE system was interfaced with the detection system for the following optimization of instrumental conditions and analytical method.2.Construction and evaluation of the GPE devices.Herein,a gold trap(GT)and nickel trap(NT)were selected to trap and release Hg and Cd based on the GPE principle,respectively.The NT made of foamed nickel wafers(diameter 5 mm,thickness 0.2 mm,aperture 100 μm)was first investigated to trap Cd following the sample introduction by IETV.The results showed that 5 ng Cd could be 100% trapped by more than 40 pieces of foamed nickel wafers.3.Method establishment and application for the fast detection of Hg in aquatic animal samples by IETV-DBD-GT-AFS.Due to abundant organics existing in aquatic animal products,a DBD device was designed to fulfil the online digestion for volatile organic compounds(VOCs),and a GT was used to further eliminate interference for Hg trapping.The optimized conditions were as follows: 50-125 W(190 s)for ashing power,150 W(20 s)for vaporization power,200 mL/min for air flow rate,41 W for DBD discharge power,600 mL/min for carrier gas flow rate,and 180 W(20 s)for releasing power.Under the optimized condition,the calibration curve of the IETV-DBD-GT-AFS method was verified with the regression coefficient(R2)> 0.996 in the range of 20 pg~5 ng;the limit of detection(LOD)were 0.5 μg/kg.The RSD of 11 repeated measurements were 5% and 10% using 100 μg/L Hg standard solution(10 μL)or 10 mg certified reference material(CRM)sample,respectively.The results mentioned above indicated sensitivity and precision for the fast Hg detection by IETV-DBD-GT-AFS within 5 min analysis time.4.Method establishment and application for the fast detection of Cd in soil by IETV-NT-AFS.Theoptimized conditions were as follows: 265 W(60 s)for vaporization power,600 mL/min for air flow rate,500 mL/min for carrier gas flow rate,500 mL/min for releasing gas flow rate,and 225 W(35 s)for releasing power.Under the optimized condition,the LOD were 0.08 μg/kg,the linear ranges of IETV-NT-AFS were 1 pg~10 ng with R2> 0.992;the RSD values of were less than 8%(standard solution)and 12%(samples),respectively.There were no significant differences between the measurement results by IETV-NT-AFS and the microwave digestion inductively coupled plasma mass spectrometry(ICP-MS)methods or CRMs.The results showed that the IETV-NT-AFS can meet the requirements of fast determination Cd in soil.