Study On The Speciation Of Mercury By Atomic Fluorescence Spectrometry With Electrochemical Reduction Cold Vapor Generation

Electrochemical cold vapor generation?EcVG?based on electrochemical reduction of mercury is a high efficient gas sampling technique for mercury determination with atomic spectrometry analytical methods.Compared with the traditional cold vapor generation?CV?widely used in the common commercializing atomic spectrometry technique,the atomizing process of Ec VG is realized by electron transfer in the cathode chamber of the electrolytic flowing cell,without introduction of the unstable and high-purity KBH₄/NaBH₄ reductant.This work mainly applied the EcVG technique for the atomic fluorescence spectrometry method,and the detection of the total mercury amount and mercury species was realized by thisEcVG-AFSorEcVG-AFScoupledwithhighperformanceliquid chromatography?HPLC?.The main research included:1?The home-made electrolytic flow cell was adopted to generate mercury vapor by AFS analysis as the equipment of electrochemically reducing cold vapor generation.The parameters of the electrolytic flow cell,including the volume of the cathode chamber,the electrode materials,the electrolytic current and the velocity of the electrolyte flow,and the related parameters effecting the sensitivity of mercury analysis were optimized.As the results showed,the best mercury reduction efficiency was acquired when the glassy carbon was used as the cathode,especially for the organic species of mercury.Under the optimized conditions,the limits of detection?LOD?for Hg²⁺,HgCH₃⁺and HgC₂H₅⁺were 2.8ng/L,1.9ng/L and 2.4ng/L,and the relative standard deviations for the 3 mercury species were below 5%.Compared with the commercializing CV-AFS technique,the merit of lower LODs for organic mercury were remarkable.2?The methods for determination of total mercury and total organic mercury content were established with the EcVG-AFS technique.The two pretreatment methods for the samples of Chinese herbs,including microwave digestion and wet digestion under ordinary pressure for total mercury determination were compared,and the results showed that the microwave digestion method is better in both the recovery target and the sample preparation efficiency.Six samples of Chinese herbs,involved Achyranthes bidentata Blume,Rehmannia glutinosa Libosch,Morinda officinalis How,Psoralea corylifolia Linn.,Cistanche deserticola Ma.and cortex cinnamomi were tested by this method,and the recoveries were in the range of 78.0%-111.5%.The results were in great agreement with the results obtained by the CV-AFS technique.,which proved that this method was suitable for the real sample analysis of the Chinese herbs.Besides,a convenient and sensitive method for evaluation of the total amount of organic mercury species was established,using the acid-leaching pretreatment method and EcVG-AFS detecting technique,which was examined by real samples.3?The novel method for mercury species by EcVG-AFS technique coupled with HPLC separation was established.The systems of chromatography separation,the mercury vapor generation with electrolytic reduction and the AFS detection were systemicly optimized.The C18 reversed-phase column was used for the HPLC separation while the mobile phase was constituted with 5%CH₃OH,4.62 g/L?0.06 mol/L?NH₄Ac and 1.2g/L L-cysteine.Under the optimized conditions,the LODs for Hg²⁺,HgCH₃⁺and HgC₂H₅⁺were0.42ng/m L,0.26ng/mL and 0.37ng/m L,and the relative standard deviations for the 3mercury species were below 5%.The similar LODs results were obtained by this method,referring to the results by HPLC-UV-CV-AFS,which is better than the HPLC-CV-AFS method without ultraviolet on-line digestion.4?The method of mercury species for the Chinese herbs was established by HPLC-EcVG-AFS technique assisted with simulated gastric fluid extraction.The extraction efficiency for mercury species for 5 Chinese herbs,including Achyranthes bidentata Blume,Rehmannia glutinosa Libosch,Morinda officinalis How,Psoralea corylifolia Linn.and Cistanche deserticola Ma.,were compared.,using the two extraction methods of simulated gastric fluid extraction and ultrasonic assisted acid extraction.And obvious different extraction efficiency results could be seen from the analytic results.The extraction ratios for the 5 Chinese herbs were in the range of 66.2%⁸9.0%.And the spiked recoveries with different gradient levels were in the range of 79.8%¹09.3%for the 3species of Hg²⁺,HgCH₃⁺and HgC₂H₅⁺,which showed that no obvious species conversion phenomenon with different mercury species was observed during the wholeextraction and analytic process.And it's also proved that this method is feasible for mercury species of the real Chinese herbs samples.