Electrochemical Vapor Generation Of Mercury And Arsenic On Nickel Foam

In the field of atomic spectroscopy,the efficiency of sample introduction is a key factor affecting the accuracy and precision of the results.This paper introduced the development,advantages and disadvantages of current vapor generation.Then the principle of electrochemical vapor generation,the influence of electrode materials and its practical application was systematically analyzed.Subsequently,the electrolytic reduction behavior of mercury and arsenic on the nickel foam electrode（NFE）was studied.The electrochemical vapor generation of Hg²⁺on commercial nickel foam was tested for the first time.The spectral data showed that the electrochemical vapor generation efficiency of mercury on nickel foam reached more than 90%of the chemical vapor generation,more than 1.5 times of that on graphite and platinum.A series of electrochemical tests demonstrated that the multilayer structure did not change the electronic transmission and catalytic properties of the material,but the specific surface area up to 6～14 times of the same size foil electrode provided enough reaction sites;and lower current density(～20 m A cm^-2 v.s.200 m A cm^-2),which made the reaction more stable[the precision is 4.2%(0.5μg L^-1),4.7%(2.0μg L^-1)and 5.7%(5.0μg L^-1);the gas evolution effect was smaller and the anti-interference performance was better(e.g.,>20 mg L^-1 Cu²⁺).Under the optimal conditions,the detection limit can be as low as 0.017μg L^-1.Au/Ag modified nickel foam was prepared by potentiostatic deposition.The reduction behavior of Hg²⁺and CH₃Hg⁺on the electrode was systematically investigated.The spectra showed that the Hg²⁺signal increased by 30%,while the CH₃Hg⁺was nearly ten times.This was attributed to the greater surface area,easier hydrogen evolution and lower electron transfer resistance of the electrode after precious metal deposition.In addition,compared with Ag modified electrode,Au modified electrode can further catalyze the electroreduction of CH₃Hg⁺.While controlling the electrolytic current can distinguish the spectral signals of Hg²⁺and CH₃Hg⁺.The mercury speciation analysis method based on above result had the characteristics of low detection limit[0.007μg L^-1(Hg²⁺)v.s.0.008μg L^-1（CH₃Hg⁺）],good stability（RSD<6%）,strong anti-interference ability.It was verified in codonopsis pilosula,salvia and tea.The feasibility of preconcentration and electroreduction for the quantitative analysis of ultra-trace arsenic was discussed.The data displayed that the flow electrical enrichment（1.4 V）efficiency of 2μg L^-1 As（III）on Mn O₂@Fe₃O₄/NFE was over 97%.The detection limit of As（III）was as low as 0.008μg L^-1 and the relative standard deviation was 2.8%.